Exploring Lubricants: Inves6ga6ng the Solid-‐ Liquid Interface Using Molecular Simula6on Kelly E. Anderson Department of Chemistry, Roanoke College, Salem, VA 24153 9.0 Ether
8.0
Alkane 7.0 6.0 Density (g/mL)
Monte Carlo simula6ons provide an ideal method to examine atomic-‐scale behavior, such as the interac6on of the molecules within a lubricants with a solid surface. In par6cular, we are interested in compe66ve adsorp6on from mul6component, alkane-‐ rich liquids, as well as the effects of the substrate on molecular orienta6on within the liquid. Strong evidence of preferen6al adsorp6on as a func6on of strength of aQrac6on with the solid substrate is seen in all simula6ons. For example, the figures to the right show densi6es profiles of these two mixtures near the solid substrate. For a strongly interac6ng ether molecule in an equimolar mixture with a linear alkane of the same length, the ether is the majority species at the interface (leV). In the region within six angstroms of the solid, the mole frac6on of the ether is 0.99. When the number of interac6on sites in the alkane is increased, the composi6on shiVs toward more alkane at the surface. This is evident in mixtures of the same ether with an alkane with a similar total heat of adsorp6on with the surface. In this case, the mole frac6on of the ether within six angstroms of the surface is 0.76 (right).
5.0 4.0 3.0 2.0 1.0 0.0 0
5
0 5 10 10 15 20 0 Distance from Solid Surface (Å)
15
20
