In Situ Lubrication of SU-8/Talc Composite with Base Oil (SN150) and Perfluoropolyether as Fillers (original) (raw)
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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.
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.
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.
Tribology Letters, 2014
In an earlier work, we demonstrated the development of SU-8 composites using perfluoropolyether (PFPE) as lubricant filler which reduced friction coefficient by *7 times and enhanced wear life of SU-8 by more than four orders of magnitude. In this work, we have investigated the role of chemical bonding between SU-8 and PFPE molecules using two types of PFPE lubricants (i.e., Fomblin Ò Z-dol and Z-03) in improving the tribological properties of the composite. Z-dol has polar (-OH) end groups whereas Z-03 has non-polar (CF 3 ) end groups. SU-8 with Z-dol (SU-8 ? Z-dol) films yielded *8 times greater wear life than SU-8 with Z-03 (SU-8 ? Z-03) films and more by four orders of magnitude than pure SU-8. The nature of the films was analyzed in detail by chemical and physical characterization techniques like X-ray photoelectron spectroscopy, water contact angle and thermo-gravimetric analysis. The results validated the role of polar end functional group of Z-dol in covalent binding with SU-8 upon UV plasma treatment that resulted in improved tribological properties.
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.
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.
The effect of lubricant additives on friction and wear studies of polyphenylene sulphide
Journal of Synthetic Lubrication, 1987
Polyphenylene sulphide is a polymer with good thermal stability and high crystallinity. This paper summarizes the results of friction and wear studies of polyphenylene sulphide and its composites made with conventional solid lubricants to ascertain the suitability of the material as a matrix for solid lubricant additives. The polymer itself has a high coefficient of friction. Wear rate increases with load and speed. Addition of solid lubricant additives helps in improving the friction and wear of the polymer. Composites with MoS2-Sb203 and PTFE gave better results than composites made b y the addition of graphite and MoS2graphite. Wear rate of these composites increased with load and speed; but load and speed had little effect on friction.
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.
Wear Behaviour of Polyphenylene Sulphide Composites During Dry Sliding Tests
Two polyphenylene sulphide matrix-based composites were investigated: PPS GF 40 (PPS -polyphenylene sulphide +40% glass fibers) and PPS PVX (PPS -polyphenylene sulphide +10% PTFE+10% carbon fibers +10% graphite). The tribological properties of these composites were tested on a Universal Tribometer UMT-2 (CETR) apparatus (pin-on-disc test, in dry sliding, with the help of a pin-on-disk tribotester. The tribological behaviour was found to depend on the adding material(s) in the tested composites and better results were obtained for the composite containing solid lubricants (PTFE and graphite).