Intrinsic viscosity of flexible polymers in unbounded and bounded Newtonian shear flow

Abstract

The zero-shear-rate intrinsic viscosity of a polymer in an athermal and THETA solvent in free space and confined in a slit is investigated by Monte Carlo simulations of self-avoiding random walks on a simple cubic lattice. The intrinsic viscosity in a Newtonian shear flow is calculated by Zimm's algorithm. The results for an unbounded system are in excellent agreement with several scaling predictions. The intrinsic viscosity is below its unbounded value when the coil is squeezed. The effect of hydrodynamic interactions between walls and chain segments on the intrinsic viscosity is negligible. The differences between THETA and athermal solvent conditions gradually diminish with a decrease in the width of the slit as witnessed by the intrinsic viscosity and the scaling exponent for the radius of gyration. This is due to the fact that the solvent quality improves for a decreasing slit width; i.e., a THETA-solvent in three dimensions becomes a good solvent in two dimensions. The increase in excluded volume implies that there is a distinct difference between THETA-chains (i.e., chains that behave as random walks in free space) and real random walks. In the latter case the value of the component of the radius of gyration parallel to the walls is independent of the slit width. For real THETA-chains it increases.