Stretching flow tests on polymer-thickened motor oils using an accelerated-film technique

Abstract

Tests are described in which a film of oil or other liquid is accelerated along the surface of a rotating cylinder. This new technique gives extensional strain rates in the region of 50–250 s −1; this is higher than the values obtained when using an earlier device that involved the stretching of a liquid jet. Five oils that contain different polymers are tested, together with an aqueous elastic liquid, at a temperature of 25.5 °C. The extensional viscosities of the polymer-thickened oils, as measured by the accelerated-film method, lie between 1.53 and 4.18 Pa s, with Trouton ratios between 11.6 and 29.7. (Trouton ratios of up to 120 are shown to be obtained by the jet thrust method for the same oils at an extensional strain rate of 10 3 s −1.) Plots of axial stress against extensional strain rate obtained by the accelerated-film method show good agreement with data obtained by the convergent-nozzle jet thrust technique. The aqueous solution is more elastic than the oils, and permits a horizontal liquid filament to be formed, so that data obtained by this method (low strain rates) may be compared with data obtained by the accelerated-film method (moderate strain rates) and by the jet thrust method (high strain rates). This helps to validate the method and also throws new light on the differences that exist between different types of extensional flow regime.