Cubic Phase Formation and Interplay between Alkyl Chains and Hydrogen Bonds in 1,2-Bis(4′-n-alkoxybenzoyl)hydrazines (BABH-n)

Abstract

The phase transitions of a homologous series of 1,2-bis(4′-n-alkoxybenzoyl)hydrazines (BABH-n, where n is the number of carbon atoms in the alkyl chain and in this investigation varies from 4 to 22) were investigated by differential scanning calorimetric (DSC), polarizing optical microscopic (POM), X-ray diffraction (XRD), and infrared (FT-IR) measurements. The formation of bicontinuous type cubic (Cub) mesophases was observed enantiotropically for n ≥ 6 and only on cooling for n = 5. The structures were examined by XRD, which revealed the presence of two types with symmetries Ia3d and Im3m, depending on n, and for n = 13, 15, and 16, phase transitions between the two Cub phases were observed. The FT-IR studies elucidated the formation of intermolecular hydrogen bonding between the C═O bond of one molecule and the NH group of another molecule, whose binding strength was temperature-dependent. The temperature dependence of the Cub lattice parameter (da/dT) varied from a large positive to a large negative v...