Confined KCl solution between two mica surfaces: equilibrium and frictional properties.

International audienceWe have simulated the molecular dynamics of a KCl solution confined between two mica surfaces in equilibrium with a reservoir. For comparison, the simulations were also performed with pure water under the same conditions. The relation between normal pressure, lateral pressure in the solution layer, and quantity of water was first investigated. The position and orientation of the chemical species were then determined, showing the local molecular structure. Lastly, we simulated the mechanical response of the system submitted to a constant slip velocity for determining its frictional properties

Calculations of potential of mean force: application to ion-pairs and host–guest systems

International audienceWe report the calculation of the potential of mean force (PMF) of different types of associations by various techniques: two no biased methods (thermodynamic integration and finite difference thermodynamic integration), a constraint biased technique (adaptive biasing force) and an umbrella biased method (umbrella sampling). We apply these methodologies to the association between two methane molecules in water, to the formation of an ion pair in water and to the formation of an insertion complex between a macrocycle and a cation. The different PMFs are compared to each other on the basis of the depth of the free energy minimum and on the location of different specific points

Thermalized Drude Oscillators with the LAMMPS Molecular Dynamics Simulator.

International audienceLAMMPS is a very customizable molecular dynamics simulation software, which can be used to simulate a large diversity of systems. We introduce a new package for simulation of polarizable systems with LAMMPS using thermalized Drude oscillators. The implemented functionalities are described and are illustrated by examples. The implementation was validated by comparing simulation results with published data and using a reference software. Computational performance is also analyzed

Multi-scale modeling of the polymer–filler interaction

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Molecular interactions at the metal-liquid interfaces

International audienceWe reported molecular simulations of the interactions between water, an epoxy prepolymer (DGEBA) and an hardener (IPDA) on an aluminum surface. This work proposes a comprehensive thermodynamic characterization of the adhesion process from the calculation of the different interfacial tensions. The cross-interactions between the atoms of the metal surface and the different molecules are adjusted so as to reproduce the experimental work of adhesion. Water nanodroplets on the metal surface are then simulated to predict its contact angle. Liquid-vapor surface tensions of the epoxy prepolymer (DGEBA) and hardener (IPDA) and the solidvapor surface tension of the aluminum surface are also calculated to provide the solid-liquid interfacial tension that remains very difficult to obtain from the mechanical definition

Impact of the Force Field on the Calculation of Density and Surface Tension of Epoxy–Resins

International audienceThe molecular simulation of interfacial systems is a matter of debate because of the choice of many input parameters that can affect significantly the performance of the force field of reproducing the surface tension and the coexisting densities. After developing a robust methodology for the calculation of the surface tension on a Lennard-Jones fluid, we apply it with different force fields to calculate the density and surface tension of pure constituents of epoxy resins. By using the model that best reproduces the experimental density and surface tension, we investigate the impact of composition in mass fraction on uncured epoxy resins and the effects of degree of cross-linking on cured resins

Leaching of plasticizers from PVC medical devices: A molecular interpretation of experimental migration data

International audienceHigh pressure liquid chromatography (HPLC) experiments and molecular simulations were combined to investigate the leaching process of DINCH, DEHT and TOTM plasticizers from PVC materials. Methodologies based on statistical thermodynamics were used to rationalize the migration of the different plasticizers in water and ethanolic solutions from different free energy contributions. We extended this combined approach to the study of the adsorption of a model drug (diazepam) on different plasticized-PVC materials. The drug loss by sorption was investigated in different solutions and rationalized at an energy level. The combination of experiments and theoretical approaches proved to be effective for these sophisticated systems and processes forwhich various energy contributions are involved