Journal
JOURNAL OF COLLOID AND INTERFACE SCIENCE
Volume 325, Issue 1, Pages 228-235Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcis.2008.05.015
Keywords
fluorinated monolayer; hydrolysis and condensation; low-energy surface; alkylsiloxane; fluoroalkylsiloxane
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Funding
- The Norwegian Research Council
- StatoilHydro
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Alkylsiloxane and perfluoroalkylsiloxane monolayers are prepared on siliceous surface:; using the techniques of Langmuir-Blodgett deposition and solid-liquid chemical adsorption. Acid-catalyzed hydrolysis and polycondensation reactions provide two-dimensional siloxane networks at the liquid-vapor interface, which can be compressed to mean molecular areas of similar to 22 and similar to 32 angstrom(2) for pendent hydrocarbon and fluorocarbon chains, respectively. Subsequent Langmuir-Blodgett transfer onto glass substrates at moderate surface pressures leads to compact monolayers for single-component precursors, while mixed alkyl- and perfluoroalkylsilanes produce nonhomogeneous films characterized by transfer ratios greater than unity. As an alternate monolayer preparation technique, silane polymerization was performed directly on siliceous surfaces via a chemical adsorption mechanism. XPS analysis of a chemically adsorbed 1H,1H,2H,2H-perfluorodecylsiloxane film confirms a single adsorbed monolayer thickness in which the pendent fluoroalkyl chains align nonperpendicularly with respect to the surface. The surface free energy was determined to be 11.4 dyn cm(-1) based on static contact angle measurements. AFM imaging shows the presence of surface defects due to oligomer deposition during the drying process. The use of solubilized trichloro-based silane coupling agents under anhydrous conditions is shown to produce surfaces with a minimal number of surface defects. The presence of undissolved silane material in the bulk solution significantly increases the number of surface defects. (C) 2008 Elsevier Inc. All rights reserved.
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