Structural effects of the solvent composition in colloidal liquids

This paper is concerned with the microstructure observed in colloidal dispersions of charged polymeric particles and their interaction potential at very low ionic strength. Both aspects are probed with the aid of new experimental data for nonaqueous media. The structure factor of ordered dispersions (with methanol-water and ethanol-water solvent mixtures) was determined using static light scattering. A different behavior (in the studied range of molar fraction) depending on the alcohol type is found. These results are analyzed assuming a Yukawa potential and applying integral equation theories (the Ornstein-Zernike equation and the HNC closure). The obtained effective charge is almost constant for methanol-water mixtures, whereas a decrease with the alcohol molar fraction is observed for ethanol-water. In order to account for these effects, a charge renormalization procedure is applied and discussed. The surface charge turns out to be an unsuitable input parameter for such an approach. (C) 1999 American Institute of Physics. [S0021-9606(99)51212-9].