Polymer Colloids: Formation, Characterization and Applications
Chapter 10: Pickering Emulsions Stabilized by Polymer Colloids
Published:02 Dec 2019
Yang Lan, Yankai Jia, Daeyeon Lee, 2019. "Pickering Emulsions Stabilized by Polymer Colloids", Polymer Colloids: Formation, Characterization and Applications, Rodney Priestley, Robert Prud'homme
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Emulsions are ubiquitous in our daily lives and are widely encountered in a variety of industries.1 Emulsions are mixtures of two or more immiscible fluids, one being dispersed in the other, in the presence of surface-active agents.2 Based on the nature of the dispersed phase, emulsions are classified into oil-in-water (O/W), water-in-oil (W/O) and multiple emulsions such as water-in-oil-in-water (W/O/W) emulsions. When pure oil and water are mixed, the system favors the state with the minimum area between the two liquid phases, leading to macroscopic phase separation. Thus, surface-active agents such as surfactants are added to lower the interfacial tension and stabilize emulsion droplets. Traditional surfactants include amphiphilic small molecules and polymers which preferentially adsorb to oil–water interfaces. The other role of surfactants is to form kinetic barriers that prevent destabilization of emulsions and to facilitate formation of smaller emulsion droplets. The surface activity of surfactants strongly depends on their molecular structures. The Bancroft rule states that “the phase in which an emulsifier is more soluble constitutes the continuous phase”.3 The hydrophile–lipophile balance (HLB) number of surfactants can be employed to quantitatively describe the Bancroft rule.4 For example, surfactants with HLB values larger than 10 stablize O/W emulsions whereas those with HLB lower than 10 stabilize W/O emulsions.