Shear and Surfactant-Assisted Breakdown and Recovery of a Particle-Stabilized Oil-Water Interface

Particle-stabilized water-in-oil emulsions are found in a wide range of products, from foods to petrochemicals. The interfacial particle layer in such emulsions plays a crucial role in resisting physical breakdown and ensuring long-term stability. This study aimed to clarify the rheological breakdown and recovery of a planar interfacial particle film under different shear conditions, as well as the effects of a structure-breaking surfactant. Experiments were conducted on a planar oil-water interfacial film composed of glycerol monostearate (GMS) crystals, representative of a water-in-oil emulsion stabilized by the same crystals. The film exhibited a reversible transition from an elastic-dominant state to a viscous-dominant state when subjected to strain amplitudes above and below its critical strain. The addition of the structure-breaking surfactant, sorbitan monooleate (SMO), led to a permanent reduction in both the interfacial elastic modulus and the interfacial tension of the film. These changes in viscoelastic properties were correlated with the destabilization of the corresponding model emulsion. Shearing this now-weakened film beyond its elastic limit led to a further reduction in elastic modulus (G') and an inability to recover its initial viscoelastic properties post-recovery. Overall, this study demonstrated that while particle-stabilized oil-water interfaces can recover their G' in response to a range of shear conditions, their viscoelasticity can be irreversibly altered by the presence of a structure-breaking surfactant. These findings offer novel insights into the design of emulsions with controllable breakdown properties.