Roberts GS, Sanchez R, Kemp R, Wood T, Bartlett P. Electrostatic charging of nonpolar colloids by reverse micelles.
LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008;
24:6530-6541. [PMID:
18537276 DOI:
10.1021/la703908n]
[Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
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.
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