CONTROL OF ACCESS TO SURFACES WITH SELF-ASSEMBLING SURFACTANTS BEARING FLUOROCARBON CHAINS

Cyclic voltammetry and microgravimetry via the electrochemical quartz crystal microbalance have been used to examine ion and solvent transpo rt in self-assembled viologen monolayers on gold metal surfaces. Fluor ocarbon chains have been incorporated into these viologen monolayers a s outer spacers in order to vary systematically the steric bulk of the monolayer. Ions can be electrochemically driven into and out of the m onolayer by virtue of the redox chemistry of the viologen group embedd ed within the monolayer. The transport of these ions provides a straig htforward way of evaluating the barrier properties of the fluorocarbon chain region of the monolayer. We find that the larger size of these fluorocarbon chains compared with alkyl chains makes a more formidable barrier to ion transport than hydrocarbon outer spacers of viologens in previous studies. Trends in ion-pairing strength and the simultaneo us transport of water during ion transport have been evaluated for sev eral counter-anions. Relative transport rates for anions of various si zes and hydration numbers have also been ascertained. The structure an d orientation of the monolayers were also investigated using advancing contact angle measurements and IR reflectance spectroscopy.