Dynamic mechanical properties of cyclohexane-based glass-forming liquid crystals and a linear side chain polymer analogue

Abstract

A nematic and a cholesteric liquid crystal, both derived from trans-1,3,5-cyclohexanetri-carboxylic acid, and a linear side chain polymer analogue were characterized in terms of storage (G″) and loss (G″) moduli as functions of frequency and temperature. It was found that all three model compounds show a shear shinning flow behaviour with zero shear viscosities of the low molar mass systems significantly less than that of the polymer system at the same reduced temperature, T/T ^g. With shift factors prescribed by the WLF equation, both the G″ and G″ data of all three compounds are adequately represented by master curves. Furthermore, within the framework of the stretched exponential model, the relaxation behaviours of the low molar mass systems are well described by a single Maxwell element, whereas the polymer system shows a relatively broad distribution of relaxation times. The observed viscoelastic properties suggest a relative ease of material processing of the low molar mass systems compared to the polymer analogue due to a lower zero shear viscosity and a single relaxation time characterizing the dynamics of response to a mechanical or thermal stimulus.