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Simulation of Thermal Stability and Friction: A Lubricant Confined Between Monolayers of Wear Inhibitors on Iron Oxide

Published online by Cambridge University Press:  10 February 2011

T. Çağin ,
Y. Zhou ,
E. S. Yamaguchi ,
R. Frazier ,
A. Ho ,
Y. Tang  and
W. A. Goddard III
T. Çağin
Affiliation:
Materials and Process Simulation Center, 139-74 California Institute of Technology, Pasadena, California 91125
Y. Zhou
Affiliation:
Materials and Process Simulation Center, 139-74 California Institute of Technology, Pasadena, California 91125
E. S. Yamaguchi
Affiliation:
Chevron Chemical Company, 100 Chevron Way, Richmond, California 94802
R. Frazier
Affiliation:
Chevron Chemical Company, 100 Chevron Way, Richmond, California 94802
A. Ho
Affiliation:
Chevron Chemical Company, 100 Chevron Way, Richmond, California 94802
Y. Tang
Affiliation:
Chevron Petroleum Technology Company, 1300 each Boulevard, La Habra, California 90631
W. A. Goddard III
Affiliation:
Materials and Process Simulation Center, 139-74 California Institute of Technology, Pasadena, California 91125
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Abstract

To understand antiwear phenomena in motor engines at the atomic level and provide evidence inselecting future ashless wear inhibitors, we studied the thermal stability of the self-assembled monolayer(SAM) model for dithiophosphate (DTP) and dithiocarbamate (DTC) molecules on the iron oxidesurface using molecular dynamics. The interactions for DTP, DTC and Fe2O3 are evaluated based on aforce field derived from fitting to ab initio quantum chemical calculations of dimethyl DTP (and DTC)and Fe(OH)2(H2O)2-DTP (DTC) clusters. MD simulations at constant-NPT are conducted to assesrelative thermal stabilities of the DTP and DTC with different pendant groups (n-propyl, i-propyl, npentyl.and i-pentyl). To investigate frictional process, we employ a steady state MD method, in whichone of the Fe2O3 slabs maintained at a constant linear velocity. We obtain the time averaged normaland frictional forces from the interatomic forces. Then, we calculated the friction coefficient at theinterface between SAMs of DTP and the confined lubricant, hexadecane, to assess the shear stability ofDTPs with different pendant groups.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 543: Symposium W – Dynamics in Small Confining Systems IV , 1998 , 79
Copyright
Copyright © Materials Research Society 1999

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