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This is done by coating the glass plates 1,2 complete with conducting electrodes 3,4 with layers of film 5 and 6 of a suitable polymer, eg polyimide. The electrodes 3,4 may be formed into row and column electrodes so that the intersections between each column and row form an x, y matrix of addressable elements or pixels. Prior to the construction of the cell the films 5,6 are rubbed with a roller covered in cloth for example made from velvet in a given direction, the rubbing directions being arranged parallel same or opposite direction upon construction of the cell.

A spacer 7 eg of polymethyl methacrylate separates the glass plates 1 and 2 to a suitable distance eg 2 microns.

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Liquid crystal material 8 is introduced between glass plates 1,2 by filling the space in between them. This may be done by flow filling the cell using standard techniques. The spacer 7 is sealed with an adhesive 9 in a vacuum using an existing technique. Polarisers 10, 11 may be arranged in front of and behind the cell.

Liquid Crystal Elastomers with Mechanical Properties of a Muscle | Macromolecules

Alignment layers may be introduced onto one or more ofthe cell walls by one or more ofthe standard surface treatment techniques such as rubbing, oblique evaporation or as described above by the use of polymer aligning layers. The device may operate in a transmissive or reflective mode. In the former, light passing through the device, eg from a tungsten bulb, is selectively transmitted or blocked to form the desired display.

In the reflective mode a mirror, or diffuse reflector, 12 is placed behind the second polariser 11 to reflect ambient light back through the cell and two polarisers. By making the mirror partly reflecting the device may be operated both in a transmissive and reflective mode. In an alternative embodiment a single polariser and dye material may be combined. The liquid crystal material 8 when introduced into the cell consists of at least one type of liquid crystal monomer and at least one type of cross-linking agent.

The monomer material may be aligned before polymerisation using standard techniques, for example by heating up to and cooling from the isotropic phase or from a liquid crystal phase such as a nematic or chiral nematic phase. It is also possible that the liquid crystal polymer may be aligned by one or more techniques including the use of surface forces, shear alignment or field alignment. Typically in shear alignment the liquid crystal material is placed on a substrate, which may be polyethersulphone PES coated with Indium Tin Oxide ITO and an aluminium grid.

This is then sheared between another substrate. After polymerisation the substrates may then be separated to yield a free standing film. It is possible that following polymerisation there may still be some amount of monomer material remaining. This may be unreacted monomer or low molar mass additives which do not bear polymerisable groups. Typically, reagents which may be used to limit the molecular weight of the polymer possess one or more thiol groups.

These may be low molecular weight materials which may or may not exhibit liquid crystalline behaviour or they may be more complex molecules, in particular they may possess similar structures to the monomer which will be the basic building block for the elastomer material. Polymerisation may be carried out by using any of the known techniques. For example the monomer material plus cross-linking agents the mixture or mixture plus chain transfer reagent may also contain a photoinitiator and be exposed to UV light.

In addition to exposing such samples to UV light, heat may also be applied to assist the polymerisation reaction. Care is taken during polymerisation due to the light sensitive nature of some ofthe materials. Polymerisation may be carried out under darkened conditions. Alternatively the polymerisation process may take place in the presence of heat and a thermal initiator.

However if this technique is used it is preferable if it is carried out at a temperature which corresponds to a liquid crystal phase ofthe monomer material. The elastomers described by the current invention may be made from any ofthe known types of polymer e. Any suitable cross-linking agent may be used. A number of examples are as follows, the first two being commercially available from Aldrich Chemical Company Limited:.

The monomer was synthesised using the methods outlined in Figs 2, 3 and 4. The silica gel used for column chromatography was standard grade BDH silica gel particle size 0. Preparation of intermediate a : Fig. R- - Octanol To this was added dropwise, whilst stirring, pyridine When all of the pyridine had been added, the mixture was stirred for 18h whilst allowing the temperature to rise to room temperature. The product was purified by column chromatography on silica using petrol as eluent. Intermediate a After allowing the reaction mixture to cool to room temperature, water ml was added and shaken with the mixture.

The aqueous layer was separated and extracted with ether 2 x ml , This organic layer was combined with the original organic solution, washed with water 2 x ml dried over anhydrous sodium sulphate and the solvent removed on a rotary evaporator. Magnesium 5. A single crystal of iodine was added and the mixture was warmed to a gentle reflux. Once the solution had begun to turn grey-blue in colour, the heat was removed and the remaining bromobenzene in tetrahydrofuran was added dropwise at a sufficient rate that the exothermic reaction supported continuous reflux of the reaction mixture.

When the addition was complete, the heating was continued to support gentle reflux for a further two hours. The reaction mixture was cooled in ice and trimethylborate The product was extracted into diethyl ether ml and shaken with water 2 x ml. The ether layer was dried over anhydrous sodium sulphate and the solvent removed on a rotary evaporator. Benzyl chloride g, 1. After allowing to cool, the solid was filtered off and washed with butanone 3 x ml. The combined butanone fractions were reduced on a rotary evaporator to an off white solid which was dissolved in dichloromethane ml , washed with water 3 x ml , dried over anhydrous sodium sulphate and the solvent removed on a rotary evaporator.

Yield nm. Intermediate d g, 1. After allowing to cool, the reaction mixture was added to cold water ml and acidified to pH with concentrated hydrochloric acid. The product precipitated out and was filtered off before recrystallisation from hot ethanol. Intermediate e 45 g, 0.

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The crude product was recrystallised from ethanol. Preparation of intermediate fg : FIG. Intermediate f Sodium carbonate 2M solution, 45 ml was then added followed by intermediate c After allowing to cool, water ml was added and the product separated into toluene ml.

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The organic layer was washed with water 2 x ml , dried over anhydrous sodium sulphate and the solvent removed on a rotary evaporator. Intermediate g The vessel was evacuated and flushed with argon three times, and then evacuated and flushed with hydrogen. The mixture was then stirred vigorously under hydrogen for 48h.

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The catalyst was filtered off and the solvent removed on a rotary evaporator. Intermediate h 6. When cool, water 30ml was added, the mixture stirred briefly and layers separated. The aqueous layer was extracted with dichloromethane 2 x 20ml , the dichlororomethane layers combined with the butanone layer and washed again with water 20ml before drying over anhydrous sodium sulphate and removing the solvent on a rotary evaporator.

Intermediate i was combined in a 50 ml flask with acryloyi chloride 0. A calcium chloride drying tube was fitted and the mixture stirred at room temperature for 18h. Monomer II l. Og was dissolved in dry 1 ,2-dichloromethane 20ml and the free radical initiator azoisobutyronitrile 0. The solid was filtered off, dissolved in a little dichloromethane 5ml and poured again into cold ethanol. The polymer was examined for residual monomer by gel permeation chromatography and this process of reprecipitation repeated until no monomer remained in the sample.

No monomer was detectable by GPC. Triphenylphosphine The mixture was stirred at room temperature for 24h under an atmosphere of nitrogen. The THF was removed on a rotary evaporator, the products taken up in dichloromethane ml , washed with water 2 x ml , the solution dried over anhydrous sodium sulphate and the solvent removed on a rotary evaporator. The crude product was purified by flash chromatography on silica using petrol as eluent.

Yield Purity There are a number of variables which may affect the photopolymerisation of liquid crystal monomers. These include the following:. All of these factors may affect one or more ofthe following: molecular weight, polydispersity, alignment, switching behaviour.

Cross-linking materials were added to a 1 : 1 mix of polymers made up from the following monomeric materials polymers made from the monomers II and III are referred to as LCP and LCP respectively :. DSCs were carried out on free standing films produced as described in the present application. Cross-linker Amount added. Response Times were measured in flow filled cells. The times given below are the average of eight readings. The formation of elastomers with a cross-linking agent under an applied DC field may also produce a biased response in the switching times. The following two tables show the response times in milliseconds against temperature as a function of DC field applied during construction of a cell.

Response time A denotes the time taken to switch the device out ofthe state produced by the biasing field applied during formation, that is, against the direction ofthe DC field. Response time B denotes the time taken to switch the device back into the state produced by the biasing field, that is, with the direction ofthe DC field imposed during formation. The cells, when attached to an electrometer or other current measuring device, exhibit a polarisation dependence either on applied stress or rate of temperature change thus showing piezoelectric and pyroelectric properties.

One advantage of this biasing is that the device can be restored to its original configuration by the elastic forces introduced by the biasing field. The methods ofthe present invention may also be used to make pyroelectric devices for example detectors, stearing arrays and vidicon cameras. Similarly, the compounds ofthe present invention may be used in such devices. Figure 5 illustrates a simple pyroelectric detector in which the materials ofthe present invention may be incorporated, such a detector may also be made according to the methods described by the present invention.

A pyroelectric detector consists of electrode plates 13,14 at least one of which may be pixellated. In operation the detector is exposed to radiation R, for example infrared radiation, which is absorbed by the electrode This results in a rise in temperature which is transmitted to a layer of pyroelectric material 15 by conduction.

The change in temperature results in a thermal expansion and a charge is generated. Light-emitting material in the cavity amplifies the light wave, which is then emitted at a precise frequency - like a pure tone from some musical instrument. However, accurate control of the laser emission frequency was not possible then. Their recent work, funded by the U. The sensor could measure strain, which is just a small change in length, or stress, which is force per area. The liquid crystal acts as both the distributed cavity host and the active medium. Simple optical pumping of such a sample results in low-threshold, mirrorless lasing at the band edges.

Liquid crystal elastomers can change their shape when the orientational order of the constituents is changed - by changing the temperature, applying a field or introducing impurities. However, tomorrow, society at large is likely to benefit. Before , liquid crystal research was mainly driven by scientific curiosity. The discovery of the twisted-nematic effect and the invention of liquid crystal displays at the Liquid Crystal Institute at Kent State University transformed display technology, benefiting people all over the world.

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By using our site, you acknowledge that you have read and understand our Privacy Policy and Terms of Use. Home Physics Condensed Matter. Credit: Kent State University. Kowalski, B. Curvature by design and on demand in liquid crystal elastomers. E 97 , Engineering of complex order and the macroscopic deformation of liquid crystal polymer networks. Thomsen, D. Liquid crystal elastomers with mechanical properties of a muscle. Macromolecules 34 , — McConney, M. Topography from topology: photoinduced surface features generated in liquid crystal polymer networks.

Liu, Y. Visible light responsive liquid crystal polymers containing reactive moieties with good processability. ACS Appl. Interfaces 9 , — Guin, T. Electrical control of shape in voxelated liquid crystalline polymer nanocomposites. Courty, S. Nematic elastomers with aligned carbon nanotubes: new electromechanical actuators. Wermter, H. Liquid crystalline elastomers as artificial muscles. Modes, C. Gaussian curvature from flat elastica sheets.

A , — Voxel resolution in the directed self-assembly of liquid crystal polymer networks and elastomers. Soft Matter 13 , — Godman, N. Synthesis of elastomeric liquid crystalline polymer networks via chain transfer. ACS Macro Lett. Broer, D. Cross-linked liquid crystalline systems: from rigid polymer networks to elastomers.

Pixelated polymers: directed self-asembly of iquid crystalline polymer networks. Spillmann, C.

Magnetic fields allow liquid crystal elastomers to follow the sun

Stacking nematic elastomers for artificial muscle applications. A: Phys. Sato, Y. Relationship between rubbing strength and surface anchoring of nematic liquid crystal. Yaroshchuk, O. Photoalignment of liquid crystals: basics and current trends. Wu, S. Birefringence measurements of liquid crystals. Nematic liquid single crystal elastomers. Chem: Rapid Commun.

Blueprinting nematic glass: systematically constructing and combining active points of curvature for emergent morphology. E 84 , Shape-programmable materials. Today 69 , 32—38 Ashby, M.

Liquid crystal elastomers: emerging trends and applications

Selection strategies for materials and processes. Sherrit, S. Multilayer piezoelectric stack actuator characterization. Agrawal, A. Electromechanically responsive liquid crystal elastomer nanocomposites for active cell culture.

Liquid Crystal Elastomers: Materials and Applications (Advances in Polymer Science)

Hager, M. Shape memory polymers: past, present and future developments. Zhao, Q. Recent progress in shape memory polymer: new behavior, enabling materials, and mechanistic understanding. Zeng, H. Xu, S. Adaptive liquid lens actuated by photo-polymer. Petsch, S. Ultrathin Alvarez lens system actuated by artificial muscles. Lachmann, G. Boundary layer and flow control: its principles and application. Download references. Initial research directions were identified by T.

Experimental examinations were undertaken by T. All authors contributed to the writing of the manuscript. Correspondence to Timothy J. Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Reprints and Permissions. Advanced Optical Materials Physical Review E Advanced Materials By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Advanced search. Skip to main content. Subjects Actuators Liquid crystals Polymers. Abstract Liquid crystalline elastomers LCEs are soft, anisotropic materials that exhibit large shape transformations when subjected to various stimuli. Introduction Responsive materials are currently subject to intense research, motivated in part by end-use applications in robotics 1.

Results and discussion Materials preparation and characterization The LCE films examined here were formulated by mixing mesogenic diacrylates RM82 and RM with a dithiol chain-transfer agent Fig. Full size image. Methods Materials synthesis RM82 1,4-Bis-[4- 6-acryloyloxyhexyloxy benzoyloxy]methylbenzene and RM 1,4-Bis-[4- 3-acryloyloxypropyloxy benzoyloxy]methylbenzene were purchased from the Synthon Chemicals, and recrystallized from methanol before use.