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Title: Characterisation and optimisation of carbazole modified polysiloxanes for electrochromic applications
Author: Bartlett, I. D.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1999
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Novel molecular materials have been the focus of a dynamic international research effort in recent years, due to their many possible applications. One such application is electrochromic devices. This thesis is concerned with the electrochromic properties of Carbazole Modified Polysiloxanes (CMPs). Electrical cross-linking forms thin films of electrochromic material adherent to either Gold of Indium Tin Oxide (ITO) substrates. Film preparation conditions are studied using analysis techniques, with constant current deposition at 50μAcm-2 found optimal. Thin films of CMP are found to be transparent in the reduced state, and deep green in the oxidised state, similar to the colour change of cross-linked polyvinyl carbazole. However the increased flexibility of the polysiloxane backbone leads to increased cross-linking efficiencies and therefore higher densities of dicarbazolyl moieties (colouration centres). Studies reveal the density in CMP films to be ≃ 1019-20cm-3. Cyclic voltammetry and potential-step chronoamperometry are used to study the dynamics of charge transfer in CMP films. The data suggests that the colouration step is rate limited by charge transfer across the electrolyte-film interface, while the bleaching step is controlled by a double charge extraction mechanism dependent on colour-ion mobility. Film lifetime, defined as the number of redox cycles a film may undergo whilst maintaining acceptable colour contrast, is measured under a wide range of conditions. Deposition conditions and switching potential are found to have a strong influence, whilst counter-ion choice (C1O4', PF6 or BF4) has only a weak influence. Film lifetimes of ≃ 3 x 103 are observed with contrast ratios of ≃ 9.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available