Spectroturbidimetry of fractal clusters: Test of density correlation function cutoff

I have measured the relative increase in turbidity pi/pi(t = O) as a function of wavelength exponent w = -partial derivative(log tau)/partial derivative(log lambda) in the process of the reaction-limited cluster-cluster aggregation of polystyrene latex with a particle diameter of 90 nm. It is shown that this dependence is not sensitive to particular details of sample preparation and is described for independent measurements by one master curve. Theoretical calculations made in the single-scattering and Berry-Percival mean-held theory approximations considering small-angle light-scattering effects and cluster polydispersity also demonstrate that this dependence is sufficiently universal and its shape can be practically determined solely by the choice of the density correlation function cutoff model. Comparing the experimental tau/tau(0) = f(w) curves With calculated theoretical plots I conclude that the Gaussian cutoff model is the best among all the models of the exponential family. This is in accord with a previous finding [Langmuir 8, 2964-2069 (1992)] that was obtained by using angular scattering from diffusion-limited cluster-cluster aggregation soot aggregates. (C) 1996 Optical Society of America