Probing structural relaxation in complex fluids by critical fluctuations
A. F. Kostko*+, M. A. Anisimov*, J. V. Sengers*
*Institute for Physical Science and Technology and Department of Chemical Engineering, University of Maryland
College Park, MD 20742, USA
+Department of Physics, St. Petersburg State University of Refrigeration and Food Engineering
191002 St. Petersburg, Russia
PACS: 61.41.+e, 83.80.Rs, 83.85.Ei
Abstract
Complex fluids, such as polymer solutions and blends, colloids and gels, are
of growing interest in fundamental and applied soft-condensed-matter science.
A common feature of all such systems is the presence of a mesoscopic
structural length scale intermediate between atomic and macroscopic scales.
This mesoscopic structure of complex fluids is often fragile and sensitive to
external perturbations. Complex fluids are frequently viscoelastic (showing a
combination of viscous and elastic behaviour) with their dynamic response
depending on the time and length scales. Recently, non-invasive methods to
infer the rheological response of complex fluids have gained popularity
through the technique of microrheology, where the diffusion of probe spheres
in a viscoelastic fluid is monitored with the aid of light scattering or
microscopy. Here we propose an alternative to traditional microrheology
that does not require doping of probe particles in the fluid (which can
sometimes drastically alter the molecular environment). Instead, our proposed
method makes use of the phenomenon of "avoided crossing" between modes
associated with the structural relaxation and critical fluctuations that are
spontaneously generated in the system.