The size, charge, and electrokinetic potential of gold nanoparticles in solutions of sodium bis(2-ethylhexyl) sulfosuccinate in n-decane-chloroform mixtures

The hydrodynamic diameters and electrokinetic potentials of gold nanoparticles in n-decane, chloroform, and mixtures thereof have been studied as functions of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) concentration. At AOT concentrations in n-decane below 2 mM, gold nanoparticles are covered with AOT monolayer and do not reveal electrophoretic mobility. At a concentration of 0.3 M that, according to the data of photon-correlation spectroscopy, corresponds to the onset of adsorption of AOT micelles on the nanoparticle surface, the ζ-potential reaches a maximum value of 190 mV; then, it decreases with increasing surfactant concentration. A rise in the volume fraction of chloroform in decane-chloroform mixtures drastically increases the ζ-potential even at low AOT concentrations. The obtained results have been analyzed in terms of the Debye-Hückel theory.