Particle-induced bridging in immiscible polymer blends
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Pickering emulsions are emulsions whose drops are stabilized against coalescence by particles adsorbed at their interface. Recent research on oil/water/particle systems shows that particles can sometimes adsorb at two oil/water interfaces. Such “bridging particles” can glue together drops of oil in water or vice versa. We hypothesize that the same effect should apply in immiscible polymer blends with droplet-matrix morphologies, viz., added particles should glue together drops and give rise to particle-bridged drop clusters. We test this hypothesis in PIB-in-PDMS blends [PIB, poly(isobutylene); PDMS, poly(dimethylsiloxane)] with fumed silica particles. Direct visualization shows that the particles can indeed induce clustering of the drops, and the blends appear to show gel-like behavior. Such gel-like behavior is confirmed by dynamic oscillatory experiments. However, we are unable to conclusively attribute the gel-like behavior to droplet clustering: Association of the fumed silica particles in the bulk, which itself causes gel-like behavior, confounds the results and prevents clear analysis of the gluing effect of the particles. We conclude that PIB/PDMS/fumed silica is not a good model system, for studying particle-containing polymer blends. We instead propose that spherical monodisperse silica particles can offer a far more convenient model system, and provide direct visual evidence of gluing of PIB drops in a PDMS matrix.
KeywordsSpherical monodisperse silica particles Drop clustering PIB PDMS Fumed silica
This research was supported by grant #ENG-CTS-0431349 from the National Science Foundation. We are grateful to Soltex, Inc., Rhodia, Inc., and Degussa for making the PIB, PDMS, and the silica particles available for this research.
Note added to proofs
A very recent article, Horozov et al., Angewandte Chemie-International Edition (2006) Particle–stabilized emulsions: A bilayer or a bridging monolayer? 45:773–776, discusses oil/water emulsions stabilized by bridging particles. They have followed the same strategy as described at the end of this paper: using monodisperse micron-sized silica particles rendered hydrophobic by silanization, to visualize bridging directly.
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