| Summary: | Absorbance-vs-time dependences have been determined for well characterized monodisperse colloidal silica spheres of three different diameters, aggregating under the influence of monovalent electrolyte (KCl) at pH 6. Subsequently, absolute aggregation rate constants and corresponding stability ratios were determined from these experimental dependences by using a proper aggregation model. The electrophoretic mobility of the silica spheres was measured as a function of the KCl concentration. This provided the -potential values inserted as the surface electrostatic potentials in the calculation of the stability ratios following the DLVO theory. An essential disagreement was found between the experimentally and theoretically evaluated stability ratios that points toward a systematic underestimation of actual aggregation rate by the theory. Thus, values of theoretical surface potential were calculated in turn for the experimental stability ratios using the same (DLVO) calculus and compared with these of -potential. In this way, an information has been obtained as to the origin of the disagreement.
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