No abstract

No abstract

No abstract

Desorption of decane molecules from a graphite surface using sodium dodecyl sulfate surfactants (SDS) with and without the presence of electric fields has been investigated. Different constant electric field strengths, E Z = ±1, ±2, ±3, ±4, ±5, and ±6 V/nm were applied perpendicular to the interface and removal of decane molecules was analyzed. It is observed that positive fields keep alkanes next to the surface whereas negative fields help desorption of the hydrocarbon chains. Moreover, weak negative electric fields do not have much influence on the SDS molecules, whereas strong electric fields have significant effects on the surfactant headgroups and consequently on the decane molecules attached to the SDS tails. Simulations were carried out for different water models, SPC/E, TIP4P/ϵ, and a polarizable one as well as a united and all-atom models for the surfactant molecules, and no significant differences were found in the results. By analysis of different properties, such as the radius of gyration and diffusion coefficients, it is noted that the complete alkane desorption started at electric field values around E Z ≈ −3 and −4 V/nm.

The applicability of the three steps systematic parametrization procedure (3SSPP) to develop a force field for primary amines was evaluated in the present work. Previous simulations of primary amines show that current force fields (FF) can underestimate some experimental values under room conditions. Therefore, we propose a new set of parameters, for an united atom (UA) model, that can be used for short and long amines which predict correctly thermodynamic and dynamical properties. Following the 3SSPP methodology, the partial charges are chosen to match the experimental dielectric constant whereas the Lennard-Jones (LJ) parameters, ε and σ, are fitted to reproduce the surface tension at the vapor-liquid interface and the liquid density, respectively. Simulations were initially conducted for the propylamine molecule by introducing three different types of carbon atoms, Cα and Cβ, with electric charges, and Cn, without charge. Then, modifying the charges of the carbons and using the transferable LJ parameters, the new set of constants for long amines were found. The results show good agreement for the experimental dielectric constant and mass density with a percentage error less than 1% surface tension the error is up to 4% ethylamine, the new charges were obtained from a fitting function calculated from the long amines results. For these molecules, the values of the dielectric constant and the surface tension present errors of the order of 10% with the experimental data. Miscibility of the amines was also tested with the new parameters and the results show reasonable agreement with experiments.