Diffusing wave spectroscopy for the study of emulsions on-ground and in microgravity

We review the approaches, both experimental and modelling, and the main results obtained recently in the investigation of emulsions by diffusing wave spectroscopy (DWS). DWS is a correlation spectroscopy based on the analysis of the time structure of the scattered light emerging from a laser-illuminated opaque sample. Such a noninvasive technique is well suited to the investigation of drop size distribution and drop dynamic in emulsions. This dynamic determines the evolution, and finally the fate, of emulsions. The results obtained in a laboratory are complemented by the very recent results obtained in microgravity (the condition of absence of weight obtained in orbit) onboard the International Space Station: mastering emulsions in such exotic conditions not only offers new insight into the basic physical phenomena but may also provide new enabling technologies to ensure comfortable living environments and safe foods to the astronauts engaged in long space flights. • A review of applications of DWS to emulsions. • A novel interpretation scheme for DWS, based on optical Monte Carlo simulations provides unique insight into drop dynamics. • Review of recent DWS results obtained in microgravity. • A dynamic transition is observed in emulsions in microgravity.