Nanostructure and Dynamics of Humidified Nafion/Graphene-Oxide Composites via Molecular Dynamics Simulations

Abstract

In this work, we elucidated the nanostructure and dynamics of Nafion-doped graphene-oxide (GO) systems from molecular dynamics simulations at varying hydration levels and temperature. It was found that the presence of GO resulted in the formation of Nafion layers along a direction normal to the GO surface. Chain conformations in the Nafion layers close to the GO interface were characterized by a backbone preferably oriented parallel to the GO plane, whereas the size of the formed nanochannels was found to be commensurate to the average dimensions of the Nafion side chains. The mechanism of water cluster growth was found to change drastically upon introduction of Nafion chains, although addition of GO in the membranes did not impart further measurable changes at the examined temperatures. Hydronium ions were found to adsorb partly onto the GO surface, whereas the pertinent adsorption/desorption rate increased significantly with hydration. Translational dynamics of water molecules was much slower close to the GO surface compared to that at distances far from GO. In the temperature range examined, the dynamics of the effectively confined water molecules was found to follow an Arrhenius-like dependence. Water retention at the Nafion/GO interface appears only at high hydration levels of Nafion.

Bound Layer Polymer Behavior on Graphene and Graphene Oxide Nanosheets

“…In the case of GP, conformational transitions are present, manifesting a dynamic behavior known also as rippling or wrinkling. − In addition, GO was found to exhibit a higher tendency for curvature compared to GP. , The distribution of functional groups’ charges may lead to such long-lasting curvature effects. ,, …”

“…For this purpose, a series of layers parallel to the graphene flake are defined. The coordination system for the layer analysis, at each time ( t ), is based on the eigenvectors of the radius of gyration ( R g ) tensor of the nanosheet . The gyration tensor ( S ij ) is defined based on the distance of each atom ( k ) from the Center of Mass (CM) of the molecule with mass m tot , weighted with the mass of each atom ( m k ), as In this analysis, only moieties (polymer atoms or CMs of chains) whose projection in the x , y axes lie within the central 80% of the average dimensions of the nanosheet in these directions are taken into account.…”

“…Usually, mixing of the one-atom-thick graphene flakes with bulk polymer leads to an increase of the glass transition temperature ( T g ), , although cases of a reduction in the T g have also been reported . Semicrystallization is also affected since GP-based sheets can promote heterogeneous crystallization, resulting in an increase in the crystallization temperature ( T c ). ,,, Based on such effects, tuning of mechanical, thermal, electrical, and permeability properties can be performed ,,− to meet specific needs in materials technology.…”

Molecular dynamics simulations of hyperbranched poly(ethylene imine)–graphene oxide nanocomposites as dye adsorbents for water purification

“…To examine a possible orientational ordering of the GO and MB molecules, we calculated the orientational order parameter defined through the second-order Legendre polynomial 77 ,…”

Liposome-Templated Indocyanine Green J- Aggregates for In Vivo Near Infrared Imaging and Stable Photothermal Heating

“…To further elaborate on the characteristics of the formed ICG aggregates, we performed a cluster formation analysis as shown in Figure S8 (Supporting Information) [35]. The minimum number of molecules considered to form a cluster was taken to be 2; the maximum separation between two ICG molecules for the detection of the cluster was taken to be 17 Å (in order to include both, first and second neighbors) for all systems; this was inferred from Figure S7 (Supporting Information).…”