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A5: Wärmetransport in Polymer-Nanokompositen

Es soll ein Multiskalen-Verfahren für den Wärmetransport in weicher Materie entwickelt werden. Insbesondere werden wir ein vergröbertes Modell für Polymer-Nanokompositmaterialien wie zum Beispiel Graphitfragmente entwickeln und dann verwenden, um die relaxierten Strukturen dieser Materialien zu beschreiben. Dabei werden wir atomare Details dieser Strukturen zurückgewinnen und den Wärmetransport in einer solchen atomaren Beschreibung untersuchen, um Referenzdaten zu gewinnen. Anschließend werden wir uns mit der Frage auseinandersetzen wie vergröberte Modelle modifiziert werden müssen, damit der Wärmetransport in Nanokomposit-Systemen direkt in einer vergröberten Beschreibung ermittelt werden kann.

Communication: Is a coarse-grained model for water sufficient to compute Kapitza conductance on non-polar surfaces?
Vikram Reddy Ardham, Frédéric Leroy
The Journal of Chemical Physics 147 (15), 151102 (2017);
URL: http://aip.scitation.org/doi/10.1063/1.5003199

Coarse-grained models have increasingly been used in large-scale particle-based simulations. However, due to their lack of degrees of freedom, it is a priori unlikely that they straightforwardly represent thermal properties with the same accuracy as their atomistic counterparts. We take a first step in addressing the impact of liquid coarse-graining on interfacial heat conduction by showing that an atomistic and a coarse-grained model of water may yield similar values of the Kapitza conductance on few-layer graphene with interactions ranging from hydrophobic to mildly hydrophilic. By design the water models employed yield similar liquid layer structures on the graphene surfaces. Moreover, they share common vibration properties close to the surfaces and thus couple with the vibrations of graphene in a similar way. These common properties explain why they yield similar Kapitza conductance values despite their bulk thermal conductivity differing by more than a factor of two.

Thermodynamics of atomistic and coarse-grained models of water on nonpolar surfaces
Vikram Reddy Ardham, Frédéric Leroy
The Journal of Chemical Physics 147 (7), 074702 (2017);
URL: http://dx.doi.org/10.1063/1.4999337

In order to study the phenomena where interfaces play a dominant role through molecular simulations, the proper representation of the interfacial thermodynamic properties of a given model is of crucial importance. The use of coarse-grained rather than atomistic models makes it possible to simulate interfacial systems with larger time and length scales. In the present work, we compare the structure and thermodynamic behavior of one atomistic and two single-site coarse-grained models of water on nonpolar surfaces, namely, graphite and the basal plane of molybdenum disulfide. The three models interact with the surfaces through Lennard-Jones potentials parametrized to reproduce recent experimental contact angle measurements. The models form a layered structure close to the surface, which is usually observed on sufficiently attractive nonpolar substrates. However, differences in the structure and thermodynamic behavior are observed between the models. These differences are explained by certain features of the water models, such as short range tetrahedral order and liquid density fluctuations. Besides these results, the approach employed in the present study may be used to assess the ability of coarse-grained models for solid-liquid systems to represent consistent interfacial thermodynamics.

Revisiting the droplet simulation approach to derive force-field parameters for water on molybdenum disulfide from wetting angle measurements
Frédéric Leroy
The Journal of Chemical Physics 145 (16), 164705 (2016);
URL: http://scitation.aip.org/content/aip/journal/jcp/145/16/10.1063/1.4966215

Solid-liquid work of adhesion of coarse-grained models of n-hexane on graphene layers derived from the conditional reversible work method
Vikram Reddy Ardham, Gregor Deichmann, Nico F. A. van der Vegt, Frédéric Leroy
The Journal of Chemical Physics 143 (24), 243135 (2015);

Parametrizing Nonbonded Interactions from Wetting Experiments via the Work of Adhesion: Example of Water on Graphene Surfaces
Frédéric Leroy, Shengyuan Liu, Jianguo Zhang
J. Phys. Chem. C 119 (51), 28470-28481 (2015);


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