DYNAMICS OF A POLYMER-SOLUTION IN A RIGID MATRIX

We report dynamic light scattering measurements of solutions of a low molecular weight polymer (dextran M-w = 70 000), both in the free stat e and inside agarose hydrogels of varying concentrations. The light sc attered from the rigid agarose matrix strongly heterodynes the signal from the mobile component, thereby allowing measurements both of the d iffusion coefficient D-c and of the Rayleigh ratio R-theta of the dext ran. For dextran concentrations c less than or equal to the overlap co ncentration c, D-c decreases as the concentration of the gel matrix c (g) increases. The product DcRtheta, which depends only on hydrodynami c factors, is, however, independent of the agarose concentration. It i s concluded that the principal influence of the static gel matrix is t o reduce the entropy and hence the osmotic pressure of the dextran sol ution. For concentrations of dextran greater than c, the gel structur e undergoes a phase separation.