Liquid crystals comprising hydrogen-bonded organic acids - I. Mixtures of non-mesogenic acids

Stable nematic phases are reported for binary mixtures of p-alkylbenzoic acids (nBA; where n = 1,2,3 denotes methyl, ethyl and propyl), p-alkoxybenzoic acids (nOBA, n = 1,2), and p-fluorobenzoic acid, which separately do not exhibit liquid crystalline phases. The mesophase stability increases in equimolar mixtures of acids having incomensurate lengths; the larger the difference in the tail substituents in the mixed organic acids. the broader the nematic phase. The trends in excess nematic range exhibited by the H-bonded supramesogens in binary mixtures parallels the behaviour of covalent mesogens. This is indicative of an influence of heterodimers comprising H-bonded pairs of the two different acids in equimolar mixtures of the non-mesogenic acids. It would appear that dimerized organic acids constitute a viable molecular-structural 'bread-board' for rapid screening for potential mesogen constituents.