Tuning particle properties to control rheological behavior of high internal phase emulsion gels stabilized by zein/tannic acid complex particles

In the present work, we studied the influence of particle size and charge density on the structure formation and rheological property of high internal phase emulsion gels (HIPE-gels) stabilized with zein/tannic acid complex particles (ZTPs). The size (68 and 108 nm) and charge density (+38, +20, and +1 mV) of ZTPs were controlled by adjusting the pH during the preparation of the particles and in the respective particle suspensions. Extensive centrifugation of the emulsions stabilized by those ZTPs resulted in stable HIPE-gels with an oil content ranging between 72 and 87% (w/w) and a particle concentration of 0.7–1.4% (w/w) only. Microscopy showed that even at these high oil volume fractions, limited coalescence between the oil droplets occurred. A decrease in the particle size resulted in a decrease in the oil content in the HIPE-gels, due to a more efficient particle network in the continuous phase. This increased the storage modulus of the HIPE gels, indicating that this particle network plays an important role for the gel strength. When increasing the interactions between the particles (by lowering the charge density), the gel strength increased even further. It was noted that the gel strength was independent of the oil content, suggesting that the oil droplets do not contribute a lot to the gel strength. These HIPE-gels with tunable rheological property may have various applications in industry.