Pickering Emulsions: Wetting and Colloidal Stability of Hairy Particles—A Self-Consistent Field Theory

Abstract

The assembly of sterically stabilized colloids at liquid-liquid interfaces is studied with the self-consistent field (SCF) theory using the discretization scheme that was developed by Scheutjens, Fleer, and co-workers. The model is based on a poly(methyl methacrylate) (pMMA) particle with poly(isobutylene) (pIB) grafted to the surface. The stabilizing groups on the particle surface have a significant effect on the interfacial assembly and, therefore, also on the formation and properties of Pickering emulsions. The wetting behavior of the particle is altered by the presence of the stabilizing groups, which affects the equilibrium position of the particles at the interface. The stabilizing groups can also lead to an activation barrier before interfacial adsorption, analogous to the steric repulsion between two particles. These effects are numerically solved with the SCF theory. It is commonly known that flocculating conditions enhance the interfacial adsorption and yield stable Pickering emulsions, which is confirmed in this work. Additionally, it is concluded that those conditions are not an absolute requirement. There is a window of stabilizer concentrations Γ(pIB), 2.2-3.3 mg/m(2) pIB, that shows both partial wetting and colloidal stability. The activation barrier for interfacial assembly is 140-550 k(B)T and is an order of magnitude higher than the colloidal stability. The difference can be attributed to the unfavorable interaction of pIB with water and a difference in geometry (plate-sphere vs sphere-sphere). This study demonstrates the interplay and provides a quantitative comparison between the wetting behavior and the colloidal stability, and it gives a better understanding of the colloidal assembly at soft interfaces and formation of Pickering emulsions in general.

Deformation of the Water/Oil Interface during the Adsorption of Sterically Stabilized Particles

“…According to the exponential fit in Figure 8, E A and E K should be of the same order of magnitude. In previously published work, 13 we found for similar particles an E A ranging from 225k B T to 450k B T depending on Γ PIB (Table 2). Therefore, we expect that E K should be of the same order of magnitude.…”

Fabrication and characterization of novel Pickering emulsions and Pickering high internal emulsions stabilized by gliadin colloidal particles

“…When the pH of GCPs dispersion was adjusted to 5.0, the dispersions changed to be translucent, and they settled to produce thin deposit at bottom of the vessel after 1 h of incubation. In fact, the correlation between effective Pickering stabilization and particle flocculating conditions was well established experimentally (Binks & Rodrigues, 2007), and it was also confirmed theoretically (Salari, Leermakers, & Klumperman, 2011). The tendency of GCPs to aggregate facilitates the formation of stable Pickering emulsions.…”

Recent Studies of Pickering Emulsions: Particles Make the Difference

“…Other studies also showed that the electrostatic force would affect the adsorption of particles at the oil‐water interface, the assembly separation of particles on the interface, and the stability of the formed Pickering emulsions . Klumperman et al studied the effect of the surface concentration of graft on the stability of Pickering emulsions . They established a theoretical model and calculated a suitable surface concentration of graft for particles to achieve both the partial wetting and colloidal stability that are necessary for preparing stable Pickering emulsions.…”