Organic pigment particle-stabilized pickering emulsions

Pickering emulsions sometimes dry to obtain macro-porous or sheet-like structural materials. However, the process through which these materials form is unknown. This work uncovers the processes through which sheet-like structural materials form in an evaporating water-in-oil Pickering emulsion. Small samples of water-in-heptane Pickering emulsions, stabilized by colored organic pigment particles, were diluted with n-heptane and allowed to evaporate quiescently on a hydrophilic glass slide under an optical microscope. The colored nature of the particles enabled direct visualization of the behavior of the particle-coated water droplets as evaporation of oil progresses without the need for added dye. Optical microscopy revealed that a sheet-like material is formed from complete coalescence of particle-coated water droplets which locks the enwrapping particle layers. Initially, the water droplets become flattened and then change from spherical to a polyhedral shape, coalescing in areas defunct of particles and locking the particle layers into a sheet-like material.