Applying the reptation algorithm to a simplified perfluoropolyether Z off-lattice polymer model an NVT Monte Carlo simulation has been performed. Bulk condition has been simulated first to compare the average radius of gyration with the bulk experimental results. Then the model is tested for its ability to describe dynamics. After this, it is applied to observe the replenishment of nanoscale ultrathin liquid films on solid flat carbon surfaces. The replenishment rate for trenches of different widths (8, 12, and 16？nms for several molecular weights) between two films of perfluoropolyether Z from the Monte Carlo simulation is compared to that obtained solving the diffusion equation using the experimental diffusion coefficients of Ma et al. (1999), with room condition in both cases. Replenishment per Monte Carlo cycle seems to be a constant multiple of replenishment per second at least up to 2？nm replenished film thickness of the trenches over the carbon surface. Considerable good agreement has been achieved here between the experimental results and the dynamics of molecules using reptation moves in the ultrathin liquid films on solid surfaces. 1. Introduction The diffusion of molecules on surfaces is fundamental to phenomena such as heterogeneous catalysis, wetting, self-assembly, and nanofabrication [1]. Recent studies have focused on the behavior of mechanical properties [2, 3], glass transitions [4–11], diffusion in thin films [12–15] and colloidal particles [16, 17], and phase separation [18–20]. Obtaining detailed microscopic-level information on the interfacial structure and mobility of a polymer, and establishing links between this information and overall thermodynamic and mechanical performance, could greatly aid in the improvement of existing polymeric coatings and the development of new ones. Spreading of molecularly thin films is key to many physically and industrially important processes that rely upon thin film adhesion and lubrication [21–23]. One specific industrial application is the use of submonolayer perfluoropolyether (PFPE) films to lubricate magnetic recording media (computer hard disks) within magnetic storage devices (hard disk drives). Reflow of the PFPE lubricant on the hard disk is vital to the reliability of disk drive [24]. The importance of lubricant mobility in hard disk drives motivated the initial studies investigating the spreading of PFPEs on silicon surfaces. These studies were done on PFPE Z with nonpolar end groups [25] and the spreading profile exhibits a smooth, monotonically increasing thickness profile. A rapid
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