SALTING-IN BEHAVIOR OF ISOTROPIC AND ANISOTROPIC AQUEOUS HYDROXYPROPYLCELLULOSE SOLUTIONS

Salts with large polarizable ions are capable of salting-in complex aq ueous polymer solutions exhibiting microstructure, thereby inducing ch anges in the phase behavior and properties of the solutions. In this w ork, the dynamic rheological properties of isotropic and mesomorphic h ydroxypropylcellulose (HPC) in aqueous media have been investigated in the presence of one such salt, guanidine thiocyanate (GuSCN). Additio n of this salt to isotropic aqueous HPC solutions is found to induce a n increase in the magnitude of the elastic shear modulus (G'). At HPC concentrations above the isotropic --> mesophase transition, however, addition of GuSCN results in a substantial reduction in G' due to micr ostructural changes in the chiral nematic HPC mesophase. This reductio n in G' indicates that the microstructure of a water-soluble polymer e xhibiting supramolecular organization can be tailored through salting- in, and is likewise expected to facilitate the commercial processing o f HPC at high solids concentrations.