Polyamic acid: nanoprecipitation and electrophoretic deposition
on porous supports
Libor Brabec
, Petr Sysel, Jan Plsek, Milan Kocirik, James H. Dickerson
Ó
American Coatings Association 2017
Abstract Polyamic acid (PAA, a precursor of poly-
imide) was synthesized from 4,4¢-oxydiphthalic anhy-
dride and 4,4¢-oxydianiline. PAA, dissolved in
dimethylsulfoxide (DMSO), was precipitated into col-
loidal particles after its injection into acetone. The
resulting particle size distribution was found to depend
on aging time of PAA solutions, their concentration,
and the manner in which the solutions were mixed with
acetone. PAA particles of any size down to 10 nm
appeared to be achievable by decreasing the acetone/
DMSO ratio. Particles in DMSO/acetone suspensions
were found to have a significant negative zeta poten-
tial. Therefore, there was no need to add organic bases
to form PAA anions, in contrast to all previously
published studies on the PAA electrodeposition. EPD
was performed onto porous stainless-steel or alumina
disks, which are suitable supports (reinforcements) for
membranes. The slow evaporation of DMSO residue
yielded dried polymer layers, comprised of 50–100 nm
PAA globules. The outer surface of layers was usually
covered with a very thin, continuous PAA skin. Such
supported PAA layers—after a simple imidization step
via a heat treatment—could be applied as thermally
resistant membranes for gas separation.
Keywords Dimethylsulfoxide, EPD, Polyimide,
Precipitation, Zeta potential
Introduction
Aromatic polyimides (PIs) are appreciated for their
good thermal and mechanical resistance and low
permittivity. Their precursors—aromatic polyamic
acids, in particular 4,4¢-oxydiphthalic anhydride and
4,4¢-oxydianiline (ODPA-ODA)—possess possible
advantages, in that the ether oxygen in ODPA leads
to the formation of PI with a lower glass transition
temperature that can influence its intrinsic rigidity/
flexibility. Numerous procedures such as the vapor
deposition of precursors and solid-state reactions,
1
spin-coating,
2,3
and liquid-phase casting
4–6
have been
used to prepare polymeric surface layers. In the last
decade, increasing interest has been invested into the
use of electrophoretic deposition (EPD) to fabricate
polymer films. This is because EPD is an easy and
controllable technique to coat supports/substrates with
layers of miscellaneous materials that exist in stable col-
loidal suspensions and solutions with an adequate zeta
potential. PAA can be easily dissolved in some organic
solvents, in contrast to many PIs, and subsequently
precipitated into charged colloidal particles.
Several studies on the EPD of PAA have been
reported in the distant past.
7–12
Those were based on
using commercially available types of PAA and focused
on particular parameters (composition of suspension,
voltage, transferred charge, time of EPD) and their
effect on the PAA deposition yield. Until now, triethy-
lamine or other organic bases were always added to
PAA solutions, which ultimately led to the production
of undesirable polyamic acid salts (PAAS). According
Electronic supplementary material The online version of this
article (doi:10.1007/s11998-017-0004-9) contains supplementary
material, which is available to authorized users.
L. Brabec (&), J. Plsek, M. Kocirik
J. Heyrovsky Institute of Physical Chemistry of the CAS,
Dolejs
ˇ
kova 2155/3, 182 23 Prague 8, Czech Republic
e-mail: brabec@jh-inst.cas.cz
P. Sysel
University of Chemistry and Technology, Technicka
´
5, 166
28 Prague 6, Czech Republic
J. H. Dickerson
Department of Physics, Brown University, Providence, RI
02912, USA
J. Coat. Technol. Res., 15 (3) 489–496, 2018
https://doi.org/10.1007/s11998-017-0004-9
489
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