Sl. Hiley et Da. Buttry, CONTROL OF ACCESS TO SURFACES WITH SELF-ASSEMBLING SURFACTANTS BEARING FLUOROCARBON CHAINS, Colloids and surfaces. A, Physicochemical and engineering aspects, 84(1), 1994, pp. 129-140
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.