(660d) Microrheology and Structure Evolution of Monodisperse Double Emulsions By Diffusive Wave Spectroscopy (DWS)

Diffusing wave spectroscopy (DWS) is an extension of dynamic light scattering measurements to concentrated and highly turbid colloidal samples with multiple scattering. However, the application of DWS to the double emulsions (DEs) systems has been relatively limited so far despite their significant potential in the diverse fields of applications including food, pharmaceuticals, and cosmetics. DWS treats the transport of photons through turbid samples as a diffusion process, thereby making it possible to extract the dynamics and structure of the internal droplets in DEs from measured correlation functions and most importantly, to understand their stability.

In this study, we demonstrate a new method for producing highly monodisperse DEs using a co-axial capillary pendant drop set-up using water and representative oils (dodecane, dichloromethane, and medium chain triglycerides). This method enables independent control of formulation parameters such as the number of internal droplets, their size, and volume fraction (ϕ_i) by varying the device geometry or process parameters. DWS measurements using a standard dynamic light scattering setup (ALV/CGS-3 Goniometer System) are made to probe internal dynamics. We interpret dynamic light scattering data as a function of both the transport mean free path (l*) and the detection angle for variable formulation parameters of double emulsions. This method can reliably determine l* and mean square displacement (MSD) to probe a range of time scales encompassing structural evolution and local microrheology.