Impact of Interfacial Properties, Colloidal Interactions and Colloidal Structures on Coalescence of Oil/Water Interfaces

Controlling emulsion stability is essential to the design of oil/water separation processes and the formulation of emulsion-based products. Hindering coalescence is the crucial step in stabilizing emulsions. Surface-active materials are commonly used in formulation to control properties of the oil/water interfaces and impact coalescence. However, the connection between interfacial properties and

coalescence is not unequivocally determined. This work aims to separate the impact of interfacial properties of a single interface, colloidal interactions, and colloidal

structures on coalescence of oil/water interfaces.

We develop the capability of measuring the coalescence time of two identical interfaces on the microtensiometer after interfacial characterizations. This technique is used to characterize several systems, including asphaltenes,

copolymers and colloidal particles on oil/water interfaces. The measured interfacial tension and mechanics are correlated with the coalescence time. These outcomes

highlight that the stability of oil/water interfaces cannot be exclusively predicted by the interfacial properties. Colloidal interactions between two identical interfaces with or without the adsorbed molecules are studied by changing the bulk aqueous conditions. The resulting coalescence behaviors show a strong dependence on the length scale of the attractive and repulsive potential between two interfaces, and their interaction behavior can be tuned by the ionic strength and colloidal properties of the adsorbed particles to achieve the desired interfacial stability. The impact of

this work contributes to the fundamental understanding of coalescence mechanisms and provides insight into controlling the emulsion stability.