Liquid crystalline solution temperature effect

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. 

The absorbance of liquid crystalline solutions of PBLG as calculated from the relation, ) = Vs (On + 2 >x), dightly increases or decreases with time, depending on the solvent used when an electric field is applied to the solution, whereas, it should be constant for inddent light perpendicular to the field direction (and to the orientation direction), as in this case if wall effects are not involved. The steady-state absorbance, however, becomes independent of both temperature and external field strength in case the ratio of 730 is obtained, indicating that wall effects are then ne igible (25). 

A further method of producing amorphous phases is by a strain-driven solid-state reaction (Blatter and von Allmen 1985, 1988, Blatter et al. 1987, Gfeller et al. 1988). It appears that solid solutions of some transition metal-(Ti,Nb) binary systems, which are only stable at high temperatures, can be made amorphous. This is done by first quenching an alloy to retain the high-temperature solid solution. The alloy is then annealed at low temperatures where the amorphous phase appears transiently during the decomposition of the metastable crystalline phase. The effect was explained by the stabilisation of the liquid phase due to the liquid—>glass... 

For ionic surfactants micellization is surprisingly little affected by temperature considering that it is an aggregation process later we see that salt has a much stronger influence. Only if the solution is cooled below a certain temperature does the surfactant precipitate as hydrated crystals or a liquid crystalline phase (Fig. 12.4). This leads us to the Krafft temperature1 also called Krafft point [526]. The Krafft temperature is the point at which surfactant solubility equals the critical micelle concentration. Below the Krafft temperature the solubility is quite low and the solution appears to contain no micelles. Surfactants are usually significantly less effective in most applications below the Krafft temperature. Above the Krafft temperature, micelle formation becomes possible and the solubility increases rapidly. 

This polymer assumes a smectic B-type liquid-crystalline phase when cast from solution. Then, using LiCF3S03 (LiOTf) as the alkali metal salt (Li/O = 0.4), a conductivity in excess of 1 x 10 2 Q m l is achieved at room temperature, the amorphous EO matrix effectively remaining above its Tg. The molecular architecture of the whole structure is depicted in Fig. 8.9. 

The recent studies on the structure and properties of polypeptide liquid crystals, which are formed in solution as well as in the solid state, are reviewed in this article. Especially the cholesteric pitch and the cholesteric sense (right-handed or left-handed), which are characteristic factors of cholesteric liquid crystals, are discussed in detail in relation to the effects of temperature, concentration, and solvent. Further cholesteric liquid crystalline structure retained in cast fdms and thermotropic mesomorphic state in some copolypeptides are also discussed. 

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. 

We have now said everything necessary about activities and standard states, but the overall effect for the newcomer is often one of confusion at this stage. To try to draw the various threads together we consider in Figure 12.5a a hypothetical three-phase equilibrium at temperature T and pressure P. A solid crystalline solution of B in A is in contact with an aqueous solution of A(aq) and B(a<7), which is in turn in contact with a vapor phase containing A(v) and B(v) in addition to water vapor. We can suppose the dissolution of (A,B)(5) to be stoichiometric so that the ratio of A to B is the same in all three phases, but this is irrelevant to our development as we consider only component A. Let s say that for a solid solution composition of A"a = 0.5, Vr = 0.5, the concentration of A aq) at equilibrium rri/ ) is 10 molal, and the fugacity of A in the vapor (/a) is 10 bars. Assuming activity coefficients in the solid and liquid... 

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