Induced Smectic-G through intermolecular H-Bonding - Part XVII: Influence of identical end chain lengths on phase behaviour

Abstract

An induced smectic-G phase through intermolecular hydrogen bonding has been studied systematically in a new series of complexes resulting from mesogenic p-n-alkoxy benzoic acids (nAoBA) and non-mesogenic n-alkyl p-hydroxy benzoates (nAHB), in which the alkoxy and alkyl carbon chain lengths of both acid and ester moieties are equal (with n = 5 to 9 and 12). The phase behaviour of the new H-bonded complexes is studied by using the polarising microscope (TM) and differential scanning calorimeter (DSC). The formation of the intermolecular hydrogen bond between the -COOH of the acid moiety and the phenolic -OH group of the ester moiety is characterised by IR solid state spectra. Further, the IR spectral study in solution reveals the stabilisation of the hydrogen bond in the dissolved state. From the comparative thermal and phase analyses of the p-n-alkoxybenzoic acids and hydrogen-bonded complexes, the induction of the crystal smectic-G phase can be readily understood. Further, the thermal range of the smectic-G phase is analysed in terms of the influence of the identical end carbon chain lengths. The transition temperatures across the series show an odd-even effect.

Keywords:

• H-Bonding
• n Aoba
• n Ahb
• Smectic-G