The pH-dependent phase separation kinetics of type-A gelatin and dextran with different initial microstructures

Abstract

The phase separation kinetics of type A gelatin and dextran (GE/DE) with different microstructures were investigated to get information on the relation between technofunctional properties and structures using static multiple light scattering (S-MLS), fluorescence microscopy, and macroscopic observations. GE/DE mixtures of 5.0 wt%/2.0 wt% and 5.0 wt%/3.0 wt% at pH = 5.50–9.00 were selected as the typical samples with the DE-in-GE and bicontinuous microstructures, respectively. Macrophase separation was found to occur in both the two mixtures at pH = 5.50–9.00 with the upper phase rich in GE and the lower phase rich in DE. However, the effect of pH on the phase separation rates of the two mixtures was different: pH-independent in DE-in-GE mixtures, while pH-dependent in bicontinuous mixtures. Specifically, the order of phase separation rates for the bicontinuous mixtures at pH = 5.50–9.00 was pH5.50 > pH6.00 > pH9.00 > pH7.00 ≈ pH8.00. Changes in the electrostatic interaction or steric exclusion effect among GE (DE) droplets at pH = 5.50–9.00 were used to explain the different phase separation kinetics of GE/DE mixtures with GE-in-DE, DE-in-GE, and bicontinuous microstructures. This work characterized the phase separation processes of GE/DE mixtures with three kinds of microstructure and provided the parameters for the phase separation kinetics at the macro-level.