Filament or Fibre

Abstract

A filament or fibre comprising a liquid crystalline elastomer, and an actuator for enabling actuation of the filament or fibre to thereby cause a change in the dimensions of the filament or fibre.

Description

This invention relates to a filament or fibre, especially one that is suitable for inclusion in a fabric or garment, with the aim of producing changes in one or more of the properties of the garment or fabric.

Various methods of producing a change in the dimensions of a fibre or filament are known. The change in a dimension of a fibre expressed as a fraction of the original dimension is known as strain. It is known to make use of actuators in order to product dimensional changes within a fibre. However, most known materials exhibit only a very limited strain, i.e., very limited displacement or shape change in response to a stimulus. For example, piezo materials can exhibit a strain of less than 1%, shape memory alloys exhibit a strain of less than 8%, and ferro-electric polymers exhibit a strain of less than 5%.

Materials with significantly larger strains such as ionic polymer gels and dielectric elastomers are known. However, these materials have the disadvantage of either a need for an ion conductor, usually in the form of a liquid, or a need for an extremely high electrical field, of the order of 10²V/micron. Materials with large, linear strains, are scarce.

It is an object of the present invention to provide a filament or fibre in which the dimensions of the filament or fibre can be controllably and reversibly altered in response to an actuator.

It is a further object of the present invention to provide a filament or fibre in which a relatively large strain can be induced in the filament or fibre.

According to the present invention there is provided a filament or fibre comprising a liquid crystalline elastomer, and an actuator for enabling actuation of the filament or fibre to thereby cause a change in a dimension of the filament or fibre.

Preferably, actuation of the filament or fibre results in a change in the axial, or linear dimension of the filament or fibre. Such a change in linear dimension when expressed as a ratio of the original linear dimension is known as linear strain.

Liquid crystalline elastomer comprises a functional long chain elastomer, a plurality of mesogenic side chains, and a crosslinker.

The mesogen forming the mesogenic side chains is a liquid crystal active group.

The crosslinker cross links long-chain elastomers to one another and may be liquid crystal active.

It is known that liquid crystals have an isotropic phase boundary which separates the isotropic phase from the liquid crystal phase.

Due to the nature of liquid crystal elastomers, particularly due to the coupling of the liquid crystal ordering, and the conformation of the long-chain elastomer, the length of the elastomer decreases when the liquid crystal passes the isotropic phase boundary from the liquid phase.

The process is reversible, so from the isotropic phase to the liquid crystal phase, the material will again expand.

It is known for a liquid crystal to expand by 300% when passing from the isotropic phase to the liquid crystal phase.

Advantageously, at least some of the mesogenic side-chains are aligned. For large uniaxial contraction and expansion it is required to align substantially all of the mesogenic groups. In this way, changes induced by the phase change are unidirectional throughout the elastomer, so that local strains can be added to produce a large overall strain. Aligned liquid crystal elastomers are referred to as liquid single-crystal elastomers (LSCE).

The liquid crystal isotropic phase transition is generally induced by temperature, which value can be tuned depending on the type of mesogenic side-chains, the type of crosslinker as well as by the concentration ratio of these two compounds. This allows a large range of transition temperatures, from room temperature or below, up to temperatures larger than 100° C.

For example, when 4′-methoxyphenyl-4-(1-buteneoxy) bezoate is used as the mesogenic side-chain, the nematic (or smectic) to isotropic phase transition temperature can be lowered by over 25 degrees C. by changing the buteneoxy group to an etheneoxy group. Similarly, it can be increased by about 25 degrees C. by changing the buteneoxy group to a hexeneoxy group. In addition an increase of the number of mesogenic side-chains per unit of main-chain length for this example will generally increase the nematic (or smectic) to isotropic phase transition temperature.

Advantageously, the actuator comprises an electrode extending axially along the fibre or filament.

Preferably, the electrode is elastic. This allows the electrode to expand and contract as the fibre expands and contracts on actuation.

The elastic electrode may be, for example, corrugated.

Advantageously, the electrode comprises chromium-gold.

A chromium-gold film having a thickness of between 5 and 100 nm may be deposited by electron beam evaporation onto the fibre or filament in order to form a compliant electrode. Such an electrode can remain conductive up to strains of more than 20%. Such a film can be homogeneously applied to the filament or fibre.

Preferably, the electrode comprises a spiralled wire extending at least partially along the length of the fibre or filament.

The electrode may extend substantially along an outer surface of the filament or fibre. Alternatively, the electrode may extend within the fibre or filament. When the electrode extends within the fibre or filament it may extend substantially coaxially with the axis of the fibre or filament.

Conveniently, the actuator comprises a conducting species. The conducting species may be, for example, carbon fibres or conducting polymers.

Actuators of the type described hereinabove, may be used to create ohmic heating in a fibre or filament. In such filaments or fibres the liquid crystalline elastomer is one in which the isotropic phase change is induced by temperature.

The liquid crystalline elastomer may comprise an elastomer backbone comprising poly(methylhydrogensiloxane), a side chain mesogen comprising 4-but-3-enyloxybenzoic acid 4-methoxyphenyl ester, and a crosslinker comprising a polyether based on 1-(4-hydroxy-4′-biphenyl)-2-[4-(10-undecenyloxy)phenyl]butane which has nematic properties, for example.

Advantageously, the actuator comprises first and second electrodes, each of which are separate from one another. Such an electrode arrangement may be used to apply an electric field across the fibre and therefore enable the fibre to be electrically addressed. In such filaments or fibres, the liquid crystalline elastomer is one in which the state of the liquid crystalline phase (e.g. a smectic) is changed by the application of an electric field. For this mesogens are needed with chiral atoms. For example, (2S)-2-methylbuthyl 4-(4′-hydroxybenzoyloxy)benzoate.

Conveniently, each of the first and second electrodes extend substantially along an outer surface of the filament or fibre.

Alternatively, the first electrode extends substantially along an outer surface of the filament or fibre, and the second electrode extends within the filament or fibre. In another embodiment both the first and second electrodes may extend within the filament or fibre.

Alternatively, the first and second electrodes each comprise finger electrodes. Such an arrangement may be used to induce electrical fields along the length direction of the fibre.

Preferably, each of the first and second electrodes is elastic. Advantageously, at least one of the first and second electrodes is corrugated. Conveniently, at least one of the first and second electrodes comprises chromium-gold. One or both of the first and second electrodes may be formed from a chromium-gold film having a thickness of between 5 and 100 nm. Such electrodes can remain conductive for strains of more than 20%. Such a film can be homogeneously applied to the filament or fibre.

Preferably, the liquid crystalline elastomer comprises a ferro-electric liquid crystal elastomer, preferably a liquid single crystal elastomer.

In such a material, the phase transformation and hence actuation of the material is induced by the application of an electric field.

Very large lateral electrostriction may be achieved using ferro-electric liquid crystalline elastomers, preferably ferro-electric liquid single-crystalline elastomers.

The phase transformation of such a liquid crystal elastomer may be induced by an application of an electrical field of the order of 1V/micron.

Conveniently, the actuator comprises azo groups incorporated into the mesogenic side-chains.

The incorporation of azo groups in the mesogenic side-chains enables radiation to be used to induce a trans-to-cis-photoisomerisation reaction in which the cis-isomer has a kinked non-mesogenic shape. This means that radiation of the filament or fibre leads to an expansion of the filament or fibre. Upon radiation with light of another wavelength a relaxation or shrinkage of the filament or fibre occurs.

Such a fibre is formed from a liquid crystalline elastomer in which the isotropic phase change is induced by radiation, by incorporating light sensitive mesogenic sidegroups, for example [4-(4-buteneoxy)-4′-methyloxy]azobenzene and/or light sensitive mesogenic crosslinking agents like for example di-[4-(11-undeceneoxy)]azobenzene.

The invention will now be described by way of example only with reference to the accompanying drawings in which:

FIG. 1 shows a basic structure of a liquid crystal elastomer forming part of a filament or fibre according to the present invention;

FIG. 2 is a graphical representation showing strain in a filament or fibre according to the present invention as a function of the normalised temperature T/TN-I, where T N-I is the liquid crystal nematic to isotropic transition temperature;

FIGS. 3a to 3h are schematic representations of a filament or fibre according to the present invention formed from liquid crystalline elastomer in which the isotropic phase change is induced by temperature;

FIGS. 4a, 4b and 4c are schematic representations of a second embodiment of the present invention in which the filament or fibre is formed from a liquid crystalline elastomer in which the isotropic phase change is induced by application of an electric field;

FIG. 5 is a schematic representation of a third embodiment of the present invention in which the filament or fibre is formed from a liquid crystalline elastomer containing azo groups, in which the strain is induced by radiation;

FIG. 6 is a schematic representation of a variable conductive textile formed from filaments or fibres according to the present invention;

FIG. 7 is a schematic representation of a garment formed from the textile of FIG. 6 incorporating a cuff in a sleeve;

FIG. 8 is a graphical representation of the resistance of the cuff of FIG. 7 as a function of the strain induced in the textile forming the garment;

FIG. 9 illustrates a calibration curve that correlates the force exerted by the cuff shown in FIG. 7 onto a wearer;

FIGS. 10a to 10d illustrate time dependent resistance measured at different strains (i.e., different cuff resistance).

Referring to FIG. 1, a basic structure of a liquid crystalline elastomer (LCE) suitable for forming a filament or fibre according to the present invention is designated generally by the reference numeral 2. The LCE comprises a functional long chain elastomer 4, for example, PDMS, a mesogenic side-chain 6 and a crosslinker 8. Mesogen is a liquid crystal active group, and the crosslinker crosslinks one long chain elastomer 4 to a second long chain elastomer 4.

Turning now to FIG. 2, strain expressed as the length of the fibre normalised to its length at low temperatures, as a function of the normalised temperature T/TN-I, where TN-I is a liquid crystal to isotropic transition temperature, is shown.

The liquid crystal phase may be nematic, smetic or cholesteric, depending on the liquid crystal material.

As can be seen from FIG. 2, a temperature increase induces a strain. At a temperature well before TN-I, a length change occurs which is significant at temperature T/TN-I=1.

Turning now to FIG. 3, an embodiment of a fibre or filament according to the present invention is shown. Each of the fibres or filaments shown in FIGS. 3a to 3h is configured to cause heating of the fibre 10. The fibre 10 comprises a liquid crystalline elastomer 12 which is responsible for the change in the dimensions of the fibre, and an actuator.

In FIG. 3a, the actuator is in the form of a corrugated electrode 14. Because the electrode is corrugated it is able to stretch axially as the length of the fibre 10 increases on heating. The electrode may extend either partially or completely along the length of the fibre 10.

In FIG. 3b, the actuator is in the form of an electrode 16 which is formed from a compliant or elastic material in order to enable the electrode to stretch with stretching of the fibre 10.

In FIG. 3c, the actuator is in the form of an electrode 18 also made of a compliant or elastic material and extending within the fibre 10.

The electrodes 14, 16, 18 may be formed from any suitable material, for example, a chromium-gold alloy.

Referring to FIG. 3d, the fibre 10 is shown incorporating a conducting species 20 in the form of, for example, carbon fibres or conducting polymers.

In FIG. 3e, the actuator is in the form of a spiralled wire which may extend partially or entirely along the length of the fibre 10.

FIGS. 3f and 3g show a fibre according to the present invention interwoven with one or more conducting wires 24. The conducting wires 24 may be metallic, conducting organic etc. A heating effect on the fibre may be created by means of the conducting wires 24.

In FIG. 3h the fibre 10 is shown with spiral conducting electrode 26 extending within the fibre 10.

Each of the arrangements shown in FIGS. 3a to 3h enable ohmic heating of the fibre to take place via an actuator in the form of the various electrodes illustrated.

Turning now to FIGS. 4a and 4b, a fibre 28 according to another embodiment of the invention is shown.

In FIG. 4a, the fibre 28 comprises separated top and bottom compliant electrodes 30.

In FIG. 4b, the fibre 28 comprises two sets of finger electrodes 32, 34.

The embodiment shown in FIG. 4a can also be combined with the embodiment shown in FIGS. 3a, 3b or 3c.

The embodiment shown in FIG. 4a will create an electric field that is perpendicular to the length of the fibre. This means that the fibre will broaden on application of the electric field, leading to a decrease in the length of the fibre upon applying an electric field.

In the arrangement shown in FIG. 4b, the electrode layout defined by electrodes 32, 34 is used to induce electric fields in the length direction of the fibre. The field direction alternates as indicated by arrows 36. This means that the fibre 28 will lengthen upon application of an electric field, leading to a corresponding decrease in the width of the fibre.

Turning now to FIG. 5, a further embodiment of a fibre according to the present invention is designated generally by the reference numeral 38. The fibre 38 comprises azo groups within the liquid crystalline elastomer. Such a fibre may be exposed to radiation 40 which radiation causes strain in the fibre.

Typical wavelength for the cisàtrans conformation change is 365 nm, whereas the process can be reversed by irradiation with UV radiation of typically 465 nm. In order to complete the photoisomerisation reaction, irradiation times may vary from seconds to minutes, depending on the exact materials used.

Turning now to FIG. 6, a variable conductive textile formed from a plurality of filaments or fibres according to the present invention is designated generally by the reference numeral 42. The textile 42 is formed from conventional textile yarns at least some of which are formed from an elastic material 44, and conductive fibres 46.

The fibres formed from elastic material comprise, at least partially, fibres according to the present invention. Such fibres will lengthen and shorten in a response to one of the stimuli mentioned hereinabove, such as temperature, electrical field, radiation, electrical current. This leads to a change in the electrical conductance of the fabric.

The thermally insulating property of textiles depends on various properties, one of which is the amount of air trapped inside the textile structure. Textiles can consist of stacked and interconnected layers. In addition textiles can be formed from a warp interlockor open course structures. Further a textile may have a three-dimensional orthogonal weave structure.

A three-dimensional orthogonal weave structure typically comprises first, second and third fibres, all of which are mutually orthogonal to one another. Fibres which are perpendicular on the warp and weft are formed from a liquid crystal elastomer according to the present invention. The liquid crystal elastomer forming the third fibres has length which is determined by temperature. High temperatures will lead to a contraction of the third fibres. This leads to the layers in the weave structure being pushed towards each other. This in turn results in less air being trapped within the textile which means that the thermal insulation of the textile will decrease. When the temperature drops, the length of the third fibres will increase which will allow the stacked layers to expand. This will lead to more air being trapped within the weave structure which in turn, will lead to an increase in the thermal insulation.

Use of a different liquid crystal elastomer to form the third fibres can result in a textile which can be triggered using different stimuli.

A textile of this type can be used in many different ways. For example, the textile could be used to form a bra, the degree of support provided by the bra being variable. For example, during strong physical activity, it is desirable for a bra to give maximum support. This can be achieved by combining fibres according to the present invention into a textile used to form the bra. Expansion of the fibres will lead to a less close fit of the bra, yielding suppressed breast support. On the other hand, contraction of the fibres will lead to enhanced breast support.

The drape of garments is important in determining the characteristic appearance of the garment. The drape of garments is affected by many different parameters that are related to the mechanical and physical properties of the fibre and yarn used to make the garment. In addition, the drape is affected by the arrangement of the yarns, i.e., whether the yarns are knitted and/or woven and/or braided etc, and the interaction of the garment with the body of the person wearing the garment.

By forming a garment partially or entirely from fibres or filaments according to the present invention reversible expansion and contraction of the fibres forming the garment will induce changes in drape which may be desirable for e.g aesthetic reasons.

A garment formed entirely or partially from fibres or filaments according to the present invention can also be used to form a blood pressure measuring device.

It is known to measure blood pressure in a person by pumping up a cuff on the arm of the person whose blood pressure is to be measured to thereby close the veins in that person.

During the measuring of the blood pressure, the heartbeat of the person is measured. The pressure at which two sub-beats forming the complete heartbeat are detectable corresponds to the systolic blood pressure. The pressure at which only one sub-beat is detectable corresponds to the diastolic pressure.

Measurement can be automated so that a medical doctor is not required and people can measure their blood pressure themselves at home. However, known devices are relatively bulky, and the cuff has to be accurately attached to the arm.

Through use of a garment formed from filaments or fibres according to the present invention, a textile blood pressure measuring device can be used to measure blood pressure.

Referring to FIGS. 7 to 10, a garment according to an embodiment of the present invention is designated generally by the reference numeral 60. The garment is in the form of a shirt or jacket or the like, and comprises a textile cuff 62 formed from filaments or fibres according to the present invention and therefore having a variable electrical insulating property. This means that the resistance of the cuff 62 will vary with the strain in the cuff.

FIG. 8 shows graphically the relationship between the resistance of the cuff 62 and the strain in the cuff for two different liquid crystalline elastomers. Dotted line I shows the relationship between resistance of strain where the resistance decreases with increasing strain. Solid line II shows the relationship between resistance and strain in a situation where resistance increases with increasing strain.

The strain in the material forming the cuff 62 is induced by an external stimulus as described hereinabove and most preferably is induced through application of an electrical current or an electrical field.

The liquid crystalline elastomer forming the fibres forming the cuff 62 is chosen so that strain induced in the cuff 62 leads to a contraction of the cuff. The contraction of the cuff can be correlated to a contraction force F which in turn corresponds to a certain pressure P. P is equal to the force F divided by the cuff surface A. This means that
P=F/A

The cuff is first contracted to such an extent that no fluctuations in resistance are measured. At this stage the cuff pressure is larger than the systolic pressure and is shown in FIG. 10a. At several stages during the subsequent relaxation of the cuff, the strain is kept constant for some time and the resistance of the cuff is measured as a function of time. When the cuff pressure becomes smaller than the systolic pressure, the pulse of the heart will make the cuff expand and contract periodically, leading to either a decrease or increase in the resistance, depending on the strain-resistance function as shown in FIG. 8.

Assuming an ascending function as illustrated by line 11 in FIG. 8, the temporal expansion of the cuff caused by the heart pulse will lead to a decrease in the resistance, since an expansion of the cuff implies a decreased stain.

At resistance R2 and strain S2 as shown in FIG. 8, a first oscillation of the resistance is measured as shown in FIG. 10b. At this point the cuff pressure is equal to the systolic pressure Ps. The repetition time Δt yields the heartbeat frequency f=60*Δt−1. The corresponding force that follows from the calibration curve is F2 so that at R2, the cuff pressure is F2/A=Ps.

When the strain is further decreased, and the cuff further relaxes, at resistance R1 and strain S1, the measured resistance signal is maximum as shown in FIG. 10c. The corresponding pressure F1/A is referred to as the average blood pressure.

Upon further decreasing the strain, at resistance R0, the signal disappears as shown in FIG. 10d. This implies that, at that moment, the cuff pressure F0/A equals the diastolic pressure Pd.

The garment 60 will further comprise electronic control units (not shown) that can address the liquid crystalline elastomer forming the fibres forming the cuff 62, and that can measure the time dependent cuff resistance. Further the control units will calculate pressures from the measured time dependent resistances by applying predetermined calibration curves. Finally the control units will measure the lengths of time from which beat frequencies are calculated.

Claims

1. A filament or fibre (10) comprising a liquid crystalline elastomer (2), and an actuator (14) for enabling actuation of the filament or fibre to thereby cause a change in the dimensions of the filament or fibre.

2. A filament or fibre according to claim 1 wherein the liquid crystalline elastomer comprises a functional long chain elastomer (4), a plurality of mesogenic side chains (6), and a cross linker (8).

3. A filament or fibre according to claim 2 wherein at least some of the mesogenic side chains are aligned.

4. A filament or fibre according to claim 1 wherein the actuator comprises an electrode (14) extending axially along the fibre or filament.

5. A filament or fibre according to claim 4 in which the electrode (16) is elastic.

6. A filament or fibre according to claim 5 in which the electrode (14) is corrugated.

7. A filament or fibre according to claim 1 wherein the electrode comprises a spiralled wire (22) extending at least partially along the length of the fibre or filament.

8. A filament or fibre according to claim 4 in which the electrode is a Cr—Au electrode.

9. A filament or fibre according to claim 4 in which the electrode extends substantially along an outer surface of the fibre or filament.

10. A filament or fibre according to claim 4 in which the electrode extends within the fibre or filament.

11. A filament or fibre according to claim 1 wherein the actuator comprises first (30) and second (30) electrodes, each of which are separate from one another.

12. A filament or fibre according to claim 11 wherein each of the first and second electrodes extends substantially along an outer surface of the filament or fibre.

13. A filament or fibre according to claim 11 wherein the first electrode extends substantially along an outer surface of the filament or fibre, and the second electrode extends within the filament or fibre.

14. A filament or fibre according to claim 11 wherein the first and second electrode each comprise finger electrodes (32, 34).

15. A filament or fibre according to claim 1 wherein the actuator comprises a conducting species.

16. A filament or fibre according to claim 15 in which the conducting species comprises carbon fibres.

17. A filament or fibre according to claim 15 in which the conducing species comprises conducting polymers.

18. A filament or fibre according to claim 1 wherein the liquid crystalline elastomer comprises a ferro-electric liquid crystalline elastomer.

19. A filament or fibre according to claim 2 dependent thereon wherein the actuator comprises azo groups incorporated into the mesogenic side chains.

20. A fabric (42) comprising a plurality of elastomer fibres formed form a liquid crystalline elastomer, and a plurality of conductive wires interwoven with the elastomer fibres.

21. A fabric formed from a plurality of filaments or fibres according to claim 1.

22. A garment formed from fabric according to claim 20.

23. A blood pressure measuring device formed from a fabric according to 20.

24. A device for controlling thermal insulation formed from a fabric according to claim 20.