Dynamics of rod-like macromolecules in concentrated solution. Part 2

Abstract

As a continuation of a previous paper, the rheological properties of a concentrated solution of rod-like macromolecules are discussed. A procedure for calculating the stress tensor for a given flow history is presented and, as a special case, simple steady shear flow is studied in detail. Some interesting feature of the results are: (i) the steady state viscosity η(0) at zero shear rate and the first and second normal stress coefficients Ψ₁(0) and Ψ₂(0) all depend very strongly on molecular weight M and mass concentration ρ, with η(0)∝ρ³M⁶ and Ψ₁(0), Ψ₂(0)∝ρ⁵M¹³; (ii)Ψ₂(g) is negative and about –2/7 of Ψ₁(g) where g is the velocity gradient; (iii) the shear stress shows an extremum as a function of shear rate, indicating an instability of flow at certain shear rate. As a byproduct of the theory, a stress-optical law is predicted.