Molecular simulation study of nanoscale friction between alkyl monolayers on Si„111... immersed in solvents

Nonequilibrium molecular dynamics simulations were performed to study nanoscale friction between two Si~111! surfaces covered with alkyl monolayers immersed in liquid solvents. Three pairs of interfaces, ranging from hydrophobic CH3 /CH3 to hydrophilic OH/OH, were studied. Three solvents, including water, methanol, and n-decane were used to represent different solvent polarities. It was showed that friction was dependent not only on surface hydrophobicity, but also on solvent polarity. In polar solvents ~e.g., water!, friction is much larger for hydrophilic than hydrophobic interfaces, while in nonpolar solvents, e.g., n-decane, friction has no significant difference for both hydrophobic and hydrophilic monolayers. A fundamental understanding of friction at different interfaces in various solvents is very important to microor nanoelectromechanical systems ~MEMS/NEMS!, particularly, bio-MEMS/NEMS. © 2003 American Institute of Physics. @DOI: 10.1063/1.1578055#