Rheology of a thermotropic polyester in the nematic and isotropic states

Abstract

The rheological properties of a thermotropic polyester were determined in the nematic and isotropic states. In the isotropic state, the viscosity is almost constant and the polymer is only slightly elastic. The nematic phase has a lower viscosity than the isotropic, except at low frequencies or shear rates, where the viscosity increases as though the polymer had a yield stress. There is a marked dependence of the rheology on shear history. The effects of shearing can be erased by returning the material first to the isotropic state and then back to the nematic state. The results are discussed with reference to analogous observations in small‐molecule liquid crystals and in thermotropic aromatic co‐polyesters.

Viscoelastic properties of decrosslinked irradiation‐crosslinked polyethylenes in supercritical methanol

“…An investigation of the relaxation behavior of the samples is useful when seeking to account for differences in the rheological properties of polymers. On the basis of the data from the dynamic shear measurements, the λ value can be calculated by eq 4, as suggested by Wissbrun and Griffin 26 Here, λ, J ′, η*, G ′, and ω are relaxation time, compliance, complex viscosity, storage modulus, and frequency, respectively.…”

Polyesters

“…178 -182 The melt rheology of LCPs in the LC state is quite complex. 173,183,184 LCPs generally present a non-Newtonian behavior with a rapid decrease in viscosity with increasing shear rates. As a consequence, the bulk viscosity of polyester LCPs can be two orders of magnitude less than that of PET under normal processing conditions.…”

Characterization of thermotropic liquid crystalline polyester/polycarbonate blends: Miscibility, rheology, and free volume behavior

“…The influence of Vectra then comes into play (although not in a dominant fashion) at greater Vectra contents (Ն50%). Figure 4 shows the relaxation times () of Vectra/PC blends, calculated from dynamic rheological parameters by an empirical equation [25][26][27] :…”