STUDY OF AQUEOUS DEXTRAN SOLUTIONS UNDER HIGH-PRESSURES AND DIFFERENT TEMPERATURES BY DYNAMIC LIGHT-SCATTERING

The behaviour of dextrans of different molar masses in aqueous solutions was investigated by dynamic light scattering at different temperatures, ranging from 30 to 100-degrees-C and different pressures, in the range 1-3000 bar. It has been shown that concentration dependence of the apparent diffusion coefficient, D(app), of all samples changes the behaviour about the overlap concentration C*. It has also been shown, that the diffusion coefficient increases with temperature (as a consequence of faster fluctuations of the molecules) and decreases with pressure. This could be accounted for by increase of solvent (water) viscosity with pressure. The activation energy of diffusion is independent of molar mass of dextran for the samples of molar masses from 7.4-21.1 x 10(6) g mol-1, but it is considerably lower for the sample of molar mass of 1.0 x 10(6) g mol-1. Pressure has a very small effect on activation energy of diffusion. The characteristic exponent for diffusion coefficient D(o) dependence on molar mass was found to be 0.32.