title: Origins of hydration lubrication.
abstract: Why is friction in healthy hips and knees so low? Hydration lubrication, according to which hydration shells surrounding charges act as lubricating elements in boundary layers (including those coating cartilage in joints), has been invoked to account for the extremely low sliding friction between surfaces in aqueous media, but not well understood. Here we report the direct determination of energy dissipation within such sheared hydration shells. By trapping hydrated ions in a 0.4-1 nm gap between atomically smooth charged surfaces as they slide past each other, we are able to separate the dissipation modes of the friction and, in particular, identify the viscous losses in the subnanometre hydration shells. Our results shed light on the origins of hydration lubrication, with potential implications both for aqueous boundary lubricants and for biolubrication.
authors.affiliation: 1] Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel [2] State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
authors.forename: Liran
authors.initials: L
authors.lastname: Ma
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Anastasia
authors.initials: A
authors.lastname: Gaisinskaya-Kipnis
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Nir
authors.initials: N
authors.lastname: Kampf
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Jacob
authors.initials: J
authors.lastname: Klein
mesh_terms: D017276:Friction; D007596:Joints / Q000378:metabolism*; D008153:Lubrication; D008962:Models, Theoretical