Project B6: Topological validation of coarse-grained polymer models

Computational studies of polymer-based materials on large length and time scales require mesoscopic models: drastically coarse-grained descriptions where non-bonded potentials between interacting particles are on the order of the thermal energy. Such “soft” models are either used as “stand alone” descriptions or as elements of strategies, where the microscopic description of the material is recovered through sequential backmapping in a hierarchy of mesoscopic models. In the previous funding period, we focused on using single-chain topology ─ polymer knots ─ to validate mesoscopic models and hierarchical backmapping schemes for bulk high-molecular-weight polymer melts.

We made three important findings: A) We demonstrated that polymer knots are, in general, multiscale objects, i.e. they simultaneously depend on microscopic and medium-scale features. As such, they cannot be always accurately described by mesoscopic models. B) Nevertheless, we identified conditions when mesoscopic models can quantitatively reproduce knotting properties of underlying microscopically-resolved melts. This happens when the Kuhn length substantially exceeds characteristic scales of excluded volume interactions. C) We demonstrated that two different state-of-the-art algorithms — configurational assembly and a hierarchical backmapping strategy — used for equilibrating high-molecular-weight bulk polymer melts deliver samples with consistent knotting behaviour.

Building upon these results we will expand our research to polymer films. Combining extensive microscopic and mesoscopic simulations of melts confined by solid or vapour interfaces, we will understand the behaviour of knots in these systems and corroborate theoretical concepts of films. Conformational, topological, and structural properties in our “brute-force” microscopic simulations will be extensively compared with their counterparts in films generated with a novel hierarchical backmapping strategy.

Apart from studying films, we will modify the configuration assembly and backmapping algorithms to prepare bulk melts with different amounts of knotted chains. Analysing these samples will provide insights whether (and if yes how) knots affect material properties.

The response of polymer knots to symmetry-breaking phenomena is a largely unexplored theoretical question. In the new funding period, we will use special mesoscopic models with anisotropic potentials to explore the behaviour of knotting properties during two basic symmetry-breaking events: the isotropic-nematic transition in main-chain polymer liquid crystals and emergence of chirality in helical polymers.

Dynamic coarse-graining of polymer systems using mobility functions
Bing Li, Kostas Daoulas, Friederike Schmid
Journal of Physics: Condensed Matter 33 (19), 194004 (2021)
see publication

Comparing equilibration schemes of high-molecular-weight polymer melts with topological indicators
Luca Tubiana, Hideki Kobayashi, Raffaello Potestio, Burkhard Duenweg, Kurt Kremer, Peter Virnau, Kostas Daoulas
Journal of Physics: Condensed Matter, (2021)
see publication

A minimal Gō-model for rebuilding whole genome structures from haploid single-cell Hi-C data
S. Wettermann, M. Brems, J.T. Siebert, G.T. Vu, T.J. Stevens, P. Virnau
Computational Materials Science 173, 109178 (2020)
see publication

Can Soft Models Describe Polymer Knots?
Jianrui Zhang, Hendrik Meyer, Peter Virnau, Kostas Ch. Daoulas
Macromolecules 53 (23), 10475-10486 (2020)
see publication

Generic Model for Lamellar Self-Assembly in Conjugated Polymers: Linking Mesoscopic Morphology and Charge Transport in P3HT
Cristina Greco, Anton Melnyk, Kurt Kremer, Denis Andrienko, Kostas Ch. Daoulas
Macromolecules 52 (3), 968-981 (2019)
see publication

Mapping onto Ideal Chains Overestimates Self-Entanglements in Polymer Melts
Hendrik Meyer, Eric Horwath, Peter Virnau
ACS Macro Letters 7 (6), 757-761 (2018)
see publication