Investigation of nanotriboloical properties of alkylthiol and biphenyl thiol self assembled monolayers

Huiwen Liu, Bharat Bhushan

Computer Microtribology and Contamination Laboratory

206 W. 18 th Avenue, The Ohio State University
Columbus, OH 43210-1107, USA

Understanding the relationships between molecular structure and nanotribological performance, as well as the nanotribological mechanisms of self-assembled monolayers are quite important for molecular tailoring for efficient lubrication. For this purpose, five kinds of alkylthiol and biphenyl thiol SAMs with different surface terminals (-CH₃, -COOH and -OH) and head groups (-SH and -OH) were prepared. The influences of spacer chains (carbon chain and biphenyl chain), crosslinking of biphenyl spacers and the head groups (-SH and -OH) on the nanotribological properties of SAMs were investigated by AFM. The stiffness of SAMs was determined by AFM in force modulation mode and penetration depths are measured from load-displacement curves. The adhesion, friction and wear mechanisms of SAMs at molecular scale are discussed. A molecular spring model is presented to clarify the frictional behavior of SAMs.