Diffusion of low‐molecular‐weight permeants through semi‐crystalline polymers: combining molecular dynamics with semi‐empirical models

Abstract

A molecular dynamics‐based computational approach was used to study the diffusion of oxygen through a model semi‐crystalline polymer, namely linear low‐density polyethylene. The simulated molecules were validated by comparing the predicted properties with experimental values of available free volumes, on atomic scale, using positron annihilation lifetime spectroscopy and measured values of density. The semi‐crystalline polymer was considered as a composite network of a continuous amorphous phase and a dispersed crystalline phase. Based on this observation, the overall diffusion was simulated, including the diffusion through the crystalline phase, which has not been previously reported. A tight correlation was then achieved between experimental and simulated data by utilising several semi‐empirical and analytical models developed for composite materials. The proposed methodology in this work can be effectively used as a basis for designing polymer networks with controlled diffusion characteristics in a bottom‐up approach. © 2018 Society of Chemical Industry

Predicting trends in structural and physical properties of a model polymer with embedded natural fibers: Viability of molecular dynamics studies for a bottom up design

“…This technique employs a positronium, Ps (a bound state between a positron and an electron) to probe the void sites associated with free volume in condensed matter systems and can measure the average diameters of pores from 0.1 to 20 nm . The average lifetime of the positronium is measured with ORTEC spectrometers usingNa as the positron source. The exponential decay data obtained from the PALS measurement was fitted to three components with the characteristic lifetimes of τ 1 , τ 2 , and τ 3 .…”

“…MD simulations were carried out using the materials and process simulation (MAPS) Platform: Version 4.0.1, France, (2018) developed by Scienomics and run on the gstar high‐performance cluster (HPC) at Swinburne University of Technology. The development of the amorphous and crystalline simulation cells and the effective modeling of diffusion of oxygen through LLDPE were shown in our previous work . The AMBER force field was used to carry these MD simulations.…”

“…Therefore, MD methods are highly effective techniques for carrying bottom up design of composite materials . In our previous work, we utilized MD to visualize LLDPE as a composite system consisting of 100% crystalline dispersed phase and 100% amorphous continuous phase and used it to predict oxygen diffusion accurately as a function of temperature for a given polymer crystallinity . In this work, MD was used to simulate both semicrystalline PE and pine flour.…”

On the Use of Molecular Dynamics Simulations for Elucidating Fine Structural, Physico-Chemical and Thermomechanical Properties of Lignocellulosic Systems: Historical and Future Perspectives

“…The data from the final 5 ns of each simulation were analysed, once the system had reached equilibration. This methodology, where the initial non equilibrium simulation data is discarded and the final few ns post equilibrium is only taken into account, was utilised for estimating diffusion coefficients in semicrystalline polymer-lignocelluosic composites by Prasad et al [32,33]. In [32,33], semi empirical multiphase modelling was used to further increase the accuracy of the simulated data combined with the use of the PCFF (Polymer Consistent Force Field) for MD simulations.…”

“…This methodology, where the initial non equilibrium simulation data is discarded and the final few ns post equilibrium is only taken into account, was utilised for estimating diffusion coefficients in semicrystalline polymer-lignocelluosic composites by Prasad et al [32,33]. In [32,33], semi empirical multiphase modelling was used to further increase the accuracy of the simulated data combined with the use of the PCFF (Polymer Consistent Force Field) for MD simulations. O'Neill et al [30] in Figure 9 correlated the elastic intensity 'S el (T)' at a temperature 'T' for the neutron scattering wave vector 'Q' to the mean squared displacement/MSD (∆r 2 ) of the bound water molecules using the Gaussian approximation given by Equation (18).…”