Intrinsic viscosity and laser light scattering studies of selected cellulose derivatives in dilute solution

The dilute solution properties of selected cellulose derivatives, especially hydroxypropyl cellulose (HPC) were investigated. Specifically, the interaction between polymer and solvent molecules and its effect on the hydrodynamic radius in dilute solution was studied. This has been accomplished by determining the dilute solution characteristics of the different cellulose derivatives of varied molecular weights in several solvents at several temperatures and concentrations. The polymer chemical structure and the solvents used have been chosen so as to determine any effect of molecular weight, temperature, and solvent power on the hydrodynamic radius, diffusion coefficient, and intrinsic viscosity.

The dilute solution behavior provides knowledge of the size and shape, state of aggregation and solubility, and interaction of these macromolecules in solution. This information is of importance in determining whether these macromolecules in solution more nearly resemble randomly configured chains or long thin rods. It may also be possible to use these studies to predict the properties of more concentrated solutions. This is especially significant now that it has been found that these molecules can form a liquid crystal state under appropriate conditions.

The main techniques used for studying the cellulose derivatives in dilute solution were dynamic laser light scattering (at ORNL) and intrinsic viscosity measurements. Thus, structural information can be obtained from suitable experimental quantities like the diffusion coefficient from dynamic light scattering, which can be related to the hydrodynamic radius of the molecules through the Stokes-Einstein relation, and the intrinsic viscosity from dilute solution viscosity measurements as a function of molecular weight, temperature, and solvent.

The solutions showed high intrinsic viscosities and high negative temperature coefficients of viscosity. The effect of solvent and temperature is molecular weight dependence. The diffusion coefficients of HPC were found to be an order of magnitude lower than those of a standard sample of polystyrene. The diffusion coefficient was found to decrease with temperature and concentration, while increased with solvent "quality."