Speaker
Description
Understanding the microscopic response of complex fluids to localized perturbations is a central problem in soft condensed matter. Here, we investigate the dynamics of a colloidal probe driven through a viscoelastic medium composed of interacting polymer chains using Langevin dynamics simulations.
Recent experimental protocols have provided direct access to stored elastic forces in such systems. In these experiments, a colloidal probe is driven either at constant force or constant velocity and, upon release, exhibits a recoil motion. This back-motion reflects memory effects in the viscoelastic medium and encodes information about its relaxation dynamics.
Motivated by this approach, we analyze the recoil of the probe after switching off the external driving. By tuning the strength of polymer–polymer interactions, we control the viscoelastic character of the medium, ranging from purely repulsive to increasingly adhesive systems. Our results reveal a nontrivial dependence of the recoil on both the driving protocol and interaction strength. In weakly interacting systems, the recoil is reasonably described by linear response theory at intermediate forces, while deviations emerge at low forcing. For intermediate adhesion, we observe enhanced recoil and subdiffusive dynamics, indicating strong memory effects and persistent correlations. At higher adhesion, particle motion becomes increasingly constrained, leading to reduced recoil despite increased structural rigidity.
These findings highlight the interplay between microscopic interactions, memory, and nonlinear response in viscoelastic media, providing a minimal framework to interpret active microrheology experiments.