Comparison of Linear and Branched Molecular Structures of Two Fluorocarbon Organosilane Surfactants for the Alteration of Sandstone Wettability

The aim of this work is to build a molecular dynamics model to represent the experimental evaluation of the wettability alteration of sandstone surfaces due to the action of partially fluorocarbonated organosilane surfactants with linear (perfluorodecyl) and branched (fluorocarbamate) chains using the contact angles of water and n-decane droplets as the evaluation parameters. The thickness obtained for a monolayer coating with each surfactant was ∼13 A, in excellent agreement with the experimental measurements of the thickness of a monolayer of fluorocarbonated surfactants in similar systems. The contact angles obtained with molecular dynamics simulations deviate, in most cases, by less than 3° with respect to experimental measurements. The phenomenological model reveals that for the coating with a monolayer, the fluorocarbonated chains of perfluorodecyl were mostly oriented away from the sandstone surface, while the branches of fluorocarbamate are distributed between being adsorbed on the surface and ori...