CONTROL OF MOLECULAR CHAIN TILT IN SELF-ASSEMBLED MONOLAYERS AND ITS EFFECT ON WETTING PROPERTIES

Self-assembled monolayers with different degrees of molecular chain tilt were prepared on silver by adsorption of amphiphiles containing head groups of varying ''effective'' size: mercapto, carboxyl, biphenylcarboxyl and naphthyl carboxyl groups. The structures of these films were characterized by ellipsometry, reflection absorption IR spectroscopy and contact angle measurement. The chain tilt of the alkyl tail groups depend on the effective head group. The contact angle of hydrocarbon liquid exhibits a clear correlation with the orientation of the terminal methyl group (odd-even effect). The variation in contact angle was rationalized as a result of different exposures of methylene unit in the top 2 approximately 3 angstrom region of the film.