Polymers and complex fluids

PhD (ESR) positions are available within the "DYNACOP" Marie Curie Initial training network. (DYNamics of Architecturally COmplex Polymers). Two positions in Leeds, others at Universities across Europe. See here for more details.

This group is concerned with theoretical modelling of polymeric materials and complex fluids such as particle suspensions, colloids and biological fluids. There is close collaboration, including joint research projects, with the Polymer IRC centred in the Department of Physics and Astronomy. In particular, we are heavily involved in the Microscale Polymer Processing project.

PhD projects are available in all the areas below, and in more areas on the individual staff webpages. If you are interested, then please get in touch.

Dr. Richard Blackwell Molecular Rheology of Branched Polymers and its Application to Wire Coating
Dr. Richard Graham Molecular modelling of entangled polymer fluids under flow
Dr. Sally Everitt Bubble dynamics in polymeric foams

Polymer dynamics and rheology

Oliver Harlen, Daniel Read

Polymers are long molecules made from joining together lots of small molecules (or monomers). Sometimes polymer molecules are linear, but very often - notably in the case of Low Density Polyethylene (LDPE) used to make plastic bottles - they include many branches.

During the manufacture of polymeric (or plastic) materials and commodities, liquids containing polymers are subjected to flow. The way these liquids react is determined by the shapes, or configurations that the molecules adopt. Polymer molecules behave like springs, and become stretched by the flow, giving rise to the strongly elastic behaviour of polymeric fluids. The study of the dynamics of polymer molecules is very important for the understanding of flow of polymeric fluids.

If polymer molecules overlap sufficiently, then they get tangled up (like spaghetti) so that they are constrained in their movement. The "tube model" for entangled polymers provides a conceptual framework for understanding the constrained motion, and for making mathematical predictions about the polymers' response to flow.

Branchpoints in the polymer molecules provide addtional obstacles to the motion of entangled polymers, so that the distribution of branchpoints in polymer molecules can be a critical factor in determining flow properties.

Non-Newtonian fluids

Oliver Harlen

Elastic stresses in polymeric and other complex fluids can give rise to strange flow behaviour not seen in Newtonian fluids. This can, for example, produce undesirable instabilities in industrial processes. The aim of our research is to predict how these fluids will flow in various flow geometries and to determine the conditions for the flow to become unstable. Our current research includes investigations of how bubbles grow in polyurethane foams; how filaments of polymer stretch and break-up; and flow instabilities in extrusion.

Reaction chemistry and branched polymer architecture

Daniel Read

There are different chemical routes used to produce branched polymers in an industrial setting. The particular reaction chemistry, and the reactor type and conditions, have a large effect on the number and distribution of branches throughout the polymer molecules. Current research is examining this relationship between reaction chemistry and branched polymer architecture with a view towards the reaction design for polymer melts with tailored flow properties.

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Polymer dynamics and neutron scattering

Daniel Read

It is important to understand the shapes, or conformations that polymers take under flow conditions. Although polymer rheology (the stress response of the fluid) is one way of probing this, it is important to have other independent tools to check that the theory is right. A more direct measure of polymer shape is obtained via neutron scattering from polymers that are parially labelled with deuterium. We aim to predict neutron scattering patterns from deformed polymer melts.

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Suspension mechanics

Oliver Harlen

Another important class of non-Newtonian fluids is suspensions of solid particles, such as spheres and fibres, or droplets or bubbles in Newtonian or non-Newtonian fluids. For example, short glass and carbon fibres are often added to injection moulded plastics to reduce cost and to improve the mechanical or thermal properties of the finished product. Small spheres are often suspended in a fluid in order to transport, for example, pharmaceutical powders around processing plants; and many food-stuffs and skin-care products are formed from oil-in-water emulsions. While the motion of single particles in Newtonian fluids is well understood, suspensions of large numbers of particles that interact through the fluid remain challenging, both analytically and numerically. Our current research includes investigations of how rough particle surfaces can affect the flow of a suspension of solid spheres; how collisions between fibres affect the flow properties of concentrated fibre suspensions; propagation of sound waves through colloidal suspensions; and how droplets deform in a polymeric fluid flow.