Transient Viscoelastic Properties of Linear Polymer Solutions

Shear and normal stress developments after stepwise increases of shear rate from a steady shear rate γ₁to a higher one γ₂ were observed with a Weissenberg rheogoniometer Type R-17 in linear polystyrene solutions. The initial parts of the stress-development curves at different γ₂ compose a single line if γ₁is kept constant, and the initial slope becomes lower with increasing γ ₁ It was concluded that the original quasi-network structure of polymer solutions remains unchanged until a certain critical strain is accumulated in the solution. The difference in the initial slope at different γ₁ may be caused by a change in the effective entanglement density with γ. It is also pointed out that the additivity of responses in viscoelastic behavior of polymer solutions does not hold in nonlinear regions.