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Thesis Supervisor: Prof. Dr. A. Sezai SARAÇ
İSTANBUL TECHNICAL UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY
M.Sc. Thesis by
Nazif Uğur KAYA
Department : Polymer Science and Technology
Programme : Polymer Science and Technology
July 2010
SYNTHESIS AND CHARACTERIZATION OF COMPOSITES BY
POLYMERIZATION OF PYRROLE AND N-PHENYL PYRROLE ON
POLY(ACRYLONITRILE-CO-ACRYLIC ACID) MATRIX
İSTANBUL TECHNICAL UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY
M.Sc. Thesis by
Nazif Uğur Kaya
(515071015)
Date of submission : 30 July 2010
Date of defence examination: 2 August 2010
Supervisor (Chairman) : Prof. Dr. A.Sezai SARAÇ (ITU)
Members of the Examining Committee : Prof. Dr. Metin H. ACAR (ITU)
Prof. Dr. H. Yıldırım ERBİL (GIT)
July 2010
SYNTHESIS AND CHARACTERIZATION OF COMPOSITES BY
POLYMERIZATION OF PYRROLE AND N-PHENYL PYRROLE ON
POLY(ACRYLONITRILE-CO-ACRYLIC ACID) MATRIX
July 2010
İSTANBUL TEKNİK ÜNİVERSİTESİ FEN BİLİMLERİ ENSTİTÜSÜ
YÜKSEK LİSANS TEZİ
Nazif Uğur Kaya
(515071015)
Tezin Enstitüye Verildiği Tarih : 30 Temmuz 2010
Tezin Savunulduğu Tarih : 2 Ağustos 2010
Tez Danışmanı : Prof. Dr. A. Sezai SARAÇ (İTÜ)
Diğer Jüri Üyeleri : Prof. Dr. Metin H. ACAR (İTÜ)
Prof. Dr. H. Yıldırım ERBİL (GYTE)
PİROL VE N-FENİL PİROL’ ÜN POLİ(AKRİLONİTRİL-KO-AKRİLİK
ASİT) MATRİSİNDE POLİMERİZASYONU İLE KOMPOZİT
SENTEZİ VE KARAKTERİZASYONU
v
FOREWORD
I would like to express my deep appreciation and thanks for my advisor Prof. Dr. A.
Sezai SARAÇ. I am grateful to my family for their everlasting support.
I am also thankful to my collegues Suat ÇETĠNER, Bilge KILIÇ, Cansev TEZCAN,
Cem ÜNSAL, Damla ECEVĠT, Fatma Gül GÜLER, Ġlkkan ġENTÜRK, Melahat
ġAHĠN, Seher UZUNSAKAL, Timuçin BALKAN, Ulviye DALGIÇ for their helps
and composing our warm office atmosphere.
I would like to thank to my friends Tevfik Çağlar YÜCEL, Tuğba ANDER, Tuluhan
ERGĠN, Çağlar FIRAT, Kaan DEMĠRKAZIKSOY, S.Esra ÖZGÜL, Aslı
GENÇTÜRK, Koray YILMAZ, Can Metehan TURHAN, Ercan MUTLU, Saadettin
GÖKÇE, Erdal ÖNDER, Ġpek ÖSKEN, Argun Talat GÖKÇEÖREN, Erdem
YAVUZ, ġebnem ĠNCEOĞLU, Ari ġant BĠLAL, for their friendships and sincere
helps.
This work is supported by ITU Institute of Science and Technology.
July 2010
Thesis Nazif Uğur Kaya
Chemical Engineer
vi
vii
TABLE OF CONTENTS
Page
TABLE OF CONTENTS ......................................................................................... vii ABBREVIATIONS ................................................................................................... ix LIST OF TABLES .................................................................................................... xi
LIST OF FIGURES ................................................................................................ xiii SUMMARY .............................................................................................................. xv ÖZET ....................................................................................................................... xvii 1. INTRODUCTION .................................................................................................. 1
2. THEORETICAL PART ........................................................................................ 3 2.1 Electrical Conductivity ....................................................................................... 3
2.2 Conductive Polymers ......................................................................................... 4 2.2.1 Increase in conductivity with doping .......................................................... 7 2.3.1 Frequency and temperature variations with interfacial and dipolar
polarization ......................................................................................................... 14
3. EXPERIMENTAL PART ................................................................................... 17 3.1 Materials ........................................................................................................... 17 3.2 Synthesis of P(AN-co-AA) .............................................................................. 17
3.3 Preparation of P(AN-co-AA)/PPy Composite Films ....................................... 19 3.4 Preparation of Nanofibers of P(AN-co-AA)/PPy Composites ......................... 21 3.5 Synthesis of PPy ............................................................................................... 22
3.6 Characterization of P(AN-co-AA), Composite Films and Nanofibers ............ 22 3.7 Results and Discussion ..................................................................................... 25
3.7.1 FTIR-ATR spectrophotometric analysis ....................................................... 25 3.7.1.1 FT-IR calibration curve for P(AN-co-AA) pellet .............................. 25 3.7.1.2 P(AN-co-AA) ..................................................................................... 26
3.7.1.3 P(AN-co-AA)-PPy and P(AN-co-AA)-PNPhPy composite films ..... 28 3.7.1.4 P(AN-co-AA), P(AN-co-AA)-PPy and P(AN-co-AA)-PNPhPy
composite nanofibers ..................................................................................... 30 3.7.2 UV-Visible spectrophotometric analysis .................................................. 31 3.7.3 Nuclear magnetic resonance measurements (NMR) ................................. 32
3.7.3.1 NMR of P(AN-co-AA) ...................................................................... 32 3.7.3.2 NMR of PPy ....................................................................................... 34
3.7.4 Molecular weight determination ............................................................... 34 3.7.5 Dielectric and conductivity measurements ............................................... 35
3.7.6 Thermogravimetric analysis measurements (TGA) .................................. 43 3.7.7 Differential scanning calorimetry measurement (DSC) ............................ 45 3.7.8 Scanning electron microscope measurements (SEM) ............................... 45
4. CONCLUSION AND RECOMMENDATIONS ............................................... 51 REFERENCES ......................................................................................................... 53 CURRICULUM VITA ............................................................................................ 57
viii
ix
ABBREVIATIONS
AA : Acrylic Acid
AN : Acrylonitrile
CAN : Ceric Ammonium Nitrate
DMF : Dimethylformamide
DSC : Differential Scanning Calorimetry
FT-IR : Fourrier Transform Infrared
NMR : Nuclear Magnetic Resonance
NPhPy : N-Phenyl Pyrrole
PAA : Polyacrylic acid
PAN : Polyacrylonitrile
PNPhPy : Poly(N-Phenyl Pyrrole)
PPy : Polypyrrole
Py : Pyrrole
SEM : Scanning Electron Microscope
TGA : Thermogravimetric Analysis
x
xi
LIST OF TABLES
Page
Table 3.1: C(mole%) of PAN in PAN/PAA blends and log(T0/T) values at 2243cm-1
.
............................................................................................................................ 26
xii
xiii
LIST OF FIGURES
Page
Figure 2.1 : Band gap differences metals, semiconductors and insulators [20]…….. 5 Figure 2.2 : Repeat units of several electronic polymers [23]………………………. 6 Figure 2.3 : Electromagnetic spectrum. The wavelength λ depends on the medium
in which the electromagnetic wave propagates [24]……………………………. 8
Figure 2.4 : Elelctric flux between the metal plates in vacuum space [24]…………. 9 Figure 2.5 : Dielectric material is placed between the metal plates [24]…………... 11 Figure 2.6 : Principles of polarizations and frequency trend of polarization effects
[18]…………………………………………………………………………….. 13 Figure 3.1 : Monomers used in synthesis of P(AN-co-AA). .................................... 17
Figure 3.2 : Copolymerization mechanism of AN and AA. ..................................... 18 Figure 3.3 : Experimental setup for synthesis of P(AN-co-AA)............................... 18
Figure 3.4 : Procedure for P(AN-co-AA)/PPy and P(AN-co-AA)/PNPhPy composite
film formation. ................................................................................................... 19 Figure 3.5 : Pyrrole (Py) and N-Phenyl pyrrole (NPhPy). ........................................ 20
Figure 3.6 : Polymerization mechanism of PPy [30]. ............................................... 20 Figure 3.7 : Experimental setup of electrospinning [31]. ......................................... 21
Figure 3.8 : Perkin Elmer, Spectrum One FTIR-ATR Spectrophotometer. ............. 22 Figure 3.9 : Perkin Elmer, Lambda 45 UV-Visible Spectrophotometer. .................. 23
Figure 3.10 : 250 MHz Brucker AC Aspect 3000 NMR spectrometer [32]. ............ 23 Figure 3.11 : Novocontrol broadband dielectric spectrometer. ................................ 24
Figure 3.12 : Placing film samples between electrodes on Novocontrol broadband
dielectric spectrometer. ...................................................................................... 24 Figure 3.13 : Mini-SEM, SEC, SEN-3000M. ........................................................... 25
Figure 3.14 : Figure FT-IR of KBr pellets of synthesized P(AN-co-AA) and blends
including varying ratio of PAA and PAN in transmission mode. ...................... 25
Figure 3.15 : Calibration curve for blends of PAN and PAA including varying CPAN.
............................................................................................................................ 26 Figure 3.16 : FTIR-ATR Characterization PAN (Aldrich) and P(AN-co-AA). ....... 27
Figure 3.17 : FTIR-ATR Characterization P(AN-co-AA) with different AN/AA
ratios. .................................................................................................................. 27 Figure 3.18 : Tentative mechanism for intermolecular interaction between P(AN-co-
AA), PPy chains and DMF. ............................................................................... 29
Figure 3.19 : FTIR-ATR Characterization of P(AN-co-AA) films and PPy including
P(AN-co-AA) films. ........................................................................................... 29 Figure 3.20 : FTIR-ATR Characterization of P(AN-co-AA) films and PNPhPy
including P(AN-co-AA) films. .......................................................................... 30 Figure 3.21 : FTIR-ATR characterization of P(AN-co-AA), P(AN-co-AA)/PPy and
P(AN-co-AA)/PNPhPy nanofibers. ................................................................... 31 Figure 3.22 : UV-Visible absorbance vs. wavelength of solution of PPy in methanol.
............................................................................................................................ 32
xiv
Figure 3.23 : 1
H NMR spectroscopy of P(AN-co-AA) in DMSO-d6 solvent (0.0-
10ppm). .............................................................................................................. 33 Figure 3.24 :
1H NMR spectroscopy of P(AN-co-AA) in DMSO-d6 solvent (0.0-5.0
ppm). .................................................................................................................. 33
Figure 3.25 : 1
H NMR spectroscopy of P(AN-co-AA) in DMSO-d6 solvent (6.0-10.0
ppm). .................................................................................................................. 34 Figure 3.26 :
1H NMR spectroscopy of PPy in DMSO-d6 solvent. .......................... 34
Figure 3.27 : ηsp/C vs. C of the P(AN-co-AA) in DMF. ........................................... 35 Figure 3.28 : a. Conductivity (S/cm) values of P(AN-co-AA) and P(AN-co-
AA)/PNPhPy films (For 0.72 and 1.44 mmoles of initially added NPhPy) b.
Conductivity (S/cm) values of P(AN-co-AA), P(AN-co-AA)/PPy and P(AN-co-
AA)/PNPhPy films (For 1.44 mmoles of initially added Py and NPhPy). ........ 36 Figure 3.29 : a. Real permittivity (Eps’) and b. imaginary permittivity (Eps”) of
P(AN-co-AA) and P(AN-co-AA)/PNPhPy films (For 0.72 and 1.44 mmoles of
initially added NPhPy). ...................................................................................... 37 Figure 3.30 : a. Real permittivity (Eps’) and b. Imaginary permittivity (Eps”) of
P(AN-co-AA), P(AN-co-AA)/PPy and P(AN-co-AA)/PNPhPy films (For 1.44
mmoles of initially added Py and PhPy). ........................................................... 38 Figure 3.31 : a. Modulus’ (M’) and b. Modulus” (M”) of P(AN-co-AA) and P(AN-
co-AA)/PNPhPy films (For 0.72 and 1.44 mmoles of initially added NPhPy). 40
Figure 3.32 : a. Modulus’ (M’) and b. Modulus” (M”) of P(AN-co-AA), P(AN-co-
AA)/PPy and P(AN-co-AA)/PNPhPy films (For 1.44 mmoles of initially added
Py and PhPy). ..................................................................................................... 41
Figure 3.33 : Modulus’ (M’) vs. Modulus” (M”) of P(AN-co-AA), P(AN-co-
AA)/PPy and P(AN-co-AA)/PNPhPy films (For 1.44 mmoles of initially added
Py and PhPy). ..................................................................................................... 42
Figure 3.34 : Temperature vs. Derivative Weight (%Weight/min) from TGA of
P(AN-co-AA), PPy and P(AN-co-AA)/PPy composite film including 1.44
mmoles initially fed Py. ..................................................................................... 43
Figure 3.35 : Temperature vs. % Weight from TGA of P(AN-co-AA), PPy and
P(AN-co-AA)/PPy composite film including 1.44 mmoles initially fed Py. ..... 44 Figure 3.36 : DSC of P(AN-co-AA) including 2.67 AA by % mole. ....................... 45
Figure 3.37 : SEM images of nanofibers of pure P(AN-co-AA). ............................. 46 Figure 3.38 : SEM images of nanofibers of P(AN-co-AA)/PPy composite with
magnification of x1500. ..................................................................................... 47 Figure 3.39 : SEM images of nanofibers of P(AN-co-AA)/PPy composite with
magnification of x3000. ..................................................................................... 47
Figure 3.40 : Nanofiber diameter distribution of P(AN-co-AA)/PPy composite. .... 48 Figure 3.41 : SEM images of nanofibers of P(AN-co-AA)/PNPhPy composite with
magnification of x1000. ..................................................................................... 48 Figure 3.42 : SEM images of nanofibers of P(AN-co-AA)/PNPhPy composite with
magnification of x5000. ..................................................................................... 49 Figure 3.43 : Nanofiber diameter distribution of P(AN-co-AA)/PNPhPy composite.
............................................................................................................................ 49
xv
SYNTHESIS AND CHARACTERIZATION OF COMPOSITES BY
POLYMERIZATION OF PYRROLE AND N-PHENYL PYRROLE ON
POLY(ACRYLONITRILE-CO-ACRYLIC ACID) MATRIX
SUMMARY
In this study, influence of conjugated polymer on AC electrical conductivity and
dielectric properties of copolymer of acrylonitrile (AN) and acrylic acid (AA)
(P(AN-co-AA)) composite films were investigated. In-situ polymerized polypyrrole
(PPy) and poly(N-phenylpyrrole) (PNPhPy) on P(AN-co-AA) matrix were used as
conductive polymer. First, P(AN-co-AA) was synthesized by oxidative
copolymerization of AN and AA monomers in aqueous medium. Afterwards, pyrrole
(Py) and N-phenyl pyrrole (NPhPy) were polymerized on P(AN-co-AA) matrix in
dimethylformamide (DMF). Ce(IV) salt was used as an oxidant for both copolymer
formation and polymerization of Py and NPhPy on P(AN-co-AA) matrix. Composite
films were then acquired by evaporation of DMF. Spectroscopic, electrical and
thermal properties of composite films were analyzed. In fourier transform infrared
spectroscopoy (FTIR-ATR) measurements, as the ratio of initially added acrylic acid
to acrylonitrile increased, the ratio of absorbance values of characteristic peaks of
PAA segments to PAN segments also increased. Concurrently, the ratio of
absorbance values of peaks respectively relating to PPy and PAN rose as initially
feed amount of PPy increased. Molecular weight of P(AN-co-AA) was calculated
from intrinsic viscosity, [η], which was measured with Ubbelohde viscometer and
AA composition in copolymer was calculated with 1H NMR. In all samples, real
permittivity (Eps’) and imaginary permittivity (Eps”) decreased as the frequency (f)
increased; they remained stable in the region of 10 Hz to 107. -H atoms related to
PPy did not enhance conductivity and dielectric permittivity values of composite
films as compared to PNPhPy including of those due to less polarization of –H atoms
than phenyl groups. TGA thermograms of pure P(AN-co-AA), P(AN-co-AA)/PPy
including initially fed 1.44 mmoles of Py composite film and PPy which was
synthesized in DMF medium without P(AN-co-AA) matrix indicated intrinsic weight
losses showing intermolecular interaction between PPy, DMF and P(AN-co-AA).
Also, nanofibers of P(AN-co-AA) and in-situ polymerized PPy, PNPhPy on P(AN-
co-AA) matrix were acquired by electrospinning method; nanofiber diameters of
composites were calculated. Spectroscopic and morphological properties of
nanofibers were investigated.
xvi
.
xvii
PİROL VE N-FENİL PİROL’ ÜN POLİ(AKRİLONİTRİL-KO-AKRİLİK
ASİT) MATRİSİNDE POLİMERİZASYONU İLE KOMPOZİT SENTEZİ VE
KARAKTERİZASYONU
ÖZET
Bu çalıĢmada, konjuge polimerlerin akrilonitril-akrilik asit kopolimeri (P(AN-ko-
AA)) kompozitlere ait AC elektriksel iletkenlik ve dielektrik özellikleri üzerine
etkileri incelenmiĢtir. Akrilonitril (AN) ve akrilik asidin (AA) kopolimeri (P(AN-ko-
AA)) matrisi üzerinde pirol (Py) ve N-Fenilpirol (NFPy) polimerleĢtirilmiĢtir.
Polipirol (PPy) Poli(N-Fenilpirol) (PNFPy) iletken polimer olarak kullanılmıĢtır. Ġlk
olarak, akrilonitril (AN) ve akrilik asit (AA) monomerlerinin sulu ortamda oksidatif
kopolimerizasyonları gerçekleĢtirilmiĢtir. Py ve NFPy’ nin dimetilformamid (DMF)
içerisinde çözülmüĢ P(AN-ko-AA) matrisinde polimerizasyonları
gerçekleĢtirilmiĢtir. Ce(IV) tuzu, hem kopolimer sentezinde, hem de Py ve NFPy’
nin polimerleĢtirilmesinde oksidant olarak kullanılmıĢtır. OluĢturulan kompozitlerin
filmleri çözücünün (DMF) uzaklaĢtırılmasıyla elde edilmiĢ ve bu filmlerin
spektroskopik, elektriksel ve ısıl özellikleri incelenmiĢtir. Yapılan FTIR-ATR ölçüm
sonuçlarında, değiĢik AA ve AN oranlarında çalıĢıldığında, AA/AN oranı arttıkça
poliakrilik asite (PAA) ait CO gerilme pikinin absorbansının poliakrilonitrile (PAN)
ait C≡N gerilme pikinin absorbansına oranının da arttığı gözlemlenmiĢtir. Ayrıca,
PPy’ ye ait CN gerilme pikinin absorbansının PAN’ a ait C≡N gerilme pikinin
absorbansına oranının Py monomer miktarının artıĢıyla uyum gösterdiği tespit
edilmiĢtir. Ubbelohde viskozimetresi ile P(AN-ko-AA) nın Mv değeri bulunmuĢ, 1H
NMR yöntemiyle kopolimerdeki AA yüzdesi hesaplanmıĢtır. Bütün film
örneklerinde, dielektrik sabiti (Eps’) ve dielektrik kaybı (Eps”) artan frekans (f) ile
birlikte azalma göstermiĢ; 10 Hz ile 107 Hz aralığında sabit bir değer göstermiĢtir.
PPy’ ye ait –H atomlarının iletkenlik ve dielektrik geçirgenlik değerlerine katkıları,
PNFPy’ ye ait fenil gruplarınınkinden daha az olmuĢtur. Bunun sebebi yan grup olan
fenil gruplarının, -H atomlarına oranla iletken polimer zincirine daha polar bir yapı
kazandırmasıdır. Termogravimetrik Analiz (TGA) ölçümlerinde, saf P(AN-ko-AA),
PPy içeren P(AN-ko-AA) kompozit film ve P(AN-ko-AA) matrisi olmadan DMF
içerisinde polimerleĢtirilen PPy’ nin kütle kayıpları gözlemlenmiĢtir. Bu Ģekilde PPy,
DMF ve P(AN-ko-AA) arasındaki moleküllerarası etkileĢim gözlemlenmiĢtir.
Ayrıca, PPy ve PNFPy içeren ve içermeyen P(AN-ko-AA) kompozitlerin
nanofiberleri elektrospining metoduyla elde edilmiĢtir. Nanofiberlerin çapları
hesaplanmıĢtır, spektroskopik ve morfolojik karakterizasyonları gerçekleĢtirilmiĢtir.
xviii
.
1
1. INTRODUCTION
Polyacrylonitrile (PAN) has been used in many applications as a constituent of a
membrane, fiber manufacturing [1]. Polyacrylic acid (PAA) is commonly used in
toothpaste, cosmetics, hydraulic fluids, and even liquid rocket fuels . Floor coverings
and waterproof gloves are the polymeric materials that can be thickened during
fabrication. Acrylic acid and its copolymers are purposed as an assistant to provide
dispersion of pigments in paints [2]. Cross-linked PAA has also common uses as ion
exchange resins and hydrogels [3]. Copolymer of acrylonitrile (AN) and acrylic acid
(AA) has an application in water-swollen artificial kidney membranes due to its
transport properties [4]. Molecularly imprinted membranes is another region for
P(AN-co-AA). Copolymer has the properties of both a good membrane due to PAN
section and recognition capacity supplied by PAA [5]. P(AN-co-AA) is also
constructed as glucose biosensor [6]. Various polymerization methods are chosen for
synthesizing P(AN-co-AA) such as chemical [6,7,8,9], electrochemical [7-10] and
photopolymerization [11]. Dimethylformamide (DMF), dimethylsulfoxide (DMSO),
water can be used as medium in chemical method [7,8,9]. Despite conductive
polymers benefit excellent electrical properties due to extended π-electron
conjugation, depending on their weak stability and having difficulties while
processing, are applied in limited regions [12-13]. Polypyrrole (PPy) is one of the
most common conjugated polymer for commercial uses due to its good
environmental stability, simple synthesis and higher electrical conductivity as
compared to other conducting polymers [14]. Polymer composites of PAN/PPy,
P(AN-co-AA)/PPy and P(AN-co-SS)/PPy were synthesized by impregnating pyrrole
monomer into the matrix followed by the polymerization of pyrrole in the matrix
film. Anionic moieties supplied better electrostatic interaction between the polymer
matrix and conducting polymer resulting better electrical properties as polymeric
matrix roled as polymeric dopant [12]. In the case pyrrole is oxidatively polymerized
on P(MMA-co-AA) matrix, carboxylate groups provided stable dispersions [4].
Electromagnetic interference (EMI) shielding has crucial importance on electronic
2
and communication industries [15]. Conducting polymers are suitable materials for
eliminating EMI due to their high values of conductivity and dielectric permittivity
as compared with other polymers. Not only they are lightweight, but also more
flexible than metals and do not corrode [16]. In order to absorb radar, materials
should include resistive or magnetic materials transforming electromagnetic energy
into heat. PPy has satisfactory electrical properties to be selected for a radar
absorbing material [17].
In this study, influence of conjugated polymer on AC electrical conductivity and
dielectric properties of P(AN-co-AA) composite films were investigated, while
polypyrrole (PPy) and poly(N-phenylpyrrole) (PNPhPy) were used as conductive
polymers. P(AN-co-AA), which was used as matrix in composite film formation,
was synthesized by oxidative copolymerization of AN and AA monomers in aqueous
medium. Afterwards, pyrrole (Py) and N-phenylpyrrole (NPhPy) were polymerized
on P(AN-co-AA) matrix in dimethylformamide (DMF). Ce(IV) salt was used as an
oxidant for both copolymer formation and in-situ matrix polymerization due its
strong oxidizing power. Composite films were then acquired by partially evaporation
of DMF. Py was polymerized in DMF without copolymer matrix by using Ce(IV)
salt as the oxidant. Spectroscopic, electrical and thermal properties of thin films and
PPy were analyzed. Also, nanofibers of P(AN-co-AA) and in-situ polymerized
pyrrole (Py) and N-phenyl pyrrole (NPhPy) on P(AN-co-AA) matrix were acquired
by electrospinning method. Spectroscopic and morphological properties of
nanofibers were investigated.
3
2. THEORETICAL PART
2.1 Electrical Conductivity
The electron conductivity of solids is determined by their atomic, crystal, or
amorphous structure. Metals are good electron conductors. Their atoms all have in
their outer shell one to three electrons that are free to move throughout the metals
and alloys in “conduction bands”, since the electrons in this state are not associated
with any particular atom, pair or group of atoms.
If the atoms of these same elements are combined into molecules with different types
of atoms which are lacking one to three electrons in their outer shell, such as oxygen,
sulfur or the halogens (fluorine, chlorine, bromine, and iodine), the electrons from
the outer shell of the metallic elements tend to transfer completely to the outer shell
of the combining elements, filling that shell and thereby forming compound
molecules that are ion pairs (for example: Na+C1
– and Mg
+2O
+2). These compounds
form solid ionic crystals where the electrons are tightly bound in negative ions
balanced by an equal total charge of positive ions. These are not usually electron
conductors, except at very high electric fields or under ionizing radiation conditions
In other cases, binding between atoms in molecules occurs by sharing electrons
between atoms forming some common electron orbits. This type of bonding is
predominant in organic carbon compounds. Electrons in organic materials are usually
attached to particular molecules forming negative ions with an equal charge of
positive ions so they do not contribute to electron conduction. Electrons restricted to
individual atoms or interatomic bonds are in the “band theory” representation of
conduction said to be in the “valence band”. Sufficient thermal energy or ionizing
radiation can lift some into the conduction band, but the required energy is high in
the case of most insulating materials. Therefore, electron conduction is not common
(except at very high electric fields) in conventional insulating materia1s.
The energy gap between the valence band and the conduction band in metals is
negligible, and the valence and conduction bands are said to overlap. In intrinsic
4
semiconductors, such as pure silicon and pure germanium, the conduction-valence
band gaps are 1.1 to 1.2 and 0.72 to 0.78 eV (electron volts), respectively; and these
pure crystals are not very good electron conductors compared to metals.
Also, electron semiconduction has been noted with inorganic molecules with
extended chains of alternating double and single carbon-carbon bonds. As in
benzene, naphthalene, and anthracene, the pi orbit electrons associated with
alternating single and double bonds are not associated with any particular atom and
are able to move around the ring or along molecular chains having “conjugated”
double bonds. The energy barrier between such internally semiconducting molecules
is high, however, so electrons do not easily move from molecule to molecule, unless
some doping agent is added to reduce this barrier [18].
2.2 Conductive Polymers
In 1970s, a new class of polymers possessing high electronic conductivity
(electronically conducting polymers) in the partially oxidized (or, less frequently, in
the reduced) state was discovered. Three collaborating scientists, Alan J. Heeger,
Alan G. MacDiarmid and Hideki Shirakawa, played a major role in this
breakthrough, and they received the Nobel Prize in Chemistry in 2000 “for the
discovery and development of electronically conductive polymers”.
There were several precursors to this discovery, including theoretical predictions
made by physicists and quantum chemists, and different conducting polymers that
had already been prepared. For instance, as early as 1862, Henry Letheby prepared
polyaniline by the anodic oxidation of aniline, which was conductive and showed
electrochromic behavior. Nevertheless, the preparation of polyacetylene by
Shirakawa and coworkers and the discovery of the large increase in its conductivity
after “doping” by the group led by MacDiarmid and Heeger actually launched this
new field of research [19].
5
Conducting polymers are organic materials that generally possess an extended
conjugated π-electron system along a polymer backbone. For this reason, the terms
conducting polymer and conjugated polymer are often used synonymously. Like
dyes, conjugated polymers differ from saturated systems by having a smaller highest-
occupied molecular orbital to lowest-unoccupied molecular orbital (HOMO–
LUMO)-energy gap which gives the visual impression that they are colored but does
not necessarily provide any electrical conductivity. Conduction of electric charges
requires unoccupied energy states for extra electrons or electron deficiencies (holes)
to be available and the relatively unhindered movement of charge throughout the
conducting material.
Figure 2.1 : Band gap differences metals, semiconductors and insulators [20].
Conducting polymers have high electron affinities or low oxidation potentials (in
most cases either one or the other). They can be either readily reduced (doped with
electron donors) or readily oxidized (doped with electron acceptors). Addition of
charge creates new and unfilled electronic energy states that lie within the original
HOMO–LUMO energy gap. It is the formation of these gap levels and the quasi-one-
dimensional rather than crystal lattice structure which distinguishes the
semiconductor physics of conjugated polymers from that of conventional inorganic
semiconductors. Both classes of materials have in common that the presence of
added charge by the doping process causes a significant rise in electrical
conductivity, confirming that charge can be transported through the material [21].
6
The common electronic feature of pristine (undoped) conducting polymers is the π-
conjugated system which is formed by overlap of carbon pz orbitals and alternating
carbon-carbon bond length. (In some systems, notably polyaniline, nitrogen pz
orbitals and C6 rings also are part of the conjugation path.) Figure 2.2 shows the
chemical repeat units of the pristine forms of several families of conducting and
semiconducting polymers, i.e., trans-polyacetylene [t-(CH)x], the leucoemeraldine
base (LEB), emeraldine base (EB) and pernigraniline base (PNB) form of polyaniline
(PAN, polypyrrole (PPy) polythiophene (PT), poly(p-phenylene) (PPP), and poly(p-
phenylene vinylene) (PPV) [22].
Figure 2.2 : Repeat units of several electronic polymers [23].
7
2.2.1 Increase in conductivity with doping
The conductivities of the pristine electronic polymers aretransformed from insulating
to conducting through doping. Both n-type (electron donating, e.g., Na, K, Li, Ca,
tetrabutylammonium) and p-type (electron accepting, e.g., PF6, BF4, Cl, AsF6)
dopants have been used. The doping typically is done using vapors or solutions of the
dopant, or electrochemically. (In some circumstances, the polymer and dopant are
dissolved in the same solvent before forming the film or powder.) The polymer
backbone and dopant ions form a rich variety of new three-dimensional structures
[22].
2.3 Electrical Properties of Polymers
The basic distinction between a semiconductor and a dielectric (or insulator) lies in
the difference in the energy band gap. At the normal ranges of temperatures and
pressures, the dominant charge carriers in a semiconductor are generated mainly by
thermal excitation in the bulk because the semiconductor has a small energy band
gap; hence, a small amount of energy is sufficient to excite electrons from full
valence band to an upper empty conduction band. In a dielectric, charge carriers are
mainly injected from the electrical contacts or other external sources simply because
a dielectric’s energy band gap is relatively large, so a higher amount of energy is
required for such band-to-band transitions. A material consists mainly of atoms or
molecules, which comprise electrons and nuclei. The electrons in the outermost shell
of atoms, bound to the atoms or molecules coupled with the free charges interact
with external forces, such as electric fields, magnetic fields, electromagnetic waves,
mechanical stress, or temperature, resulting in the occurrence of all dielectric
phenomena. For nonmagnetic dielectric materials, the dielectric phenomena include
mainly electric polarization; resonance; relaxation; energy storage; energy
dissipation; thermal, mechanical, and optical effects and their interrelations; and
electrical aging and destructive breakdown it [24].
8
Figure 2.3 : Electromagnetic spectrum. The wavelength λ depends on the
medium in which the electromagnetic wave propagates [24].
Since electrical insulation is used primarily for its nonconducting characteristic, the
relatively low level of conductivity it does have can be an important limitation to its
effective use. Therefore, it is very important to know what this level is and the
factors that influence it. The conductivity or the AC loss tangent, tan δ, or loss factor,
ε′ tan δ, (ε′ is the relative dielectric constant) are commonly used as quality control
parameters for electrical insulation.
The metals and semiconductors are primarily electron conductors with structures
which permit extensive movement of electrons in conduction bands. “Hole” or P
(positive) type semiconductors also physically conduct by electrons moving from
hole to hole. Since a “hole” is a positive site where an electron is missing, it seems as
if positive charges were moving in the opposite direction. In contrast, except at very
high electric fields or under ionizing radiation conditions, there are very few
electrons in common insulating materials, which are not strongly attached to an atom
or molecule forming ions. Consequently conductivity of dielectrics is usually due to
the translation of positive and negative charged ions of atomic or molecular size [18].
9
Electric polarization refers to a phenomenon of the relative displacement of the
negative and positive charges of atoms or molecules, the orientation of existing
dipoles toward the direction of the field, or the separation of mobile charge carriers at
the interfaces of impurities or other defect boundaries, caused by an external
electric field. Electric polarization can also be thought of as charge redistribution in a
material caused by an external electric field. The work done for the charge
redistribution and the energy loss involved in the redistribution process require an
energy supply. The whole polarization process is performed at the expense of the
potential energy released from this process, because the total potential energy of the
system in an electric field is smaller after electric polarization than before it [24].
When an atom or molecule is placed in an electric field, the electrons in the atom are
displaced very slightly toward the positive direction of the field. This occurs almost
instantly within times less than a half cycle of optical frequency [18].
A simple system in vacuum space (free space) was demonstrated in Figure 2.4
consisting of two metal plates parallel to each other with an are A, each and a
separation d, which is much smaller than the linear dimension of the plates, so that
the fringing effect at the edges can be ignored by approximation.
Figure 2.4 : Elelctric flux between the metal plates in vacuum space [24].
When a positive charge +Q was introduced on the upper plate and a negative charge -
Q of the same magnitude on the lower plate by connecting a steady DC voltage
supply across the plates, the system was charged as a capacitor. Then disconnecting
the supply from the system as soon as the charge has been accumulated to the desired
10
value Q, will create a potential difference between the plates V that is proportional to
Q.
(2.1)
(2.2)
C is called the capacitance. By denoting the surface charge density on the plates as
δs, the charge Q can be expressed as:
(2.3)
E was the electric field strength between the plates and A is the area of the plates.
(2.4)
Thus,
(2.5)
(2.6)
Where ε is the real permittivity, also dielectric constant, of the material filled
between the two plates. Therefore, permittivity of vacuum space was:
(2.7)
When a material is placed inside the space between the metal plates with the original
surface of density δs (blue part in the Figure 2.5), unaltered, this causes the potential
between the plates produced by the original charge Q on the plates to decrease to a
smaller value.
11
Figure 2.5 : Dielectric material is placed between the metal plates [24].
However, the induced charges on the surfaces of the material, δi, decrease the
original electric field by causing an opposing electric field to the original field. Thus,
dielectric permittivity, , is calculated as:
(2.8)
(2.9)
The dielectric material between the plates is not in phase with the applied voltage,
but by an angle, Δ (0° < Δ < 90°), which is called as the loss angle.
ε″ is called as imaginary permittivity, also dielectric loss, of the material, and tan Δ
as the dissipation factor. So tan Δ is shown as [25]:
(2.10)
Complex modulus is obtained by converting permittivity values; real (M’) and
imaginary (M”) parts of the complex electric modulus can be written as [25]:
(2.11)
(2.12)
12
For most materials, the dielectric constant is independent of the electric field strength
for fields below a certain critical field, at or above which carrier injection into the
material becomes important. The dielectric constant depends strongly on the
frequency of the alternating electric field or the rate of the change of the time-
varying field. It also depends on the chemical structure and the imperfections
(defects) of the material, as well as on other physical parameters including
temperature and pressure, etc. A dielectric material is made up of atoms or molecules
that possess one or more of five basic types of electric polarization as it is seen in
Figure 2.6:
1. Electronic polarization
2. Atomic or ionic polarization
3. Dipolar polarization
4. Spontaneous polarization
5. Interface or space charge polarization.
Each type of polarization requires time to perform; this is why the degree of the
overall polarization depends on the time variation of the electric field (frequency of
the applied AC) [24].
Ionic-interfacial and dipolar polarization are the most important for most organic
liquid and resin electrical insulation, since they are associated with conduction and
dielectric loss at commonly used frequencies. A form of polarization and associated
conduction like ionic-interfacial are also observed in inorganic glasses and ceramics
at lower frequencies and increases with increased temperature [18].
13
Figure 2.6 : Principles of polarizations and frequency trend of polarization
effects [18].
Electron polarization is responsible for the optical refractive index, η, and is part of
the dielectric constant of all dielectric materials. The magnitude of the refractive
index and its contribution to the dielectric constant, ε’∞ = η2, is essentially constant
from zero frequency up to the optical frequency range where dispersion (a slight
increase) and resonance absorption, attenuation, occurs at specific frequencies. This
type of polarization does not contribute to conduction or dielectric loss in
conventional electrical insulating materia1s at frequencies common1y used in
insulation app1ications. The values of η for dielectric liquids range from about 1.2
for fluorocarbon liquids up to about 1.6 for chlorinated hydrocarbon liquids. η
increases with the electron density and with aromatic (benzene like) molecular
structures, which have a greater electron polarizability. For example, η for benzene is
1.498 compared with 1.372 for hexane [18].
14
2.3.1 Frequency and temperature variations with interfacial and dipolar
polarization
Interfacial and dipolar polarizations depend on the effective internal viscosity
presented by the material to the movement of ions or rotation of dipole molecules,
respectively. The longer range movement of ions up to barriers typically takes a
longer time to develop polarization than the simple rotation of dipoles. Therefore,
ionic interfacial polarization is observed at lower frequencies, where the half cycle is
of sufficient time [18].
2.4 Electrospinning Method
Electrospinning technique was originally developed by Zeleny (1914) to prepare
interconnected webs of fibers from polymer solutions or melts. It is a process that
applies a high voltage to create electrically charged jets of a polymer solution. The
jets within the electric field are directed toward the grounded target, during which
they dry to form fibers [26]. This technique has been recognized as an effective way
to fabricate polymeric nanofibers with diameter ranging from several micrometers
down to tens of nanometers. Among various polymers, acrylonitrile-based homo-
and co-polymers were most recently fabricated into nanofibrous materials with
reinforcing, superhydrophobic and catalytic properties [27]. Electrospinning uses
electrostatic forces to produce fine fibers from polymer solutions or melts and the
fibers thus produced have a thinner diameter and a larger surface area than those
obtained from conventional spinning processes. Furthermore, a DC voltage in the
range of several tens of kVs is necessary to generate the electrospinning [28].
The minimum equipment requirements for demonstration of simple electrospinning
in the laboratory are as follows:
1. A viscous polymer solution or a melt.
2. An electrode (hollow tubular or solid) that is maintained in contact with
the polymer solution.
3. A high-voltage DC generator connected to the electrode.
4. A grounded or oppositely charged surface to collect the nanofibers.
Figure 3.4 is the schematic description of experimental setup for electrospinning.
15
The electrospinning process is solely governed by many parameters, classified
broadly into solution parameters, process parameters, and ambient parameters.
Solution parameters include viscosity, conductivity, molecular weight, and surface
tension and process parameters include applied electric field, tip to collector distance
and feeding or flow rate [28,29].
16
17
3. EXPERIMENTAL PART
3.1 Materials
AN (Acrylonitrile, C3H3N, AKSA), AA (Acrylic Acid, C3H4O2, SGS), Py (Pyrrole,
C4H5N, Aldrich), NPhPy (N-Phenyl pyrrole, C10H9N, Aldrich), DMF
(Dimethylformamide, C3H7NO, Riedel-de Haen), CAN (Ceric Ammonium Nitrate,
(NH4)2Ce(NO3)6, BDH), HNO3 (Fluka, 65%). PAN (Polyacrylonitrile, (C3H4N)150,000,
Aldrich), PAA (Polyacrylic acid, (C3H4O2)100,000, Fluka)
3.2 Synthesis of P(AN-co-AA)
A mixed solution of acrylic acid (AA) and water was put into a three-necked round
bottomed flask with a condenser, after acrylonitrile (AN) was placed. Monomers
were shown in Figure 3.1.
Figure 3.1 : Monomers used in synthesis of P(AN-co-AA).
P(AN-co-AA) was synthesized in four different initial feed AA/AN ratios by weight
(5/95, 10/90, 20/80, 40/60) Constant total weight of monomers of 5g was applied at
each polymerizations. Thus, for the reaction including AA/AN ratio of 5/95, AA
amount was 0.25g and AN amount was 4.75g. The mixture was stirred with a
magnetic stirrer for 15 minutes at 60°C. Then solution of 5 mM ceric ammonium
nitrate (CAN) in 0.1M HNO3 was added dropwise with a syringe in 5 minutes. Free-
radical copolymerization mechanism was shown in Figure 3.2.
18
Figure 3.2 : Copolymerization mechanism of AN and AA.
Figure 3.3 : Experimental setup for synthesis of P(AN-co-AA).
Reaction carried on for 1.5 hour. Experimental setup of the polymerization was
demonstrated in Figure 3.3. The composed polymer was washed with dilute aqueous
19
HNO3 solution, water and ethanol consecutively. Copolymer was dried at 25°C for
24h. Polymerization yield for process having AA/AN ratio of 5/95 was calculated as
50%.
3.3 Preparation of P(AN-co-AA)/PPy Composite Films
0.25g P(AN-co-AA) (2.67%mole of final AA content by NMR measurement,) was
dissolved in Dimethylformamide (DMF) at 98°C and mixed for 10 hours. Py and
NPhPy were shown in Figure 3.5. After Py (i.e., 0.72, 1.44, 2.16, 2.88 mmoles) was
introduced into the solution, mixture was stirred for 1 hour at 25°C. Then, for the
formation of free-radical, CAN (30% amount of Py) was added as an oxidant and
temperature was increased to 80°C, stirring carried on until a viscous solution was
obtained following the solvent casting of the viscous solution as film on 5 x 5 cm2
glass substrate area at about 1 mm height (Figure 3.4).
Figure 3.4 : Procedure for P(AN-co-AA)/PPy and P(AN-co-AA)/PNPhPy composite
film formation.
Homogeneous viscous film was dried under 760 mmHg and 50°C. In oxidative
polymerization of NPhPy on P(AN-co-AA) matrix the same procedure was applied.
20
The film thicknesses (≈ 80-130 µm) was measured with Mitutoyo Digimatic Outside
Micrometer (MDC-25SB).
Figure 3.5 : Pyrrole (Py) and N-Phenyl pyrrole (NPhPy).
Figure 3.6 : Polymerization mechanism of PPy [30].
21
3.4 Preparation of Nanofibers of P(AN-co-AA)/PPy Composites
1g of P(AN-co-AA) (Including initially feed AA/AN ratio of 5/95) was dissolved in
Dimethylformamide (DMF) at 98°C and mixed for 10 hours. After Py and NPhPy
(0.72 mmoles) was introduced into the solution, mixture was stirred for 1 hour at
25°C. Water bath was used to set the temperature and provide homogeneous heat
transfer. Then, for the formation of free-radical, CAN (30% amount of Py) was
added as an oxidant and the mixture was stirred for 2 hours at 25°C. To acquire a
viscous solution, temperature was increased to 80°C, stirring carried on until a
viscous solution was achieved, afterwards it was put into a syringe with the diameter
of 12mm. Electrospinning apparatus was shown in figure 3.4. The weight ratio of
copolymer in DMF for pure P(AN-co-AA) was ≈25%. P(AN-co-AA)/PPy and
P(AN-co-AA)/PNPhPy composites included ≈50% by w/w.
Weight ratio of P(AN-co-AA) %
The distance between the electrodes was 10 cm. The applied voltage was 16 kV, 17
kV and 12 kV for P(AN-co-AA), P(AN-co-AA)/PPy and P(AN-co-AA)/PNPhPy
composites respectively. Rate of feed for pure P(AN-co-AA) was 1ml/h; for P(AN-
co-AA)/PPy and P(AN-co-AA)/PNPhPy composites were 0.5ml/h.
Figure 3.7 : Experimental setup of electrospinning [31].
22
3.5 Synthesis of PPy
Polymerization of Py monomer was performed without copolymer matrix in DMF
medium. 2ml of Py was dissolved in 100ml of DMF at 25°C and the mixture was
stirrred for 15 minutes. Then, 0.5802g CAN was introduced into the solution. As
soon as the initiator was added, the temperature was set to 80°C. Water bath was
used to set the temperature and provide homogeneous heat transfer. Reaction
continued for 2 h. Then DMF in the mixture was evaporated and the particles in the
mixture was washed with dilute HNO3, water and methanol respectively to purify
PPy from CAN, DMF and Py monomer. PPy was dried at 50°C for 24h. During PPy
was being washed with methanol for separation from the monomer, methanol
partially dissolved PPy. After methanol and Py were evaporated with Heidolph
Rotary Evaporator at 55 mmHg and 95°C, 1H NMR in deuterated
dimethylsulphoxide (DMSO-d6) of this PPy was measured. However, PPy which
remained above the filter after washing with HNO3, water and methanol, was
partially soluble in DMSO and not soluble in methanol. Polymerization efficieny was
calculated to % 4.
3.6 Characterization of P(AN-co-AA), Composite Films and Nanofibers
FTIR analysis of P(AN-co-AA), composite films and nanofibers were carried out
with FTIR-ATR reflectance spectrophotometer (Perkin Elmer, Spectrum One, with a
Universal ATR attachment with a diamond and ZnSe crystal) (Figure 3.8).
Figure 3.8 : Perkin Elmer, Spectrum One FTIR-ATR Spectrophotometer.
23
UV-Visible measurements were performed with UV-Visible spectrophotometer
(Perkin Elmer, Lambda 45) (Figure 3.9).
Figure 3.9 : Perkin Elmer, Lambda 45 UV-Visible Spectrophotometer.
Nuclear Magnetic Resonance measurements were performed with 250 MHz Brucker
AC Aspect 3000 using 1H NMR (Figure 3.10).
Figure 3.10 : 250 MHz Brucker AC Aspect 3000 NMR spectrometer [32].
Real permittivity, imaginary permittivity and conductivity measurements of
composite films were executed with Novocontrol broadband dielectric spectrometer
(Alpha-A High Performance Frequency Analyzer, frequency domain 0.001Hz to 3
GHz) at 25°C (Figure 3.11). Samples were fixed between two copper electrodes with
diameters of 20 mm (Figure 3.12).
24
Figure 3.11 : Novocontrol broadband dielectric spectrometer.
Figure 3.12 : Placing film samples between electrodes on Novocontrol broadband
dielectric spectrometer.
Thermogravimetric analysis (TGA) were made with TA, TGA Q50 with a heating
rate of 20°C/min. Differential Scanning Calorimeter (DSC) measurement was
operated with DSC TA Q10 with 3 cycles. Scanning Electron Microscope images of
nanofibers were obtained with Mini-SEM (SEC, SEN-3000M) (Figure 3.13).
Nanofiber diameters were measured with Adobe Acrobat 8 Professional.
25
Figure 3.13 : Mini-SEM, SEC, SEN-3000M.
3.7 Results and Discussion
3.7.1 FTIR-ATR spectrophotometric analysis
3.7.1.1 FT-IR calibration curve for P(AN-co-AA) pellet
KBr pellets of P(AN-co-AA) including 2.67 % AA segments calculated by NMR
measurements and blends of having 5 different ratios of PAN/PAA were preapared.
KBr pellets were compressed with hydraulic press under 10 tons/cm2 for 10s,
afterwards compression was quickly released. FT-IR measurements were operated
with transmission mode (Figure 3.14).
4000 3500 3000 2500 2000 1500 1000 500
cm-1
Pellet 5
Tra
nsm
itta
nce %
Pellet 4
Pellet 3
Pellet 2
Pellet 1
1725 cm-1
1725 cm-1
1725 cm-1
2243cm-1
2243cm-1
2243cm-1
2243cm-1
2243cm-1
1725 cm-1
Pellet P(AN-co-AA)
2243cm-1
Figure 3.14 : Figure FT-IR of KBr pellets of synthesized P(AN-co-AA) and blends
including varying ratio of PAA and PAN in transmission mode.
26
For constitution of calibration curve for blends including varying ratios of
PAN/PAA, graph of log(T0/T) vs. concentration (C) was drawn (Figure 3.15). T was
the transmittance value of CN stretching of PAN segments at 2243cm-1
. CPAN was
the concentration of PAN in the blends by mole%. Table of C and log(T0/T) was
shown in Table 3.1 and the calibration curve of blends was due. C=O stretching
vibration belonging to PAA at 1725cm-1
segments can also be shown in Figure 3.14.
Pellet No CPAN (mole%) log(T0/T)
1 0.2492 0.8409
2 0.4370 0.5895
3 0.6624 0.5031
4 0.8445 0.4918
5 1.0 0.2052
P(AN-co-AA) 0.6078
0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
log (
T0 / T
)
CPAN
(mole%)
y = -0.7078x + 0.9781
R2 = 0.8427
Figure 3.15 : Calibration curve for blends of PAN and PAA including varying CPAN.
Equation y = -0.7078x + 0.9781 with R2 =0.8427 was obtained for calibration curve
(Figure 3.15). From this equation, unknown CPAN could be found by replacing y
value with log(T0/T) of P(AN-co-AA) pellet. Thus, as it was seen in Table 3.1,
log(T0/T) value of P(AN-co-AA) pellet was achieved to be 0.6078, which gave the
concentration of AN segments in the copolymer, CAN, as 0.5232. So, CAA was
0.4768.
3.7.1.2 P(AN-co-AA)
FTIR-ATR spectrum of P(AN-co-AA) were given in Figure 3.16 2939 cm-1
, 2243
cm-1
, 1452 cm-1
and 1720 cm-1
peaks respectively referred to CH bending, C≡N
Table 3.1: C(mole%) of PAN in PAN/PAA blends and log(T0/T) values at 2243cm-1
.
27
stretching and CH stretching of PAN segments and carboxyl C=O stretching of PAA
segments. Peak assignments were consistent with literature [9-10]. P(AN-co-AA)
with different feed ratio of AA/AN were seen in Figure 3.17; the peak belonging to
carboxyl C=O group at 1720 cm-1
was rising as AN/AA ratio was descending.
4000 3600 3200 2800 2400 2000 1600 1200 800
0.01
0.02
0.03
0.04
0.05
0.06 P(AN-co-AA)(95-5 w%)
PAN
2939 cm-1
2243 cm-1
1720 cm-1
1452 cm-1
Ab
so
rba
nce
cm-1
Figure 3.16 : FTIR-ATR Characterization PAN (Aldrich) and P(AN-co-AA).
4000 3600 3200 2800 2400 2000 1600 1200 8000.00
0.01
0.02
0.03
0.04
0.05
0.06
C=O Stretching (PAA)
1720 cm-1
CN Stretching (PAN)
2243 cm-1
CH Bending (PAN)
1453 cm-1
% 95-5 (AN / AA)
% 90-10 (AN / AA)
% 80-20 (AN / AA)
% 60-40 (AN / AA)
A
Frequency (cm-1)
Figure 3.17 : FTIR-ATR Characterization P(AN-co-AA) with different AN/AA
ratios.
28
3.7.1.3 P(AN-co-AA)-PPy and P(AN-co-AA)-PNPhPy composite films
In Figure 3.19 and Figure 3.20, FTIR-ATR analysis of PPy and PNPhPy including
and not including composite films were indicated. Sequentially 2939 cm-1
, 2243 cm-
1, 1452 cm
-1 and 1720 cm
-1 peaks were related with CH bending, C≡N stretching and
CH stretching of PAN and carboxyl (C=O) stretching of PAA. Furthermore, C=O
stretching, the characteristic peak of DMF at 1660 cm-1
shifted to 1663 cm-1
, in the
case the composite film without PPy showing DMF still existed after drying of the
film, which could be attributed to the interaction between the amide group of DMF
and nitrile group of PAN [33] segments of the copolymer (Figure 3.18). It could be
seen that, C=O stretching which was the characteristic peak of DMF at 1660 cm-1
shifted to 1646 cm-1
, in case composite films comprised PPy, which might be related
to intermolecular ionic interaction between partially negative C=O group of DMF
and partially positive NH group of PPy. Likewise, this peak shifted from 1660cm-1
to
1649cm-1
when films included PNPhPy showing that the interaction between DMF
was stronger with PPy than PNPhPy. Moreover, C=O stretching of PAA segments
shifted from 1720cm-1
to 1715cm-1
with the addition of rising PPy or PNPhPy
content into the composite films. Therefore, PPy and PNPhPy existed in strong
interactions with PAA segments in P(AN-co-AA). Furthermore, CN stretching
vibration of PPy and PNPhPy at 1452 cm-1
was observed in composite films. The
results were consistent with the literature [17]. The ratio of the absorbance values of
CN stretching of PPy and PNPhPy to C≡N stretching of PAN segments was
increasing as initially added Py and NPhPy was rising up. Thus, intermolecular
interaction between PPy, PNPhPy, P(AN-co-AA) and DMF could be seen form FT-
IR results and tentative mechanism for this interaction was demonstrated in Figure
3.18.
29
Figure 3.18 : Tentative mechanism for intermolecular interaction between P(AN-co-
AA), PPy chains and DMF.
4000 3600 3200 2800 2400 2000 1600 1200 800
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.00 0.72 1.44 2.16 2.881.6
2.0
2.4
2.8
3.2
3.6
4.0
4.4 CN Ring Stretching (1452cm
-1)
/CN Stretching (2243cm-1)
Ab
sro
ba
nce
(1
45
2cm
-1/2
24
3cm
-1)
Ra
tio
Initially Added Pyrrole (mmoles)
1452-1438 cm-1
1720-1715 cm-1
1663-1646 cm-1
2243 cm-1
P(AN-co-AA)/NoPy
P(AN-co-AA)/PPy (0.72mmoles)
P(AN-co-AA)/PPy (1.44mmoles)
P(AN-co-AA)/PPy (2.16mmoles)
P(AN-co-AA)/PPy (2.88mmoles)
Absorb
ance
cm-1
Figure 3.19 : FTIR-ATR Characterization of P(AN-co-AA) films and PPy including
P(AN-co-AA) films.
30
4000 3600 3200 2800 2400 2000 1600 1200 800
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.00 0.72 1.44 2.16 2.88
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.2
3.4
3.6 CN Ring Stretching (1452cm
-1)
/CN Stretching (2243cm-1)
Ab
sro
ba
nce
(1
45
2cm
-1/2
24
3cm
-1)
Ra
tio
Initially Added N-phenylpyrrole (mmoles)
1452-1451 cm-1
1720-1715 cm-1
1663-1649 cm-1
2243 cm-1
P(AN-co-AA)/NoPNPhPy
P(AN-co-AA)/PNPhPy (0.72mmoles)
P(AN-co-AA)/PNPhPy (1.44mmoles)
P(AN-co-AA)/PNPhPy (2.16mmoles)
P(AN-co-AA)/PNPhPy (2.88mmoles)A
bsorb
ance
cm-1
Figure 3.20 : FTIR-ATR Characterization of P(AN-co-AA) films and PNPhPy
including P(AN-co-AA) films.
3.7.1.4 P(AN-co-AA), P(AN-co-AA)-PPy and P(AN-co-AA)-PNPhPy composite
nanofibers
CN stretching vibration of PPy, PNPhPy at 1452 cm-1
was observed in composite
nanofibers (Figure 3.21) [17]. The ratio of the absorbance values of CN stretching of
PPy and C≡N stretching of PAN segments was increasing as initially added Py was
rising up. In Figure 3.11, it can be seen that, C=O stretching which was the
characteristic peak of DMF at 1660 cm-1
shifted to 1647 cm-1
might be related to
intermolecular ionic interaction between partially negative C=O group of DMF and
partially positive NH group of PPy [33]. P(AN-co-AA) composite nanofibers
31
including PNPhPy showed same peaks as PPy comprising composites.
4000 3600 3200 2800 2400 2000 1600 1200 800
0.00
0.03
0.06
0.09
0.12
0.15
0.18
0.21
0.24
cm-1
1.65
1.70
1.75
1.80
1.85
1.90
1.95
2.00
P(AN-co-AA)
/PNPhPy
(0.72mmoles)
P(AN-co-AA)
/PPy
(0.72mmoles)
P(AN-co-AA)
CN Ring Stretching of PPy (1452cm-1)
/CN Stretching of PAN (2243cm-1)
Ab
so
rba
nce
(1
45
2cm
-1/2
24
3cm
-1)
Ra
tio
1452 cm-1
P(AN-co-AA)
P(AN-co-AA)/PPy (0.72mmoles)
P(AN-co-AA)/PNPhPy (0.72mmoles)
1647 cm-1
2937 cm-1
1720 cm-1
2243 cm-1
Ab
so
rba
nce
Figure 3.21 : FTIR-ATR characterization of P(AN-co-AA), P(AN-co-AA)/PPy and
P(AN-co-AA)/PNPhPy nanofibers.
3.7.2 UV-Visible spectrophotometric analysis
Thin film of 2.88 mmoles initially added pyrrole including P(AN-co-AA)/PPy was
treated with methanol, which turned into greenish color after 1 hour stirring at 40°C.
UV-Visible spectrophotometric measurement of greenish colored solution was
performed while methanol was taken as reference. An increase at the wavelength of
470 nm (Figure 3.22) was observed indicating low molecular weight PPy presence
[4].
32
300 400 500 600 700 800
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Ab
so
rba
nce
Wavelength (nm)
50 l Sol.
150 l Sol.
250 l Sol.
PPy (470 nm)
Figure 3.22 : UV-Visible absorbance vs. wavelength of solution of PPy in methanol.
3.7.3 Nuclear magnetic resonance measurements (NMR)
3.7.3.1 NMR of P(AN-co-AA)
Final composition of P(AN-co-AA) including 95/5 w/w ratio of initially fed AN and
AA was determined by 1H NMR spectroscopy (400 MHz, DMSO-d6, δ(ppm)).
Two strong peaks at δ=2.5065ppm and δ=3.6337ppm corresponded to
dimethylsulphoxide (DMSO) and the water in DMSO.
The chemical shifts for P(AN-co-AA) were indicated as δ=8.1268ppm (c, -COOH)
(Figure 3.23 and Figure 3.25), δ=2.0247ppm ( -CH2- belonging to PAN and PAA)
(Figure 3.23 and Figure 3.24). The degree of acrylic acid (DAA) was calculated with
the following equation [34]:
(3.1)
corresponds to the peak area of protons from carboxyl group (-COOH) of AA
segments, and indicated the peak area of protons from methylene
(-CH3) groups belonging to AA and AN segments in the copolymer respectively.
was shown in Figure 3.25 and calculated as 0.040; and
were shown in Figure 3.24 and was calculated as 2.991. Thus,
of copolymer was found to be 2.67 mole%. As, DAA(%) calculated from
33
NMR measurments and CAA, which was 0.4768, calculated from FT-IR calibration
curve were compared, CAA was higher than DAA. However, the polymerization
efficiency was 50% resulting 2.5g polymer. The reaction included initial feed of AA
as 0.25g (3.469x10-3
moles) and AN as 4.75g (8.952x10-2
moles) giving the initial
AA % by mole was 3.73%. This showed, even all of the acrylic acid was
incorporated into copolymerization, CAA in P(AN-co-AA) could not exceed 3.73%.
So, DAA (%) = 2.67% from NMR result was assumed to be the result for percentage
of AA segments in the copolymer.
Figure 3.23 : 1H NMR spectroscopy of P(AN-co-AA) in DMSO-d6 solvent (0.0-
10ppm).
Figure 3.24 : 1H NMR spectroscopy of P(AN-co-AA) in DMSO-d6 solvent (0.0-5.0
ppm).
34
Figure 3.25 : 1H NMR spectroscopy of P(AN-co-AA) in DMSO-d6 solvent (6.0-
10.0 ppm).
3.7.3.2 NMR of PPy
PPy is not soluble in DMSO [35]. In this study, PPy was synthesized in DMF
medium. After washing PPy with HNO3, water and methanol on filter paper, PPy
remained above the filter was partially dissolved in DMSO-d6 at 90°C for 0.5h.
However, this PPy was not soluble in methanol. 1H NMR in DMSO-d6 solvent of
PPy which was synthesized in DMF medium was shown in Figure 3.26. Three peaks
were observed at 7.0536, 7.2361 and 7.4163 indicating aromatic protons of PPy.
Figure 3.26 : 1H NMR spectroscopy of PPy in DMSO-d6 solvent.
3.7.4 Molecular weight determination
The viscosity average molecular weight of P(AN-co-AA) was calculated by the
Mark-Houwink equation [34]:
35
(3.2)
The intrinsic viscosity, [η] of the copolymer in DMF was determined by Ubbelodhe-
type viscometer (Figure 3.27) at 25 ± 0.3°C. C is the concentration of P(AN-co-AA)
in the solution. Relative viscosity ηr is the ratio t/t0 of flow times of solution and
solvent. Specific viscosity ηsp is ηr – 1. ηsp/C was plotted against C and data was
linearly regressed. y-intercept of the line was [η] (Figure 3.27).
Mark-Houwink parameters; K and α for the copolymer was found to be 2.78 x 10-4
g/dL and 0.76 respectively from the literature [34]. [η] was found to be 1.0101. From
Equation 3.2, = 48300.
Figure 3.27 : ηsp/C vs. C of the P(AN-co-AA) in DMF.
3.7.5 Dielectric and conductivity measurements
Conducting polymers constructed with short conjugation lengths, while electrical
conduction eventuates by charge hopping between two localized states between
polymeric chains [32]. A semiconductor and a dielectric material differ basically by
means of their band gap values. The dominant charge carriers in a semiconductor are
formed essentially by thermal excitation in the bulk owing to its small energy band
gap. However in a dielectric material, charge carriers are primarily coming from
electrical contacts or other external sources due to its energy band gap is relatively
large as compared with a semiconductor. Hence, a higher amount of energy is
required for band to band transitions in a dielectric material comparing with a
y = 0,0956x + 1,0101R² = 0,9388
1,063
1,068
1,073
1,078
1,083
1,088
0,59 0,64 0,69 0,74 0,79 0,84
ηsp
/ C
C (g/dL)
36
semiconductor. Real permittivity is one of the most significant electrical properties
of dielectric materials which is strongly related with frequency of the alternating
electric field [33].
10-2
10-1
100
101
102
103
104
105
106
107
0,0
1,0x10-5
2,0x10-5
3,0x10-5
4,0x10-5
5,0x10-5
6,0x10-5
7,0x10-5
8,0x10-5
10-2
10-1
100
101
102
103
104
105
106
107
0,0
1,0x10-5
2,0x10-5
3,0x10-5
4,0x10-5
5,0x10-5
6,0x10-5
7,0x10-5
8,0x10-5
P(AN-co-AA)
P(AN-co-AA)/PNPhPy (1.44 mmoles)
P(AN-co-AA)/PNPhPy (0.72 mmoles)
Co
nd
uctivity (
S/c
m)
Frequency (Hz)
a
P(AN-co-AA)
P(AN-co-AA)/PNPhPy (1.44 mmoles)
P(AN-co-AA)/PNPhPy (0.72 mmoles)b
Co
nd
uctivity (
S/c
m)
Frequency (Hz)
Figure 3.28 : a. Conductivity (S/cm) values of P(AN-co-AA) and P(AN-co-
AA)/PNPhPy films (For 0.72 and 1.44 mmoles of initially added
NPhPy) b. Conductivity (S/cm) values of P(AN-co-AA), P(AN-co-
AA)/PPy and P(AN-co-AA)/PNPhPy films (For 1.44 mmoles of
initially added Py and NPhPy).
37
10-2
10-1
100
101
102
103
104
105
106
107
100
101
102
103
104
105
106 P(AN-co-AA)
P(AN-co-AA)/PNPhPy (0.72 mmoles)
P(AN-co-AA)/PNPhPy (1.44 mmoles)
Re
al P
erm
ittivity (
Ep
s')
Frequency (Hz)
a
10-2
10-1
100
101
102
103
104
105
106
107
10-1
100
101
102
103
104
105
106
107 P(AN-co-AA)
P(AN-co-AA)/PNPhPy (0.72 mmoles)
P(AN-co-AA)/PNPhPy (1.44 mmoles)
Ima
gin
ary
Pe
rmittivity (
Ep
s")
Frequency (Hz)
b
Figure 3.29 : a. Real permittivity (Eps’) and b. imaginary permittivity (Eps”) of
P(AN-co-AA) and P(AN-co-AA)/PNPhPy films (For 0.72 and 1.44
mmoles of initially added NPhPy).
Conductivity and dielectric measurements were performed between 102-10
7 Hz at
25°C. In all samples, real permittivity (Eps’) and imaginary permittivity (Eps”)
decreased as the frequency (f) increased; beginning from 10 Hz to 107 remained
stable. In all composite films, conductivity values did not vary up to 104 Hz,
while over this frequency they were increased. In our measurements, P(AN-co-
AA) composite films had low frequency conductivity of 2.2x10-9
S/cm, while
P(AN-co-AA) films including 1.44 mmoles of PPy and PNPhPy had conductivity
of 9.3x10-9
S/cm and 1.6x10-8
S/cm respectively (Figure 3.27). Cetiner et al [33]
38
reported that, at 107 Hz, pure PAN composite film had conductivity value of
1.2x10-7
S/cm, PAN film including 1.44 mmoles of PPy has shown the
conductivity of 5.0x10-7
S/cm. In this study, conductivity values of P(AN-co-AA)
and 1.44 mmoles of PPy and PNPhPy containing P(AN-co-AA) composite films
were observed as 1.9x10-5
S/cm, 3.3x10-5
S/cm and 7.7x10-5
S/cm sequentially at
this frequency. Thus, PAA segments in composite films had significant effect on
conductivity values.
10-2
10-1
100
101
102
103
104
105
106
107
0,0
2,0x105
4,0x105
6,0x105
8,0x105
1,0x106
1,2x106
10-2
10-1
100
101
102
103
104
105
106
107
0,0
5,0x105
1,0x106
1,5x106
2,0x106
2,5x106
3,0x106
P(AN-co-AA)
P(AN-co-AA)/PPy (1.44 mmoles)
P(AN-co-AA)/PNPhPy (1.44 mmoles)
Re
al P
erm
ittivity (
Ep
s')
Frequency (Hz)
b
a
P(AN-co-AA)
P(AN-co-AA)/PPy (1.44 mmoles)
P(AN-co-AA)/PNPhPy (1.44 mmoles)
Ima
gin
ary
Pe
rmittivity (
Ep
s")
Frequency (Hz)
Figure 3.30 : a. Real permittivity (Eps’) and b. Imaginary permittivity (Eps”) of
P(AN-co-AA), P(AN-co-AA)/PPy and P(AN-co-AA)/PNPhPy films
(For 1.44 mmoles of initially added Py and PhPy).
At low frequencies Eps’ had high values (Figure 3.29 and Figure 3.30) as a result of
interfacial polarization meaning that charges growing on the boundaries at interfaces
39
inside bulk samples. This situation is the consequence of dispersion of islands of
conductive regions in the polymer inside an insulating polymer matrix according to
Rocha et al. [33,38]. At low frequency values, the side groups or small units of main
chain might have the tendency of following the variation of the electric field which
assist polarization [38]. As phenyl-substituted PPy had much more polar character
than PPy, dielectric permittivity values of PNPhPy were higher than those of PPy.
However at high frequencies, those small units and side groups such as phenyl
groups lack their capacity of moving along the field, lessens the contribution to the
polarization [38]. Opposing of charges defines the amount of dipole moment and
polarizability is a property of linkage between dipole moment and electric field [30].
Our composites had zero dielectric loss beyond 1 kHz pointing out they were lossless
at high frequencies, also dielectric constant showed resembling behavior.
It was observed that inclusion of phenyl substituents led to a decrease in the band gap
[39] as PNPhPy including composites had higher conductivities. The frequency
dependent dielectric constant at room temperature is due to interfacial space charge
(Maxwell Wagner) polarization leading to the high value of dielectric constant [33].
According to the conductivity results in composite films, it can be observed that high
conjugation of conjugated polymeric chains can be obtained in the presence of
phenyl groups due to additional phenyl ring conjugations compared to hydrogen
substitution.
40
10-2
10-1
100
101
102
103
104
105
106
107
1E-7
1E-6
1E-5
1E-4
1E-3
0,01
0,1
10-2
10-1
100
101
102
103
104
105
106
107
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0,01
0,1
1
P(AN-co-AA)
P(AN-co-AA)/PNPhPy (0.72mmoles)
P(AN-co-AA)/PNPhPy (1.44mmoles)
b
Mo
du
lus"
(M")
Frequency (Hz)
a
P(AN-co-AA)
P(AN-co-AA)/PNPhPy (0.72mmoles)
P(AN-co-AA)/PNPhPy (1.44mmoles)
Mo
du
lus' (M
')
Frequency (Hz)
Figure 3.31 : a. Modulus’ (M’) and b. Modulus” (M”) of P(AN-co-AA) and P(AN-
co-AA)/PNPhPy films (For 0.72 and 1.44 mmoles of initially added
NPhPy).
As it was shown in Figure 3.31(a) and Figure 3.32(a), M’ represented low values at
low frequencies (10-2
Hz), approaching to 10-7
Hz, pointing out to electrode
polarization negligibly making assistance to M’. Furthermore, M’ increased with
frequency, because of the lack of restoring force which is responsible from the
mobility of charge carriers exposing to an induced electric field [40].
41
10-2
10-1
100
101
102
103
104
105
106
107
1E-7
1E-6
1E-5
1E-4
1E-3
0,01
0,1
1
10-2
10-1
100
101
102
103
104
105
106
107
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
0,01
0,1
1
b
P(AN-co-AA)
P(AN-co-AA)/PPy (1.44mmoles)
P(AN-co-AA)/PNPhPy (1.44mmoles)
Mo
du
lus"
(M")
Frequency (Hz)
a
P(AN-co-AA)
P(AN-co-AA)/PPy (1.44mmoles)
P(AN-co-AA)/PNPhPy (1.44mmoles)
Mo
du
lus' (M
')
Frequency (Hz)
Figure 3.32 : a. Modulus’ (M’) and b. Modulus” (M”) of P(AN-co-AA), P(AN-co-
AA)/PPy and P(AN-co-AA)/PNPhPy films (For 1.44 mmoles of
initially added Py and PhPy).
According to Figure 3.31 and Figure 3.32, as the frequency increased M’ and M”
increased to a maximum. In Figure 3.31(b) and Figure 3.32(b), a peak was observed
in the transition region from DC to AC conductivity M” curve showed a peak. This
peaks also shifted to higher frequencies due to increasing initially fed N-phenyl
pyrrole amount; and composite films including PNPhPy also exhibited M” peak at
higher frequency as compared with PPy. While conductivity value of P(AN-co-
AA)/PNPhPy composite films were higher P(AN-co-AA)/PPy, faster movement of
charge carriers signifying lower relaxation time [41]. Moreover, P(AN-co-AA)
composites containing 1.44mmoles of NPhPy also exhibited M” peak at higher
frequency due to higher conductivity.
42
0,0 5,0x10-2
1,0x10-1
1,5x10-1
0,0
1,0x10-2
2,0x10-2
3,0x10-2
4,0x10-2
0,0 5,0x10-2
1,0x10-1
1,5x10-1
0,0
1,0x10-2
2,0x10-2
3,0x10-2
4,0x10-2
a
P(AN-co-AA)
P(AN-co-AA)/PPy (1.44mmoles)
P(AN-co-AA)/PNPhPy (1.44mmoles)
Mo
du
lus"
(M")
Modulus' (M')
b
P(AN-co-AA)
P(AN-co-AA)/PNPhPy (0.72mmoles)
P(AN-co-AA)/PNPhPy (1.44mmoles)
Mo
du
lus"
(M")
Modulus' (M')
Figure 3.33 : Modulus’ (M’) vs. Modulus” (M”) of P(AN-co-AA), P(AN-co-
AA)/PPy and P(AN-co-AA)/PNPhPy films (For 1.44 mmoles of
initially added Py and PhPy).
In Figure 3.33, M’ vs. M” graphs (complex planes of electric modulus) of P(AN-co-
AA), P(AN-co-AA)/PPy and P(AN-co-AA)/PNPhPy composite films were
demonstrated. Curves represented a shape like distorted arc beginning from the
origin and ending in various M” values due to frequency in the range of 10-2
to 105,
which were not semicircles suiting to idealized Debye model [40].
In addition, the electrical properties of alkyl pyrroles are found to be dependent on
alkyl chain length and known that the presence of alkyl pyrroles efficiency on
electrical properties [33,42]. According to the fluorescence measurements of N-
43
phenyl pyrrole conjugated monomer in argon/acetonitrile matrix, it is determined that
vertical angle (90°) situation of phenyl and pyrrole rings to each other in a highly
polar environment may be required minimum energy [33,43].
3.7.6 Thermogravimetric analysis measurements (TGA)
TGA thermograms of pure P(AN-co-AA) having DAA of 2.67 mole%, PPy which
was synthesized in DMF without copolymer matrix, and P(AN-co-AA)/PPy
composite film were shown in Figure 3.34 and Figure 3.35.
100 200 300 400 500
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
P(AN-co-AA)
@450oC
P(AN-co-AA)
@385oC
PPy
@191oC
P(AN-co-AA)
@311oC
P(AN-co-AA)
PPy
P(AN-co-AA)/PPy (1.44mmoles)
De
riva
tive
We
igh
t (%
We
igh
t/m
in)
Temperature ( oC )
DMF
@163oC
PPy
@265oC
P(AN-co-AA)
@300oC
Figure 3.34 : Temperature vs. Derivative Weight (%Weight/min) from TGA of
P(AN-co-AA), PPy and P(AN-co-AA)/PPy composite film including
1.44 mmoles initially fed Py.
Degradation of polymers and DMF solvent can be analyzed clearly from derivative
weight vs. temperature graph (Figure.3.34). DMF disappearance at 163°C in P(AN-
co-AA)/PPy composite film, which is above the boiling point of pure DMF, can be
attributed to intermolecular interaction between copolymer matrix, DMF and PPy.
PPy synthesized in DMF without P(AN-co-AA) matrix indicated degradation at
191°C. However, PPy presented in P(AN-co-AA)/PPy composite revealed the
degradation at 265°C which may also be due to the hydrogen bonding between PPy
chain, copolymer matrix and DMF. AN and AA segments in pure copolymer
exhibited weight loss at 300°C and 295°C respectively. AA segments indicated
44
degradation at 385°C. AN and AA segments both indicated a weight loss at 450°C.
In literature P(AN-co-AA) used as membrane exhibited weight losses at 350°C and
410°C which is lower than the values in this study [5]. Pure PPy signified its major
weight loss at 210°C which is a higher value than the PPy synthesized in DMF
medium without copolymer matrix, whilst lower than the PPy degradation concerned
with P(AN-co-AA)/PPy composite film. Also pure PAN nanofiber started its weight
loss at 310°C [44]. PAA chains showed weight loss at 290°C due to anhydride
formation and 420°C due to polymer degradation [45]. PPy synthesized in DMF
medium without copolymer matrix generally showed a gradual weight loss, whilst
P(AN-co-AA) exhibited discrete weight losses. Thus, in P(AN-co-AA)/PPy
composite film not only appeared gradual weight loss, but also discrete losses
(Figure 3.35). Results showed that intermolecular interaction between copolymer
matrix, PPy and DMF (Figure 3.18) stabilized the composite film towards higher
degradation temperatures of the components as compared to their individual
degradation temperatures.
100 200 300 400 500 600
40
50
60
70
80
90
100 P(AN-co-AA)
PPy
P(AN-co-AA)/PPy (1.44mmoles)
% W
eig
ht
Temperature (oC)
Figure 3.35 : Temperature vs. % Weight from TGA of P(AN-co-AA), PPy and
P(AN-co-AA)/PPy composite film including 1.44 mmoles initially fed
Py.
45
3.7.7 Differential scanning calorimetry measurement (DSC)
Differential Scanning Calorimeter (DSC) measurement of P(AN-co-AA) including
2.67 AA by % moles was operated with 3 cycles. First cycle was heating from -30°C
to 150°C, second cycle was cooling from 150°C to -30°C and third cycle was heating
from -30°C to 250°C. Third cycles were considered for DSC analysis. Heating rate
was 10°C/min. Tg of P(AN-co-AA) including 2.67 AA by % mole, from NMR
measurement, was calculated as 101.14°C (Figure 3.36). This value was lower than
130°C Tg value of a blank copolymer membrane of AN and AA [5]. Although, it was
a higher value than Tg = 85°C of commercial PAN [45]. showing AA segments in
P(AN-co-AA) gained a more stable structure to copolymer.
Figure 3.36 : DSC of P(AN-co-AA) including 2.67 AA by % mole.
3.7.8 Scanning electron microscope measurements (SEM)
The weight ratio of copolymer in DMF for pure P(AN-co-AA) was ≈25%. P(AN-co-
AA)/PPy and P(AN-co-AA)/PNPhPy composites included ≈50% by w/w. Because,
lower weight ratio of P(AN-co-AA) in P(AN-co-AA)/PPy and P(AN-co-
AA)/PNPhPy nanofibers could not be achieved due to low viscosities. The distance
between the electrodes was 10 cm. The applied voltage was 16 kV, 17 kV and 12 kV
for P(AN-co-AA), P(AN-co-AA)/PPy and P(AN-co-AA)/PNPhPy nanofibers
Tg = 101.14°C
-1.4
-1.2
-1.0
-0.8
-0.6
He
at
Flo
w (
W/g
)
-10 10 30 50 70 90 110 130 150 170 190
Temperature (°C)
––––––– P(AN-co-AA) (2.67 AA %mole)
Exo Up Universal V3.9A TA Instruments
46
consecutively. Rate of feed for pure P(AN-co-AA) was 1ml/h; for P(AN-co-AA)/PPy
and P(AN-co-AA)/PNPhPy composites were 0.5ml/h. Scanning electron microscope
(SEM) images of nanofibers were taken.
As it was seen in Figure 3.37, beads were observed in SEM image of P(AN-co-AA)
nanofiber. x1000 magnification was applied. The sample was without gold coating.
For higher magnification, sample can be coated with gold supplying the sample
conductivity. Also, beads were observed in Figure 3.37 due to processing conditions
such as viscosity of the solution, applied voltage and the distance between the
electrodes.
Figure 3.37 : SEM images of nanofibers of pure P(AN-co-AA).
SEM images of P(AN-co-AA)/PPy nanofibers were shown in Figure 3.38 and 3.39
with magnification of x1500 and x3000 respectively. Less beads were observed than
P(AN-co-AA) nanofiber and higher magnification much clearly without gold
coating. This can be attributed to higher conductivity of P(AN-co-AA) with respect
to P(AN-co-AA).
47
Figure 3.38 : SEM images of nanofibers of P(AN-co-AA)/PPy composite with
magnification of x1500.
Figure 3.39 : SEM images of nanofibers of P(AN-co-AA)/PPy composite with
magnification of x3000.
Average diameter of P(AN-co-AA)/PPy nanofibers were measured. Narrow
distribution of nanofibers were observed giving highest value for ≈180 nm (Figure
3.40).
48
150 200 250 300 350 400 450 5000
5
10
15
20
25
30
35
40
45
50
55
Fre
qu
en
cy (
%)
Nanofiber Diameter (nm)
Figure 3.40 : Nanofiber diameter distribution of P(AN-co-AA)/PPy composite.
SEM images of P(AN-co-AA)/PNPhPy nanofibers were shown in Figure 3.41 and
3.42 with magnification of x1000 and x5000 respectively. Less beads were observed
than P(AN-co-AA) and P(AN-co-AA)/PPy nanofibers and higher magnification
much clearly without gold coating. This can be attributed to higher conductivity of
P(AN-co-AA) with respect to P(AN-co-AA) and P(AN-co-AA)/PPy.
Figure 3.41 : SEM images of nanofibers of P(AN-co-AA)/PNPhPy composite with
magnification of x1000.
49
Figure 3.42 : SEM images of nanofibers of P(AN-co-AA)/PNPhPy composite with
magnification of x5000.
Average diameter of P(AN-co-AA)/PNPhPy nanofibers were measured (Figure
3.43). Narrow distribution of nanofibers were observed giving highest value for ≈300
nm. Thus, nanofibers of P(AN-co-AA)/PNPhPy composites had higher diameter
values than P(AN-co-AA)/PPy. This case might be attributed to higher applied
voltage of P(AN-co-AA)/PPy nanofibers than P(AN-co-AA)/PNPhPy, while weight
ratio of P(AN-co-AA), feed rate (0.5 ml/h) and distance between the electrodes
(10cm) were the same. Also, considering the conductivity of composite films of
P(AN-co-AA)/PNPhPy was higher than P(AN-co-AA)/PPy, P(AN-co-AA)/PNPhPy
composite in the syringe might have overcome the surface tension of the liquid easier
and higher amount of composite material might have crossed over onto the collector
200 250 300 350 400 450 500 5500
5
10
15
20
25
30
35
Fre
eq
ue
ncy (
%)
Nanofiber Diameter (nm)
Figure 3.43 : Nanofiber diameter distribution of P(AN-co-AA)/PNPhPy composite.
50
51
4. CONCLUSION AND RECOMMENDATIONS
FTIR-ATR and UV-Visible spectroscopy results of composites clearly showed the
presence of PPy in the P(AN-co-AA) matrix indicating the successful reaction and
dispersion of PPy particles on matrix by the use of Ce(IV).
Dielectric spectroscopic measurements of composite films indicated that at low
frequencies eps’ had high values as a result of interfacial polarization meaning that
charges growing on the boundaries at interfaces inside bulk samples. This situation is
the consequence of dispersion of islands of conductive regions in an insulating
P(AN-co-AA) matrix. PAA segments in composite films had significant effect on
dielectric properties. Phenyl substitution enhanced conductivity and dielectric
properties of composites. Electromagnetic interference (EMI) shielding is important
in electronic and communication industries. So composites which had high dielectric
permittivity seemed to be very suitable materials for eliminating EMI shielding
applications. The electrical properties of alkyl pyrroles are found to be dependent
on alkyl chain length and the presence of alkyl pyrroles should have an effect on
electrical properties of composites. From NMR results, although P(AN-co-AA)
included little AA segments (2.67 % by mole), conductivity and dielectric
permittivity values was enhanced considerably as compared to PAN. According to
thermogravimetric analysis results, that intermolecular interaction between
copolymer matrix, PPy and DMF stabilized the composite film towards higher
degradation temperatures of the components as compared to their individual
degradation temperatures. DSC results showed AA segments in P(AN-co-AA),
gained a more stable structure to copolymer due to higher Tg value of P(AN-co-AA)
than commercial PAN. Nanofibers of P(AN-co-AA)/PNPhPy composites had higher
diameter values than P(AN-co-AA)/PPy which might be an indication of higher
conductivity value of P(AN-co-AA)/PNPhPy than P(AN-co-AA)/PPy composite
films
52
53
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57
CURRICULUM VITA
Candidate’s full name: Nazif Uğur KAYA
Place and date of birth: Seyhan/ADANA, TÜRKĠYE, 09.12.1985
Permanent Address: CemalpaĢa Mah., Atatürk Cad., 1 Sok., Altın Apt., B Blok,
3/9, Seyhan/ADANA
Universities and
Colleges attended: Bachelor’s Degree: Istanbul Technical University, Chemical
Engineering (2003-2007)
Publications: Cetiner, S., Karakas, H., Ciobanu, R., Olariu, M., Kaya, N.U.,
Unsal, C., Kalaoglu, F., Sarac, A.S.; 2010: Polymerization of Pyrrole Derivatives
on Polyacrylonitrile Matrix, FTIR-ATR and Dielectric Spectroscopic
Characterization of Composite Thin Films, Synthetic Metals, Vol.160, pp. 1189-
1197.
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