Anomalous Extensional-Flow Effects in the Use of Commercial Viscometers

Abstract

The last three decades have been characterized by a strong and healthy research activity in various aspects of Rheometry (cf. 1–8). Individual topics of interest have often been tackled with a global and saturation coverage to the extent that a subject in vogue at one international congress has all but been forgotten by the next, only to be replaced by other timely interests. We have attempted to portray this idea of transience in Fig. 1, which contains a selective (and necessarily subjective) impression of the rise (and sometimes the fall) of research activity in some important aspects of rheometrical studies. The fact that the picture is selective is immediately apparent from the lack of mention of the viscosity function in simple shear η(q) or the complex viscosity η*(ω)) associated with an oscillatory shear flow. For these, there has been an ongoing theoretical and practical interest, not marked by wild fluctuation, but very consistent and important (see, for example, 6,8). Indeed, the existing preeminence of shear viscosity in practical studies is our fundamental premise in the arguments to be developed later.