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

Area of Science:

• Materials Science
• Physical Chemistry
• Soft Matter Physics

Background:

• Accurate microrheology of Pickering emulsions is crucial but hindered by challenges in identifying tracer particles.
• Diffusing wave spectroscopy (DWS) is a powerful technique for microrheology, but its application to Pickering emulsions requires precise tracer identification.

Purpose of the Study:

• To identify the true tracer particles in Pickering emulsions (macroemulsions and microemulsions).
• To validate the role of identified tracer particles in DWS measurements for microrheology.
• To provide a strategy for accurate characterization of Pickering emulsion microrheology using DWS.

Main Methods:

• Utilized diffusing wave spectroscopy (DWS) to analyze Pickering emulsions.
• Employed computational simulations to compare the mobility of colloids and droplets.
• Cross-validated DWS results with rotational rheometry measurements.

Main Results:

• Demonstrated that colloidal particles, not emulsion droplets, act as tracers in Pickering emulsions.
• Simulations showed colloids exhibit greater mobility, dominating the DWS signal decay.
• Excellent agreement was found between rheometry and DWS-derived viscoelastic parameters when using the colloidal radius.

Conclusions:

• Colloids are the dominant tracer particles in Pickering emulsions due to their smaller size and faster Brownian motion.
• This identification strategy significantly enhances the reliability and accuracy of DWS for Pickering emulsion microrheology.
• The findings offer a pathway to improved characterization of complex soft materials.