Diffusing-wave-spectroscopy investigation of latex particle motion in polymer gels

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Abstract
Dynamic light scattering studies of particle motion in cross-linked chemical gels are limited by the fact that when the cross-linking ratio is increased, the scattered intensity becomes quenched, and time-dependent concentration fluctuations contribute less and less to the overall scattering signal. The concentration fluctuations then occur at very small length scales, which can become inaccessible to classical dynamic light scattering techniques. Diffusing wave spectroscopy can help overcome these experimental difficulties. We extend this technique to the case of nonergodic systems, and apply it to the detection of the motion of probe particles trapped inside chemically cross-linked gels. We measure the mean square displacement of the nanometric probes, leading to the measurement of local mechanical properties of the gel matrix.