Temperature, concentration, and molecular weight dependence of the twist elastic constant of cholesteric poly-γ-benzyl-L-glutamate

Abstract

Aspects of the behavior of the twist elastic modulus K22 of a lyotropic liquid crystal formed by the α-helical polypeptide poly-γ-benzyl-L-glutamate of three molecular weights (MW= 300 000, 310 000, and 550 000) in three solvents (dioxane, dichloromethane, and chloroform) were investigated as a function of concentration and temperature. We find that K22 in this system may be made to vary over a wide range by adjustment of solvent and polymer molecular weight. Only a slight concentration dependence of K22 throughout the liquid crystal range was, however, noted. The variations can be at least partially understood in terms of changing macromolecular interactions and recent statistical hard-rod theoretical treatments of liquid crystal elasticity. The functional form for the temperature dependence of the order parameter was also determined for the system through the clearing point.