Flow Properties of Liquid Crystals of Polypeptides

Abstract

Viscosities and normal stresses in steady shear flow and viscoelastic properties under oscillatory motion were measured on concentrated solutions of poly-γ-ethyl-L-glutamate, its equimolar mixture with the D-isomer, and poly-γ-benzyl-L-glutamate, especially when in a liquid crystalline state. With increasing polymer concentration, the steady shear viscosity increased noticeably because interactions among the polymer molecules became strong. It, however, underwent a marked decrease when the solution became liquid crystalline. Under the action of shear stresses, long rod-like molecular clusters are produced in the solution, and oriented in the direction of the flow showing a strong Weisenberg effect. Even in an isotropic state, aggregation of the polypeptide molecules and their orientation under shear stresses were observed. When the shear rate increased, the steady shear viscosity decreased because of the orientation of the molecular clusters or of the aggregates in which their degradation was involved. Some differences in the flow properties were seen among the systems being observed.