INFLUENCE OF MULTIPLE LIGHT-SCATTERING ON THE ESTIMATION OF HOMOCOAGULATION AND HETEROCOAGULATION RATE CONSTANTS BY TURBIDITY MEASUREMENTS

In this work, the homocoagulation and heterocoagulation rates of aqueo us dispersions of uniform spherical particles of surfactant-free catio nic and anionic latexes were measured with a spectrophotometer. Two po lymer colloids with similar particle sizes and different surface charg e densities were used. The homocoagulation and heterocoagulation rate constants (K-D and K-D12 respectively) were determined as a function o f the total particle number N and the wavelength lambda of the spectro photometer. Constant values of K-D and K-D12 were found when N and lam bda had specific values. The decreasing of the rate constants for lowe r lambda or higher N values was explained as a consequence of the appe arance of multiple light scattering at some experimental conditions. I t was possible to detect critical N and lambda values which prevent th is phenomenon. By calculating the effective volume of solid in the cel l at the critical wavelength V-ef(lambda(c)), it is possible to define an experimental parameter NVef which provides a critical value above which the multiple light scattering takes place. (C) 1998 Elsevier Sci ence B.V.