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published_or_final_version / Chemistry / Master / Master of Philosophy

According to different sources, from forty to sixty percent of the overall energy generated in the world today is squandered in waste heat. The existing energy conversion technologies are either close to their efficiency limits or too costly to justify their implementation. Therefore, the development of new technological approaches for waste heat recovery is highly demanded. The field of thermoelectrics can potentially provide an inexpensive, clean and efficient solution to waste heat underutilization, given that a new type of thermoelectric materials capable of meeting those requirements are available. This thesis reports on strategies to optimize a thermoelectric efficiency (ZT) of conducting polymers, more specifically poly(3,4-ethylenedioxythiophene) (Pedot). Conducting polymers constitute a special class of semiconductors characterized by low thermal conductivity as well as electrical conductivity and thermopower that can be readily modified by doping in order to achieve the best combination of thermoelectric parameters. Conducting polymers that have never previously been regarded as hypothetically compatible for thermoelectric energy conversion, can exhibit promising thermoelectric performance at moderate temperatures, which is a sought-after quality for waste heat recovery. A rather substandard thermoelectric efficiency of Pedot-Pss can be markedly improved by various secondary dopants whose addition usually improves polymer’s morphology accompanied by a drastic increase in electrical conductivity and, consequently, in ZT. In order to enable further enhancement in thermoelectric properties, the optimization of the charge carrier concentration is commonly used. The oxidation level of Pedot-Pss can be precisely controlled by electrochemical doping resulting in a tenfold increase of ZT. In contrast to Pedot-Pss, another conducting polymer Pedot-Tos exhibits superior thermoelectric performance even without secondary doping owning to its partially crystalline nature that allows for an improved electronic conduction. With the aid of a strong electron donor, positively doped Pedot-Tos gets partially reduced reaching the optimum oxidation state at which its thermoelectric efficiency is just four times smaller than that of Be2Te3 and the highest among all stable conducting polymers. The downsides associated with chemical doping of Pedot-Tos such as doping inhomogeneity or chemical dopants air sensitivity can be surmounted if the doping level of Pedot-Tos is controlled by acidity/basicity of the polymer. This approach yields similar maximum thermoelectric efficiency but does not necessitate inert conditions for sample preparation. Optimized Pedot-Tos/Pedot-Pss can be functionalized as a p-type material in organic thermogenerators (OTEG) to power low energy electronic devices. If printed on large areas, OTEGs could be used as an alternative technique for capturing heat discarded by industrial processes, households, transportation sector or any natural heat sources for electricity production.

Derivados do politiofeno são promissores para obtenção de sensores ópticos devido as suas propriedades crômicas, enquanto que polímeros azosubstituídos (azopolímeros) têm sido estudados para várias aplicações, tal como memórias ópticas. Neste trabalho procurou-se unir as propriedades dos derivados politiofênicos as dos azopolímeros através da preparação de um polímero tiofênico azosubstituído, obtido pela funcionalização do monômero tiofênico com um grupo azobenzênico. Para fins de comparação, foram também sintetizados um derivado polialquiltiofeno, o poli(3-octiltiofeno), e um copolímero formado a partir da união dos monômeros 3- octiltiofeno e do tiofeno azosubstituído. A obtenção do monômero azosubstituído foi feita a partir de uma reação de esterificação entre o ácido 3-tiofeno acético e o corante comercial vermelho disperso 1 (disperse red 1, DR1), ao passo que o monômero alquilado foi adquirido comercialmente. Os polímeros foram sintetizados por polimerização oxidativa com cloreto fénico e caracterizados químicoestruturalmente pelas técnicas de FTIR, 1H RMN, análise elementar, HPSEC e análise térmica (TG e DSC). Dessas análises comprovou-se a formação dos homopolímeros, mas não foi possível confirmar a formação do copolímero e ainda para esse caso, obteve-se uma menor quantidade de unidades azosubstituídas do que a pretendida. A análise da fotoluminescência destes materiais mostrou a influência do tipo de cadeia lateral na intensidade e no formato do espectro de emissão desses polímeros. A espectroscopia de UV-Vis foi utilizada para o estudo de suas propriedades crômicas, sendo observada a presença de termo- e solvatocromismo. O termocromismo foi analisado em solução e na forma de filmes e o solvatocromismo em soluções de solventes puros e em misturas de THF/ n-hexano com diferentes proporções. Esses polímeros também apresentaram alterações em seus espectros de absorção como resposta à variação do pH da solução. A birrefringência fotoinduzida, técnica de estudo visando a aplicação dos polímeros em memórias ópticas, somente foi observada para o homopolímero azosubstituído. Os resultados obtidos neste trabalho indicam que o politiofeno azosubstituído é um candidato promissor para elemento ativo em uma série de aplicações, tais como sensores de diversos tipos e em dispositivos de marcação oculta / Polythiophene derivatives are promising for optical sensors due to their chromic properties while azofunctionalized polymers have been used in several applications such as optical memories. In this work, an azosubstituted polythiophene was prepared by the functionalization of the thiophenic monomer with an azobenzene moiety in order to combine the polythiophene properties with those from the azopolymers. For the sake of comparison, a polyalkylthiophene, the poly(3- octylthiophene), and a copolymer of 3-octylthiophene and the azothiophene were synthesized. The azosubstituted monomer was synthesized by the esterification reaction of 3-thiopheneacetic acid and the commercial dye Disperse Red 1 (DRI), whilc the alkyl thiophene monomer was purchased. The polymers were prepared by oxidative polymerization reactions with ferric chloride and characterized chemically and structurally using FTIR, 1H NMR, elemental analysis and thermal analysis (TG and DSC) techniques. From these analyses, the formation of homopolymers was confirmed, but it was not possible to confirm the formation of the copolymer. In the latter, the amount of azosubstituted units was smaller than expected. The analysis of the polymers photoluminescence showed the influence of the side chain in the intensity and shape of the emission spectra. UV-Vis spectroscopy was used to study the polymer chromic properties which showed thermo- and solvatochromism. Thermochromism was analyzed in solution and in thin solid films and the solvatochromism was studied in pure solvent solutions and mixtures of THF/hexane in different ratios. These polymers also had their absorption spectra affected by changing the concentration of a protonic acid (HCI) solution. Photoinduced birefringence, aiming at optical memories applications, was only observed for the azosubstituted homopolymer. The overall results indicate that the azosubstituted polythiophene is promising as active material for several applications, such as different types of sensors and security-labeling devices

Filmes de politiofeno foram eletroquimicamente depositados em diversos substratos eletródicos em meio aquoso fortemente ácido e as características dos materiais formados foram estudadas através de técnicas voltamétricas, espectroscópicas (FTIR e UV-Vis. e raios X) e por microscopia eletrônica de varredura. As propriedades foram comparadas com as de filmes sintetizados em meio não-aquoso concluindo-se que o material produzido em meio aquoso mostra-se mais adequado para a aplicação como suporte de partículas eletrocatalisadoras, por sua maior atividade eletroquímica, homogeneidade e estabilidade. Foram então incorporadas partículas de Pd e Pt que foram investigadas quanto a ação catalítica frente as reações de oxidação de hidrogênio (ROH) e redução de oxigênio (RRO) em ácido sulfúrico 2,0 M. Os materiais produzidos foram primeiramente caracterizados através de técnica de absorção de raios X, tendo sido observada a formação de aglomerados de partículas bastante pequenas que não alteram seu estado de oxidação com a mudança do potencial eletródico. Verificou-se que ambos os catalisadores apresentam uma certa atividade inicial frente a ROH, mas o desempenho não é estável devido à ocorrência de processos degradativos da cadeia polimérica. Por outro lado, observou-se que os filmes contendo Pt apresentam elevada atividade catalítica frente a RRO, substancialmente maior que a de filmes contendo Pd. O mecanismo da reação mostrou-se dependente da natureza do catalisador, sendo também influenciado pelo contato com o filme polimérico. Para a Pt em contato direto com o eletrólito, a reação ocorre com envolvimento de 4 elétrons e com formação de água como produto final. Para o caso em que as partículas de Pt são recobertas por politiofeno, verifica-se a participação do peróxido de hidrogênio como intermediário, sendo que somente uma certa fração do mesmo reduz-se para formar água. No caso do Pd, o processo leva à formação de peróxido de hidrogênio em baixos sobrepotenciais, que depois é reduzido, com formação de água, em sobrepotenciais mais elevados. / Polythiophene films were electrochemically grown on several electrode substrates from strong acid aqueous solutions, and the characteristics of the materials investigated using cyclic voltammetry, FTIR and UV-Vis spectroscopies, and scanning electron microscopy. Compared to the materials prepared in non-aqueous media, the polymer synthesized in aqueous media shows more adequate characteristics for using as support for electrocatalytic particles, because of its higher electrochemical activity and stability, and bulk homogeneity. Particles of Pd and Pt were electrochemically incorporated on these polymer films, and the electrocatalytic properties of such composites investigated with respect to the hydrogen oxidation (HOR) and oxygen reduction (ORR) reactions in 2.0 M sulfuric acid solutions. Previously to these kinetic studies, the composites were characterized using X-ray absorption spectroscopy from which it is seen that the catalysts are deposited as agglomerates composed of very small particles whose oxidation states are not changed by changing the electrode potential. Both catalysts present some initial activity for the HOR, but the performance is not stable due to the occurrence of a degradation process involving the polymer chain. On the other hand, it is observed that the films containing Pt show an enhanced catalytic activity for the ORR which is considerably higher than of that containing Pd. The reaction mechanism is dependent on the catalyst nature and also influenced by the contact with a polymer film coating. For Pt in direct contact with the supporting electrolyte, the reaction occurs involving 4 electrons leading to water as final product. For Pt particles covered with a polymer layer, participation of hydrogen peroxide seems to be important with only a fraction of this specie being reduced to water. In the case of Pd, the process involves formation of hydrogen peroxide at low overpotentials, which is then reduced to water at higher overpotentials.

L’objet de cette thèse sera de réaliser et d’évaluer un démonstrateur électrochrome dont l’architecture repose sur l’empilement des trois pixels primaires (C) (M) et (J). Chaque pixel est contrôlé indépendamment en imposant une faible tension entre l’électrode frontale (sur laquelle repose le polymère électrochrome) et une contre-électrode. Lors des commutations, le polymère passe d’un état coloré à un état transparent et ce de manière réversible lorsque la tension est inversée aux bornes du dispositif. Plusieurs architectures de la brique pourront être envisagées. Enfin parmi les architectures retenues, les caractéristiques du dispositif seront évaluées essentiellement en terme de coordonnées colorimétriques (CIE L*a*b*), et de contrastes entre deux états optiques. D’autres aspect techniques tels que la tenue au cyclage, le vieillissement, la tenue d’un état optique en circuit ouvert… seront également évalués au cours de projet. / The purpose of this thesis is to implement and evaluate an electrochromic demonstrator whose architecture is based on the stacking of three primary pixels (C) (M) and (J). Each pixel is controlled independently by imposing a low voltage between the front electrode (where the electrochromic polymer is) and the counter-electrode. During switching, the polymer changes from a colored state to a transparent state and reversibly when the voltage is reversed. Several architectures of the brick could be considered. Finally, among the chosen architectures, device characteristics will be primarily evaluated in terms of color coordinates (CIE L * a * b *), and contrasts between the two optical states. Other technical aspects such as cycling, aging and holding an constant optical state in open circuit, will also be evaluated during the project.

Yip Hin-lap = 以PEDOT:PSS為本的高份子發光器件中銦的擴散之研究 / 葉軒立. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 113). / Text in English; abstracts in English and Chinese. / Yip Hin-lap = Yi PEDOT:PSS wei ben de gao fen zi fa guang qi jian zhong yin de kuo san zhi yan jiu / Ye Xuanli. / Abstract --- p.ii / 論文摘要 --- p.iv / Acknowledgements --- p.v / Table of Contents --- p.vi / List of Figures --- p.x / List of Tables --- p.xii / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / Chapter 1.1 --- Overview --- p.1 / Chapter 1.2 --- Conjugated Polymer --- p.3 / Chapter 1.2.1 --- Electronic and Geometric Configuration --- p.3 / Chapter 1.2.2 --- Charge Carriers --- p.7 / Chapter 1.2.3 --- Concept of Doping --- p.9 / Chapter 1.2.4 --- Electrical Conductivity and Charge Transport Mechanisms --- p.15 / Chapter 1.3 --- "Poly(3,4-ethylenedioxythiophene) [PEDOT]" --- p.16 / Chapter 1.4 --- Polymer Light Emitting Diodes --- p.20 / Chapter 1.4.1 --- Device Fabrication --- p.21 / Chapter 1.4.2 --- Material Design and Properties --- p.23 / Chapter 1.4.3 --- Interface and surface of PLED --- p.25 / Chapter 1.5 --- """Chemistry"" and Diffusion at Interface" --- p.27 / Chapter 1.6 --- Surface/Interface Modification with Self-Assembled Monolayers --- p.30 / Chapter 1.7 --- Aims of This Thesis --- p.33 / References --- p.34 / Chapter CHAPTER 2 --- INSTRUMENTATION --- p.38 / Chapter 2.1 --- X-ray Photoelectron Spectroscopy --- p.38 / Chapter 2.1.1 --- Fundamental Theory of XPS --- p.39 / Chapter 2.1.2 --- Qualitative Analysis using XPS --- p.43 / Chapter 2.1.2.1 --- Chemical Shifts --- p.43 / Chapter 2.1.2.2 --- Shake-up satellites --- p.45 / Chapter 2.1.2.3 --- Valence band structure --- p.45 / Chapter 2.1.3 --- Quantitative Analysis Using XPS --- p.46 / Chapter 2.1.4 --- Depth Profiling --- p.47 / Chapter 2.1.4.1 --- Non-Destructive Method Using Angled-Resolved XPS --- p.47 / Chapter 2.1.4.2 --- Destructive Method Using Ion Sputtering --- p.49 / Chapter 2.1.5 --- Instrumental Setup of XPS --- p.49 / Chapter 2.2 --- PLED Fabrication and Characterization System --- p.51 / Chapter 2.3 --- Current-Voltage-Luminescence (I-V-L) Measurement --- p.53 / Chapter 2.4 --- Electrical Measurement --- p.54 / Chapter 2.5 --- Kelvin Probe Measurement --- p.55 / Chapter 2.6 --- pH Measurement --- p.56 / Chapter 2.7 --- Film Thickness Measurement --- p.56 / Chapter 2.8 --- Contact Angle Measurement --- p.57 / References --- p.60 / Chapter CHAPTER 3 --- STABILITY OF PEDOT:PSS/ITO INTERFACE --- p.61 / Chapter 3.1 --- Introduction --- p.61 / Chapter 3.2 --- Sample Preparation --- p.62 / Chapter 3.3 --- Results and Discussion --- p.63 / Chapter 3.3.1 --- XPS of Core levels in PEDOT:PSS --- p.63 / Chapter 3.3.1.1 --- XPS of S 2p Core Level --- p.64 / Chapter 3.3.1.2 --- XPS of O Is Core Level --- p.66 / Chapter 3.3.1.3 --- XPS of C Is Core Level --- p.68 / Chapter 3.3.2 --- Composition Analysis of PEDOT:PSS Films --- p.71 / References --- p.80 / Chapter CHAPTER 4 --- ELECTRICAL AND ELECTRONIC PROPERTIES OF PEDOT:PSS WITH DISSOLUTED INDIUM --- p.81 / Chapter 4.1 --- Introduction --- p.81 / Chapter 4.2 --- Sample Preparation --- p.81 / Chapter 4.2.1 --- Four-Point Probe Measurement --- p.82 / Chapter 4.2.2 --- Current-Voltage Measurement --- p.82 / Chapter 4.2.3 --- Work Function Measurement --- p.83 / Chapter 4.2.4 --- XPS Experiment --- p.83 / Chapter 4.3 --- Results and Discussion --- p.85 / Chapter 4.3.1 --- Electrical Properties of PEDOT:PSS --- p.86 / Chapter 4.3.2 --- Electronic Properties of PEDOT:PSS --- p.89 / References --- p.97 / Chapter CHAPTER 5 --- BLOCKING REACTIONS BETWEEN ITO AND PEDOT:PSS WITH A SELF-ASSEMBLY MONOLAYER --- p.98 / Chapter 5.1 --- Introduction --- p.98 / Chapter 5.2 --- Sample Preparation --- p.99 / Chapter 5.3 --- Result and Discussion --- p.103 / Chapter 5.3.1 --- In Diffusion Blocking Effect by SAM --- p.103 / Chapter 5.3.2 --- PLED Devices Performance --- p.107 / References --- p.113 / Chapter CHAPTER 6 --- CONCLUSION --- p.114 / Chapter CHAPTER 7 --- FURTHER WORKS --- p.116