This thesis describes the development of high performing low-cost and low-power ammonia sensors on plastic substrates using solution processing techniques. As a part of the Marie Curie Initial Training Networks, FlexSmell project aimed at the realisation of such sensors as elements of a sensing system on flexible tags for wireless compatible applications. Ammonia was selected as the target analyte due to its importance in many application fields including food industry, air and water quality monitoring. Polyaniline, a conjugated polymer, was used as the sensing layer for chemiresistive detection of ammonia because of its well-known gas sensing properties. Two distinctive strategies were adapted to tackle doped polyaniline’s lack of solution processablity. Firstly, dopant engineering was utilised to prepare doped polyaniline formulations in aprotic solvents such as n-methyl-2-pyrrolidone. Hybrid composites were then prepared by simply mixing the polyaniline solutions and carbon nanoparticles. Sensors made by spin coating the polyaniline hybrid composites on plastic substrates operating at ~80 °C showed sensitivities more than 6 times higher than that of a commercial metal oxide sensor when exposed to sub-ppm concentrations of ammonia in air. The incompatibility of the multifunctional dopants used in this method with printed electronics, as well as the high boiling point and toxicity of the solvent led to the second approach. A two-step vapour-phase deposition polymerisation method was exploited to in-situ polymerise different polymeric acid-doped polyaniline thin films on plastic substrates. Polyaniline sensors doped with poly(4-styrenesulphonic acid), demonstrated sensitive response to sub-ppm concentrations of ammonia vapour under both dry and humid conditions. These sensors showed enhanced recovery and repeatability when operated at elevated temperatures. Moreover, room temperature ammonia sensors were realised using Nafion as the dopant. Finally, ammonia sensors were made on small (~1 mm^2) printed polymeric micro-hotplates using a vapour-phase deposited polyaniline sensing layer in order to allow reliable operation at ~95 °C with power consumptions as low as 35 mW. Such low-cost, low-power, sensitive and selective ammonia chemiresistors may be incorporated in smart RFID tags for food, air and water quality monitoring.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:618087 |
| Date | January 2014 |
| Creators | Danesh, Ehsan |
| Contributors | Persaud, Krishna |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/novel-polyanilinebased-ammonia-sensors-on-plastic-substrates(2c9f641e-fc69-49ea-886f-fdd888dc076c).html |
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