Ultrathin coatings from isocyanate-terminated star PEG prepolymers: layer formation and characterization

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Title: Ultrathin coatings from isocyanate-terminated star PEG prepolymers: layer formation and characterization
Author(s): Groll, Juergen; Ameringer, Thomas; Spatz, Joachim P.; Moeller, Martin
Abstract: In this study we present the preparation of thin and ultrathin coatings from six-arm star-shaped isocyanate-terminated prepolymers on amino-functionalized silicon wafers. The backbone of the stars is a statistical copolymer of ethylene oxide and propylene oxide in the ratio 80:20 (Star PEG). Film preparation by spin coating from aqueous THF resulted in a variety of film morphologies that are determined by the water content of the solvent. Water is indispensable for activation of the isocyanate-terminated stars in solution and for proper cross-linking of the coatings on the substrate. This cross-linking results in a dense network of PEG chains on the substrate linked via urea groups with a mesh size of the network that corresponds to the arm length of the stars. Layer thickness variations between 3 and 500 nm revealed a strong dependence of the contact angle with water on the layer thickness which is explained by the chemical composition of the coatings. Due to the high functionality of the star-shaped prepolymers, free amino groups remain in the films that were detected by fluorescence microscopy after reaction with 4-chloro-7-nitrobenzofurazan (NBF). To test the system for the ability to prevent unspecific interaction with proteins, adsorption of fluorescence-labeled avidin was examined with fluorescence microscopy. For layer thicknesses between 3 and 50 nm, no protein adsorption could be detected.
Publication type: Journal article
Source: Langmuir, Vol. 21, no. 5 (Feb 2005), pp. 1991-1999
Publication year: 2005
Keyword(s): Crosslinking; Fluorescence microscopy; Hydrogels; Microscopic examination; Morphology; Oscillation frequency; Plastic films; Polyethylene glycols; Scanning force microscopy; Self assembly; SFM; Silicon wafers; Ultrathin coatings
Publisher: American Chemical Society
ISSN: 0743-7463
Publisher URL: http://dx.doi.org/10.1021/la047439f
Peer reviewed