(138i) Oscillatory Active Nanorheology Simulations of Colloidal Suspensions: Effect of Probe Size

Over the last two decades, probe microrheology has become a reliable experimental technique for determining the rheological properties of complex fluids. Recently, we developed an analogous molecular dynamics (MD) simulation technique that utilizes the inertial generalized Stokes-Einstein relation (IGSER) for predicting the linear viscoelasticity of polymer melts from the simulated probe motion. In this work, the technique’s ability for extracting the linear viscoelasticity of colloidal suspensions is investigated. Specifically, we performed oscillatory active nanorheology simulations on colloidal suspensions of volume fraction (φ) ranging from 0.15 to 0.49 (i.e. covering the regimes of dilute and concentrated suspensions up to the liquid/solid transition point). The hydrodynamics in our molecular models of colloidal suspension systems are governed by the intermolecular interactions; such models are representative of nanocolloidal dispersions. The distribution of colloidal particles around the probe is found to be symmetric, which is consistent with the system being in the linear response regime. The resulting linear viscoelastic properties determined from the probe rheology simulations are found to be in good agreement with those obtained from the non-equilibrium molecular dynamics (NEMD) simulations and literature experiments. The effect of relative size ratio of probe and colloidal particles on the measured values of moduli will be discussed.