Flow induced by an oscillating sphere in probing complex viscosity of polymer solutions

Abstract

A theoretical investigation is presented for a linear viscoelastic flow induced by an oscillatory colloidal particle in nonadsorbing polymer solutions. At small-amplitude oscillations, the polymer distribution is assumed to be at equilibrium and forms a depletion zone around the particle based on the mean-field approximation. The goal of the theoretical approach is to predict the apparent complex viscosity sensed by the particle and compare this with the actual viscosity of the bulk fluid. Due to the local inhomogeneity, substantial deviation between the apparent and true viscosity in the bulk needs to be corrected quantitatively. The resulting apparent complex viscosity or friction coefficient in the Fourier domain will help to interpret active and passive microrheological measurements of colloid-polymer mixtures that take polymer depletion into account.

Controlled gel expansion through colloid oscillation

“…Since the pioneering work of Batchelor [43][44][45], theoretical efforts have primarily focused on relating the interactions between a "probe" colloid and the local microstructure to global material properties [46][47][48][49][50]. In addition, the motion of the "probe" particle itself, as it is driven through the polymer environment, has also been studied extensively, where particular focus has been given to the role of hydrodynamics [51,52], depletion interactions [53][54][55][56], and viscosity [57]. Notwithstanding these important contributions, our focus is instead on how the motion of such a colloid can perturb the local microstructure.…”