Effect of Graphite Concentration on the Tribological and Mechanical Properties of filled SU-8 Effect of Graphite Concentration on the Tribological and Mechanical Properties of Filled SU-8 Polymer (original) (raw)
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Tribology Online, 2016
Different concentrations of graphite powder (particle size < 20 µm) were added for the enhancement in mechanical and tribological properties of SU-8 polymer. The materials were studied as thick coatings with thickness in the range of ~ 35-40 µm on glass substrate. SU-8 and SU-8/graphite composite properties were examined using atomic force microscope (for nanoindentation test) and pin-on-disc tribometer (for friction and wear). The surface characteristics were studied using Optical Microscope, Goniometer and 3D Profilometer. At 10 and 20 wt% graphite concentration, it was found that several properties were enhanced such as elastic modulus ~ 2.2 times, marginal increment in hardness and approximately same water contact angle and same surface free energy (SFE) as compared with those of pure SU-8. More importantly, 10 wt% graphite concentration has given two-times lower steady-state coefficient of friction and ~ 10 times more wear life compared to those of pure SU-8. The 20 wt% composite gave higher coefficient of friction but lower wear rate than the 10 wt% composite.
SU8 nanocomposite coatings with improved tribological performance for MEMS
Surface & Coatings Technology, 2006
The increasing interests in micro-electro-mechanical systems (MEMS) has raised the requirement for photoresist materials with improved friction and wear properties for mechanically loaded 3D shaped microstructures. In this work, SU8 photoresist layers reinforced with different amounts of silica nanoparticles were produced and thermally treated. Dry sliding tests indicate that SU8 composite epoxies produced in the form of thin films exhibit similar or even better tribological properties than bulk epoxies. The SU8 nanocomposites exhibit reduced wear rates and frictional coefficient compared to the un-reinforced material. Further, nanoparticle content, heat treatment and nature of the sliding counter piece were found to affect wear and friction. The tribological behaviour was discussed in terms of mechanical properties and contact pressures.
Lubrication Mechanism of SU-8/Talc/PFPE Composite
Tribology Letters, 2017
SU-8, a very promising structural polymer for the next-generation 3D fabrication of micro-electromechanical systems (MEMS), has extremely poor tribological properties. The improvement in tribological properties has been recently addressed by developing SU-8/talc (30 wt%) /perfluoropolyether (PFPE) (30 wt%) composite. This composite showed wear durability approximately five orders of magnitude greater in comparison with that of pure SU-8. This drastic increment was found to be because of the in situ lubrication mechanism provided by the PFPE liquid droplets present in the composite. In this present investigation, the lubrication mechanism for SU-8/talc (30 wt%)/PFPE (10, 20 and 30 wt%) composites was further investigated by varying sliding speed (0.1-1.0 m/s) and normal load (2 N and 4 N) using silicon nitride ball of 4 mm diameter as the counterface. The data show that the coefficient of friction and interfacial shear strength follows linear relations with the logarithm of the sliding velocity. Normal load has effect on marginally reducing the coefficient of friction.
Tribology - Materials, Surfaces & Interfaces, 2016
SU-8, an epoxy-based negative photoresist polymer, is highly suitable for making micro-electromechanical systems (MEMS) structures. Despite fabrication advantages, its bulk mechanical and tribological properties are the main limitations for application as MEMS material. Carbon filler materials such as graphene, graphite and multi-walled carbon nanotube (MWCNT) are added to SU-8 for tribological and mechanical property enhancements. SU-8/(5 wt%) graphite composite has performed better for the steady-state coefficient of friction at all loads including for the speed effect. SU-8/(5 wt%) MWCNT has shown excellent wear resistance. At 10 wt% graphite content, SU-8/graphite is superior in tribological performance to other composites tested.
An in-situ heating effect study on tribological behavior of SU-8+PFPE composite
Wear, 2013
SU-8 polymer is an emerging structural material for micro-fabrication of MEMS/NEMS devices using photolithography process. However, poor tribological properties of SU-8 restrict its wide applications as a very reliable MEMS material. In our earlier work [1], we have developed SU-8 composites which reduced friction and enhanced wear life of SU-8 by more than four orders of magnitude. The improvements in the properties were attributed to the self-lubricating nature of the composite by continuous supply of the lubricant into the worn areas, the lubricious nature of the filler lubricant perfluoropolyether (PFPE), and possible chemical bonding between SU-8 and PFPE. In this current work, we further investigated the effect of in-situ heating on the tribological performances of the SU-8þ PFPE composite. In-situ heating from room temperature (25 1C) to 100 1C showed a strong effect on the tribological behavior of SU-8þPFPE composite by reducing its initial and steady-state friction coefficients by $ 2 and $ 7 times, respectively. Wear life (n) increased by more than three times due to in-situ heating. Greater surface area coverage by the spreading of PFPE lubricant and migration of PFPE from the bulk to surface are found responsible for this superior tribological performance of the composite at high temperatures.
AFM Characterization of Temperature Effect on the SU-8 Mechanical and Tribological Properties
Polymers, 2022
This study presents the effect of temperature on the mechanical and tribological properties of SU-8 polymer. The temperature of investigated samples increasing during testing and the variation of mechanical and tribological properties were monitored. The samples for tests were SU-8 hard baked at different temperatures. The hard bake temperature changes the mechanical and tribological properties of polymers. The aim of this research work is the reliability design improvement of SU-8 microstructures from electro-thermally actuated devices where a thermal gradient produces the softening and modification of SU-8 behavior. As a function of the hard baked temperature, different mechanical and tribological properties were experimentally determined using the atomic force microscopy (AFM) technique. The mechanical properties of interest are the modulus of elasticity and hardness. The investigated tribological properties involve the adhesion and friction forces. The modulus of elasticity and ...
Friction, 2019
In this study, SU-8 and its composites are fabricated by blending 10 wt.% hexagonal boron nitride (h-BN) fillers with/without lubricants, such as 10 wt.% base oil (SN150) and 20 wt.% perfluoropolyether (PFPE). The thickness of SU-8 and its composites coating is fabricated in the range ~100-105 μm. Further, SU-8 and its composites are characterized by a 3D optical profilometer, atomic force microscopy, scanning electron microscopy, a thermal gravimetric analyzer, a goniometer, a hardness tester, and an optical microscope. Under a tribology test performed at different normal loads of 2, 4, and 6 N and at a constant sliding speed of 0.28 m/s, the reduction in the initial and steady-state coefficient of friction is obtained to be ~0.08 and ~0.098, respectively, in comparison to SU-8 (~0.42 and ~0.75), and the wear resistance is enhanced by more than 103 times that of pure SU-8. Moreover, the thermal stability is improved by ~80-120 °C , and the hardness and elastic modulus by ~3 and ~2 times that of pure SU-8, respectively. The SU-8 composite reinforced with 10 wt.% h-BN and 20 wt.% PFPE demonstrated the best thermo-mechanical and tribological properties with a nano-textured surface of high hydrophobicity.
Key Engineering Materials, 2013
The aim of the present work is the investigation of the influence of graphite powder addition to an unsaturated polyester type polymer (32% styrene content in mass) on the mechanical and tribological properties. For this purpose, we conducted bending tests and wear tests with a combination of four loads and three speeds for three different compositions (0, 1 and 2% graphite). The wear tests are carried out on a dry type pin on disk tribometer. The disk is made of quenched and annealed C48 steel (540 Hv hardness). Before the rubbing process, the discs are subjected to polishing in order to obtain approximately the same initial surface roughness. The results show that the addition of graphite powder improves the tribological properties; a noticeable decrease of the coefficient of friction, the mass loss and the wear rate are achieved with the increase of the graphite powder percentage for all sliding speeds and loads. A 2% graphite content causes a drop of the friction coefficient fro...
SU-8 Composite Based “Lube-tape” for a Wide Range of Tribological Applications
Micromachines, 2014
In a previous work, we have developed a perflouropolyether (PFPE) lubricant droplet-filled SU-8 composite which promotes bonding between the molecules of SU-8 and PFPE and provides excellent boundary lubrication. The SU-8 + PFPE composite has enhanced the wear durability of SU-8 by more than four orders of magnitude. In this work, the same SU-8 + PFPE composite was used to fabricate a stand-alone laminate film called "Lube-tape". It has integrated two layers of approximately 90 microns thickness each; the top layer is made of SU-8 + PFPE composite and the bottom layer of pristine SU-8. Thus, a single tape can have drastically contrasting high friction and low friction properties on its two surfaces. The composite side has the initial coefficient of friction ~7 times lower and the wear life more than four orders of magnitude than those of the pristine SU-8 side. This lube tape can be used on any load bearing surface to improve the tribological performance by simply pasting the pristine SU-8 side onto the substrate.