Polymeric Particles with Structural Complexity from Stable Immobilized Emulsions Shin-Hyun Kim, † Chul-Joon Heo, † Su Yeon Lee, † Gi-Ra Yi,* ,‡ and Seung-Man Yang* ,† National CreatiVe Research InitiatiVe Center for Integrated Optofluidic Systems and Department of Chemical and Biomolecular Engineering, Korea AdVanced Institute of Science and Technology, Daejeon, 305-701 Korea, and Nano-Bio System Research Team, Seoul Center, Korea Basic Science Institute, Seoul 136-713 Korea ReceiVed March 27, 2007. ReVised Manuscript ReceiVed July 1, 2007 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. Introduction Colloidal spheres absorbed at liquid-liquid interface can form two-dimensional (2D) ordered structures by self- organization as they form 3D colloidal crystals in the bulk phase. Recent interest in 2D sphere packing at a spherical interface stems from its relevance to drug delivery, spherical crystallography, and materials science. 1-3 However, sphere packings in 2D arrangement at a liquid-liquid interface have not been fully understood relative to 3D sphere packings. In particular, 2D arrangement of spheres at the spherical interface of droplets has been known as Thompson’s problem for a century and was analyzed by the classical Euler theorem. 4-6 Experimentally, Bausch et al. explored this packing problem using particle-stabilized emulsions or Pickering emulsions as a model system for spherical crystal- lography, 2,7 which have unique properties unlike those of surfactant stabilized emulsions as reported by Binks et al. 3,8-11 By evaporating the emulsion drop phase, the particle- stabilized emulsions were used to produce so-called “col- loidosomes,” which are selectively permeable capsules of rigid colloidal shells. 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