Applications of Mixed Surfactant Systems in the Construction and Regulation of High Internal Phase Emulsions (HIPEs)

High internal phase emulsions (HIPEs) are widely used in fields such as porous materials and food delivery, owing to their solid-like viscoelastic properties. Single low-molecular-weight surfactant systems require high emulsifier dosages and have limited biocompatibility, whereas Pickering particle systems face limitations such as difficulty in wettability regulation and insufficient stability at ultra-high internal phase fractions. Surfactant mixing, through synergistic effects among components, has become an important route for constructing high-performance HIPEs. This review summarizes the structural characteristics, preparation methods, and typical applications of HIPEs, compares the limitations of the two types of single stabilization systems, elaborates the synergistic stabilization mechanisms of the two types of mixed systems, and analyzes the regulation patterns of mixing ratio, concentration, environmental conditions, and emulsification process on the microstructure and macroscopic properties of HIPEs. Composite systems primarily enhance the compactness and mechanical strength of interfacial films through synergistic interactions between components at the interface; specifically, small-molecule combinations rely on interfacial molecular rearrangement, whereas particle-surfactant combinations achieve stability mainly through the modulation of wettability and the complementarity of the two-component interfacial film. This review can provide a reference for the rational design of mixed systems; however, the quantification of mechanisms and the development of green components still require further investigation and represent important directions for future research.