Dynamic light scattering is the most popular technique for determining dynamic properties in soft matter. It enables one to monitor particle dynamics over an enormous time-interval of 11 decades. Ensemble-averaged dynamics in ergodic media can be determined using rather standard techniques. However, in non-ergodic samples (e.g. glasses) special experimental techniques are needed.
We have designed a new setup for multi-speckle dynamic light-scattering, which allows us to measure spatially-resolved autocorrelation functions of the scattered intensities. This is done to probe dynamics in spatially-separated sub-ensembles. Using well-designed detection optics, we detect the scattered light under a single scattering vector and image the scattering volume on a fast CCD-camera directly. The spatially-heterogeneous and ensemble-averaged dynamics can thus be measured. Time-resolved dynamics can be analyzed, as well.
MSCS reveals itself as a powerful tool in analyzing any colloidal sample of interest; specifically, in the temporal evolution of the ensemble-averaged intermediate scattering function and in the local particle dynamics. Dynamical heterogeneities in meta-stable colloidal samples can be made visible in great detail, which makes this an especially marked technique.
