Microscopic movements of latex particles in the water-filled voids of a glass bead packing are investigated with a variant of dynamic light-scattering, diffusive wave illumination. We are able to measure simultaneously diffusive and convective motion of the scatterers within the pore spaces of the completely opaque medium. The influence of increased seepage velocity on the diffusion coefficient and on the speed distribution of the particles is studied. We find an exponential distribution of the convective speed. From the average speed we determine the tortuosity of the packing. Using this investigation system as an illustration, we address the methodological aspects of diffusive wave illumination and discuss its possibilities and limitations: (1) the possibility of tuning the amount of local oscillator mixed to the dynamic signal, (2) the inclusion of residual dynamics of the porous medium into the fitting model, and (3) a study of the influence of increased particle concentration on the signal correlation function.
© 1998 Optical Society of AmericaFull Article | PDF Article
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