Ongoing

Below are some ongoing projects:

 

Kuhn Characterization of the KG model of varying stiffness

The Kremer-Grest model is the most used Molecular Dynamics model for flexible polymers. The standard theoretical polymer model is due to Kuhn and is based on random walk. Using about 175 core years of effort, we have now made a Kuhn characterization of the KG model, such that we can take existing theories and make parameter free predictions and hence quantitative accurate predictions for KG simulation results. If the theory prediction does not agree with the simulation data, then the theory is wrong!

 

Mapping of KG polymers models to real polymers chemistries

With recent progress we now know how to convert a given real polymer species into the equivalent KG polymer model, and vise versa convert KG units sigma, epsilon, and tau into SI units.  (Collaboration: Continental researchers, Ralf Everaers ENS Lyon)

 

Damage and wear in polymer materials

We are studying how allowing cross-link and backbone bonds to break changes the properties of rubbery materials, and try to gain a microscopic understanding how such damage effects evolve. (Ph.D. Student: Igor Gula)

 

Mori-Zwanzig based coarse-graining

Structure based coarse-graining is routinely used to develop coarse-grained models that reproduce static structural properties of a more detailed model of e.g. biophysical systems.  However, dynamic non-equilibrium behaviour is also of significant interest. Currently only one method exists for systematically deriving coarse-grained equations of motion: Mori- Zwanzig theory was developed more than 50 years ago. Despite this fact it has yet to be used as a basis for deriving coarse-grained Molecular Dynamics models. (Collaboration Ass. Prof. K. Debrabant, Ph.D. Student: Nicky Mattson)

 

Stiff polymers

DPD polymer models with segmental repulsive interactions allows gels of biopolymers to be modelled without too high a computational cost. We have studies chain statistics, force-extension relationships and the relation between entanglement length and plateau moduli for gels of rigid polymers. (Bachelor student Peter Møller Kirketerp)

 

Casin micelle network formation

When acid is added to skimmed milk, the casein micelles can aggregate to form a network. We are developing models based on granular particles to simulate the self-assembly of such network structures. The resulting structures will be compared to experimental results. (Collaboration with Adam Cohen Simonsen, ARLA, and run by Jens Phannoi Hansen).

 

Continuum modelling of damage in rubbery materials.

Kremer-Grest molecular dynamics simulations gives detailed insights into what happens when individual cross-links break. But to study the large scale material response, we need to build this microscopic knowledge into constituitive relations in continuum elasticity theory. Finite element simulations are not a natural description for systems where holes and interfaces can appear, we have experimented with using Smoothened Particle Hydrodynamics (SPH) (ISA project Jonathan Lund) and peridynamics techniques. (ISA project Kristoffer Pedersen)

 

Polymers in crowded environments

Polymers physics is governed by entropic interactions. We study polymers in media where most of the volume is taken up by spherical filler particles, and study how this impacts polymer conformations and dynamics. (collaboration with Federica Lo Verso, and Ph.D. students Erik Kjellgren and Peter Reinholdt)

 

Dynamics in glassy colloids

Hard sphere colloids are an ideal system for studying the glass transition. The dynamics can be characterized experimentally using confocal microscopy. We perform very long simulations of nearly hard sphere colloids to study the in-cage ratteling and in particular the statistics and properties of rare relaxation events where the cage rearranges itself. (collaboration with Paolo Sibani)

 

 

 

Previous activities:

Redistribution of hydrophobic pharmacuticals between oil droplets

Naively one would expect hydrophobic agents would stay well partitioned in oil droplets or micelles in a aqueous solution, however, experiments suggests they are rather rapidly distributed if a mixture of loaded and unloaded droplets is prepared. We will study if this redistribution process follows a type of Ostwald ripening dynamics. (with F. Lo Verso and J. Kunche SDU)

LNA/DNA probes

Chemically modified DNA molecules (LNA - Locked nucleic acids) offers a promise as probes for detecting specific mutations. In order to optimize the pharmaceutical application of such probes, molecules we need to understand and predict their hybridization behaviour (melting temperature) and sequence specificity. This is currently being studied by developing a Poland-Scheraga type model of the thermodynamics of DNA/LNA hybrid hybridization. (Collaboration Ass. Prof. I. Kira Astakhova, Students: Peter Reinholdt, Erik Kjellgren, Oliver Glue)

Scattering theory

Small-angle Neutron and X-ray Scattering techniques (SANS/SAXS) are ideal techniques for investigating nano-structures in soft-condensed matter and biological matter. However, to analyze the results of such experiments detailed knowledge is required about the scattering form and structure factors. I have developed a formalism for predicting the scattering from a large class of structures comprising polymers, and geometric objects. Currently this is being expanded by developing theory for the scattering from self-avoiding random walks.