Electrostatic Interactions of Colloidal Particles in Nonpolar Solvents: Role of Surface Chemistry and Charge Control Agents

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This paper studies the interactions of colloidal particles in nonpolar solvents. Even though ionization in nonpolar solvents is not possible because of the high energy cost under environments with low dielectric polarizability, it is possible to charge colloidal particles in nonpolar solvents with the use of certain charge control agents.

Generally, the electrostatic interaction between the colloidal particles depends on 1) the surface potential, and 2) the screening length of the solvent. In a polar solvent, the screening length can be easily determined through the concentration and valence of the ionic species and the associated conductivity. However, this is difficult in nonpolar solvents because the ionic species are not very well characterized. In addition, the surface potential is difficult to be determined because it is difficult to measure accurately the electrophoretic mobility of particles, since it is too low. Then there are debates about the validity of using the DLVO theory to predict the interaction forces between the colloidal particles in nonpolar solvents.

In this paper, they studied the forces between polystyrene (PS) and poly(methyl methacrylate) PMMS particles in hexadecane and using aerosol-OT as charge control agents. They observed that the concentration and composition of the charge control agents affect the surface potential and screening length.