Shear‐rate‐dependent viscosity of non‐Newtonian suspensions and entangled polymer systems

Abstract

AbstractA simple equation is proposed to calculate the shear‐rate‐dependent viscosities of entangled polymers and particle suspensions. The rate‐dependence of the viscosities is attributed to changes in certain structural parameters associated with the fluids, such as entanglement density or degree of particle agglomeration. The state of these structural parameters for fluids subjected to a given shear flow is determined by two competing process, i.e., structural breakdown and reformation, which in steady How arc in a state of dynamic equilibrium. For the polymer systems structural degradation and reformation are tantamount to entanglement loss and creation, whereas for the suspensions they are correlated with the particle breakup and flocculation. The regeneration process is driven by thermal diffusion and is assumed to be independent of shear rate. The degradation process is caused primarily by the imposed shear and is assumed to be proportional to the shear rate to a power m (0<m<1). Based on these assumptions, structural variation for fluids undergoing not only steady‐state but a I so transient flows can be calculated. Model predictions and their implications are discussed. The derived equation can be applied to many non‐Newtonian pseudo‐plastic fluids.