Self-lubricating SU-8 Nanocomposites for Microelectromechanical Systems Applications
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ORIGINAL PAPER
Self-lubricating SU-8 Nanocomposites for Microelectromechanical Systems Applications Prabakaran Saravanan • Nalam Satyanarayana Sujeet K. Sinha
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Received: 20 April 2012 / Accepted: 3 October 2012 / Published online: 14 October 2012 Ó Springer Science+Business Media New York 2012
Abstract SU-8 is an industrially useful photoresist polymer for micro-fabrication because of its unique UVsensitive 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 SiO2, 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 by *6–9 times and increased wear life by more than four orders of magnitude. The mechanical properties such as the elastic modulus and the hardness have increased by *1.4 times. These SU-8 nanocomposites can be used as a self-lubricating structural material for MEMS applications requiring no external lubrication. As well, these nanocomposites can find applications in many tribological components of traditional machines. Keywords MEMS
Lubrication Polymer Self-lubrication
1 Introduction Micro-electro mechanical system (MEMS) is an emerging field of interest in almost every industry including automotive, P. Saravanan N. Satyanarayana S. K. Sinha (&) Department of Mechanical Engineering, National University of Singapore, Singapore 117576, Singapore e-mail: [email protected]
bio-engineering/biomedical, telecommunications, electronics, space, military, gaming industry, etc. [1]. There are many challenges to the effective operation of these devices primarily because of their small length scale. As the size of the MEMS devices is in micrometer (or sub-millimeter) range, the surface-to-volume ratio is very high and hence surface forces such as van der Waals, capillary, electrostatic, and chemical forces play important roles when compared to the gravity and inertial forces on the device performance [2]. Hence, in these devices, the interfacial forces are comparable or higher than the forces causing the device motion. The major challenge is from the tribological issues i.e., high friction, high adhesive force, and low wear durability [2–4]. Hence, if these tribological issues are not addressed properly, they limit the performance, durability, and reliability of the MEMS devices [2]. Although Si has been the mainstay structural material for fabricating MEMS devices, recently SU-8 has been replacing Si for certain applications. Si has the advantage of compatibility with MEMS micro-fabrication processes; however, it has many inherent drawbacks such as brittle
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