On the phase separation kinetics of an aqueous biopolymer mixture in the presence of gelation: the effect of the quench depth and the effect of the molar mass

We present new investigations of the kinetics and subsequent structure of phase separation in an aqueous mixture of gelatine and dextran in the presence of gelation. We were able to quantify the effect of the quench depth in temperature on the kinetics. Not only at the early stage of phase separation, but also at the late stage where gelation plays a significant role the dominant length scale of the system is described by an equation derived by Van Aartsen ‘Eur. Pol. J. 6 (1970) 919’. The estimated critical point from this quantitative relation agrees with the one determined with turbidity measurements. At shallow quenches below the gel temperature the power law describing the growth of domain sizes has an exponent larger than 1, at deeper quenches it is smaller than 1. However, at all quenches the power law behaviour of the peak position in time is consistent with that of the peak intensity, i.e. the ratio of the exponents is 1–3. Furthermore, we determined the effect of the size of the polymer. We varied the molar mass of the non-gelling component, dextran, and we observed a difference in the wavevector of the dominant concentration fluctuation. An increase of the molar mass gives a decrease in qm, the wavevector of the fastest growing fluctuation. This relation was found both at the initial and final state of the phase separation. With these results it is possible to control the coarseness of the phase separating system in the presence of gelation. The experiments were performed with small angle light scattering (SALS) and confocal scanning laser microscopy (CSLM). The results were interpreted in the framework of spinodal decomposition as described by the Cahn–Hilliard theory.