The Use of Optical Elastohydrodynamics to Investigate Viscosity Loss in Polymer-thickened Oils

Abstract

This paper is in two parts. In the first, a comparison is made between film thicknesses determined by point and by line contact. The two are shown to give identical results. In the second part, fourteen test fluids were chosen to provide a variety of molecular structures. Eight polymers were studied at several concentration. A considerable amount of viscosity loss was observed at both point and line contacts. The difference between the two was negligible. This is important a it shows that the polymer molecules were moving straight through the contact and not going round the point contact. This is useful experimentally as point contact devices are much easier to build and use than line contact devices. The viscosity loss under EHL conditions was found to be 10 to 20 percent larger than that observed in a capillary high-shear viscometer. This is thought to be due to the completely different stress pattern in the two. The entry viscosity of the polymer-thickened oil differs hardly at all from the straight oi...