Modeling the influence of effective oil volume fraction and droplet repulsive interaction on nanoemulsion gelation

The aim of this work was to test the applicability of the Mason-Scheffold model, developed for monodispersed systems, on predicting the storage modulus of sodium dodecyl sulfate-stabilized polydisperse canola oil nanoemulsion gels as a function of oil volume fraction (ϕ) and average droplet size. The storage moduli increased with ϕ, but at a constant ϕ they increased with a decrease in droplet size. An effective oil volume fraction (ϕeff) was calculated by combining the effects of ϕ, average droplet size, their inter-droplet repulsive interaction using the Debye screening length and the counterion dissociation factor (f). With increasing ϕeff, storage modulus rapidly increased at the onset of jamming, followed by a gradual increase at higher ϕeff where gelation is controlled by deformation of droplets and their surrounding charge cloud. The model fits the data well, although, the values of critical volume fraction for jamming (ϕc) did not seem appropriate for the polydisperse nanoemulsions. It was proposed that the influence of f on ϕc could be significant and values lower than 0.1 could be more appropriate for high concentration of ionic emulsifier.