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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 5: Interfaces
CPP 5.9: Talk
Monday, March 23, 2009, 12:30–12:45, ZEU 160
Direct measurement of normal and shear forces between grafted-from polyelectrolyte layers — •Iain Dunlop1,4, Wuge Briscoe1, Simon Titmuss1, Robert Jacobs1, Vicky Osborne2, Steve Edmondson2, Wilhelm Huck2, and Jacob Klein1,3 — 1Dept. Chemistry, University of Oxford, South Parks Road, Oxford, OX1 3QZ, U.K. — 2Melville Laboratory for Polymer Synthesis, University Chemistry Laboratory, Lensfield Road, Cambridge, CB2 1EW, U.K. — 3Dept. Materials and Interfaces, Weizmann Institute of Science, PO Box 26, Rehovot 76100, Israel — 4Present address: Dept. New Materials and Biosystems, Max-Planck-Institute for Metals Research, Heisenbergstraße 3, 70569 Stuttgart, Germany, and University of Heidelberg, Biophysical Chemistry, INF 253, D-69120 Heidelberg.
We present direct measurements, using the surface force balance (SFB), of the normal and shear forces in aqueous solutions between grafted-from polyelectrolyte layers that were grown by surface-initiated atom transfer radical polymerization on mica substrates. The successful formation of the grafted-from polyelectrolyte layers was confirmed using X-ray reflectometry. Normal force measurements in water showed a long-range force due to an electrical double layer that extended beyond the swollen polyelectrolyte layers, as well as a stronger repulsion when the layers were in contact. Upon addition of 1:1 electrolyte, the long-range force became undetectably small, due to screening effects. Shear force measurements in pure water showed a measureable friction that may arise from the bridging of polymer chains between the surfaces.