May 24, 2019
Professor Thomas Mason
PhD student Ha Seong Kim and Professor Thomas Mason have substantially refined diffusing wave microrheology of highly scattering concentrated dispersions.
When illuminated with white light, many soft materials, such as concentrated emulsions and latex paint, have a white appearance because these materials multiply scatter visible light. A light scattering technique, known as diffusing wave spectroscopy (DWS), had been previously developed to probe the dynamics of scattering objects in such soft materials. However, the prior analytical framework for DWS did not account for collective scattering effects caused by the close proximity of scattering objects to each other in a dispersion, so it was strictly valid only for dilute dispersions.
The breakthrough made by UCLA graduate student, Ha Seong Kim, and Professor Thomas Mason, in conjunction with collaborators in Professor Frank Scheffold's group at the University of Fribourg, involves correcting DWS signals for such collective scattering effects. This new advance enables quantitatively accurate passive microrheology to be performed on highly scattering soft materials containing high concentrations of scattering objects through an improved analysis of DWS that takes collective scattering effects into account. This advance, which they empirically demonstrated using concentrated uniform emulsions, has been published recently in the Proceedings of the National Academy of Sciences (PNAS). 
Professor Thomas Mason and graduate student Ha Seong Kim.