ELASTICITY IN POLYMER-SOLUTIONS

Capillary flow of polymeric liquids is afflicted with considerable end effects, strongly depending on fluid elasticity. Usually, they are determined by means of the Bagley correction, merely to reject the viscometric errors. The idea of the present work is to extend the observations to such short capillaries, knowing that the shearing time of the fluid is not sufficient for attaining a steady state of relaxation. Measurements with poly (ethylene oxide) solutions in water are reported. We obtained non-linear Bagley plots. They are discussed in terms of a proper time constant of the viscoelastic material which matches with the residence time when reaching the steady state. We propose that the liquid starts capillary flow with great elastic strain, which decreases under constant shear rate to a finite value known as recoverable shear.