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Complex Fluids and Theoretical Polymer Physics – University of Reading

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Complex Fluids and Theoretical Polymer Physics

The Complex Fluids and Theoretical Polymer Physics group focuses on the structure and dynamics of complex fluids, with polymeric fluids being the overarching theme.

Our research ideology is to work on theoretical models of complex fluids and use extensive computer simulations to inform and verify these models. The theoretical models we are working with range from stochastic differential equations to partial differential equations to constitutive equations (tensor ODE's). The simulation techniques include Molecular Dynamics, Monte-Carlo and Brownian Dynamics, as well as field-theoretic simulations.

The Complex Fluids and Theoretical Polymer Physics group became part of Department of Mathematics and Statistics in 2007. Currently it is based around Dr Zuowei Wang and Dr Patrick Ilg.

We collaborate with a wide range of theoretical and experimental groups around the world, including Universities of Kyoto, Michigan, ETH Zurich, Julich and others. Our research is mainly funded by EPSRC.

In the department and school, we have growing links with the group of Data Assimilation and Inverse Problems and Probability and Stochastic Analysis. Over the last 6 years the group has built significant computational resources, with 500 processor cores available currently.

Professor Alexei Likhtman, 1971-2015

Professor Alexei Likhtman, professor of Mathematical Physics at the University of Reading and a highly valued, well-loved member of staff, died in October 2015.


Research

Molecular dynamics and entanglements (Likhtman, Wang, Cao)

polymer_molecularMost of the problems of polymer dynamics arise from the lack of clear definition of polymer entanglement. We perform large scale molecular dynamics simulations of dense polymeric system of various topology (linear, stars, rings) and propose microscopic definition of polymer entanglements. Much of the work is then directed to investigating entanglement properties in different systems and thus informing simpler and coarser models.

Slip-spring model of entangled polymers (Zhu, Likhtman, Wang)

polymer_slip-springA single chain stochastic model (Likhtman, 2005) represents a crucial step in hierarchical modelling, bridging the gap between multi-chain molecular dynamics simulation and the tube theory. We are working on improving the model and its relationship to the tube model.

Branched polymer rheology (Zhu, Cao, Wang, Likhtman)

Branched polymers such as stars, H-shaped polymers and combs, is a relatively new direction of the group. The challenge here is extremely slow dynamics due to the fact that usual reptation motion is supressed by the branch points. We are working on new computational methods such as forward flux sampling and others to speed up MD and slip-springs simulations.

First passage problems and extreme events in many dimensions (Cao, Likhtman)

The problem of estimating the time something very unlikely occurs for the first time has wide range of applications from theory of chemical reactions and protein folding to predictions of catastrophic climate or financial events. We study this problem in the general context of a multidimensional random walk on the potential landscape, and apply it to disentanglement rates of branched polymers.

Computational and theoretical modelling of supramolecular polymer networks (Amin, Wang, Likhtman)

Supramolecular polymer networks are formed by the reversible cross-linking of macromolecules via transient physical interactions, such as hydrogen bonding, p-p stacking and ionic interactions. These nanostructured materials, sometimes known as self-healing materials, have a wide range of potential applications due to their unique ability to self-repair.

We are interested in the dynamic and rheological properties of these fascinating systems in relation to their topological structure formation. Our studies are performed using hybrid molecular dynamics/Monte Carlo simulations and theoretical modelling. These works are done in close collaborations with experimental groups.

Wetting processes and dynamic contact angle (Lukyanov, Likhtman)

Wetting processes and dynamic contact angle (Lukyanov, Likhtman)Phenomena associated with dynamic contact angle at a moving contact line are central to various microfluidic applications, coating and ink-jet printing technologies. Many aspects of the dynamic wetting problem have been haunting researchers over the last 40 years due to various paradoxes which appear in macroscopic modelling of this problem.

Our recent studies of the moving contact-line problem via molecular dynamics simulations have shown that the dynamic contact angle effect (Lukyanov, Likhtman 2013) is essentially conditioned by the microscopic processes in a small region, several atoms wide, around the contact line, basically at nanoscale. We are interested in microscopic modelling of the processes taking place at moving contact lines to understand the origin of the dynamic wetting effects in situations involving simple and complex interfaces, e.g. interfaces laden with polymers, particles and surfactants.

Capillary effects and interfaces in simple and complex liquids (Lukyanov, Likhtman)

Capillary effects and interfaces in simple and complex liquids (Lukyanov, Likhtman)The modern drive towards miniaturization and nanotechnology raises the importance of interfacial science to a new level. Due to widespread of microfluidic applications, the flows during their operation become more and more dominated by the effects of capillarity.

This presents an opportunity to control and fine tune various micro-flows by manipulating interfacial properties via the creation of complex interfaces. On the other hand, this calls for detailed theoretical analysis of structure and dynamics of such interfaces in strongly non-equilibrium conditions. We study such dynamic interfacial processes in our group from the first microscopic principles, using large scale molecular dynamics simulations.

Magnetoviscosity of dipolar colloidal fluids (Ilg)

polymer_magnetoviscosityThe viscosity of dipolar colloidal fluids (ferrofluids) can be manipulated by varying an external magnetic field. Current constitutive models suffer from the lack of knowledge about the relevant microstructure. Our simulations provide information on the field- and flow-induced structural changes and will allow us to formulate improved constitutive equations for dipolar colloidal fluids.

Field-dependent mechanical properties of ferrogels (Ilg)

When magnetic particles are brought into polymer gels, their soft solid-like behaviour responds strongly to external fields. From a theoretical point of view, the coupling of the translational and rotational dynamics of the magnetic particles to the polymer matrix is largely unknown. From detailed microscopic simulations we want to extract information on how to modify the classical Brownian Dynamics of the particles when they move not through a simple liquid but through a viscoelastic environment.

Rheology of supercooled liquids (Ilg)

polymer_rheologyThe viscosity of liquids increases enormously when cooled down towards the glass transition without apparent change of their microstructure. By analysing the underlying potential energy landscape of a binary Lennard-Jones system, we identify cooperative rearranging regions that grow in size upon cooling.

Our simulation results help to improve and provide a microscopic basis of current theories of the dynamics and rheology of glassy systems.

Polymer brushes under shear (Ilg)

polymer_brushesPolymer brushes are very effective in lubricating surfaces. We use nonequilibrium Molecular Dynamics simulations in order to investigate the effect of semi-flexibility as well as different polymer architectures on the resulting coefficient of friction of the polymer-coated surface.

Complex fluid-fluid interfaces (Ilg)

polymer_complexFluid-fluid interfaces can be stabilized by adsorbed multi-block copolymers that self-assemble into complex microstructures. The influence of the microstructure on the stability and surface rheology we study with a
multi-scale approach, combining molecular simulations and nonequilibrium thermodynamics modelling.

Conformational transition and self-assembly of charged polymers (Wang)

polymer_conformationalCharged polymers are abundant both in nature, such as DNA and proteins, and in synthesized materials. The study of charged polymers is not only inspired by the rich physical properties and so numerous applications resulted from the long-range Coulombic interactions among charged groups, but also the understanding of the functioning of biological systems.

Our researches in this direction are focused on theoretical and computational modelling of the conformational transition of diblock polyampholyte chains and the self-assembly behaviour of charged block copolymers and mixtures of oppositely charged polyelectrolytes. Thesestudies are related to the DNA and protein association.

Colloidal dipolar fluids (Wang, Ilg)

polymer_colloidalColloidal dipolar fluids, such as ferrofluids, electrorheological (ER) and magnetorheological (MR) fluids, are composed of magnetic particles of nano- to micrometer sizes suspended in carrier liquids. Their magnetic, structural and rheological properties are reversibly tunable by the application of magnetic field.

We study the field-induced physical properties of these fluids using computer simulations and theoretical modelling. Special attentions are paid to effectively handling the long-range dipole-dipole interactions among magnetic particles.

Atomistic simulation of nanostructured polymeric and surfactant materials (Wang)

polymer_atomistic_simulationMolecular dynamics simulations at the atomistic level can provide microscopic understanding of physical properties of soft matter materials that are generally hard to achieve in experiments. This type of simulations also constructs the basis for developing more coarse-grained computational models.

The systems we are working on include polymer melts, surfactant micelles, polymer-drug conjugates, etc. The simulation results are directly compared with experimental measurements and contribute to the development of coarse-grained models in the group.

Field-theoretic simulations for block copolymers (Stasiak, Matsen)

polymer_ftmc2Monte Carlo field-theoretic simulation is a novel and very promising technique for studying the fluctuation effects in block copolymers. In opposite to the chain-based simulation methods, the field-theoretic approach allows to consider very large polymerisation indexes.

Mathematically, the technique is related to the well-known self-consisted field theory, but instead of using the mean-field approximation, it exactly describes the composition fluctuations, which are particularly important
in the proximity of the order-disorder transition and in the disordered phase.

We focus on the fluctuation corrections to the mean-field predictions for the disordered-state structure factor and the order-disorder transition in a symmetric diblock-copolymer melt.

People

polymer group photo

From the left: Alex Lukyanov, Changqiong Wang, Jian Zhu, Dipesh Amin, Chris Davies, Simon Stephan,
Jack Kirk, Alexei Likhtman, Patrick Ilg, Pawel Stasiak, Zuowei Wang and Jing Cao. 

  

Name Position Telephone
+44 (0) 118 378
Email
@reading.ac.uk
Dr Patrick Ilg Associate Professor 8544 p.ilg
Dr Alex Lukyanov Senior Research Fellow 8992 a.lukyanov
Dr Zuowei Wang Associate Professor 4618 zuowei.wang
Dr Jing Cao Research Associate 3423
Dr Pawel Stasiak Research Fellow 8556 p.stasiak
Dr Anoop Varghese Research Associate a-varghese
Dr Apostolos Evangelopoulos Research Associate 5336 a.e.a.s.evangelopoulos

PhD Students

  • Dipesh Amin
  • Jack Kirk
  • Changqiong Wang
  • Jian Zhu
  • Chris Davies

Past group members

Publications

Seminars

We run a regular weekly seminar on Wednesday at 2pm, with a mixture of internal and external speakers.

Our aim is to provide for all of us the chance to engage with the different research projects going on and to stimulate discussions and new ideas. Therefore, we want this seminar to be informal and lively, with the emphasis on explaining ideas, plans and problems.

 

Atumm Term 2016

13 October 2016
11am
Room URS 2n14

Hisham Al-Obaidi, Pharmacy, University Reading   
Analysis of molecular interactions in polymeric solid dispersions

20 October 2016
2pm
Room JJT141
Alex Lukyanov
Hydrodynamics of moving contact lines: macroscopic versus microscopic

Summer Term 2016

22 June 2016
2-3pm
Room M100

Adrian Baule, Queen Mary College, London
Mean-field approach for random close packings of non-spherical particles

Spring Term 2016

2 February 2016
2-3pm
Room M100

Jing Cao
Simulating Startup Shear of Entangled Polymer Melts

10 February 2016
2-3pm
Room M100
Dipesh Amin
Thursday
11 February 2016
4-5pm
Room M104

Richard Graham, University of Nottingham
Modelling entangled polymers under flow: recent observations and analytic results

17 February 2016
2-3pm
Room M100

Jack Kirk
Surface dynamics of flexible polymer melts

Friday
26 February 2016
2-3pm 
Room M100

Michael Rubinstein, University of North Carolina
Complexation of oppositely charged polyelectrolytes and diblock polyampholytes

2 March 2016
2-3pm
Room M100

Anoop Varghese
Mesoscopic hydrodynamic simulations of simple fluids and colloids under shear flow

16 March 2016
2-3pm
Room M100

Jing Cao
Microscopic picture of constraint release effect in entangled star polymer melts

23 March 2016
2-3pm
Room M100

Jing Cao
Microscopic picture of constraint release effect in entangled star polymer melts - continued

13 April 2016
2-3pm
Room M100

Alex Lukyanov
The mechanism of dynamic contact angle at nano-scale

Thursday
21 April 2016
2-3pm
Room JJT141

Alex Lukyanov
The mechanism of dynamic contact angle at nano-scale

27 April 2016
2-3pm
Room M100

Apostolos Evangelopoulos
Wetting of polymer nanodroplets

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