title: Particle shape anisotropy in pickering emulsions: cubes and peanuts.
abstract: We have investigated the effect of particle shape in Pickering emulsions by employing, for the first time, cubic and peanut-shaped particles. The interfacial packing and orientation of anisotropic microparticles are revealed at the single-particle level by direct microscopy observations. The uniform anisotropic hematite microparticles adsorb irreversibly at the oil-water interface in monolayers and form solid-stabilized o/w emulsions via the process of limited coalescence. Emulsions were stable against further coalescence for at least 1 year. We found that cubes assembled at the interface in monolayers with a packing intermediate between hexagonal and cubic and average packing densities of up to 90%. Local domains displayed densities even higher than theoretically achievable for spheres. Cubes exclusively orient parallel with one of their flat sides at the oil-water interface, whereas peanuts preferentially attach parallel with their long side. Those peanut-shaped microparticles assemble in locally ordered, interfacial particle stacks that may interlock. Indications for long-range capillary interactions were not found, and we hypothesize that this is related to the observed stable orientations of cubes and peanuts that marginalize deformations of the interface.
authors.affiliation: Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for NanoMaterials Science, Utrecht University , Padualaan 8, Utrecht, The Netherlands.
authors.forename: Julius W J
authors.initials: JW
authors.lastname: de Folter
authors.forename: Eline M
authors.initials: EM
authors.lastname: Hutter
authors.forename: Sonja I R
authors.initials: SI
authors.lastname: Castillo
authors.forename: Kira E
authors.initials: KE
authors.lastname: Klop
authors.forename: Albert P
authors.initials: AP
authors.lastname: Philipse
authors.forename: Willem K
authors.initials: WK
authors.lastname: Kegel
mesh_terms: D000327:Adsorption; D016880:Anisotropy; D004655:Emulsions; D005290:Ferric Compounds / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D009821:Oils / Q000737:chemistry*; D010316:Particle Size; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D004655:Emulsions; D005290:Ferric Compounds; D009821:Oils; D013501:Surface-Active Agents; D014867:Water; C000499:ferric oxide