Effects of simple salts on the transport of polyvinylpyrrolidone in dextran solutions

Rapid transport of polyvinylpyrrolidone (PVP) in dextran solutions accompanied by a 'finger'-like dissipative structure, first reported by Preston et al. [Nature, 1980, 287, 499], was found to be further accelerated when a simple salt was present in both upper and lower compartments of a diffusion cell. The enhancement effect was found on various salts to different extents when compared at a given salt concentration C. The effect depended on C for a given kind of salt. The effect was suggested to be of mechanical origin rather than of thermodynamic one. When the transport rates, after corrected for different viscosities, were plotted against the densities of the solutions, most data for different salts at 2 M as well as those for different salt concentrations in the case of CsCl and NaBr approximately fell on a single curve. The curves differed for different PVP concentrations. Effect of the salts were examined on the flow patterns, such as the width of fingers, onset time and the critical PVP concentration for the appearance of fingers. Effect of the molecular weight of PVP was also examined.