Optical Properties of Pickering Emulsions and Foams

A significant number of studies have been conducted on particle adhesion phenomena as pertaining to the oil-water interface of droplets and the air-liquid interface of bubbles, known as Pickering emulsions and Pickering foams, respectively. However, few of the literature reports have discussed the optical properties of these materials. In this study, the optical properties of Pickering particles were calculated by using an electromagnetic field analysis via a finite element method, and their optical responses are discussed. The changes in scattering due to the differences in the number of adhering particles and particle size are compared for three composition systems: an oil-in-water Pickering emulsion, a water-in-oil Pickering emulsion, and a Pickering foam. It was determined that changes in the amount of scattering are due to the mixing of the phases in the scattering field. This effect is more pronounced when the size of the scatterer is significantly smaller than the wavelength. For systems with particles larger than the wavelength, changes in the amount of scattering were suppressed because of destructive interference of the electromagnetic waves. This work revealed that the variation in the amount of scattering due to the constituent material and size of the Pickering particles is affected by two different factors, and the change in the amount of scattering is 10 times greater than in a uniformly dispersed system.