An Atomistic Investigation of Solubility and Diffusion of Ethylene in Polyethylene Confined in a Pore

Molecular Dynamics Simulation of a Polymer Melt/Solid Interface: Local Dynamics and Chain Mobility in a Thin Film of Polyethylene Melt Adsorbed on Graphite

“…Unfortunately, for confined systems, the Einstein limit is never reached; in this case, the new approach provides an excellent alternative method to get at the transport properties of the adsorbed melt. 55 According to the proposed strategy, the diffusion of adsorbed carbon atoms in the polymer film obeys an unsteady 1-d diffusion equation of the following form: 26 In eq 9, C denotes the concentration of tagged molecules at time t and position z in the external field or potential U(z) caused by the rest of segments and the confining boundary, and D their effective diffusion or transport coefficient. Equation 9provides a macroscopic description to the dynamics of the diffusing Brownian particles and dates back to the pioneering works of Einstein on Brownian motion.…”

“…Analyzing MD trajectories of multichain melt systems in confined geometries such as the adsorbed PE films studied here in order to extract their long-time diffusive properties presents a number of difficulties. These are related to (a) the inherent limitations of the MD technique in vigorously sampling the configuration space of highly connected dense systems, − (b) the fact that segments and chains diffuse in restricted volume and therefore cannot achieve the Einstein limit for diffusion due to the presence of boundaries, and (c) the anisotropic and inhomogeneous character of the motion at the interface . Even if we are interested only in the diffusion coefficient perpendicular to the confining boundary, the diffusive motion depends strongly on mass location across the film, which cannot be neglected in the analysis.…”

“…For bulk polymers, of course, both methods give identical results, as will also be demonstrated below. Unfortunately, for confined systems, the Einstein limit is never reached; in this case, the new approach provides an excellent alternative method to get at the transport properties of the adsorbed melt …”

How Many Monomer Repeat Units are Necessary for Reliable Molecular Dynamics Simulation?

“…In the molecular dynamics of polymers, each monomer unit is modelled as a lumped mass, like a bead, and their interaction is described by a potential function. The Lennard-Jones type of potential has been frequently used for polymers 1,5,6,8 . The Lennard-Jones potential features a short-range repulsive potential, together with a long-range attractive potential.…”

“…Therefore, mechanical properties of polymers have been studied intensively. Recently, molecular dynamics has been applied to characterize the behaviour of polymers or their composites [1][2][3][4][5][6][7][8][9][10][11] . While ab initio molecular dynamics is more accurate, it is limited to a very small number of atoms.…”