Tetracosane (C$_{24}$H$_{50})$ trilayers physisorbed onto the basal plane of graphite: perpendicular patches*

Results of explicit - hydrogen Molecular Dynamics computer simulations of tetracosane (C$_{24}$H$_{50}$, or C24) trilayers deposited on a graphite substrate in the temperature range 100 K $\le \quad T \quad \le $ 550 K are presented. The third layer is perpendicular to the alkane underlayers as well as to the graphite substrate. Diffusion thakes place predominantly at the bottom of the patch through a ratcheting mechanism that is coupled to dihedral (torsional) defects. In the low - temperature solid the patch exhibits a dome - like shape and, with increasing temperature rolling of the interior molecules couple to the collapse of the patch into a droplet - like shape and, ultimately a liquid C24 patch atop the graphite layer results. Structural, thermodynamic and bond - orientational distributions and parameters are utilized in understanding the temperature evolution of the system and results are compared to those under the United Atom approximation.