Here we report a larger-scale atomic-level molecular dynamics (MD) simulation for the self-assembly of sodium dodecyl sulfate (SDS) surfactant on single-walled carbon nanotube (SWNT) surfaces and the interaction between supramolecular SDS/SWNT aggregates. We make an effort to address several important problems in regard to carbon nanotube dispersion/separation. At first, the simulation provides comprehensive direct evidence for SDS self-assembly structures on carbon nanotube surfaces, which can help to clarify the relevant debate over the exact adsorption structure. We also, for the first time, simulated the potential of mean force (PMF) between two SWNTs embedded in SDS surfactant micelles. A novel unified PMF approach has been applied to reveal various cooperative interactions between the SDS/SWNT aggregates, which is different from the previous electrostatic repulsion explanation. The unique role of sodium ions revealed here provides a new microscopic understanding of the recent experiments in the electrolyte tuning of the interfacial forces on the selective fractionation of SDS surrounding SWNTs.

The design of high glass transition temperature (T g ) thermoset materials with considerable reparability is a challenge. In this study, a novel biobased triepoxy (TEP) is synthesized and cured with an anhydride monomer in the presence of zinc catalyst. The cured TEP exhibits a high T g (187 °C) and comparable strength and modulus to the cured bisphenol A epoxy. By adopting the vitrimer chemistry, the cross-linked polymer materials are imparted significant stress relaxation and reparability via dynamic transesterification. It is noted that the reparability is closely related to the repairing temperature, external force, catalyst content, and the magnitude of rubbery modulus of the sample. The width of the crack from the cured TEP can be efficiently repaired within 10 min. This work introduces the first high-T g biobased epoxy material with excellent reparability and provides a valuable method for the design of high-T g self-healing materials suitable for high service temperature.

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The icosahedral core-shell structures, with an icosahedral Pt core covered with an icosahedral Au shell, were taken as the initial configurations in this simulation. To compare with Pt-Au nanoparticles, the pure metals (Pt and Au) with the same particle size were also studied here. The results demonstrate that the coreshell bimetallic nanoparticles exhibit a two-stage melting, and their melting points rise as the concentration of Pt increases. A detailed analysis of the melting processes indicates that the premelting nature of the pure metal nanoparticles does not purely correspond to the surface premelting, but all atoms even including the center atom contribute to the premelting behavior through interlayer diffusion. For all the core-shell structures investigated, however, the premelting only occurs at the Au shells, and the Pt cores always keep a typical solid state before the homogeneous melting transition. Furthermore, the extent of the premelting of the Au shell is suppressed as the size of Pt core increases. The difference in the melting mechanism can be explained on the basis of the distribution of potential energy between the Pt and Au atoms in the pure metal and coreshell bimetallic nanoparticles.

Self-assembly of amphiphilic molecules on the surfaces of nanoscale materials has an important application in a variety of nanotechnology. Here, we report a coarse-grained molecular dynamics simulation on the structure and morphology of the nonionic surfactant, n-alkyl poly(ethylene oxide) (PEO), adsorbed on planar graphene nanostructures. The effects of concentration, surfactant structure, and size of graphene sheet are explored. Because of the finite dimension effect, various morphological hemimicelles can be formed on nanoscale graphene surfaces, which is somewhat different from the self-assembly structures on infinite carbon surfaces. The aggregate morphology is highly dependent on the concentration, the chain lengths, and the size of graphene nanosheets. For the nonionic surfactant, the PEO headgroups show strong dispersion interaction with the carbon surface, leading to a side edge adsorption behavior. This simulation provides insight into the supramolecular self-assembly nanostructures and the adsorption mechanism for the nonionic surfactants aggregated on graphene nanostructures, which could be exploited to guide fabrication of graphene-based nanocomposites.

We used molecular dynamics simulation to demonstrate the microscopic wetting behavior of two solid model surfaces for the first time. Hydrophilic and hydrophobic features were modeled in a dense CO 2 fluid environment under various densities. The water droplet loses contact with the surface under the influence of higher density CO 2 fluids on the hydrophobic surface. For the hydrophilic surface, no separation between the water droplet and the surface was observed. However, the contact angle of the water droplet on the hydrophilic surface was found to increase with the fluid density. The effect of dense CO 2 fluid on the surface wettability can be interpreted in terms of enhanced interactions from the surrounding CO 2 molecules. wettability, solid surface, molecular simulation, hydrophilic, hydrophobic, supercritical CO 2 Citation:Liu S Y, Yang X N, Qin Y. Molecular dynamics simulation of wetting behavior at CO 2 /water/solid interfaces.

Molecular dynamics simulation was conducted to study ethanol−water mixtures and the corresponding pure species, confined within slit-shaped graphene nanopores. Extensive structural and dynamical properties of the confined fluids, including hydrogen-bonding behavior, were investigated. The effects of pore width and mixture composition on the confined behavior were illustrated. It is observed that a layered structure is formed within the confined spaces and the ethanol− water mixtures show segregation at larger pores, with ethanol molecules preferentially adsorbing on graphene surfaces. This microphase demixing behavior stems from the competitive effect of the solid−fluid and fluid−fluid interactions. Moreover, miscellaneous diffusion mechanisms have been revealed for the hydrogen-bonding mixtures within the graphene pores. In the mixtures, water and ethanol generally display analogous diffusion mechanism due to ethanol−water association, converting from short-time subdiffusion to long-time Fickian diffusion in the larger nanopores. In the smaller pore (7 Å), both ethanol and water show a suppressed single-file diffusion behavior at the initial time and then display subdiffusion or single-file diffusion behavior. The complex diffusion behavior of ethanol−water mixtures can be described by the collaborating effects of pore confinement and enhanced interaction in the hydrogen-bonding mixtures.