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Electrostatic Charging of Nonpolar Colloids by Reverse Micelles

2008; American Chemical Society; Volume: 24; Issue: 13 Linguagem: Inglês

10.1021/la703908n

1520-5827

G. Seth Roberts, Rodrigo Sánchez, Roger Kemp, Tiffany A. Wood, Paul D. Bartlett,

Surfactants and Colloidal Systems

Colloids dispersed in a nonpolar solvent become charged when reverse micelles are added. We study the charge of individual sterically stabilized poly(methyl methacrylate) spheres dispersed in micellar solutions of the surfactants sodium bis(2-ethyl 1-hexyl) sulfosuccinate [AOT], zirconyl 2-ethyl hexanoate [Zr(Oct)2], and a copolymer of poly(12-hydroxystearic acid)-poly(methyl methacrylate) [PHSA-PMMA]. Although the sign of the particle charge is positive for Zr(Oct)2, negative for AOT, and essentially neutral for PHSA-PMMA, the different micellar systems display a number of common features. In particular, we demonstrate that over a wide range of concentrations the particle potential is a constant, independent of the number of micelles added and independent of the colloid size. A simple thermodynamic model, in which the particle charge is generated by the competitive adsorption of both positive and negative micelles, is in good agreement with the experimental data.