In addition, different wetting properties of particles in two phases are represented by three-phase contact angle θ, which can determine the types of Pickering emulsions. Solid particles have certain wettability in both aqueous and oil phases but are insoluble in any phase, so they can irreversibly adsorb and fix on the oil-water interface and then around the droplets to form a dense adsorption layer, which provides a physical barrier in space to prevent the contact between the droplets. It is reported that emulsification of emulsions relied on the size of solid particles, which could be adsorbed on the globules to form a coating to prevent them from gathering. This phenomenon was first discovered by Ramsden in 1903, but first described in literature by Pickering in 1907. Pickering emulsion is an emulsion which was stabilized by solid particles as an emulsifier. However, some of these emulsifiers are harmful to human health, so applications are limited in food, cosmetics, and pharmaceutical industries. Conventional emulsifiers are generally small molecule surfactants which mainly include ionic surfactants and non-ionic surfactants and amphiphilic biopolymers. Since the emulsion is a thermodynamically unstable system, an emulsifier is essentially required to achieve desired stability. Emulsions are ordinarily composed of water and oil and it is customary to refer to organic liquids that are insoluble in water as oil phase. Emulsions are a dispersion system composed of two incompatible liquids, that is, a mixture of one liquid in the form of small droplets dispersed in another liquid.
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