S-1 SUPPORTING INFORMATION Influence of environmental humidity on the wear and friction of a silica / silicon tribopair lubricated with a hydrophilic ionic liquid Andrea Arcifa a , Antonella Rossi a, b , Rosa M. Espinosa-Marzal a, c , Nicholas D. Spencer a * a Lab. for Surface Science and Technology, Dept. of Materials, ETH Zurich, CH-8093 Zurich, Switzerland b Dipartimento di Scienze Chimiche e Geologiche, Università di Cagliari, 09042 Cagliari, Italy c Laboratory for Smart Interfaces in Environmental Nanotechnology, Department of Civil & Environmental Engineering, University of Illinois at Urbana-Champaign 3215 Newmark Lab, MC 2, Urbana, IL 61801, USA Corresponding Author *To whom correspondence should be addressed. Phone: +41-44-632-5850; fax: +41- 44-633-1027; e-mail: nspencer@ethz.ch