ON THE INTRINSIC-VISCOSITY OF ANIONIC AND NONIONIC RODLIKE POLYSACCHARIDE SOLUTIONS

The ionic strength dependence of intrinsic viscosity as a function of molecular weight was observed substantially for the anionic xanthan polyelectrolyte, while the intrinsic viscosity of nonionic schizophyllan does not change with ionic strength. Ultrasonic degradation was applied as the best mean of obtaining polymer fractions of different molecular weights. It is true, as expected, that schizophyllan has a more rigid triple helix backbone than that of xanthan. As the molecular weight increases, the extension coefficient epsilon of the xanthan chain with ionic strength is found empirically to increase by order 1,48 of molecular weight. Using the Yamakawa-Fujii theory for worm-like chains, both the persistence length q and the contour length L(c) were determined from the best fit of the experimental data of intrinsic viscosity for different ionic strengths to the theoretical curves. The stiffness parameter was established from the ratio of the Kuhn statistical segment length (i. e., twice the persistence length) to the contour length. As the molecular weight decreases, stiff chains of short degraded xanthan become rodlike, while they become gradually worm-like with increasing molecular weight. It also can be seen that the chain stiffness depends on the ionic strength.