(626d) Molecular Dynamics Investigation on Branched Alkane-Air/Water Interfaces.

Alkanes are prominent components of most petroleum crudes, and the branched alkanes population is significant in asphalt. Alkanes have a wide applications in water flooding and surfactant flooding in enhanced crude oil recovery, thus working on the interfaces between alkane with air/water is important. CHARMM forcefield and NAMD simulations have been used to examine the properties of branched alkanes in the air and water interface systems. A total of eight branched alkanes (2-methyloctane and some isomers of C11 and C12) have been focused on at four different temperatures (300K, 358K, 400K, 443K). Periodic boundary conditions were defined. The surface tension, diffusion coefficient and radial distribution functions of alkanes in the bulk and on the interface were calculated. To determine the surface tension correctly, the density profiles were also calculated and compared with the available experimental data. As the temperature increases, surface tension and density decrease while diffusion coefficient increases. The alkane-water interfaces always have a higher surface tension than the corresponding alkane-air interfaces. Branched alkanes always diffuse faster on the air/water interfaces than in the bulk. At temperatures greater than the boiling points of alkanes, the density profile shows uneven behavior because of the liquid-vapor phase transition. The simulation predictions are found to be consistent with the available experimental data. The findings in this work can supply insight in molecular level on the warm-mix asphalt technology.