Synthesis and Physical Characterisation of Doped Conducting Polyaromatic Amines

210 Pages·2011·2.45 MB·English

by  Joseph, M J

SYNTHESIS AND PHYSICAL CHARACTERISATION
OF DOPED CONDUCTING POLYAROMATIC AMINES
Thesis submitted to the
Cochin University of Science and Technology
in partial fulfilment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY
under the faculty of Science
by
M. J. JOSEPH
DEPARTMENT OF APPLIED CHEMISTRY
COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY
eaCH IN - 682 022
INDIA
PECEMBEA 1995
CERTIFICA TE
This is to certify that this thesis is an authentic record of the research work carried
out by the author under our joint supervision, in partial fulfillment of the
requirements for the degree of Doctor of Philosophy under the Faculty of Science
of Cochin University of Science and Technology and further that no part thereof
has been presented before for any other degree.
Professor P. Madhal1an Pillai
(Supervising Teacher)
Professor and Head
Department of Applied ChemistI)'
o
Cochin University of Science and Technology
Kochi 682 022
Professor Jacob Pl. .
·I-i·n----~ _,
(Co-Guide) ~~---T-~ ·
Professor and Head
Department of Instrumentation (USIC)
Kochi - 22 Cochin University of Science and Technology
2811211995 Kochi 682 022
CONTENTS
PREFACE
CHAPTER J
CONDUCTING POLYMERS - AN OVERVIEW
I. I INTRODUCTION TO ORGANIC CONDUCTORS
I. 2 CONDUCTING POLYMERS 2
I. :l CHEMICAL SYNTHESIS OF CONDUCTING POLYMERS :l
I. -l ELECTROCHEMICAl SYNTHESIS .'i
I . .'i PLASMA POLYMERIZATION 7
I. (, DOPING 7
I. 7 TRANSPORT PROPERTIES OF CONDUCTING POLYMERS 8
I. 8 MECHANISM OF ELECTRICAL CONDUCTION 12
I. 8a DC CONDUCTIVITY 13
I Xb AC CONDUCTIVITY 21
I. 8e THERMOELECTRIC POWER H
I. I) WORK DONE IN THE THESIS 27
REFERENCES 21)
CHAPTER 2
SYNTHESIS OF POLY AROMATIC AMINES 34
2. I INTRODUCTION
2.2 CHEMICAL SYNTHESIS OF POLYAROMATIC AMINES
2. .1 POLYMERISATION MECHANISMS
2. ... EXPERIMENTAL PROCEDURE
2. .'i SYNTHESIS OF POLYANILlNE
2. (, SYNTHESIS OF POLYANISIDINE
2.7 COPOL YMERISATION
or
2. 8 PURIFICATION CONDUCTING POLYMERS
2. I) DOPING
REFERENCES
CHAPTER 3
CHARACTERISATION OF POLY AROMATIC AMINES 53
:I. I INTRODUCTION 5~
\.2 IR SPECTROSCOPY FOR POLYMER CHARACTERISATION .5-l
1.2a. SAMPLE PREPARATION 56
I. 2b. RESULTS AND DISCUSSION 56
I. :I NMR SPECTROSCOPYFOR POLYMER CHRACTERISATION 62
1.3a. SAMPLE PREPARATION 63
:I. lb. RESULTS AND DISClJSSION 63
I. -l UV SPECTROSCOPY FOR POLYMER CHARACTERISATION .6X
I. -la. SAMPLE PREPARATIONS .(1)
~. -lb. RESULT AND DISCUSSION ()!)
:I. 5 X-RA Y DIFFRACTION FOR POL YMER RESEARCH 7-l
:I.5a. WIDE-ANGLE X-RAY SCATIERING (WAXS) 75
1.5b. SMALL ANGLE X-RAY SCATIERING (SAXS) 76
:I.5e. SAMPLE PREPARATION 77
I . .'id. RESULTS AND DISCUSSIONS 77
:I. 6 THE PROPOSED STRUCTURES OF THE POL YMERSXO
RI:FERENCES
CIIAPTER .J
ELECTRICAL TRANSPORT PROPERTIES OF
I>OLYAROMATIC AMINES -'1. nc AND AC CONnUCTIVITY 8. .
-l. I INTRODUCTION
-l.2 DC CONDUCTION MECHANISM
-l. I THEORY OF DC CONDUCTIVITY
-l. la. CONDUCTION BY POLARONS
-l. lb. INTERSOLlTON HOPPING CONDUCTION
-l. le TUNNELlNG CONDUCTION
-l. -l EXPERIMENTAL TE('IINIQlJE
-l. :; RESUI.TS AND DISClISSION
-l. (, AC CONDUCTIVITY In
-l. (,a ROLE OF VRH ON AC CONDUCTIVITY 126
-l. 7 EXPERIMENTAL TECHNIQUE FOR AC CONDUCTIVITY 12X
-l. X RESULTS AND DISCUSSION I"'~
REFERENCES l-ll
CHAPTER 5
ELECTRICAL TRANSPORT PROPERTIES OF POLYAROMATIC
AMINES -11. THERMO ELECTRIC POWER 145
S. 1 INTRODUCTION I-lS
S 2 SIGNIFICANCE OF THERMOELECTRIC POWER I-lX
S. 1 EXPERIMENT AL METHOD 151
S ·1 RESlILTS AND DISCUSSION I S(,
REFERENCES 17l)
CIIAPTER (,
THERMAL PROPERTIES OF CONDUCTING POLYMERS
POLYANILlNE. POLYANISIDINE AND CO-POLYMERS 181
INTRODUCTION IXI
EXPERIMENTAL METHOD IX7
RESULTS AND DISCUSSION Il) I
REFERENCES
CIIAP1'ER 7
SIJMMERY AND CONCUJSION It)(,
PREFACE
Conducting polymers have emerged as a new class of
electronic materials recently. They have attracted
considerable attention as the investigations on these
systems have generated entirely new scientific concepts as
well as potential for new technology. Since these materials
are polymers, they have highly anisotropic quasi-one
dimensional structures which make them fundamentally
different from conventional inorganic semiconductors. Their
chain like structure leads to strong coupling of the
electronic states to conformational excitations peculiar to
a one dimensional system. Electron processes in organic
polymers cause modifications of chain geometry leading to
strong electron-phonon coupling. The relatively weak
interchain binding allows diffusion of dopant molecules into
the structure while the strong intra chain C-C bonds
maintain the integrity of the polymer. Several of the
conjugated polymers exhibit very interesting nonlinear
optical properties. A number of intrinsically insulating
conjugated organic polymers can be doped to near metallic
conductivities. The doping process involves exposure of the
polymer to electron donors (such as alkali metals) or
i
electron accepters (such as 12 or AsF 5)' The conductivity
of organic polymers like polyacetylene, polyphenylenes,
polyphenylene chalcogenides, polypyrrole etc. can be
increased by several orders of magnitude by doping.
So far, maximum work has been done on polyacetylene because
of its simple chain structure which allows extensive
theoretical calculations and predictions to be made on their
properties. But of late, more experimental as well as
theoretical work are increasingly being devoted to nitrogen
containing cond ucting polyaromatics such as polypyrrole,
polyaniline etc. The conductivity and other properties of
polyaromatics can also be modified substantially by doping .
The interest in these materials is due to their potential
applications in high energy density batteries, solar cells
and novel electronic devices. Moreover, their properties
are very exciting from the point of view of basic physics
and chemistry. The area of conducting polymers is still a
virgin field with plenty of scope for doing good work. Most
of the work so far have been concentrated around a few
materials such as polyacetylene, polypyrrole, polythiophene
etc. The synthesis, characterization and investigation of
the properties of many more conducting polymers,
particularly polyaromatic amines, still remain to be done.
ii
The unique properties of polyaromatic amines such as their
charge conjugation asymmetry, high redox activity and the
presence of nitrogen atoms in the conjugation path make them
different from other conducting polymers. In this thesis
we present the work we have done a few polyaromatic amines
such as polyaniline, polyanisidine, and their copolymers.
We have synthesised and characterized these material •.
Selected physical properties of these materials have been
studied and the effect of copolymerisation on the electrical
properties of these materials have been investigated.
The thesis opens with an introductory chapter on the
synthesis and physical properties of conducting polymers.
This chapter is bifurcated into two parts, dealing with the
synthesis and with the physical properties of conducting
polymers. An introduction to organic conductors in general
and conducting polymers in particular is given in this
chapter. The techniques adopted for the preparation of
these materials and their chemical, electrochemical and
plasma polymerisation are briefly reviewed.
As l)as already been mentioned, conducting polymers have very
exciting physical properties, particularly with regard to
electrical conductivity. The general properties of these
ill
materials are reviewed in Chapter 1. The electMcal
conductivity of these materials can be modified by doping
and the mechanisms of electrical conduction are very
peculiar and interesting. These aspects are also reviewed
in this chapter. Further, work done by previous workers on
dc conductivity, ac conductivity and thermoelectric power
are reviewed here. Reference to the work done by earlier
workers are cited at the end of the same chapter.
The wor k reported in the thesis basically is centered around
the following conducting polymers: polyaniline,
polyanisidine, and their copolymers. The details of the
techniques used by us· for synthesising these polyaromatic
amines are described in Chapter 2 of the thesis. Chemical
polymerisation techniq ues adopted by us for synthesising
these materials are described in detail. Method of
synthesising the copolymers is also described. The various
methods adopted for purifying the materials and details of
doping the polymer to make them electrically conducting are
also discussed.
The various techniques used by us for characterizing the
materials prepared and the results obtained are outlined in
Chapter 3 of the thesis. The characterization methods used
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by us include UV-Vis., FT-IR, NMR spectroscopy and X-ray
diffraction studies. The details of all these techniq ueB
and experimental procedures are described in this chapter.
The results obtained from each of the above characterization
methods when e.pplied to each of the materials under study
are given and the results are discussed in each case.
Chapter 4 and 5 are devoted to details of the investigation
of the electrical properties of the polyaromatic amines
which we have stUdied. The theory of charge transport in
polymeric conductors is outlined in Chapter 4. DetailB of
dc conductivity, ac conductivity and thermoelectric power
measurements on these samples are descr!bed. We have made
these measurements on doped samples over a temperature range
of 30K to 295K. Computer controlled measurement setups have
been used in these studies. We have got some very
interesting and new results and a detailed discussion of
these results are given in Chapter 5. Measurements of the
temperature variation of conductivity in some ot these
polymers are reported for the first time and so are the
measurements on thermoelectric power. Our results on
conductivity and thermoelectric power measurements enable us
to predict the nature of the charge carriers in these
materials upon doping.
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