A study of perfluro polymeric nanoscale systems

Perfluoro polymeric systems, which exhibit chemical/thermal stability and low cohesive energies in liquids, have been developed by the modification of molecular structures. Perfluoropolyether (PFPE) lubricant film in the hard disk drive (HDD) system utilizes these advantages by modifying the functional groups on the linear polymer chain, which give physical stability under the harsh environment of the rapidly rotating disk.;The equilibrium molecular dynamics (EMD) using the coarse-grained, bead-spring model was performed to investigate the nanostructure of PFPE films via endbead density profile and the radius of gyration. Their dependences on the molecular structure, endgroup functionality, blend ratio, and polydispersity effect were also examined. The dynamics of PFPE nanofilms, including self-diffusion and spreading phenomenon, was examined via the above EMD simulations as well, where their dependences on the molecular structure, endgroup functionality, blend ratio, and polydispersity were investigated. Our EMD simulations give a qualitative agreement with our previous observations.;Viscoelastic property is another focus of PFPE dynamics in this dissertation for the tribological issues during the intermittent contact between head and disk. Using non-equilibrium molecular dynamics (NEMD), we studied the oscillatory shear of PFPE system, including the contributions from blend ratio and temperature. Dynamic moduli are calculated and examined as functions of molecular structure, blend ratio, and temperature. Cole-Cole plots were constructed to analyze the relationship between microstructure and viscoelastic response of PFPEs.;A multi-scale simulation is desirable for advanced HDI integration. We have implemented LBM with the Langmuir slip model based on the theory of the adsorption phenomena which can predict the slip velocity at the wall with a number of advantages. To verify the accuracy of our LBM model, we calculated simple two-dimensional benchmark flows, channel and cavity flows, which are the key elements of air bearing simulation. The numerical experiment performed in this study can be utilized directly to handle the system incorporating the flow channel between the slider and the disk and the complex cavity underneath the slider.;The work in this dissertation focuses on the study of perfluoro polymeric nanoscale systems as well as the development of a multi-scale simulation tool capable of the system design integration. The static and dynamic properties of PFPE nanofilms were examined via both experimental and theoretical methodologies. Blending effect in nanoscale on PFPE properties was first incorporated by using binary mixture of different type PFPEs. The spontaneous spreading of PFPE nanofilms was measured via the optical surface analyzer. Using the Einstein relationship and the moving distance of spreading edge, the diffusion coefficient of PFPE films was estimated to illustrate their dependences on the PFPE nanostructure as well as the film thickness. By considering the film coating mechanism arguments, the thickness and structure of single component and binary mixture PFPE films were analyzed as a function of molecular structure and blend ratio.;Relationship between proton transfer and microstructure in PEM are critical issues in fuel cell performance since the microstructure varies depending on the water uptake. Via EMD simulation modified by Coulombic interaction, we examined PEM with the water uptake variation. Fuel transfer distribution on catalyst layer through gas diffusion layer (GDL) as well as multi-phase fuel flow effects in porous media are important to the fuel cell performance and its durability. Using LBM modified by Brickman-Forchheimer-extended Darcy equations, we examined the flow in the porous media and compared the solution to the analytical method and complex geometry approach, which can be combined to contribute the multi-physics analysis of the entire part of GDL.;Our long-term goal is to find optimized conditions for the systems ( i.e., HDI and DMFC) via a novel middle-out integration framework for multiscale-modeling, by passing information from an intermediate space/time scale to top level (i.e., macroscale) and bottom level ( i.e., quantum mechanical scale). The middle level simulation methods (i.e., MD and LBM) and the examined properties will be incorporated to the bottom level approach with atomic scale and ab-initio MD. LBM will be applied to the macroscopic HDI and DMFC systems by utilizing the nanoscale parameters from MD calculation as the top level approach. (Abstract shortened by UMI.)...