• Tribology and Lubricants
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• v.20 no.6
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• pp.343-349
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• 2004

The adsorption of soot particles onto a sensor surface of the engine soot detector posses a critical problem in the measurement. In order to prevent the optical rod surface from soot contamination, various functional coatings and flow-induced cleaning were applied to the surface in this work. For surface coatings, various materials of self-assembled monolayers (SAM) such as OTS (octadecyltrichlorosilane), PFDTES (perfluorodecyl-triethoxysilane) and PFDTMS (perfluorodecyltrimethoxysilane) were coated on the optical rod surface ,which have different characteristics in both hydrophobicity and oleophobicity. These coatings were tested with soot content varying from $0\%\;to\;3wt\%$ and oil temperature from 20 to $70^{\circ}C$. Test results showed that surface coatings were not effective for preventing the adsorption of soot panicles on the surface of optical rod. It was thought that these coatings provided the surface with additional attractive surface forces. However, it was found that adsorption of soot particles onto a sensor surface was minimized by flow-induced cleaning. This effect was tested with varying the flow velocity.

• KSTLE International Journal
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• v.3 no.1
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• pp.12-16
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• 2002

Micro/nano tribological and water wetting characteristics of ion beam treated PTFE (polytetrafluoroethylene) surfaces were experimentally studied. The ion beam treatment was performed with a hollow cathode ion gun at different argon ion dose conditions in a vacuum chamber to modify the topography of PTFE surface. Micro/nano tribological characteristics, water wetting angles and roughness were measured with a micro tribe tester, SPM (scanning probe microscope), contact anglemeter and profilometer, respectively. Results showed that surface roughness increased with the argon ion dose. Water wetting angle of the ion beam treated samples increased with the ion dose, so the surface shows an ultra-hydrophobic nature. Micro-adhesion and micro-friction depend on the wetting characteristics of the PTFE samples. However, nano-tribological characteristics showed different results. The scale effect of surface topography on tribological characteristics was discussed. Also, the water wetting characteristics of modified PTFE samples were discussed in terms of the surface topographic characteristics.

• KSTLE International Journal
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• v.5 no.1
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• pp.1-6
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• 2004

Nano-scale studies on adhesion and friction were conducted in Si-wafer (100) using Atomic Force Microscopy (AFM). Glass (Borosilicate) balls of radii 0.32$\mu\textrm{m}$, 1.25$\mu\textrm{m}$, and 2.5$\mu\textrm{m}$, mounted on cantilever (Contact Mode type NPS) were used as tips. Adhesion and friction between Si-wafer and glass tips were measured at ambient temperature (24${\pm}$1$^{\circ}C$) and humidity (45${\pm}$5%). Friction was measured as a function of applied normal load in the range of 0-160 nN. Results showed that, both adhesion and friction increased with the tip radii. Also, friction increased linearly as a function of applied normal load. The effect of tip size on adhesion and friction was explained as the influence of the capillary force exerted by meniscus and that of the contact area on these parameters respectively. The coefficient of friction was estimated in two different ways, as the slope from the plot of friction force against the applied normal load and as the ratio between the friction force and the applied normal load. Both these estimates showed that the coefficient of friction increased with the tip size. Further, the influence of the adhesion force on the coefficient of friction was also discussed.

• Tribology and Lubricants
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• v.18 no.1
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• pp.1-8
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• 2002

Nano adhesion and friction between a $Si_{3}N_{4}$ AFM(atomic force microscope) tip and thin silver films were experimentally studied. Tests were performed to measure the nano adhesion and friction in both AFM and LFM(lateral force microscope) modes in various range of normal loads. Thin silver films deposited by IBAD (ion beam assisted deposition) on Si-wafer (100) and other Si-wafers of different surface roughness were used. Results showed that nano adhesion and friction decreased with the surface roughness. When the Si surfaces were coated by pure silver, the adhesion and friction decreased. But the adhesion and friction were not affected by the thickness of IBAD silver coating. As the normal force increased, the adhesion forces of bare Si-wafer and IBAD silver coating film remained constant, but the friction forces increased linearly. Test results suggested that the friction was mainly governed by the adhesion as long as the load was low.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2003.11a
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• pp.56-63
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• 2003

Micro/nano adhesion and friction properties of mixed self-assembled monolayer (SAM) with different chain length for MEMS application were experimentally studied. Many kinds of SAM having different spacer chains(C6, C10 and C18) and their mixtures (1:1) were deposited onto Si-wafer, where the deposited SAM resulted in the hydrophobic nature. The adhesion and friction properties between tip and SAM surfaces under nano scale applied load were measured using an atomic force microscope (AFM) and micro scale applied load were measured using ball-on-flat type micro-tribotester. Surface roughness and water wetting angles were measured with SPM (scanning probe microscope) and contact anglemeter. Results showed that wetting angles of mixed SAMs showed the similar value of pure SAMs. The coating surface morphology was increased as mixing of SAM. Nano adhesion and nano friction decreased as increasing of the spacer chain length and mixing of SAM. Micro friction was decreased as increasing of the spacer chain, but micro friction of mixed SAM showed the value between pure SAMs. Nano adhesion and friction mechanism of mixed SAM was proposed in a view of stiffness of spacer chain modified chemically and topographically.

• Tribology and Lubricants
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• v.18 no.5
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• pp.324-332
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• 2002

In order to enhance the thermal stability of binder materials of bonded type solid lubricants, several metal-alkoxide based sol-gel materials such as methyltrimethoxysilane(MTMOS), titaniumisopropoxide$(Ti(Opr^i)_4),$ zirconiumisopropoxide $(Zr(Opr^i)_4)$ and aluminumbutoxide$(Al(Obu^t)_4)$ were chemically modified by epoxy-, acrylic- and fluoro-silane compounds, respectively. Friction and wear characteristics of these hybrid ceramic materials were tested with a micro tribo-tester, and evaluated with respect to both heat-curing temperature and the time. Test results generally showed that hybrid ceramic materials modified by epoxy-silane compounds had a low friction compared to others. And the higher het-curing temperature and the longer heat treatment time resulted in the higher friction and the lower wear. IR spectroscopic analyses revealed that these results were caused mainly by the increased metal oxide content in hybrid ceramics when the heat-curing temperature was over $320^{\circ}C.$

• KSTLE International Journal
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• v.5 no.2
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• pp.37-43
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• 2004

Abstract : Nano/micro-scale friction properties were investigated on Si (100) and three self-assembled monolayers (SAMs) (PFOTC, DMDM, DPDM) coated on Si-wafer by chemical vapor deposition technique. Experiments were conducted at ambient temperature(24$pm$1$circ$C) and humidity(45$pm$5%). Friction at nano-scale was measured using Atomic Force Microscopy (AFM) in the range of 0-40nN normal loads. In both Si-wafer and SAMs, friction increased linearly as a function of applied normal load. Results showed that friction was affected by the inherent adhesion in Ssi-wafer, and in the case of SAMs the physical/chemical structures had a major influence. Coefficient of friction of these test samples at the micro-scale was also energies. In order to study the effect of contact area on coefficient of friction at the micro-scale, friction was measured for Si-wafer and DPDM against Soda Lime balls (Duke Scientiffic Corporation) of different radii (0.25 mm, 0.5 mm and 1 mm) at different applied normal loads (1500, 3000 and 4800 mN). Results showed that Si-wafer had higher coefficient of friction than DPDM. Further, unlike that in the case of DPDM, friction in Si-wafer was severely influenced by its wear. SEM evidences showed that solid-solid adhesion was the wear mechanism in Si-wafer.

• Tribology and Lubricants
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• v.21 no.3
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• pp.107-113
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• 2005

Micro/nano adhesion and friction properties of self-assembled monolayers (SAMs) with different head- and end-group were experimentally studied according to the coating methods. Various kinds of SAM having different spacer chains (C10 and C18), head-group and end-group were deposited onto Si-wafer by dipping and chemical vapour deposition (CVD) methods under atmospheric pressure, where the deposited SAM resulted in the hydrophobic nature. The adhesion and friction properties between tip and SAM surfaces under nano scale applied load were measured using an atomic force microscope (AFM) and also those under micro scale applied load were measured using a ball-on-flat type micro-tribotester. Surface roughness and water contact angles were measured with SPM (scanning probe microscope) and contact anglemeter respectively. Results showed that water contact angles of SAMs with the end-group of fluorine show higher relatively than those of hydrogen. SAMs with the end-group of fluorine show lower nano-adhesion but higher micro/nanofriction than those with hydrogen. Water contact angles of SAMs coated by CVD method show high values compared to those by dipping method. SAMs coated by CVD method show the increase of nano-adhesion but the decrease of nano-friction. Nano-adhesion and friction mechanism of SAMs with different end-group was proposed in a view of size of fluorocarbon molecule.

• Tribology and Lubricants
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• v.18 no.4
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• pp.241-248
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• 2002

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.13-16
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• 2000