Emulsions are essential in our modern daily life. The influences and applications of different kinds of emulsions reach pharmaceutical,¹  petroleum,²  biocatalysis^3,4  and food industries.^5,6  An emulsion is a heterogeneous system which consists of a dispersed liquid in another liquid as a continuous phase.⁷  However, the mixing of two or more liquids which have very different polarity is obviously not favourable. As a result, these thermodynamically unstable systems undergo separation in the matter of seconds.

Therefore, one might use surfactants to kinetically stabilize them, slowing the coalescence process of the dispersed droplets and phase separation.⁸  Besides amphiphilic molecules of surfactants, there is another category of emulsion stabilizer, which is the solid particle. At the beginning of the last century, Ramsden and Pickering described that colloidal-sized solid particles were also capable of stabilizing emulsion droplets.^9,10  Nowadays, this particle-stabilized emulsion is usually called a “Pickering emulsion”. In some senses, particle stabilizers are quite similar to amphiphilic surfactants. For both of them, the relative wettability by the two liquids is a very important factor for one to predict the properties of the resulting emulsion. This relevant wettability is described by the hydrophile–lipophile balance (HLB) and interfacial contact angle for surfactants and particles, respectively. However, there are some important differences between them.¹¹  For example, the orders of energy of the adsorptions of them are very different. Compared with small surface active molecules, individual colloidal particles are adsorbed to the interface with so much higher energy, which is often in the order of 10⁵ k_BT. The high desorption energy of the particle leads to the irreversible adsorption of it and results in outstanding stability for the emulsion droplets.