Fiber-optical quasi-elastic light scattering of concentrated dispersions

Abstract

A fiber-optical experimental setup is presented to measure the quasi-elastic light scattering from concentrated dispersions. The geometry of the setup is described and the coherence requirements are discussed. Experimental results are obtained for two systems of latex spheres with diameters of 0.13 and 0.61 μm in the concentration range from φ = 0.02 to φ = 0.5. At all concentrations the observed correlation functions consist of a fast initial decay followed by a more slowly decaying tail. The initial decay is attributed to multiple scattering. For the 0.61-μm latex, the tail of the correlation function is shown to be due to self-diffusion, whereas for the 0.13-μm latex collective motions may also contribute. The concentration dependence of the diffusion coefficients has been measured. The observed slopes are discussed in the light of theoretical predictions.