Thermally activated lubrication with alkanes: The effect of chain length

¹ Laboratoire de Physique Statistique de l'Ecole Normale Supérieure associée au CNRS et aux universités Paris VI et Paris VII 24, rue Lhomond, 75231 Paris Cedex 05, France
² Tribology Research Institute, Southwest Jiaotong University Chengdu 610031, Sichuan Province, PRC

Received: 24 July 2002
Accepted: 29 October 2002

Abstract

Friction forces measurements between smooth surfaces across two layers of linear alkanes over five decades of speeds are presented. A maximum friction dissipation is observed at a characteristic speed. This behaviour is described by a new approach: the formation and destruction of molecular bridges between confined alkane layers. These bridges which interdigitate between the layers exhibit a thermally activated resistance to shear. An analytical model involving activation barriers accounts for the overall behaviour of the speed dependence of the forces over four decades. This first simple semi-quantitative description sheds new light on the subtle mechanisms of friction at the nanoscale level and shows how the molecular length influences the tribological properties of the liquid.