Introduction as well; same polymers are being used

Introduction

Conjugated
polymers have led to many applications such as rechargeable batteries,
capacitors, modified electrodes and bio sensors among many others(Nalwa 1997). There are many conducting
polymers e.g. polyaniline and polypyrrole among which dc conducts. Because of
the ease of fabrication processes these conducting polymers are good for bio
sensors as well; same polymers are being used for different procedures at low
cost. These polymers are also being used for the sensing properties of some
toxic gases like chlorine, solvent vapors and ammonia etc(Radhakrishnan and Paul 2007). Because of these properties the
polymers have got attention of both scientific and industrial interest. By
irradiation of these polymers with ions we can get different properties of
these polymers. By targeting these materials with heavy ions exceptional
modification have been observed. Scissoring of chains of polymers by irradiated
ions, formation of carbon clusters, breakage of covalent bonds, cross linking,
removal of some volatile species and formation of new bonds(Chandra, Annapoorni et al. 2009). High energy irradiation of ions
creates cracks in polymers and also formation of triple bonds in polymers.

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

In
the last decade conducting polymers have got special attention such as aryl
amine derived polymers, e.g. poly aniline and its derived compounds. The
polymers has been using as sensors, electrochromic devices, secondary batteries
actuators and supercapacitors as described previously(Kaneto, Kaneko et al. 1995). Upon redox switching polyaniline
compounds and their derivatives undergo changes in volume from complete reduced
form, leucoemeraldine (LE) to medium reduced form, emeraldine (EM)(Franke and Zimmer 1996). Polymers have been studied
extensively in the past years due to their potential usage and their special
characteristics. The conductor /insulator transitions have been studied from LE
to EM in acid medium by redox switching but whole process is still not known so
far(Huang and Humphrey 1986). Mechanical modification has also
been studied but less. Polymers gels and deformations by electric field have
been known for a long time and described by swelling and deswelling because of
ionic field induction (De Gennes, Okumura et al. 2000). The volume change by oxidation of
LE to EM was studied by using PANI as it was observed for mechanical actuators(Avlyanov, Min et al. 1995). Change of thickness of PANI films
has been changed by oxidation was observed by Barbero and Kotz. Recently, a
study was done on a material related to polyaniline in 1 M solution of acid,
showed volume changes under redox switching which was electrolyte dependent.
First cycle effects were observed during this study when polymer is fully
reduced and oxidized(De Gennes, Okumura et al. 2000). The result was expressed in two
different time scales i.e. slower one change of polymer backbone and the faster
one exchange of water and ions with external solutions. Otero et al. described
the term relaxation as conformational change of polymer backbone and
rearrangement of conformations by conduction polymers with the effect of
electrochemical effects(Otero, Grande et al. 1995). Thus relaxation suggests the
opening of polymers chains which activates anion ingress.

A
derivative of PANI, poly 2-methoxyaniline, there was observed some modification
in dimensional change and deformations in electrochemomechanical behavior were
solution acidity dependent and proposed as electrostatic repulsions or polymer
conformation.

The
study of polymers films deformations due to mechanical and electrical effects
have special interest by both scientists have led to their special attention
because of the modified properties of films after such effects. There was
swelling and deswelling of films except their utility as in many applications.
Changes in volume by redox switching were also studied by using PANI films
between LE to EM forms. Different acidic mediums (HClO4, H2SO4,
and HCl) were used to study the effect of acidity and influence of electrolytic
solutions of anions over films(Lizarraga, Andrade et al. 2004).

Literature
Review

A
lot of research has been done on different properties of polyaniline thin
films. Firstly we see the swelling and deswelling of polyaniline to remove the
electrolyte in dilute ammonia solutions. The films were rinsed, dried and placed
below 50 ?C(Gull, Khan et al. 2016). To keep the films in their
reduced forms a small amount of hydroxylamine was used both in rinsing water
and in ammonia solution. To get reproducible stationary voltammogram following
procedure was used. In the monomer free electrolyte, electrode was placed and
the potential was cycled continuously at v=0.012 V s-1 till required
voltammogram was obtained.

Polymer swelling

The
following figure shows the clear swelling of PANI films during the interaction
of electrolyte solutions. The film is in reduced and relaxed states. The
thickness of film was h, of almost 180-200 µm and 750-500 µm of maximum
diameter D. These measurements were measured on calibrated images. It is
evident from the data and conditions employed here that the PANI films are
swelled considerably by the electrolyte solutions.

Fig
1: video images of fully reduced and relaxed polyaniline films, (a) in 1M H2SO4
(b) in base NH3

Volume changes

There
was also the study of volume changes of films with the interaction of different
electrolytes. We interacted the films with different electrolytes with
different concentrations of the same electrolyte to study the respective
comparison and over all comparison of volume changes. HClO4, H2SO4,
and HCl were used as electrolytes to study the volume changes. Table 1 showing
the effect of different concentrations of electrolytes over these films.

Table
1:

The
following points are derived from the above data:

·        
The changes in volume are higher in 1 M
than 4 M solutions at the upper limit.

·        
At the same molarity, the total volume
at the upper limit increases in these electrolyte solution follows the order
HCl ? H2SO4 > HClO4.

·        
The volume of film is higher in 4 M than
in 1 M solutions

Volume
changes are due to the following parameters:

                   
i.           
Volume changes by swelling/deswelling
are caused by the process of ion exchange in electrolyte.

                 
ii.           
Positively charged quinoid units, anion
interactions for the type of donor acceptor systems.

               
iii.           
The pH dependence is due to the H+
binding as the positive charges on the polymer backbone.

Effect of ion
implantation on electrical conductivity, stability and color change of
polyaniline

As
PANI is conducting polymer, so the key property is conductivity. The
conductivity is being increased by the ion implantation of the conjugated
polymers and non-conjugated polymers. The conductivity depends upon ion specie,
dose rate and ion dose. The Conductivity of polymers is prone to increase owing
to the movement of electrons and charged species. In the target materials
n-type conductivity is produced due to the all ions implantation of polymers(Gull, Khan et al. 2016).

The
stability of polyaniline polymer films was increased due to the induced cross
linking and other such like processes. The conductivity of polymers showed no
change on exposure to the moist air. Ion implantation also changes the color of
PANI. The change in color which was observed was purple to dark green and
finally to black blue at ion dose rate of some tens of eV/A3(Jin-Liang, Zhao-Min et al. 1994)
.

The
resistivity of polyaniline polymer films which were electrochemically synthesized,
measured as the films was submerged in the electrolyte. The study suggested
that the resistivity is dependent on the pH of electrolyte, on the reduction
state of films and to some extent on the anionic species present in the
solutions. It was also described that the resistivity was dependent on the
moisture content of polyaniline films. For wet polymer small extent of
protonation drastically decreases the resistivity more than in the orders of 6
of magnitude. This can be explained by the charge transport mechanism of chain,
exchange of protons and intermolecular transport of electron as well.

Voltammogram
which was obtained in 1 M HCl is shown below in fig 2. There is two peaks
showing the two redox processes which is reversible as well as there is an
irreversible process for which only oxidation peak is being observed in the
plot (Focke, Wnek et al. 1987). Depending on the synthesis route
and conditions a third peak of oxidation and reduction suddenly revers was also
observed between 0.8 to 1.0 V vs SCE(Huang, Humphrey et al. 1986).

  Fig 2: showing two reversible and one
irreversible process where just oxidation occurs

The
resistivity of electrochemically synthesized polyaniline was dependent at pH 2
on anionic nature of ions. The typical U-shaped curve was obtained by Paul et
al. This means that the resistivity is dependent in a small value of range and
exceed suddenly in the out range of small region as in fig 3(Huang, Humphrey et al. 1986).

In
the fig 4 there is dependency of resistivity on pH. As the value of pH
increases the potential window reduces its base range. This was done after
masking the effect of anions and buffer solution was diluted by adding 0.2 M
KCl solution.

The
stability of intermediate state reduces with an increase in pH, and the
potential range of smallest resistivity range decreases with increasing pH(Huang, Humphrey et al. 1986).

Fig
3:

 

 Fig 4:

In
the electrolyte the effect of added ions also affect the electrical properties
of polyaniline films. There was addition of Cs+ ion in the 0.1 M
aniline/0.5 M H2SO4. Electrochemical impedance
spectroscopy was used to study the ohmic resistance, charge transfer resistance
and capacitance. There was decrease in charge transfer resistance and increase
in conductivity and capacitance. For the less solvated ions Cs+
>> K+ > Li+ > Na+ higher rates
were obtained. In the oxidized conducting state the film behaves as it is a
combination of capacitors and resistors in series(Maggio, Oliveira et al. 1994).

It
is evident from the study that from aqueous media the electro polymerization
leads to partial oxidative degradation of polyaniline polymer to p-aminophenol
and p-benzoquinone which reduces the capacity of charging of the resulting
polymer(Maggio, Oliveira et al. 1994). There was an increase in current
density with increase in power density and energy density shown in table 2 (Maggio, Oliveira et al. 1994):

Table
2:

The
poor electrical conductive form of PANI base is emeraldine base, in aqueous
acid can be protonated consequently the emeraldine salt with conductivity of
metals. The chemical structure, redox scheme of each polyaniline salt:
leucoemeraldine salt (LES), emeraldine salt (ES) and pernigraniline salt (PNS)
are given in the following(Kaneto, Kaneko et al. 1995):

Fig
5:

The
effect of electrolyte and solvent on electrochemical behavior and degradation
of polyaniline polymers suggests that some factors affect electrochemical and
degradation of polyaniline which are electron accepting and donating ability of
solvents, nucleophilicity of anions and acceptor power of cations. The non-aqueous
media has advantage over aqueous media as used in different electronic devices
for electrochemical redox processes because of their high doping level and
absence of decomposition by hydrolysis(Morita 1994). For the batter electrochemical
stability of polyaniline polymers in non-aqueous media the following
instruction keep in mind:

                  
i.           
Solvents with high electron donating and
accepting ability are to be avoided.

                
ii.           
Employment of electrolytic cations with
higher acceptor strength.

              
iii.           
Anions of electrolyte with high
nucleophilic character should be employed.

              
iv.           
Prefer composite films with matrix
polymers that trap protons and anions.

Study
of electrochemical redox processes of polyaniline with varying pH values in aqueous
electrolytes shows two types of redox processes happening at different
potentials. These processes are accompanied by protonation during reduction or
deprotonation during oxidation(Kurys, Krylov et al. 1996).

Conclusion

Polyaniline
polymer has a lot of application in electronics usage. Interaction of
polyaniline thin films with electrolytes creates a lot of modified properties
in the polymers which are very beneficial for us. There are a lot of
modifications has been done in the polymeric natures by interacting the
polymers with electrolytes and studied different parameters such as volume
changes, polymer swelling, conductivity, stability, color change, resistivity,
integrity, current density, energy density and power density etc. A lot of further
work needs to be done over the interaction of electrolytes with polyaniline
polymers.

x

Hi!
I'm Barry!

Would you like to get a custom essay? How about receiving a customized one?

Check it out