Liquid crystals comprising hydrogen-bonded organic acids II. Heterodimers in mixed mesogenic acids

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Abstract
Nematic mesophase stability, as determined by the excess mesophase range in mixtures of organic acids (supramesogen derived from par a-substituted phenyl, 4-substituted cyclohexane and bicyclo[2.2.2]octane carboxylic acids), is increased in mixtures of disparate species - mixed acids with differing substituent sizes (different supramesogen tail lengths) and different acid types (aliphatic and aromatic supramesogen cores). These trends enable one to estimate contributions to mesophase stability stemming from tail disparity and core differences, contributions that appear to carry over into analogous covalent mesogens. IR measurements of solid mixtures of acids suggest that the heterodimer acids population dominates, and deuterium NMR studies of labelled acids in the nematic phase emphasize the dynamic character of this class of supramesogens: dimer lifetimes are shorter than microseconds.