Effects of Doping and Post-Treatments on PANI Films

Effects of Doping and Post-Treatments on PANI Films

DOI: 10.4018/978-1-5225-9896-1.ch005

Abstract

It is well known that the sample preparation, experimental measurement, and technique have played a vital role in empirical research work. In this chapter, the detailed discussions on the doping and various post-treatments on the PANI thin films have been made. The in-depth studies on gold, silver, aluminum, lithium, HCl, and camphor sulfonic acid (CSA) doped PANI nanocomposites and thin films have been undertaken in this chapter, followed by discussing the effect of post-annealing treatment and ion reaction medium. The impact of different doping and post-treatment on the properties of PANI films viz. microstructural, optical-electrical, thermal, etc., have been analyzed herein. The structural and optoelectrical properties of PANI films and its nanocomposites have also been discussed in which metal-nanoparticles inserted PANI films achieve particular consideration due to its relatively thought-provoking non-linear optical properties.
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Introduction

Chemical Synthesis of Gold Nanocomposite PANI

The PANI can be produced by standard oxidation polymerization procedure of aniline hydrochloride utilizing ammonium peroxodisulphate (APS) as an oxidant (Saikia and Sarmah, 2011). They used freshly distilled aniline in 1M HC1 solution at 3 °C, which was stirred for 15 minutes in an ice-chamber, and subsequently, 1 M APS solution was added up to it, and finally the gold solution was added by opening the burette to the core solution. The stirring of the solution was continued for about 2 hours as before, and the resulting solution was kept overnight for complete polymerization. The precipitate was washed out by using first tetrahydrofuran (3 mL tetrahydrofuran in 15 mL distilled water) and secondly by sodium hydroxide (NaOH) solution to eliminate any oligomers and then dried in an oven at 45 °C for 20-24 hrs. Thus the powdered gold nanocomposite polyaniline sample was obtained.

Drop Coating Method For Gold Nanocomposite Pani Film

The powdered sample of gold nanocomposite polyaniline was dissolved in 1-methyl 1-2-pyrrolidinone (NMP) in a beaker with continuous stirring for about four hours. The solution was filtered, and drops of it were placed over a glass slide already cleaned by chemical wash and subsequently in an ultrasonic bath. The drops were spread over by small glass spoon to make it in the form of a film. For fabrication of junction, ITO coated glass substrate was used after proper cleaning. This was dried in a specially made vacuum chamber, which was fitted with a heater and a temperature controller. The temperature was maintained at 45 °C for drying in vacuum for about four hours. Four sets of ultra-thin films of (p)gold nanocomposite polyaniline having thicknesses in the range of 20-50 nm were produced in a cycle to study various parameters where one set of the film so produced was taken to the thermal evaporation unit for deposition of electrodes. For gap type cell geometry, the sample was made by using two co-planar electrodes separated by a gap to study electrical parameters. Two wires of pure silver were deposited onto the film prepared on a glass substrate, keeping a gap of 1 mm using a mask. For making of the junction, high purity A1 foil for Schottky barrier or zinc oxide material (n-type, 99.99% purity) for heterojunction was vacuum deposited onto the (p)gold nanocomposite polyaniline film prepared on ITO coated glass substrate in the form of small disc or rectangular shaped electrodes (Saikia et al., 2013). The schematic diagrams of gap-type and sandwich structures are illustrated in Figure 1.

Figure 1.

Schematic diagrams of gap and sandwich structures of gold nanocomposite PANI film

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Electrochemical Method For Gold Nanocomposite Pani Film

The gold nanocomposite PANI thin films were prepared by the electrochemical process, where the working electrode was replaced with PANI/ITO and Au-NPs/PANI/ITO. The platinum wire and Ag/AgCl were used as counter and reference electrodes, respectively. Before the electropolymerization, the ITO coated glass plate was thoroughly cleaned with methanol and then rinsed with deionized (DI) water. The polymerization of aniline was achieved in a potentiodynamic mode following methodology (Radhapyari et al., 2012). The cell consists of Ag/AgCl as a reference, Pt wire as the counter electrode and ITO coated glass plate as the working electrode. The electropolymerization was demonstrated for seven cycles in the potential range -2.0 V to 1.1 V. The p-type Au/PANI/ITO structure formed on the electrode was washed with DI water to clean off the untreated Au-PANI films having a thickness within the range of 110-130 nm (Saikia et al. 2013).

Key Terms in this Chapter

Doping: The addition of any impurities to a semiconductor to tune or alter the properties (especially electrical conductivity) of semiconducting materials, primarily electrical resistivity.

Annealing (heat treatment): A process in which any material is heated to a specific temperature and then cooled in a certain way to tune its internal structure for obtaining the desired degree of physical and mechanical properties. Heat treatment is the heating and cooling of metals to change their physical and mechanical properties, without letting it change its shape. It is a procedure for strengthening materials but could also be used to alter some mechanical properties such as improving formability, machining, etc. This process involves the use of heating or cooling, usually too extreme temperatures to achieve the wanted result.

Specific Energy: The specific energy is the total electrical energy obtainable from a cell in one discharge cycle divided by the mass of the individual cell. This quantity is often incorrectly called energy density.

Coulombic Efficiency: For secondary cells, the Coulomb efficiency represents the ratio of charge released during the discharge to the charge necessary for charging the battery.

Energy Density: The energy density is the total electrical energy obtainable from a cell under specified discharge conditions divided by the volume of the cell.

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