Pressure-induced mesomorphism

3 Pressure-induced mesomorphism Theoretical phase diagrams for two representative values of v are illustrated in fig. 2.1.9. In fig. 2.1.9(a) the orientational barrier is large enough for the nematic phase to occur at zero pressure. As the pressure is raised, both the solid-nematic and the nematic-isotropic transition temperatures increase, 

Experiments were done on the first two members of the p-n-alkoxybenzoic acid series to verify this prediction. These two compounds, methoxy- and ethoxybenzoic acids, do not form liquid crystals at atmospheric pressure, whereas propoxybenzoic acid and the higher homologues show at least one liquid crystalline phase. As the pressure is raised, both compounds exhibit mesophases, initially a nematic phase and 

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High isotropic pressure has also been proved to induce mesomorphism [133], and in particular to induce a liquid crystalline behavior in compounds that do not form liquid crystalline phases at atmospheric pressure (Fig. 17) [134]. The case of the reentrant nematic phase, discovered by applying high pressure, is also now famous ([135] and Sec. 6.4 of Chap. VII of Vol. 1 of this handbook). 

The change from a crystalline into a liquid crystalline state can be brought about by changes in, for example, temperature or pressure. Furthermore, some molecules may be induced to form liquid crystals by the addition of a solvent such as water. This behavior is in reality a liquid crystalline formation in a two component system and is called solvent-induced liquid crystal formation or lyotropic mesomorphism (Small, 1986, p. 49). 

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