Recent advances in the rheology of thermotropic liquid crystal polymers

Abstract

Thermotropic Liquid Crystal Polymers (TLCPs) are advanced high temperature processing polymers with unique physical properties, which have recently gained more attention while being useful for many applications. Although considerable amount of study has been carried out on the rheology of lyotropic liquid crystal polymers not much has been reported on the rheology of TLCPs. Some recent study incorporating carbon nanotubes, graphene and graphene oxide in TLCPS have been reported. The polydomain structure of TLCP molecules as well as their phase change from nematic to isotropic due to shearing and temperature variation significantly affects the rheological and morphological properties. This chapter will describe the recent developments in rheological, thermal and morphological properties of filled and unfilled TLCPs. In rheological characterization, focus will be on low to high shear rate regions as very limited data exists for TLCPs. Filled TLCPs (aspect ratio of filler greater than 100) exhibit negative first normal stress difference (N1) in the low shear rate region. Moreover, in the high shear rate region the viscosity of filled TLCPs show more shear thinning behaviour compared to the unfilled TLCPs due to the rheological hybrid effects. The anomalous rheological behavior due to temperature change will also be discussed. The complicated rheological properties of TLCPs can be simulated by the recently developed Leonov’s viscoelastic model. Recent study indicates a good fit in the high shear rate range.