Nanoemulsion gels are a new class of soft materials that manifest stronger elasticity even at lower dispersed phase volume fraction. In this work, gelation in 40 wt % canola oil-in-water nanoemulsions was investigated as a function of emulsifier type (anionic sodium dodecyl sulfate (SDS) or nonionic Tween 20) and concentration. It was observed that the liquid nanoemulsions transformed into viscoelastic gels at a specific concentration range of SDS, whereas no gelation was observed for Tween 20. The apparent viscosity, yield stress, and storage modulus of the nanogels increased with SDS concentration until 15 times critical micelle concentration (CMC), thereafter decreased steadily as the gelation weakened beginning 20 CMC. Three regimes of colloidal interactions in the presence of emulsifier were proposed. (1) Repulsive gelation: at low SDS concentration (0.5-2 times CMC) the repulsive charge cloud around the nanodroplets acted as interfacial shell layer that significantly increased the effective volume fraction of the dispersed phase (ϕ(eff)). When ϕ(eff) became comparable to the volume fraction required for maximal random jamming, nanoemulsions formed elastic gels. (2) Attractive gelation: as the SDS concentration increased to 5-15 times CMC, ϕ(eff) dropped due to charge screening by more counterions from SDS, but depletion attractions generated by micelles in the continuous phase led to extensive droplet aggregation which immobilized the continuous phase leading to stronger gel formation. (3) Decline in gelation due to oscillatory structural forces (OSF): at very high SDS concentration (20-30 time CMC), structural forces were manifested due to the layered-structuring of excess micelles in the interdroplet regions resulting in loss of droplet aggregation. Tween 20 nanoemulsions, on the other hand, did not show repulsive gelation due to lack of charge cloud, while weak depletion attraction and early commencement of OSF regime leading to liquid-like behavior at all concentrations. The nanogels possess great potential for use in low-fat foods, pharmaceuticals and cosmetic products.

In this research, the stability of sodium dodecyl sulfate (SDS)-stabilized canola oil nanoemulsion gels was investigated as a function of repeated rotational shear, oscillatory strain and storage time. Nanoemulsion gels, termed nanogels, were formed from oil-in-water nanoemulsions, prepared with various concentrations of SDS to get a range of droplet sizes, interdroplet interactions, and gel strengths.Repulsive nanogels were formed with 0.5, 1 and 2 times the critical micelle concentration (CMC), while attractive nanogels were prepared with 5, 10 and 15 times the CMC of SDS. No change in droplet size of the nanoemulsions was observed over a period of 90 days and an accelerated gravitation study indicated extremely high stability against creaming. All nanogels showed a remarkable recovery in viscosity and gel strength during repeated shear and strain sweep experiments, respectively. Interestingly, the elastic storage moduli (G 0 ) for the repulsive nanogels significantly decreased, converting the nanogels into flowable weak gels. For attractive nanogels, the decrease in G 0 was less. It was proposed that generation of surface active components due to lipid oxidation may alter the interfacial composition and ultimately reduce the thickness of the charge cloud leading to a reduction in G 0 in the repulsive nanogels. For attractive nanogels, the uptake of lipid oxidation products in the excess micelles and their inter-droplet transfer led to a decrease in the attractive depletion interactions and charge cloud, with subsequent loss of the gel structure. The nanogels possess great potential for use in food and related soft materials provided the loss of gel strength with time could be prevented.

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