scholarly journals Nanorheometry of Molecularly Thin Liquid Lubricant Films Coated on Magnetic Disks

2012 ◽  
Vol 2012 ◽  
pp. 1-12
Author(s):  
Shintaro Itoh ◽  
Yuya Hamamoto ◽  
Koki Ishii ◽  
Kenji Fukuzawa ◽  
Hedong Zhang
Keyword(s):  
Shear Force ◽  
Hard Disk Drives ◽  
Measuring Method ◽  
Disk Drives ◽  
Magnetic Disks ◽  
Magnetic Disk ◽  
Liquid Lubricant ◽  
Magnetic Spacing ◽  
Highly Sensitive ◽  
Lubricant Films

Molecularly thin lubricant films are used for the lubrication of head disk interfaces in hard disk drives. The film thickness is reduced to 1-2 nm to minimize the magnetic spacing, and optimal, precise design is required to obtain sufficient lubrication. However, until now, there was no generally applicable method for investigating such thin films. Therefore, we developed a highly sensitive shear force measuring method and have applied it to the viscoelastic measurement of lubricant films coated on magnetic disk surfaces. In this paper, we review the method and summarize the useful findings we have demonstrated so far.

Simultaneous Measurements of Friction Forces and Contact Areas During Shearing of Nanometer-Thick Liquid Lubricant Films

2012 ◽  
Author(s):  
Shintaro Itoh ◽  
Takumi Mizuno ◽  
Yusuke Norizuki ◽  
Kenji Fukuzawa ◽  
Hedong Zhang
Keyword(s):  
Mechanical Properties ◽  
Contact Area ◽  
Microelectromechanical Systems ◽  
Hard Disk Drives ◽  
Disk Drives ◽  
Shear Forces ◽  
Friction Forces ◽  
Liquid Lubricant ◽  
Highly Sensitive ◽  
Lubricant Films

Nanometer-thick liquid lubricant films are useful for the lubrication of miniaturized mechanical systems, such as hard disk drives or microelectromechanical systems. However, there are no established methods for measuring the mechanical properties of such thin films, which can be an obstacle to the optimal design of lubrication systems. We previously developed a highly sensitive method for measuring shear forces, which we called the fiber-wobbling method (FWM). In the FWM, we used a ball-ended optical fiber to probe shear and we measured the friction force acting on the probe tip by detecting the deflection of the fiber. By this means we succeeded in measuring friction forces in nanometer-thick liquid lubricant films. However, we could not evaluate the mechanical properties of the films quantitatively because the contact area between the probe tip and lubricant film was unknown. Here, we developed a method for measuring the contact area during shearing of nanometer-thick liquid lubricant films in the FWM.

Depletion of Moleculary Thin Lubricant Under Flying Head in Hard Disk Drives

2007 ◽  
Author(s):  
Kenji Yanagisawa ◽  
Youichi Kawakubo ◽  
Masato Yoshino
Keyword(s):  
Thin Film ◽  
Hard Disk Drives ◽  
Hard Disk ◽  
Lubricant Film ◽  
Simulation Program ◽  
Disk Drives ◽  
Lubricant Thickness ◽  
Magnetic Disk ◽  
Lubricant Depletion ◽  
Lubricant Films

In Hard Disk Drives, lubricants are very important materials to reduce head and disk wear. Therefore, it is necessary to know the lubricant depletion under flying heads. Lubricant depletion due to flying heads has been studied experimentally. We developed simulation program to calculate numerically the change in lubricant thickness under a flying head on a thin-film magnetic disk from 10nm thick lubricant film. In recent HDDs, the lubricants thickness has become molecularly thin and polar lubricants have been used. In this paper, we took account of thickness-dependent lubricants diffusion and viscosity in our simulations to calculate a 1.2 nm thick polar lubricant film used in recent HDDs. The simulated results considering the thickness-dependent diffusion and viscosity showed that depletion was small in molecularly thin lubricant films. We considered it necessary to include thickness-dependent diffusion and viscosity in lubricant depletion simulation.

Effects of End Groups on the Spreading Characteristics of Molecularly Thin Liquid Lubricant Films in Hard Disk Drives

2007 ◽  
Vol 43 (9) ◽  
pp. 3705-3709 ◽  
Author(s):  
N. Tagawa ◽  
M. Korenaga ◽  
A. Mori ◽  
N. Kobayashi ◽  
M. Ikegami
Keyword(s):  
Hard Disk Drives ◽  
Hard Disk ◽  
Disk Drives ◽  
Liquid Lubricant ◽  
End Groups ◽  
Lubricant Films

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

2004 ◽  
Vol 126 (3) ◽  
pp. 565-572 ◽  
Author(s):  
Norio Tagawa ◽  
Noritaka Yoshioka ◽  
Atsunobu Mori
Keyword(s):  
Film Thickness ◽  
Hard Disk Drives ◽  
Lubricant Film ◽  
Flying Height ◽  
Air Bearing ◽  
Disk Drives ◽  
Lubricant Film Thickness ◽  
Liquid Lubricant ◽  
Lubricant Films ◽  
Bearing Dynamics

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.

Effect of Temperature on the Spreading Characteristics of Molecularly Thin Liquid Lubricant Films in Hard Disk Drives

2008 ◽  
Author(s):  
Norio Tagawa ◽  
Kenta Mori ◽  
Atsunobu Mori ◽  
Masako Ikegami
Keyword(s):  
Diffusion Coefficient ◽  
Hard Disk Drives ◽  
Hard Disk ◽  
Effect Of Temperature ◽  
Disk Drives ◽  
Liquid Lubricant ◽  
Quantitative Correlation ◽  
Lubricant Films ◽  
Apparent Diffusion ◽  
Mobile Fraction

In this study, the effect of temperature on the spreading characteristics of ultra-thin liquid lubricant films in hard disk drives (HDD) was investigated by using three types of lubricants, namely, Zdol2000, Ztetraol2000, and A20H2000. The apparent diffusion coefficient of individual lubricants was evaluated and compared by varying the temperature of disk substrates. As a result, it was found that the mobility of each lubricant increases with the temperature. However, the rate of mobility increase is different for each lubricant, depending on the lubricant material. Furthermore, there exists no quantitative correlation between the mobility increase for ultra-thin liquid lubricant films and the viscosity decrease in bulk lubricant materials due to a rise in the temperature. It was also found that among the test lubricants, A20H2000 has the highest robustness for temperature change. In addition, it could be observed that the evaporation of the mobile fraction of lubricants occurred remarkably over a temperature range of 50– 80 °C.

Nanorheological Measurement of Monolayer Lubricant Films Using the Oscillating Optical Fiber Probe

2008 ◽  
Author(s):  
Yuya Hamamoto ◽  
Shintaro Itoh ◽  
Kenji Fukuzawa ◽  
Hedong Zhang
Keyword(s):  
Shear Force ◽  
Accurate Determination ◽  
Measuring Method ◽  
Mechanical Responses ◽  
Optical Fiber Probe ◽  
Sliding Surfaces ◽  
Highly Sensitive ◽  
Lubricant Films ◽  
Substrate Surfaces

We achieved a viscoelastic measurement of monolayer lubricant films using the fiber wobbling method, which is the highly sensitive shear force measuring method that we have developed. In order to make the measurement possible, we attained the accurate determination of nanometer-sized gap widths between sliding surfaces. In addition, we developed a new method to align the parallelism between the sliding surfaces. We observed the differences in the mechanical responses of sheared lubricant films due to their adsorptivity to the substrate surfaces.

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