Kinetics of Exchange of Alkanethiol Monolayers Self-Assembled on Polycrystalline Gold

We report on the exchange between a hydrophilic thiol (11-mercapto-1-undecanol) in a liquid or gas
phase and a hydrophobic thiol (dodecanethiol) of similar length self-assembled on a polycrystalline gold
surface for a wide range of temperatures and times. The molecular composition of the mixed monolayers
is determined by the static water contact angle and X-ray photoelectron spectroscopy measurements.
Atomic force microscopy in lateral forcemodeis used to characterize the molecular domains at the nanometer
level. The exchange first occurs rapidly at the gold grain boundaries, with an activation energy of about
66 ( 4 kJ/mol. Then, boundaries of ordered thiol domains are progressively replaced, and the exchange
is slowed because only regions of increasing perfection are left untouched. Higher temperatures lead to
faster kinetics of replacement and the removal of larger amounts of the original thiol. No significant
difference could be detected between exchange occurring in an ethanol solution or in the gas phase, and
the initial rate of exchange was found to be similar for the displacement of dodecanethiol by 11-mercapto-
1-undecanol molecules and for the converse displacement