# Microrheology

From Soft-Matter

Original Entry: Ian Burgess, Fall 2009 (currently under construction)

## Definition

Microrheology is a form of rheology in which the properties of a complex fluid are measured with microscopic spatial precision by tracking the movement of a small, micron-sized, particle embedded in the fluid.

## Passive Microrheology

In passive microrheology, Brownian motion of the particle due to thermal energy is observed. The viscoelastic modulus of a complex fluid <math>G(\omega)</math> can be determined from the mean square displacement <math>\<\delta r^2\></math> of the tracer particle undergoing thermal motion. Mason and Weitz showed that