COLL 504 |
| Suzanne Giasson, Department of Chemistry, Department of Chemistry, University of Montreal, FAS-Chimie, CP 6128 Succ. Centre-VIlle, Montreal, QC H3C 3J7, Canada |
| Polymeric brushes are formed by end-tethering polymer chains at surfaces while extending the chains into the medium. For the case of charged polymeric brush surfaces in aqueous solutions, counterions play an important role. When two charged brushes are mutually compressed, entropic factors associated with the counterions result in very limited interpenetration between them even at high loads leading to strongly-repulsive forces between the brush surfaces. When two charged brush-bearing surfaces slide past each other, therefore, the interfacial region remains very fluid and low friction results. The mobile counterions inducing brush swelling as well as the fluid hydration sheath around charged segments contribute to overcome the factors leading to friction. Charged polymers at surfaces, ubiquitous for example in living or aqueous 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 Surface Force Apparatus to measure the resulting normal and particularly frictional forces between them as they slide. Our results, to be presented, reveal a remarkable behaviour which we attribute to a combination of the steric-entropic factors encountered in neutral brushes in conjunction with the hydration sheaths that surround charges in polyelectrolytes (Nature, Vol 425, p.163-165, September 2003). |
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“Smart” Polymers on Surfaces and Colloids
8:30 AM-11:30 AM, Thursday, April 1, 2004 Marriott -- Grand Ballroom J, Oral
Division of Colloid and Surface Chemistry |