title: Modelling clustering of vertically aligned carbon nanotube arrays.
abstract: Previous research demonstrated that arrays of vertically aligned carbon nanotubes (VACNTs) exhibit strong frictional properties. Experiments indicated a strong decrease of the friction coefficient from the first to the second sliding cycle in repetitive measurements on the same VACNT spot, but stable values in consecutive cycles. VACNTs form clusters under shear applied during friction tests, and self-organization stabilizes the mechanical properties of the arrays. With increasing load in the range between 300 µN and 4 mN applied normally to the array surface during friction tests the size of the clusters increases, while the coefficient of friction decreases. To better understand the experimentally obtained results, we formulated and numerically studied a minimalistic model, which reproduces the main features of the system with a minimum of adjustable parameters. We calculate the van der Waals forces between the spherical friction probe and bunches of the arrays using the well-known Morse potential function to predict the number of clusters, their size, instantaneous and mean friction forces and the behaviour of the VACNTs during consecutive sliding cycles and at different normal loads. The data obtained by the model calculations coincide very well with the experimental data and can help in adapting VACNT arrays for biomimetic applications.
authors.affiliation: Functional Morphology and Biomechanics, Zoological Institute , Kiel University , Am Botanischen Garten 1-9, 24118 Kiel , Germany.
authors.forename: Clemens F
authors.initials: CF
authors.lastname: Schaber
authors.affiliation: Functional Morphology and Biomechanics, Zoological Institute , Kiel University , Am Botanischen Garten 1-9, 24118 Kiel , Germany ; Department of Electronic and Kinetic Properties of Non-linear Systems , Donetsk Institute for Physics and Engineering, National Academy of Sciences , 83114 Donetsk , Ukraine ; FG Systemdynamik und Reibungsphysik , Technische Universität Berlin, Institut für Mechanik , Sekr. C8-4, Raum M 122, Straße des 17. Juni 135, 10623 Berlin , Germany.
authors.forename: Alexander E
authors.initials: AE
authors.lastname: Filippov
authors.affiliation: Technische Universität Darmstadt, Fachbereich Chemie , Eduard-Zintl-Institut für Anorganische und Physikalische Chemie , Alarich-Weiss-Straße 12, 64287 Darmstadt , Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Heinlein
authors.affiliation: Technische Universität Darmstadt, Fachbereich Chemie , Eduard-Zintl-Institut für Anorganische und Physikalische Chemie , Alarich-Weiss-Straße 12, 64287 Darmstadt , Germany.
authors.forename: Jörg J
authors.initials: JJ
authors.lastname: Schneider
authors.affiliation: Functional Morphology and Biomechanics, Zoological Institute , Kiel University , Am Botanischen Garten 1-9, 24118 Kiel , Germany.
authors.forename: Stanislav N
authors.initials: SN
authors.lastname: Gorb
keywords: biomimetics; carbon nanotubes; clustering; friction; gecko-inspired attachment; vertically arranged carbon nanotube arrays