title: Does rotational melting make molecular crystal surfaces more slippery?
abstract: The surface of a crystal made of roughly spherical molecules exposes, above its bulk rotational phase transition at T = Tr, a carpet of freely rotating molecules, possibly functioning as "nanobearings" in sliding friction. We explored by extensive molecular dynamics simulations the frictional and adhesion changes experienced by a sliding C60 flake on the surface of the prototype system C60 fullerite. At fixed flake orientation both quantities exhibit only a modest frictional drop of order 20% across the transition. However, adhesion and friction drop by a factor of ∼2 as the flake breaks its perfect angular alignment with the C60 surface lattice suggesting an entropy-driven aligned-misaligned switch during pull-off at Tr. The results can be of relevance for sliding Kr islands, where very little frictional differences were observed at Tr, but also to the sliding of C60-coated tip, where a remarkable factor ∼2 drop has been reported.
authors.affiliation: Empa-Swiss Federal Laboratories for Materials Science and Technology, CH-8600 Dübendorf, Switzerland. andrea.benassi@empa.ch tosatti@sissa.it.
authors.forename: Andrea
authors.initials: A
authors.lastname: Benassi
authors.forename: Andrea
authors.initials: A
authors.lastname: Vanossi
authors.forename: Carlo A
authors.initials: CA
authors.lastname: Pignedoli
authors.forename: Daniele
authors.initials: D
authors.lastname: Passerone
authors.forename: Erio
authors.initials: E
authors.lastname: Tosatti