High Internal Phase Polymeric Emulsions by Self-Assembly of Colloidal Systems

We propose a new procedure to synthesize high internal phase polymeric emulsions (polyHIPE) that is based on the self-assembly of colloidal systems. Colloidal suspensions were used as precursors of the final polyHIPE. These were obtained by dispersing 500 nm diameter, lightly cross-linked polystyrene (PS) emulsion particles in ethanol at room temperature under continuous sonification. A polystyrene-poly(2-vinylpyridine) (PS−PVP) block copolymer with a short PS block and a long PVP block was synthesized and dissolved in the ethanol-colloidal dispersion. After solvent removal, owing to the asymmetric composition of the block copolymer and the high volume fraction of the colloid, a closely packed colloidal system was obtained, where voids were partially filled by the block copolymer discrete phase. However, under appropriate annealing, the colloidal system was shown to undergo a rearrangement in which the particles deform to polyhedrons and closely pack within a percolating phase formed by the poly(2-vinylpyridine) block of the copolymer. The volume fraction threshold for percolation of this PVP domain structure was shown to be as low as 0.10 by doping the PVP and performing conductivity measurements. We argue that the physical driving force leading to this rearrangement is the reduction of the interfacial tension of the colloidal system.