Coarse grained MD simulation of bulk and interfacial behavior of mixture of CTAB/SDS surfactants

This study involves simulating the process of inhibiting corrosion through the formation of micelles by surfactants and their deposition on iron (Fe) surfaces. The primary focus is on examining CTAB/SDS mixtures in aqueous solutions with different concentrations. Micelle properties, including size, shape, aggregation number, cluster size, and surfactant diffusion, were calculated and validated with experimental data. The coarse-grained Fe surface was modeled and validated against experimental water contact-angle data. Subsequently, the deposition of CTAB/SDS mixtures on the Fe surface and air-water interface was studied systematically. We found that the relative ratio of CTAB/SDS in the solution directly influences surfactant deposition behavior, which might impact the corrosion inhibition efficiency.

All the MD simulations were performed using the GROMACS software with MARTINI2 force field and Martini polar water. The molecules are packed using PACKMOL software. Both NVT and NPT simulations are caried out at temperature and pressure of 303 K and 1 bar respectively, with a nonbonded interaction cut-off (r_cut) of 1.1 nm. The LJ potential was shifted from 0.9 nm to r_cut, while the electrostatic potential was shifted from 0.0 nm to r_cut. For electrostatics, reaction-field coulomb type is used, relative dielectric constant (epsilon-r) and the reaction field dielectric constant (epsilon-rf) are equal to 2.5 and infinity respectively. The dielectric constant below r_cut is epsilon-r, and beyond the cut-off is epsilon-rf. Coulomb-modifier used as potential-shift which leads to shift in the coulomb potential by a constant such that it is zero at the r_cut. This makes the potential of the integral of the force . The neighbor list was updated every 10 steps, employing a neighbor list cut-off equal to r_cut. Using a polar water model, we used a constant time step of 0.02 ps throughout the simulation. The used epsilon-r = 2.5, is recommended for polar water.