Atomistic Simulation of Poly(dimethylsiloxane):  Force Field Development, Structure, and Thermodynamic Properties of Polymer Melt and Solubility of n-Alkanes, n-Perfluoroalkanes, and Noble and Light Gases

Abstract

Poly(dimethylsiloxane) (PDMS) is a widely used polymer for a number of industrial applications. In order that PDMS is selected for a specific application, accurate knowledge of its physical properties is necessary. Physical properties can be either measured or calculated based on reliable suitable methods. Molecular simulation using realistic models is a powerful tool for the elucidation of microscopic structure of polymers and the subsequent estimation of macroscopic physical properties. In this work, a force field is developed for the prediction of thermodynamic and structure properties of PDMS melts. Force field development was based on existing force fields for PDMS together with fitting to experimental thermodynamic data at ambient pressure. Extensive NPT molecular dynamics (MD) simulations were performed at different temperature and pressure values. In all cases, good agreement was obtained between literature experimental data and model predictions for the melt density. Calculations are reported also for the solubility parameter of the polymer melt at different temperatures. Furthermore, radial distribution functions for the intra-and intermolecular interactions are presented and shown to be in good agreement with previous literature work. The new force field is used subsequently for the calculation of solubility of 17 different compounds in PDMS using the Widom test particle insertion method. The solubility of n-alkanes from methane to n-hexane at 300 and 450 K and different pressures was calculated. In addition, solubility calculations for n-perfluoroalkanes at 300 and 450 K and for noble and light gases at 300, 375, and 450 K and ambient pressure were performed. Model predictions are in very good agreement with experimental data, in all cases. The infinite dilution solubility coefficient is shown to increase with temperature for very light gases and decrease for the heavier ones.

Solubility of gases and solvents in silicon polymers: molecular simulation and equation of state modeling

“…In the UA representation, hydrogen atoms in the methyl and methylene groups are not accounted explicitly, thus reducing the number of "atoms" significantly. Details on the force field development and parameters for the various terms and UAs can be found in refs [11][12][13]. A brief description is given here only.…”

“…The initial configurations were obtained using the Cerius 2 software package of Accelrys Inc. and relaxed with molecular mechanics before MD [11,13]. MD simulations were performed with an integration time step of 0.5 fs to ensure system stability over time.…”

“…In each run, 5,000 configurations were recorded at equal time intervals and they were used for the calculation of the thermodynamic and of the structural properties of polymer melt reported in refs. [12,13]. The chemical potential was calculated using the Widom's test particle insertion method [14].…”

“…Research in "Demokritos" has been directed towards the development of a force-field for silicon polymers able to provide accurate prediction of microscopic structure, thermodynamic and transport properties over a wide temperature and pressure range [11][12][13]. This force-field is tested here for the prediction of solubility of six n-alkanes, four n-perfluoroalkanes, five noble gases and two light gases in poly(dimethylsilamethylene) (PDMSM), poly(dimethylsilatri-methylene) (PDMSTM), their alternating poly(DMSM-alt-DMSTM) copolymer and poly(dimethylsiloxane) (PDMS).…”

The Free Energy of Solvation for N-Decane in Ethanol-Water Solutions

“…Recent molecular simulations and force field development have indicated that computational methods can offer significant insight into the behavior of surfaces [1], polyethoxy [2] and polysilicone [3] systems, hydrogen bonding [4], solvent-water interactions [5], and alkane properties [6]. Of particular interest are several studies which treat mixing thermodynamically [7], as well as those discussing the source of the hydrophobic effect [8].…”