Transient extensional rheology and the influence of strain history

Abstract

This paper presents new experimental results on the measurement of transient extensional viscosity (TEV) and on the three-dimensional (3D) surface formed when TEV, strain and time of deformation data are plotted. In order to test the validity of the hypothesis that such 3D surfaces are unique for a particular polymer at a given temperature, a terpolymer of 2-ethyl hexyl acrylate, n-butyl acrylate and acrylic acid has been extended at varying rates including step changes in rate of extension. These experiments also throw light on the influence of strain history on extensional viscosity. It is shown that a step drop in rate of extension, produces a step increase in TEV which then relaxes back on to the 3D surface. A step increase conversely causes a step fall in TEV with a subsequent rise back to the original surface. The results support the view formed from previous experimental results that these surfaces are a valid representation of TEV although alternative methods of forming the plots should also be considered. Prior straining is shown to be significant only during the period in which the fluid is relaxing from previous deformation modes.