Susumu Ogata

Quantification of the Surface Morphology of Lubricant Films With Polar End Groups Using Molecular Dynamics Simulation: Periodic Changes in Morphology Depending on Film Thickness

Using a coarse-grained molecular dynamics simulation based on the bead-spring polymer model, we reproduced the film distribution of molecularly thin lubricant films with polar end groups coated on the disk surface and quantified the film surface morphology using a molecular-probe scanning method. We found that the film surface morphology changed periodically with increasing the film thickness. The monolayer of a polar lubricant that entirely covers the solid surface provides a flat lubricant surface by exposing its nonpolar backbone outside of the monolayer. By increasing film thickness, the end beads aggregate to make clusters, and bulges form on the lubricant surface accompanying an increase in surface roughness. The bulges continue to grow up even though the averaged film thickness reaches or exceeds the bilayer thickness. With further increases in film thickness, the clusters start to be uniformly distributed in the lateral direction to clearly form a third layer. As for the formation of fourth-fifth layers, the process is basically the same as that for the second-third layers. Through our calculations of the intermolecular potential field and the intermolecular force field, these values are found to change periodically and are synchronized with the formation of molecule aggregations, which explains the mechanism of forming the layered structure that is inherent to a polar lubricant.Copyright

Simulations for Nanoscale Meniscus Formation and Rupture by Using Molecular Dynamics

To investigate the dynamic behaviors of nanoscale meniscus intervening between a solid surface and a probe tip of a scanning probe microscope in molecular scale, meniscus formation and rupture process were simulated by using molecular dynamics method. Lennard-Jones molecules were used to model both the lubricant film and the solid probe, and the techniques to analyze the normal force exerting between the film and the probe were introduced to identify the meniscus formation time and the meniscus elongation. We clarified that the meniscus formation time became longer for wider spacings between the film surface and the probe, and that the meniscus elongation became longer for larger probe retracting velocity.Copyright

A Simulation Method for Spreading Dynamics of Molecularly Thin Lubricant Films on Magnetic Disks Using Bead-Spring Model

An effective simulation technique for describing the spreading properties of molecularly thin lubricant films on magnetic disks has been developed. We propose a molecular precipitation method that can simulate initial molecule arrangement of the films dip-coated onto the disks. Reptation and Rouse models as the model of the molecular motion, and molecular insertion and molecular precipitation methods as the method for putting molecules in initial positions were compared. From the results of the spreading profiles and diffusion coefficients, it has been revealed that the molecular precipitation method combined with the Rouse model is effective in simulating the spreading of the lubricant films.© 2005 ASME