Particle self-assembly in oil-in-ionic liquid Pickering emulsions.

Journal of colloid and interface science (2011-08-16)
Elizabeth M Walker, Denzil S Frost, Lenore L Dai
ABSTRACT

We have studied polydimethylsiloxane (PDMS)-in-1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]) Pickering emulsions stabilized by polystyrene microparticles with different surface chemistry. Surprisingly, in contrast to the consensus originating from oil/water Pickering emulsions in which the solid particles equilibrate at the oil-water droplet interfaces and provide effective stabilization, here the polystyrene microparticles treated with sulfate, aldehyde sulfate, or carboxylate dissociable groups mostly formed monolayer bridges among the oil droplets rather than residing at the oil-ionic liquid interfaces. The bridge formation inhibited individual droplet-droplet coalescence; however, due to low density and large volume (thus the buoyant effect), the aggregated oil droplets actually promoted oil/ionic liquid phase separation and distressed emulsion stability. Systems with binary heterogeneous polystyrene microparticles exhibited similar, even enhanced (in terms of surface chemistry dependence), bridging phenomenon in the PDMS-in-[BMIM][PF(6)] Pickering emulsions.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Micro particles based on polystyrene, size: 500 nm
Sigma-Aldrich
Micro particles based on polystyrene, size: 600 nm
Sigma-Aldrich
Micro particles based on polystyrene, size: 800 nm

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