RHEOLOGY OF A SIMULTANEOUSLY PHASE-SEPARATING AND GELLING BIOPOLYMER MIXTURE

The dynamic shear modulus of aqueous solutions of the biopolymers gela tin and dextran was found to be highly sensitive to thermal history ev en for samples of identical composition. Rheological differences could be correlated with differences in morphology, visible by optical micr oscopy, arising from the interaction of gelation with phase separation . Quenching a single-phased morphology to a temperature at which phase separation and gelation occurred simultaneously, gave a relatively hi gh shear modulus-reflecting the maintenance of a connected gelatin ric h phase. A sample which before its final quench was annealed at an int ermediate temperature, in the two-phase region but above the gelation temperature, developed a much lower modulus. In both cases, the mechan ism of phase separation at early stages was spinodal decomposition, bu t in the latter case the much lower modulus reflects a transition to a morphology of disconnected gelatin rich droplets during the late stag e of phase separation.