Hello, and welcome!
I am a Reader
working in the Department of Applied Mathematics, where
I am part of the
Polymers and Non-Newtonian Fluid Mechanics group.
My main research
interests are in the fields of theoretical polymer physics and rheology.
You can find some outline descriptions of the specific research topics
I'm working on (or have worked on in the past) below. If you want to know
more, then my publication list is here.
I am a joint administrator for the DYNACOP
Marie Curie Initial training network.
(DYNamics of Architecturally COmplex Polymers) - a joint venture with 9 other Universities and two companies across Europe.
I am a member of the Polymer IRC,
which involves several departments across the University. I did my PhD
and postdoc work in the Department of Physics, and maintain
several collaborations with people over there.
PhD projects are available in all the areas below.
Please get in touch if you are interested.
Polymer dynamics and rheology
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
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
I run a masters-level course (jointly with
Dr Oliver Harlen) on
Polymeric Fluids where some of these issues are explored.
Reaction chemistry and branched polymer architecture
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.
As an example of this, metallocene catalysts form branches via the formation
of "macromomonomers" (chains with double-bonds at the end) and the
incorporation of these into growing chains (see left). Based on this
simple mechanism, it is possible to derive mathematically the distributions
of molecular size and branching.
One can extend these ideas to treat situations where there are several types
of metallocene catalysts, or different reactor conditions, or different reaction
chemistry (e.g. LDPE is usually manufactured via a free-radical chemistry
which gives branching via an entirely different mechanism). The goal is an
understanding of how chemistry affects branching, and how this in turn affects
the flow properties of polymers.
Polymer dynamics and neutron scattering
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.
Polymer molecules can be wholly, or partially "labelled" by replacing
hydrogen atoms in the molecules with deuterium. Neutrons interact with deutrium
differently to hydrogen, so that a beam of neutrons passing through a
labelled melt of polymers will be scattered. The intensity, and angle,
of scattering is related to polymer shapes.
The above picture shows neutron scattering patterns from a melt of H-shaped
branched polymers, in which the middle of the polymers are deuterium-labelled.
The melt was stretched, and scattering patterns taken at various times
following the stretch (experimental results along top row). Theoretical calculations
(bottom row) of the scattering pattern
must account not only for the polymer shapes, but also the
correlations between polymer molecules due to their interactions with one