We have investigated the kinetics of formation for n-alkanethiolate self-assembled monolayers (SAMs)
onto gold in aqueous micellar solutions of n-alkyltrimethylammonium bromides (C
m
TAB; m = 12, 14, 16,
and 18). The cationic micelles provide hydrophobic domains to solubilize the alkanethiols and facilitate
their delivery to the gold surface. The kinetics results for SAM formation in aqueous micellar solutions
of C
m
TAB are well described by a first-order Langmuir adsorption model. The measured rate constant
decreases exponentially with increasing hydrophobicity (chain length) of the alkanethiol adsorbate and
the C
m
TAB surfactant. The measured rate also decreases with increasingly positive potentials of the gold
electrode. A mechanism to describe SAM formation in C
m
TAB(aq) that is consistent with reported results
of solute exchange between ionic micelles in solution consists of (1) fragmentation of thiol-laden micelles
to produce submicelles, (2) incorporation of thiol-laden submicelles into adsorbed micelles (admicelles) at
the gold surface, (3) displacement of surfactants and counterions (rate-limiting step) by the alkanethiols,
and (4) chemisorption of the alkanethiol.
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