Abstract:

We describe a method for measuring the rheological properties of complex materials by embedding small probe particles within the material and monitoring the thermal motion of the probe using either light scattering or particle tracking. If the probe particle is large compared to the characteristic length scales of the surrounding material, then its motion will reflect the average behavior of the medium. This can be interpreted in terms of the frequency dependent elastic modulus of the medium, providing a simple, non intrusive method for measuring rheological properties. Examples are shown of the measurement of the actin networks using this method, and an unexpected scaling behavior is observed.

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