[en] Long-ranged forces between surfaces in a liquid control effects from colloid stability [1] to biolubrication [2], and can be modified either by steric factors due to flexible polymers [3], or by surface charge effects [4]. In particular, neutral polymer 'brushes' may lead to a massive reduction in sliding friction between the surfaces to which they are attached [5-7], whereas hydrated ions can act as extremely efficient lubricants between sliding charged surfaces [8]. Here we show that brushes of charged polymers (polyelectrolytes) attached to surfaces rubbing across an aqueous medium result in superior lubrication compared to other polymeric surfactants. Effective friction coefficients with polyelectrolyte brushes in water are lower than about 0.0006-0.001 even at low sliding velocities and at pressures of up to several atmospheres (typical of those in living systems). We attribute this to the exceptional resistance to mutual interpenetration displayed by the compressed, counterion-swollen brushes, together with the fluidity of the hydration layers surrounding the charged, rubbing polymer segments. Our findings may have implications for biolubrication effects, which are important in the design of lubricated surfaces in artificial implants, and in understanding frictional processes in biological systems.
Research Center/Unit :
Center for Education and Research on Macromolecules (CERM)
Disciplines :
Chemistry Materials science & engineering
Author, co-author :
Raviv, Uri; Weizmann Institute of Science, Rehovot, Israel
Giasson, Suzanne; University of Montreal, Québec, Canada > Department of Chemistry and School of Pharmacy
Kampf, Nir; Weizmann Institute of Science, Rehovot, Israel
Gohy, Jean-François; Université de Liège - ULiège > Department of Chemistry > Center for Education and Research on Macromolecules (CERM)
Jérôme, Robert ; Center for Education and Research on Macromolecules (CERM) > Department of Chemistry > Center for Education and Research on Macromolecules (CERM)
Klein, Jacob; Weizmann Institute of Science, Rehovot, Israel and Oxford University, UK > Physical and Theoretical Chemistry Laboratory
BELSPO - SPP Politique scientifique - Service Public Fédéral de Programmation Politique scientifique F.R.S.-FNRS - Fonds de la Recherche Scientifique The Eshkol Foundation (U.R.) The Canadian Friends of the Weizmann Institute (Charpak-Vered) The US-Israel BSF The Deutsche-Israelische Program, and the Israel Science Foundation
Commentary :
The authors acknowledge Nature (Nature Publishing Group) for allowing them to archive this paper.
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