Characterization of Lyotropic Polysaccharide Liquid Crystal Blends

Abstract Liquid crystalline polymers (LCPs) have been the focus of much interest over the past decade or so, due principally to the fact that they exhibit a structured mesophase under certain thermal or solvent conditions. Such supramolecular organization not only provides useful insight into the conformational behavior of these materials but also makes this family of polymers particularly attractive for specialized applications. Derivatives of crystalline cellulose have received considerable attention in this vein, since many commercial products employ these and other polysaccharides, and one of the most studied cellulosic LCPs is hydroxypropylcellulose (HPC). While past efforts have focused on the phase diagram of this polymer in various solvents and at elevated temperatures (HPC possesses both lyotropic and thermotropic properties), the objective of the present work is to characterize blends of HPC with another semiflexible polysaccharide, xanthan gum (XG), which also possesses lyotropic properties. Here, we have employed deuterium nuclear magnetic resonance ( 2 H NMR) and freeze-fracture transmission electron microscopy (FF/TEM) to characterize the mesophases of these homopolymers and their blends in both aqueous and organic solvents. We provide evidence that HPC and XG, when blended together in an aqueous medium, are synergistic in mesophase formation over a finite composition range, appearing more anisotropic than either component individually (at identical solution concentration). However, addition of XG to HPC in an organic solvent results in a two-phase isotropic/anisotropic system.