A Review On Synthesis Of Polyaniline And Its Doping With Lewis Acid And Base

ABSTRACT

During last few years, many researchers have worked and are working in the field of conducting polymers . This review article focuses on conducting polymers and their applications. Conducting polymers (CPs) have drawn considerable attention because of their economical importance, good environmental stability and electrical conductivity as well as due to their useful mechanical, optical and electronic properties. The effect of this oxidation or reduction on polymer is called doping.

INTRODUCTION

Intrinsically conducting polymers (ICPs) are organic polymers that conduct electricity[1]. Everyday polymers, which are more commonly known as plastics, are composed of simple repeating molecule units called monomers. Polymer name derived from the Greek words „poly‟ means „many‟ and „mer‟ means „part‟. Polymers are well known for their insulating properties, indeed it is this characteristic that has led to their wide usage in the packaging and electronics. Conducting polymers (CPs) are differ greatly from these insulating polymers because of they are intrinsically conducting. Developments of conducting polymers are largely due to the work of three scientists namely as A. J. Heeger, A. G. MacDiarmid and H. Shirakawa, who received the Nobel Prize in Chemistry in 2000 for their work on polyacetylene [2].

Polyaniline (PAN) is one of the most interesting conducting polymers due to its environmental stabilit, [3−6] ease of synthesis and preparation,[7−10] and wide-ranging potential use through its particular electrochemical, optical, and electrical properties.[11−14] The physics and chemistry of polyaniline in its many forms have been the subject of intense study because of its fundamental and important technological properties with their possible applications in rechargeable batteries[15,16] microelectronics devices, biosensors,[17−19] chemical sensors,[20,21] electrochromic displays,[22] and electromagnetic shielding.[23−27] Superior control over the conductivity of polyaniline through doping is regarded as very promising due to the relative ease of scaling to large quantities and of designing electromagnetic behavior through final oxidation and protonation states determined by adjustable reaction conditions.[28,29]

SYNTHESIS AND CHARACTERIZATION OF CONDUCTING POLYMERS

PANI is a CP of the semi-flexible rod polymer family. Among all the above classes PANI is of much importance worldwide because of its unique properties. PANI was first explained in the mid-19th century by Henry Lethe by who studied the electrochemical and chemical oxidation products of aniline in acidic media.[30] Lee et al investigated the effect of the electrode material on the electrical-switching type of a non-volatile resistivememory apparatus based on an active poly(o-anthranilic acid) thin film.[31] They found that bottom-electrode material is responsible for the switching characteristics of the active polymer layer. Athawale et al studied PANI and its substituted derivatives as methanol, ethanol, propanol, butanol and heptanol sensors.[32] Author found that the PANI exhibits good responses for ethanol. Misra et al synthesized the high quality doped PANI thin films using vacuum deposition technique has been found to be appropriate for detection of CO.[33] Crawley investigated the fabrication and operation of a PANI/CuCl2 as a hydrogen sulphide sensor.[34] Banerjee reported the fabrication of PANI nanofiber reinforced nanocomposite crystal microbalance sensor as HCl sensor.[35] The author found rapid detection of HCl at low concentration in natural water systems. Subsequently, DeSurville reported high conductivity in a PANI by electrochemical polymerization.[36] Likewise in 1980, Diaz and Logan synthesized electroactive films of PANI that can serve as electrodes.[37]

BACKGROUND OR ASSOCIATED WORK

Polyaniline has many attractive processing properties. Because of its rich chemistry, polyaniline is one of the most studied conducting polymers of the past 50 years. [38] Conducting polymers have π-conjugation across the polymer backbone made up of carbon and hydrogen, along with heteroatoms such as nitrogen or sulphur. They include polyaniline (PANi), polypyrrole (PPy), polythiophene and polyacetylene. Polyaniline is a typical phenylene-base polymer having a chemically flexible –NH– group in the polymer chain flanked on either side by a phenylene ring.

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Polymers have semi conducting properties due to their unique structural behavior such as formation alternating single and double bonds between the adjacent back bone carbon atoms. The semi conducting polymers have attracted considerable attention due to wide application. Since carbon atom is the main building blook of most polymers the type of bond that their Vance electrons make with other carbon atom or other element determines the overall electronic properties of the respective polymer. In general they can be categorized as saturated and unsaturated based on the number of the type of the carbon valance electron involved in the chemical bonding between consecutive carbon atoms along the main chain of polymer. Saturated polymers are insulator since all the four valence electron of carbon atom are used up in covalent bonds, whereas most conductive polymers have unsaturated conjugated structure. The fundamental single source of semi conducting property of conjugated polymer originates from the overlap of molecular orbital’s formed by the valence electrons chemically bonded carbon atoms [39,40].

Somewhat surprisingly, a new class of polymers possessing high electronic conductivity (electronically conducting polymers) in the partially oxidized state was discovered. 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” [41-46 ].

EXPERIMENTAL

Polyaniline (PANI) is one of most extensively studied conducting polymers due to its strong bimolecular interaction, superficial synthesis, existing electrochemical, electrical and optical features. Due to outstanding tuneable conductivity either by charge transfer doping and protonation, it holds great potential in comparison to other conducting polymers [47]. Due to its low synthetic cost, and outstanding thermal and environmental stability, it is most extensively studied conducting polymer.

There are three main forms of PANI, namely the fully oxidized (pernigraniline) state, fully reduce (leucoemeraldine) and the more conducting emeraldine base (half oxidized). Thus by doping to form emeraldine salt, emeraldine is most conductive form. Polyaniline can be easily synthesized either electrochemically or chemically from acidic aqueous solutions. The chemical route has great importance because it is sensible route for PANI mass production. Thus, the most common synthesis route is the oxidative polymerization with ammonium peroxodisulfate as oxidant [48]. Polyaniline is ranked among the most studied conducting polymers. Besides its electrical features, catalytic, optical, electrochemical, and surface features have been considered. However, in the typical approaches, PANI is synthesized from aniline, oxidant, and small molecule. It has very poor solubility in common solvents such as ethanol, methanol, and acetone. PANI nanostructures with large interfacial areas between PANI and their surroundings can have an enhanced dispersibility in the hosting matrixes [49].

Chemical polymerization In this polymerization monomers can be polymerized by various oxidizing agents like ammonium per sulphate, hydrogen per oxides etc. [50].

CONLUSION

From this review it can be concluded that, polymers are applicable in different ways for example solar energy cell sensors and corrosions in heritors and also polymers can be synthesized by differ techniques that is chemical and electro chemical polymerization and can be characterized by different techniques electrical, mechanical and elector chemical characterization and also polymer are doping with other field for example physics, due to this polymers it is more applicable.

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