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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Investigation of the electrode/electrolyte interface using ultra fast electrochemical ellipsometry

Abel, Julia Catherine January 2001 (has links)
Electrochemical ellipsometry is employed to determine the real and imaginary parts of the refractive index and the thickness of thin films as functions of the potential applied to the electrode upon which the film is grown. The relatively recent advent of an analyser with no moving parts, the Stokesmeter, has removed previous time restraints and allows microsecond resolution. The Newcastle system is extremely novel, using a Stokesmeter, and thus being capable of 325 gs resolution, and also being electrochemically interfaced. The ellipsometric studies have concentrated on the growth and behaviour of a series of electroactive polymers derived from salicylaldehydes (Salens). [Ni(SaltMe)] and [Ni(SaIdMe)] were found to yield stable homogeneous films upon polymerisation, however while the behaviour during film growth was similar, marked differences were observed during potential cycling, poly[Ni(SaIdMe)] showing a marked decrease in thickness near the anodic limit not observed for poly[Ni(Saltme)], indicating that even minor changes to ligand structure well away from the site of polymerisation may have significant effects on the resulting film. The behaviour of poly[Ni(OMeSaltMe)] during polymerisation is more complicated; initially a homogeneous film is produced, however about half way through the growth process the film becomes inhomogeneous, and remains so during subsequent potential cycling. This behaviour was also observed for poly[Pd(OMeSalen)], indicating electron donating groups around the phenyl rings of the ligand have a profound effect on the nature of the polymer films, possibly far more so than the identity of the central metal.
2

DC & AC Transport In Conducting Polymers And Devices

Mukherjee, Ayash Kanto 06 1900 (has links) (PDF)
No description available.
3

OPTIMIZATION OF THE OPTICAL AND ELECTROCHEMICAL PROPERTIES OF DONOR-ACCEPTOR COPOLYMERS THROUGH FUNCTIONAL GROUP AND SIDE CHAIN MODIFICATION

Seger, Mark J. 01 January 2013 (has links)
Donor-acceptor copolymers have received a great deal of attention for application as organic semiconductors, in particular as the active layers in low-cost consumer electronics. The functional groups grafted to the polymer backbones generally dictate the molecular orbital energies of the final materials as well as aid in self-assembly. Additionally, the side chains attached to these functional groups not only dictate the solubility of the final materials, but also their morphological characteristics. The bulk of the research presented in this dissertation focuses on the synthesis and structure-property relationships of polymers containing novel acceptor motifs. Chapter 2 focuses on the synthesis of 1,2-disubstituted cyanoarene monomers as the acceptor motif for copolymerization with known donors. It was found that cyanation of both benzene and thiophene aromatic cores resulted in a decrease of the molecular orbital energy levels. Additionally, the small size of this functional group allowed favorable self-assembly and close π-stacking to occur relative to related acceptor cores carrying alkyl side chains as evidenced by UV-Vis and WAXD data. Chapter 3 describes the systematic variation of side chain branching length and position within a series of phthalimide-based polymers. Branching of the side chains on bithiophene donor units resulted in the expected increase in solubility for these materials. Furthermore, a correlation was found between the branching position, size, and the HOMO energy levels for the polymers. Additionally, it was demonstrated that branching the alkyl side chains in close proximity to polymer backbones does not disrupt conjugation in these systems. A novel acceptor motif based on the 1,3-indanedione unit is presented in Chapter 4. Despite the stronger electron withdrawing capability of this functional group relativeto phthalimide, it was found that polymers based on this unit have the same HOMO molecular orbital energy levels as those presented in Chapter 3. It was found, however, the presence of orthogonal side chains greatly enhanced the solubility of the final polymers. Additionally, UV-Vis and WAXD measurements revealed that thermal annealing had a profound effect on the ordering of these polymers. Despite the presence of orthogonal side chains, long range order and close π-stacking distances were still achieved with these materials. Finally, alkynyl “spacers” were used in Chapter 5 to separate the solubilizing alkyl side chains from the polymer backbones on bithiophene donor monomers. The alkynyl groups allowed for conjugated polymer backbones to be achieved as well as low HOMO energy levels. A correlation between the side chain size, π-stacking distances and HOMO-LUMO energy levels was measured in this polymer series.
4

Conducting Polymers Containing In-Chain Metal Centres : Electropolymerisation and Charge Transport

Hjelm, Johan January 2003 (has links)
<p>Conjugated polymers that exhibit high electronic conductivities play key roles in the emerging field of molecular electronics. In particular, linking metal centres with useful electrochemical, photophysical, or catalytic properties to the backbone, or within the polymer chain itself, is a topic which has attracted a significant amount of interest lately. Structurally rigid monomers that can be electropolymerised to form highly conducting molecular wires may provide new insights into conduction mechanisms, e.g., exploiting resonant superexchange (electron-hopping) by tuning the energies of redox centre and bridge states. The focus of this thesis lies on the electrochemical investigation of preparation, growth dynamics, and charge transport dynamics of oligothiophene/transition metal hybrid materials. The incorporation of ruthenium(II) and osmium(II) terpyridine complexes into such polymeric assemblies was accomplished by an electropolymerisation procedure, to produce rod-like oligothienyl-bridged metallopolymers. The properties of the monomers used were characterised by optical spectroscopy and electrochemical techniques. Charge transport was studied in detail for some of the materials created, and it was found that the electron transport rate and dc conductivity was enhanced by up to two orders of magnitude compared to relevant non-conjugated polymers, demonstrating the usefulness of this approach for optimization of charge transport in metallopolymers. The charge transport diffusion coefficent was determined to (2.6 ± 0.5) x 10<sup>-6</sup> cm<sup>2</sup> s<sup>-1</sup> for a quaterthienyl-bridged {Os(tpy)<sub>2</sub>} polymer by use of an electrochemical steady-state method carried out using a transistor-like experimental geometry. It was found that charge transport in these materials is concentration-gradient driven. The rate limiting step of the charge transport process was investigated using electrochemical impedance spectroscopy. The electropolymerisation dynamics of one of the monomers was studied using microelectrodes, and the results obtained shows that electropolymerisation is highly efficient, and indicate that mass transport controls this process. Through a combination of controlled potential deposition and SEM imaging it was demonstrated that it is possible to exploit the edge effect of microelectrodes to promote film growth in a direction co-planar with the electrode surface.</p>
5

Conducting Polymers Containing In-Chain Metal Centres : Electropolymerisation and Charge Transport

Hjelm, Johan January 2003 (has links)
Conjugated polymers that exhibit high electronic conductivities play key roles in the emerging field of molecular electronics. In particular, linking metal centres with useful electrochemical, photophysical, or catalytic properties to the backbone, or within the polymer chain itself, is a topic which has attracted a significant amount of interest lately. Structurally rigid monomers that can be electropolymerised to form highly conducting molecular wires may provide new insights into conduction mechanisms, e.g., exploiting resonant superexchange (electron-hopping) by tuning the energies of redox centre and bridge states. The focus of this thesis lies on the electrochemical investigation of preparation, growth dynamics, and charge transport dynamics of oligothiophene/transition metal hybrid materials. The incorporation of ruthenium(II) and osmium(II) terpyridine complexes into such polymeric assemblies was accomplished by an electropolymerisation procedure, to produce rod-like oligothienyl-bridged metallopolymers. The properties of the monomers used were characterised by optical spectroscopy and electrochemical techniques. Charge transport was studied in detail for some of the materials created, and it was found that the electron transport rate and dc conductivity was enhanced by up to two orders of magnitude compared to relevant non-conjugated polymers, demonstrating the usefulness of this approach for optimization of charge transport in metallopolymers. The charge transport diffusion coefficent was determined to (2.6 ± 0.5) x 10-6 cm2 s-1 for a quaterthienyl-bridged {Os(tpy)2} polymer by use of an electrochemical steady-state method carried out using a transistor-like experimental geometry. It was found that charge transport in these materials is concentration-gradient driven. The rate limiting step of the charge transport process was investigated using electrochemical impedance spectroscopy. The electropolymerisation dynamics of one of the monomers was studied using microelectrodes, and the results obtained shows that electropolymerisation is highly efficient, and indicate that mass transport controls this process. Through a combination of controlled potential deposition and SEM imaging it was demonstrated that it is possible to exploit the edge effect of microelectrodes to promote film growth in a direction co-planar with the electrode surface.

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