Collective diffusion of gels in a theta solvent

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Abstract
Experimental measurements are reported of the deswelling process in presence of an external applied pressure of polyacrylamide gels at theta conditions. Analysis of the profile of the concentration gradient enables the swelling pressure as a function of concentration to be deduced as well as the collective diffusion coefficient D. To obtain an explicit expression for D, the polymer-solvent friction constant f is assumed to vary with the concentration as cm, where m is an adjustable parameter. It is found that the best fit is obtained for m = 2.0, in accordance with scaling theory for semi-dilute theta solutions