Polymer Films on Electrodes. 22. Electrochemical, Spectroscopic ...

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

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Polymer Films on Electrodes. 22. Electrochemical, Spectroscopic, and Transmission Electron Microscopic Studies on Morphological Changes in Films of Polymeric Surfactants. 7.

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Yu-Min Tsou, Hsu-Yang Liu, and Allen J. Bard

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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

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EDITION OF , O r - 014-6o0 S/R 0

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Unclassified Unclassifi0d SECURITY

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%,N -a.'_,,

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*(_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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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

% -