Multiscale Treatment of Thin-Film Lubrication

A multiscale technique that combines an atomistic description of the interfacial (near) region with a coarse-grained (continuum) description of the far regions of the solid substrates is proposed. The new hybrid technique, which represents an advance over a previously proposed dynamically-constrained hybrid atomistic-coarse-grained treatment (Wu et al.J. Chem. Phys., 120, 6744, 2004), is applied to a two-dimensional model tribological system comprising planar substrates sandwiching a monolayer film. Shear–stress profiles (shear stress versus strain) computed by the new hybrid technique are in excellent agreement with “exact” profiles (i.e. those computed treating the whole system at the atomic scale).

Thermocapillary flow in an annular liquid layer painted on a moving fiber

In the present paper, a theoretical model is studied on the flow in the liquid annular film, which is ejected from a vessel with relatively higher temperature and painted on the moving solid fiber. A temperature gradient, driving a thermocapillary flow, is formed on the free surface because of the heat transfer from the liquid with relatively higher temperature to the environmental gas with relatively lower temperature. The thermocapillary flow may change the radii profile of the liquid film. This process analyzed is based on the approximations of lubrication theory and perturbation theory, and the equation of the liquid layer radii and the process of thermal hydrodynamics in the liquid layer are solved for a temperature distribution on the solid fiber.

Preparation and Tribological Studies of Stearic Acid Self-Assembled Monolayers on Polymer-Coated Silicon Surface

We present a good alternative method to improve the tribological properties of polymer films by chemisorbing a long-chain monolayer on the functional polymer surface. Thus, a novel self-assembled monolayer is successfully prepared on a silicon substrate coated with amino-group-containing polyethyleneimine (PEI) by the chemical adsorption of stearic acid (STA) molecules. The formation and structure of the STA-PEI film are characterized by means of contact-angle measurement and ellipsometric thickness measurement, and of Fourier transformation infrared spectrometric and atomic force microscopic analyses. The micro- and macro-tribological properties of the STA-PEI film are investigated on an atomic force microscope (AFM) and a unidirectional tribometer, respectively. It has been found that the STA monolayer about 2.1-nm thick is produced on the PEI coating by the chemical reaction between the amino groups in the PEI and the carboxyl group in the STA molecules to form a covalent amide bond in the presence of N,N'-dicyclohexylcarbodiimide (DCCD) as a dehydrating regent. By introducing the STA monolayer, the hydrophilic PEI polymer surface becomes hydrophobic with a water contact angle to be about 105degrees. Study of the time dependence of the film formation shows that the adsorption of PEI is fast, whereas at least 24 h is needed to generate the saturated STA monolayer. Whereas the PEI coating has relatively high adhesion, friction, and poor anti-wear ability, the STA-PEI film possesses good adhesive resistance and high load-carrying capacity and anti-wear ability, which could be attributed to the chemical structure of the STA-PEI thin film. It is assumed that the hydrogen bonds between the molecules of the STA-PEI film act to stabilize the film and can be restored after breaking during sliding. Thus, the self-assembled STA-PEI thin film might find promising application in the lubrication of micro-electromechanical systems (MEMS).

Micro- and macro-tribological study on a self-assembled dual-layer film

A novel self-assembled dual-layer film as apotential excellent lubricant for micromachines was successfully prepared on single-crystal silicon substrate by chemical adsorption of stearic acid (STA) molecules on self-assembled monolayer of 3-aminopropyltri

Rheological effect on thermocapillary flow of a liquid film jet painted on a moving boundary

In the present paper, a liquid (or melt) film of relatively high temperature ejected from a vessel and painted on the-moving solid film is analyzed by using the second-order fluid model of the non-Newtonian fluid. The thermocapillary flow driven by the temperature gradient on the free surface of a Newtonian liquid film was discussed before. The effect of rheological fluid on thermocapillary flow is considered in the present paper. The analysis is based on the approximations of lubrication theory and perturbation theory. The equation of liquid height and the process of thermal hydrodynamics of the non-Newtonian liquid film are obtained, and the case of weak effect of the rheological fluid is solved in detail.

IP Simulation of Micro Gas Flows under 3-D Head Sliders

Gas film lubrication of a three-dimensional flat read-write head slider is calculated using the information preservation (IP) method and the direct simulation Monte Carlo (DSMC) method, respectively. The pressure distributions on the head slider surface at different velocities and flying heights obtained by the two methods are in excellent agreement. IP method is also employed to deal with head slider with three-dimensional complex configuration. The pressure distribution on the head slider surface and the net lifting force obtained by the IP method also agree well with those of DSMC method. Much less (of the order about 10(2) less) computational time (the sum of the time used to reach a steady stage and the time used in sampling process) is needed by the IP method than the DSMC method and such an advantage is more remarkable as the gas velocity decreases.

Development And Characterization Of Composite Ni-Cr-C-Caf2 Laser Cladding On Gamma-Tial Intermetallic Alloy

A process of laser cladding Ni-CF-C-CaF2 mixed powders to form a multifunctional composite coatingd on gamma-TiAl substrate was carried out. The microstructure of the coating was examined using XRD, SEM and EDS. The coating has a unique microstructure consisting of primary dendrite or short-stick TiC and block Al4C3 carbides reinforcement as well as fine isolated spherical CaF2 solid lubrication particles uniformly dispersed in the NiCrAlTi (gamma) matrix. The average microhardness of the composite coatings is approximately HV 650 and it is 2-factor greater than that of the TiAl substrate. (C) 2008 Elsevier B.V. All rights reserved.

Counterion exchange at the surface of polyelectrolyte multilayer film for wettability modulation

Counterions present at the surface of polyelectrolyte multilayers (PEMs) were utilized for modulation of surface wettability via ion exchange. The PEM film was dipped in aqueous solutions of different anions, respectively, and the water contact angle of the surface varied from about 10 degrees to 120 degrees, depending on the hydration characteristics of the anion. The ion exchange mechanism was verified by X-ray photoelectron spectroscopy. The process was rapid and reversible. Ionic strength of the polyelectrolyte solution used for preparing the PEMs was found to be crucial to the surface wetting properties and the reversibility and kinetics of the process, and the effects were correlated to the surface density of the excess charge and counterion. This work provides a general, facile and rapid approach of surface property modulation.