Rheological applications of a drop elongation experiment



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A new method for determining the extensional flow properties of polymer melts and solutions has recently been proposed which is based upon the physical principle that a fluid drop placed in a rotating field of a higher density fluid will experience axisymmetrical extension when the rotational speed is varied with time. Under rather general conditions an analysis of the dynamic response of the drop in terms of measurable and controllable variables can be obtained which gives rise to a number of different steady and transient extensional flow experiments. It is the objective of the present work to experimentally test the overall validity of this proposed method. In this connection, both Newtonian and non-Newtonian fluids were used in the tests. In the Newtonian tests, the proposed elongating drop method was proved to be valid by using Cannon ASTM standard oil(visc. no. N190000-68-lb) as a Newtonian fluid. The experimental results for the extensional viscosity of this oil show a nearly constant value which is equal to approximately 3 times the shear viscosity in agreement with Trouton's law. In the non-Newtonian tests, three polystyrene in dibutyl phthalate solutions(PS-DBP) were tested under unsteady conditions and the resulting normal stress difference data were measured and compared with the predictions of the Bird-Garreau model. In comparison, the experimental results of normal stress difference follow the model predictions quite well and the quantitative agreement is reasonably good.