Sistan and Baluchistan
Department of Chemistry
Sistan and Baluchistan
Sistan and Baluchistan
Iran University of Science & Technology
B3LYP and MP2 methods with the most popular basis set, 6-311++G(d,p) are applied to optimize the equilibrium conformers of 4-amino-3-pentene-2-thial. Furthermore, to have more reliable energies, the total electron energies of all forms are recomputed at the CBS-4M level of theory. A theoretical investigation of the equilibrium conformers clearly shows that various intramolecular hydrogen bonds (IHBs) such as N–H⋯S, S–H⋯N, S–H⋯π, C–H⋯N, and C–H⋯S are the most effective factors in the conformational preference of thialamine, thiolimine, and thialimine groups. Hence, the IHB strengths are evaluated in various resonance-assisted hydrogen bond systems by geometrical factors, topological parameters, and charge transfers corresponding to orbital interactions. Also, the solvent effect on the IHB strength is considered using Tomasi′s PCM. Our results in the gas phase reveal that the thialamine group has extra stability with respect to thiolimine and thialimine ones. The population analyses of all the possible conformers by the NBO method predict that the origin of this tautomeric preference is mainly due to more significant π electron delocalization in the framework of thialamine forms, especially πC=C → C=S π * and Lp(N) → C=C π * charge transfers. Moreover, the excited state properties of IHBs in these systems are investigated theoretically using the time-dependent DFT method.
Graphene nanosheets are unique materials with distinctive mechanical, thermal, optical and electrical properties. Therefore, they have the potential to be used in various fields [1, 2]. However, these applications rely on large-scale production or controllable synthesis of individual graphene nanosheets with high quality. Unfortunately, the van der Waals attraction interactions between the graphene nanosheets and their tendency to aggregate together make them hard to disperse and separate. This has limited the commercial use of these substance. One of graphene preparation methods is noncovalent functionalization of graphene nanosheets with the surfactants to produce stable aqueous suspensions of graphene nanosheets .In the present study, we use molecular dynamics simulations to investigate the surface adsorption of surfactants on the surface of graphene nanosheets.The GROMACS software package version 4.6 was used to perform molecular dynamics simulations .The simulations showed that the random adsorption model first changes to the monolayer model and then the hemispherical model with an increased surfactant concentration. The simulation snapshots showed that graphene nanosheets with DS-/CTA+ ions were coated with negative/positive charges.The ζ-potential about surfactant mixture-graphene assemblies was estimated using the results of MD simulation and Poisson\\\\\\\\\\\\\\\'s theory, and the results conformed to the experimental results favorably.
The insolubility of graphene nanosheets in aqueous media has been a limitation for the practical applications of this unique material [1, 2]. The non-covalent functionalization of graphene with surfactants is an effective procedure for preparation of stable graphene dispersions . Physical adsorption of surfactants onto graphene surfaces is a significant stage in the dispersion of graphene nanosheets in the aqueous environment.To quantify the interactions between two parallel graphene sheets coated with surfactant mixture, the PMF between them was calculated as a function of the intersheet separation using molecular dynamics simulations (Figure 1).All simulations were performed in GROMACS 4.6 software package (GROningen Machine for Chemical Simulations), and the OPLS-AA (All-Atom Optimized Molecular Potential for Liquid Simulation) force field was utilized to model graphene nanosheets and surfactant mixture. The results showed thatincreasing surfactant surface coverage would lead to an enhanced repulsive barrier of PMF.This repulsive barrier prevents the two dispersed sheets of graphene approach each other and inhibits their re-aggregation.
Because of two-dimensional structure, large surface area and unique mechanical, thermal, optical and electrical properties of graphene, it has attracted much attention for promising applications, such as in energy, composites, biotechnology and electronics . However, these applications rely on the mass production of high-quality and low-cost graphene. Owing to the hydrophobic nature of graphene nanosheets, their non-covalent functionalization with surfactants is an effective method for the production of graphene stable aqueous suspensions . Computer simulation has been a powerful tool for gathering information at molecular-level about the process of adsorption and assembly of different molecules on nanomaterials . In this study, large-scale and all-atomistic molecular dynamic simulations were used to study the effect of mixing two surfactants on micelle assemblies structure formed on graphene. For examination of the structural assemblies’ characteristics formed from surfactants on graphene, the density profiles of the head and tail groups of surfactant were plotted as a function of the z distance perpendicular to graphene (Fig. 1). The simulations showed thatthe random adsorption model first changes to the monolayer model and then the hemispherical model with an increased surfactant concentration.