Molecular dynamics simulations of dotriacontane films supported on a SiO$_{2}$ surface

Dotriacontane (C$_{32}$H$_{66}$, C32) films supported on SiO$_{2}$ surfaces were studied using very high-resolution ellipsometry, atomic force microscopy (AFM) and x-ray reflectivity techniques. For almost complete layers a model was proposed [1] in which the C32/SiO$_{2}$ interfacial region is characterized by a parallel bilayer and perpendicular layers on top. Recent AFM measurements performed on samples forming sea-weed like structures, showed that for these particular perpendicular ``fractal like'' layers the heights are lower than the all-trans length of dotriacontane (42.5 {\AA}). To gain insights on the internal molecular ordering and layering of C32 supported on SiO$_{2}$ surfaces, we used all-atom molecular dynamics to simulate C32 films at different temperatures. Our results confirm the presence of the parallel bilayer suggesting the existence of a mixed layer on top, formed by molecules with both parallel and perpendicular segments. These findings suggest a different molecular architecture for sea-weed like structures of dotriacontane supported on SiO$_{2}$.\\[4pt] [1] H. Mo et al., Chem. Phys. Lett. \textbf{377}, 99-105~ (2003); U. G. Volkmann, et al., J. Chem. Phys. \textbf{116}, 2107 (2002).