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°) 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 μmol/m2, the water contact angle on the surfactant-covered surface is properly reproduced (94°). 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°). 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.

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This work presents a stochastic procedure designed to formulate a discrete set of molecular structures that, as a whole, adjust properly to experimental asphaltene data. This algorithm incorporates the pentane effect concept and Clar's sextet rule to the formulation process. The set of viable structures was constructed based on probability distribution functions obtained from experimental information and an isomer database containing all plausible configurations for a given number of rings, avoiding high-energy structures. This procedure was applied to a collection of experimental data from the literature. Ten sets, consisting of 5000 structures each, were obtained. Each set was then optimized. For the most accurate representation, four molecules were sufficient to properly reproduce the experimental input. The asphaltene system obtained is consistent with the reported molecular weight, number of aromatic rings and heteroatom content. Molecular dynamic simulations showed that the asphaltene representation adequately reproduced asphaltene aggregation behavior in toluene and n-heptane. In toluene, a single three-molecule aggregate was observed, and the majority of asphaltene molecules remained in a monomeric state. In n-heptane, aggregates containing up to four molecules were observed; both porous and compact aggregates were found. The asphaltene molecular representation obtained, which allows researchers to avoid inappropriate torsions in the molecule, is able to reproduce interplanar distances between aromatic cores of 4 Å or less for the aggregation state, as supported by experimental results.