SINGLE-MODE FIBERS IN FIBEROPTIC QUASI-ELASTIC LIGHT-SCATTERING - A STUDY OF THE DYNAMICS OF CONCENTRATED LATEX DISPERSIONS

The concentration dependence (range 1-40%) of the dynamics of monodisperse polymer latex dispersions (particle diameters 41-326 nm) is studied by fiber-optic quasielastic light scattering (FOQELS). The experiments reveal that despite the high turbidity of the samples multiple light scattering has negligible influence on the data when single-mode fibers are employed. This is explained by the diameter of the single-mode fiber core being much smaller than the scattering mean free paths in the dispersions. It is further shown that the autocorrelation functions can be interpreted in terms of the dynamic structure factor of the dispersions. When the particle diameter is raised from 41 to 326 nm the data show that FOQELS probes mutual diffusion for the smaller particles and self-diffusion for the larger ones.