Spectroscopic, and Transmission Electron Microscopic. Studies on
Morphological .... chloromethylstyrene (60% meta, 40% ortho) (Aldrich,
Milwaukee, WI) were distilled under ..... (b) Watanabe, T.; Honda, K. J. Phys.
Chem. 1982, 86, 2617. 18.
OFFICE OF NAVAL RESEARCH Contract NOOO14- 84-K-0428 Task No. NR 051-693 TECHNICAL REPORT No. 9
Polymer Films on Electrodes. 22. Electrochemical, Spectroscopic, and Transmission Electron Microscopic Studies on Morphological Changes in Films of Polymeric Surfactants. By
NYu-Min
Tsou, Hsu-Yang Liu, and Allen J. Bard
00
Prepared for Publication
fin J. Electrochem. Soc.
7..
The University of Texas at Austin
Department of Chemistry
JL
Austin, Texas 78712
Reproduction in whole or in part is permitted for any purpose of the United States Government. This document has been approved for public release and sale; its distribution is unlimited.
UL2
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READ z ; RICTIONS
REPORT DOCUMENTATION PAGE I
WUPBCR
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BEFORE COMPLETrNG FORM ACEISION
NO.
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RECPfIINV'S CATALOG NUMMER
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TYPE
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I
9 4
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COVREO
Polymer Films on Electrodes. 22. Electrochemical, Spectroscopic, and Transmission Electron Microscopic Studies on Morphological Changes in Films of Polymeric Surfactants. 7.
AUT NoR(s)
, PCRVOR S.
tNOR.RPoR
CONTRACT
r
ULR
OR GRANT NUMBER(.)
Yu-Min Tsou, Hsu-Yang Liu, and Allen J. Bard
N00014-84-K-0428 9. PERFORMING
ORGANIZATION
NAME AND ADRESS
10.
Department of Chemistry
PROGRAM ELEMENT. PROJECT, TASK
AREA A WORK UNIT NUMBERS
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AND ADDRESS
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15._ECUITYLAS._(o & ADDRESS(I
diflereit from Con rolling Office)
IS.
SECURITY CLASS.
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(of til
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rport)
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NOTES
Prepared for publication in the
It.
KEY WORDS (Continue on rover#@
aide It noceseaty
Jounial of the Electrochemical Society.
wnd identity by block nurber) '
Z0.
ABSTRACT (Contfnue on revere
sid
It necoeosw-
and identity by block number)
An electroactive polymeric surfactants with pendent long-chain viologen redox groups, PCMS-VC1 6 , was synthesized, by the reaction of poly(chloromethylstyrene) with N-hexadecyl-4(4'-pyridyl)pyridinium bromide. Films of this polymeric-surfac tant on glassy carbon electrodes were studied by electrochemical, spectroscopic (absorption-probe), and electron spin resonance techniques. The results suggest that upon reduction of the viologen groups in aqueous solution, the structure of the polymeric surfactant becomes more compact, probably because of reorganizatio induced by a decrease in the coulombic repulsive interaction. Spherical domains
DD
jAN 73
1473
EDITION OF , O r - 014-6o0 S/R 0
IsOBSOLETE 1S 1
I
" .1,
Unclassified Unclassifi0d SECURITY
CLASSIFICATION OF THIS PAGE (When Dato Bnd
... '
%,N -a.'_,,
--
*(_flATY CL.ASSIFICATION Of THIS P&GE("wl,
D.e. roegm~d)
(Block 20 cont.) 1
formed by the aggregation of the long-chain hydrocarbon groups were observed in the transmission electron micrographs of both the oxidized form and reduced form of the polymeric surfactants.
Ii
:7 *
%
%
Polymer Films on Electrodes. 22. Electrochemical,
Spectroscopic, and
Transmission Electron Microscopic Studies on Morphological Changes in Films of Polymeric Surfactants
Yu-Min Tsou, Hsu-Yang Liu, and Allen J. Bard Department of Chemistry, The University of Texas Austin, TX 78712
Abstract -"An electroactive polymeric surfactants with pendent long-chain viologen redox
groups,
PCMS-VC 1 6,
poly(chloromethylstyrene) Films by
synthesized,
by
the
reaction
of
with N-hexadecyl-4(4'-pyridyl)pyridinium bromide.
of this polymeric-surfactant on glassy carbon electrodes were studied
electrochemical,
resonance
techniques.
viologen
groups
surfactant by
was
in
spectroscopic The aqueous
(absorption-probe),
results solution,
suggest
that
the
structure
and
electron spin
upon reduction of the of
the
polymeric
becomes more compact, probably because of reorganization induced
a decrease
in the coulombic repulsive interaction.
Spherical domains
formed by the aggregation of the long-chain hydrocarbon groups were observed in
the
transmission
electron
micrographs
of
both the oxidized form and
reduced form of the polymeric surfactants.,
--
,-
-
AccesionFor
End of abstract
GRA&I
.Nf'IS
D}TIC TAB
iU'i n c u ic cd
Jut
Submitted to the Journal of Physical Chemistry
i
E-]
if ication--__
Jtr
b1,
ri
December 1986
SOTIC COP
2
INTRODUCTION Studies
of
investigate
polymeric
films
on
electrodes
have been carried out to
&
the mechanism of mass and charge transport in polymeric layers, %
to characterize their redox properties, and for possible applications (e.g., 1 displays, electrocatalysis). Several investigations concerned the morphology
of
polymer
films,
the
changes
that occur upon oxidation and
reduction, and how these changes affect film properties. 2 concerns
the
polymeric
effect
of
surfactants.
The present study
oxiaation
and reduction of films of redox active
Polymeric
surfactants,
or
4
I
polysoaps, have been
studied extensively (e.g., in their application in the catalysis of chemical reactions). 3 species
4
Related
of
the electrochemistry of redox
in the micelles, 5 and of vesicles with electroactive
incorporated
groups 6 a - c
head
investigations
have
carried out.
been
also
For example, Saji et al., 7
studied
the formation and disruption of micelles by control of redox states
of
(monomeric)
the
study
of
the
surfactant ferrocene tail groups.
morphology
of
However, no detailed
electroactive polymeric surfactants has been
In this article, we report studies of the polymeric surfactant, I,
made. PCMS-VC
16
,
containing
long-chain
viologen
side
groups.
Other polymers
containing viologen (V2 +) groups have been studied previously, because these groups
show reversible electrochemical reactions and large spectral changes 8
upon be
reduction. switched
In these polymers, the charge of the viologen groups can
reversibly
electrochemically. monitored
by
V2+ (oxidized form) and V+ (reduced form)
between
The change in the structure of the polymer coatings was spectroscopic,
electrochemical,
and
electron
microscopic
methods. EXPERIMENTAL SECTION Materials.
4-Vinylpyridine
-, Z.],-. t , - ..
, L
.
_ "
'..;-
-
Inc., Warrington, PA) and
(Polyscience,
-,.-.,-%'.."
'
-. ,-
-.
..-
-
'.
%-
.
-.
,.-...
-
--
.-
-
4%
PCMS-MV
PCMSNVC 1 6
- - C 2x
( H - -C ) y --
-C 2
2C2H2CH
p. 40 % so 6%
C H .
2
-H
) =
2
(
P-
o
40 %
CH
a.
4
Pvp
0
PVP-C 12 -(OH )~----f 2
N
-cI--S 2H
~
IV
N, Br' (&DH 2 11
-7
V
5
chloromethylstyrene under
distilled
by
synthesized
4.9
Poly(4-vinylpyridine), PVP, III, was
pressure.
reduced
(Aldrich, Milwaukee, WI) were
ortho)
bulk polymerization of 4-vinylpyridine initiated by benzoyl
(Polyscience, Inc.) at 500 C.9
peroxide of
40%
meta,
(60%
It was purified by reprecipitation The molecular weight was
the nitromethane solution with excess toluene. 105
x
Quaternization of poly(4-vinylpyridine) with
(viscometry). 10
p.-
bromide
dodecyl
at
nitroethane product
11
C.3
out in degassed 1:1 nitromethane-
carried
The extent of quaternization was 50% (NMR). here
Poly(chloromethylstyrene) was
IV.
PVP-C 1 2 ,
This .
by radical chain polymerization in degassed benzene using AIBN Inc.) as the initiator. It was purified by the precipitation
(Polysciences, of
500
is designated
synthesized
was
(Aldrich)
a benzene solution with MeOH.
The average molecular weight was 8 x 104
(GPC).
1NMR(DMSO-d
characterized according to reference 12. -CH3 ), 1.1
synthesized and
was
bromide
N-(n-hexadecyl)-4-(4'-pyridyl)pyridinium
6 ),
(ppm): 0.88 (t, 3H,
2.3 (m, 28H, -CH2 -), 4.7 (t, 2H, N-CH2; aromatic H-8.13 (d,
-
2H), 8.73 (d, 2H), 8.96 (d, 2H), 9.33 (d, 2H). PCMS-VC 16 ,
N-hexadecyl -4-(4' -pyridyl )pyridinium
I.-
poly(chloromethylstyrene) N,N-dimethylformamide washed,
(DMF)
were for
heated 48
and redissolved in warm MeOH.
h.
at The
C
800
and
"
degassed
,
bromide
in dry
precipitate was collected,
The MeOH solution was added dropwise
to rapidly stirred dioxane and the resulting cloudy mixture was centrifuged. The
precipitate was washed with dioxane, then acetone. by
obtained result
of
groups
were
PCMS-V
another
A yellow powder was
reprecipitation of a MeOH solution with dioxane.
The
elemental analysis indicated that 40% of the chloromethylstyrene functionalized
with
viologen groups.
Elemental analysis for
(40%), Idioxane/monomer unit: Found: C,66.8; H,8.05; N,3.32. Calcd: 166
C,66.4; H,8.05; N,3.25.P
P
6 PCMS-MV,
II, was synthesized according to the procedure for a similar
polymer. 12a was
Elemental
42%.
N,4.05.
a
PCMS-MV
analysis indicated that the extent of substitution
(42%),
1 dioxane/monomer unit: Found: C,56.2; H,5.74;
U
Calcd: C,56.3; H,5.66;N,3.93.
Apparatus.
spin resonance (ESR) measurements (X band) were
Electron
made with a Varian E-9 spectrometer (100 kHz field modulation) equipped with a TE1 o2
dual-sample
designed
1 mm
ESR studies. SnO 2
(PPG
thick flat ESR cell
were
Research
on
X-Y
elect-on
with
SnO
electrode
epoxy cm was
a PAR model 175 universal programmer, a
a model
a Norland
micrc raphs
179
digital coulometer (Princeton
Current-time curves were recorded Model
weto
3001
obtained
digital on
oscilloscope.
a JEOL 1200 EX STEM
5500 energy dispersive spectroscope.
in voltammetric
with
was
cement.
paint
and
._
The working
experiments was a glassy carbon electrode W.
The
prepared by attaching a Cu wire to the conducting SnO2
silver
. .
covering the contact with a nonconducting
The working electrode for the ESR experiment was a 0.3 x 0.6
5
Pt flag. The counter electrode was a Pt wire and the reference electrode a
saturated
calomel
electrochemical-ESR as
or
S
Electrochemical
area of 0.07 cm2 (Bioanalytical Systems, Wst Lafayette,
an
surface
with
and
a Tracor
used
with
22
suitable for both electrochemical and
Corp., Princeton, NJ).
recorder
Transmissicn
electrode
performed
potentiostat,
Applied
equipped
13
Glass) electrodes and an HP-8450A spectrometer.
173
a
The ESR-electrochemical cell was a specially
Visible absorption measurements were obtained with transparent
measurements model
cavity.
(SEESR)
electrode
(SCE),
except
in the
simultaneous
experiment where an Ag/AgCl electrode was used Viscometry was performed with
N-.
electrodes were prepared by covering the conducting
0
both the counter and reference electrode.
a Bausch and Lomb Viscomatic-1 viscometer. Procedures. substrates
(C, Pt,
The
SnO 2 ) with an aliquots of the polymer solution (0.25%
---'-. --
7 w/v);
solvents
PCMS-MV. a
were
MeOll
for
PCMS-VC 16 ,
PVP,
and PVP-C
16'
12'
and DMF for
Before every experiment the potential of the electrode was held at
positive
value
to
iodide to iodate. supporting
oxidize
microscopy
carbon-coated
bromide in the polymer to bromate, and
Both bromate and iodate are replaced by chloride from the solution very rapidly. 12 a
electrolyte
electron
any
were
copper
prepared
grid.
by
coating
Samples for transmission a
thin polymer film on a
The films were then stained with a 2% aqueous
uranyl acetate solution.
RESULTS AND DISCUSSION Electrochemical
Experiments--PCMS-VC 16 is a polymeric surfactant.
long-chain viologen groups are the charged pendent groups. charged
viologen
group
can
be
reduced
The
Since the doubly
reversibly to the singly charged
cation
radical, this provides the opportunity to investigate the effects of
charge
on the morphology of the film of a polymeric surfactant.
voltammograms shown
in
(CV)
Figure
of a PCMS-VC16 coating on a glassy carbon electrode are 1.
In Figure la, the initial potential was -0.1 V, where 2+
all the viologen groups were in the V in
Figure
,
oxidized, form.
In both cases, the coated electrode was held at the initial
potential
for 30 min before the potential scan.
CV
depends
waves
those
of
a
completely Under
upon the initial potential.
surface-confined
reduced
these
provides
On the other hand,
lb, the initial potential was -0.6 V, where they were in the V+, form.
reduced,
The cyclic
(or
conditions,
information
species
oxidized) the
about
during
shape the
with
and
Note that the shape of the In both cases the waves are the
viologen
groups
being
each cathodic (or anodic) scan. the width at half-height (AE1 /2 )
extent of interaction between the reduced
groups. 14
In
Figure 1b, the width at half-height is 75 mV and 120 mV for
the
and
cathodic wave, respectively, while it is 95 mV and 120 mV,
anodic
.1
%5. 4
N
-.
8 respectively, wave
with
for Figure la.
n=1
interaction
and
solution
pendent
groups
coatings. 15 charged
noninteracting
decreases
aqueous
The width at half-height for an ideal redox
groups
is
90
mV.
surface
Attractive
the width and repulsive interaction increase it.
AE1/2 or
is
usually
redox
larger
complexes
than
In
90 mV for charged redox
incorporated
in
polyelectrolyte
This is presumably due to the coulombic repulsion between the
groups.
hydrocarbon
However,
groups,
such
if as
the those
redox in
groups
are charged long-chain
PCMS-VC 16 ,
both
hydrophobic and
coulombic interactions would contribute to the overall interaction. The in
distinctly different AE
Figure
1/2
-values
for the anodic and cathodic wave
lb indicate the morphology of the polymer in the reduced form is
different
from
that
in the oxidized form.
The 75 mV width for the anodic
wave in Figure la suggests that there are quite strong attractive interactions among
the
viologen
interaction 2+
reduced and
is
the
results
attractive.
+e
(V
groups
+
>
1ong-chai n
in
the When
reduced the
form
charge
so
that
the
overall
on the viologen groups is
), the coulombic replsion between them is decreased
hydrocarbon
groups
can
approach
one another.
This
of the hydrophobic interaction.
This
in
significant
enhancement
hydrophobic
interaction
(attractive) would also cause the structure of the
reduced
polymer
in
•
the
aqueous
solution
to be more compact than in the
oxidized form. We schematically represent this process as:
)A+
where
A
and
respectively. mV)
B
e
(V+v
represent
more
-
)> )A
(V+
extended
)B
and
more
compact
structures,
The fact that the AE /2-value for the oxidation is larger (95
2 when the scan occurs on reversal from an initial potential where all of
W""'.. d'. p'W- '.'- ' -wm
,
', ' '. W,-w "''W.W
. -" "-.'- -"
-
"
" "
." " • " ' '.
"-
. -."w" ' " " " - . -" ,U ''
I.
9 the viologens are in the V viologen
has
indicates form
slow
experiment
the
the
V+-form
time
performed
was
for
a
much
it is (75 mV) when the longer time (Figure Ib)
allowed
scale
to
of
estimate
this CV experiment. the
rate
of
The following
change.
The coated
to equilibrate at -0.1 V and then the potential was
to -0.6 V, and held at this potential for different periods of time
before
longer depend
on
was
electrode scanned
in
than
la)
that the rate of change in polymer morphology from the A to the B
is
( )
been
(Figure
-form
it
was
than 4 on T .
depended on T.
scanned
positively
to obtain the anodic wave.
ForT.
the AE was 75 mV and the shape of the wave did not smaller T-values, AEI1/2 was larger and the wave shape
min, For
1//2
Thus, the time required for the change in polymer morphology
upon reduction is about 4 min. Although reduction, fast
on
the
the the
AE /2-values
rate
rate
of
of
change
in
polymer
morphology is slow during
change in polymer morphology upon re-oxidation is
voltammetric
time
scale
as
indicated
by the almost equal
for the cathodic waves in Figure la and lb.
Different rates of
change for expansion and contraction of charged polymers have been discussed
16
previously. time
However, the present observation demonstrates for the first
that
voltammetric methods can be used to study the kinetics of change
in the morphology of a polymeric surfactant in aqueous solution. The
rate
estmated
by
potential
of
charge
potential
was
transport
through
the
chronoamperometry. 1
step
stepped either from -0.1
films
of PCMS-VC
16
was
In this experiment, the
to -0.6 V (for measurement with the
polymer
initially
polymer
initially in the reduced form) and the slope of the current (i) vs.
in
the
oxidized
form) or from -0.6 to -0.1
V (for the
-1/2 line for times (t) of 0.8 ms to 1.4 ms was used to determine the effective diffusion coefficient, Def f . Def f was 1.4 x 10- 8 cm2 -1 for an form
initiallyoxidized
,
"
, .',,
.
,. If
.
'.
" " -
"
.
and
"
1.0 x 10-8 cm2 s- 1 for an initially reduced form,
,,
, ...
.!
,,'.
"
,
10
The
respectively.
significant difference is consistent with a morphology
change accompanying the redox process. To the
intensity
groups,
the
PCMS-MV. all
that the variation in AE
demonstrate of
the
hydrophobic
1/2
is due to the variation in
interaction
among the long-chain side
same experiment was carried out with another viologen polymer,
As shown in Figure 2a and 2b, AE1/2 for the two pairs of waves are
in the
range
of
138-145
mV.
This
finding not only supports the
structural change upon reduction of PCMS-VC 1 6 , but suggests that even in the 16'w
oxidized
form
the
attractive
interactions
of
the
hydrocarbon
chains
partially compensates for the repulsive interactions of the V2+ groups. greater
stabilization of the radical cation of PCMS-VC16 by the attractive,
hydrophobic
interaction
among the charged long-chain hydrocarbon groups is The redox potential of PCMS-VC 1 6 is
reflected in the redox potential.
also
The
16-
-0.44 V, compared to that of PCMS-MV, -0.38 V vs. SCE. Spectroscopic the
change
and
without
absorption SnO
with
Absorption Probe--To gain more insight into
in polymer morphology, spectroscopy in the visible region with methyl spectrum
electrode
2
Study
orange
as
a absorption
probe was carried out.
(Figure 3) of the reduced form of PCMS-VC16 film on an
shows
an
absorption
maximum
1
predominantly dimeric species in the film matrix. 1 7 cation
radical
compact
head
aggregation
The
groups of
the
could polymer
at
540
nm,
indicating
The dimerization of the
contribute
to some extent to the more
in the
reduced form, but we do not
believe that it is the major factor. Absorption probes, such as methyl orange, have been used to investigate the
microenvironments
coworkers orange
has
have
applied
long
hydrophobicity
been
matrices. 18
in polymer this used
techniques as
an
For
example, Martin and
in several studes.l1bd
absorption
probe
Methyl
to investigate the
of the binding sites. 19 The absorbance maximum is 460 nm in
*5*5~
.55
5*"*
I
water,
but
is
420-430
nm
in
organic
solvents.
When
lop
it is bound to
biopolymers or charged polymers, the maximum is at a shorter wavelength than 460
nm.
higher methyl
By
Thus,
absorbance
maximum of shorter wavelength indicates a
hydrophobicity at the binding site. The difference spectra for orange in PCMS-VC16 coating on SnO 2 electrodes is shown in Figure 4.
taking
the
incorporated groups
is
from
a
between
of
the
(reduced
the
absorption
from
solution,
Two
spectrum of PCMS-VC 16
form
at -0.1 V (oxidized form of PCMS-VC 16),
of PCMS-VC 1 6 ). in
that
the contribution from the viologen
difference spectra were taken by holding the
electrode
incorporated
shifted
dilute
eliminated.
potential
orange
difference
alone and that of PCMS-VC 1 6 coating in which methyl orange has been
coating
-0.6
an
the
or at
That the absorption spectrum of methyl
reduced
incorporated
S
form
in
the
of the polymer coating is
blue
oxidized form indicates that the
environment of the binding sites of methyl orange in the reduced form of the polymer
is more hydrophobic.
long-chain
hydrocarbon
hydrophobic
groups
domains.
The
drawn from the variation of AE This
is
hydrophobicity polymer emission
the of
Thus, in the reduced form of the polymer, the
first the
approach
result
1/2
in aqueous solution. spectrum
one another and form more compact
here is consistent with the conclusion
of the CV waves.
demonstration binding
sites
of (or
the
g. effect
of
the to
study
of
charge on the
the domains) associated with a 20
Previously, Ikemi et al.,
8-anilino-naphathlene-l-sulfonate
S
used the shift of
fluorescent the
effect
probe, of
polymer
concentration on the hydrophobicity of the hydrophobic domains formed by the triblock the
copolymer, poly(2-hydroxyethyl methacrylate)
poly(2-hydroxyethyl
methacrylate).
-
S
poly(ethylene oxide
Their study and this one demonstrate
usefulness of probe molecules in the investigation of the morphology of
•
polymers.
-
*- *~* --
% .
.0
12
ESR
ESR
Experiment--The
of the reduced form of PCMS-VCI6 is
spectra
shown in Figure 5 for (a) aqueous and (b) acetonitrile (MeCN) solutions. MeCN
(Figure
5b)
approximately of
the
the
by
spectrum
of
polymeric radicals, namely, an
structure exhibited by the monomer in dilute solution is .
dipolar interactions and/or electron and spin exchange reactions
in systems of high concentration of radicals. 2 1 solution
A,
symmetric single line spectrum is observed. The disappearance
hyperfine
caused
usual
In
5a) approaches the solid-state (or powder) spectrum 22 and
(Figure
indicates
The ESR spectrum in aqueous
immobile
radical
cation
side
groups in the reduced PCMS-VC 16.
Thus, in aqueous solution the long-chain viologen radical cation side groups are embedded in very hydrophobic, only slightly swollen hydrocarbon domains. The
rotational
spectrum
in
hydrophobic
motion
is
severely
retarded.
The difference between the
aqueous and that in MeCN solution also points to the so-called effect--the
aggregation
of
the amphiphilic molecules is only
pronounced in those solvents with high strength of hydrogen bonding and high dielectric constant, such as water.
23
Transmission Electron Microscopy -- It has long been known that the size of
micelles
investigating surfactants film-forming the
is
in
the and
the size
the
range of
of
the
effect
of
15-30
A. 2 4
We
were
hydrophobic
domains
the
on the size.
charge
interested in
formed in polymeric Because of the
property of polymeric surfactants, we were able to investigate
morphology of polymeric surfactants by transmission electron microscopy
(TEM).
Figure
6
shows
the
micrographs of several charged polymers.
A
polymer film cast on a carbon-coated copper grid, was stained with 2% uranyl acetate shows
solution continuous
(Figure
6a-e).
The film of oxidized PCMS-VC
16
clearly S
spherical domains, with typical domain diameters of about
0
200-500
A (Figure
6a).
The
size
of
the
domains is similar to those
. v,., '"*,,,,,,i.-".-? .... '/ ',;. ,' ".,.; "'.;', ;-': :,. ..- " ../... ,." ,_% .-,'.%-,, .::,:.:,...:
.".-
.. , 2,, .%;,,;..
2,',
Sb~b;
_' '-? "...
13 exhibited
by
synthetic
vesicles
are
discrete
We
believe
formed
the
vesicles. 6
However, the domains in the films of
whereas in PCMS-VC 16 , the domains are close-packed.
hydrophobic
domains observed in the film of PCMS-VC16 are
both inter- and intramacromolecularly by the aggregation of the long We.
chain viologen groups. If the
film of PCMS-VC 16 was first reduced chemically before staining
with uranyl acetate, the size of the hydrophobic domains became smaller; the typical
diameters were about 100 A (Figure 6b). This is consistent with the
results
of
electrochemical
and
absorption experiments, which indicates a
more compact structure for the reduced form of the polymer. Another was
also
domains
polymeric
surfactant
investigated were
also
PVP-C 12, IV (see Experimental section),
for comparison.
observed.
As shown in Figure 6c, hydrophobic
However, in this case the domains showed an
elliptical rather than a spherical shape. not
clear.
For
The origin
of this difference is
charged polymers that do not have long-chain hydrocarbon
groups, such as PCMS-MV (Fig. 6d) and sodium polystyrenesulfonate (Fig. 6e), domain
structure
observed
was
not
observed.
This supports the view that domains
in the polymeric surfactant film are formed by the aggregation of
long-chain hydrocarbon groups. Incorporation particularly polymeric
of
interested surfactants
electrocatalysis.
both
inorganic
in the for
(as
potential
Conventional
catalysts
or
incorporate organic substrates. formed
by
observed.
PVP-C 12
organic
incorporation
protonated-polyvinylpyridine 19 b compounds
and
are
of
compounds--We
organic
applications
of
molecules such
polyelectrolytes, capable
mediators)
such
of as
such
incorporating Fe(CN)6 3
films
4
are by in as
inorganic but do not
We anticipated that the hydrophobic domains
would incorporate organic compounds and this was indeed
Previous
studies
of
perflurosulfonate
(Nafion)
and
14
perfluro-carboxylate (Flemion) 1 5 ,18 indicated these perfluro polyelectrolytes can incorporate both hydrophilic and hydrophobic compounds. Figure
7a illustrates one such experiment.
A PVP-C 12 -coated electrode
was dipped in 1 mM anthraquinone-a-sulfonate (AQS) aqueous solution and then transferred response with
a
pure
supporting
electrolyte solution.
The much larger
(reduction and reoxidation of AQS), (solid line) obtained compared
the
response
electrode the
to
PVP-C
(dashed
indicates coating.
12
protonated
that
line)
of
a 1 mM AQS solution at an uncoated
a large amount of AQS has been incorporated into When
the
same
experiment
was carried out for a
PVP-coated electrode, the amount of incorporation was very small
(Figure 7b). Figure this
7c shows CV with the co-incorporation of Fe(CN) 6 3- and AQS.
experiment
dipped
in 1 mM
supporting response
an
electrode
Fe(CN) 63-
electrolyte. due
diffusion
to
AQS
coefficient
with incorporated AQS, as in Figure 7a, was
solution, Note
became
then washed and transferred to pure
that after incorporation of Fe(CN) 6 smaller.
incorporated film.
presumably caused by the crosslinking of the film by Fe(CN) 6 The
co-incorporation
substrate
could
electrocatalysis concentrated)
be
in the
environment
in
concentrated.
This is
3- 25
-S.
.2
of an inorganic catalyst or mediator and organic
useful
involve
the
This indicates a smaller effective
AQS in the Fe(CN) 63
of
In
in the design of electrocatalytic films.
Most
systems where only catalysts are incorporated (or
polymer coatings.
which
both
catalyst
Polymeric surfactants provided an and
nonpolar
substrate
can
".'
be
This might increase the efficiency of electrocatalysis.
CONCLUSIONS The
investigation
of
electroactive
number of interesting properties. more
useful
polymeric surfactants revealed a
The film-forming property might make them
than micelles or even vesicles in some applications.
Although 1%,
"
". .w ,-," ,, ,, " w ,"' w- w' ..,, ...' ,,' -.. .,.." ',.-.... ',,'.'.]- "-
-.., ,..-.•,
.,',,.
-' ,
W'-
'.TW,_-,T-,[ .€' w W''p
15 vesicles form can
do
good
films
behave
as
hydrophilic and with
retain
their structure after solvent evaporation, they do not
and the domains are discrete. These polymeric surfactants bound
or
domains.
immobilized
of
with both hydrophobic and
Films of Nafion also exhibit segregated hydrophobic
hydrophilic domains. those
micelles
,.
It would be interesting to compare their behavior
the polymeric surfactants.
These polymeric surfactants may
also be useful as model systems for electron or energy transfer reactions in organized of
assemblies.
electrochemical,
With stable films, investigation by the combination spectroscopic,
and
other
techniques
can
'I
be easily
carried out. The effects of charge on the side groups on the morphology of polymeric surfactants
groups
viologen of
the
have
been demonstrated, and it was shown that reduction of the leads to a more compact structure in the polymer.
morphology
and
Studies
".
properties of blends of polymeric surfactants with
other polymers should also be of interest. ACKNOWLEDGMENT The
support and
(CHE8402135)
of
this
research
by
the
National
Science Foundation
of Naval Research is gratefully acknowledged.
Office
We
thank Dr. M. Scherling for his help with the TEM, Professor P. Munk for the use
of
Doblhofer
the
viscometer, Dr. C.-H. Change for his help with GPC, and Dr. K. of
Max-Plank-Gesellschaft
preparation of PVP-C 12.
I
"
'.
for
valuable
suggestions
in the
S
16
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i"--"-l" t-' ..i° . i'i . . . ..
.. . .'i
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I
18 Anson, F. C. Anal. Chem. 1977, 49, 1589. 15. (a) Tsou, Y.-M.; Anson, F. C. J. Electrochem. Soc. 1984, 131, 595; N.; Anson, F. C. Anal. Chem. 1980, 52, 1192; (c) Buttry, D. A.;
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19
24. (a) Thomas, J. K. Chem. Rev. 1980, 80, 283; (b) Fendler, J. H. Acc. Chem. Res. 1976, 9, 1953. 25. Tsou,
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references therein.
JLA
JP
20
.0
FIGURE CAPTIONS Figure I
Cyclic on
a glassy
before
carbon
potential
rate: 10 mV s - .
Figure 2
scan,
(b) equilibrated at -0.6 V before potential scan.
potential
scan, (b) equilibrated at -0.7 V before potential scan.
1.
The electrode was (a) equilibrated at -0.2 V before Scan rate: 10
Supporting electrolyte: 0.2 M KCl.
Absorption
16
spectrum film on SnO
of
2
fully
- mol cm -2 reduced 2.5 x 10-7 (viologen groups) of
electrode.
-
Difference absorption spectra of methyl orange incorporated in the PCMS-VC Figure
film
Scan
Supporting electrolyte: 0.2 M KCl.
carbon electrode.
of
film
The electrode was (a) equilibrated at -0.1 V
a glassy
PCMS-VC
Figure 4
electrode.
6
voltammograms of 2.6 x 10- 9 mol cm-2 (viologen groups) of PCMS-MV film on
Cyclic
mV s
Figure 3
of 1.3 x 108 mol cm 2 (viologen groups) of PCMS-VC
voltammogrars
16
film
3. Solid line, PCMS-VC 16 film fully oxidized; dotted line, PCMS-VC 1 6
fully
reduced.
Supporting
electrolyte:
0.2 M KCI and 0.01 M CH3 COONa,
pH=5.6.
Figure 5
ESR film
spectra on
a
of Pt
fully reduced 1.4 x 10- 6 mol cm-2 (viologen goups) of PCMS-VC 1 6 flag
electrode; (a) in 0.2 M KCI aqueous solution, (b) in 0.1 M
(n-C4 H9 )4NBF 4 MeCN solution. 0
Figure 6 Transmission electron micrographs of polymer films; (a) fully oxidized PCMS-VC 1 6, (b)
fully
reduced
pol ystyrenesul fonate.
PCMS-VC 16 ,
(c)
PVP-C 12,
(d)
PCMS-MV,
(e) sodium
y,,,,
21
Figure 7 Cyclic
voltarnmograrns
uncoated Cmr
electrode,
(dodecyl
for
anthroquinone-a-sulfonate
(AQS); (a) dotted line, on
1 ruM AnS; solid line, electrode coated with 4.6 x 10-
groups)
mol
of PVP-C 12 ' dipped in 1 ruM AQS solution, and replaced in
pure supporting electrolyte solution; (b) repeat of (a) but with electrode coated with
2.0
x 10
mol
cm2 (pyridine groups) of PVP; (c) electrode coated with
PVP-C 12used to record Figure 7 (a) (solid line) after it was dipped in 1 mM 12 Fe(CN) 6 solution, washed, and replaced in pure supporting electrolyte solution.
0A
4_4
P-.
10 mv/s
H 2 0/0.2M KCI .
PCMS
5pA.
VC1
/GC
.
I -0.2
I -0.4
I
I
:'
-0.6
V vs. SCE "S"
S
10 mv/s
PCMS
-MVO5A
/GC
-0.2S.
-0
4
0.
V
vs.
SC
A.7
-n~8
r ~p.
I QJI
U'.
F /
-
__
S p.
/
E
.~
?
C U-
'U
N
-3
-
-
N
S
/i
I
-
'I
U',
I
-~
I
1
~
L~L...
_____JL...~
U
~...
I eou~qJOSqV
U,
'U
IlkDi ff ere nce SpectraMe
h l O a g
in PCMS
-VC,6/SnO
2 measured In oxidized PCMVS
0.08
V1
mesue PCMS
in PCIVIS -vC
o
0.06
0(
0 004
0. 0
400
440
Wavelength (nm)
480
520
1
V.'. W~'- W ~ U ~J U
1.4
q I 'I.
AP~~ H2 0/O.2 M KOI
'I,
4 4
'p
20G
PCMS-VC 1 ~
F-I
/Pt
a'
a', a' a' 'p.
CH 3 CN/O.1 M TBABF 4
p
'a' -a.-' 'p
~
'-~'
.4 'a.
~.
~'
*~*'~**
-a~,'.
\**~*~~aa%.4a"p'Pf~.,
'a',
a-' .~.
X.~L
.
A
00
0 0
6 Ii4
6
0
CO' 0j
"I
0I
CL
>
Q
Co-incorporation of Fe(CN) 6B and AQ-SO 3 Na PVP -012
/GC NO
0.4
0.0 V vs. SCE
-0.4
LL
N
4.
%
%
%
'r w
%
% "I
'p
"
%J
%A,
%
1
% -