Synthetic Metals: Synthesis and Applications

• Main Author: Papammagari, Lekha
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2023
• Subjects: Chemical engineering; Materials science; Organic chemistry; Polymer chemistry
• ISBN: 9798379594145

The objectives of the present thesis study were: (1) to chemically synthesize polyaniline and its derivatives using greener oxidants such as H2O2 in a high ionic strength system without any added metal or an enzyme catalyst, (2) to chemically synthesize conducting polymers using a benign oxidant such as CaO2, which is used as a confectionary flour additive, (3) to elucidate the true electrochemical behavior of polyaniline and its derivatives in highly acidic solutions and then to recommend this material as a possible cathode/anode material for aqueous charge storage applications at low temperatures (-65 oC), (4) to use electrochemically polymerized polypyrrole on a PET plastic substrate as a potentiometric biosensor for thyroid stimulating hormone (TSH).This thesis has been organized in the following way:Chapter 1 presents the history of conducting polymers, which started with the synthetic metals made of organic charge transfer salts (not organic polymers) and then gradually evolved into the diverse field we know today. Chapter 1 also touches on the basic concepts of band theory and Peierls instability, followed by fundamentals of electrochemistry needed to navigate through this thesis. In the last section of Chapter 1, we have attempted to give an insight into the doping processes encountered in conducting polymers (synthetic metals).Chapter 2 is related to the first project – green synthesis of polyanilines using H2O2 in a high ionic strength system. This project involves using 5M CaCl2 to boost the reaction yield and also an investigation into nature of oxidant in this system. All the polymers synthesized in this chapter are characterized in a traditional way to know the component purity.Chapter 3 introduces a novel benign oxidant, CaO2 for the synthesis of conducting polymers such as polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene) - PEDOT in quantitative yields. CaO2 is a solid peroxide used predominantly for soil decontamination and recently in bone tissue engineering applications as a stable source of H2O2 and O2 respectively. CaO2 has not been used for organic synthesis (conducting polymers) without the use of a metal catalyst and we have overcome that limitation by playing with the acid concentration.Chapter 4 shifts to the application part of this thesis. Project 3 deals with the aqueous electrochemistry of polyaniline and its derivatives at low temperatures (-65 oC). As one would suspect, it is not possible to work with water-based electrolytes at such low temperatures, as water starts freezing below 0o C. We were able to circumvent this issue by increasing the ionic strength of aqueous solutions through adding an alkali salt to lower the freezing point of water from 0 oC to (-65 oC). In a way, the use of high ionic strength electrolyte to lower freezing point of water in project 4 is derived from project 1.Chapter 5 describes a disposable electrochemical biosensor made of two-layered polypyrrole for the detection of thyroid stimulating hormone (TSH). The transducing element, polypyrrole is electrochemically synthesized by galvanostatic polymerization on screen-printed carbon on a PET substrate. The biosensor is fabricated based on standard sandwich ELISA protocol and signal response is measured by continuously monitoring the open circuit potential (OCP) of the systems with time vs. Ag/AgCl reference (also screen-printed). This low-cost technology is rapid (~15 min), sensitive (< 0.1 mIU/L) and reproducible (CV < 5% at 0.1 mIU/L).