Elastic Properties of Liquid Crystalline Mixtures in Relation to Their Molecular Composition

Abstract

The ratios of the bend and splay elastic constants k ₃₃/k ₁₁ as a function of the reduced temperature t _r = T[K]/T _N–1[K] are reported for binary mixtures of different liquid crystalline classes. A distinct change in k₃₃/k₁₁ between the various classes has been observed. The elastic constants of 4-n-alkylphenyl 4-n-alkanoyloxybenzoates, comprising one of these binary mixtures, are influenced considerably by adding appropriate liquid crystal compounds. Absolute values of k₃₃/k₁₁ down to 0.64 at low reduced temperatures have been obtained. It is shown that the significant lowering in k₃₃/k₁₁ is due to an interaction between a terminal CN-group of the added liquid crystal and the ester mixture. However, alkyl chain length, conjugation, and overall molecular length of the additive play a minor role. For certain mixing ratios of the esters with components containing terminal polar groups, an induced smectic phase is observed.