Structure and dynamics of confined flexible and unentangled polymer melts in highly adsorbing cylindrical pores

Abstract

Coarse-grained molecular dynamics simulations are used to probe the dynamic phenomena of polymer melts confined in nanopores. The simulation results show excellent agreement in the values obtained for the normalized coherent single chain dynamic structure factor, S(Q,Δt)/S(Q,0). In the bulk configuration, both simulations and experiments confirm that the polymer chains follow Rouse dynamics. However, under confinement, the Rouse modes are suppressed. The mean-square radius of gyration ⟨R(g)(2)⟩ and the average relative shape anisotropy ⟨κ(2)⟩ of the conformation of the polymer chains indicate a pancake-like conformation near the surface and a bulk-like conformation near the center of the confining cylinder. This was confirmed by direct visualization of the polymer chains. Despite the presence of these different conformations, the average form factor of the confined chains still follows the Debye function which describes linear ideal chains, which is in agreement with small angle neutron scattering experiments (SANS). The experimentally inaccessible mean-square displacement (MSD) of the confined monomers, calculated as a function of radial distance from the pore surface, was obtained in the simulations. The simulations show a gradual increase of the MSD from the adsorbed, but mobile layer, to that similar to the bulk far away from the surface.

Chain conformation of polymer melts with associating groups

“…The simulations were carried out using the LAMMPS [29] software package with GPU acceleration [30] at the Oak Ridge Leadership Computing Facility. The initial equilibrated configuration of the polymer melt, composed of Lennard-Jones bead having a diameter σ, was obtained from a previous simulation [31]. There are m c =1417 chains inside a cubic box with volume s = L 38.793 3 3 and number density, ρ=0.85σ −3 .…”

Description of poly(ethylenepropylene) confined in nanopores by a modified Rouse model

“…It is not clear why an agreement with the DK model is found in Ref. 18 even with a very low confinement parameter d = 5 Å (converted to the units here) corresponding to R cyl = 15 Å which is nearly an order of magnitude lower than the actual pore size. One possible explanation would be that the strong interaction with the walls (intended by the experimenters) superimposes the "pure" confinement effect.…”

“…From the calculations above, it is clear that to see an effect of the internal dynamics of a polymer chain a ratio R confinement /R e in the order of 0.2 or less is necessary. It is surprising that in a study 18 partially based on NSE data 15 an agreement with the DK model was found. In the NSE experiment, oriented pores with a radius of 130 Å were used and a polymer with R e = 85 Å.…”

“…But it also has to be noted that in the interpretation of Ref. 18 the isotropically averaged formula (16) was used while the system used in the experiment 15 had oriented pores.…”

Effects of spherical confinement and backbone stiffness on flexible polymer jamming

“…On the other hand, few studies of polymer packings in confined geometries address mechanical properties. Previous investigations have largely focused on chain conformation within the packing [43][44][45][46][47] and topological ordering of segments [48]. Long polymers with specified bondbond angles typically coil during packaging in SC to minimize bending energy [49][50][51][52][53][54][55] and thus exhibit boundaryinduced layering [53].…”