Angewandte
Research Articles
Chemie
How to cite:
Electrochemistry
Fabrication of Gradient and Patterned Organic Thin Films by Bipolar
Electrolytic Micelle Disruption Using Redox-Active Surfactants
Abstract: Bipolar electrochemistry could be regarded as
a powerful approach for selective surface modification due to
the beneficial feature that a wirelessly controllable potential
distribution on bipolar electrodes (BPEs). Herein we report
a bipolar electrolytic micelle disruption (BEMD) system for
the preparation of shaped organic films. A U-shaped bipolar
electrolytic system with a sigmoidal potential gradient on the
BPE gave gradient-thin films including various interesting
organic compounds, such as a polymerizable monomer, an
organic pigment and aggregation induced emission (AIE)
molecules. The gradient feature was characterized by UV–Vis
absorption, thickness measurements and surface morphology
analysis. Corresponding patterned films were also fabricated
using a cylindrical bipolar electrolytic setup that enables site-
selective application of the potential on the BPE. Such a facile
BEMD approach will open a long-term perspective with
respect to organic film preparation.
designed several electrolytic cells that achieved effective
control of the potential distribution on the BPE.[6] One of the
most attractive features for bipolar electrolysis is that the
BPE can act as an in situ generated controllable template for
gradient surface modification. We have achieved electro-
chemical chlorination across polythiophene films,[7] gradient
electrochemical doping of conducting polymers,[8] gradient
electrochemical surface modification of a poly(3,4-ethylene-
dioxythiophene)-based conducting polymer using an electro-
click reaction[9] and the formation of a 3D gradient polymer
brush by electrochemically mediated atom transfer radical
polymerization.[10] In addition, another electrolytic system
with an insulating cylinder has also been investigated, in
which the driving anode and cathode are separated by
a plastic shielding cylinder, which generated a mountain-like
potential distribution on a wireless BPE plate. The cylindrical
setup was successfully used to perform bipolar site-selective
patterning on a BPE.[10,11] These bipolar electrolytic setups
provide a significantly facile and effective method to fabricate
gradient and patterned polymeric films. Here, all gradient or
patterned films prepared were subjected to electrochemical
reaction during the film-formation process. In this context,
the preparation of gradient or patterned thin films that
maintain a consistent chemical composition after film for-
mation represents a significant challenge that when achieved
will extend the application range of the present wireless
bipolar electrochemical technique.
The method for the preparation of organic thin films is
significant because of its attractive potential applications in
various devices such as photovoltaic cells,[12] transistors[13] and
sensors.[14] Most of the methods used to prepare films of
organic small molecules are dry processes, such as chemical
vapor deposition (CVD) and physical vapor deposition
(PVD).[15] However, these methods are time-consuming and
require expensive equipment. On the other hand, Sajiꢀs group
has developed a unique and practical wet process known as
the electrolytic micelle disruption method, where thin films
are deposited by the release of organic compounds during the
oxidation of redox-active surfactants containing a ferrocene
moiety.[16] This method is based on the breaking up of micelles
formed by surfactants with a ferrocenyl group when the
surfactants are electrochemically oxidized on an electrode
surface. Solubilizate is released from the micelles and then
deposited onto the electrode surface to form a film. This film
formation technique is simple, cost-effective and can be
applied to many compounds. It is not only suitable for organic
compounds,[16c,17] but also for polymers[18] and fullerenes.[19]
Unlike general electrochemical film formation processes via
electrochemical reactions where the starting compounds
undergo reactions, this approach gives films of intact organic
Introduction
Bipolar electrochemistry has attracted a renewed interest
in the last two decades due to its use within broad fields
ranging from materials science[1] to analytical chemistry[2] and
beyond.[3] The bipolar electrochemical technique involves
electrochemical reactions in a wireless manner with respect to
the classical electrochemical method.[4] A general electro-
chemical setup includes a pair of driving electrodes connected
to a power supply, and a bipolar electrode (BPE) embedded
in an electrolytic solution. The driving electrodes involve not
only electrochemical reaction on their surfaces, but also
generate an electric field in the solution in a low concen-
tration of supporting salts, which induces the BPE. The BPE
surface can promote electrochemical reactions, even in the
absence of a direct ohmic contact. The potential distribution
along the BPE can be regulated by the applied voltage, the
shape and the position of the driving electrodes, as well as the
electrolytic cell design, considering the principles of bipolar
electrochemistry.[5] In previous work, our group originally
[*] Y. Zhou, Dr. N. Shida, Prof. Dr. I. Tomita, Prof. Dr. S. Inagi
Department of Chemical Science and Engineering, School of
Materials and Chemical Technology, Tokyo Institute of Technology
4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502 (Japan)
E-mail: inagi@cap.mac.titech.ac.jp
Prof. Dr. S. Inagi
PRESTO, Japan Science and Technology Agency (JST)
4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan)
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
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ꢀ 2021 Wiley-VCH GmbH
Angew. Chem. Int. Ed. 2021, 60, 2 – 12
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