Relationship Between the Viscoelasticity of Span 65 Films Formed at the Oil/Water Interface and the Stability of W/O Emulsions
The viscoelasticity of surfactant films formed by the nonionic surfactant Span 65 (sorbitan tristearate) at the oil/water interface was evaluated using a bi-cone interfacial rheology system. Saturated hydrocarbons with different alkyl chain lengths were used as the oil phase to investigate how oil species influence the interfacial storage modulus and loss factor.
Emulsions are widely used in fields such as food, cosmetics, and pharmaceuticals, as they enable water-soluble and oil-soluble components to coexist within a single liquid system. However, emulsions are thermodynamically unstable, and over time they undergo creaming, flocculation, and particularly droplet coalescence, which leads to phase separation. Coalescence is irreversible, and once large droplets are formed, it becomes difficult to revert the system back to its original dispersed state. Therefore, understanding the mechanical strength of the surfactant film formed on the droplet surface is essential for stabilizing emulsions.
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