Probing linear and nonlinear microrheology of viscoelastic fluids
Physikalisches Institut, Universität Stuttgart - Pfaffenwaldring 57, 70569 Stuttgart, Germany and Max-Planck-Institute for Intelligent Systems - Heisenbergstrasse 3, 70569 Stuttgart, Germany
Received: 6 August 2014
Accepted: 27 November 2014
Bulk rheological properties of viscoelastic fluids have been extensively studied in macroscopic shearing geometries. However, little is known when an active microscopic probe is used to locally perturb them far from the linear-response regime. Using a colloidal particle dragged periodically by scanning optical tweezers through a viscoelastic fluid, we investigate both, its linear and nonlinear microrheological response. With increasing particle velocity, we observe a transition from constant viscosity to a thinning regime, where the drag force on the probe becomes a nonlinear function of the particle velocity. We demonstrate that this transition is only determined by the ratio of the fluid's equilibrium relaxation time and the period of the driving.
PACS: 47.50.-d – Non-Newtonian fluid flows / 83.60.Rs – Shear rate-dependent structure (shear thinning and shear thickening) / 83.85.-c – Techniques and apparatus
© EPLA, 2014