Paper Number
RS29 

Session
Techniques and Methods: Rheometry & Spectroscopy/Microscopy

Title
Photon transport in diffusing wave spectroscopy microrheology

Presentation Date and Time
October 12, 2022 (Wednesday) 3:45

Track / Room
Track 6 / Mayfair

Authors (Click on name to view author profile)

  1. Furst, Eric M. (University of Delaware, Chemical and Biomolecular Engineering)
  2. Li, Qi (University of Delaware)
  3. Sbalbi, Nicholas (University of Delaware)

Author and Affiliation Lines (in printed abstract book)
Eric M. Furst1, Qi Li2 and Nicholas Sbalbi2
1Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716; 2University of Delaware, Newark, DE

Speaker / Presenter 
Furst, Eric M.

Keywords
experimental methods; colloids; rheometry techniques; suspensions

Text of Abstract
Diffusing wave spectroscopy (DWS) measures dynamics by light scattering in a high multiple-scattering regime. It is a non-invasive way to study dynamics and microrheology in soft materials, and has been widely used in academic and industrial research, including studies of colloid dynamics, polymer solution dynamics, protein aggregation kinetics, drug stability, and soft characterization under extreme conditions. The precise determination of light transport properties is essential in light scattering microrheological measurements such as DWS. Based on Mie scattering theory, we determine the form factor, structure factor, and transport mean free path l*, of model repulsive (hard sphere with excluded annulus) and attractive (sticky hard sphere) suspensions. Good agreement are observed between the calculated and experimental measurements. It is further found that for particles that are larger than the light wavelength in the medium, l* is generally insensitive to particle interactions. But for small particles, l* can exhibit significant interaction dependency depending on the volume fraction. Our results provide an operating regime for suspension microrheology measurements from low to high concentrations and also suggest new methods to interpret the microrheological response from DWS measurements, which will be discussed.