Year

2012

Degree Name

Doctor of Philosophy

Department

School of Chemistry

Abstract

Carrageenan is an anionic, water soluble biopolymer which is well known for its gelforming capabilities. To date it has been mainly employed in the food processing industry and for medical applications. This project aimed to assess its ability to form composite materials with conducting fillers such as carbon nanotubes (CNTs) and conducting polymers (CPs).

As a result of the research conducted for this thesis, the biopolymer carrageenan was found to act as an excellent dispersant of CNTs and as a dopant during the polymerisation of CPs such as polyaniline (PANi) and polypyrrole (PPy). In addition, carrageenan was shown to have the appropriate flow properties to act as a thickener for the controlled dispensing of carbon nanotube networks. Four wet-processing methods were used to fabricate the composite dispersion into films: evaporative casting, vacuum filtration, inkjet printing and extrusion printing. Rheological studies indicate that 0.8% w/v and 0.5% w/v were the appropriate ι-carrageenan (IC) and κ-carrageenan (KC) concentrations, respectively, for dispersing CNTs. Multi-walled nanotubes (MWNTs) required less sonic energy (0.96 kJ/mg) than single-walled nanotubes (SWNTs) (1.68 kJ/mg) to complete the dispersion process.

The synthesis method, dopant type and dialysis treatment used affect the properties of the obtained PANi-carrageenan and PPy-carrageenan composite films. Incorporation of MWNTs results in a change in surface morphology, increase in conductivity and reinforcement of films at a cost in ductility. Inclusion of MWNTs also improves thermal stability of the composite film relative to those without MWNTs.

It was demonstrated that the contact angle which is used to compare the properties of films prepared by vacuum filtration with those prepared by evaporative casting, is proportional to the CNT mass and volume fraction. The electrical conductivity for MWNT films prepared by the evaporative cast method was higher than that of SWNT films at similar CNT mass and volume fractions. The opposite trend was recorded for the vacuum filtration method. Composite films prepared by evaporative casting were stiffer and more flexible than those prepared by vacuum filtration. Varying either the absolute amount of CNTs or IC while keeping the other value constant resulted in different physical properties. It was shown that the electrical properties are governed by the relative amounts of mass of CNTs and biopolymer while the mechanical properties are determined by absolute amounts of mass. The addition of plasticiser (glycerin) improved the mechanical handle-ability, but at a cost in electrical conductivity.

Conducting MWNT tracks were produced by inkjet and extrusion printing using IC and a Newtonian fluid, glycerin (G), as dispersants. The conductivity values of extruded GMWNT tracks was two-orders of magnitude higher compared to that for IC-MWNT printed tracks. It was found that the substrate nature played an important role in the width and cross-sectional area of the printed tracks. Solid substrates (glass) resulted in a larger width and cross sectional area compared to the narrower but higher tracks printed onto absorbing IC films.

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