E. Smela, THIOL-MODIFIED PYRROLE MONOMERS - 4 - ELECTROCHEMICAL DEPOSITION OF POLYPYRROLE OVER 1-(2-THIOETHYL)PYRROLE, Langmuir, 14(11), 1998, pp. 2996-3002
The electrochemical deposition of polypyrrole (PPy) potentiodynamicall
y and potentiostatically over monolayers of 1-(2-thioethyl)pyrrole (1-
TEP) is described. The relationship between monolayer oxidation and PP
y growth depended strongly on the electrolyte. In propylene carbonate/
LiClO4, the PPy polymerization potential was higher than that for 1-TE
P monolayer oxidation, and the monolayer oxidation peak was identical
to that seen in monomer-free electrolyte. In water/LiClO4, the oxidati
on and polymerization potentials were almost the same, with the result
that the onset of polymerization was prevented until after the monola
yer oxidation process had been completed. In water/(sodium dodecylbenz
enesulfonate), an anionic surfactant, the PPy polymerization potential
was lower than that in water/LiClO4, and polymerization apparently oc
curred without monolayer oxidation. In all cases, PPy growth was found
to be essentially the same on 1-TEP, oxidized 1-TEP, and clean gold a
s evidenced by cyclic voltammograms, chronoamperograms, and film appea
rance. These results show that the 1-TEP monolayers probably decompose
d before PPy polymerization began or were, in the case of sodium dodec
ylbenzenesulfonate, most likely inaccessible because they were covered
by the surfactant. This indicates that 1-TEP cannot be used to covale
ntly bind Pgr to gold. These results also demonstrate that the general
approach to adhesion promotion through the use of thiol-modified pyrr
oles has conditions and limits that must be recognized. The electroche
mistry of PPy grafting to surface-bound pyrrole depends critically on
the electrolyte, which is important for application of this technique
in real devices. In addition, the oxidation reactions undergone by suc
h a monolayer cannot be assumed to be different in the absence and pre
sence of pyrrole. Finally, the technique will probably not work with s
urfactant anions, which are of most practical interest.