dodecyl benzene sulphonic acid mixture

Synthetic Metals 69 (1995)

Phase

behavior

of polyaniline/dodecyl

135-136

benzene

sulphonic

acid mixture

O.T. Ikkalaa, T.M. Lindholmb, H. Ruohonenc, M. Selantausb, and K. Vakipartac acorporate ~Elu&~~

bscientific Services, cchemicals, Conducting Polymers . , P.0 Box 310, Porvoo FIN-06101, Finland

Abstract

Processibili of polyaniline (PANI) can be increased by usm functionalized counter ions, such as dodecyl benzene sulphonic acid (DBS 2 ). Recently it has been observed that extra DB f A yields plasticized and protonated melt processable corn lexes. In this study the reaction between PAN1 and DBSA has been investigated by DSC and dielectric thermal analysis (DE&. A ph ase diagram has been compiled for the PANI/DBSA system.

1. INTRODUCTION Pol aniline is a promising candidate for an industrial 1.n;( erently conducting pol mer due to its stabili and potentially attractive economics Y11. One of the metho 2 s is to use functionalized to increase its 8 rocessability counter-ions [2]. ertam functionalized sulphonic acids can be used, such as dodecyl benzene sul honic acid (DBSA) or camphor sulphonic acid (CSA) [2]. &tra amount of DBSA ren ers an electrically conducting, plasticized l’ANI(DBSA)salt corn lex with which electrically conducting blends with commod?~~lymers can be przared [2,3]. SA protonates PA I and causes a phase change from a paste to a solid material [3]. This phase transition as a function of DBSA weight fraction is in this work studied with differential scanning calorimetry (DSC) and dielectric thermal anal sis (DEA) to characterize the reaction between DBS and olyaniline. DEA was expected to be suitable beiuse 8 BSA 1s highly . l olar and dielectric to monitor curin measurements have also been use phenomena in e oxies [4]. The electrical conductivity an 3 thermopower of F ANI(DBSA)-system is reported elsewhere [51.

response (capacitance, conductance and phase angle shift) was converted internally into permittivity E’and loss factor E”. To study the dc-conductivity, a reference sam le was heated to a temperature high enough to induce tK e reaction but low enou h not to cause degradation. Therefore a heat treatment of 188 “C for 690s was selected. 3. RESULTS

AND DISCUSSION

Fi ure 1 shows the reaction therm0 rams of PANI(DBS w )x, where x=O.5,...,4. Pure PAN1 and b BSA are shown as a reference. The latter two do not show any clear specific thermal behavior below 200°C. In contrast, PAN1 eak mixed with DBSA has relatively large exothermic around 150°C which shifts upwards as a function oP the DBSA weight fraction.

*, \

PANI

2. METHODS Polyaniline was polymerized and subsequently reduced to emeraldine base (EB) usin conventional methods [2]. After dr ing at 60°C for 60h, E i has been stored in a desiccator. D EY SA was of laboratory purity, produced by Tokyo Kasei. Due to its extreme hygroscopic nature, it was also stored in a desiccator. rotonation is expected to take place The { . preferably on t e immrc nitrogen sites, whose mole fraction is approximately 0.5. We varied the molar ratio of DBSA relative to EB from 4 (which means excess DBSA) to 0.5. Emeraldine base and DBSA were first mixed by using an agate mortar at room temperature resultin a Immediately thereafter the sample was taken for &Za:te; DEA-measurements to study the reaction of the two components. A s ecial DSC instrument Mettler DSC 27 HP with 4 MPa r3-2 overpressure was used to suppress volatiles. The temperature swee was 5”C/min, starting from 30°C to 200°C. Due to t R e extreme reactivity of EB/DBSA paste the use of Pt (instead of Al) pans was required. The dielectric analyzer DEA 2970 (TA Instruments), cou led to a TA2100 thermal analyzer, was used to record diePectric data. The sam le was pasted on a single surface uartz plate and the B ata were collected between l-1000 R z over the temperature range of 25”C220°C at the heating rate 3”C/min. The measured data 0379-6779/95/$09.500 1995 Elsevier Science S.A. All rights resewed 0379-6779(94)02390-K

SSDI

‘LP

ANI(DBSA~

ll:i PANI(DBSA)z.o

,/

k /L__Y-

DBSA \

50

100

150

TEMPERATURE

200 (“C)

I_

Figure 1. DSC thermograms showing emeraldine base with DBSA.

the

reaction

of

Fi ure 2 shows the dielectric and loss moduli of the reaction of ?J AN1 and DBSA at different molar fractions at 1Hz. Pure EB and DBSA do not show any articular behavior below 200°C. DBSA robably starts to dp ecompose above 200°C. The peaking in l!?, suggests a phase transition

136

O.T.

Ikkala

et al. I Synthetic Met& 69 (1995) 135-136

from a liquid to a solid like material, as commonly observed in epoxy curin At the same time a steep rise of E” is observed whit % is due to to the increasing electrical conductivity. As the conductivity reaches 10-4 S/cm, the measuring system is saturated and the instrument is thereafter not linear. 60-

PANl(DBSA)x

0

50

150

100 TEMPERATURE

200

It is expected that Figure 3 is not a true equilibrium phase diagram. In fact, in the companion aper it will be shown that conductivity can be achieve B even at room temperature if long enou h waiting times can be allowed, for example days or weeks P51. Comparison of DSC and DETA data yield sli htly different temperatures. It may be explained so ta at the DSC peak yields the temperature where the reaction conversion rate is at its maximum. Also the slower swee rate in DEA measurements might play a role. DEA yiel B s the mformation when the dielectric loss starts to considerably increase due to the onset of the plasticization/protonation behavior. Figure 4 shows that the conductivities up to approximately 1 S/cm were achieved.

250

0

(“C)

00 0 x= 0.5 .’

2.0

0.7 1.0

::

;

::

;:

L

6

0

0.001

2 4.0

0.0001 B

DBSA

50

0.00001

I

0

&J

0.2

0.4

1

OC 0

50

100

200

150

TEMPERATURE

0.6

0.8

1

DBSA WEIGHT FRACTION IN

250

PANI(DBSA)x

(“C)

Figure 2 Dielectric E’ and E” as a function of temperature at sweep rate 3”C/min at 1Hz. Figure 3 shows the phase diagram of PANI/DBSA system at the used sweev rates. Extra DBSA. onlv mechanically mixed with PAN1 leads to a paste where PAN? uarticles are disoersed in DBSA. The material is mainlvJ ionicall conduc’ting. Heating over the phase boundary, denote cy.m the figure, causes solidification of the paste and it becomes electronically conducting, as is shown in Fi 4. If there is ross amount of extra DBSA, the material is so ?t and rubber11.&e. If the molar amount of DBSA is reduced towards 0.5, the semi-solid doped complex is more and more “hard” until PANI(DBSA)o.s does not appreciably soften at 180200°C [6].

Figure 4 Conductivity of the PANI(DBSA),-complex heat treatment at 180°C for 690 s.

after

4. SUMMARY The phase transition of PANI/DBSA-system from ionically conducting pastelike material to semi-solid electronically conductmg do ed complex at elevated temperature has been studied. I$gher amount of DBSA leads to hi her transition temperature. If lar e amounts of extra DBS i is used, such as PANI(DBSA 7 1.0, a plasticized complex is created from which films can be pressed. REFERENCES

;a

200

1

150

-

.o

DSC YC/min 0

9 2

100

A.G. MacDiarmid f’e~~kP~oc. 328

2.

Y. Cao, I?. Smith, and A.J. Heeger, Synth. Met., 48 (1992) 91; Y. Cao, P. Smith, and A.J. Heeger, PCT Patent Application WO 92/22911.

3.

T Karnl, J. Laakso, E. Savolainen, and K. Levon, E.P. Patent Application 545729 AZ, to Neste Oy.

4.

See, e. ., A.J. MacKinnon, McGraw? , and R.A.Pethrick, 3252, and references therein.

5.

M. Ahlsko , H, Isotalo, 0. Ikkala, J. Laakso, Stubb, and P.-E. Osterholm, this proceedings.

6.

T. Vikki and O.T. Ikkala, this proceedings.

0

-

B DEA

5

0

1.

0

3”Clmin

50-

!+ 0

-

I

I

I

I

0

0.2

0.4

0.6

0.8

DBSA WEIGHT FRACTION IN PANI(DBSA)x Figure 3 Transition temperatures

of PANI/DBSA.

1

and A.J. Epstein Mat. Res. Sot. (1994) 133 and the references

S.D. Jenkins, P.T. Polymer, 34, (1993) H.