The Diffusion of Compact Macromolecules Within Hydrogels

Abstract

Studies of the diffusion of globular proteins and dextran fractions within polysaccharide and poly-acryamide gels by laser light scattering are described. Gels of stiff polysaccharide chains scatter light which exhibits little spectral broadening, since apart from a small amount of structural relaxation they are almost stationary at a molecular level. Well defined diffusion coefficient of compact macromolecules within these gels can be measured. However, gels of relatively flexible polymers such as polyacrylamide are highly mobile at a molecular level, and scatter light which is spectrally broadened by the diffusion of fluctuations in acrylamide concentration. In this case there is a complex interaction between the two diffusion coefficients, with the diffusing compact macromolecules dominating at low gel concentrations, and the diffusing gel fluctuations dominating at high gel concentrations where they tend to control the movement of the compact macromolecules.