Modeling Replenishment of Ultrathin Liquid Perfluoropolyether Z Films on Solid Surfaces Using Monte Carlo Simulation

M S Mayeed,T Kato

doi:10.1155/2014/104137

Abstract

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.

Highlights

The diffusion of molecules on surfaces is fundamental to phenomena such as heterogeneous catalysis, wetting, self-assembly, and nanofabrication [1]
From the Monte Carlo (MC) simulations the average radii of gyration of PFPE Z for molecular weights (MWs) of 3840, 2500, and 1700 gms/mol are 1.38, 1.10, and 0.91 nms, respectively
The work presented here is on the development of an MC simulation program, which generates average conformation and longer time dynamics of PFPE Z in the ultrathin liquid films on solid surfaces

Summary

Introduction

The diffusion of molecules on surfaces is fundamental to phenomena such as heterogeneous catalysis, wetting, self-assembly, and nanofabrication [1]. 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. The diffusion coefficient derived from the dispersive force is a monotonically decreasing function of film thickness [27]. This component of the diffusion coefficient can account for the rapid spreading front and asymmetry in the spreading profile [27, 28]

Methods

Results

Conclusion