Molecular Dynamics Methodology for the Evaluation of the Chemical Alteration of Wettability with Organosilanes

In this work, a methodology to evaluate and represent the wettability alteration phenomenon caused by the action of organosilane surfactants using molecular dynamics simulations is presented. This methodology is based on four major steps: (i) the tuning of the energetic parameter of the surface potential to achieve an adequate description of the initial wettability state, (ii) the representation of the adsorption/reaction of the surfactant on the surface, (iii) the evaluation of the coverage degree of the surface and the alteration of the wettability promoted by the surfactant, and (iv) the prediction of the alteration of the wettability of the surface in contact with a hydrocarbon phase. To evaluate this methodology, a case study is presented, in which the variation of the contact angle of water drops on a glass surface by the action of the surfactant C8F17CH2CH2Si-[O-CH2CH3](3) is determined. The methodology results in an adequate reproduction of the contact angle of water drops on untreated surfaces (24.7 degrees) and enables the calculation of the adsorption energy of individual molecules on the surface (44.93 kJ/mol). Additionally, it was found that, with a surfactant surface concentration of 0.76 mu mol/m(2), the water contact angle on the surfactant-covered surface is properly reproduced (94 degrees). This methodology is sufficiently robust to extend the results obtained for the water system to the evaluation of the contact angle of a system, where n-heptane is the fluid phase (60.7 degrees). All of these results are in excellent agreement with experimental findings. These procedures have shown that the presence of surfactant molecules reduces the affinity of the fluid phase (water or n-heptane) with the surface, increasing the compactness and height of the resulting drop.