Effect of oil on emulsion characteristics: manipulating the interfacial domain

In this paper, two ternary systems (water, Triton X-100, and octane or tetradecane) were investigated using freeze-fracture transmission electron microscopy, rheology, laser diffraction particle sizing, and pulse field gradient NMR (PFG-NMR). Oil-in-water dispersed droplet emulsions were prepared for Triton X-100 concentrations of 8-12 wt % while maintaining a surfactant-to-oil weight ratio of 1:5. The stability of the emulsions significantly increased with both the surfactant concentration and the chain length of the oil component. The PFG-NMR results could be explained as a superposition of three different types of diffusion: restricted diffusion of the oil in the droplets and free and restricted diffusion of the droplets themselves. The PFG-NMR results were correlated with the electron microscopy images and the particle-sizing data. Moreover, to gain a greater understanding of the role of the oil-surfactant interactions, in particular, the present investigations were placed in context with an earlier publication where toluene was used as the oil with the same emulsifier. The change from the aromatic oil, which is a better solvent for the surfactant, to an alkane-based oil dramatically changed the characteristics of the interfacial domain. On one hand, the concentration range for the formation of emulsions and the variety of microstructures realized were severely restricted and reduced when using the alkanes as compared with toluene. On the other hand, the interfacial film was much more stable leading to an extremely reduced rate of droplet coalescence.