KINETICS OF THE SIMULTANEOUS PHASE-SEPARATION AND GELATION IN SOLUTIONS OF DEXTRAN AND GELATIN

Influences of gelation on the kinetics of the phase separation in a mi xed, aqueous solution of dextran and gelatin have been studied. The so lution separates into dextran-rich and gelatin-rich phases below a pha se transition temperature. For a deeper quench, the solution gels as w ell as phase separates. Results of time-resolved small-angle elastic l ight scattering and phase contrast microscopy for quenches near the cr itical point show that above the gelation temperature phase separation is followed by spinodal decomposition and a fast coarsening process, with dynamical scaling being obeyed for a restricted time regime. Belo w the gelation temperature,nearly the entire phase separation process is influenced by the gelling tendency of the gelatin. The rate of gela tion relative to that of the phase separation determines the final mor phology of the gel. A variety of morphologies are observed. Apart from slowing the separation, gelation is found to preclude the coarsening, which is dominated by hydrodynamics, and to cause dynamic scaling to fail as a consequence of the introduction of a wide range of distance scales. In this system, the effect of cross-link formation as a separa tion-enhancing force can be observed.