title: Boundary lubrication with a liquid crystal monolayer.
abstract: We study boundary lubrication characteristics of a liquid crystal (LC) monolayer sheared between two crystalline surfaces by nonequilibrium molecular dynamics simulations, using a simplified rigid bead-necklace model of the LC molecules. We consider LC monolayers confined by surfaces with three different atomic structures, subject to different shearing velocities, thus approximating a wide variety of materials and driving conditions. The time dependence of the friction force is studied and correlated with that of the orientational order exhibited by the LC molecules, arising from the competition between the effect of the structure of the confining surfaces and that of the imposed sliding direction. We show that the observed stick-slip events for low shear rates involve order-disorder transitions, and that the LC monolayer no longer has enough time to reorder at high shear rates, resulting in a smooth sliding regime. An irregular stick-slip phase between the regular stick-slip and smooth sliding is observed for intermediate shear rates regardless of the surface structure.
authors.affiliation: COMP Centre of Excellence, Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 AALTO, Espoo, Finland.
authors.forename: W
authors.initials: W
authors.lastname: Chen
authors.affiliation: Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33010 Tampere, Finland.
authors.forename: S
authors.initials: S
authors.lastname: Kulju
authors.affiliation: COMP Centre of Excellence, Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 AALTO, Espoo, Finland.
authors.forename: A S
authors.initials: AS
authors.lastname: Foster
authors.affiliation: COMP Centre of Excellence, Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 AALTO, Espoo, Finland.
authors.forename: M J
authors.initials: MJ
authors.lastname: Alava
authors.affiliation: COMP Centre of Excellence, Department of Applied Physics, Aalto University, P.O. Box 11100, FI-00076 AALTO, Espoo, Finland.
authors.forename: L
authors.initials: L
authors.lastname: Laurson
mesh_terms: D050866:Liquid Crystals / Q000737:chemistry*; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation