Influence of the adsorption of non-ionic surfactant Triton X-100 on the homocoagulation and heterocoagulation processes of model colloids with equal sizes and opposite sign of charge

Turbidimetric and nephelometric techniques have been used to study the homocoagulation and heterocoagulation of aqueous dispersions of monodisperse latices. Cationic and anionic latices of similar particle size (361 and 370 nm) and different surface charge density (+ 16.4 and -3.6 mu C cm(-2)) were used. The colloidal stability of both latices was modified by adsorption of a non-ionic surfactant (Triton X-100). The stability factors and the rate constants (K-D,K-F) for doublet formation were determined for the homocoagulation process when the latices were partially or totally covered by the surfactant. Similar K-D,K-F values were obtained for both latices, even when they were totally or partially covered by the surfactant. These results were confirmed by spectrophotometric and nephelometric measurements at different wavelengths and particle concentrations. The heterocoagulation fate constant (K-D12) was calculated from turbidity and nephelometry data as a function of the wavelength and total particle concentration. The heterocoagulation process was studied for cationic and anionic latices: bare cationic latex-bare anionic latex; bare anionic latex-totally covered cationic latex; and totally covered anionic and cationic latices. Even in the last case heterocoagulation occurs, but the kinetic constant (K-D12) was lower in comparison with the process when both bare latices were used or when one of them was saturated by the surfactant. The K-D12 values were calculated versus the wavelength and particle concentration of the suspension, and these results were confirmed by nephelometry measurements. Thus, a sterically stabilized latex could be coagulated by colloids of opposite sign of surface charge. (C) 1998 Elsevier Science B.V. All rights reserved.