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Title: Ultra-low voltage electrowetting
Author: Cousens, Nico
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2013
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Electrowetting, the manipulation of surface wettability with an electric field, is an emerging technology used in next generation displays and cameras. This has been made possible by the development of 'electrowetting -on- die lectric' by Berge in 1993. Howev er, such a system operates on large voltages poorly suited to portable devices. In recent years, theoretical and experimental results have suggested that electrowetting using the interface between two immiscible electrolyte solutions (ITIES) may provide a solution to this problem. By applying less than 1 V to such a system, it is possible to induce substantial changes in the wettability - and hence the shape - of liquid droplets. However, there is a large degree of hysteresis in such a system meaning that there is a poor correlation between droplet shape and applied potential. Furthermore, the stability of the ITIES over long periods is of concern. This thesis attempts to address the current problems with ITIES electrowetting highlighted above. By moving to smoother and more lubricated surfaces, a substantial reduction in hysteresis was seen. These surfaces were produced by template stripping. In addition, several other surfaces were prepared as potential electrowetting substrates. These involved surface functionalisation by plasma treatment or the reduction of diazonium compounds; preparation of ultra smooth glassy carbon and preparation of a hydrophobic conducting polymer. The potential range over which an ITIES is stable was also improved with the use of a novel mixed organic solvent phase. By optimising the electrode and electrolyte compositions, an electrowetting system operating on less than 1 V with a contact angle range of 53 o and a gap of only 100 mV between forward and reverse scans was possible. Other electrowetting systems with no hysteresis were also developed, although these did not operate within the potential limits defined by the onset of Faradaic processes.
Supervisor: Kucernak, Anthony Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral