Vapor-phase formation of alkyl isocyanate-derived self-assembled monolayers on titanium dioxide.
Titanium dioxide (TiO2) surfaces were modified at atmospheric pressure by exposure to the vapor of alkyl isocyanates having different alkyl chain lengths (CH3[CH2]nN=C=O, where n = 3, 4, 7, 11, 15, and 17). Dynamic water contact angle measurements, X-ray photoelectron spectroscopy, and atomic force microscopy confirmed that the vapor-phase treatment produced self-assembled monolayers (SAMs) of the isocyanate molecules on the TiO2 surface through a carbamate linkage without any marked changes in surface morphology. The thickness and hydrophobicity of the isocyanate-derived SAMs depend on both the alkyl chain length and process temperature. As a control, an oxidized silicon (SiO2/Si) surface was treated under the same conditions. Water contact angle hysteresis for the SAM-covered TiO2 surfaces is greater than that observed for SAM-covered SiO2/Si surfaces, suggesting that SAMs on TiO2 surfaces are disordered and/or insufficiently cover the surfaces. This leads to their water sensitivity. Desorption kinetics are also strongly affected by the alkyl chain length, and the SAMs of adsorbed molecules with n = 15 and 17 are relatively stable among these six isocyanate-derived SAMs.
National Institute of Advanced Industrial Science & Technology (AIST), Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan. a.hozumi@aist.go.jp
Atsushi
A
Hozumi
Bokyung
B
Kim
Thomas J
TJ
McCarthy
D000327:Adsorption; D002621:Chemistry / Q000379:methods*; D007700:Kinetics; D008027:Light; D018625:Microscopy, Atomic Force; D010100:Oxygen / Q000737:chemistry; D011312:Pressure; D012825:Silicon / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission / Q000379:methods; D013499:Surface Properties; D013997:Time Factors; D014025:Titanium / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D014965:X-Rays
D014867:Water; C009495:titanium dioxide; D014025:Titanium; D010100:Oxygen; D012825:Silicon