Multiscale computer simulation and theoretical modelling of linear and nonlinear dynamics and rheology of entangled polymers for environmental sustainability (Dr Zuowei Wang)
Understanding the dynamics and rheology of entangled polymers plays an important role in developing environmentally friendly polymer processing techniques and novel recyclable polymeric materials. We combine multiscale computer simulation and mathematical modelling methods, including molecular dynamics simulations based on fine-grained bead-spring and coarse-grained slip-spring models, statistical sampling algorithms and tube theories, to study the linear and nonlinear dynamic and rheological behaviours of various entangled polymer systems, aiming to provide microscopic insights in the dependence of these behaviours on the molecular weights, architectures, compositions (such as binary blends), and various flow conditions. These studies are carried out in collaborations with many experimental and theoretical groups.
Nonequilibrium response of magnetic nanoparticles: from statistical physics of irreversible processes to engineering, environmental and medical applications (Dr Patrick Ilg)
Magnetic nanoparticles provide fascinating model systems to study and test recent physical theories like fluctuation theorems, dynamical mean-field theories and nonlinear response. Due to their strong responses to external fields, magnetic nanoparticles find a whole range of promising applications, e.g. as field-adaptive materials, in environmental analysis and removal of pollutants, as well as biomedical applications such as hyperthermia, drug targeting and magnetic particle imaging. Therefore, improved modelling does not only help to better understand these systems, but also to improve the efficiency of applications.
Modelling the rheology of biopolymers and sustainable food systems: exploring new challenges for soft matter research (Dr Patrick Ilg)
Since soft matter physics and food science are closely related, we explore what progress can be made in better understanding biopolymer dynamics and rheology in the light of recent advances in soft matter science with regards to theory and modelling as well as advanced, multi-scale computer simulations. In a first step, we focus on physically crosslinked networks, which are often formed by biopolymers. We analyse their often overlooked slow coarsening and ageing dynamics and investigate the results effects on mechanical properties such as elastic moduli.
Molecular dynamics and entanglements (Dr Zuowei Wang)
Most 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 systems 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 (Dr Zuowei Wang)
A 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 (Dr Zuowei Wang)
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 suppressed 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.
Computational and theoretical modelling of supramolecular polymer networks (Dr Zuowei Wang)
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 (Dr Alex Lukyanov)
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 (Dr Alex Lukyanov)
The modern drive towards miniaturisation 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.
Conformational transition and self-assembly of charged polymers (Dr Zuowei Wang)
Charged polymers are abundant both in nature, such as DNA and proteins, and in synthesised 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. These studies are related to the DNA and protein association.
Colloidal dipolar fluids (Dr Zuowei Wang, Dr Patrick Ilg)
Colloidal 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 fields.
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.
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