CHARACTERISATION OF PEDOT AND ITS DERIVATIVES
IN ELECTROCHEMICAL SENSING APPLICATIONS

Abstract

The emergence of a new class of polymer, namely conducting polymers (CPs) in late 1970s, has attracted many hysicists, chemists and materials researchers to study them in depth due to the unique properties and broad applications of this material. Poly(3,4-ethylenedioxythiophene) (PEDOT) has been found to be the most chemically stable CP to date. The aim of this project was to characterise PEDOT and its derivatives for applications in ion sensing. In this work, PEDOT and its derivatives i.e. poly(3,4-propylenedioxythiophene) (PProDOT) and poly(3,3-dibenzyl-3,4-propylenedioxythiophene) (PDBPD) doped with perchlorate ( ClO-4) have been electrochemically synthesised on glassy carbon (GC) and indium-tin-oxide coated glass (ITO) electrodes in acetonitrile. PEDOTs were also prepared in aqueous solutions using perchlorate ( ClO-4) and chloride( Cl-) counterions as comparison. Scanning electron
microscopy (SEM), atomic force microscopy (AFM), contact angle (CA) measurements and Raman spectroscopy have been used to characterise the physical properties of the polymer coated glassy carbon (GC) and ITO electrodes. PDBPD has shown to have the most compact morphology, roughest and least wettable surface. The electrochemical studies have shown that PEDOT has the highest capacitive current. The combination of this property and mixed electronic and ionic conductivity make the PEDOT suitable to be used as a solid contact (transducer) in all-solid-state ion-selective electrode (ASSISE). PEDOT doped with poly(sodium 4-styrenesulfonate) (PSS) was found to be superior to
hyaluronic acid (HA) as a solid contact for ASS Ca2+-, K+- and Na+-selective electrodes. Measurements of Ca2+ and K+ upon plant stress using ion ion-selective microelectrodes
have been demonstrated. Chiral electrodes based on electrodeposited PEDOT doped with chiral molecules (collagen, HA and hydroxypropyl cellulose) were shown to discriminate between (R)-(−)- and (S)-(+)-mandelic acid. The work carried out in this thesis has shown that PEDOT is one of the most versatile conducting polymers.