PROCESS FOR PREPARING A METALLIZED SUBSTRATE, SAID SUBSTRATE AND USES THEREOF
The present invention relates to a process for preparing a metallized substrate, comprising the steps consisting in: grafting onto said substrate a compound of polymer type optionally bearing a group that is capable of chelating at least one metal ion; placing said compound of polymer type that is capable of chelating at least one metal ion in contact with at least one metal ion, and subjecting the compound of polymer type to conditions for reducing said chelated metal ion(s), and repeating the chelation/reduction steps until a metallized substrate is obtained. The present invention also relates to the substrate obtained during this process and to the uses thereof.
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The invention relates to the technical field of surface coatings.
More particularly, the present invention relates to a metallization process using substrates coated with organic films that are capable of developing interactions of the chelation or complexation type with metal ions. The present invention also relates to the intermediate or final products obtained during this metallization process and also to their use in various fields of application.
PRIOR ARTMetallization, which consists in coating the surface of a component with a thin layer of metal, is used in many fields such as aeronautics and the motor industry in which certain accessories are coated with chromium, the electronics industry, tapware, decoration, especially with silver-plated tableware, the cosmetics industry, tin-plated food containers, etc. There is thus great interest in the development of a metallization process.
The prior art already discloses various techniques for obtaining such metallization. For example, electrodeposition using a solution containing the metal salt to be electrodeposited and in which the object to be metallized, which is conductive, is placed, is the technique generally used. To obtain a uniform metallic coating having a good grain quality and solidly and closely attached to the object to be metallized, electrodeposition requires rigorously controlled conditions such as the current density and the temperature used, and also careful cleaning of the surface of the object.
Metallization of the surface of small objects such as particles or nanoparticles is useful in the medical field, both therapeutically and diagnostically. Specifically, in order to obtain extremely specific and localized images of the biological phenomenon under study, it is necessary to correlate at least two types of imaging. Currently, certain imaging platforms coupling magnetic resonance imaging (MRI) and fluorescence have shown efficacy in the study of tumour development in small animals. However, on account of the attenuation of the fluorescence by tissues, systems of this type cannot allow the visualization of a deep tumour in man and thus cannot superimpose the two images.
Magnetic (nano)particles, i.e. particles comprising a magnetic metal or coated with such a metal, are widely used in various biomedical applications especially as MRI contrast agents, but also for vectorizing active principles, treating anaemia or diagnosing cancer. Among these particles, superparamagnetic iron oxides are used as MRI contrast agents and for treating cancer by hyperthermia on account of their high degree of efficacy (relaxivity) and their intrinsic bioresorbability.
The development of methods for detecting 19F by NMR at very high magnetic field appears to offer new perspectives. Specifically, fluorine is considered as a trace element present in trace amount in the human body (bones and teeth). The detection of perfluoro molecules thus makes it possible to obtain a very large signal/noise ratio (Srinivas et al., Magnetic Resonance in Medicine, 2007, 58, 725-734; Neubauer et al., Journal of Cardiovascular Magnetic Resonance, 2007, 9, 565-573; Brix et al., Magnetic Resonance Imaging, 2005, 23, 967-976; Neubauer et al., Circulation, 2006, 114, 251-251).
At the present time, there are few examples involving contrast agents/perfluoro molecules. Only liposomes used especially for imaging integrins use fluorine and gadolinium (Winter et al., Journal of Magnetism and Magnetic Materials, 2005, 293, 540-545; Morawski, et al., Magnetic Resonance in Medicine, 2004, 52, 1255-1262; Morawski et al., Current Opinion in Biotechnology, 2005, 16, 89-92; Anderson et al., Magnetic Resonance in Medicine, 2000, 44, 433-439; Caruthers et al., Investigative Radiology, 2006, 41, 305-312). However, these systems suffer from having a large size (>150 nm), making them unlikely to be used for certain applications.
Designing nanoparticles incorporating metals, metal oxides or metal ions such as iron oxides and perfluoro molecules would make it possible to obtain bimodal contrast agents (high-contrast 1H and 19F MRI), the correlation of the two signals making it possible to obtain more precise images.
There is thus a real need for a metallization process for obtaining (nano)particles incorporating metals or metal oxides and perfluoro molecules, and more generally for a metallization process that is easy to perform and adaptable to all the surfaces encountered in the abovementioned fields.
DESCRIPTION OF THE INVENTIONThe present invention meets this expectation and satisfies the drawbacks of the prior art. Specifically, it proposes a process that may be used for (nano)particles that are useful in therapy and in diagnostic imaging, but also for any type of surface, making it possible to obtain an object metallized at the surface and/or in its thickness, having a uniform metallic coating, with a good grain quality and solidly attached to said object. The invention also makes it possible to dispense with metallization catalysts such as platinum particles.
Thus, the present invention proposes a process for preparing a metallized substrate, comprising the steps consisting in:
a) grafting onto said substrate a compound of polymer type optionally bearing a group (or structure) capable of chelating at least one metal ion;
b) optionally subjecting said compound of polymer type to conditions for functionalizing it with a group (or structure) capable of chelating at least one metal ion;
c) placing said compound of polymer type capable of chelating at least one metal ion obtained after step (a) or (b) in contact with at least one metal ion;
d) subjecting the compound of polymer type obtained in step (c) to conditions for reducing said chelated metal ion(s);
e) optionally repeating steps (c) and (d) until a metallized substrate is obtained.
In the context of the present invention, a “metallized substrate” means a substrate:
surface-coated with a thin layer, typically from a few nanometres to several micrometres, of a metal and/or of a metal oxide and/or
comprising in its bulk metals and/or metal oxides, dispersed and/or distributed therein.
Among the metallized substrates, substrates metallized only with a metal or only with a metal oxide and substrates metallized with the two types of metallic species may especially be distinguished.
During step (a) of the process according to the invention, any technique for grafting a compound of polymer type onto a substrate may be used, i.e. any technique for forming at least one covalent bond between an atom belonging to said substrate and an atom belonging to said compound of polymer type. The grafting technique may consist in:
generating close to the substrate a first reactive species such as a species derived from an adhesion primer, which grafts onto the substrate and initiates the subsequent formation of the compound of polymer type, especially by radical polymerization, and/or
generating at the surface of the substrate a reactive species such as a radical species that initiates the subsequent formation of the compound of polymer type.
As a result, the process according to the invention may be performed with any type of substrate, inorganic or organic, bearing one or more atom(s) or group(s) of atoms that may be involved in a radical substitution or addition reaction, such as CH, carbonyls (ketone, ester, acid, aldehyde), —OH, —SH, phosphates, ethers, amines or halogens, such as F, Cl or Br.
The substrate of inorganic nature may especially be made of a material chosen from conductive materials such as metals, noble metals, metal oxides, transition metals or metal alloys, for example Ni, Zn, Au, Pt, Ti or steel.
The substrate may also be chosen from a material chosen from semiconductive materials such as Si, SiC, AsGa or Ga. The term “semiconductive” refers to an organic or inorganic material with electrical conductivity intermediate between that of metals and insulators. The conductive properties of a semiconductor are mainly influenced by the charge carriers (electrons or holes) present in the semiconductor. These properties are determined by two particular energy bands known as the valency band (corresponding to the electrons involved in the covalent bonds) and the conductive band (corresponding to the electrons in an excited state that are capable of moving in the semiconductor). The “gap” represents the energy difference between the valency band and the conductive band. A semiconductor also corresponds, unlike insulators or metals, to a material whose electrical conductivity can be controlled, to a large extent, by adding dopants, which correspond to foreign elements inserted into the semiconductor.
The substrate may also be chosen from a material chosen from photosensitive semiconductive materials, i.e. semiconductive materials whose conductivity may be modulated by magnetic field, temperature or illumination variations, which have an influence on the electron-hole pairs and the density of the charge carriers. These properties are due to the existence of the gap as defined previously. This gap generally does not exceed 3.5 eV for semiconductors, as opposed to 5 eV in materials considered as insulators. It is thus possible to populate the conductive band by exciting the carriers across the gap, especially by illumination. The elements of group IV of the periodic table, such as carbon (in diamond form), silicon and germanium have such properties. The semiconductive materials may be formed from several elements, either from group IV, for instance SiGe or SiC, or from groups III and V, for instance GaAs, InP or GaN, or alternatively from groups II and VI, for instance CdTe or ZnSe.
Advantageously, in the context of the present invention, the photosensitive semiconductive substrate is of inorganic nature. Thus, the photosensitive semiconductor used in the context of the present invention is chosen from the group formed by group IV elements (more particularly silicon and germanium); alloys of group IV elements (more particularly SiGe and SiC alloys); alloys of group III and group V elements (known as “III-V” compounds, such as AsGa, InP, GaN) and alloys of group II and group VI elements (known as “II-VI” compounds, such as CdSe, CdTe, Cu2S, ZnS or ZnSe). The preferred photosensitive semiconductor is silicon.
As a variant, it is possible for the photosensitive semiconductor to be doped with one (or more) dopant(s). The dopant is chosen as a function of the semiconductor, and the dopant is of p or n type. The choice of dopant and the doping techniques are routine techniques for a person skilled in the art. More particularly, the dopant is chosen from the group formed by boron, nitrogen, phosphorus, nickel, sulfur, antimony and arsenic, and mixtures thereof. By way of example, for a silicon substrate, among the dopants most commonly used of p type, mention may be made especially of boron, and, for the dopants of n type, arsenic, phosphorus and antimony.
It is also possible to apply the process to substrates made of a non-conductive material, for instance non-conductive oxides such as SiO2, Al2O3 and MgO.
More generally, an inorganic substrate may be formed, for example, from an amorphous material, such as a glass generally containing silicates or alternatively a ceramic, or from a crystalline material, for instance diamond, graphite, which may be more or less organized, such as graphene or highly oriented graphite (HOPG), or carbon nanotubes.
As other substrates of organic nature, mention may be made especially of natural polymers, for instance latex or rubber, or artificial polymers, for instance polyamide and polyamide derivatives, polyethylene derivatives, and especially polymers containing bonds of n type such as polymers bearing ethylenic bonds or carbonyl or imine groups. As particular examples of such polymers, mention may be made of acrylonitrile-butadiene-styrene (ABS) and acrylonitrile-butadiene-styrene/polycarbonate (ABS/PC). It is also possible to apply the process to more complex organic substrates such as leather, substrates comprising polysaccharides, for instance wood or paper cellulose, artificial or natural fibres, for instance cotton or felt, and also to a polymer matrix or two polymers bearing basic groups, for instance tertiary or secondary amines, for example pyridines, such as poly-4 and poly-2-vinylpyridines (P4VP and P2VP) or more generally polymers bearing aromatic and nitroaromatic groups. In the context of the present invention, the term “polymer matrix” means a matrix made of a polymer chosen from polyurethanes, polyolefins, polycarbonates and polyethylene terephthalates, these polymers being advantageously fluorinated or even perfluorinated. Advantageously, the polymer matrix may be chosen from matrices made of fluoro polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and of tetrafluoropropylene (FEP), copolymers of ethylene and of tetrafluoroethylene (ETFE), copolymers of hexafluoropropene and of vinylidene fluoride (HFP-co-VDF), of vinylidene fluoride and of trifluoroethylene (VDF-co-TrFE) and of vinylidene fluoride, trifluoroethylene and monochlorotrifluoroethylene (VDF-co-TrFE-co-chloro-TrFE).
The size of the substrate used in the context of the present invention may be nanometric, micrometric, millimetric or metric. Specifically, the present invention applies to nanoparticles, microparticles, electronic components, mirrors, decorative objects, optical data storage discs (compact discs), bodywork components, etc.
Advantageously, the grafting step (a) of the process according to the invention is a grafting chosen from the group consisting in chemical grafting, electrografting and radiochemical grafting.
In the context of the present invention, the term “chemical grafting” means grafting using extremely reactive molecular species (typically radical species) capable of forming bonds of covalent bonding type with a surface of interest, said molecular species being generated independently of the surface onto which they are intended to be grafted. Thus, “radical grafting” is such a “chemical grafting”.
More particularly, the grafting step (a) involving chemical grafting comprises the steps consisting in:
a1) placing the substrate to be metallized in contact with a solution S1 comprising at least one adhesion primer and optionally at least one monomer different from the adhesion primer and capable of undergoing radical polymerization;
b1) subjecting said solution S1 to non-electrochemical conditions enabling the formation of radical species from said adhesion primer.
In the context of the present invention, the term “adhesion primer” means any organic molecule that is capable, under certain non-electrochemical or electrochemical conditions, of forming either radicals or ions, and more particularly cations, and thus of participating in chemical reactions. Such chemical reactions may especially be chemisorption and in particular chemical grafting or electrografting. Thus, such an adhesion primer is capable, under non-electrochemical or electrochemical conditions, of being chemisorbed onto the surface of the substrate, especially by radical reaction, and of bearing another function that is reactive towards another radical after this chemisorption. Thus, the radical reaction leads to the formation of covalent bonds between the surface and the grafted adhesion primer derivative and then between said grafted derivative and molecules present in its environment such as radical-polymerizable monomers or other adhesion primers.
The adhesion primer is advantageously a cleavable aryl salt chosen from the group formed by aryldiazonium salts, arylammonium salts, arylphosphonium salts, aryliodonium salts and arylsulfonium salts. In these salts, the aryl group is an aryl group that may be represented by R as defined below.
Among the cleavable aryl salts, mention may be made in particular of the compounds of formula (I) below:
R—N2+, A− (I)
in which:
A represents a monovalent anion and
R represents an aryl group.
As aryl group of the cleavable aryl salts and especially of the compounds of formula (I) above, mention may be made advantageously of optionally monosubstituted or polysubstituted aromatic or heteroaromatic carbon-based structures, formed from one or more aromatic or heteroaromatic rings each comprising from 3 to 8 atoms, the heteroatom(s) possibly being N, O, P or S. The substituent(s) may contain one or more heteroatoms, such as N, O, F, Cl, P, Si, Br or S and also C1 to C6 alkyl groups or thioalkyl groups, especially of C4 to C12.
Within the cleavable aryl salts and especially the compounds of formula (I) above, R is preferably chosen from aryl groups substituted with electron-withdrawing groups such as —NO2, ketones, —CN, —CO2H and esters, and salts thereof.
Within the compounds of formula (I) above, A may be chosen especially from inorganic anions such as halides, for instance I−, Br− and Cl−, haloborates such as tetrafluoroborate, perchlorates and sulfonates, and organic anions such as alkoxides and carboxylates.
As compounds of formula (I), it is particularly advantageous to use a compound chosen from the group formed by 4-nitrobenzenediazonium tetrafluoroborate, tridecylfluorooctylsulfamylbenzenediazonium tetrafluoroborate, phenyldiazonium tetrafluoroborate, 4-nitrophenyldiazonium tetrafluoroborate, 4-bromophenyldiazonium tetrafluoroborate, 4-aminophenyldiazonium chloride, 2-methyl-4-chlorophenyldiazonium chloride, 4-benzoylbenzenediazonium tetrafluoroborate, 4-cyanophenyldiazonium tetrafluoroborate, 4-carboxyphenyldiazonium tetrafluoroborate, 4-acetamidophenyldiazonium tetrafluoroborate, 4-phenylacetic acid diazonium tetrafluoroborate, 2-methyl-4-[(2-methylphenyl)diazenyl]benzenediazonium sulfate, 9,10-dioxo-9,10-dihydro-1-anthracenediazonium chloride, 4-nitronaphtalenediazonium tetrafluoroborate and naphtalenediazonium tetrafluoroborate.
In the context of the present invention, the term “adhesion primer derivative” means a chemical unit resulting from the adhesion primer, after it has reacted with the surface, by chemical grafting, and optionally by radical reaction, with another molecule present in its environment such as an adhesion primer or a radical-polymerizable monomer, said other molecule giving the second unit of the organic film. Thus, the first unit of the organic film is an adhesion primer derivative that has reacted with the surface and with another molecule present in its environment.
The radical-polymerizable monomer(s) used in the context of the process of the invention correspond to monomers capable of undergoing radical polymerization after initiation with a radical chemical species. Typically, they are molecules comprising at least one bond of ethylenic type. In particular, the polymerizable monomer(s) are chosen from the monomers of formula (II) below:
in which the groups R1 to R4, which may be identical or different, represent a non-metallic monovalent atom such as a halogen atom or a hydrogen atom, a saturated or unsaturated chemical group, such as an alkyl or aryl group, a group —COOR5 or —OC(O)R5 in which R5 represents a hydrogen atom or a C1-C12 and preferably C1-C6 alkyl group, a nitrile, a carbonyl, an amine or an amide.
The radical-polymerizable monomers are advantageously chosen from the group formed by vinyl esters such as vinyl acetate, acrylic acid, acrylonitrile, methacrylonitrile, methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and glycidyl methacrylate, and derivatives thereof; acrylamides and especially aminoethyl, propyl, butyl, pentyl and hexyl methacrylamides, cyanoacrylates, diacrylates and dimethacrylates, triacrylates and trimethacrylates, tetraacrylates and tetramethacrylates (such as pentaerythrityl tetramethacrylate), styrene and derivatives thereof, para-chlorostyrene, pentafluorostyrene, N-vinylpyrrolidone, 4-vinylpyridine, 2-vinylpyridine, vinyl, acryloyl or methacryloyl halides, divinylbenzene (DVB) and more generally vinyl or acrylate- or methacrylate-based crosslinking agents, and derivatives thereof.
The solution S1 may also comprise a solvent. This solvent may be a protic solvent or an aprotic solvent. It is preferable for the adhesion primer that is used to be soluble in the solvent of the solution S1.
In the context of the present invention, the term “protic solvent” means a solvent that comprises at least one hydrogen that can be released in proton form.
The protic solvent is advantageously chosen in the group consisting in water, deionized water and distilled water, which may or may not be acidified, acetic acid, hydroxylated solvents, for instance methanol and ethanol, low molecular weight liquid glycols such as ethylene glycol, and mixtures thereof. In the first variant, the protic solvent used in the context of the present invention is formed only by a protic solvent or by a mixture of different protic solvents. In another variant, the protic solvent or the mixture of protic solvents may be used as a mixture with at least one aprotic solvent, it being understood that the resulting mixture has the characteristics of a protic solvent.
In the context of the present invention, the term “aprotic solvent” means a solvent that is not considered as protic. Such solvents are incapable of releasing a proton or of accepting one under non-extreme conditions.
The aprotic solvent is advantageously chosen from dimethylformamide (DMF), acetone, tetrahydrofuran (THF), dichloromethane, acetonitrile, dimethyl sulfoxide (DMSO) and ethyl acetate, and mixtures thereof.
It is preferable for the adhesion primer to be soluble in the solvent of the solution S1. For the purposes of the invention, an adhesion primer is considered as soluble in a given solvent if it remains soluble up to a concentration of 0.5 M, i.e. until its solubility is at least equal to 0.5 M and under standard temperature and pressure conditions (STP). The solubility is defined as the analytical composition of a saturated solution as a function of the proportion of a given solute in a given solvent; it may be expressed especially as molarity. A solvent containing a given concentration of a compound will be considered as saturated when the concentration is equal to the solubility of the compound in this solvent. The solubility may be finite or infinite. In the latter case, the compound is soluble in all proportions in the solvent under consideration.
The amount of adhesion primer present in the solution S1 used in accordance with the process according to the invention may vary as a function of the experimenter's wishes. This amount is especially linked to the desired thickness of the organic film and also to the amount of adhesion primer that it is possible and envisageable to incorporate into the film. Thus, to obtain a film grafted over the entire surface in contact with the solution, it is necessary to use the minimum amount of adhesion primer that it is possible to estimate by molecular bulk calculations. According to one particularly advantageous embodiment of the invention, the concentration of adhesion primer in the liquid solution is between 10−6 and 5 M approximately and preferably between 10−3 and 10−1 M.
When the solvent is a protic solvent, and advantageously when the adhesion primer is an aryldiazonium salt, the pH of the solution is typically less than 7. It is recommended to work at a pH of between 0 and 3 when the preparation of the adhesion primer is performed in the same medium as that for the grafting. If necessary, the pH of the solution may be adjusted to the desired value using one or more acidifying agents that are well known to those skilled in the art, for example using mineral or organic acids such as hydrochloric acid, sulfuric acid, etc.
The adhesion primer can either be introduced in the solution S1 as defined previously, or be prepared in situ therein. Thus, in one particular embodiment, the process according to the present invention comprises a step of preparing the adhesion primer, especially when it is an aryldiazonium salt. Such compounds are generally prepared from arylamines, which may comprise several amine substituents, by reaction with NaNO2 in acidic medium or by reaction with NOBF4 in organic medium. For a detailed account of the experimental methods that may be used for such an in situ preparation, a person skilled in the art may refer to the article by Belanger et al., 2006 (Chem. Mater., vol. 18, pages 4755-4763). Preferably, the grafting will then be performed directly in the solution for preparing the aryldiazonium salt.
The radical-polymerizable monomers may be soluble up to a certain proportion in the solvent of the solution S1, i.e. the value of their solubility in this solvent is finite, especially less than 0.1 M and in particular between 5×10−2 and 10−6 M. The invention also applies to a mixture of two, three, four or more elements chosen from the elements described previously. The amount of these monomers in the solution S1 may vary as a function of the experimenter's wishes. This amount may be greater than the solubility of the element under consideration in the solvent of the solution S1 used and may represent, for example, from 18 to 40 times the solubility of said element in the solution at a given temperature, generally room temperature or the reaction temperature. Under these conditions, it is advantageous to use means for dispersing the monomer molecules in the solution, such as a surfactant or ultrasonication.
The solution S1 comprising an adhesion primer and optionally at least one radical-polymerizable monomer may also contain at least one surfactant, especially to improve the solubility of said monomer(s). A precise description of surfactants that may be used in the context of the invention is given in patent application FR 2 897 876, to which a person skilled in the art may refer. A single surfactant or a mixture of several surfactants may be used.
In the context of the present invention, the term “non-electrochemical conditions” used in step (b1) of the process according to the invention means the absence of an electrical voltage. Thus, the non-electrochemical conditions used in step (b1) of the process according to the invention are conditions that allow the formation of radical species from the adhesion primer, in the absence of application of any electrical voltage at the surface onto which the organic film is grafted. These conditions involve parameters such as, for example, the temperature, the nature of the solvent, the presence of a particular additive, stirring, and the pressure, whereas the electrical current does not participate in the formation of the radical species. The non-electrochemical conditions allowing the formation of radical species are numerous, and this type of reaction is known and studied in detail in the prior art (Rempp & Merrill, Polymer Synthesis, 1991, 65-86, Hüthig & Wepf).
It is thus possible, for example, to modify the thermal, kinetic, chemical, photochemical or radiochemical environment of the adhesion primer so as to destabilize it in order for it to form a radical species. Needless to say, it is possible to modify simultaneously several of these parameters.
In the context of the present invention, the non-electrochemical conditions enabling the formation of radical species are typically chosen from the group consisting in thermal, kinetic, chemical, photochemical and radiochemical conditions, and combinations thereof. Advantageously, the non-electrochemical conditions are chosen from the group consisting in thermal, chemical, photochemical and radiochemical conditions, and combinations thereof and/or combinations with kinetic conditions. The non-electrochemical conditions used in the context of the present invention are more particularly chemical conditions.
The thermal environment depends on the temperature. It is easy to control with the heating means usually used by a person skilled in the art. Using a thermostatically controlled environment is particularly advantageous since it allows precise control of the reaction conditions.
The kinetic environment essentially corresponds to stirring of the system and to the friction forces. It is not in this case agitation of the molecules themselves (stretching of bonds, etc.), but the global movement of the molecules. Applying pressure especially makes it possible to supply energy to the system for the adhesion primer to be destabilized and to be able to form reactive species, especially radical species.
Finally, the action of various types of radiation such as electromagnetic radiation, γ radiation, UV rays or electron or ion beams also makes it possible to destabilize the adhesion primer sufficiently for it to form radicals and/or ions. The wavelength used will be chosen as a function of the primer used. For example, a wavelength of about 306 nm will be used for 4-hexylbenzenediazonium.
In the context of the chemical conditions, one or more chemical initiator(s) are used in the reaction medium. The presence of chemical initiators is often coupled to non-chemical environmental conditions, as outlined above. Typically, a chemical initiator will act on the adhesion primer and give rise to the formation of radical species therefrom. It is also possible to use chemical initiators whose action is not essentially linked to the environmental conditions and which may act over wide ranges of thermal or kinetic conditions. The initiator will preferably be suited to the reaction environment, for example to the solvent.
Many chemical initiators exist. Three types are generally distinguished, as a function of the environmental conditions used:
thermal initiators, the most common of which are peroxides or azo compounds. Under the action of heat, these compounds dissociate into free radicals. In this case, the reaction is performed at a minimum temperature corresponding to that required for the formation of radicals from the initiator. Chemical initiators of this type are generally used specifically within a certain temperature range, as a function of their decomposition kinetics;
photochemical or radiochemical initiators which are excited by radiation triggered by irradiation (usually by UV, but also by y radiation or by electron beams) allowing the production of radicals via more or less complex mechanisms. Bu SnH and I2 are among photochemical or radiochemical initiators;
essentially chemical initiators, initiators of this type acting rapidly and under standard temperature and pressure conditions on the adhesion primer to enable it to form radicals and/or ions. Such initiators generally have a redox potential that is lower than the reduction potential of the adhesion primer used under the reaction conditions. Depending on the nature of the primer, it may thus be a reductive metal, such as iron, zinc or nickel; a metallocene such as ferrocene; an organic reducing agent such as hypophosphorous acid (H3PO2) or ascorbic acid; an organic or inorganic base in proportions sufficient to destabilize the adhesion primer. Advantageously, the reductive metal used as chemical initiator is in finely divided form, such as metallic wool (also known more commonly as “steel wool”) or metal filings. Generally, when an organic or inorganic base is used as chemical initiator, a pH of greater than or equal to 4 is generally sufficient. Structures of radical reservoir type, for instance polymer matrices irradiated beforehand with an electron beam or with a beam of heavy ions and/or with all of the irradiation means mentioned previously, may also be used as chemical initiators for the stabilizing the adhesion primer and especially leading to the formation of radical species therefrom.
Reference may appropriately be made to the article by Mévellec et al., 2007 (Chem. Mater., vol. 19, pages 6323-6330) for the formation of active species.
In a second variant of step (a) of the process according to the invention, the grafting used is electrografting.
In the context of the present invention, the term “electrografting” refers to a process of electro-initiated and localized grafting of an adhesion primer that may be electrically activated, on an electrically conductive or semiconductive surface or a composite surface comprising electrically conductive and/or semiconductive portions, by placing said adhesion primers in contact with said surface. In this process, the grafting is performed electrochemically in a single step on the electrically conductive or semiconductive surface or on chosen, defined zones of said conductive and/or semiconductive portions. Said surface (or said zones) are brought to a potential greater than or equal to a threshold electrical potential determined relative to a reference electrode, said threshold electrical potential being the potential above which grafting of said adhesion primers takes place. Once said adhesion primers have been grafted, they bear another function that is reactive towards another radical and capable of triggering a radical polymerization that is independent of any electrical potential.
Advantageously, this second variant comprises the steps consisting in:
a2) placing the conductive or semiconductive substrate in contact with a solution S2 comprising at least one adhesion primer and optionally at least one polymerizable monomer other than said adhesion primer and capable of undergoing radical polymerization especially as defined previously;
b2) polarizing said substrate at a more cathodic electrical potential than the reduction potential of the adhesion primer used in step (a2),
steps (a2) and (b2) being performed in any order.
This variant applies to the conductive or semiconductive substrates as defined previously. Thus, if the substrate used in the context of the present invention is a photosensitive semiconductive material as defined previously, the process also comprises a step (c2) that consists in exposing said substrate to light radiation whose energy is at least equal to that of the gap of said semiconductor. For further details regarding this particular embodiment, reference should be made to the patent application published under the number FR 2 921 516.
Everything that has been described, in the context of chemical grafting, for the adhesion primer, for the radical-polymerizable monomer(s), for the solution S1, i.e. the solvent, the amounts of adhesion primers and polymerizable monomers, the in situ preparation of the adhesion primer and the possible presence of a surfactant also applies to electrografting. However, it should be pointed out that the solvent of the solution S2 is advantageously a protic solvent as defined previously.
According to the invention, it is preferable for the electrical potential used in step (b2) of the process according to the present invention to be close to the reduction potential of the adhesion primer that is used and that reacts at the surface. Thus, the value of the applied electrical potential may be up to 50% higher than the reduction potential of the adhesion primer; more typically it will not be greater than 30%.
This variant of the present invention may be used in an electrolysis cell comprising different electrodes: a first working electrode constituting the surface intended to receive the film, a counterelectrode and optionally a reference electrode.
Polarization of said surface may be performed by any technique known to those skilled in the art and especially under linear or cyclic voltammetry conditions, potentiostatic, potentiodynamic, intensiostatic, galvanostatic or galvanodynamic conditions or by simple or pulsed chronoamperometry. Advantageously, the process according to the present invention is performed under static or pulsed chronoamperometric conditions. In static mode, the electrode is polarized for a duration generally of less than 2 hours and typically less than hour, for example less than 20 minutes. In pulsed mode, the number of pulses will preferentially be between 1 and 1000 and even more preferentially between 1 and 100, their duration generally being between 100 ms and 5 seconds, typically 1 second.
In the context of the present invention, the term “radiochemical grafting” means grafting by reaction, especially radical reaction, involving a substrate, such as a polymer matrix, which has been irradiated beforehand. Thus, this variant applies mainly to organic substrates and in particular to substrates of polymer matrix type as defined previously.
More particularly, the grafting step involving radiografting comprises the steps consisting in:
a3) irradiating a substrate of polymer matrix type especially as defined previously;
b3) placing the irradiated substrate obtained in step (a3) in contact with at least one adhesion primer and/or at least one radical-polymerizable monomer.
The irradiation step (a3) has the function of creating free radicals in the constituent material of the matrix, this creation of free radicals being a consequence of the energy transfer during the irradiation of said material.
In a first variant of step (a3), this step may consist in subjecting the polymer matrix to an electron beam (variant known as “electron irradiation”). More particularly, this step may consist in scanning the polymer matrix with a beam of accelerated electrons, especially emitted by an electron accelerator (for example a 2.5 MeV Van der Graaf accelerator). In the case of irradiation with an electron beam, the energy deposition is uniform, which means that the free radicals created by this irradiation will be uniformly distributed in the volume of the matrix. The irradiation dose generally ranges from 10 to 500 kGy and especially from 50 to 150 kGy.
In a second variant of step (a3), this step may consist in subjecting the polymer matrix to bombardment with heavy ions and especially with a beam of heavy ions. The term “heavy ions” means ions whose mass is greater than that of carbon. Generally, they are ions chosen from krypton, lead and xenon.
From a mechanistic viewpoint, when the energy-vector heavy ion crosses the matrix, its speed decreases. The ion yields its energy, creating damaged zones, the shape of which is approximately cylindrical. These zones known as “latent traces” comprise two regions: the core and the halo of the trace. The core of the trace is a totally degraded zone, i.e. a zone in which there is rupture of the constituent bonds of the material, generating free radicals. This core is also the region in which the heavy ion transfers a considerable amount of energy to the electrons of the material. Next, from this core, there is emission of secondary electrons, which will cause defects far from the core, thus generating a halo.
In the case of irradiation with heavy ions, the energy deposition is distributed as a function of the irradiation angle and is non-uniform. It is possible to create traces arranged in a predetermined pattern, and thus consequently to induce the grafting of units derived from the adhesion primers and/or from the radical-polymerizable monomers only in the abovementioned traces, which thus form “grafting domains”. Thus, it is possible to induce different grafting patterns especially by modifying the irradiation angle relative to the normal of the faces of the matrix. The irradiation dose generally ranges from 1 to 1000 kGy.
In a third variant of step (a3), this step may consist in subjecting the polymer matrix to (i) irradiation with heavy ions, (ii) followed by chemical revelation, generally by hydrolysis, of the latent traces created by the passage of the heavy ions, after which open channels are obtained, and then to (iii) electron irradiation as defined previously of said open channels, from which the radiografting may proceed. The chemical revelation consists in placing the matrix in contact with a reagent capable of hydrolysing the latent traces bearing short polymer chains formed by splitting of the existing chains during the passage of a heavy ion into the material during the irradiation (i), so as to form hollow channels in their place, the rate of hydrolysis during the revelation being greater than that for the non-irradiated parts. The reagents capable of ensuring the revelation of the latent traces, which may be selective, depend on the constituent material of the matrix. For fluoro polymer matrices as described previously, a strongly basic and oxidative solution may be used, for instance a 10N KOH solution in the presence of 0.25% by weight of KMnO4 at a temperature of 65° C., and, for polymers such as polyethylene terephthalate or polycarbonate, a basic solution may be used, optionally coupled with UV sensitization of the traces. The treatment leads to the formation of hollow cylindrical pores whose diameter can be modified as a function of the time of attack with the basic oxidative solution. Generally, the irradiation with heavy ions will be performed such that the membrane comprises a number of traces per cm2 of between 106 and 1011, especially between 5×107 and 5×1010, more especially about 1010. Other information concerning the reagents and the operating conditions that may be used for the chemical revelation as a function of the constituent material of the matrix may be found in Rev. Mod. Phys., 1983, 55, p-925.
After this revelation step, electron irradiation (iii) is performed to induce the formation of free radicals on the wall of the channels, the implementation in this case being similar to that outlined for the electron irradiation in general and enables the formation of a polymer coating to fill the pores. In general, the beam is oriented in a direction normal to the surface of the membrane and the surface thereof is uniformly scanned. The irradiation dose generally ranges from 10 to 200 kGy for the subsequent radiografting, and will typically be close to 100 kGy for PVDF. The dose is generally such that it is higher than the gel dose, which corresponds to the dose at and above which recombinations between radicals are promoted, resulting in the creation of inter-chain bonds leading to the formation of a three-dimensional network (or crosslinking), i.e. the formation of a gel, so as simultaneously to induce crosslinks, thus making it possible to improve the mechanical properties of the final polymer. Thus, for PVDF, it is recommended that the dose should be at least equal to 30 kGy.
In a fourth variant of step (a3), this step may consist in subjecting the polymer matrix to UV radiation. In this variant, the UV radiation, as a function of its intensity and its duration, may result in the formation of free radicals uniformly distributed in the bulk of the matrix or only at the surface. Furthermore, as presented in paragraph I.1.g of the experimental section, UV irradiation may result in activation of the defects and impurities of the polymer matrix prior to the creation of free radicals. Advantageously, the UV radiation may be generated by any UV radiation lamp such as an excimer lamp emitting incoherent radiation in the V-UV range, especially at 172 nm (surface and bulk modification of the polymer matrix) or a UV lamp emitting at 320-500 nm (surface modification of the polymer matrix). The irradiation may be continuous or sequential. The duration of continuous irradiation generally ranges from 5 minutes to 1 hour and especially from 15 to 45 minutes. In the case of sequential irradiation, the polymer matrix may be subjected to more than two irradiations, of identical or different duration and intensity. The duration of these irradiations generally ranges from 5 to 30 minutes and especially from 10 to 20 minutes.
As mentioned previously, step (a3) of irradiation of the polymer matrix makes it possible to create free radicals generally via the prior creation of non-radical reactive species derived from the activation of the defects and impurities in the material of the matrix.
The radicals and reactive species present in such an irradiated matrix and obtained after any of the variants of step (a3) may be trapped in polymer crystals, which correspond to crystalline domains in a polymer material and are generally known as crystallites, so as to extend the lifetime of the matrix in irradiated form. It is thus recommended to use matrices comprising crystallites and preferably between 30% and 50%, generally 40%. Thus, such irradiated matrices may be used immediately or stored under inert atmosphere, for instance nitrogen, and generally in the cold (˜18° C.), for several months before use and especially before performing step (b3).
During step (b3), the adhesion primer and the radical-polymerizable monomer are as defined previously and are especially in the form of a compound of formula (I) or (II) as defined previously. This primer or monomer is capable of reacting with a free radical so as, on the one hand, to form a covalent bond with the matrix, and, on the other hand, to initiate a radical polymerization reaction involving other primers and/or other radical-polymerizable monomers. Advantageously, the (mixture of) primer(s) and/or the (mixture of) monomer(s) used during step (b3) are in a solution S3 in the presence of a protic or non-protic solvent as defined previously. As protic solvents and non-protic solvents that may be used during step (b3), mention may be made, respectively, of water and ethyl acetate.
The amounts of adhesion primer(s) and/or of monomer(s) present in solution S3 are identical to the amounts of these components in solutions S1 and S2 as defined previously. The presence of surfactants as defined previously is also possible. As examples, when solution S3 contains only one (or a mixture of) monomer(s), the amount thereof is between 10% and 90% by weight in solution S3. Solution S3 can also contain a compound that limits the homopolymerization of the monomers used, such as Mohr's salt, in amounts of between 0.01% and 1% by mass and especially between 0.05% and 0.5% by mass.
After steps (b1), (b2) and (b3) and thus after step (a) according to the invention, the substrate bears at least one compound of polymer type grafted on its surface and/or in its bulk.
The compounds of polymer type used in the context of the present invention may be prepared from:
(i′) one (or a mixture of) adhesion primer(s) as defined previously (chemical grafting, electrografting or radiografting);
(ii′) one (or a mixture of) adhesion primer(s) as defined previously, mixed with one (or a mixture of) radical-polymerizable monomer(s) as defined previously (chemical grafting, electrografting or radiografting);
(iii′) one (or a mixture of) radical-polymerizable monomer(s) as defined previously (radiografting).
Thus, the compound obtained after the grafting step is polymeric or copolymeric, when the grafting is of the radiografting type and when this compound is derived from several monomer units of identical or different chemical species that is (are) the radical-polymerizable monomer(s) used during this grafting.
The compound obtained may also be “essentially” polymeric or copolymeric, derived from several identical or different radical-polymerizable monomer units and/or from adhesion primer molecules (case (ii′) above). The compounds obtained are “essentially” of the polymer type insofar as the film also incorporates species derived from the adhesion primer and not only from the monomers present. The compound obtained after the grafting step has a sequence of monomer units (or moieties) in which the first moiety (or first unit) is formed from an adhesion primer derivative or derived from an adhesion primer, the other moieties (or units) being, without preference, derived or obtained from the adhesion primers and/or from the polymerizable monomers.
Furthermore, it should be pointed out that, in case (i′) above, the adhesion primer molecules may be termed polymerizable insofar as, via a radical reaction, they can lead to the formation of molecules of relatively high molecular mass whose structure is formed essentially from multi-repeating units derived, actually or conceptually, from adhesion primer molecules. When the chemical grafting, electrografting or radiografting is performed only in the presence of identical or different adhesion primer molecules, the compounds obtained after this step may be formed solely from units derived or obtained from identical or different adhesion primers.
For these reasons, the compound obtained after any of the variants of step (a) is a compound of polymer type.
The average length of the compound(s) of polymer type is readily controllable, irrespective of the variant used of the grafting process of the present invention. For each of the parameters such as the duration of step (b1), (b2) or (b3) and as a function of the reagents it will use, a person skilled in the art will be capable of determining by repetition the optimum conditions for obtaining a compound of given length. As several compounds of polymer type may be grafted onto the substrate (potentially onto each free radical created on the substrate (radiografting or electrografting) or grafted onto the substrate (chemical grafting)), the compounds of polymer type obtained after step (a) may be in the form of an organic film.
Advantageously, the process according to the present invention includes an additional step, prior to the grafting (chemical, electrochemical or radiografting), of cleaning the surface onto which it is desired to graft the organic film, especially by buffing, polishing, oxidative treatment and/or abrasive treatment. A treatment additional to ultrasonication with an organic solvent such as ethanol, acetone or dimethylformamide (DMF) is even recommended. It is preferable for the chosen solvent not to impair the substrate.
Thus, according to one particular embodiment, the substrate undergoes an oxidative pretreatment before step (a). This mode applies particularly to substrates of organic nature and more specifically to polymers. Such treatments are described especially in Garbassi, F. Morra, M. Occhiello, E. Polymer Surfaces From Physics to Technology. 1995. John Wiley & Sons Ltd, England.
Application of the pretreatment enables oxidation and/or abrasion of the surface.
Physical oxidative treatments may be distinguished from chemical oxidative treatments. Among the physical treatments, mention may be made especially of:
“flame treatment” or “flaming”: exposure to a flame,
treatment by the corona effect: exposure to the ionized medium surrounding an electrical conductor brought to a particular electrical potential that does not result in the formation of an electric arc,
plasma treatment: exposure to a plasma, generally a cold plasma for which the degree of ionization of the reactive species contained in the plasma is less than 10−4 (globally less than 5000 K),
UV treatment: exposure to UV radiation in the presence of oxygen or ozone,
x-ray or γ ray treatment: exposure to high-energy photons in the presence of oxygen,
treatment by irradiation with electrons or with heavy ions: exposure to a beam of electrons or of heavy ions in the presence of oxygen (Zenkiewicz, M. et al. Applied Surface Science. 2007. 253, 8992-8999).
Among the chemical treatments, mention may be made especially of:
chemical reactions of Fenton type: correspond to oxidation in the presence of metal ions and hydrogen peroxide,
oxidation with alcoholic potassium hydroxide,
treatment with chemical oxidizing agents such as, in a non-limiting manner, KMnO4/H2SO4, K2Cr2O7/H2SO4, KClO3/H2SO4, CrO3/H2SO4,
treatment with ozone: exposure to a stream of ozone,
electrochemical treatments: exposure to an electrolytic bath in the presence of an electrical voltage (Brewis, D. M.; Dahm, R. H. International Journal of Adhesion & Adhesives. 2001. 21, 397-409).
The oxidative treatment makes it possible especially to improve the quality of the grafting and also the reduction of the reaction time during this step.
Advantageously, the compound of polymer type grafted after step (a) of the process according to the invention is, by nature, capable of chelating (complexing) at least one metal ion. Specifically, by virtue of the radical-polymerizable monomer(s) and/or the adhesion primer(s) from which it is obtained, the organic film bears at least one structure capable of chelating (complexing) at least one metal ion. In this variant, step (b) of the process is optional.
A group (or structure) that is capable of chelating (complexing) at least one metal ion is a molecular structure, which is advantageously neutral, for complexing cations, i.e. a structure bearing lone pairs, and thus containing non-quaternized nitrogen atoms, sulfur atoms or oxygen atoms. Advantageously, a group (or a structure) that is capable of chelating (complexing) at least one metal ion is chosen from the group formed by amines, amides, ethers, carbonyls, carboxyls, carboxylates, phosphines, phosphine oxides, thioethers, disulfides, ureas, crown ethers, aza-cryptands, sepulcrands (sepulcrates), podands, porphyrins, for instance tetrakis(benzoic acid)-4,4′,4″,4′″-(porphyrin-5,10,15,20-tetrayl), calixarenes, for instance calix[4]arene, pyridines, bipyridines, terpyridines, quinolines, ortho-phenanthroline compounds, naphthols, isonaphthols, thioureas, siderophores, antibiotics, ethylene glycol, cyclodextrins (CD), for instance natural cyclodextrins and peranhydrocyclodextrin derivatives, and also molecular structures substituted and/or functionalized with these functional groups, and/or one or more complexing cavity(ies) of verrous redox type. For further details regarding such groups (or structures), a person skilled in the art may consult patent applications FR 2 813 208 and FR 2 851 181.
Thus, the adhesion primers and the radical-polymerizable monomers that may be used in this variant bear at least one group from among R, R1, R2, R3 and R4 as defined previously, which is a group (or a structure) that is capable of chelating (complexing) at least one metal ion as listed above, or which is substituted with such a group. Examples that may be mentioned include acrylic acid; 4-carboxyphenyldiazonium tetrafluoroborate; methyl methacrylate in which the methyl group of the ester has been replaced with a crown ether; 4-vinylpyridine and aminoethyl, propyl, butyl, pentyl and hexyl methacrylamides.
As a variant, the compound of polymer type grafted after step (a) of the process according to the invention is not capable of chelating (complexing) at least one metal ion. Thus, this compound of polymer type must be subjected to conditions enabling it to be functionalized with a group or a structure that is capable of chelating at least one metal ion and step (b) of the process according to the invention is obligatory.
Thus, if the adhesion primer(s) and/or the radical-polymerizable monomer(s) bear one or more precursor(s) or groups of structures that are capable of chelating metal ions, step (b) consists in carrying out a modification of the precursor(s) borne by the compound of polymer type using one or more simple chemical reactions. By way of example, for a compound of polymer type in which at least one unit is derived from 4-nitrophenyldiazonium tetrafluoroborate, the nitro function may be reduced with iron to give a compound of polymer type having an amine as group capable of chelating metal ions. Similarly, a polyacrylonitrile polymer comprising a nitrile group gives access, after treatment with LiAlH4, to a compound comprising an amine as group capable of chelating metal ions. For practical purposes, a person skilled in the art may refer to international patent application WO 2004/005 410.
Similarly, this functionalization may involve other chemical reactions such as nucleophilic additions and substitutions, electrophilic additions and substitutions, cycloadditions, rearrangements, transpositions and metatheses, and also, more generally, click-chemistry reactions (Sharples et al., Angew. Chem. Int. Ed., 2001, 40, 2004-2021). Such reactions may be performed to functionalize the compound of polymer type obtained in step (a) with a structure comprising a cyclodextrin, a calixarene or a porphyrin, said structure also comprising another group capable of reacting with a group of the compound of polymer type.
The functionalization of the compound of polymer type may involve groups at the surface of this compound, but also groups that are a little less accessible especially when this compound has been radiografted onto a polymer matrix irradiated with heavy ions and thus bearing latent traces. Step (b) may use a swelling solvent and solution. A swelling solvent corresponds to a solvent that can penetrate into the compound of polymer type. Such solvents, when placed in contact with the compound of polymer type, generally lead to swelling of this compound that is perceptible by optical means, with the naked eye, or by simple optical microscopy. A standard test for determining whether a solvent is particularly suitable for a compound of polymer type consists in placing a drop of solvent on the surface of the compound and observing whether the drop is absorbed into the compound. It is desirable to use, among a set of solvents tested, those for which the absorption is fastest. The use of such a solvent leads to deeper functionalization in the compound of polymer type. Needless to say, it is also preferable for the reagents used for performing the reaction to be soluble in such a solvent.
Step (c) of the process according to the present invention consists in placing the compound of polymer type that is capable of chelating (or complexing) metal ions in contact with such metal ions. This step (c) is thus a chelation (or complexation) step.
In the context of the present invention, the term “metal ion” means an ion of the type Mn+, with M representing a metal and n being an integer between 1 and 7 and generally between 1 and 4. Typically, it is an ion of an alkali metal, an alkaline-earth metal, a poor metal (especially Al, Ga, In, Sn, Pb, Tl or Bi) or a transition metal. The present invention more particularly relates to ions of a transition metal. Advantageously, a metal ion according to the invention is chosen in the group consisting in Ag+, Ag2+, Ag3+, Au+, Au3+, Cd2+, Co2+, Cr2+, Cu+, Cu2+, Fe2+, Hg2+, Mn 2+, Ni2+, Pd+, Pt+, Ti4+ and Zn2+.
During step (c) of the process according to the invention, the metal ion is in a saline solution S4, advantageously in an aqueous saline solution, in the presence of an anionic counterion. As anionic counterions that may be used, mention may be made of a chloride (Cl−), bromide (Br−), a fluoride (F−), an iodide (I−), a sulfate (SO2−), a nitrate (NO3−) or a phosphate (PO43−).
It may be necessary to control the pH of the saline solution used during step (c), especially in order for the groups (or structures) that are capable of chelating the metal ions borne by the compound of polymer type to be in a form that is suitable for this chelation, for example in an ionized form. A person skilled in the art will know, as a function of the chelating groups borne by the compound of polymer type and of the solution S4, whether or not it is necessary to modify the pH of this solution. If it is necessary, a person skilled in the art knows various acid/base pairs that are capable of modifying the pH, such as CH3COOH/NH3 or CH3COOH/NaOH.
Finally, the chelation step (c) may be performed with stirring especially using a stirrer, a magnetic bar, an ultrasonication bath or a homogenizer and at a temperature below 60° C., especially between 5 and 50° C. and in particular between 10 and 40° C. Step (c) according to the invention is performed, in one more particular embodiment, at room temperature. The term “room temperature” means a temperature of 20° C.±5° C.
According to one particular mode, steps (a), (b) and (c) are performed simultaneously. Under these conditions, the solutions that may be used correspond to the same reactive solution S0 that contains the species necessary for performing the steps under consideration.
Step (d) of the process according to the invention consists in reducing the metal ions chelated (or complexed) by the compound of polymer type. Any reduction technique known to those skilled in the art may be used during this step. Advantageously, this reduction step is a chemical reduction, a photochemical reduction or an electrochemical reduction, especially when the substrate is conductive.
When step (d) according to the invention is a chemical reduction step, this step uses a reducing solution S5. Advantageously, the reducing solution S5 is basic. The reducing solution S5 comprises a reducing agent chosen especially from the group formed by sodium borohydride (NaBH4), dimethylaminoborane (DMAB) —H(CH3)2NBH3 and hydrazine (N2H4). When the reducing agent is NaBH4, the pH of the reducing solution S5 is neutral or basic, whereas, for DMAB, the pH of solution S5 is basic. The reducing agent is present in the reducing solution S5 at a concentration of between 10−4 and 5 M, especially between 0.01 and 1 M and in particular of about 0.1 M (i.e. 0.1 M±0.01 M). The chemical reduction step may be performed at a temperature of between 30 and 90° C., especially between 40 and 80° C. and in particular between 50 and 80° C. Furthermore, the chemical reduction step (d) may last between 30 seconds and 1 hour, especially between 1 and 30 minutes and in particular between 2 and 20 minutes.
When step (d) according to the invention is an electrochemical reduction step, this step may use an electrochemical cell in which the substrate obtained after step (c) (i.e. substrate onto which is grafted a compound of polymer type that chelates metal ions) serves as a measuring electrode, in the presence of a reference electrode such a KCl-saturated calomel electrode and a counterelectrode such as a graphite counterelectrode.
In this electrochemical cell, the electrodes are placed in a solution S6 comprising a polar solvent, at least one metal ion and at least one counterion as defined previously. The amount (ions+counterions) may range from 0.1 to 100 g/L, especially between 0.5 and 50 g/L and in particular between 1 and 20 q/L of solution S6. From the ions and counterions present in solution S6 of the initial potential thereof, a person skilled in the art will be capable of determining by repetition the optimum conditions for the reduction step (c) such as the duration and the cyclic voltammetry profile and the imposed voltage during this cycle.
Step (d) according to the invention may be a photochemical reduction step. Typically, Ag|, Pt|, Pd+, and Au+ ions may be reduced by UV irradiation (Redjala T et al., New Journal Of Chemistry, Vol. 32, Issue 8, 2008.; Eda Ozkaraoglu, Ilknur Tunc and Sefik Suzer, Polymer, Vol. 50, Issue 2, 2009). Generally, this reduction involves an intermediate that may typically be a counterion or an organic molecule which, when subjected to UV irradiation, provides the electrons necessary for the reduction of the metal ions. Furthermore, this type of process may involve linear optical phenomena and non-linear optical phenomena (typically a multiphoton process). The use of a laser may make it possible to obtain nano- or microstructuring of the metallic deposit (Tanaka T., Ishikawa A., Kawata S., Applied Physics Letters, vol. 88, issue 8, 2006; Kaneko K., Sun H. B., Duan X. M., Kawata S., Applied Physics Letters, vol. 83, issue 7, 2003). This photochemical reduction is advantageously performed in a solution S7. The various characteristics and properties of solution S6 as defined previously also apply to solution S7.
The chemical reduction of the metal ions chelated onto or in the compound of polymer type grafted onto the substrate or the electrochemical deposition of a metal onto the measuring electrode, i.e. onto or in the compound of polymer type grafted onto the substrate, is readily verifiable, typically visually and especially with the naked eye.
It should be pointed out that the use of a single step (c) and of a single step (d) may not suffice to achieve the desired metallization. In this case, at least one new cycle with a new step (c) and a new step (d) must be performed. It may be envisaged to perform, after the first chelation/reduction cycle, from 1 to 20 additional cycles, especially from 1 to 15 additional cycles and in particular from 1 to 10 additional cycles. The term “additional cycle” means a step (c) followed by a step (d). From 1 cycle to another, the conditions may be:
the same (same conditions during the chelation step and especially same chelating solution S5 or chelating solution S5 of the same composition; same type of reduction and reduction conditions; same reducing solution S6 or reducing solution S6 of the same composition);
slightly different (similar conditions during the chelation step and especially chelating solution S5 of similar composition and/or same type of reduction with similar conditions and especially a reducing solution S6 of similar composition);
different, especially with a change of the type of reduction. Examples that may be envisaged include a first cycle with chemical reduction followed by a second cycle with electrochemical reduction such as those defined previously.
It should also be pointed out that, despite several chelation/reduction cycles, it is possible for there not to be any formation of a metal, but only of a more reduced form than that of the metal ion, namely a metal oxide. This variant depends on the metal under consideration, the conditions during the reduction steps and the environment, especially the presence of oxygen. An appropriate choice of the conditions (redox potential of the reducing agent in the context of the chemical reduction, for example) makes it possible to obtain the desired type of metallic species. By modifying the experimental conditions, it is thus possible to obtain metallized substrates comprising various metal species: metal or metal oxide and also metal ions.
According to one embodiment of the invention, the process is applied to only part of the substrate, and it is thus possible to prepare a selectively metallized substrate. To do this, it is possible to selectively expose only one (or more) given surface(s) of the substrate to certain steps of the process or alternatively to mask one (or more) surface(s) that should not be treated according to the process.
A mask, or pad, typically corresponds to a physical entity that is neither grafted to the surface that should not be treated, nor covalently bonded thereto. It may especially be a bulk material or a thin layer of material, typically of a few Angstroms to a few microns, generally of organic nature, deposited onto the surface.
The mask makes it possible to locally “mask” the chemical reactivity of the substrate, the surface zones of the substrate that are equipped with the mask being protected from the reaction environment (for example the chemical or radiochemical environment). After removing the mask, the surface that was protected, unlike that which was not equipped with a mask, will not have reacted.
The mask may be formed, for example, from a thin layer of inorganic or organic material acting as a layer of reduced cohesion that may be readily removed under mild conditions. A layer of material is considered as such insofar as it does not necessitate the use of extreme conditions harmful to the metallized substrate in order to be removed. Typically, the mild conditions correspond to simple chemical washing, generally performed using a solvent in which the mask is soluble, an ultrasonication treatment in a solvent in which the mask is soluble, or raising of the temperature. Needless to say, it is desirable for the mask not to be soluble in the solvent used in the step under consideration. Thus, it is recommended to use a mask that has higher affinity for the surface than for the reaction solvent.
The material constituting the mask may thus be chosen within a wide range. It will generally be chosen as a function of the nature of the substrate.
The mask may react with the species generated during the process. In any case, it is possible to remove it to expose the protected zones of the surface of the substrate (which may be likened to “lift-off” methods in lithography).
Mask deposition techniques are well known to those skilled in the art. It may especially be a case of coating, vaporization or dipping. Thus, the mask, in the form of a thin layer of material, may, for example, be deposited either by direct drawing using a felt (pencil type) impregnated with the chosen material. On glass, it is possible, for example, to use as mask a marker such as those sold in stationery shops, or alternatively fatty substances. It is also possible to use the “padding” technique. This technique is applicable especially in the case of substrates with a surface for complexing sulfur atoms, such as a gold surface; in this case, the mask will generally be composed of alkylthiols, in particular long-chain alkylthiols often of C15-C20 and typically C18 (technique known as microcontact printing). More generally, standard lithography techniques may be used to form the mask: spin coating, followed by exposure through a physical mask or via a guidable beam of light or of particles, followed by revelation.
The present invention also relates to the substrate that may be obtained after step (a) or step (b) of the process of the invention as defined previously, said substrate being grafted by at least one compound of polymer type capable of chelating at least one metal ion, referred to hereinbelow as “substrate A”. All the variants in terms of substrate, compound of polymer type and type of grafting apply to substrate A according to the invention.
Substrate A may advantageously be used for complexing at least one metal ion and especially for purifying a solution liable to contain at least one metal ion. Thus, the present invention relates to a process for purifying a solution liable to contain at least one metal ion, which consists in placing said substrate A in contact with said solution and then in subjecting said substrate to at least one reduction step as defined previously (step (d) defined previously). The solution that may be used for this purification process may be any solution liable to contain one (or more) metal ions. Advantageously, said solution is chosen from the group consisting in any sample of wastewater, mains water, river water, seawater, lake water and groundwater. A substrate that is particularly suited to this use is a substrate, especially with a surface area from 1 cm2 to 10 m2, made of a polymer matrix as defined previously, especially irradiated with an electron beam, and which thus bears compounds of polymer type grafted throughout its bulk. Furthermore, the purification process may comprise an additional step, after the reduction, of recovering the metals or metal oxides.
The present invention also relates to the substrate that may be obtained after step (c) of the process of the invention as defined previously, said substrate being grafted with at least one compound of polymer type chelating at least one metal ion, referred to hereinbelow as “substrate B”. All the variants in terms of substrate, compound of polymer type and type of grafting and of metal ion apply to substrate B according to the invention.
Substrate B may advantageously be used for its particular properties such as its antifungal or antibacterial properties. Specifically, a substrate B onto or in which are chelated Cu2+ or Fe2+ ions may be used, for example, as an antifungal agent, and a substrate B onto or in which are chelated ions, especially those specified in international patent application WO 2001/05233, and particularly silver ions, for instance Ag+, Ag2+ or Ag3+, may be used as an antibacterial and/or antifungal agent. As examples of substrates B that may be used for these applications, mention may be made of substrates coated with an organic film formed by several compounds of polymer type, which are especially useful in the medical field, such as a fabric, an implant, a surgical device, or a container for foodstuffs or pharmaceutical products.
Finally, the present invention relates to the substrate that may be obtained via the process of the invention as defined previously, referred to hereinbelow as “substrate C”.
Substrate C may be in the form of a substrate as defined previously (i.e. inorganic or organic, conductive, semiconductive or insulating), coated (i.e. grafted) with a metallic or metal oxide organic film. Examples of such substrates C that may be mentioned include a tapware component, a motor vehicle accessory, tableware, a container for foodstuffs, cosmetic products or therapeutic products, (micro)particles used in cosmetics, etc.
As a variant, substrate C may have, on its surface and/or in its bulk, several compounds of metallic or metal oxide grafted polymer type, dispersed or grouped in nanodomains. This variant applies most particularly to substrates obtained by using a process according to the invention using a polymer matrix and radiografting as defined previously.
Specifically,
In the case of
As a function of the type of metal ion used in the process according to the invention, substrate C obtained may be magnetic and used for this property. An example that may be mentioned is a substrate C in the form of a magnetic metallized clapper membrane used with an electromagnetic in a opening/closing clapper system.
Similarly, a substrate B or a substrate C according to the invention in the form of magnetic micro- or nanoparticles according to the invention may be useful in imaging and especially for detecting ions by paramagnetic resonance (EPR). Furthermore, PVDF, which constitutes the polymer matrix of these particles, has the advantage of being a fluoro polymer and thus of having a large fluorine number. Since the 19F signal is proportional to the amount of fluorine present in the molecule of interest, it appears to be a candidate of choice for 19F imaging. Furthermore, on account of its structure and its polymerization method, the 19F signal of PVDF has a relatively fine intense signal. By combining the effect induced on the relaxation of water by metals or metal oxides or metal ions or the various combinations of the various elements present that have been described previously, either at the surface of the system or throughout it, and the fluorine signal of the base polymer, a potential H/F bimodal system for MRI imaging is obtained.
Substrate C according to the invention may also be used to make the triple point for fuel cells (or PEMFC: Proton Exchange Membrane Fuel Cells). The triple point or triple point zone is a zone in an alkaline fuel cell that simultaneously allows electronic conduction, ionic conduction and a catalytic reaction. In this application, substrate C is advantageously in the form of a flexible membrane metallized, for example, with platinum.
Finally, substrate C that may be obtained via the process according to the invention may have a biological or biologically active molecule immobilized on its surface. In the context of the present invention, the term “biological or biologically active molecule” means a molecule chosen from the group consisting in amino acids; peptides; proteins such as gelatin, protein A, protein G, streptavidin, biotin, an enzyme such as glucose oxidase; antibodies and antibody fragments; cell or membrane receptors; polysaccharides, for instance glycosaminoglycans and especially heparin; lipids; cells or cell parts such as organelles or cell membranes, and nucleic acids such as DNA and RNA. The present invention thus relates to a biochip comprising a substrate C according to the invention on which is immobilized at least one biological or biologically active molecule as defined previously.
A person skilled in the art knows various techniques for immobilizing on a substrate C according to the invention at least one biological or biologically active molecule by functionalizing the substrate with or without using coupling agents. As a variant, substrate C may bear at least one biological or biologically active molecule immobilized on its surface, without functionalization. Substrate C may thus be used as a biochip with magnetic addressing or magnetochip.
Irrespective of the variant, a substrate C onto which is immobilized, with or without functionalization, a biological or biologically active molecule as defined previously, and preferably metallized according to given mapping, may be used as a biochip or for monitoring a biological phenomenon of the redox type or a phenomenon involving electron transfer.
As examples of particular applications, substrate C according to the invention can immobilize biological or non-biological catalysts for dissociating hydrogen, the metallic layer of said substrate C enabling the electrons to be recovered.
Other characteristics and advantages of the present invention will emerge more clearly to a person skilled in the art on reading the examples below, which are given as non-limiting illustrations, with reference to the attached figures.
In the examples that follow, various substrates were treated according to the invention to give particular products and devices, the properties and applications of which are outlined. The examples presented are summarized in Table 1 below.
In order to take precise measurements, substrates were carefully cleaned; the results were able to be reproduced successfully under less rigorous conditions.
Unless otherwise specified, the substrates used, when they are of the same type, have the same characteristics and were obtained from the same supplier.
In the protocols presented, Mohr's salt was used in order to limit the homopolymerization of acrylic acid (AA).
The PVDF particles illustrating the examples may be prepared according to the process outlined in patent EP 1 454 927 corresponding to patent U.S. Pat. No. 7,012,122.
The degree of grafting of the organic films onto the various substrates was determined by measuring the gain in mass found after treatment.
I—Preparation of the Substrates
I-1 Use of Radiografting
I-1-a Heterogeneous Membranes
In a first stage, a polyvinylidene fluoride (PVDF) matrix (6×30 cm, 9 μm thick) was subjected to bombardment with Xe heavy ions. The flux ranged from 5×107 to 5×1010 ions per cm2. This corresponds to a dose ranging from one Gy to 1000 kGy. The irradiation angle was set at 90°. This step enabled the creation of latent traces comprising radical species.
The matrices prepared according to this mode may be used immediately or stored under an inert atmosphere, such as nitrogen, and generally in the cold (−18° C.), for several months before use.
In a second stage, the irradiated matrix was placed in contact with AA in an aqueous solution, having undergone sparging with nitrogen for 15 minutes, containing from 20% to 80% by mass of acid and 0.1% by mass of Mohr's salt, at 60° C. for 1 hour with stirring. The same protocol was performed with ethyl acetate as solvent.
The membrane obtained was then extracted from the solution, cleaned with water and extracted with boiling water using Sohxlet apparatus for 24 hours. It was then dried for 12 hours under high vacuum.
The degree of grafting obtained via this protocol is generally between 10% and 300% by mass.
I-1.b Homogeneous Membranes with Electron Irradiation
In a first stage, a PVDF matrix (6×30 cm, 9 μm thick) was subjected to electron irradiation. The dose ranged from 50 to 150 kGy. The irradiation angle was set at 90°. This step enabled the creation of radicals trapped within the PVDF crystallites.
In a second stage, the irradiated matrix was placed in contact with AA. To do this, the matrix was dipped in a solution, degassed beforehand, comprising from 20% to 80% by mass of acid in water (or ethyl acetate) and 0.1% by mass of Mohr's salt at 60° C. for 1 hour with stirring. The membrane obtained was then extracted and treated as previously.
The degree of grafting obtained by this protocol is between 10% and 120% by mass.
I-1.c Membrane Grafted on One Face
Electron irradiation was performed as previously.
In a second stage, the irradiated matrix was placed, for a time of between 10 minutes and 1 hour, between two compartments, one of which contains a solution, degassed beforehand and then placed at 60° C. with stirring, comprising from 20% to 80% by mass of AA in water (or ethyl acetate) and 0.1% by mass of Mohr's salt. The membrane obtained was then extracted and treated as previously.
The degree of grafting obtained via this protocol is between 1% and 30% by mass. Modification of only one of the faces was confirmed by Fourier-transform infrared (or FTIR) spectrometry.
I-1.d Microparticles
In a first stage, PVDF microparticles with a mean diameter ranging from 1 to 8 μm were subjected to electron irradiation whose dose ranged from 50 to 150 kGy.
In a second stage, the microparticles were dipped in a solution, degassed beforehand, comprising from 20% to 80% by mass of AA as used previously.
The microparticles obtained were then isolated by filtration on a sinter of suitable size and then cleaned with water. Next, boiling 0.1 N sodium hydroxide solution was added. The microparticles were then cleaned twice with boiling water and treated with 1 N HCl solution before being isolated by filtration.
After drying for 12 hours under high vacuum, a degree of grafting of between 10% and 20% by mass was found.
I-1.e Nanoparticles
PVDF nanoparticles with a mean diameter ranging from 20 to 200 nm were treated according to a protocol identical to that used for the microparticles, with the exception that the grafting was performed by ultrasonication.
The degree of grafting found is between 10% and 120% by mass.
I-1.f Homogeneous Membranes—UV Irradiation
A PVDF membrane (2.15 cm×3.8 cm, 13.68 mg) was attached to a glass plate and the assembly was degassed under nitrogen for 20 minutes. The assembly was then irradiated for 30 minutes using an excimer lamp placed 7 cm away, emitting incoherent radiation in the V-UV range at 172 nm. EPR analysis confirmed the presence of radicals in the PVDF. The membrane was then immersed in a solution containing 80% by weight of acrylic acid in water. After sparging for 15 minutes under nitrogen, the assembly was heated at 60° C. for 1 hour. The polymerization yield obtained is 260% after 18 hours of extraction using Sohxlet apparatus and 2 hours of drying in a vacuum oven.
The modified membrane was analysed by FT IR in ATR mode, and the presence of the carbonyl band of acrylic acid was detected at 1703 cm−1.
The membrane was also dipped in a saturated copper sulfate solution in order to exchange the proton of acrylic acid and to check by EDX whether the presence of Cu2+ is observed in the thickness of the membrane. After analysis, it was found that polyacrylic acid is present throughout the thickness of the matrix.
The membrane was modified in the thickness.
I-1.g Membrane Surface Modification—UV Irradiation
A PVDF membrane (1 cm×4 cm×9 μm) was placed in a heat-shockproof tube (Pyrex®) and then degassed for 30 minutes and placed under a nitrogen atmosphere. After this period, the tube was placed 4 cm from the fibre optic of a UV lamp (320 to 500 nm) and four irradiations, of 15 minutes each, were successively performed. After irradiation, the membrane was placed in ambient atmosphere for 10 minutes, and then dipped in a solution of pure AA degassed beforehand and having been subjected to sparging with nitrogen throughout the irradiation. The assembly was then degassed for 10 minutes, then dipped in a thermostatically maintained at 60° C. for 6 hours.
The modified membrane extracted from the reaction medium was cleaned with water for 15 minutes in the presence of ultrasound or extracted with boiling water using Sohxlet apparatus for 18 hours and then dried under high vacuum.
The FTIR (ATR) spectrum of the membrane shows an absorbance peak at 1703 cm−1 characteristic of the C═O band of poly(acrylic acid). Contact angle measurements were also performed and confirmed a difference between the contact angles found before and after grafting, the membrane becoming more hydrophilic after the treatment.
The signal observed on EPR as a function of the irradiation time made it possible to show that the mechanism does not correspond to the creation of radicals, but to “activation” of the pre-existing defects or impurities in the membrane, which do not appear to be detectable before irradiation.
In this case, the membrane was only modified at the surface.
I-2 Use of Chemical Grafting
I-2.a Gold-Coated Glass Plate
A solution of a diazonium salt was first prepared from 10 ml of a 0.1 M solution of 1,4-phenyldiamine in HCl (0.5 M), to which were added 10 ml of a 0.1 M solution of NaNO2 in water. To this solution of diazonium salt were added 200 mg of iron filings and then, after 5 minutes, 10 mL of AA.
A glass slide (3.8×0.7×0.1 cm) covered with a layer of chromium about 9 nm thick, followed by a layer of gold about 60 nm thick, cleaned beforehand under ozone for 10 minutes, was then introduced into the reaction medium for 2 hours, before being rinsed with water and introduced into a sodium hydroxide solution at pH 9.5 in the presence of ultrasonication so as to dissolve the ungrafted polyacrylic acid (PAA). After rinsing with water, the slide was dried. The thickness of the layer formed is a few nanometres.
I-2 .b Acrylonitrile-Butadiene-Styrene, Polyamide and Acrylonitrile-Butadiene-Styrene/Polycarbonate Plates
The protocol used for the gold-coated glass slide was successfully applied to acrylonitrile-butadiene-styrene (ABS), acrylonitrile-butadiene-styrene/polycarbonate (ABS/PC) and polyamide plates (4×1×0.25 cm) cleaned beforehand by ultrasonication in a soapy aqueous solution and in 0.5 M hydrochloric acid solution.
I-2.c Microparticles
A diazonium salt was prepared from phenyldiamine as indicated previously.
According to a first protocol, after 5 minutes, 2 g of PVDF microparticles, with a mean diameter of between 1 and 8 μm, were then introduced into the reaction medium for 2 hours with stirring, under nitrogen and at room temperature. The microparticles thus obtained were then isolated by filtration and rinsed with water, followed by washing with sodium hydroxide solution (0.1 N) in the presence of ultrasound, rinsed twice with water, with HCl solution (0.1 N) and then with water, and finally dried under high vacuum for 12 hours.
According to a second protocol, after 5 minutes, 2 mL of AA were added, and then, after 10 minutes, 2 g of PVDF microparticles were introduced into the reaction medium, which was stirred for 2 hours under a nitrogen atmosphere and at room temperature.
The microparticles thus obtained were isolated by filtration and then rinsed with water, washed with sodium hydroxide solution (0.1 N) in the presence of ultrasound for 5 minutes, and then isolated again by filtration and rinsed twice with water, with HCl solution (0.1 N) and then with water, and finally dried under high vacuum for 12 hours.
I-2.d Nanoparticles
Nanoparticles (1 g) were treated according to the methods outlined for the microparticles.
The protocols were also performed on activated nanoparticles. The activation was performed by first adding the nanoparticles to an alcoholic potassium hydroxide solution (3 g of potassium hydroxide in 15 mL of absolute ethanol) at room temperature for 10 minutes. Next, the nanoparticles were extracted by filtration and then rinsed twice with ethanol and then with water until a neutral pH of the filtrate was obtained. This step allowed the creation of unsaturated bonds of the —CH═CF— type at the surface of the nanoparticles, thus allowing an “activated” surface for the grafting of a layer via the chemical process.
I-3 Oxidative Pretreatment of the Substrates
An oxidative pretreatment was performed on various materials before preparing them. Various protocols were used for substrates of ABS and ABS/PC plates.
I-3.a Fenton Reaction Using Iron (II) Sulfate
The samples were dipped in 25 ml of an aqueous solution of iron sulfate (3.47 g, 5×10−2 mol) and of sulfuric acid (10−3 M). 5 mL (6.2×10−2 mol) of aqueous 35% hydrogen peroxide solution were then added and the pH maintained at 3. After 25 minutes, the samples were rinsed with MilliQ water and exposed to ultrasound in water for 10 minutes, followed by drying.
I-3.b Treatment with KMnO4
The samples were dipped in 25 mL of a solution of 0.75 g of potassium per manganate (5×10−3 mol) in sulfuric acid (3.3 M). After 15 minutes, the samples were rinsed with MilliQ water and exposed to ultrasound in water for 10 minutes, followed by drying.
II—Chelation of Metal Ions
The materials coated with chelating organic films were introduced into solutions of metal salts for variable times, and infrared (IR) spectrometry measurements before and after exposure made it possible to confirm the complexation. Table 2 below presents the infrared band, expressed in cm−1, for various metal ions.
The parameters used are outlined in Table 3 below.
The experiments were performed with aqueous solutions (0.1 M) of the following salts: FeSO4.7H2O, CuSO4.5H2O, NiSO4.7H2O, CoSO4.7H2O, Mn(NO3)2.4H2O, NiSO4.7H2O, AgSO4.
The pH of the solutions was buffered with a CH3COOH (0.1 M) /NH3 (0.6 M) or CH3COOH (0.1 M) /NaOH (0.1 M) mixture in order for the carboxylic acid functions present on the substrate to be in ionized form. The AgSO4 solution was not buffered.
During the exposure, the saline solutions were stirred and, for some of them, exposed to ultrasound (US). After the exposure, the materials were rinsed with deionized water (18 M Ω, MilliQ), optionally in the presence of ultrasound. In the case of the micro- and nanoparticles, they were extracted from the saline solutions by filtration, before being rinsed in aqueous solutions and extracted therefrom.
The charged materials, i.e. comprising metal ions in complexed form, were dried under high vacuum after rinsing to facilitate the EPR measurements.
After the treatment of the saline solutions, electron paramagnetic resonance spectra were acquired (Brüker ER-200D Band X spectrophotometer equipped with a helium and nitrogen cryostat for the acquisition of spectra at low temperatures) on the micro- and nanoparticles after drying. Measurements were taken at 20 kelvins and at 293 kelvins and made it possible to observe that the response of these systems varies as a function of the temperature and that they follow a Curie law (super- and/or paramagnetic effect).
The results obtained for the chelation are similar with the samples that underwent an oxidative treatment.
The step of preparing chelating organic films on a substrate presented in I was also successfully performed simultaneously with the chelation step presented in II.
III—First Reduction Cycle
The charged materials, prepared previously, were then treated with an aqueous reducing solution or by photochemistry to reduce the metal salts within the films. The conditions are given in Table 4 below.
III-1 Chemical Reduction
The reducing solutions used corresponded to aqueous NaBH4 solutions (0.1 M) at neutral or basic pH.
In this case, the pH of the solution was modified with NaOH solution (0.01 M).
The reduction was performed at a temperature of between 50 and 80° C. for 2 to 20 minutes. After reaction, the treated samples were rinsed with ethanol and with deionized water (18 M Ω, MilliQ), optionally in the presence of ultrasound. In the case of the micro- and nanoparticles, they were extracted from the solutions by filtration before being rinsed in aqueous solutions and extracted therefrom. Each of the materials was then dried under high vacuum.
Reduction of the metal ions was observed by monitoring the change in the IR spectra of the materials.
After this first reduction step, new electron paramagnetic resonance spectra were acquired on the micro- and nanoparticles (
As a function of the ions that were chelated, the materials have magnetic properties that are clearly visible to the naked eye. Specifically, the proximity of a magnet makes it possible to move them, both as solutions and in dry form.
III-1 Photochemical Reduction
In the case of the Ag salts, the reduction was performed by photochemistry, and is a photochemical reduction.
Various membranes were subjected to UV irradiation (320 to 500 nm) under ambient atmosphere or in aqueous NaCl solution (9 g/L), about 3 cm from the lamp, for 1 to 15 minutes.
The treatment leads to browning of the membrane, which, after analysis, corresponds to metallization. XPS analysis of the Ag 3d5/2 band shows an energy of 368 eV corresponding to the presence in and on the membrane of Ag in metallic form Ag0.
IV—Chelation/Chemical Reduction Cycles
In order to obtain uniform metal layers, the protocols described previously (chelation and reduction) were performed again, still alternating a first complexation phase followed by a reduction phase. The number of complexation/reduction phases varies from to 10 times. From a cycle, metallization is detectable with the naked eye following the change observed on the material.
The experimental protocols are summarized in the tables that follow.
To check the conductive nature of the deposited layers, the resistance was measured using a standard ohmmeter, for the substrates based on PVDF membranes (results IV.1 to IV.5 below), in length and thickness. Various lengths were taken into account (0.2-0.8 and 2 cm).
To check the mechanical strength of the layers that follow, a test with an adhesive tape was performed. It consists in bonding to the layer a piece of adhesive tape and then in removing it from the layer. If the deposited layer comes off with the adhesive, the mechanical strength is considered as poor. If the layer remains insensitive to the adhesive, the mechanical strength is considered as good. The adhesive tape that was used is a Progress brand high-performance invisible adhesive tape.
IV-1 Creation of a Uniform Metallic Layer of Ni on a PAA Radiografted PVDF Membrane
This example was performed with various reducing agents. The conditions are summarized in Tables 5 and 6.
ATR-FTIR attenuated total reflectance polarized spectroscopy made it possible to determine the presence of the proton on the COOH/COO− group of the polyacrylic acid (
On the XPS spectrum, the binding energy peak equal to 853 eV corresponds to nickel in its reduced form Ni0 of the electrons of the 2p3/2 shell. The peak at 856 eV reveals the presence of nickel oxide (
IV-2 Creation of a Uniform Cu Metal Layer on a PAA Radiografted PVDF Membrane
Various reducing agents were used in this example. The conditions are summarized in Tables 7 to 9 below.
In
In the XPS spectrum, the peaks as solid and dashed lines at 933 and 953 eV confirm the presence of copper Cu0 according to the literature data for this metal (
IV-3 Creation of a Uniform Fe Metallic Layer on a PAA Radiografted PVDF Membrane
The experimental conditions of this example are summarized in Table 10 below.
IV-4 Creation of a Uniform Co Metallic Layer on a PAA Radiografted PVDF Membrane
The experimental conditions of this example are summarized in Table 11 below.
In
IV-5 Creation of a Uniform Ni Metallic Layer on Only One Side of a PAA Radiografted PVDF Membrane
The experimental conditions of this example are summarized in Table 12 below.
In
Moreover, the deflection of the absorption baseline appears to be characteristic of the absorption of metals, and in this case of nickel.
As expected, the presence of the characteristic band of the COOH/COO− group of PAA is virtually not observed (
This example demonstrates the importance of PAA. Without chelation of the PAA, there is no metallization.
IV-6 Creation of a Uniform Ni Metallic Layer on a PAA Chemically Grafted ABS Plate
The experimental conditions of this example are summarized in Table 13 below; the baths used were developed on the basis of industrial standards.
IV-7 Creation of a Uniform Ni Metallic Layer on a PAA Chemically Grafted ABS Plate
The experimental conditions of this example are summarized in Table 14 below.
IV-8 Creation of a Uniform Ni Metallic Layer on a PAA Chemically Grafted Polyamide Plate
The experimental conditions of this example are summarized in Table 15 below.
IV-5 Creation of a Uniform Cu Metallic Layer on PAA Chemically Grafted ABS/PC and PC Plates that have Undergone an Oxidative Treatment
The experimental conditions are summarized in Tablets 16 to 18.
The Fenton or KMnO4 pretreatments improve the grafting and thus the properties of the treated surfaces.
V—Chelation/Electrochemical Reduction Cycles
A PVDF membrane radiografted with PAA having undergone a first step of chelation/chemical reduction with a nickel salt was used as measuring electrode. The electrochemical system adopted was formed by a KCl-saturated calomel reference electrode and a graphite counterelectrode.
The electrodes were dipped in a CuSO4 solution at 10 g/L, and the initial potential was about 0.1 V.
A voltammetry cycle down to −0.6 V over 60 seconds was imposed on the system. During the voltage rise, the experiment was stopped at about −0.35 V (
This cycle demonstrated the deposition of copper on the measuring electrode. Specifically, the current increased when the voltage decreased and copper was deposited on the membrane acting as the measuring electrode. Reduction of the copper took place at the measuring electrode.
Confirmation was able to be made visually. Specifically, after electro-reduction, the membrane had a coppery colour.
Claims
1) Process for preparing a metallized substrate, comprising:
- a) grafting onto said substrate a compound of polymer type optionally bearing a group (or structure) capable of chelating at least one metal ion;
- b) optionally subjecting said compound of polymer type to conditions for functionalizing it with a group (or structure) capable of chelating at least one metal ion;
- c) placing said compound of polymer type capable of chelating at least one metal ion obtained after step (a) or (b) in contact with at least one metal ion;
- d) subjecting the compound of polymer type obtained in step (c) to conditions for reducing said chelated metal ion(s);
- e) optionally repeating steps (c) and (d) until a metallized substrate is obtained.
2) Process according to claim 1, characterized in that the grafting of said step (a) is grafting chosen from the group formed by chemical grafting, electrografting and radiochemical grafting.
3) Process according to claim 1, characterized in that said grafting step (a) involves chemical grafting comprising the steps consisting in:
- a1) placing the substrate to be metallized in contact with a solution S1 comprising at least one adhesion primer and optionally at least one monomer different from the adhesion primer and capable of undergoing radical polymerization;
- b1) subjecting said solution S1 to non-electrochemical conditions enabling the formation of radical species from said adhesion primer.
4) Process according to claim 1, characterized in that said grafting step (a) involves electrografting comprising the steps consisting in:
- a2) placing the conductive or semiconductive substrate in contact with a solution S2 comprising at least one adhesion primer and optionally at least one polymerizable monomer other than said adhesion primer and capable of undergoing radical polymerization especially as defined previously;
- b2) polarizing said substrate at a more cathodic electrical potential than the reduction potential of the adhesion primer used in step (a2),
- steps (a2) and (b2) being performed in any order.
5) Process according to claim 1, characterized in that said grafting step (a) involves radiografting comprising the steps consisting in:
- a3) irradiating a substrate of polymer matrix type;
- b3) placing the irradiated substrate obtained in step (a3) in contact with at least one adhesion primer and/or at least one radical-polymerizable monomer.
6) Process according to claim 5, characterized in that said step (a3) consists in subjecting the polymer matrix to an electron beam.
7) Process according to claim 5, characterized in that said step (a3) consists in subjecting the polymer matrix to bombardment with heavy ions and especially with a beam of heavy ions.
8 Process according to claim 5, characterized in that said step (a3) consists in subjecting the polymer matrix to UV radiation.
9) Process according to claim 3, characterized in that said adhesion primer is a cleavable aryl salt chosen from the group formed by aryldiazonium salts, arylammonium salts, arylphosphonium salts, aryliodonium salts and arylsulfonium salts.
10) Process according to claim 3, characterized in that said adhesion primer is a compound chosen from the group formed by 4-nitrobenzenediazonium tetrafluoroborate, tridecylfluorooctylsulfamylbenzenediazonium tetrafluoroborate, phenyldiazonium tetrafluoroborate, 4-nitrophenyldiazonium tetrafluoroborate, 4-bromophenyldiazonium tetrafluoroborate, 4-aminophenyldiazonium chloride, 2-methyl-4-chlorophenyldiazonium chloride, 4-benzoylbenzenediazonium tetrafluoroborate, 4-cyanophenyldiazonium tetrafluoroborate, 4-carboxyphenyldiazonium tetrafluoroborate, 4-acetamidophenyldiazonium tetrafluoroborate, 4-phenylacetic acid diazonium tetrafluoroborate, 2-methyl-4-[(2-methylphenyl)diazenyl]benzenediazonium sulfate, 9,10-dioxo-9,10-dihydro-1-anthracenediazonium chloride, 4-nitronaphtalenediazonium tetrafluoroborate and naphtalenediazonium tetrafluoroborate.
11) Process according to claim 3, characterized in that the radical-polymerizable monomer(s) are chosen from the monomers of formula (II) below:
- in which the groups R1 to R4, which may be identical or different, represent a non-metallic monovalent atom such as a halogen atom or a hydrogen atom, a saturated or unsaturated chemical group, such as an alkyl or aryl group, a group —COOR5 or —OC(O)R5 in which R5 represents a hydrogen atom or a C1-C12 and preferably C1-C6 alkyl group, a nitrile, a carbonyl, an amine or an amide.
12) Process according to claim 3, characterized in that the radical-polymerizable monomer(s) are chosen from the group formed by vinyl esters such as vinyl acetate, acrylic acid, acrylonitrile, methacrylonitrile, methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and glycidyl methacrylate, and derivatives thereof; acrylamides and especially aminoethyl, propyl, butyl, pentyl and hexyl methacrylamides, cyanoacrylates, diacrylates and dimethacrylates, triacrylates and trimethacrylates, tetraacrylates and tetramethacrylates (such as pentaerythrityl tetramethacrylate), styrene and derivatives thereof, para-chlorostyrene, pentafluorostyrene, N-vinylpyrrolidone, 4-vinylpyridine, 2-vinylpyridine, vinyl, acryloyl or methacryloyl halides, divinylbenzene (DVB) and more generally vinyl or acrylate- or methacrylate-based crosslinking agents, and derivatives thereof.
13) Process according to claim 1, characterized in that said group (or said structure) that is capable of chelating (complexing) at least one metal ion is chosen from the group formed by amines, amides, ethers, carbonyls, carboxyls, carboxylates, phosphines, phosphine oxides, thioethers, disulfides, ureas, crown ethers, aza-crowns, thio-crowns, cryptands, sepulcrands (sepulcrates), podands, porphyrins, calixarenes, pyridines, bipyridines, terpyridines, quinolines, ortho-phenanthroline compounds, naphthols, isonaphthols, thioureas, siderophores, antibiotics, ethylene glycol, cyclodextrins, and also molecular structures substituted and/or functionalized with these functional groups, and/or one or more complexing cavity(ies) of venous redox type.
14) Process according to claim 1, characterized in that, during step (c), the metal ion is chosen from the group formed by Ag+, Ag2+, Ag3+, Au+, Au3+, Cd2+, Co2+, Cr2+, Cu+, Cu2+, Fe2+, Hg2+, Mn2+, Ni2+, Pd+, Pt30, Ti4+, and Zn2+.
15) Process according to claim 1, characterized in that said reduction step (d) is a chemical reduction, a photochemical reduction or an electrochemical reduction.
16) Process according to claim 1, characterized in that said step (d) is a step of chemical reduction using a reducing solution S5 comprising a reducing agent chosen from the group formed by sodium borohydride (NaBH4), dimethylaminoborane (DMAB) and hydrazine (N2H4).
17) Process according to claim 1, characterized in that said step (d) is a step of electrochemical reduction using an electrochemical cell in which the substrate obtained after step (c) serves as measuring electrode, in the presence of a reference electrode and a counterelectrode.
18) Substrate obtained after step (a) or step (b) of a process as defined in claim 1.
19) Use of a substrate according to claim 18, for complexing at least one metal ion and especially for purifying a solution liable to contain at least one metal ion.
20) Substrate obtained after step (c) of a process as defined in claim 1.
21) Use of a substrate according to claim 20, as an antifungal agent or as an antibacterial agent.
22) Substrate obtained via a process as defined in claim 1.
23) Substrate according to claim 22, characterized in that it is in the form of a tapware component, a motor vehicle accessory, kitchenware, a container for foodstuffs, cosmetic products or therapeutic products or (micro)particles used in cosmetics.
24) Substrate according to claim 22, characterized in that it is magnetic.
25) Substrate according to claim 34, characterized in that it bears a biological or biologically active molecule immobilized on its surface.
26) Process according to claim 4, characterized in that said adhesion primer is a cleavable aryl salt chosen from the group formed by aryldiazonium salts, arylammonium salts, arylphosphonium salts, aryliodonium salts and arylsulfonium salts.
27) Process according to claim 4, characterized in that said adhesion primer is a compound chosen from the group formed by 4-nitrobenzenediazonium tetrafluoroborate, tridecylfluorooctylsulfamylbenzenediazonium tetrafluoroborate, phenyldiazonium tetrafluoroborate, 4-nitrophenyldiazonium tetrafluoroborate, 4-bromophenyldiazonium tetrafluoroborate, 4-aminophenyldiazonium chloride, 2-methyl-4-chlorophenyldiazonium chloride, 4-benzoylbenzenediazonium tetrafluoroborate, 4-cyanophenyldiazonium tetrafluoroborate, 4-carboxyphenyldiazonium tetrafluoroborate, 4-acetamidophenyldiazonium tetrafluoroborate, 4-phenylacetic acid diazonium tetrafluoroborate, 2-methyl-4-[(2-methylphenyl)diazenyl]benzenediazonium sulfate, 9,10-dioxo-9,10-dihydro-1-anthracenediazonium chloride, 4-nitronaphtalenediazonium tetrafluoroborate and naphtalenediazonium tetrafluoroborate.
28) Process according to claim 4, characterized in that the radical-polymerizable monomer(s) are chosen from the monomers of formula (II) below:
- in which the groups R1 to R4, which may be identical or different, represent a non-metallic monovalent atom such as a halogen atom or a hydrogen atom, a saturated or unsaturated chemical group, such as an alkyl or aryl group, a group —COOR5 or —OC(O)R5 in which R5 represents a hydrogen atom or a C1-C12 and preferably C1-C6 alkyl group, a nitrile, a carbonyl, an amine or an amide.
29) Process according to claim 4, characterized in that the radical-polymerizable monomer(s) are chosen from the group formed by vinyl esters such as vinyl acetate, acrylic acid, acrylonitrile, methacrylonitrile, methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and glycidyl methacrylate, and derivatives thereof; acrylamides and especially aminoethyl, propyl, butyl, pentyl and hexyl methacrylamides, cyanoacrylates, diacrylates and dimethacrylates, triacrylates and trimethacrylates, tetraacrylates and tetramethacrylates (such as pentaerythrityl tetramethacrylate), styrene and derivatives thereof, para-chlorostyrene, pentafluorostyrene, N-vinylpyrrolidone, 4-vinylpyridine, 2-vinylpyridine, vinyl, acryloyl or methacryloyl halides, divinylbenzene (DVB) and more generally vinyl or acrylate- or methacrylate-based crosslinking agents, and derivatives thereof.
30) Process according to claim 5, characterized in that said adhesion primer is a cleavable aryl salt chosen from the group formed by aryldiazonium salts, arylammonium salts, arylphosphonium salts, aryliodonium salts and arylsulfonium salts.
31) Process according to claim 5, characterized in that said adhesion primer is a compound chosen from the group formed by 4-nitrobenzenediazonium tetrafluoroborate, tridecylfluorooctylsulfamylbenzenediazonium tetrafluoroborate, phenyldiazonium tetrafluoroborate, 4-nitrophenyldiazonium tetrafluoroborate, 4-bromophenyldiazonium tetrafluoroborate, 4-aminophenyldiazonium chloride, 2-methyl-4-chlorophenyldiazonium chloride, 4-benzoylbenzenediazonium tetrafluoroborate, 4-cyanophenyldiazonium tetrafluoroborate, 4-carboxyphenyldiazonium tetrafluoroborate, 4-acetamidophenyldiazonium tetrafluoroborate, 4-phenylacetic acid diazonium tetrafluoroborate, 2-methyl-4-[(2-methylphenyl)diazenyl]benzenediazonium sulfate, 9,10-dioxo-9,10-dihydro-1-anthracenediazonium chloride, 4-nitronaphtalenediazonium tetrafluoroborate and naphtalenediazonium tetrafluoroborate.
32) Process according to claim 5, characterized in that the radical-polymerizable monomer(s) are chosen from the monomers of formula (II) below:
- in which the groups R1 to R4, which may be identical or different, represent a non-metallic monovalent atom such as a halogen atom or a hydrogen atom, a saturated or unsaturated chemical group, such as an alkyl or aryl group, a group —COOR5 or —OC(O)R5 in which R5 represents a hydrogen atom or a C1-C12 and preferably C1-C6 alkyl group, a nitrile, a carbonyl, an amine or an amide.
33) Process according to claim 5, characterized in that the radical-polymerizable monomer(s) are chosen from the group formed by vinyl esters such as vinyl acetate, acrylic acid, acrylonitrile, methacrylonitrile, methyl methacrylate, ethyl methacrylate, butyl methacrylate, propyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and glycidyl methacrylate, and derivatives thereof; acrylamides and especially aminoethyl, propyl, butyl, pentyl and hexyl methacrylamides, cyanoacrylates, diacrylates and dimethacrylates, triacrylates and trimethacrylates, tetraacrylates and tetramethacrylates (such as pentaerythrityl tetramethacrylate), styrene and derivatives thereof, para-chlorostyrene, pentafluorostyrene, N-vinylpyrrolidone, 4-vinylpyridine, 2-vinylpyridine, vinyl, acryloyl or methacryloyl halides, divinylbenzene (DVB) and more generally vinyl or acrylate- or methacrylate-based crosslinking agents, and derivatives thereof.
34) Substrate according to claim 23, characterized in that it is magnetic.
35. Substrate according to claim 22, characterized in that it bears a biological or biologically active molecule immobilized on its surface.
36. Substrate according to claim 23, characterized in that it bears a biological or biologically active molecule immobilized on its surface.
37. Substrate according to claim 24, characterized in that it bears a biological or biologically active molecule immobilized on its surface.
Type: Application
Filed: Apr 30, 2010
Publication Date: Dec 9, 2010
Applicant: COMMISSARIAT A L'ENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES (PARIS)
Inventors: Thomas Berthelot (Villebon Sur Yvette), Pascal Viel (Meudon), Alexandre Garcia (Ivry Sur Seine), Sébastien Roussel (Soisy Sur Seine)
Application Number: 12/772,126
International Classification: B32B 1/02 (20060101); C25D 11/18 (20060101); C08F 8/42 (20060101); C08J 3/28 (20060101);
