G. Popescu, A Dogariu, and R. Rajagopolan, Spatially resolved microrheology using localized coherence volumes, Phys. Rev. E, vol. 65, 041504 (2002).
We propose an optical technique, based on dynamic light scattering, for investigating the local rheological response of a complex fluid over a frequency range larger than that provided by standard mechanical instrumentation. The low-coherence radiation used in a fiber optics configuration allows the measurements to be confined to a small volume around a tenth of a picoliter. The ability of the method to accurately measure both loss and storage moduli has been tested using both simple Newtonian liquids and viscoelastic, complex fluids. The possibility to monitor liquid-gel transitions in polymer solutions has also been demonstrated. The unique capability of the technique to localize the measurement volume suggests that this novel approach can be used for three-dimensional mapping of rheological properties in heterogeneous systems.