LUBRICATION BY CHARGED POLYMERS JACOB KLEIN PHYSICAL

LUBRICATION AND SEALER SPECIFICATIONS FLYWHEEL BOLTS ENGINE OIL I
LUBRICATION BY CHARGED POLYMERS JACOB KLEIN PHYSICAL



LUBRICATION BY CHARGED POLYMERS


Lubrication by Charged Polymers


Jacob Klein*

Physical and Theoretical Chemistry, Oxford University, Oxford OX1 3QZ, U.K. and Weizmann Institute, Rehovot 76353, Israel.



Neutral polymer brushes form extended structures at surfaces, and when two brushes are mutually compressed entropic factors result in very limited interpenetration between them even at high loads. When brush-bearing surfaces slide past each other, therefore, the interfacial region remains very fluid and low friction results [1]. For the case of charged surfaces in aqueous electrolyte solutions, counterions play an important role. Such counterions have recently been shown [2] to act like molecular ball bearings when trapped between charged sliding surfaces, due to the fluidity of the hydration layer about them together with the tenacious nature of the water of hydration. Charged polymers at surfaces, ubiquitous for example in living systems, should lead to interesting new effects when utilized as friction-modifiers. We have constructed polyelectrolyte brushes on a hydrophobized mica surface in aqueous solution by self-assembly of polyelectrolytic-hydrophobic diblock copolymers, and have used a state of the art surface force balance to measure the resulting normal and particularly frictional forces between them as they slide. Our results, to be presented at the meeting, reveal a remarkable behaviour which we attribute to a combination of the steric-entropic factors that play a role in neutral brushes in conjunction with the hydration sheaths that surround charges in polyelectrolytes.


[1] Klein, J., Kumacheva, E., et al., Nature, 370, 634 - 636 (1994)

[2] Raviv, U. and Klein, J., Science 297, 1540-1543 (2002)

[3] Raviv, U., Giasson, S., Kampf, N., Gohy, J-F., Jerome, R. and Klein, J., - submitted



* I thank my collaborators U. Raviv, S. Giasson, N. Kampf, J-F. Gohy and R. Jerome





Tags: charged polymers, hydration. charged, klein, jacob, polymers, lubrication, physical, charged