We report on a new type of experiment that enables us to monitor spatially and temporally heterogeneous dynamic properties in complex fluids. Our approach is based on the analysis of near-field speckles produced by light diffusely reflected from the superficial volume of a strongly scattering medium. By periodic modulation of an incident speckle beam we obtain pixel-wise ensemble averages of the structure function coefficient, a measure of the dynamic activity. To illustrate the application of our approach we follow the different stages in the drying process of a colloidal thin film. We show that we can access ensemble averaged dynamic properties on length scales as small as ten micrometers over the full field of view.
@article{arxiv.0704.0681,
title = {Monitoring spatially heterogeneous dynamics in a drying colloidal thin film},
author = {P. Zakharov and F. Scheffold},
journal= {arXiv preprint arXiv:0704.0681},
year = {2012}
}