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   COLLOQUIUM OF THE LABORATORY FOR COMPUTER DESIGN OF MATERIALS        
                   School of Computational Sciences	
                           (CSI 898-Sec 001) 
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            Molecular Dynamics Simulations of the Friction of 
                     Self-Assembled Monolayer Systems

                            Judith A. Harrison
     Chemistry Department,United States Naval Academy, Annapolis, MD 

Hydrocarbon materials have traditionally been used to prevent the 
friction and wear of mechanical components in sliding contact. One 
important example of this is the use of oil in conventional 
combustion engines. The advent of chemical vapor deposition 
technology has piqued interest in the use of solid hydrocarbons as 
lubricants in systems such as microelectromechanical devices. A 
detailed knowledge of the molecular-scale mechanisms responsible for 
lubrication would be invaluable in the design of novel solid 
lubricants. We are using molecular dynamics to examine the 
atomic-scale phenomena governing the tribology of 
hydrocarbon-containing systems. Because liquid hydrocarbons and 
boundary layer lubricants, such as self-assembled monolayers, are to 
be studied, the potential energy function must include intermolecular 
interactions. 

The new adaptive intermolecular reactive empirical 
bond-order potential can simulate reactive and non-reactive 
processes in a wide range of environments including liquid 
hydrocarbons and self-assembled monolayers. We have conducted 
extensive simulations that have examined the friction of alkane 
monolayers attached to diamond surfaces or model self-assembled 
monolayer systems. We have examined friction as a function of packing 
density, chain length, and sliding direction. Recent atomic force 
microscope measurments unambiguously demonstrate that decreasing the 
packing density, or the disorder of the film, increases the friction. 
Our simulations reproduce this trend and provide an atomic-scale 
explanation for this observation.

                         Monday , October 15, 2001
                                  4:30 pm
                        Room 206, Science & Tech. I

Refreshments will be served at 4:15 PM.
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Find the schedule at http://www.csi.gmu.edu/lcdm/seminar/schedule.html