Year

1999

Degree Name

Doctor of Philosophy

Department

Department of Chemistry

Abstract

Polyacrylamide (PAAm) hydrogels were synthesised chemically prior to the preparation of hydrogel and PPy blends. PAAm hydrogel was used as a matrix to grow polypyrrole electrochemically in the three dimensional structure. The redox nature of the blends was studied using electrochemical (EC) methods such as cyclic voltammetry, chronoamperometry, chronopotentiometry. The effect of electropolymerisation time, monomer concentration and dopant size on the preparation of the hydrogel and PPy blend has been investigated. It was found that electropolymerisation time and monomer concentration affected the growth of polypyrrole in the hydrogel network. It was also observed that smaller dopants (N03-) can easily be incorporated into the polypyrrole within the hydrogel network during electropolymerisation. Incorporation of polypyrrole into the hydrogel network did not significantly affect the physical properties such as equilibrium water content, de/rehydration behaviour and amount of bound water.

Multifunctional polyelectrolytes based on 2-acrylamido-1 -methyl-1- propane sulfonic acid (AMPS), a polyelectrolyte with low critical solution temperature (LCST), and a polyelectrolyte containing carboxy groups, were synthesised and used as dopants during electropolymerisation of pyrrole. Polypyrrole doped with these polyelectrolytes was prepared potentiostactically and investigated using conventional EC methods. It was found that the chemical composition of the polyelectrolytes significantly affected the polymer formation. With higher AMPS ratio in the polyelectrolytes, deposition potentials decreased. Polypyrrole doped with these polyelectrolytes exhibited redox properties typical of polypyrrole and had high water content. The properties of the resultant polymer films did not vary significantly with temperature. Adhesion of the conducting polymer films to metal substrates was found to be dependant on the carboxy content of the polyelectrolyte.

The production of conducting polymer within processable hydrogel blends for large scale coating operations was investigated in a qualitative manner. Firstly, a multiblock copolymer consisting of PEO (polyethylene oxide) and ε-caprolactone was synthesised for the preparation of soluble hydrogel/conducting polymer blends. Secondly, thermal crosslinking of a viscous mixture of poly(acrylic acid) and a glycol compound ("polyester hydrogel)" containing polypyrrole colloids was carried out. Thirdly, simultaneous cathodic electropolymerisation of acrylamide and electrocoagulation of conducting polymer colloids was conducted to form a conducting polymer/hydrogel blend on the cathode surface. It was found that the concentration of conducting polymer in the hydrogels significantly affected the electrochemical and physical properties of the blends. An increased concentration of conducting polymer in the hydrogels resulted in good electroactivity and conductivity, but poor mechanical properties.

A potential industrial application of the processable hydrogel and polypyrrole blends was investigated. The potentiodynamic technique was used to assess the corrosion protection capabilities of polymer coatings on aluminum. It was found that that the poly(acrylamide) hydrogel/PPy blend provided some corrosion resistance to aluminium.

The level provided depended on the counterion used for the oxidation of polypyrrole. However, the other hydrogel/conducting polymer blend had insignificant effect on anodic corrosion protection of aluminium.

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