Understanding the effect of droplet size and polydispersity on random jamming-induced repulsive gelation in Citrem-stablized nanoemulsions

Nanoemulsions are known to form repulsive gelation due to the random jamming of droplets at a lower oil volume fraction (ϕ) compared to conventional emulsions. Monodispersed emulsions can randomly jam at ϕ=0.64, whereas predicting the critical ϕ for maximal random jamming (ϕMRJ) for polydisperse systems has been challenging as small droplets can fit into the voids between large droplets. The objective of this research is to understand how droplet size and polydispersity can influence random jamming-induced repulsive gelation in food-grade nanoemulsions. Citrem-stabilized O/W nanoemulsions (D32 150 nm, polydispersity index (PDI) 1.5) were prepared using high-pressure homogenization, which was size-fractionated using ultracentrifugation, and the cream layer was cut into multiple slices of pseudo-monodisperse nanoemulsions with a range of droplet size, but constant PDI. The cut slices were mixed with aqueous Citrem solution such that nanoemulsions with a range of ϕ (0.4 to 0.7) were obtained. The effective ϕ (ϕeff) of the nanoemulsions was calculated based on the droplet size and the thickness of the repulsive charge cloud around them. The viscoelasticity of the pseudo-monodisperse nanoemulsions with a constant PDI, but a range of average droplet sizes (100 to 300 nm) and ϕeff were determined. The data showed that at a constant droplet size elastic moduli increased with an increase in ϕeff as the systems pass through viscous and glassy state followed by electrostatic and interfacial jamming. The experimental data was fitted using entropic-electrostatic-interfacial model (Kim et al., Rheologica Acta, 2016), which would help in predicting the ϕMRJ for gelation in repulsive nanoemulsions at a particular droplet size for a fixed PDI. This research will pave the way to create new knowledge on the effect of ϕ, droplet size and PDI on repulsive gelation, which will lead to the development of nanoemulsion-based products with improved texture, stability, and reduced amount of oil.