Diffusing Wave Spectroscopy Studies of Pickering Emulsion: Which Are the Tracer Particles?

Accurate identification of tracer particles contributing to diffusing wave spectroscopy (DWS) is essential for reliable microrheology but remains challenging in Pickering emulsions. Herein, we demonstrate that colloids are the tracer particles in Pickering emulsions of varying droplet scales, i.e., macroemulsion or microemulsion. Simulations reveal that colloids are more mobile than droplets, thereby dominating the decay of the intensity autocorrelation function. This conclusion is further supported by the agreement between the viscoelastic parameters from rotational rheometry and those calculated from DWS using the colloidal radius. The reason is that colloids are inherently orders of magnitude smaller than droplets, leading to much faster Brownian motion. This work provides a strategy for tracer particles identification and for enhancing the utility of DWS in the accurate characterization of Pickering emulsion microrheology.