Pure and Molecularly Mixed Methyl- and Hydroxyl-Terminated Self-Assembled Dialkylammonium Monolayers on Mica: Wettability and Conformational Order

Abstract

Muscovite mica surfaces were coated with methyl- and hydroxyl-terminated dialkyldimethylammonium monolayers via ion exchange by immersion of the substrates into solutions of the corresponding salts. The samples were examined by water contact-angle measurements and near edge X-Ray absorption fine structure spectroscopy (NEXAFS). The purely methyl-terminated species was found to form self-assembled monolayers (SAMs) of comparable quality to those of a similar thiol/gold system as has been reported earlier. The hydroxyl-terminated surfactant established films with a lower degree of orientation under the same preparation conditions and showed a high water contact angle value for a hydrophilic surface (47°). The molecularly mixed film where one alkyl chain of the surfactant is methyl terminated and one hydroxyl terminated had a significantly lower wettability but established a similar degree of orientation as the film prepared from the purely OH-terminated species.