THE EFFECT OF SOLVENT PARTITION ON THE MECHANICAL-PROPERTIES OF BIPHASIC BIOPOLYMER GELS - AN APPROXIMATE THEORETICAL TREATMENT

The effect of solvent partition is considered for a biphasic mixed gel of two biopolymers (X and Y) which, at their nominal concentrations across the whole system. would have shear moduli of M(X) and M(Y), with M(Y) = n2M(X). Using the simplifying assumptions that 1) each polymer is confined entirely to a single phase. 2) modulus is proportional to the square of polymer concentration and 3) the direct contribution of the polymer chains to phase volume (phi) is negligible, the moduli of the individual phases (G(X) and G(y)) are calculated as a function of x, the proportion of solvent in phase X (with phi-x = x and phi-Y = 1 - x). The isostrain and isostress blending laws for polymer composites are then used to calculate 'upper and lower bound' moduli (G(U) and G(L)), corresponding to a continuous network of respectively, the stronger and weaker component, with the other phase dispersed within it: G(U) = G(X)phi-X + G(Y)phi-Y 1/G(L) = phi-X/G(X) + phi-Y/G(Y) The upper and lower bound curves (G(U) versus x and G(L) versus x) touch at a single 'critical point' where G(X) = G(Y) = G(U) = G(L) = M(x)(n + 1)2, with the two bounds passing through, respectively, minimum and maximum values. At the critical point. which occurs when x = 1/(n + 1), the physical significance of the upper bound changes, with increasing x. from X continuous to Y continuous. with a corresponding change for the lower bound from Y continuous to X continuous. Practical application of this approach is suggested, with elimination of assumptions (2) and (3) by experimental measurements.