The Frustrated Spin-Gas Theory of Multiply Reentrant Liquid Crystals
Quadruply reentrant phase diagrams (nematic↔smectic Ad ↔ nematic ↔ smectic Ad ↔ nematic ↔ smectic A1), smectic layer thicknesses, and transition enthalpies have been obtained from the frustrated spin-gas model, in satisfactory agreement with experiments. The stringent requirement on the molecular tail length for quadruple reentrance, seen in experiments, also occurs in this theory. The microscopic mechanism underlying the two smectic Ad peninsulae is found to be relief of dipolar frustration by permeation either on atomic length scale, or on librational length scale, respectively, at higher or lower temperatures. The distinctive transition enthalpies can be related to the molecular dimers, which form a nematic background in the smectic Ad phase, but which break up at the onset of the smectic Al phase.
KeywordsSmectic Layer Transition Enthalpy Dime Concentration Positional Fluctuation Phase Transition Peak
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