MULTICRITICAL PHENOMENA IN FLOW OF VISCOELASTIC LIQUIDS .1. ZAREMBA-FROMM-DE WITT LIQUID

It has been shown that multicritical phenomena caused by nonlinearity of viscosity and high elasticity, and forced anisotropy at finite shea r rates take place during flow of viscoelastic polymer melts which are isotropic in the resting state. The sign of the low-frequency asympto tic values of the dynamic viscosity and elasticity measured during ste ady flow is a criterion of the appearance of instability. These argume nts are illustrated by the solution and analysis of the complex reacti on to low-amplitude, periodic shear of a steady-flowing, very simple v iscoelastic liquid - ZFD liquid. It was shown that the instability of viscoelastic liquids for a given steady shear rate is due to the effec t of perturbations lasting for no less than some limiting value and it s manifestations are caused by superposition of different types of ins tability - multicritical phenomena.