The Cholesteric Pitch in Lyotropic Solutions of a Semi-Rigid Macromolecule: Hydroxypropyl-Cellulose

The cholesteric pitch P of lyotropic mesophases of hydroxypropyl-cellulose are determined from optical measurements, i.e., angular dependence of the scattered light intensity and transmission spectra. The observed results are explained with help of Pincus’ theory for cholesteric liquid crystals. The variations of the twisting power with physical parameters such as polymer concentration C, nature of solvent, molecular weight, and ageing are investigated. The power law P = P oC−α is well satisfied for all polymer solvent combinations. It is proposed that the solvent could influence the cholesteric pitch not only through its intrinsic properties, but also through modifications of the macromolecular characteristics themselves.