Eur. Phys. J. E (2008) 27: 37-46
https://doi.org/10.1140/epje/i2008-10349-8

Frictional properties of confined polymers

¹ IFF, FZ-Jülich, 52425, Jülich, Germany
² Novo Nordisk A/S, Research and Development, DK-3400, Hillerod, Denmark
³ Department of Mechanical Engineering, Technical University of Denmark, DK-2800, Lyngby, Denmark
⁴ Physics Faculty, Moscow State University, 117234, Moscow, Russia

^* e-mail: B.Persson@fz-juelich.de

Received: 25 February 2008
Revised: 11 April 2008
Published online: 24 July 2008

Abstract

We present molecular dynamics friction calculations for confined hydrocarbon solids with molecular lengths from 20 to 1400 carbon atoms. Two cases are considered: a) polymer sliding against a hard substrate, and b) polymer sliding on polymer. In the first setup the shear stresses are relatively independent of molecular length. For polymer sliding on polymer the friction is significantly larger, and dependent on the molecular chain length. In both cases, the shear stresses are proportional to the squeezing pressure and finite at zero load, indicating an adhesional contribution to the friction force. The friction decreases when the sliding distance is of the order of the molecular length indicating a strong influence of molecular alignment during run-in. The results of our calculations show good correlation with experimental work.