Contact angle and electrochemical characterization of multicomponent thiophene-capped monolayers

We have investigated the wetting behavior and electrochemical response of s elf-assembled monolayers made from omega-(3-thienyl)-alkyltrichlorosilanes and alkyltrichlorosilanes on indium-tin oxide coated glass slides. Contact angle measurements and cyclic voltammetry show that the properties of the m onolayers change as the relative loading of the two components is changed b y altering the concentration of the deposition solution. The water contact angles indicate that a fully loaded hydrophobic layer is formed, and both w ater and hexadecane contact angle measurements show that the tethered thiop henes are at the periphery of the monolayer. However, the hexadecane contac t 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 t hat as the relative amount of thienyl-bearing chains in the monolayer decre ases, the oxidation peak position shifts to higher potential and the peak a rea, which is related to the amount of charge transferred, decreases. Integ ration of the oxidation peak area from the cyclic voltammetry experiments y ields a coverage that is consistent with a monolayer. Preliminary evidence for formation of a surface-tethered redox-active polymer is observed by cyc ling the self-assembled monolayers at low potentials.