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Phase inversion of emulsions stabilized by lipophilic surfactants and SiO2 nanoparticles

Jiang, Ping, Zhang, Lei, Ge, Jijiang, Zhang, Guicai, Pei, Haihua
Colloids and surfaces 2019 v.562 pp. 42-53
adsorption, colloids, droplet size, emulsions, lipophilicity, nanoparticles, oils, oleic acid, rheological properties, silica, stabilizers, surfactants, wettability
This paper investigates the effects of the SiO2 nanoparticle mass concentration (w/v %) and oleic acid imidazoline mass fraction (w/w %) on the property of the emulsion stabilized jointly by SiO2 and oleic acid imidazoline, with SiO2 nanoparticles initially dispersed in different phases. In the experiment, the SiO2 nanoparticle mass concentration in the aqueous or oil phases is fixed, and the surfactant mass fraction in oil is gradually increased, changing the emulsion from oil-in-water into water-in-oil. Moreover, in these cases, the required oil-soluble surfactant mass fraction for phase inversion is relatively low, with solid nanoparticles initially dispersed in water. Then, the surfactant mass fraction in oil is kept constant, and the emulsion type is changed from the water-in-oil into the oil-in-water by raising up the SiO2 mass concentration in water or oil. Furthermore, under these conditions the solid nanoparticle mass concentration is higher with solid nanoparticles primarily dispersed in water than that in the case of solid nanoparticles initially placed in oil. The mechanism behind the emulsion type transition is analyzed by measuring the emulsion droplet size and rheological property of different emulsion systems. It is concluded that the difference regarding the initial dispersion medium of the solid nanoparticle affects the adsorption proportion of the solid nanoparticle and oleic acid imidazoline, the adsorption morphology, and the overall wettability of the interfacial stabilizer, which consequently impacts the property of the emulsion.