Abstract
In this paper, SU-8 is an industrially useful photo resist polymer for micro-fabrication because of its unique UV sensitive curing property. It is also used as a structural material for micro-machines such as micro-electro mechanical systems (MEMS). However, it has poor tribological and mechanical properties which make SU-8 inferior to Si, the mainstay MEMS material today. In this paper, we report the fabrication of SU-8 nanocomposites which are self-lubricating and have better mechanical properties. The liquid lubricant i.e., perfluoropolyether (PFPE) and nanoparticles such as SiO<sub>2</sub>, CNTs, and graphite were added into SU-8 for this purpose. These self-lubricating SU-8 + PFPE and SU-8 + PFPE + nanoparticle composites have shown a reduction in the initial coefficient of friction, increased wear life and the mechanical properties such as the elastic modulus and the hardness have increased. We have used perfluoropolyether (PFPE) as in-situ lubricant filler to SU-8. This composite material has shown highly superior friction and wear performance over pristine SU-8 and any such alternative material for this application. We have shown that the mechanical property can also be enhanced by this method if we utilize nano-particles for further reinforcement. This self-lubricating SU-8+PFPE composite can be used for the fabrication of MEMS applications requiring no external lubrication, and also these composites can find applications in many tribological components of traditional machines. The thickness of SU-8 and its composites coating is fabricated in the range ∼100–105 ±m. 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 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.
Highlights
SU-8 is a commonly used epoxy-based negative photoresist
In order to improve the tribology of SU-8 through self-lubrication, we have developed bulk SU-8 composites by using the liquid lubricants such as PFPE lubricant and nano-fillers such as SiO2, CNTs and graphite as filler materials
Apart from this, the SU-8 nanocomposites can find application as a lubricious and wear resistant coating for several tribological components made from different materials
Summary
Negative refers to a photoresist whereby the parts exposed to UV become cross-linked, while the remainder of the film remains soluble and can be washed away during development Microsystems such as MEMS (micro electro mechanical systems) are small scale devices (from few μm to several hundred μm), designed to perform variety of operations in various industries including automotive, bio-engineering, bio-medical and military etc. In order to improve the tribology of SU-8 through self-lubrication, we have developed bulk SU-8 composites by using the liquid lubricants such as PFPE lubricant and nano-fillers such as SiO2, CNTs and graphite as filler materials. These SU-8 composites have yielded much improved tribological properties when compared to the pristine SU-8 [2, 3]. The initial and steady-state coefficients of friction were reduced [7, 8]
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