2023 Volume 23 Issue 9 Pages 483-489
Passive microrheology is a relatively modern rheology technique for measuring linear visco-elasticity of soft material such as emulsion, polymer solution and micellar solution by observing Brownian motion of micron-sized probe particles embedded in the medium. The generalized Stoles-Einstein relation (GSER) is used to derive the dynamic modulus of viscoelastic material from the mean square displacement (MSD) of probe particles undergoing Brownian motion in the material. In this review article, we briefly explain fundamental concept of passive microrheology and derivation of the GSER. Among several methods for observing mean square displacement of probe particles, we focus on the light scattering technique called diffusing-wave spectroscopy (DWS) that is performed in multiple scattering regime. A merit of using DWS-based microrheology is its ability to probe higher frequency regime than the other techniques such as more conventional dynamic light scattering method made in the single-scattering regime and particle-tracking method. Some examples of DWS-based micro-rheology are presented.
