Interfacial adsorption dynamics of solid lipid particles at oil/water interfaces through QCM-D technique

The interfacial adsorption dynamics of solid particles are important processes in the formation of Pickering emulsion, and its stabilities and functionalities are critically dependent on the particle interfacial structures. In this study, we investigated the interfacial behaviors of solid lipid particles (SLPs) within six food-grade SLPs using the quartz crystal microbalance with dissipation (QCM-D) technique. These SLPs had been subjected to surface modification with varying emulsifier contents, specifically 1, 2, and 4 wt% of both Polysorbate 40 (T40) and sodium caseinate (Na-Cas), referred to as T40-SLPs and Na-Cas-SLPs. Two distinct interface behaviors have been identified: Type 1, characterized by with weak interfacial activity, which included the 1 and 2 wt% T40-SLPs, and Type 2, exhibiting stronger interfacial activity, encompassing the 4 wt% T40-SLPs as well as the 1, 2 and 4 wt% Na-Cas-SLPs. Subsequently, the mechanism through which the emulsifiers influenced the interfacial dynamic behaviors was established by correlating the interfacial behaviors with the properties of SLPs. Briefly, larger and more electronegative spherical Na-Cas-SLPs exhibited stronger interfacial activity, which facilitated the formation of smaller and more stable Pickering droplets. The interfacial films formed by the short plate-like T40-SLPs were not sufficiently consolidated, which led to instability of the hydrophobic interfaces. These results were confirmed with macrostability tests of the Pickering emulsions stabilized by the SLPs and are expected to provide basic information for the functionalization of multicomponent Pickering emulsions.