The effect of temperature and composition on the interfacial tension and rheology of separated phases in gelatin/pullulan mixtures

The effect of temperature on the interfacial tension and rheology of separated phases in two phase pullulan/gelatin mixtures was investigated over a range of concentrations of both biopolymers. Interfacial tension was measured in a computer controlled Couette device using the retracting drop method and the rheological properties, where determined using Carrimed AR1000 rheometer. It was found that above gelling temperature the gelatin rich phase is approximately Newtonian but as the temperature approaches gelation point it becomes strongly non-Newtonian, with G′ and G″ being time dependent. The pullulan rich phase is also approximately Newtonian at low shear rates and becomes non-Newtonian at a higher shear rate and high concentrations. Above gelling temperature the interfacial tension increases with total concentration of polymers, or in other words with length of tie-lines and at each tie-line it is temperature independent. As the temperature approaches gelation point the interfacial tension for a given mixture decreases sharply.