Contact Angle and Electrochemical Characterization of Multicomponent Thiophene-Capped Monolayers

We have investigated the wetting behavior and electrochemical response of self-assembled monolayers made from ω-(3-thienyl)-alkyltrichlorosilanes and alkyltrichlorosilanes on indium−tin oxide coated glass slides. Contact angle measurements and cyclic voltammetry show that the properties of the monolayers change as the relative loading of the two components is changed by altering the concentration of the deposition solution. The water contact angles indicate that a fully loaded hydrophobic layer is formed, and both water and hexadecane contact angle measurements show that the tethered thiophenes are at the periphery of the monolayer. However, the hexadecane contact angles also imply that the surface roughness exposes the methylene groups of the monolayer chains. Cyclic voltammograms obtained from mixtures of 11-(3-thienyl)undecyltrichlorosilane and decyltrichlorosilane and mixtures of 16-(3-thienyl)hexadecyltrichlorosilane and hexadecyltrichlorosilane show that as the relative amount of thienyl-bearing chains in the monolayer decreases, the oxidation peak position shifts to higher potential and the peak area, which is related to the amount of charge transferred, decreases. Integration of the oxidation peak area from the cyclic voltammetry experiments yields a coverage that is consistent with a monolayer. Preliminary evidence for formation of a surface-tethered redox-active polymer is observed by cycling the self-assembled monolayers at low potentials.