Direct measurement of normal and shear forces between surface-grown polyelectrolyte layers.
This paper presents measurements, using the surface force balance (SFB), of the normal and shear forces in aqueous solutions between polyelectrolyte layers grown directly on mica substrates (grafted-from). The grafting-from was via surface-initiated atom transfer radical polymerization (surface-initiated ATRP) using a positively charged methacrylate monomer. X-ray reflectometry measurements confirm the successful formation of polyelectrolyte layers by this method. Surface-inititated ATRP has the advantages that the polymer chains can be strongly grafted to the substrate, and that high grafting densities should be achievable. Measured normal forces in water showed a long-range repulsion arising from an electrical double layer that extended beyond the polyelectrolyte layers, and a stronger, shorter-range repulsion when the polyelectrolyte brushes were in contact. Swollen layer thicknesses were in the range 15-40 nm. Upon addition of approximately 10(-2)-10(-1) M sodium nitrate, screening effects reduced the electrical double layer force to an undetectable level. Shear force measurements in pure water were performed, and the measured friction may arise from polymer chains bridging between the surfaces.
Dunlop
Iain E
IE
Department of Chemistry, University of Oxford, Oxford, UK. dunlop@mf.mpg.de
Briscoe
Wuge H
WH
Titmuss
Simon
S
Jacobs
Robert M J
RM
Osborne
Vicky L
VL
Edmondson
Steve
S
Huck
Wilhelm T S
WT
Klein
Jacob
J
D000538:Aluminum Silicates / Q000737:chemistry*; D004573:Electrolytes / Q000737:chemistry; D008567:Membranes, Artificial; D011109:Polymethacrylic Acids / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D013499:Surface Properties
D000538:Aluminum Silicates; D004573:Electrolytes; D008567:Membranes, Artificial; D011109:Polymethacrylic Acids; D000644:Quaternary Ammonium Compounds; C543347:poly(2-(methacryoyloxy)ethyl)trimethylammonium chloride; C011934:mica