Understanding the effect of polydispersity on random jamming-induced repulsive gelation in Citrem-stabilized nanoemulsions

Repulsive monodispersed emulsions are known to randomly jam at an oil volume fraction (ϕ) of 0.64, also known as the maximal random jamming oil volume fraction (ϕ_MRJ). Various mathematical models can predict the ϕ_MRJ of monodispersed emulsions. However, predicting the ϕ_MRJ for polydisperse emulsions is challenging because smaller droplets can fit into the voids between larger droplets, reducing elasticity. All real emulsions are polydisperse inherently, still experimental insights into their close packing behavior and ϕ_MRJ remain limited due to challenges in controlling polydispersity and the complexity of predictive models. This research aims to understand how polydispersity influences ϕ_MRJ in food-grade nanoemulsions. It was hypothesized that size-fractionation, a process of separating emulsion droplets based on size, could yield emulsions with varying average droplet sizes while maintaining constant polydispersity. CITREM-stabilized oil-in-water nanoemulsions (d_3,2 236±20 nm, relative polydispersity (RP) 0.54±0.21) were prepared using a high-pressure homogenizer. These nanoemulsions were ultracentrifuged to obtain cream layer with oil droplets arranged by size. The cream layer was sliced to create pseudo-monodispersed nanoemulsions with range of average droplet sizes but similar RP. The layers from the first-stage ultracentrifugation were further size-fractionated using second and third stage ultracentrifugation at ϕ = 0.4 and 0.3, respectively, to reduce polydispersity. The viscoelasticity of all size-fractionated layers showed an increase in elasticity with an increase in ϕ. The experimental data were fitted using the entropic-electrostatic-interfacial model (Kim et al., Rheologica Acta, 2016) to predict ϕ_MRJ and observe the transition of emulsion system from an entropic viscous state to an electrostatic and interfacial jamming state. The predicted ϕ_MRJ as a function of RP provides new insights into the effects of ϕ and RP on repulsive gelation. In this research challenge of controlling polydispersity was overcome, which will lead to the development of nanoemulsion-based products with improved texture, stability, and reduced oil content.