Shear-Induced network formation in colloid/polymer mixtures: A molecular dynamics study

Abstract

This paper studies the molecular mechanism of rheological behavior of mixtures of colloid particles and associating polymers with many stickers by using a non-equilibrium molecular dynamics (NEMD) simulation method. The steady shear viscosity obtained by the NEMD simulation exhibits strong shear thickening at moderate shear rates, and shear thinning at larger shear rates. The value of the viscosity in the shear-thickening regime is three times larger than that in the the Newtonian regime. By analyzing the simulation data, it is shown that strong shear-thickening is caused by the network formation induced by shear flow. The scenario of the shear-induced network formation is as follows. In the small shear-rate regime, polymer chains take compact conformations due to strong association with a few colloid particles, which suppress the network formation. In the shear-thickening regime, such associated structures are destroyed by shear flow, leading to expanded conformations of polymer chains. This conformational change promotes the intermoleular association of polymers bridging colloid particles, and as a result, the network formation is enhanced. © 2014 The Society of Rheology, Japan.