Recoil of microbeads in complex fluids

Polymer fluids are complex soft-matter systems whose response properties play a key role in many applications. In this thesis, we investigate the behavior of a colloidal probe driven out of equilibrium in a coarse-grained polymer fluid performing in-silico microrheological "recoil" experiments, in which a microbead is manipulated by optical tweezers and then released. The Langevin Dynamics simulations capture the recoil dynamics of the probe, well described by the superposition of two exponential relaxations with time scales differing by about one order of magnitude, under different "recoil" protocols. Exploiting the microscopic detail of the model, we also analyze the relaxation of the surrounding fluid, focusing on the spatial asymmetry in density and elastic energy around the probe, two quantities that decay to zero at equilibrium. Under a double-exponential decay hypothesis, these quantities are characterized by the same time scales, challenging the current interpretation of the recoil dynamics; however, careful data analysis show long-time tails that are better described by a power law.