DIFFUSING-WAVE SPECTROSCOPY IN CONCENTRATED LATEX DISPERSIONS - AN INVESTIGATION USING SINGLE-MODE FIBERS

It is shown that diffusing-wave spectroscopy (DWS) of multiple light s cattering from concentrated dispersions can be performed using immerse d single-mode fibers to emit and collect the light. The intensity auto correlation functions (ACFs) were measured from a 270 nm poly(styrene) latex dispersion (weight fractions 5, 10 and 30 ) as a function of th e separation between the source and detector fiber faces. Different or ientations between the fiber axes (0, 10, 45 and 180-degrees) were stu died. As expected from a photon diffusion approximation the logarithms of the ACFs of the multiply scattered light at the larger fiber separ ations were linear functions of the square root of time. As further pr edicted by the theory, the slopes of these curves were linear with fib er separation and were independent of fiber orientation. The slopes ar e proportional to the square root of the particle diffusion coefficien t and depend on the static scattering properties of the dispersion.