Abstract
dc:description.abstractThis thesis is concerned with the theory of polymer rheology. 'Living polymers' are chain-like structures which closely resemble ordinary polymers, except that they can break and reform reversibly. The best-studied examples are wormlike surfactant micelles. A model for these systems has recently been proposed, based on the concept of a confining 'tube', and leading to a constitutive equation related to that of Doi and Edwards for unbreakable chains. This equation is capable of describing nonlinear rheological behaviour, and in chapter 2, some of its predictions are discussed and compared with experiment. In steady shear flow, the shear stress is shown to decrease with increasing shear rate, according to the constitutive equation. This behaviour, which is also shown by the Doi-Edwards equation, is unphysical. Both theories fail to take into account the fact that the tube has a non-zero width. At high shear rates, the tube becomes aligned along the flow, but, because of the finite width, the polymer inside is still exposed to a velocity gradient. In chapter 3, several models of this are studied, all based on an elastic dumb-bell or a Rouse chain confined to a pipe. This effect, however, is not strong enough to make the shear stress a monotonic function of shear rate. There is still a region of intermediate shear rates where the shear stress decreases with shear rate. In this region, a homogeneous shear flow is unstable. However, by assuming that the flow contains bands of different shear rate, it is possible to explain, with good accuracy, the experimental shear and normal stress data for a system of wormlike surfactant micelles (chapter 2). There are still some difficulties, though, which are described in chapter 3. In chapter 4, the shear-banding flow phenomenon is studied in more detail. A linear analysis and numerical simulations are performed, on a simplified one-dimensional model of a rheometrical flow. It is confirmed that shear bands form when the shear stress is nonmonotonic, although there is still some uncertainty over the final steady stress. Chapter 5 presents some experimental data on a system of wormlike micelles, chapter 6 is a conclusion, and the remainder of this chapter describes important background material.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 1994
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Spenley, Neil Andrew
- Advisor dc:contributor.advisor
-
- Cates, Michael
Subjects
dc:subject × 3Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.90877
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/343457