This thesis describes work involving the measurement of the uniaxial extensional viscosity of mobile elastic liquids using three methods namely: the falling mass technique of Matta and Tytus (1990), the rotating drum technique of Jones <i>et al </i>(1986) and the tube arrest (T-A) experiment of Chesterman (1952). The work assesses the application of each of these methods to liquids of varying shear viscosity and elasticity. The falling mass experiment is found to be insensitive to the stretching forces generated in low viscosity liquids, but adequate for highly elastic liquids. The development of elastic instabilities is observed to occur above critical values of strain and extension rate. Using video imaging the rotating drum technique has been revised and improved theory developed. The technique is found suited to highly elastic, high viscosity liquids but cannot repeatably produce Newtonian filaments: it is shown to produce perfect uniaxial extension at moderate extensional rates. Fibrillation is observed involving an instability restricted to a single contact point. A study of the origins of the stretching force reveals that the influence of the flow instability on the stress generated in the filament is markedly reduced. The modified T-A experiment is used to produce high velocity liquid filaments, formed from collapse of a bubble beneath a liquid's surface: it facilitates the study of low viscosity, low elasticity liquids, at high extensional rates, accompanied by large strains. Studies of aqueous solutions of high molecular weight polyacrylamide show that at high rates, a marked deceleration of the filament occurs due to a significant increase in resistance to extensional flow. The relative contributions of the inertial and extensional flow components are assessed by volumetric analysis procedures. For polymer enhanced multi-grade motor oils, it was shown that the filaments contain a significant extensional component, with an upper limit of extensional rate far in excess of that achievable in commercial rheometers.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:636046 |
| Date | January 2000 |
| Creators | Barrow, M. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0021 seconds