UNIVERSALITY IN ELECTRIC LIGHT-SCATTERING PROPERTIES OF OXIDE AGGREGATES IN AQUEOUS DISPERSIONS

The calculated saturated electric light scattering (ELS) effect (alpha infinity) as a function of the product qR(g) (q = k sin Theta, k = 2 pi/lambda, lambda, is the incident light wavelength, Theta is the angle of observation, and R(g) is the radius of gyration) is compared with experimentally measured values of alpha infinity. Aqueous suspensions from aggregates of SiO2 (Aerosil OX50), Al2O3 and TiO2 particles have been investigated. The aggregates in these systems are obtained by flame hydrolysis and could be described as mass fractal objects, having a characteristic fractal dimensionality (D). D is determined by the use of the correlation between the time of centrifugation (t) and the final slope (S-1) of the ELS decay curve. The SiO2 and Al2O3 monodisperse fractions were obtained by centrifugation, while the TiO2 suspension was sonicated. The monodispersity of the fractions obtained was followed through the difference between the initial and final slopes of the ELS decay curves. As-received suspensions have characteristic mean hydrodynamic radii, determined from the relaxation time of the ELS decay curve. It was found that the experimental data for alpha(infinity) versus kR(g) for the different suspensions lie on a single curve; this is striking evidence of the universality of the regime of colloid aggregation.