Ph.D. Thesis, Postgraduate Institute of Science, University of Peradeniya (2000)

Supervisors: M. A. Careem (mac@pdn.ac.lk) and S. Skaarup (skaarup@kemi.dtu.dk)

Polypyrrole based conducting polymers and their electrochemomechanical properties
K. P. Vidanapathirana (kamalpv@sltnet.lk)

The influence of preparation condition on the properties of electroactive poly-N- methylpyrrole (PNMP file were investigated with the view of obtaining highly conductive films .PNMP films were galvanostatically polymerized in aqueous electrolytes by varying the electrolyte concentration, current density, type of doping anion, pH of the electrolyte and the polymerization temperature .The films obtained were characterized using cycle voltammetry and impedance spectroscopy. Conductivity of PNMP films was very much affected by the polymerized current density ,pH and the polymerization temperature whereas no considerable  effect was o bserved when the conductivity for PNMP films(43 mScm-2) was obtained with the following conditions: electrolyte concentration=0.5 M, current density=62.5 μA cm-2, anion=CIO4, pH=1.0 and polymerization temperature=3oC .

Mass changes occurring in PNMP films during the redox due to ion exchange were investigated using an Electrochemical Quartz crystal microbalance (EQCM) .The mass changes and dependence of peak potential of cyclic voltammograms (CVs) with respect of cycling electrolyte concentration revealed that anions are the moving species during the redox process in PNMP films that were prepared and cycled in aqueous electrolytes containing small anions.

Polypyrrole (PPy) films were prepared with large surfactant anion, dodecy1 benzenesulfonate (DBS-) and their properties were compared with those of PPy films prepared with small anion under similar conditions .It has been observed that the stability of PP/DBS films made in aqueous electrolytes was same that of the PPy films made in non aqueous electrolytes. EQCM studies and dependence of peak potentials of CVs on cycling electrolyte concentration of PPy/DBS film showed a dual step scheme for the redox process in the films when they are cycled in aqueous electrolytes. During oxidation, cation expulision takes place at lower potential whereas anion insertion takes place at higher potentials.During reduction, anion expulsion at higher potentials and cation insertion at lower potentials takes place.

Lithium rechargeable cells were fabricated using PPy/DBS as the cathode and polycrylonitrile (PAN) based electrolyte as the separator these cells were characterized by cycle voltammetry, impedance spectroscopy and continuous charge-discharge cycling. Kinetics of these cells could be cycled more than 1000 times without any appreciable charge decay.

Electrochemomechanical properties of PPy/DBS films were investigated by fabricating bi-layer and dry artificial muscles and obtaining the force exerted by these muscles and the cyclic voltammograms simultaneously. The highest chance in the force can always be associated with the main peaks of the cyclic voltammogram. It has been observed that appreciable force change occurred in a rather narrow voltage interval .Muscles fabricated with PPy films prepared using large anion and higher polymerization current densities gave higher forces .higher forces can also be obtained by limiting the cycle potential window so that cation exchange occurs