Phase inversion of hydrophobized hollow TS-1 stabilized Pickering emulsions with addition of lipophilic Span 80

There are few reports concentrated on the interactions between lipophilic surfactants and hydrophobized hollow TS-1 zeolite particles in the stabilization of emulsions. In this study, hydrophobized hollow TS-1 zeolite particles were synthesized and applied as emulsifier to stabilize the W/O Pickering emulsions employing cyclohexanone and water, and the influence of addition of lipophilic Span 80 on the stability of the W/O Pickering emulsions was systematically studied. Surprisingly, a phase inversion was induced by simply changing the Span 80 concentration. At fixed concentration of TS-1 zeolite particles (2 wt%), emulsions are water in oil (W/O) when the concentration of Span 80 is lower than 0.5 mM. Then the emulsions invert to oil in water (O/W) when the Span 80 concentration is between 1 mM and 8 mM. In this process, different emulsifiers dominate the composition of the interfacial layer, and the emulsion type is correspondingly controlled. When Span 80 concentration is lower than 0.5 mM, hydrophobized hollow TS-1 zeolite particles are in domination, and W/O emulsions are obtained. At Span 80 concentration of 1–8 mM, the emulsions are stabilized mainly by Span 80, and the emulsion type is O/W.