Polymeric particles with structural complexity from stable immobilized emulsions

Abstract

We prepared polymeric structures with unusual complexity in surface morphology derived from photocurable emulsion droplets dispersed in an aqueous medium. The emulsion droplets a few tens of micrometers in size were stabilized with relatively small hydrophobic particles that were bound to the emulsion interfaces. The particle binding tended to immobilize the oil-in-water emulsion interface and dramatically increased the structural relaxation time of the interface deformation over a few days relative to a few milliseconds for an otherwise clean interface. In particular, perfectly immobilized emulsion drops maintained nonspherical elongated structures that were formed by shear-induced emulsification and could not be relaxed to a spherical shape. This property is useful for broad research areas ranging from crystallography and buckling phenomena to materials fabrication. The configuration of small particles on the interface and the "raspberry" shape of particle-stabilized emulsions were captured successfully by photocuring the emulsion droplets because the small bound particles immobilized the emulsion droplets. By selectively removing the small particles from the particle-covered polymeric structures, we prepared dimpled microparticles with various shapes. The dimple geometry depended on the interfacial properties or phase affinity of the small particles. The contact angle and binding energy of the particles were calculated on the basis of the dimple geometry. In addition, buckling phenomena of the particle-stabilized emulsions were observed when volatile oil was added to the photocurable resin.