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Dynamics of water, hydrated-ions and charged polymers in highly-confined films, and their role in friction modification

Published online by Cambridge University Press:  01 February 2011

Jacob Klein ,
Uri Raviv ,
Susan Perkin ,
Nir Kampf  and
Suzanne Giasson
Jacob Klein
Affiliation:
Weizmann Institute of Science, Rehovot 76100, Israel P.T.C.L., University of Oxford, Oxford OX1 3QZ, U.K.
Uri Raviv
Affiliation:
Weizmann Institute of Science, Rehovot 76100, Israel
Susan Perkin
Affiliation:
P.T.C.L., University of Oxford, Oxford OX1 3QZ, U.K.
Nir Kampf
Affiliation:
Weizmann Institute of Science, Rehovot 76100, Israel
Suzanne Giasson
Affiliation:
Département de Chimie, Université de Montréal C.P. 6128, Montréal, Qué., H3C 3J7, Canada
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Abstract

Recent studies have revealed that, in contrast to non-associating liquids such as oils or organic solvents, salt-free water retains a viscosity close to its bulk value even when confined to films thinner than some 3 nm, indeed down to only one or two monolayers thick [1,2]. For the case of high concentration aqueous salt solution compressed down to subnanometer films between charged surfaces, the trapped hydrated ions serve to act as molecular ball-bearings, sustaining a large load while remaining very fluid under shear [3]. This behaviour is attributed to the tenacity of the hydration sheaths together with their rapid relaxation time. Finally, a very recent study [4] has shown that when charged polymer brushes in aqueous media are compressed and slid past each other, they provide a lubrication that is considerably superior to that afforded by neutral brushes: This is attributed on the one hand to the resistance to mutual interpenetration of the chains due to entropic barriers in the good-solvent conditions, and, on the other hand, to the hydration-sheaths on the charged polymer segments which can act – as noted above – as molecular ball-bearings.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 790: Symposium P – Dynamics in Small Confining Systems–2003 , 2003 , P6.1
Copyright
Copyright © Materials Research Society 2004

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References

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