Gradient Dependence of Intrinsic Viscosity of Freely Flexible Linear Macromolecules

Abstract

In laminar flow the randomly coiled macromolecule expands nonuniformly. The averaged distances between close‐by chain elements increase much slower than those between elements situated far away on the molecular chain. Because the latter move in opposite direction and the former in the same one, yielding a negative and positive contribution respectively to hydradynamic interaction, the nonuniform expansion results in a much faster decrease of negative terms. As a consequence hydrodynamic interaction first increases with the gradient yielding an initial drop in intrinsic viscosity proportional to the square of the gradient. With persisting coil expansion, however, the positive terms too decrease so far that the viscosity, after reaching a minimum, rises again and eventually surpasses the initial value at zero gradient. The increase is coming to an end when the rms end‐to‐end distance approaches the extended length of the molecule.