Electric fields transition, polymer solution

Incorporation of flexible siloxane spacers into side chain or main chain liquid crystalline polymers have been shown to drastically reduce the transition temperatures 255,267,271,272,277) anc[ aiso increase the response time of the resultant systems to the applied thermal, optical or electrical fields 350-353>. In addition, siloxanes also provided elastomeric properties and improved the processibility (solution or melt) of the resulting liquid crystalline copolymers. 

Liquid crystalline solutions as such have not yet found any commercial uses, but highly orientated liquid crystal polymer films are used to store information. The liquid crystal melt is held between two conductive glass plates and the side chains are oriented by an electric field to produce a transparent film. The electric field is turned off and the information inscribed on to the film using a laser. The laser has the effect of heating selected areas of the film above the nematic-isotropic transition temperature. These areas thus become isotropic and scatter light when the film is viewed. Such images remain stable below the glass transition temperature of the polymer. 

Wirtz D, Fuller GG (1993) Phase transitions induced by electric fields in near-critical polymer solutions. Phys Rev Lett 71(14) 2236-2239... 

D. Wirtz, K. Berend and G.G. Fuller, Electric field induced structure in polymer solutions near the critical point, Macromolecules, 25, 7234-7246 (1992) D. Wirtz and G. G. Fuller, Phase transitions induced by electric fields in near-critical polymer solutions, Phys. Rev. Lett., 4,2236 (1993). 

The transition moment directions of some of the absorption bands of PBLG in liquid crystalline state have been investigated in a CaF2 cell by means of the infra-red dichroic ratio (56). All the transition moment directions measured at 1 °C are very similar to those observed 32) on mechanically oriented films of PBLG (Table 2), verifying that all the polymer molecules present a parallel or nearly parallel orientation in the molecular cluster and that the main chain and the side chains of the polymer molecule are fixed as in the solid film. No significant difference is observed between the systems of solution testing. The orientation of the solvent molecules (methylene moletules) is detected in an electric field in accordance with the NMR observation (56). 

Aikawa et al. considered the effect of electric field on the phase transition in solutions of rigid-chain polymers for a PBLG solution in dioxane. Theoretical calculations have shown that the application of an electric field must shift the values of v towards lower concentrations. This conclusion was confirmed in experiments. According to the results obtained by Patel et al the application of electric fields also causes a shift in the temperature of the liquid crystalline transitions. 

Partial orientation is much easier to achieve and generally sufficient to determine the direction of the transition moments, particularly with respect to any axes of symmetry that the molecules may have. Partial orientation can be achieved by photoselection using a linearly polarized excitation source, by application of an electric field or by dissolving the solute in a transparent anisotropic medium (liquid crystals, stretched polymers).182 Photoselection is the basis of emission anisotropy measurements discussed below. It is also used for molecules that can be either generated or destroyed photochemically in a rigid medium such as poly(methyl methacrylate) or glassy solvents at low temperature. Preferential alignments of dipolar molecules that are achievable by electrostatic fields are unfortunately fairly small. 

For pH-responsive electrochemical systems, on the other hand, the electrical field indirectly influences the polymer conformation to induce a reversible volume transition. The electricity is used to electrolyze water, generating hydrogen ions at the anode and hydroxyl ions at the cathode. This produces a pH gradient across the solution, which can be used to influence the conformation of pH-responsive polymers. Strategic placement of the polymer in the solution can cause expansion, contraction, or even bending (when placed directly between the electrodes) of a polymer actuator. Switching the direction of the current creates the opposite effect. This second method of actuation... 

English AE, Edelman ER, Tanaka T (2000) Polymer hydrogel phase transitions. Chapter 6. In Tanaka T (ed) Experimental methods in polymer science. Academic, Boston, pp 547-589 Filipcsei G, Feher J, Znnyi M (2000) Electric field sensitive neutral polymer gels. J Mol Stmct 554 109-117. doi 10.1016/S0022-2860(00)00564-0 Flory PJ (1942) Thermodynamics of high polymer solutions. J Chem Phys 10 51-61. doi 10.1063/ 1.1723621... 

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