Mobile Lubricant Research Articles

Preparation and tribological properties of multiply-alkylated cyclopentane (MAC)–octadecyltrichlorosilane (OTS) double-layer film on silicon

A double-layer lubricant film consisting of a multiply-alkylated cyclopentane (MAC) mobile lubricant on octadecyltrichlorosilane self-assembled monolayer (OTS-SAM) was prepared. Atomic force microscopy (AFM) was used to examine the film surface. MAC with thickness of 25 Å was successfully coated on the OTS-SAM surface. MAC was discretely distributed on the OTS-SAM surface, and the film contained evenly distributed islands with a typical diameter of 25 nm and an average height of 25 Å. The area covered by the MAC was approximately 70%. Measurements were also performed on 50 Å Zdol-2000 film and 25 Å OTS-SAM for comparisons. The film thickness was measured by Gaerter elipsometer and the static contact angle was measured using a Kyowa contact-angle meter. The thickness of the lubricant film determined by the AFM was consistent with that measured by ellipsometer. The measured static angle of the 50 Å MAC–OTS double-layer film was about 110°, slightly greater than that of 108° of 25 Å OTS-SAM and that of 106° of 50 Å Zdol-2000. Tribological properties of the three kinds of films were evaluated using a ball-on-plate type universal DF-PM unidirectional sliding tribometer. The worn surfaces of the films were examined using a high precision non-contact surface profiler. All the films exhibited similar friction coefficients of about 0.1 at a normal load of 0.5 N, but the MAC–OTS double-layer film exhibited extended durability and higher load-carrying ability compared with 50 Å Zdol-2000 film or 25 Å OTS-SAM.

Effect of multiply-alkylated cyclopentane (MAC) on durability and load-carrying capacity of self-assembled monolayers on silicon wafer

A novel hydrocarbon mobile lubricant, multiply-alkylated cyclopentane (MAC), was deposited on two kinds of self-assembled monolayers (SAMs), i.e. 1H,1H,2H,2H-perfluorodecyltrichlorosilane self-assembled monolayer (FDTS-SAM) and decyltrichlorosilane self-assembled monolayer (DTS-SAM) to form two double-layer films by spinning coating method. The double-layer films, which are called as MAC-FDTS and MAC-DTS, respectively, consist of a strongly bonded phase lubricant (self-assembled monolayer) and a non-bonded mobile lubricant (multiply-alkylated cyclopentane). Friction behavior of FDTS-SAM, DTS-SAM, MAC-FDTS, MAC-DTS on silicon wafers was evaluated using a pin-on-plate test rig. Both FDTS-SAM and DTS-SAM markedly decreased the friction coefficient of Si substrate. However, they played the role of friction-reducing and anti-wear only at low loads of 50 and 100 mN, respectively. In contrast, when MAC deposited on the two kinds of SAMs, it could markedly reduce the friction coefficient of DTS-SAM and significantly enhance their durability and carrying-load capacity from 50 and 100 mN to 150 and 200 mN, respectively.

Effects of Molecularly Thin Liquid Lubricant Films on Slider Hysteresis Behavior in Hard Disk Drives

In order to achieve a magnetic recording density of 1Tb∕in2, the spacing is expected to be less than 2–3nm. However, a critical issue in achieving such an ultralow spacing is the dynamic instability of the head disk interface (HDI). That is, the experimentally observed hysteresis of fly sliders. The phenomenon of slider hysteresis has two features: slider touchdown and slider takeoff. The goal of this research is to experimentally clarify the effects of the lubricant bonded ratio as well as the lubricant film thickness on slider hysteresis behavior in detail. It also aims to determine the contributing factors. In this study, the difference in the touchdown and takeoff velocities was monitored by varying the lubricant bonded ratio and lubricant film thickness of the disks. Furthermore, the correlation between the observed phenomenon and the variation in the experimental parameters was investigated. The results showed that the touchdown velocities were almost independent of the lubricant bonded ratio, while the takeoff velocities were greater for a lubricant with a higher bonded ratio. These results were obtained for a constant lubricant film thickness of around one monolayer. Therefore, the slider hysteresis was greater for a lubricant with a higher bonded ratio. With regard to the effect of lubricant film thickness, it was observed that the touchdown and takeoff velocities were greater for thinner lubricants. These results for the effect of lubricant film thickness are very similar to those obtained by Ambekar, Gupta, and Bogy (2005, ASME J. Tribol., 127(3), pp. 530–536). However, the slider hysteresis was greater for thicker lubricants. Considering these experimental results as well as the experimental data for the effect of the surface roughness of a disk on the slider hysteresis obtained by (Tani et al. (2006, J. Appl. Phys. , 99(8), pp. 08N104-1–08N104-3), it was suggested that the variation in the touchdown velocity is due to a variation in the intermolecular forces. Furthermore, it was suggested that the variation in the takeoff velocity is caused by a variation in the friction forces between the slider and disk surface. This occurs because the takeoff velocity was greater for a lubricant with a higher bonded ratio or a thinner lubricant, which only has a small fraction of free mobile lubricant. The results predicted by the simulations are consistent with those observed experimentally. In addition, a design guideline for next-generation HDI, with small touchdown and takeoff velocities, resulting in small slider hysteresis, is discussed in detail in this paper.

Effects of ultra-thin liquid lubricant films on contact slider dynamics in hard-disk drives

This paper describes the effects of ultra-thin liquid lubricant films on contact slider dynamics in hard-disk drives. In the experiments, the contact slider dynamics as well as ultra-thin liquid lubricants behavior are investigated using three types of lubricants, which have different end-groups and molecular weight as a function of lubricant film thickness. The dynamics of a contact slider is mainly monitored using acoustic emission (AE). The disks are also examined with a scanning micro-ellipsometer before and after contact slider experiments. It is found that the lubricant film thickness instability occurs as a result of slider–disk contacts, when the lubricant film thickness is thicker than one monolayer. Their unstable lubricant behavior depends on the chemical structure of functional end-groups and molecular weight. In addition, it is also found that the AE RMS values, which indicate the contact slider dynamics, are almost same, independent of the end-groups and molecular weight for the lubricants, when the lubricant film thickness is approximately one monolayer. The molecular weight, however, affects the contact slider dynamics, when the lubricant film thickness is less than one monolayer. In other words, the AE RMS values increase remarkably as the molecular weight for the lubricant increases. When the lubricant film thickness is more than one monolayer, the AE RMS values decrease because of the effect of mobile lubricant layer, while the lubricant instability affects the contact slider dynamics. Therefore, it may be concluded that the lubricant film thickness should be designed to be approximately one monolayer thickness region in order to achieve contact recording for future head–disk interface.

Grease degradation in a bearing simulation device

In this study, a ball-on-disc traction (MTM) device has been used to degrade grease under controlled thermal and shear conditions over an extended period. The tests were run under both fully flooded and semi-starved conditions to simulate the lubricant supply levels found in bearings. A simple lithium hydroxystearate grease with and without an additive package was used. At the end of the test Infrared micro-reflection spectra were taken from the track and surrounding grease to determine lubricant film composition. These results were compared to IR reflection analysis of lubricant films in used bearings. The MTM results show that in the semi-starved tests the grease “runs-in” during the first few cycles as the friction coefficient drops giving a low, stable value comparable to the fully flooded condition. During initial overolling the grease is shear degraded releasing mobile lubricant, which replenishes the contact and reduces starvation. IR analysis of the lubricant film in and around the track has shown evidence of the local degradation, the formation of thickener-rich layers and new chemical species. The unadditised grease failed towards the end of the test due to incipient starvation, which was exacerbated by the formation of oxidised thickener deposits in the track. The IR spectrum from this film was very similar to that found in some bearing samples.

Slip effect for thin liquid film spreading characteristics

The spreading behaviour of thin liquid polymer perfluoropolyethers on hard disc surface was investigated theoretically. The impact of slip at the boundary was taken into consideration. The diffusion coefficient Ds(h) was modified by incorporating the effective Knudsen number and molecular weight. It is found that slip has to be negative to ensure a maximum value of Ds(h) at lubricant thickness of 1 nm. Replenishment behaviour was also investigated and it was shown that a positive slip would quicken the lubricant movement, whereas a negative slip would slow down the replenishment. Finally, the spreading profiles were examined to investigate lubricant mobility.

MEMS lubricants based on bound and mobile phases of hydrocarbon compounds: film deposition and performance evaluation

The concept of a thin layer of mobile hydrocarbon-based lubricant providing protection by replenishment to a surface already protected by a chemically bound material has been explored for the first time, for application to silicon-based microelectromechanical (MEMS) systems. Several bound/mobile pairs of lubricants were evaluated to study the effects of bound phase end group and mobile phase chemical functionality on wettability and performance. The bound species studied were derived from 1-decanol and 1,7-heptanediol. Mobile phases investigated were, a pentaerythritol ester, a multiply alkylated cyclopentane, Pennzane, and a polysilane developed for spacecraft application. Hydrocarbon lubricant performance was evaluated using electrostatic motors run in dry air, and was compared with that provided by Fomblin Zdol under identical conditions. Motors with hydrocarbon coatings showed substantial improvement in performance over uncoated motors, and for some bound/mobile pairs, was equal to Zdol within experimental error. We believe that for silicon-based devices, hydrocarbon coatings will be preferable at least for some applications, as the degradation observed due to aging of a fluorinated lubricant in direct contact with a silicon surface is absent.

Effect of Ultra-Thin Liquid Lubricant Films on Dynamics of Nano-Spacing Flying Head Sliders in Hard Disk Drives

This paper describes the effect of ultra-thin liquid lubricant films on air bearing dynamics and flyability of nano-spacing flying head sliders in hard disk drives. The dynamics of a slider was monitored using Acoustic Emission (AE) and Laser Doppler Vibrometer (LDV). The disks with lubricant on one half of disk surface thicker than the other half as well as with uniform thickness lubricant were used to investigate the interactions between the slider and lubricant film experimentally. As a result, it was found that the flying height at which the slider-lubricant contact occurs depends on the lubricant film thickness and it increases as the lubricant film thickness increases. Its flying height is also dependent on the mobile lubricant film thickness under the condition that the total lubricant film thicknesses are the same and the lubricant bonded ratios are different. It increases as the mobile lubricant film thickness increases. The slider-lubricant contact flying height based on the theory for capillary waves is in good agreement with the experimental results. Regard to air bearing dynamics due to the slider-lubricant interactions, it also depends on the mobile lubricant thickness as well as the total lubricant film thickness. However, we should carry out more experimental and theoretical studies in order to confirm and verify these experimental results. In addition, the effect of nonuniform lubricant film thickness on head/disk interface dynamics has been studied. It was found that the lubricant film thickness nonuniformity caused by the slider-lubricant interactions could be observed.

The Effect of Solvents on the Perfluoropolyether Lubricants Used on Rigid Magnetic Recording Media

The adsorption characteristics and tribological properties of the perfluoropolyether (PFPE) lubricants Zdol and Z-Tetraol on amorphous nitrogenated CNx carbon are investigated as a function of solvent used to apply the lubricants. The solvents used in these studies include perfluorohexane, CF3CHFCHFCF2CF3 and C4F9OCH3. Deposition studies indicate that the applied thickness of PFPE films is strongly solvent-dependent that can be related to differences in the solubility parameters between the various lubricants and solvents. The results of ab initio computations on the molecular electronic structure of the solvent molecules show that their solvent power is correlated to their polarity and in particular to the acidity of the protons on the CF3CHFCHFCF2CF3 and C4F9OCH3 molecules. Tribological reliability, as measured by contact start-stop testing, slider-disk clearance, lubricant pickup by the slider, lubricant smearing on the disk surface, etc., is independent of solvent and is limited to the physical properties of the adsorbed lubricant film. The kinetics of lubricant mobility are charateristic of confined liquids that are independent of solvent as shown by lubricant flow profiles, bonding kinetics, and contact angle goniometry.

Frictional properties of bilayered mixed lubricant films on an amorphous carbon surface: effect of alkyl chain length and SAM/PFPE portion

Twenty-Å-thick mixed lubricants with bilayered structures, which consist of alkylsilane monolayers (C6, C8, and C10) and mobile perfluoropolyether (PFPE) lubricants, were deposited on a hydrogenated amorphous carbon surface. The friction and durability properties of the mixed lubricants on the carbon surface were measured using an atomic force microscope and a micro-scratch tester, which were compared with 20 Å-thick perfluoropolyether lubricant coated carbon surfaces. The friction and durability properties of the mixed lubricant on a carbon surface were mainly dependent on the silane monolayers, that is, the friction force became low and the critical load was enhanced by increasing the alkylsilane chain length although the amount of the mobile lubricant decreased. On the other hand, the mixed lubricants on the carbon surfaces showed a higher friction force compared to that of the Fomblin Zdol lubricant that has a satisfactory molecular flexibility, whereas it showed a higher durability due to a higher surface coverage of the chemisorbed molecules and the rigid nature of the silane monolayers. The frictional properties of the perfluoropolyether lubricants on a carbon surface are related to the radius of gyration, R g, of the molecule. The excess mobile molecules contribute to the high friction due to the capillary effect, that is, an optimum thickness of the mobile lubricant exists for a lower friction, which is comparable to R g.

The Tribological Properties of a New Cyclotriphosphazene-Terminated Perfluoropolyether Lubricant

We have investigated the tribological properties of a novel perfluoropolyether (PFPE) lubricant truncated on one end by a hydroxyl group and on the other end by a cyclotriphosphazene derivative. A measurement of the friction force as a function of molecular weight indicates that the dynamic clearance between the slider and the disk can be reduced by ∼1.5 nm by decreasing the molecular weight from 5300 to 2400 g/mol. However, the thermodynamic film stability of the novel PFPE lubricants, as determined by surface energy measurements and ellipsometric imaging of lubricant dewetting, becomes increasingly unstable at lower film thicknesses with decreasing molecular weight. Measurements conducted on lubricant mobility indicate that the novel PFPE lubricants are relatively immobile compared to the Zdol perfluoropolyether lubricants and hence resist film thinning to a greater degree. These data provide the direction for the optimization of the molecular weight of these novel PFPE lubricants.

Nanoscale Lubricant with Strongly Bonded Phase and Mobile Phase

The best tribological properties can be obtained in a film that contains both bonded and mobile phases, and thus the ratio of the bonded phase to the mobile phase, the bonded ratio, is a critical factor for the lifetime of the mechanical components. In the present study, we deposited a mixed lubricant, which consists of a strongly bonded lubricant phase and a mobile lubricant phase, on a carbon overcoat. Islands of FDTS (perfluorodecyltrichlorosilane) SAM (self-assembled monolayer) were introduced as a strongly bonded lubricant phase and Fomblin Z03 lubricant as a mobile phase. The friction and durability properties of 2.5-in magnetic disks coated with 15 A thick mixed lubricants were investigated using a ball-on-disk tribotester and compared with disks coated with 15 A Zdol lubricants. Because the contact area of the ball increases with the bonded ratio, the friction coefficient of the disk coated with the mixed lubricant increases linearly with the bonded ratio over a range of about 25–100%. On the other hand, the friction coefficient of the disk coated with Zdol decreases with increasing bonded ratio. The mixed lubricant exhibits superior wear properties compared to Zdol. This may occur because the FDTS networks act as a barrier against the displacement of the mobile Z03 molecules, and the mobility of Z03 molecules is higher than that of Zdol molecules, which allows Z03 to replenish into the lubricant-depleted area at a higher rate.

Development of the mixed nanolubricant system by FDTS islands and PFPE mobile phase

In this paper, we have developed the mixed lubricant, which consists of bonded FDTS islands and mobile perfluoropolyether (PFPE) lubricant. The mixed lubricant was deposited on a magnetic disk surface with a carbon overcoat by immersion and dip-coating process, and the durability of the disk was evaluated by a scratch tester. The critical load of the disk coated with the mixed lubricant is higher than that of the disk coated with purely mobile PFPE lubricant even though the film thickness of the former is smaller than that of the latter. It is because that the FDTS islands allow to trap and maintain the mobile PFPE molecules on the disk surface.

The surface coverage effect on the frictional properties of patterned PFPE nanolubricant films in HDI

The surface coverage ratio of bonded and mobile phase of perfluoropolyether (PFPE) nanolubricant film on magnetic disk surface is an important factor in controlling the friction and durability in head/disk interface. In this paper, we report the optimum surface coverage ratio in a 1-nm-height ultrathin PFPE lubricant film for future hard-disk-drive technology. One-nanometer-height bonded and mobile PFPE nanolubricant films were deposited on magnetic disk surfaces and patterned by the photolithographic process. The surface coverage of lubricant film on the magnetic disk was varied in the range of 50% to 100%. Friction coefficients were measured by a ball-on-flat tribotester. The friction coefficients of patterned mobile lubricant films are lower than those of patterned bonded films. The friction coefficient of the disk coated with bonded lubricant film decreases linearly with increasing surface coverage. On the other hand, the friction coefficient of the disk coated with mobile lubricant film shows a minimum value at the surface coverage of 75%. This may be because the lubricant-free area prevents the ball slider and disk from stiction. We conclude that the optimum value of the surface coverage ratio in 1-nm-height ultrathin PFPE lubricant film in the aspect of low friction is 0.25, that is, two-dimensional pattern of 25% bonded and 75% mobile portion.

Characteristics of dual lubricant layers

Lubricant characteristics of dual lubricant layers, which consist of a first-lubricant bonded layer and second-lubricant mobile layer, were studied. The interface durability is evaluated by a pin-on-disk test. The spin-migration characteristic is evaluated based on the change in thickness of layers after disk spinning. The mobility is estimated from spreading profiles from the lubricant step. Dual lubricant layers , which consists of Z-dol as a mobile layer and Z-tetraol or AM as a bonded layer, shows high mobility, high interface durability, and low spin-migration performance. It is considered that these characteristics can be attributed to higher interaction between the bonded lubricant and the mobile lubricant due to strong polar end groups of the bonded lubricant.

Lubrication of Microelectromechanical Systems (MEMS) Using Bound and Mobile Phases of Fomblin Zdol

A lubrication scheme for MEMS electrostatic lateral output motors based on a mixture of bound and mobile lubricant was studied. Lubrication by bound monolayer alone provided some increase in operational life, but after a short time, the film wore away and the device failed in the unlubricated mode. A mobile phase was used to provide lubricant replenishment. Tribological studies were conducted on Si(100) wafers, as well as on MEMS electrostatic lateral output motors, dip-coated with a mixture of bound and mobile phases of Fomblin Zdol. Accelerated screening tests on Si(100) wafers were undertaken using a pin on disk tribometer. However, the optimum balance of bound and mobile phases was determined by studies on the device itself. The fractional surface coverage of lubricant and the ratio of bound to mobile phase was varied through selection of reaction temperature and rinse chemistry. The mobile phase on model surfaces and devices acted as a source of lubricant replenishment, and together with the bound phase provided dramatic improvement in performance. The wide variation seen in the performance of individual devices suggests that dip coating does not provide a uniform coating on the contacting surfaces of these devices.

The Effect of Carbon Overcoat Thickness on the Zdol Boundary Lubricant Film

Formation of a tribologically reliable interface between the read-write head and the computer disk in hard-disk drives is accomplished by the use of a thin, wear-resistant carbon overcoat in conjunction with a molecularly-thin perfluoropolyether (PFPE) lubricant film. The intermolecular interactions that develop between the PFPE lubricant and the carbon overcoat govern the adhesion, coverage, and physical properties of the lubricant, e.g. the lubricant structure and mobility. Consequently, the molecular interactions at the lubricant-carbon interface will contribute to the overall tribological performance of the disk-drive. Due to the ever-increasing demands for storage capacity, pressure exists to reduce the separation distance between the read-write head and disk surface. One means of reducing this separation distance is to use thinner protective overcoats on both the head and disk surfaces. In this study the interactions between Fomblin Zdol and both amorphous hydrogenated (CHx) and nitrogenated (CNx) carbon overcoats were investigated as a function of overcoat thickness from 0 to 100A. The Zdol film structure was probed by titrating the magnetic alloy, the CHx and CNx surfaces with Zdol. The molecular weight dependence of the maximum bonded Zdol thickness on these surfaces is used to deduce structural information on the adsorbed Zdol film. In progressing from CHx to CNx to the magnetic alloy, we find the Zdol boundary layer film to be characterized by an increase in average distance between the PFPE backbone and the surface, or equivalently an increase in the average Zdol monolayer thickness. On the CHx overcoat, Zdol preferentially lies more parallel to the surface, whereas on the magnetic layer, Zdol is oriented more perpendicular to the surface. When these experiments were conducted as a function of carbon overcoat thickness, we found that interaction of Zdol with the field of the underlying magnetic film becomes important at carbon film thicknesses ≤ 30A. The dependence of the Zdol adhesion on carbon overcoat thickness was quantified by determining the Zdol film thickness dependence of both the dispersive and polar components of the Helmholtz free energy. The Zdol bonding kinetics were also studied as a function of carbon thickness.

Investigation of phosphazene additive for magnetic recording lubrication

The addition of X-IP to the Fomblin Z-Dol disk lubricant is found to improve the contact start-stop (CSS) durability of hydrogenated carbon overcoated disks. Two-angle electron spectroscopy for chemical analysis (ESCA), contact angle measurements, spin-off measurements, and degradation studies on powdered AlCl/sub 3/ and Al/sub 2/O/sub 3/ are used to show that X-IP improves lubrication by perfluoropolyethers on magnetic disks by chemically interacting with disk and slider surfaces so as to block sites for lubricant degradation, to lower surface energies, and to increase lubricant mobility.

Studies on the interactions between ZDOL perfluoropolyether lubricant and the carbon overcoat of rigid magnetic media

Current high performance magnetic storage devices, i.e., hard disk drives, typically operate at elevated temperatures of nominally 45–60°C. As a consequence, understanding the thermal response of the materials used in the construction of the drive becomes imperative. In this report, we focus on the thermal behavior of a common perfluoropolyether lubricant (ZDOL) used on the carbon-overcoated, hard disk. In particular, we show that evaporative loss of this disk lubricant, as well as bonding of the lubricant to the carbon-overcoated disk, can occur at the temperatures encountered in the hard-disk drive. Surface energy measurements show that the interaction of the hydroxyl-terminated perfluoropolyether ZDOL occurs principally through the end-groups. On unannealed disks, the interaction between this “mobile” lubricant and the carbon overcoat is characterized by hydrogen bonding with the strength of these interactions being only slightly stronger than the intermolecular hydrogen bonding characteristic of bulk ZDOL. Upon annealing at temperatures in the range of 60–150°C, the ZDOL lubricant becomes “bonded” to the disk. The surface energy of the bonded lubricant is substantially lower than the mobile lubricant reflecting the increased interaction strength that occurs as a result of bonding. Since the bonded state is the lower energy state, transitions from the mobile state to the bonded state are thermodynamically favored. The kinetics of this bonding transition, as well as the kinetics of lubricant evaporation were studied as a function of temperature. Using a model of two competing reaction channels, the activation energies for both lubricant bonding and lubricant evaporation were determined to be 3.6 kcal/mole and 5.4 kcal/mole respectively. Ab initio quantum chemical modelling was used to investigate possible interaction sites on the carbon surface. Both experiment and theory indicate that interaction of the hydroxyl-terminated ZDOL to the carbon overcoat occurs via hydrogen bonding to oxygenated species on the carbon overcoat, with a binding energy of 5–8 kcal/mole. An esterification reaction between the hydroxyl end-groups of ZDOL with carboxyl groups on the carbon surface as a result of annealing is shown to be consistent with the both the surface energy data and the kinetic data.

Environmental effects on the streaming mode performance of metal evaporated and metal particle tapes

A commercial Hi-8 video cassette recorder was instrumented to measure friction force between the rotary heads and tape, rms head output, and signal dropouts to sub /spl mu/s duration. Streaming (play) mode experiments using metal evaporated (ME) and metal particle (MP) tapes were performed at design tension under equilibrium and nonequilibrium conditions inside of an environmental chamber at various temperature and specific humidity (SH=ratio of the weights of water vapor to dry air in the mixture). Interface stability and recording performance at a 0.6 /spl mu/m recording wavelength were measured to bit level resolution using a dropout counter and changes in rms head output were correlated to changes in head-to-tape spacing using the Wallace equation. ME tape performed best at moderate SH (from 0.009 to 0.013) in the operating temperature range of 15.6 to 32.2/spl deg/C, whereas MP tape performed best at low temperature. At a given temperature, higher SH increased normal and friction forces and decreased head-to-tape spacing due to spontaneous water meniscus formation between contacting and noncontacting asperities on the head, tape, and debris particle surfaces. Dropout frequency and interface stability were sensitive to both SH and temperature. Humidity dependence was governed by the relative size difference between wear debris particles and spontaneously formed water menisci. Competing mechanisms of increased lubricant mobility and spontaneously formed water menisci of smaller radii of curvature at higher temperature governed temperature dependence. A model based on capillary condensation of water vapor onto surfaces in a sliding contact is developed to explain experimental data. An expression for meniscus force consisting of both Laplace and surface tension contributions is developed for nanometer size contact spots and wear debris particles. The model predicts that meniscus force will increase and head-to-tape spacing will decrease with increasing SH which was observed experimentally. Four lubrication regimes are defined for wear debris particles passing through the contact interface. Both SH and extent of deformation of a particle determine whether menisci will form around the particle, and presence or absence of associated meniscus forces explains trends in dropout frequency data. The model allows determination of meniscus height from which minimum values of Kelvin radius and relative humidity (RH) in the contact interface can be calculated. Proximity and intimate contact of the surfaces increases RH and SH in the contact interface over that maintained in the environmental chamber to near their saturation values.