FIBER-OPTIC-DYNAMIC-LIGHT-SCATTERING AND 2-COLOR-CROSS-CORRELATION STUDIES OF TURBID, CONCENTRATED, STERICALLY STABILIZED POLYSTYRENE LATEX

Concentrated turbid colloidal suspensions were investigated by means o f dynamic light scattering. The results of two different techniques, i .e., fiber-optic quasi-elastic light scattering (FOQELS) and two-color cross-correlation (TCC) were compared. Both techniques allow one to o bserve correlation functions of singly scattered light. FOQELS determi nes backscattered light only, whereas measurements at various scatteri ng angles can be performed with TCC. At concentrations up to about 10% (w/w) only a single diffusion process is observed that can be attribu ted to the collective diffusion; At higher concentrations an additiona l slow mode occurs which can be identified as long time self-diffusion of the latex spheres. The results of both techniques agree very well and can be understood in the framework of the theories of interacting hard spheres. They demonstrate the capabilities which both methods off er to study dynamic properties of strongly scattering colloidal suspen sions.