Twist elastic constant of a cholesteric polypeptide liquid crystal

Abstract

We have determined the critical magnetic field for the cholesteric to nematic transition of a pure lyotropic liquid crystal solution of an α-helical polypeptide, poly-γ-benzyl-L-glutamate, by direct microscopic observation of the changing pitch of the structure as a function of magnetic field strength. The course of the transition is well accounted for by the theory of deGennes. An independent measurement of the anisotropy of diamagnetic susceptibility allows the determination of κ22, the twist elastic constant of the medium.