Phase-separation-induced fractionation in molar mass in aqueous mixtures of gelatin and dextran.

An overview of the effects of phase separation of aqueous mixtures of gelatin and dextran on the fractionation in molar mass of these two components is given. Molar mass distributions in coexisting phases were investigated using size exclusion chromatography with multiangle laser light scattering. The initial molar mass of the native material, concentration, and temperature were varied. The results show a strong fractionation in molar mass for both components. The molar mass of the native material and concentration appeared to be the only factors that affected the final molar mass distributions, temperature having no effect. The results show that in the molar mass range where fractionation is the strongest, i.e., roughly below the maximum in the distribution, fractionation is governed by a Boltzmann factor e(-deltaG/kT), where deltaG denotes the free energy involved in transferring a polymer with a certain length from the enriched to the depleted phase, and in this case turns out to be proportional to the molar mass. Comparison of the results of phase separation with results on dialysis shows that water affinity is not the driving force for the phase separation of gelatin and dextran in aqueous solution. The gelation properties of gelatin in both phases were also determined. The gelation properties of gelatin in the coexisting phases differ from those of native gelatin. In particular, the gelatin in the gelatin-poor phase shows strong differences compared to the native material.