Cyclic potential sweep electrolysis for formation of poly(2-vinylpyridine) coatings
X. LING**, M.D. PRITZKER*, C.M. BURNS and J.J. BYERLEY
Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
(*author for correspondence)
(**present address: Clariant Corporation, 70 Meister Avenue, Somerville, New Jersey 08876, USA)
Received 5 June 1998; accepted in revised form 1 December 1998
Key words: cyclic potential sweep electrolysis, electropolymerization, poly(2-vinylpyridine), coatings
Abstract
A cyclic potential sweep (CPS) technique has been used to form coatings of poly(2-vinylpyridine) on mild steel
substrates by electropolymerization of the monomer. This method can produce thick and uniform coatings of much
higher quality than can be formed by other electrochemical methods such as galvanostatic electrolysis, constant
cell-potential electrolysis and chronoamperometry. The range and rate of the potential sweep during the CPS are
important for successful coating formation. Potential sweeps between À1X0andÀ2X2 V vs SCE at rates from 10 to
50 mV s
À1
have been found to be most suitable for the formation of poly(2-vinylpyridine) coatings. The essential
reason for the successful application of the CPS technique to the electropolymerization process is the compatibility
of the nature of the CPS process and the mechanism of 2-vinylpyridine electropolymerization.
1. Introduction
Formation of polymer coatings by electropolymeriza-
tion has attracted considerable attention due to its
important applications in many areas [1±10]. To form a
high quality coating by electropolymerization, it is
important to use the proper electrochemical technique.
The most commonly used electrochemical methods
include galvanostatic electrolysis, chronoamperometric
electrolysis, constant cell-potential electrolysis and cyclic
potential sweep (CPS) electrolysis. The principles of
these methods are well known [5, 11, 12]. A proper
electrochemical technique should be one that is intrinsi-
cally compatible with the reaction mechanism of
electropolymerization.
The primary reason for using a galvanostatic techni-
que for electropolymerization is that it theoretically
allows control of the supply of radicals generated by
electrochemical reactions [13±16]. However, when the
polymer ®lm on the electrode surface is poorly conduct-
ing, a voltage drop occurs across the coating, leading to
a variation in the effective potential for radical genera-
tion. This makes the process more dif®cult to control,
particularly when radical generation can occur through-
out the ®lm and the potential on the working electrode is
not being controlled, as is the case during galvanostatic
electrolysis [5].
Simplicity of the instrumentation and operation is the
most distinct advantage of the constant cell-potential
technique. This technique has been used to form
polyoxyphenylene coatings [17±20], poly(acrylonitrile-
co-acrylic acid) coatings [21], poly(o-allylphenol)
coatings [22], and a variety of aniline-, phenol- and
vinyl-type polymer coatings [7]. The shortcoming of this
technique is that it allows no control over the working
electrode potential during the electrolysis and hence
current and radical generation cannot be directly
controlled. When a polymer coating forms on the
electrode surface, the current and the electrode poten-
tials of both the working and the counter electrodes will
vary to maintain the cell-potential at the preset value.
This may change the electrochemical processes on the
electrodes and may cause some undesired side-reactions
to occur.
Chronoamperometric electrolysis is widely used in
electrochemical processes. The advantage of this techni-
que is that the working electrode potential can be closely
controlled for the desired electrochemical processes. It
has often been used for coating formation via electro-
polymerization [8, 9, 23, 24]. It may be dif®cult, however,
Journal of Applied Electrochemistry 29: 1005±1013, 1999.
1005
Ó
1999 Kluwer Academic Publishers. Printed in the Netherlands.