Professor Daniel Read

Profile

I am interested in the links between molecular structure, molecular dynamics, flow properties, and reaction chemistry of polymer materials. Understanding this often involves large multidisciplinary teams, including mathematicians, physicists, chemists and engineers.

Responsibilities

• International Foundation Year Co-ordinator
• Bulletin Editor, British Society of Rheology

Research interests

I am part of the Complex Materials and Industrial Mathematics group. My main research interests are in the fields of theoretical polymer physics, rheology and coarse grained modelling of biological molecules. I'm the Leeds Local Director in the Centre for Doctoral Training in Soft Matter for Formulation and Industrial Innovation (SOFI2 CDT), and I administer the Soft Matter Mailing List.  Various areas of my research have resulted in development of useful software, as listed below.

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 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 and precessing 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.

Increasingly as we look towards intelligent paths for polymer recycling and developing new polymeric materials with lower environmental impact, we will need to better understand and control these lnks between polymer structure and flow.

Useful software
Branch-on-Branch (BoB) rheology: Predicts the linear and non-linear rheology of entangled branched polymers based on a representative set of polymer topologies.  Widely used both in industry and academia.  Authored by Dr Chinmay Das and myself. 
Reptate: RepTate (Rheology of Entangled Polymers: Toolkit for Analysis of Theory & Experiment) is a free and open source software package for viewing, exchanging and analysing experimental data, with a particular emphasis on rheology and polymer dynamics. It allows experiemtnal data to be compared against the latest theories. Latest version authored by Jorge Ramirez (Madrid) and Victor Boudara (Leeds).

Coarse-grained dynamics of globular proteins

In collaboration with Dr Sarah Harris (Physics) and Dr Oliver Harlen (Mathematics) I am developing methods for simulating coarse-grained dynamics of globular proteins. Full Molecular Dynamics simulations are computationally expensive and typically generate around 50 nanoseconds of simulation time without too much difficulty. However, the timescale of biological events for example in protein folding can be on the order of microseconds to milliseconds. In response to these problems, there are a wide variety of coarse graining techniques used to try to bridge this timescale gap and simulate larger systems. These include go-model, coarse grained force fields such as the Martini force field, Elastic Network Models , dissipative particle dynamics, etc. We are pursuing an alternative approach, in which the protein is treated as a viscoelastic continuum with material properties which vary as a function of position. We simulate this using finite element analysis, incorporating stochastic thermal noise.

Useful software
Fluctuating Finite Element Analysis (FFEA): A new molecular modelling tool, built from the ground-up to support systems that are larger and more complex than those modelled by atomistic molecular dynamics. Instead of modelling biological systems as a collection of connected atoms, it models them as 3D volumes comprised of tetrahedrons. The models FFEA generates are visco-elastic continuum solids, subject to thermal fluctuations.

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. 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. Comparison of calculated scattering (based on models for polymer motion) with experiments allows us to learn more about the mechanisms of polymer relaxation.

• Closing the Loop via Molecular Polymer Rheology

Professional memberships

• British Society of Rheology
• Institute of Physics

Research groups and institutes

• Applied Mathematics
• Complex materials and industrial maths

Current postgraduate researchers

• Merin Joseph
• Will Grant