from abstract ideas...fundamental knowledge at Esso Research
The deformed unit s p h e r e — a new
three dimensional concept — has recently e n a b l e d an Esso R e s e a r c h scientist Dr. Wladimir PhilippofF to demonstrate completely the correlation between elasticity and flow birefringence of certain viscoelastic liquids. When such liquids, for example hydrocarbon solutions of linear polymers, undergo shear, they can be "stretched'' many times farther than rubber. Dcformational mechanics predict that when viscoelastic liquids are stressed, they behave as though a unit sphere of the liquid is deformed into a triaxial ellipsoid. The existence of this ellipsoid has been demonstrated by
optical birefringence measurements of a flowing solution in all three directions in space. These measurements permitted calculation of the dimensions of the ellipsoid which were found to agree completely with theory. Flow birefringence thus becomes a convenient and accurate method of determining elasticity. In continuing studies, measurements are being made of normal stresses, another unusual property of viscoelastic liquids. These are internal pressures exerted perpendicular to the direction of flow. Although development of these normal stresses can be predicted accurately by theory, it is difficult to
predict just how and where they will appear in a given apparatus. T h e illustration shows a simple demonstration of normal stresses in a viscoelastic liquid which is being stirred by an impeller. The normal stresses force the liquid up the stirring rod. Greater understanding of the properties of viscoelastic liquids may be of great value in such divergent fields as lubrication, the forming of plastics, and treatment of certain diseases. . . . adapted from the scientist's notes at Esso Research and EngineeringCompany (P. O. Box 45B, Linden, New
Jersey)
scientific affiliate of Humble Oil & Refining
Company
