- Email: [email protected]
Orientation and conductivity in polyaniline Part 2: Chloroform cast films
S¥flTH|TIIC UgETRLS ELSEVIER
Synthetic Metals 93 (1998) 73-76
Short communication
Orientation and conductivity in polyaniline Part 2: Chloroform cast films C.D.G. Minto, A.S. Vaughan * J.J. Thomson Physical Laboratory, University of Reading, Whiteknights, PO Box 220, Reading RG6 6AF, UK Received 5 February 1997; received in revised form 1 August 1997; accepted 13 November 1997
Abstract In this short communication we report the observation of inherent orientation in films of polyaniline doped with camphor sulfonic acid and cast from chloroform. The observed orthogonal wide-angle X-ray scattering (WAXS) patterns are best interpreted in terms of a preferential molecular alignment parallel to the plane of the film, but with no particular orientation within this plane. In comparison to m-cresol cast films this orientation is not as well developed and the molecular structure itself is markedly different with a much larger interchain spacing. This degradation in the molecular architecture is proposed to account partly for differences in the observed transport behaviour. © 1998 Elsevier Science S.A. Keywords: Polyaniline; Structure; Orientation; Conductivity; Films
1. Introduction In a recent paper we reported the observation of considerable orientational order in films of polyaniline (PANI) doped with ( + )-camphor sulfonic acid (CSA) that were cast from m-cresol solutions [ 1]. We suggested that the origin of this interesting behaviour was due to a rod-like solution phase, brought about by the interactions suggested by Ikkala et al. [2] to exist between PANI-CSA and m-cresol; this hypothesis being upheld by the reports of lyotropic solutions of PANI [ 3,4]. We demonstrated that, upon removal of the solvent, this special molecular conformation results in improved molecular ordering in the amorphous inter-crystalline regions, i.e. expanded molecular coils, and suggested that this reduction in spatial disorder constitutes the beginnings of an explanation of the metallic properties found in PANI produced in this manner [5]. The metallic state in these PANIs is by now well known and provides an interesting contrast to films cast from chloroform, where traditional semiconducting behaviour has been reported [6], namely, a phonon activated process with a negative temperature coefficient of resistivity. Such materials appear more akin to traditional, isotropic films of PANI cast * Corresponding author. Tel.: + 44 118 931 8559; fax: + 44 118 975 0203; e-mail: a.s.vaughan @reading.ac.uk 0379-6779/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved P / / S 0 3 7 9 - 6 7 7 9 ( 9 7 ) 04 1 10-6
from N-methyl-pyrrolidone (NMP) and treated with HCI [7]. It would be entirely acceptable to presume that PANI cast from chloroform in the conducting state would therefore be isotropic. This communication reports the first observation of an inherent molecular orientation within chloroform cast films which, we propose, has similar origin to that found in mcresol derived materials. Although this result is initially surprising, comparison with the existing literature and analysis of X-ray scattering patterns lead to a coherent understanding of the nature of this interesting class of PANIs.
2. Experimental Emeraldine base (EB) was synthesized at 0_+0.05 °C in the conventional manner [8]; from the results of Adams et al. [9], this material should have M,, ~ 105 and a polydispersity of the order of six. The material was compounded with a stoichiometric amount of ( + )-CSA (Aldrich) (2:1 molar ratio of PhN group to CSA molecule) and dissolved in chloroform for 24 h. The resultant dark green solution was filtered through Whatman's No. 1 paper and cast onto glass which was cooled on a block of dry ice in order to prolong the deposition process. Despite this, the solvent evaporates
74
C.D.G. Minto, A.S. Vaughan / Synthetic Metals 93 (1998) 73-76
rapidly, leaving a black-purple shiny film which is of poorer cohesive quality than the previously observed m-cresol cast films. In many respects, specimens prepared from chloroform bear similarities to HC1 protonated NMP cast PANI. Where possible, films were separated from the substrate dry, but where adhesion proved too great, the films were quickly soaked in distilled water to aid removal. PANI was not dissolved completely in chloroform and hence it was difficult to obtain accurate measurements of the solution strength 1. Nevertheless, the resulting films appeared continuous when examined by scanning electron microscopy (SEM), except for some voiding that is most likely associated with solvent evaporation. X-ray measurements were performed in accordance with our standard techniques [ 1 ]. X-ray scattering was probed in both through-film (X = 0 °) and through-thickness configurations (X = 90 °, where sections of film are stacked parallel to each other, preserving their original relative orientation). A symmetric transmission geometry was utilized whereby the scattering vector remains perpendicular or parallel to the film surface in accordance with the above configurations [10].
3. Results and discussion Fig. 1 shows a diffractometer trace in the traditional, through-film (X=0°), configuration. No anisotropy is observed on a flat plate exposure and consequently only an equatorial trace is displayed here. The scattering is characterized by two peaks at 6.2 and 3.6 ,~, together with weaker shoulders at about 14 and 4.7 ,~. In Fig. 2, the same film is rotated by 90 ° so that the film thickness is now presented to the X-rays (X = 90 ° configuration); the above reflections are again evident. This figure also includes a flat plate exposure (and a schematic representation of the observed scattering), in which four additional, very weak reflections can also be seen. As is evident, a degree of orientation is now present (most noticeable in the 3.6 and 6.2 A reflections). With the film surface vertical, these are seen to orient in the meridian and equator, respectively. Fig. 2 can be contrasted with the behaviour observed in mcresol cast films, shown in Fig. 3 for equatorial and meridional scans of a film in the X = 90° configuration; again a schematic representation of the fiat plate simplifies the description. The above results initially pose somewhat of a conundrum; in our previous report we suggested, by comparison to mcresol solution extracted fibres, that the strong 3.5 ,~ reflection observed in m-cresol cast films was an interchain reflection, originating from the crystalline regions, where no solvent remains to disrupt the morphology. We established that the t This fact is in itself of interest, suggesting that the PANI that is dissolved is of a somewhat lower molecular weight than the material as a whole. Even with this caveat, the analysis that follows is still of interest and reveals much of the nature of P A N I - C S A and the influence of processing conditions on molecular structure.
6.2A '~
3.6A
0.0
0.5
1.0
1.5 q (1~ 1)
2.0
2.5
3.0
Fig. 1. Diffractometer trace of P A N I - C S A cast from chloforom in the X = 0° configuration; arrows highlight peak positions.
predominant molecular trajectory lies in the plane of the film, the 3.5 ,~ reflection was observed to orient equatorially ( with the film surface vertical, as exhibited in Fig. 3) and was thus an interchain spacing. In these chloroform cast films, the 3.6 reflection orients in the meridian and, hence, if it is assumed to arise from similar interchain correlations, would imply that the constituent molecules are preferentially aligned perpendicular to the plane of the film, i.e. from film surface to surface. Whilst there are systems in which such a molecular conformation does develop (e.g. sedimented mats of chain folded lamellar crystals and Langmuir-Blodgett films), in the absence of any specific interactions, we propose that such a structure is unlikely to develop through the precipitation of molecular coils from solution. An alternative interpretation of the above results can nevertheless be proposed which is consistent with the literature. Pouget et al. [ 11 ] described a basic wide-angle X-ray scattering (WAXS) study, in which three Debye-Scherrer rings, with d spacings of 14.2, 5.9 and 3.5 ,~, were obtained from observations of PANI cast from chloroform. These are in reasonable accordance with three of the strongest peaks observed in this study (out of a total of eight). From these limited observations, Pouget et al. suggested that the longest d spacing should be associated with the molecular axis. This 14.2 ,~ reflection represents an increase in the c-axis length over that observed in PANI cast from m-cresol (9.2 ,~) and, it was proposed, could correspond to half the periodicity of a fully t r a n s chain. The inability to identify the c-axis unambiguously in PANI cast from chloroform is a direct consequence of difficulties associated with the preparation of oriented specimens. However, this is not the case for films cast from DMSO where mechanical deformation can be used to orient the material. Despite the use of a different solvent, there is good reason to believe that films cast from DMSO and chloroform should be similar. In general, solvent-casting CSA doped PANI results in a material which can be broadly classified into two types, according to structure and charge transport behaviour. Where attractive interactions exist between polymer-counter-ion complex and solvent, films similar to that from m-cresol are
C.D.G. Minto, A.S. Vaughan / Synthetic Metals 93 (1998) 73-76
75
!
\
I
J
~!.,1
/
a zs,¢
=
0.0
0.5
1.0
1.5
2.0
2.5
3.0
q (A-t} (a)
(b)
Fig. 2. (a) Equatorial and meridional scans of thin section of chloroform cast films; film surface is in the meridian. (b) Schematic representation of flat plate and actual exposure.
2 ~A
4 .IdA J 4~'A
7 J.IA
& /,IDA
|
a,
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
q lit"1)
Fig. 3. Diffractometer traces for ( __+)-CSA doped films in the g = 90 ° (inset) configuration and flat plate representation.
derived, with similar structure and transport properties. Otherwise, in the absence of such interactions, films similar to chloroform castings are found [ 13]. Films cast from DMSO fall into this second category and, indeed, give similar reflections to those reported here; a 6.03 J, equatorial reflection and a 3.58 A meridional reflection [ 12]. In the light of these observations, it therefore seems reasonable to ascribe the 6.2 reflection described above to an interchain spacing and the 3.6 A reflection to an intrachain spacing (an inversion of that which we reported in PANI-CSA, cast from m-cresol). Thus, we propose that the reflections, listed in Table l, can be ascribed as follows; interchain (hk0) : 14, 7.8, 6.1, 4.7, 3.0 and 2.5 J~; intrachain (001) 3.6 and 3.3 J, 2. We again see 2 Note that on many of these reflections ( 14, 6.1 and 3.6 A ) the observed orientation is very weak with only areas of increased intensity being present.
Table 1 Scattering vectors (q), d spacings, orientation and relative strengths of observed peaks Chloroform film q (A 0.44 0.90 1.02 1.34 1.76 2.08 2.52 3.00
~)
d (A)
Orientation
Strength
~ 14-15 7.8 6.16 4.69 3.57 3.30 2.77 2.32
± ~ ± ± ' ±
m vw vs vw m w vw vw
II II ± _1_
a vw = very weak orientation, w = weak, m = medium, vs = very strong.
76
C.D.G. Minto, A.S. Vaughan / Synthetic Metals 93 (1998) 73-76
that the molecules are preferentially deposited with their trajectory arranged somewhat in the plane of the film, but with a much larger interchain spacing of 6.2 A as opposed to the 3.5 ,~ observed in the m-cresol derived materials. From this observation, it is evident that the 14 ,~ reflection can also be characterized as an interchain reflection, as opposed to being a c-axis reflection as proposed by Pouget (although the level of orientation is quite weak). The degree of orientation of the polymer can be ascertained in a manner similar to that used for m-cresol cast films - - by selecting a scattering vector and progressively rotating the specimen [ 14 ]. Performing this operation for the 3.6 A reflection yields an orientation parameter of 0.25, or less. This compares with the 0.5-0.6 generally observed in m-cresol cast films [1], indicating much less well-established ordering. Presumably, this lower degree of orientation for the polymer, the increased interchain spacing of 6.1 A, and differing crystalline structure all contribute to the absence of the metallic state. Nevertheless, both the WAXS results and the charge transport properties are characteristic of a material which is less disordered than either HC1 doped PANI or pressed pellets of PANI-CSA, results from which will be presented in a future publication [ 15].
4. Conclusions
The above results show that samples of polyaniline doped with camphor sulfonic acid and cast from chloroform are appreciably anisotropic and are, therefore, qualitatively similar to films cast from m-cresol. However, the crystalline
structure is completely different, with a considerably larger interchain spacing and a much reduced periodicity along the c-axis. The degree of orientation is also far less than that found in m-cresol cast films, with orientation parameters of 0.25 being typical. The lower degree of orientational order found in these materials, both in crystalline structure and anisotropy accounts, in part, for the observed semiconducting behaviour.
References [ 1] C.D.G. Minto, A.S. Vaughan, Polymer 38 (1997) 2683-2688. [2] O.T. Ikkala, L. Pietil~valign [ch, L Ahjopalovalign [ch, H. Osterholmvalign[ch, P.J. Passiniemivalign[ch, J. Chem. Phys. 103 (1995) 9855-9863. [3] Y. Cao, P. Smith, Polymer 34 (1993) 3139-3143. [4] W.Y. Zheng, R.H. Wang, K. Levon, Z.Y. Rong, T. Taka, W. Pan, Macromol. Chem. Phys. 196 (1995) 2443-2462. [5] M. Reghu, Y. Can, D. Moses, A.J. Heeger, Phys. Rev. B 47 (1993) 1758-1764. [6l A.G. MacDiarmid, A.J. Epstein, Synth. Met. 65 (1994) 103-116. [7] Z.H. Wang, H.H.S. Javadi, A. Ray, A.G. MacDiarmid, A.J. Epstein, Phys. Rev. B 42 (1990) 5411-5414. [8] Y. Wei, G.W. Jang, K.F. Hsueh, E.M. Scherr, A.G. MacDiarmid, A.J. Epstein, Polymer 33 (1992) 314. [9] P.N. Adams, P.J. Laughlin, A.P. Monkman, A.M. Kenwright, Polymer 37 (1996) 3411. [ 10] G.R. Mitchell, Polymer 27 (1986) 346-349. [ 111 J.P. Pouget, Z. Oblakowski, Y. Nogami, P.A~ Albouy, M. Laridjani, E.J. Oh, Y. Min, A.G. MacDiarmid, J. Tsukamoto, T. Ishiguro, A.J. Epstein, Synth. Met. 65 (1994) 131. [ 12] Y. Cao, P. Smith, Synth. Met. 69-71 (1995) 191. [ 13l Y. Cao, J. Qiu, P. Smith, Synth. Met. 69-71 (1995) 187. [ 14] G.R. Mitchell, A.H. Windle, Polymer 24 (1983) 1513-1520. [ 15] C.D.G. Minto, A.S. Vaughan, J. Phys.: Condens. Matter, submitted for publication.
Synthetic Metals 93 (1998) 73-76
Short communication
Orientation and conductivity in polyaniline Part 2: Chloroform cast films C.D.G. Minto, A.S. Vaughan * J.J. Thomson Physical Laboratory, University of Reading, Whiteknights, PO Box 220, Reading RG6 6AF, UK Received 5 February 1997; received in revised form 1 August 1997; accepted 13 November 1997
Abstract In this short communication we report the observation of inherent orientation in films of polyaniline doped with camphor sulfonic acid and cast from chloroform. The observed orthogonal wide-angle X-ray scattering (WAXS) patterns are best interpreted in terms of a preferential molecular alignment parallel to the plane of the film, but with no particular orientation within this plane. In comparison to m-cresol cast films this orientation is not as well developed and the molecular structure itself is markedly different with a much larger interchain spacing. This degradation in the molecular architecture is proposed to account partly for differences in the observed transport behaviour. © 1998 Elsevier Science S.A. Keywords: Polyaniline; Structure; Orientation; Conductivity; Films
1. Introduction In a recent paper we reported the observation of considerable orientational order in films of polyaniline (PANI) doped with ( + )-camphor sulfonic acid (CSA) that were cast from m-cresol solutions [ 1]. We suggested that the origin of this interesting behaviour was due to a rod-like solution phase, brought about by the interactions suggested by Ikkala et al. [2] to exist between PANI-CSA and m-cresol; this hypothesis being upheld by the reports of lyotropic solutions of PANI [ 3,4]. We demonstrated that, upon removal of the solvent, this special molecular conformation results in improved molecular ordering in the amorphous inter-crystalline regions, i.e. expanded molecular coils, and suggested that this reduction in spatial disorder constitutes the beginnings of an explanation of the metallic properties found in PANI produced in this manner [5]. The metallic state in these PANIs is by now well known and provides an interesting contrast to films cast from chloroform, where traditional semiconducting behaviour has been reported [6], namely, a phonon activated process with a negative temperature coefficient of resistivity. Such materials appear more akin to traditional, isotropic films of PANI cast * Corresponding author. Tel.: + 44 118 931 8559; fax: + 44 118 975 0203; e-mail: a.s.vaughan @reading.ac.uk 0379-6779/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved P / / S 0 3 7 9 - 6 7 7 9 ( 9 7 ) 04 1 10-6
from N-methyl-pyrrolidone (NMP) and treated with HCI [7]. It would be entirely acceptable to presume that PANI cast from chloroform in the conducting state would therefore be isotropic. This communication reports the first observation of an inherent molecular orientation within chloroform cast films which, we propose, has similar origin to that found in mcresol derived materials. Although this result is initially surprising, comparison with the existing literature and analysis of X-ray scattering patterns lead to a coherent understanding of the nature of this interesting class of PANIs.
2. Experimental Emeraldine base (EB) was synthesized at 0_+0.05 °C in the conventional manner [8]; from the results of Adams et al. [9], this material should have M,, ~ 105 and a polydispersity of the order of six. The material was compounded with a stoichiometric amount of ( + )-CSA (Aldrich) (2:1 molar ratio of PhN group to CSA molecule) and dissolved in chloroform for 24 h. The resultant dark green solution was filtered through Whatman's No. 1 paper and cast onto glass which was cooled on a block of dry ice in order to prolong the deposition process. Despite this, the solvent evaporates
74
C.D.G. Minto, A.S. Vaughan / Synthetic Metals 93 (1998) 73-76
rapidly, leaving a black-purple shiny film which is of poorer cohesive quality than the previously observed m-cresol cast films. In many respects, specimens prepared from chloroform bear similarities to HC1 protonated NMP cast PANI. Where possible, films were separated from the substrate dry, but where adhesion proved too great, the films were quickly soaked in distilled water to aid removal. PANI was not dissolved completely in chloroform and hence it was difficult to obtain accurate measurements of the solution strength 1. Nevertheless, the resulting films appeared continuous when examined by scanning electron microscopy (SEM), except for some voiding that is most likely associated with solvent evaporation. X-ray measurements were performed in accordance with our standard techniques [ 1 ]. X-ray scattering was probed in both through-film (X = 0 °) and through-thickness configurations (X = 90 °, where sections of film are stacked parallel to each other, preserving their original relative orientation). A symmetric transmission geometry was utilized whereby the scattering vector remains perpendicular or parallel to the film surface in accordance with the above configurations [10].
3. Results and discussion Fig. 1 shows a diffractometer trace in the traditional, through-film (X=0°), configuration. No anisotropy is observed on a flat plate exposure and consequently only an equatorial trace is displayed here. The scattering is characterized by two peaks at 6.2 and 3.6 ,~, together with weaker shoulders at about 14 and 4.7 ,~. In Fig. 2, the same film is rotated by 90 ° so that the film thickness is now presented to the X-rays (X = 90 ° configuration); the above reflections are again evident. This figure also includes a flat plate exposure (and a schematic representation of the observed scattering), in which four additional, very weak reflections can also be seen. As is evident, a degree of orientation is now present (most noticeable in the 3.6 and 6.2 A reflections). With the film surface vertical, these are seen to orient in the meridian and equator, respectively. Fig. 2 can be contrasted with the behaviour observed in mcresol cast films, shown in Fig. 3 for equatorial and meridional scans of a film in the X = 90° configuration; again a schematic representation of the fiat plate simplifies the description. The above results initially pose somewhat of a conundrum; in our previous report we suggested, by comparison to mcresol solution extracted fibres, that the strong 3.5 ,~ reflection observed in m-cresol cast films was an interchain reflection, originating from the crystalline regions, where no solvent remains to disrupt the morphology. We established that the t This fact is in itself of interest, suggesting that the PANI that is dissolved is of a somewhat lower molecular weight than the material as a whole. Even with this caveat, the analysis that follows is still of interest and reveals much of the nature of P A N I - C S A and the influence of processing conditions on molecular structure.
6.2A '~
3.6A
0.0
0.5
1.0
1.5 q (1~ 1)
2.0
2.5
3.0
Fig. 1. Diffractometer trace of P A N I - C S A cast from chloforom in the X = 0° configuration; arrows highlight peak positions.
predominant molecular trajectory lies in the plane of the film, the 3.5 ,~ reflection was observed to orient equatorially ( with the film surface vertical, as exhibited in Fig. 3) and was thus an interchain spacing. In these chloroform cast films, the 3.6 reflection orients in the meridian and, hence, if it is assumed to arise from similar interchain correlations, would imply that the constituent molecules are preferentially aligned perpendicular to the plane of the film, i.e. from film surface to surface. Whilst there are systems in which such a molecular conformation does develop (e.g. sedimented mats of chain folded lamellar crystals and Langmuir-Blodgett films), in the absence of any specific interactions, we propose that such a structure is unlikely to develop through the precipitation of molecular coils from solution. An alternative interpretation of the above results can nevertheless be proposed which is consistent with the literature. Pouget et al. [ 11 ] described a basic wide-angle X-ray scattering (WAXS) study, in which three Debye-Scherrer rings, with d spacings of 14.2, 5.9 and 3.5 ,~, were obtained from observations of PANI cast from chloroform. These are in reasonable accordance with three of the strongest peaks observed in this study (out of a total of eight). From these limited observations, Pouget et al. suggested that the longest d spacing should be associated with the molecular axis. This 14.2 ,~ reflection represents an increase in the c-axis length over that observed in PANI cast from m-cresol (9.2 ,~) and, it was proposed, could correspond to half the periodicity of a fully t r a n s chain. The inability to identify the c-axis unambiguously in PANI cast from chloroform is a direct consequence of difficulties associated with the preparation of oriented specimens. However, this is not the case for films cast from DMSO where mechanical deformation can be used to orient the material. Despite the use of a different solvent, there is good reason to believe that films cast from DMSO and chloroform should be similar. In general, solvent-casting CSA doped PANI results in a material which can be broadly classified into two types, according to structure and charge transport behaviour. Where attractive interactions exist between polymer-counter-ion complex and solvent, films similar to that from m-cresol are
C.D.G. Minto, A.S. Vaughan / Synthetic Metals 93 (1998) 73-76
75
!
\
I
J
~!.,1
/
a zs,¢
=
0.0
0.5
1.0
1.5
2.0
2.5
3.0
q (A-t} (a)
(b)
Fig. 2. (a) Equatorial and meridional scans of thin section of chloroform cast films; film surface is in the meridian. (b) Schematic representation of flat plate and actual exposure.
2 ~A
4 .IdA J 4~'A
7 J.IA
& /,IDA
|
a,
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
q lit"1)
Fig. 3. Diffractometer traces for ( __+)-CSA doped films in the g = 90 ° (inset) configuration and flat plate representation.
derived, with similar structure and transport properties. Otherwise, in the absence of such interactions, films similar to chloroform castings are found [ 13]. Films cast from DMSO fall into this second category and, indeed, give similar reflections to those reported here; a 6.03 J, equatorial reflection and a 3.58 A meridional reflection [ 12]. In the light of these observations, it therefore seems reasonable to ascribe the 6.2 reflection described above to an interchain spacing and the 3.6 A reflection to an intrachain spacing (an inversion of that which we reported in PANI-CSA, cast from m-cresol). Thus, we propose that the reflections, listed in Table l, can be ascribed as follows; interchain (hk0) : 14, 7.8, 6.1, 4.7, 3.0 and 2.5 J~; intrachain (001) 3.6 and 3.3 J, 2. We again see 2 Note that on many of these reflections ( 14, 6.1 and 3.6 A ) the observed orientation is very weak with only areas of increased intensity being present.
Table 1 Scattering vectors (q), d spacings, orientation and relative strengths of observed peaks Chloroform film q (A 0.44 0.90 1.02 1.34 1.76 2.08 2.52 3.00
~)
d (A)
Orientation
Strength
~ 14-15 7.8 6.16 4.69 3.57 3.30 2.77 2.32
± ~ ± ± ' ±
m vw vs vw m w vw vw
II II ± _1_
a vw = very weak orientation, w = weak, m = medium, vs = very strong.
76
C.D.G. Minto, A.S. Vaughan / Synthetic Metals 93 (1998) 73-76
that the molecules are preferentially deposited with their trajectory arranged somewhat in the plane of the film, but with a much larger interchain spacing of 6.2 A as opposed to the 3.5 ,~ observed in the m-cresol derived materials. From this observation, it is evident that the 14 ,~ reflection can also be characterized as an interchain reflection, as opposed to being a c-axis reflection as proposed by Pouget (although the level of orientation is quite weak). The degree of orientation of the polymer can be ascertained in a manner similar to that used for m-cresol cast films - - by selecting a scattering vector and progressively rotating the specimen [ 14 ]. Performing this operation for the 3.6 A reflection yields an orientation parameter of 0.25, or less. This compares with the 0.5-0.6 generally observed in m-cresol cast films [1], indicating much less well-established ordering. Presumably, this lower degree of orientation for the polymer, the increased interchain spacing of 6.1 A, and differing crystalline structure all contribute to the absence of the metallic state. Nevertheless, both the WAXS results and the charge transport properties are characteristic of a material which is less disordered than either HC1 doped PANI or pressed pellets of PANI-CSA, results from which will be presented in a future publication [ 15].
4. Conclusions
The above results show that samples of polyaniline doped with camphor sulfonic acid and cast from chloroform are appreciably anisotropic and are, therefore, qualitatively similar to films cast from m-cresol. However, the crystalline
structure is completely different, with a considerably larger interchain spacing and a much reduced periodicity along the c-axis. The degree of orientation is also far less than that found in m-cresol cast films, with orientation parameters of 0.25 being typical. The lower degree of orientational order found in these materials, both in crystalline structure and anisotropy accounts, in part, for the observed semiconducting behaviour.
References [ 1] C.D.G. Minto, A.S. Vaughan, Polymer 38 (1997) 2683-2688. [2] O.T. Ikkala, L. Pietil~valign [ch, L Ahjopalovalign [ch, H. Osterholmvalign[ch, P.J. Passiniemivalign[ch, J. Chem. Phys. 103 (1995) 9855-9863. [3] Y. Cao, P. Smith, Polymer 34 (1993) 3139-3143. [4] W.Y. Zheng, R.H. Wang, K. Levon, Z.Y. Rong, T. Taka, W. Pan, Macromol. Chem. Phys. 196 (1995) 2443-2462. [5] M. Reghu, Y. Can, D. Moses, A.J. Heeger, Phys. Rev. B 47 (1993) 1758-1764. [6l A.G. MacDiarmid, A.J. Epstein, Synth. Met. 65 (1994) 103-116. [7] Z.H. Wang, H.H.S. Javadi, A. Ray, A.G. MacDiarmid, A.J. Epstein, Phys. Rev. B 42 (1990) 5411-5414. [8] Y. Wei, G.W. Jang, K.F. Hsueh, E.M. Scherr, A.G. MacDiarmid, A.J. Epstein, Polymer 33 (1992) 314. [9] P.N. Adams, P.J. Laughlin, A.P. Monkman, A.M. Kenwright, Polymer 37 (1996) 3411. [ 10] G.R. Mitchell, Polymer 27 (1986) 346-349. [ 111 J.P. Pouget, Z. Oblakowski, Y. Nogami, P.A~ Albouy, M. Laridjani, E.J. Oh, Y. Min, A.G. MacDiarmid, J. Tsukamoto, T. Ishiguro, A.J. Epstein, Synth. Met. 65 (1994) 131. [ 12] Y. Cao, P. Smith, Synth. Met. 69-71 (1995) 191. [ 13l Y. Cao, J. Qiu, P. Smith, Synth. Met. 69-71 (1995) 187. [ 14] G.R. Mitchell, A.H. Windle, Polymer 24 (1983) 1513-1520. [ 15] C.D.G. Minto, A.S. Vaughan, J. Phys.: Condens. Matter, submitted for publication.