(400f) Dynamics of Confined Flexible and Unentangled Polymer Melts in Highly Adsorbing Cylindrical Pores

Authors: 
Carrillo, J. M., Oak Ridge National Laboratory
Sumpter, B. G., Oak Ridge National Laboratory

We performed coarse-grained molecular dynamics simulations to study the effect of the confinement of flexible and unentangled polymer chains in cylindrical pores. The results are compared with the recent neutron spin echo (NSE) experiments by Krutyeva and co-workers (Phys. Rev. Lett. 2013, 110, 108303), where anodized aluminum oxide (AAO) pores were infiltrated with polydimethyl-siloxane (PDMS) chains. The NSE experiments were designed to probe the interphase layer, which is hypothesized to have polymer chain dynamic properties between those of a glassy layer and the bulk. There is excellent agreement in the values obtained for the normalized coherent single chain dynamic structure factor, S(Qt)/S(Q,0),  between experiments and simulations. The experimentally inaccessible mean squared displacement (MSD) of the confined monomers, calculated as a function of radial distance from the pore surface was obtained in the simulations and show a gradual increase of the MSD from the adsorbed but mobile layer to that similar to the bulk. This is akin to the hypothesized interphase layer. Additionally, the simulations provide information about the static polymer chain properties such as the mean-squared radius of gyration, <Rg2>  and the average shape anisotropy, <κ2> . These two properties indicate that the chains form a pancake-like conformation near the surface and a bulk-like conformation near the center of the confining cylinder. Direct visualization of the polymers in the simulation confirm the pancake-like conformation of the adsorbed chains and the presence of trains, loops and tails in the region between the adsorbed chains and the chains not in contact with the surface. 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 and is in agreement with small angle neutron scattering (SANS) experiments.
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