Experimental Investigation of Random Jamming Transition in Polydisperse Repulsive Nanoemulsions

In repulsive emulsions stabilized by ionic emulsifiers, oil droplets and their associated interfacial charge clouds can form a random jammed structure at a critical volume fraction, thereby forming an elastic material. In monodispersed emulsions, it is well known that the droplets are randomly jammed at an effective volume fraction of 0.64; however, the knowledge of the random jamming volume fraction (ϕ_MRJ) for polydisperse emulsions is limited. The present work aims to experimentally determine the relationship between polydispersity and ϕ_MRJ using a food-grade ionic emulsifier, citric acid esters of monoglyceride (CITREM)-stabilized canola O/W nanoemulsions, with an average droplet size of 236 nm and a relative polydispersity of 0.54. The nanoemulsions were size-fractionated using ultracentrifugation to obtain a range of average droplet sizes (272 to 360 nm) and relative polydispersity (0.26 to 0.43). The cream layers obtained from the ultracentrifugation were diluted with CITREM solution to obtain a range of oil volume fractions (ϕ) from 0.4 to 0.6 at various polydispersities, and their elasticity was determined, which showed an increase in plateau storage modulus $\left(G_p^{\text{'}}\right)$ with a decrease in oil droplet size and an increase in ϕ. The ϕ_MRJ of the size-fractionated nanoemulsion was predicted with the entropic, electrostatic, and interfacial (EEI) model for monodisperse emulsions with modified parameters, which successfully predicted the repulsive jamming transition in nanoemulsions and their ϕ_MRJ, establishing a relationship between relative polydispersity and ϕ_MRJ. Such a relationship would help predict the elasticity of repulsively jammed polydisperse nanoemulsions, enabling the rational design of emulsion-based food products with reduced oil content, improved stability, and enhanced rheological properties.