Compatibility of gelatin and dextran in aqueous solution

The temperature-composition phase diagrams of aqueous solutions of gelatin and dextran, which show liquid/liquid phase segregation, were explored at temperatures above the gelation temperature of gelatin. The compositions of the coexisting phases were found to show practically no dependence on temperature between 40 and 80 degrees C. Also, the total polymer concentration at which phase separation occurred was found to be nearly independent of temperature. These observations suggest an entropy-driven phase separation. An explanation in terms of depletion, reversible clustering, and subsequent transient network formation of gelatin at temperatures well above the temperature of gelation is suggested. Phase separation is found to be accompanied by strong fractionation of the molar mass distribution in the two phases.