MICROPUMP FOR CONTINUOUS MICROFLUIDICS

Abstract

The invention relates to a micropump comprising an inclusion fluid accommodated in a chamber of the microchannel, and means to convey a portion of said inclusion into the axial area of said chamber and for displacing said portion along the longitudinal axis of the microchannel, so as to cause the flow of a fluid of interest (F) along the longitudinal axis of the microchannel (10).

Description

TECHNICAL FIELD

The present invention relates to the general field of microfluidics and concerns a micropump for “continuous” microfluidics. “Continuous” microfluidics relates to the flow of a fluid in continuous phase, and is the opposite of “discrete” microfluidics in which drops are manipulated and displaced.

STATE OF THE PRIOR ART

Micropumps make it possible to assure the controlled flow of a fluid, generally in a microchannel, and take place in numerous microfluidic systems.

For example, micropumps may be present in lab-on-chips, medical substance injection systems, or even hydraulic circuits for cooling electronic chips.

The actuation of the micropumps may be achieved in different ways, for example, by means of a piezoelectric, electrostatic, thermopneumatic, or even electromagnetic device. A presentation of these different actuating devices may be found in the document of D. J. Laser and J. G. Santiago entitled “A review of micropumps”, J. Micromech. Microeng., 14 (2004), R35-R64.

However, these actuating devices have certain drawbacks such as the necessity of deformable membranes or valves, the use of high voltages, for example for piezoelectric or electrostatic devices, or a high electric consumption, for example with thermopneumatic or electromagnetic devices.

Another approach consists in actuating the micropump by electrowetting, and more specifically by electrowetting on dielectric.

For instance, patent application FR2889633 filed in the name of the applicant discloses a micropump comprising a microchannel and an actuating device, which makes it possible to bring about the flow of a fluid of interest inside the microchannel along a given direction.

As illustrated in FIG. 1A, the actuating device comprises a chamber A40 that separates the microchannel A10 into two conducts, an input conduct A11 and an output conduct A12. Each conduct A11, A12 communicates with the chamber A40 by means of a valve A51, A52, each being arranged so as to allow the flow of the fluid of interest A31 along the single direction i.

In the chamber A40 is accommodated a piston A53, the displacement of which alternatively leads to the aspiration of the fluid from the input conduct A11, and the injection of the fluid into the output conduct A12.

The displacement of the piston A53 is controlled by means of a flexible membrane A54 in contact with a drop of liquid A32. The control of the shape of the drop A32 makes it possible to modulate the profile of the membrane A54 and thus to actuate the piston A53. The control of the shape of the drop is assured by electrowetting.

More specifically, the membrane A54 defines, with a substrate A21, the interior volume of an enclosure, which is filled by the drop of electrically conductor liquid A32 and by a second surrounding liquid A33, said two liquids being non miscible.

Electrical means are provided to modify the shape of the drop by electrowetting. These means comprise an electrode A61 integrated in the substrate A21, covered by a dielectric layer A65. The drop A32 is then in contact with said dielectric layer A65 and with the membrane A54. A counter electrode (not represented) is in contact with the drop.

When a voltage is applied between the electrode A61 and the counter electrode, the drop under voltage A32, dielectric layer A65 and activated electrode A61 assembly acts like a capacitance.

As described in the article of B. Berge entitled “Electrocapillarité et mouillage de films isolants par l'eau”, C.R. Acad. Sci., 317, series 2, 1993, 157-163, the contact angle of the interface of the drop A32 on the dielectric layer A62 is then reduced according to the relation:

$\cos \theta \left(U\right)=\cos \theta \left(0\right)+\frac{{\varepsilon }_r}{2\sigma }U^2$

where e is the thickness of the dielectric layer A65, ∈_r the permittivity of this layer and σ the surface tension of the interface of the drop A32.

This reduction in the contact angle is accompanied by a spreading of the drop and thus a modification of its shape. Thus, the activation of the electrode A61 makes it possible to control the shape of the drop A32, to modify, as a consequence, the profile of the membrane A54. The piston A53 may then be displaced along its longitudinal axis in the two directions, which assures the flow of the fluid A31 from the input conduct A11 to the output conduct A12, via the chamber A40.

FIGS. 1A and 1B illustrate two characteristic operating times of the micropump. In FIG. 1A, the electrode A61 is activated, the piston A53 then moves so as to suck up the fluid of interest A31 from the input conduct A11 into the chamber A50, then when the electrode A61 is deactivated (FIG. 1B), the drop A32 recovers its initial shape, and “pushes” the piston in such a way that the fluid A31 inside the chamber A40 is injected into the output conduct A12.

However, the micropump according to the prior art comprises a certain number of drawbacks stemming from the presence of moving or deformable mechanical parts in the actuating device.

Thus, the formation and the assembly of the mechanical parts of micrometric size are particularly difficult operations to carry out, which moreover involve high production costs.

In addition, these parts and more specifically their connection, pivot or sliding components, are particularly sensitive to the least production defects. The valves and the piston are then capable of jamming, thereby rendering inefficient the micropump as well as the microfluidic system in which it takes place.

DESCRIPTION OF THE INVENTION

The aim of the present invention is to propose an electrowetting micropump in which the actuating device does not comprise moving or deformable mechanical parts.

To do this, the object of the invention is a micropump for displacing a first fluid in a microchannel.

According to the invention, the microchannel comprises at least one chamber comprising an axial area arranged substantially along the longitudinal axis of the microchannel and at least one lateral area, and the micropump comprises:

• • an inclusion of a second fluid occupying at least partially said lateral area of the chamber,
  • electrical means to convey a portion of said inclusion into said axial area under the effect of an electrical control, comprising a plurality of actuating electrodes arranged in said axial area of the chamber, and
  • means of successively activating said actuating electrodes for displacing said portion of said inclusion covering at least partially at least one actuating electrode, substantially along the longitudinal axis of the microchannel, so as to cause the flow of said first fluid along the longitudinal axis of the microchannel.

Thus, the portion of the inclusion fluid, in its displacement, brings about the flow of the fluid of interest along the longitudinal direction of the microchannel.

It is then no longer necessary to provide moving or deformable mechanical parts, of the valve, piston or membrane type.

In addition, the pumped fluid is not discretised in the form of drops by the micropump. The liquid of the inclusion fluid always remains localised in the chamber and is thus not driven downstream of the chamber into the microchannel. It indeed involves “continuous” microfluidics.

The production operations are thus largely simplified, which reduces the production costs. The reliability is improved, in so far as there is no longer any risk of jamming or seizure of the micropump.

Moreover, unlike the micropump according to the prior art, it is possible to bring about the flow of the fluid of interest along any of the two directions parallel to the longitudinal axis of the microchannel.

Preferably, the first fluid or the second fluid is a liquid.

The successive activation means advantageously comprise electrical switching means designed to activate and to deactivate each of said actuating electrodes, said switching means being controlled by control means.

According to a first preferred embodiment, said portion of said inclusion is a local deformation of said inclusion.

Said portion of said inclusion may cover at least one actuating electrode along the entire transversal section of said axial area.

According to a second preferred embodiment, the chamber comprises a wall arranged between the axial area and the lateral area, on a part of the length of the chamber, so that the lateral area forms a secondary channel communicating with the axial area upstream and downstream of the wall.

Said portion of said inclusion may then be a secondary inclusion separated from said inclusion by said wall.

According to one embodiment, the first fluid is a dielectric fluid, the second fluid being a conductive liquid.

Said electrical means to convey said portion into said axial area may then comprises at least one counter electrode in electrical contact with said inclusion, and a voltage generator to apply a potential difference between one or more actuating electrodes and said counter electrode.

Said electrical means to convey said portion into said axial area may further comprise an electrode named confinement electrode extending substantially on the surface of said lateral area of the chamber.

According to another embodiment, the first fluid is a conductive liquid, the second fluid being a dielectric fluid.

Said electrical means to convey said portion into said axial area may then comprise at least one counter electrode in electrical contact with said first fluid, and a voltage generator to apply a potential difference between one or more actuating electrodes and said counter electrode.

The micropump may further comprise a second substrate forming lid. A second plurality of actuating electrodes may then be integrated in said lid and arranged in said axial area of the chamber, facing said first plurality of actuating electrodes of said substrate.

The first fluid may then have an electrical permittivity substantially less than that of the second fluid.

Said chamber may comprise two lateral parts arranged facing each other, each accommodating a drop of conductive liquid.

The distance separating the first substrate and the lid in said chamber is preferably substantially less than the dimensions of said chamber along the median plane of said first substrate.

Preferably, the axial area has a width substantially less than its length.

The inter-actuating electrode spacing advantageously has a curved or angular shape, so as to facilitate the passage of the portion of the inclusion from one electrode to the other.

Said electrodes may be covered by a layer of hydrophobic material.

The first fluid and the second fluid may be, one, a conductive liquid comprising zwitterionic species and, the other, a dielectric fluid.

A layer of dielectric material may be arranged between the hydrophobic layer and said electrodes.

Said actuating electrodes may be arranged in matrix form.

Other advantageous and characteristics of the invention will become apparent in the detailed non limiting description below.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described, by way of non limiting examples, while referring to the appended drawings, in which:

FIGS. 1A and 1B, already described, are schematic representations in longitudinal section of a micropump according to the prior art;

FIG. 2 is a schematic representation in top view of a micropump according to the first preferred embodiment of the invention, in which the first electrode is activated;

FIG. 3 is a schematic representation in longitudinal section of the micropump according to the first preferred embodiment of the invention, the section being taken along the axis A-A of FIG. 2;

FIGS. 4A to 4C are schematic representations in top view of a micropump according to the first preferred embodiment of the invention, and illustrate an operating mode;

FIGS. 5A to 5C illustrate another operating mode of the first preferred embodiment of the invention;

FIGS. 6A to 6D are schematic representations in top view of a micropump according to an alternative of the first preferred embodiment of the invention, wherein a liquid bridge is formed;

FIGS. 7A to 7D are schematic representations in top view of a micropump according to another alternative of the first preferred embodiment of the invention, wherein a progressive wave is generated;

FIGS. 8A to 8D are schematic representations in top view of a micropump according to the preferred second embodiment of the invention, wherein a secondary inclusion fluid is formed;

FIG. 9 is an alternative of the first preferred embodiment of the invention, in which the fluid pumped is a conductive liquid; and

FIGS. 10 and 11 are alternatives of the first preferred embodiment of the invention, wherein the axial area of the chamber has a curved or angular longitudinal axis.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The first preferred embodiment of the invention is schematically represented in FIG. 2, in top view.

The micropump comprises a first substrate 21 in which is formed a microchannel 10.

Median plane of the first substrate 21 designates a plane of the substrate substantially parallel to the plane (i,j) of the direct orthonormal coordinates (i,j,k).

The longitudinal axis of the microchannel is defined as being the median line of the microchannel. The longitudinal axis may be straight or curved.

The microchannel 10 may have a convex polygonal transversal section, for example square, rectangular, hexagonal.

It is here considered that a square section is a specific case of the more general rectangular shape. It may also have a circular transversal section. The term microchannel is taken in a general sense and includes in particular the specific case of the microtube in which the section is circular.

The microchannel 10 may be filled with a fluid of interest 31 to be displaced.

An actuating device of the micropump is provided to bring about and control the flow of the fluid of interest 31 in the microchannel 10.

The actuating device comprises a chamber 40 communicating with the microchannel so as to define within it a first conduct 11 and a second conduct 12.

The chamber 40 preferably has a substantially rectangular shape in transversal section.

The chamber 40 comprises an axial area 41 arranged in the continuity of the first and second conducts, in other words situated substantially along the longitudinal axis of the microchannel.

The chamber 40 also comprises at least one recess forming the lateral area 42, communicating with the axial area 41. The lateral area 42 extends into the median plane of the first substrate 21.

According to the invention, an inclusion of a second fluid occupies at least partially said lateral area 42 of the chamber.

In the first preferred embodiment of the invention, said inclusion of second fluid is a drop of an electrically conductive liquid 32.

Electrical means are provided to convey a portion 35 of the drop of liquid into said axial area 41 of the chamber, under the effect of an electrical control, by electrowetting.

In particular, the drop of liquid 32 may be deformed by said electrical means.

The electrical means comprise a plurality of electrodes 61(i), where i∈[1,N], and N is preferably greater than or equal to three. In the example of FIG. 2, N is equal to three.

The electrodes 61(i) are integrated in the first substrate 21 and are arranged in the axial area 41 of the chamber 40, preferably in a linear manner. The network of electrodes 61(i) may also have a square or rectangular matrix shape.

Preferably, an electrode named confinement electrode 62 is integrated in the first substrate 21 and arranged substantially in the lateral area 42 of the chamber 40. The confinement electrode 62 extends advantageously over the entire surface of the lateral area 42.

Each electrode 61(i) may have a substantially square or rectangular shape. Alternatively, the inter-actuating electrode spacing may have a curved or angular shape. In the case of an angular shape, the edge of an actuating electrode may have a saw tooth shape substantially parallel to the edge of the neighbouring electrode having a corresponding shape. This shape of electrode facilitates the passage of the drop of liquid from one electrode to the other.

Preferably, a layer of a hydrophobic material covers the electrodes 61(i) and 62.

Preferably, a layer of a dielectric material is arranged between the hydrophobic layer and the electrodes 61(i) and 62.

The dielectric layer and the hydrophobic layer that covers the actuating electrodes 61(i) and the confinement electrode 62 may be a single layer combining these two functions, for example a layer made of parylene or Teflon.

Preferably, a counter electrode 63 is arranged in electrical contact with the drop of liquid 32. This counter electrode 63 may be either a catenary, or a buried wire, or a planar electrode in the lid of the micropump (such a lid is described hereafter). In these two latter possibilities, an electrically conductive hydrophobic layer may cover the counter electrode 63.

The electrodes 61(i) and 62, as well as the counter electrode 63, may be connected to a continuous or, preferably, alternative voltage generator 64.

When the polarisation voltage is alternative, the liquid behaves like a conductor when the frequency of the polarisation voltage is substantially less than a cut-off frequency. This depends in particular on the electrical conductivity of the liquid and is typically around several tens of kilohertz (Mugele and Baret, “Electrowetting: from basics to applications”, J. Phys. Condens. Matter, 17 (2005), R705-R774). Moreover, the frequency is substantially greater than the frequency making it possible to exceed the hydrodynamic response time of the liquid, which depends on the physical parameters of the drop such as surface tension, the viscosity or the size of the drop, and which is around several hundreds of hertz. Thus, the frequency is, preferably, between 100 Hz and 10 kHz, preferably around 1 kHz.

Thus, the response of the liquid of the drop 32 depends on the root mean square value of the applied voltage since the angle of contact depends on the voltage in U², according to the relation given previously. The root mean square value can vary between several volts and several hundreds of volts, for example 200V. Preferably, it is around several tens of volts.

According to the invention, the actuating device comprises successive activation means of the actuating electrodes 61(i).

The successive activation means may comprise a system 71 of electrical switches 72, controlled by a PC type control means 73 according to a determined sequence.

Each actuating electrode 61(i) is connected to the voltage generator by means of a switch 72.

Thus, as a function of the switching state of the different switches 72, an electrical control may be transmitted to one or more actuating electrodes 61(i). In this case, these electrodes are designated activated. More specifically, the voltage generator 64 applies a potential difference between the counter electrode 63 and the activated actuating electrode(s) 61(i).

Preferably, when at least one actuating electrode 61(i) is activated, the confinement electrode 62 is also actuated.

FIG. 3 is a longitudinal sectional view of the preferred embodiment of the invention, along the axis A-A represented in FIG. 2.

A second substrate 22 forming lid may be deposited on the first substrate 21, parallel to its median plane.

The first and second substrates 21 and 22 may be made of silicon or glass, polycarbonate, polymer, ceramic.

The microchannel 10 and the chamber 40 are for example formed by lithography and selective etching. As a function of the requisite dimensions, dry etching (attack by gas, for example SF₆, in a plasma) may be used. The etching may also be wet. For glass (mainly SiO₂) or silicon nitrides, hydrofluoric or phosphoric acid etchings may be used (these etchings are selective but isotropic). The etching may be carried out by laser ablation or instead by ultrasounds. Micro-machining may also be used, in particular for polycarbonate.

The height of the microchannel 10 between the substrates 21 and 22 is typically between several tens of nanometres and 200 μm, and preferably between 1 μm and 100 μm.

Preferably, the height of the chamber 40, in particular of the axial area 41 of the chamber 40, is substantially less than the height of the microchannel 10, as shown in FIG. 3. This makes it possible to obtain a substantially “flat” drop of liquid 32, in other words spread out between the first substrate 21 and the lid 22, or even a portion 35 of substantially “flat” drop 32. The reduction in the height of the chamber 40 moreover makes it possible to optimise the actuation by electrowetting. The increase in the transversal section of the input and output channels makes it possible to reduce the head losses upstream and downstream of the pump.

In the non limiting example of FIG. 3, the counter electrode 63 is a planar electrode integrated in the lid 22 of the micropump.

The actuating and confinement electrodes 61(i), and the counter electrode 63, may be formed by deposition of a thin layer of a metal chosen among Au, Al, ITO, Pt, Cu, Cr . . . or a Al—Si alloy . . . by means of conventional microtechnologies used in microelectronics, for example by photolithography. The electrodes 61(i) and 62 are then etched according to an appropriate pattern, for example by wet etching.

The thickness of the electrodes 61(i), 62, and the counter electrode 63 may be between 10 nm and 1 μm, preferably 300 nm.

The actuating electrodes 61(i) are preferably square with a side in which the length is between several micrometres to several millimetres, preferably between 50 μm and 1 mm. The surface of these electrodes depends on the size of the drops to be transported. The spacing between neighbouring electrodes may be between 1 μm and 10 μm.

The confinement electrode 62 extends advantageously over the entire flat surface of the lateral area of the chamber 40, along the median plane.

A dielectric layer 65 may cover the electrodes 61(i) and 62. It may be formed out of Si₃N₄, SiO₂, SiN, barium strontium titanate (BST) or other high permittivity materials such as HFO₂, Al₂O₃, Ta₂O₅, Ta₂O₅—TiO₂, SrTiO₃ or Ba_1-xSr_xTiO₃. The thickness of this layer may be between 100 nm and 3 μm, generally speaking between 100 nm and 1 μm, preferably 300 nm. A plasma enhanced chemical vapour deposition (PECVD) method is preferred to the low pressure chemical vapour deposition method (LPCVD) for thermal reasons. Indeed, the temperature of the substrate is only raised to between 150° C. and 350° C. (depending on the desired properties) compared to around 750° C. for LPCVD.

Finally, a hydrophobic layer 66 may be deposited on the dielectric layer 65, and on the counter electrode 63. To do this, a deposition of Teflon by dip coating, by spray or spin coating, or SiOC deposited by plasma may be carried out. A deposition of hydrophobic silane in vapour or liquid phase may be carried out. Its thickness will be between 100 nm and 5 μm, preferably 1 μm. This layer makes it possible in particular even to avoid the hysterisis effects of the wetting angle.

The microchannel may be filled with a fluid of interest 31, preferably, insulating, and may be air, a mineral or silicone oil, a perfluorinated solvent, such as FC-40 or FC-70, or instead an alkane such as undecane.

The conductive liquid 32 is electrically conductor and may be an aqueous solution filled with ions, for example with Cl⁻, K⁺, Na⁺, Ca²⁺, Mg²⁺, Zn²⁺, Mn2+, or others. The liquid 32 may also be mercury, gallium, eutectic gallium, or ionic liquids of the bmim PF6, bmim BF4 or tmba NTf2 type.

The fluid of interest 31 is non miscible with the conductive liquid 32.

Moreover, in an alternative embodiment not represented, it should be noted that a second plurality of actuating electrodes may be integrated in the lid 22, and advantageously covered by a dielectric layer. The activation of the second plurality of actuating electrodes may be advantageously controlled by the successive activation means described previously.

In this case, a counter electrode, for example in the form of suspended wire, may be arranged in the chamber 40 so as to assure an electrical contact with the conductive liquid 32. Thus, the application of a potential difference between a pair of actuating electrodes arranged, one in the substrate 21 and the other in the lid 22, and the counter electrode makes it possible to displace the conductive liquid 32 by electrowetting in a more efficient manner, for a same applied potential difference.

The operation of the micropump according to the first preferred embodiment of the invention is as follows, in reference to FIGS. 4A to 4C.

FIGS. 4A to 4C, in which the numerical references identical to those of FIG. 2 designate identical or similar parts, represent in top view the first preferred embodiment of the invention.

The embodiment represented in these figures differs from that of FIG. 2 uniquely by the number N of electrodes, here greater than three.

For reasons of clarity, the voltage generator and the successive activation means are not represented.

The electrodes 61(i), by means of the switches, may be placed at a potential V0 or V1, indicated by the numerical references 0 or 1. In the case of an alternative voltage and as described previously, the potential V1 then corresponds to the root mean square value of the applied voltage. The switching of each switch is controlled by the control means.

During the operation of the micropump that is going to be described, the confinement electrode 62 remains advantageously activated (placed at a potential V1 different to V0), in such a way that the drop of liquid remains substantially confined in the lateral area 42 of the chamber 40, then occupying substantially the surface delimited by the confinement electrode 62.

FIG. 4A shows the electrode 61(1) activated. By electrowetting effect described previously, the drop 32 locally deforms and wets, preferably totally, the area of the hydrophobic layer 66 situated facing the activated electrode 61(1).

Local deformation 35 here designates the portion of drop of liquid 32 which occupies an area of the hydrophobic layer situated facing an activated electrode 61(i).

Thus, to displace the local deformation 35 of the drop 32 onto the line of electrodes 61(i), said electrodes only have to be activated successively, from electrode 61(1) to electrode 61(N).

More specifically, so that the local deformation 35 passes from one electrode 61(i) to the neighbouring electrode 61(i+1), the control means, at the same time, deactivate the electrode 61(i) and activate the electrode 61(i+1), by actuation of the corresponding switches.

Said local deformation 35 may then be displaced along the longitudinal axis of the microchannel, as illustrated in FIGS. 4A and 4B, from electrode 61(1) to 61(N), passing through electrodes 61(i−1), 61(i), 61(i+1), etc.

The local deformation 35 “pushes”, in its displacement, the fluid of interest 31. The flow of the fluid 31 is thereby obtained. The fluid 31 is “sucked up” from the first conduct 11 and “pushed” in the second conduct 12, by the displacement of the local deformation 35.

This sequence is repeated up to the activation of the downstream electrode 61(N).

As shown in FIG. 4B, when the electrode 61(N) is activated, the local deformation 35 is situated substantially at the downstream end of the axial area 41 of the chamber 40. To continue to assure the flow of the fluid 31, the electrode 61(1) is activated whereas the electrode 61(N) is deactivated. The local deformation 35 of the drop at the electrode 61(N) disappears, and a new local deformation 35 is generated at the electrode 61(1). The successive activation sequence of the electrodes 61(i) then continues as described previously.

The activation frequency of the electrodes 61(i) makes it possible to control precisely the flow rate imposed on the fluid 31 in the microchannel.

As may be seen, the drop of liquid 32 remains confined in the chamber 40 throughout the activation sequence of the electrodes 61(i). Thus, the fluid of interest 31 is not discretised in the form of drops or bubbles downstream of the chamber. The micropump according to the invention indeed applies to “continuous” microfluidics.

Moreover, it is clearly understood that the direction of displacement of the deformation 35 is not limited to that going from the first conduct 11 to the second conduct 12, but can also just as well go in the opposite direction.

FIGS. 5A to 5C, in which the numerical references identical to those of FIG. 2 designate identical or similar parts, represent an alternative operation of the micropump according to the first preferred embodiment of the invention.

It may in fact be advantageous to control very precisely the mass flow rate of fluid of interest 31 in the microchannel.

FIG. 4C shows however a step of the activation sequence of the electrodes 61(i) for which a free flow of fluid 31 is possible. This step is that where the local deformation 35 passes from the downstream electrode 61(N) to the upstream electrode 61(1). The mass flow rate of the fluid 31 cannot then be controlled precisely.

To overcome this, it is advantageous to have a different activation sequence in this step. As shown in FIG. 5C, the downstream electrode 61(N) is maintained activated when the upstream electrode 61(1) is activated, in such a way that the axial area 41 remains always obstructed by at least one, here two, local deformations 35 of the drop 32.

When the electrode 61(2) is activated, the upstream 61(1) and downstream 61(N) electrodes are deactivated at the same time. The local deformation 35 localised on the electrode 61(N) disappears whereas that localised on the electrode 61(1) is displaced onto the neighbouring electrode 61(2).

The activation sequence is then similar to that which has been described previously.

FIGS. 6A to 6D represent an alternative of the first preferred embodiment of the invention, in top view. The numerical references identical to those of FIG. 2 designate identical or similar parts.

In this embodiment, the chamber 40 comprises two lateral parts 42A and 42B, arranged facing each other in relation to the axial area 41 of the chamber 40.

Each lateral area 42A, 42B accommodates a drop of liquid 32A, 32B.

Each lateral area 42A, 42B comprises advantageously a confinement electrode (not represented).

The operating mode represented in these figures is substantially similar to that described in FIGS. 5A to 5C.

The activation of an electrode 61(i) generates a local deformation of drops 32A and 32B. Each local deformation then extends substantially on an area of the hydrophobic layer situated facing the activated electrode 61(i).

The local deformations can then wet a sufficient surface to coalescence with each other. A liquid bridge is then formed, which connects the two drops of liquid 32A and 32B.

The liquid bridge 36, then corresponding to the two coalesced local deformations, is then displaced by successive activation of the electrodes 61(i).

To form a liquid bridge 36 of larger dimension and to displace it, it is advantageous to actuate two neighbouring electrodes 61(i) and 61(i+1) together, as illustrated in particular in FIGS. 6A to 6C. FIG. 6D shows, moreover, an identical operation to that described in FIG. 5C.

Thus, the joint activation of the electrodes 61(1) and 61(N) makes it possible to form an inclusion 311 of fluid 31. The activation sequence of the electrodes 61(i) thus makes it possible to form this inclusion, to displace it and to merge it with the fluid 31 present in the second conduct 12.

FIGS. 7A to 7D illustrate an alternative operation, in which the two local deformations 35A and 35B do not coalesce with each other, due for example to a too low actuation voltage V1 or a high actuation frequency of the electrodes.

During the successive activation of the electrodes 61(i), each local deformation 35A, 35B is displaced while remaining facing each other, from the fluid 31 separating the two local deformations.

This alternative operation corresponds to a perisaltic micropump. The different embodiments of the invention described may operate according to this alternative operation.

FIGS. 8A to 8D represent the second preferred embodiment of the invention, in top view. The numerical references identical to those of FIG. 2 designate identical or similar parts.

In this embodiment, the chamber 40 comprises a wall 43 arranged between the axial area 41 and the lateral area 42, on a part of the length of the chamber, so that the lateral area 42 forms a secondary channel communicating with the axial area 41 upstream and downstream of the wall 43.

Preferably, the lateral area 42 communicates upstream of the wall 43 at the upstream electrode 61(1) and downstream of the wall 43 at the downstream electrode 61(N).

When the upstream electrode 61(1) is activated, a portion 35 of the drop 32 covers at least partially said activated electrode.

Then, the activation sequence of the electrodes is implemented as described previously.

The electrode 61(2) is activated whereas the electrode 61(1) is deactivated. The portion 35 of liquid is then displaced so as to cover substantially the new activated electrode.

Then, as the electrode 61(i) is deactivated and the electrode 61(i+1) activated, the portion 35 is displaced in the axial area of the chamber from the electrode 61(1) up to the electrode 61(N). In doing so, it brings about the flow of the fluid of interest 31 in the microchannel.

Due to the fact that the electrodes 61(i), where i∈[2,N−1], are separated from the lateral area of the chamber by said wall, the portion 35 forms, when it substantially covers one of these electrodes, a secondary drop separated from the principal drop accommodated in the lateral area of the chamber, as illustrated in FIG. 8B.

More specifically, the secondary drop 35 is formed by dissociation from the principal drop when the portion 35 is displaced from the electrode 61(1) to the electrode 61(2).

Then, when the secondary drop is displaced from the electrode 61(N−1) to the electrode 61(N), it coalesces with the principal drop (FIG. 8C).

It should be noted that a counter electrode is advantageously arranged so as to be in electrical contact firstly with the principal drop 32, but also with the secondary drop 35.

The activation sequence is then similar to that described in reference to FIGS. 4A to 4D.

FIG. 9 illustrates an alternative of the first preferred embodiment of the invention. The numerical references identical to those of FIG. 2 designate identical or similar parts.

In this example, the fluid of interest 31 is a conductive liquid and a liquid or gaseous dielectric fluid forms an inclusion fluid occupying at least partially said lateral area of the chamber.

A counter electrode is advantageously arranged in the microchannel or in the axial part of the chamber so as to take the conductive liquid to the requisite potential, for example V1.

The successive activation sequence is adapted in so far as all of the electrodes 61(i) are, preferably, activated beforehand. A local deformation 35 is then formed in deactivating an electrode, for example the upstream electrode 61(1). The successive activation sequence then consists in activating the electrode 61(i) and deactivating the electrode 61(i+1). The local deformation 35 of the inclusion fluid 32 is then displaced in the axial area along the longitudinal axis of the microchannel, which brings about the flow of the fluid of interest, here the conductive liquid, in the microchannel.

Moreover, with the aim of improving the confinement of the inclusion fluid 32 inside the chamber 40, two confinement electrodes may be arranged in the channel, more specifically upstream and downstream of the axial area 41 of the chamber 40. The first electrode is thus upstream and close to the first electrode 61(1), and the second electrode is downstream and close to the final electrode 61(N). When the micropump is operating, these two electrodes remain advantageously activated. Thus, the confinement of the inclusion fluid 32 in said chamber is improved.

This alternative of the first preferred embodiment may be adapted to the different embodiments described, as well as to the preferred second embodiment.

FIGS. 10 and 11 represent geometry alternatives of the micropump according to the first preferred embodiment of the invention, in top view. The numerical references identical to those of FIG. 2 designate identical or similar parts.

In FIG. 10, the axial area 41 of the chamber 40 has a curved longitudinal axis. The lateral area 42 has a substantially half-disc shape.

In FIG. 11, the axial area 41 has a U shape. The lateral area 42 then has a substantially rectangular shape.

These different geometries may be used in the different embodiments described above.

Moreover, it should be noted that in all of the embodiments described previously, the surface of the chamber, and more specifically at the electrodes 61(i), may be smooth, rough or micro-structured or nano-structured, so as to amplify the wetting effects and increase the capillarity forces. The displacement of the portion 35 is then improved.

It should be noted that, in the case where the dielectric layer is not present, the electrowetting phenomenon known as direct electrowetting may be carried out.

The intervening capacity is then no longer that of the dielectric layer 65 but that of a double electrical layer that forms in the conductive liquid 32 at the surface of the electrodes 61(i) and 62. In this case, the voltages applied must remain sufficiently low to avoid electrochemical phenomena such as electrolysis of the water.

The intervening thickness e in the relation connecting the contact angle θ to the voltage applied U, described previously, is that of the double layer, which is around several nanometres.

It is advantageous to add to the liquid 32 high permittivity species, such as for example zwitterionic species. This makes it possible to increase the permittivity ∈_r of the double layer. The zwitterions used may be amine sulphonates, amine phosphates, amine carbonates, or amine carboxylates and, in particular, sulphonate alkanes of trialkyl ammonium, sulphonate alkanes of alkyl imidazole or sulphonate alkanes of alkyl pyridine.

Moreover, in an alternative of the embodiment of the invention represented in FIG. 2, a plurality of electrodes may be integrated in the lid 22, and advantageously covered by a dielectric layer.

The activation of any electrode 61(i) of the first substrate 21 is then advantageously accompanied by a joint activation of the corresponding electrode of the lid to the potential −V1. Thus, the conductive liquid 32 situated between the substrate 21 and the lid 22 is substantially placed at potential 0V. A counter electrode may then not be present.

Finally, it should be noted that, when the frequency of the polarisation voltage is substantially greater than several tens of kilohertz, the liquid of a drop 32 has a dielectric property. In the case where the permittivity of the liquid 32 is substantially greater than that of the fluid 31, the liquid 32 is displaced at the activated electrode by dielectrophoresis.

The pumping is then obtained by using a liquid 32 occupying at least partially the lateral area 42 of the chamber 40 and a fluid of interest 31, non miscible and of different permittivities.

In the case where the liquid 32 and the fluid 31 are electrically insulating, the micropump cannot comprise a dielectric layer covering the actuating electrodes integrated in the substrate 31 and those integrated in the lid 22. Moreover, the polarisation voltage may be continuous.

Claims

1. Micropump for displacing a first fluid (31) in a microchannel (10), characterised in that

the microchannel comprises at least one chamber (40) comprising an axial area (41) arranged substantially along the longitudinal axis of the microchannel (10) and at least one lateral area (42),

and in that the micropump comprises: an inclusion (32) of a second fluid occupying at least partially said lateral area (42) of the chamber (40), electrical means to convey a portion (35) of said inclusion (32) into said axial area under the effect of an electrical control, comprising a plurality of actuating electrodes (61) arranged in said axial area (41) of the chamber (40), and means of successively activating said actuating electrodes (61) for displacing said portion (35) of said inclusion (32) covering at least partially at least one actuating electrode (61), substantially along the longitudinal axis of the microchannel (10), so as to cause the flow of said first fluid (31) along the longitudinal axis of the microchannel (10).

2. Micropump according to claim 1, characterised in that the successive activation means comprise electrical switching means (72) designed to activate and to deactivate each of said actuating electrodes (61), said switching means (72) being controlled by a control means (73).

3. Micropump according to claim 1, characterised in that said portion (35) of said inclusion (32) is a local deformation of said inclusion (32).

4. Micropump according to claim 1, characterised in that said portion (35) of said inclusion (32) covers at least one actuating electrode (61) along the entire transversal section of said axial area (41).

5. Micropump according to claim 1, characterised in that the chamber (40) comprises a wall (43) arranged between the axial area (41) and the lateral area (42), on a part of the length of the chamber (40), so that the lateral area (42) forms a secondary channel communicating with the axial area (41) upstream and downstream of the wall (43).

6. Micropump according to claim 5, characterised in that said portion (35) of said inclusion (32) may be a secondary inclusion separated from said inclusion (32) by said wall (43).

7. Micropump according to claim 1, characterised in that the first fluid (31) is a dielectric fluid, the second fluid being a conductive liquid.

8. Micropump according to claim 7, characterised in that said electrical means to convey said portion (35) into said axial area (41) comprise:

at least one counter electrode (63) in electrical contact with said inclusion (32), and

a voltage generator (64) to apply a potential difference between one or more actuating electrodes (61) and said counter electrode (63).

9. Micropump according to claim 7, characterised in that said electrical means to convey said portion (35) into said axial area (41) further comprise an electrode named confinement electrode (62) extending substantially on the surface of said lateral area (42) of the chamber (40).

10. Micropump according to claim 1, characterised in that the first fluid (31) is a conductive liquid, the second fluid being a dielectric fluid.

11. Micropump according to claim 10, characterised in that said electrical means to convey said portion (35) into said axial area (41) comprise:

at least one counter electrode (63) in electrical contact with said first fluid (31), and

a voltage generator (64) to apply a potential difference between one or more actuating electrodes (61) and said counter electrode (63).

12. Micropump according to claim 1, characterised in that it further comprises a second substrate (22) forming lid of said micropump,

and in that a second plurality of actuating electrodes is integrated in the lid (22) and arranged in said axial area (41) of the chamber (40), facing said first plurality of actuating electrodes (61) of said substrate (21).

13. Micropump according to claim 12, characterised in that the first fluid (31) has an electrical permittivity substantially less than that of the second fluid.

14. Micropump according to claim 1, characterised in that said chamber (40) comprises two lateral parts (42A, 42B) arranged facing each other, each accommodating a drop of conductive liquid (32A, 32B).

15. Micropump according to claim 1, characterised in that it further comprises a second substrate (22) forming lid of said micropump,

the distance separating the first substrate (21) and the lid (22) in said chamber (40) is substantially less than the dimensions of said chamber (40) along the median plane of said first substrate (21).

16. Micropump according to claim 1, characterised in that the axial area (41) has a width substantially less than its length.

17. Micropump according to claim 1, characterised in that the inter-actuating electrode spacing (61) has a curved or angular shape.

18. Micropump according to claim 1, characterised in that said electrodes (61, 62) are covered with a layer of hydrophobic material (66).

19. Micropump according to claim 1, characterised in that the first fluid (31) and the second fluid are, one, a conductive liquid comprising zwitterionic species and, the other, a dielectric fluid.

20. Micropump according to claim 18, characterised in that a layer of dielectric material (65) is arranged between the hydrophobic layer (66) and said electrodes (61, 62).

21. Micropump according to claim 1, characterised in that said actuating electrodes (61) are arranged in matrix form.