Surface+prop+fluorinated+brushes+Langmuir_20_10498-10506_Andruzzi_et_al(2004)

Surface+prop+fluorinated+brushes+Langmuir_20_10498-10506_Andruzzi_et_al(2004)

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Control of Surface Properties Using Fluorinated Polymer Brushes Produced by Surface-Initiated Controlled Radical Polymerization Luisa Andruzzi, ² Alexander Hexemer, Xuefa Li, ² Christopher K. Ober,* Edward J. Kramer, ‡,§ Giancarlo Galli, | Emo Chiellini, | and Daniel A. Fischer Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, Departments of Materials and Chemical Engineering, University of California, Santa Barbara, California 93106, Dipartimento di Chimica e Chimica Industriale, Universita ` di Pisa, 56126 Pisa, Italy, and Materials Science and Engineering Laboratory, National Institute for Standards and Technology, Gaithersburg, Maryland 20899 Received March 21, 2004. In Final Form: September 5, 2004 Surface-grafted styrene-based homopolymer and diblock copolymer brushes bearing semifluorinated alkyl side groups were synthesized by nitroxide-mediated controlled radical polymerization on planar silicon oxide surfaces. The polymer brushes were characterized by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and time-dependent water contact angle measure- ments. Angle-resolved XPS studies and water contact angle measurements showed that, in the case of the diblock copolymer brushes, the second block to be added was always exposed at the polymer - air interface regardless of its surface energy. Values of z */ R g were estimated based on the radius of gyration, R g ,ofthe grafted homopolymer or block copolymer chains for the grafted brushes and thickness of the brush, z *. The fact that z */ R g > 1 suggests that all these brushes are stretched. These results support the idea that aftergraftingthefirstblockontothesurfacethenitroxide-endcappedpolymerchainswereabletopolymerize the second block in a “living” fashion and the stretched brush so formed was dense enough that the outermostblockinallcasescompletelycoversthesurface.NEXAFSanalysisshowedarelationshipbetween the surface orientation of the fluorinated side chains and brush thickness with thicker brushes having moreorientedsidechains.Time-dependentwatercontactanglemeasurementsrevealedthattheorientation ofthesidechainsofthebrushimprovedthesurfacestabilitytowardreconstructionuponprolongedexposure to water. Introduction The control of surface properties represents a funda- mental issue in numerous applications ranging from coating technology and biotechnology to microelectronics. 1 - 4 Control can, for example, be achieved using “polymer brushes” applied as polymer films onto a substrate. Polymer brushes are classically prepared from block copolymer solutions where one block serves to anchor the polymertoasubstratewhilethefunctionalblock(“brush”) forms the surface. 5
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Surface+prop+fluorinated+brushes+Langmuir_20_10498-10506_Andruzzi_et_al(2004)

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