Micro/nanotribological characterization of PDMS and PMMA used for BioMEMS/NEMS applications

Tribology is the primary cause of concern for various micro/nano-electromechanical systems (MEMS/NEMS) and biological applications of MEMS/NEMS (BioMEMS/NEMS) due to failures resulting from high adhesion and friction. Polymers are gaining significant importance due to their myriad advantages over conventional silicon-based components and the related micromachining techniques. Micro/nanotribological characterization of polymers is therefore essential. Adhesion and friction of single crystal silicon with native oxide layer and two polymers-poly(dimethylsiloxane) (PDMS) and poly(methylmethacrylate) (PMMA)-are studied and their dependence on rest time, relative humidity and sliding velocity is evaluated. Contact angle measurements and Laplace force calculations show that both PDMS and PMMA are highly hydrophobic and unlike silicon, their adhesive force is independent of rest time and relative humidity. Coefficient of friction for both polymers is lower than that for silicon. Velocity dependence studies indicate higher energy dissipation and localized melting for PMMA at high velocities. The PDMS sample absorbs asperity impacts and hence friction is lower for PDMS even at high velocities. Overall, owing to their highly hydrophobic surfaces and low friction PDMS and PMMA are ideally suited for use in micro/nanodevices that operate in varying environmental conditions and at high relative sliding velocities.