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Research into the processing conditions and parameters of polymeric nanocomposites has always been challenging to scientists and engineers alike. Many have developed tools and procedures to allow materials to be exploited and their properties improved with the addition of nanofillers to achieve the desired end material for various applications. Initial trials are mostly conducted using conventional small scale experiments using specialised equipment within the laboratory that can replicate the larger industrial equipment. This is a logical approach as it could save time and costs as many nanocomposites are relatively expensive to produce. Experiments have previously been done using the likes of the Haake twin screw extruder to manufacture nanocomposites within the laboratory but this research project has used a novel minimixer specifically developed to replicate mixing like large twin screw extrusion machines. The minimixer uses a twin paddle system for high shear mixing in conjunction with a single screw thus theoretically allowing an infinitely long recirculation. It is this ability to mix intensely whilst allowing for as long as desired recirculation which enables the replication in this very small mixer (10-30g capacity) of the mixing conditions in a large twin screw extruder. An added feature of the minimixer is that it can undertake inline data analysis in real time. The main experiments were conducted using a comprehensive DOE approach with several different factors being used including the temperature, screw speed, residence time, clay and compatibiliser loading and two polymer MFI¿s. The materials used included PP, Cloisite 20A, Polybond 3200, PET, Somasif MTE, Polyurethane 80A and Single / Multi-walled Carbon nanotubes. Detailed experimental results highlighted that rheological analysis of the nanocomposite materials as an initial testing tool were accurate in determining the Elastic and Loss modulus values together with the Creep and Recovery, Viscosity and Phase Angle properties in the molten state. This approach was also used in an additional set of experiments whereby the temperature, speed, residence time and compatibiliser were kept constant but the clay loading was increased in 1% wt. increments. These results showed that the G¿ & G¿¿ values increased with clay loading. Another important finding was the bi-axial stretching step introduced after the processing stage of the nanocomposite materials which highlighted a further improvement in the modulus values using rheological testing. Other tests included using inline monitoring to look into both the viscosity and ultrasound measurements in real time of the molten polymer nanocomposite through a slit die attachment to the minimixer. / EPSRC

In this work, we performed an experimental analysis using a two-dimensional semiconducting transition metal dichalcogenide (TMD), specifically tungsten diselenide (WSe2), for gas sensor applications. Our method entailed building a chemically liquid exfoliated WSe2 gas sensing device with gold (Au) electrodes to measure its reaction and sensitivity to environmental gasses such as CO2 and N2. The 2D thin film was created through a solution processing method and electrically coupled in a two-terminal configuration; photonic curing system along with the hot plate annealing process was used on the thin film for rapid annealing, enhancing particle connectivity, stable crystal structure, and increasing overall electrical conductivity. The inkjet printing technology is used to explore the potential of the 2D thin film fabrication process that defines a well-controlled and scalable additive manufacturing process at the nano level that makes it possible to develop next-generation flexible devices. The additive nano-manufacturing process allowed us to establish the film's structure and chemical properties before measuring the electrical characteristics of the films when exposed to CO2 and N2 gases at room temperature. To explore and validate the sensitivity to human interaction with the gas-sensing device, we carried out further experiments with direct exposure to human breath in an open environmental space which shows a promising landmark for developing a next-generation flexible breath-sensing device.

Actuellement, les supercondensateurs sont au centre de beaucoup de recherches. Ils offrent une solution potentielle pour le stockage réversible de l´énergie que ce soit pour le domaine spatial, aéronautique ou encore le transport (véhicules hybrides). Un axe de recherche important, visant à augmenter les densités d'énergie et de puissance, est consacré aux systèmes oxydes de métaux de transition /charbon actif (C) asymétriques. Les systèmes à base de RuO2 présentent les capacités les plus élevées, supérieures à 700 F/g, mais leur coût et leur toxicité limitent leur application aux petits appareils électroniques. Des oxydes moins coûteux tels que les oxydes de cobalt (notamment Co3O4), MnO2, V2O5, Fe3O4, NiO, Ni(OH)2, ainsi que des polymères conducteurs électroniques, ont été étudiés de manière approfondie au cours des dernières décennies jusqu’à être utilisés, pour certains, dans des dispositifs commerciaux. Mais aucun système n’a été aussi étudié que le C / MnO2. En effet, il a été démontré que ce dernier est particulièrement intéressant car il peut fonctionner dans des milieux aqueux à des tensions pouvant aller jusqu’à 2V tout en gardant une bonne stabilité électrochimique durant le vieillissement. Néanmoins, les performances du système, en particulier en termes de densité de puissance, sont limitées à cause de la mauvaise conductivité électronique du MnO2. Il est possible de surmonter ce problème en ajoutant à l’oxyde de manganèse, des matériaux conducteurs à base de carbone (noir de carbone, nanotubes de carbone…) ou encore, en développant des stratégies de greffage ou de décoration plus élaborées. La combinaison d’oxydes avec des espèces carbonées est très largement rapportée dans la littérature alors que le mélange d’oxydes de différente nature l’est beaucoup moins. Nous proposons dans ce projet de synthétiser et de développer des matériaux originaux améliorant, par un effet synergique, les propriétés intéressantes du manganèse, du cobalt et de l'oxyde / hydroxyde de nickel. Les inconvénients de chaque composant étant compensés par les bonnes propriétés complémentaires des autres. Nous cherchons à réunir en un seul matériau (ou composite), le bon comportement pseudocapacitif du manganèse, la bonne conductivité électronique associée aux oxydes de cobalt, la grande capacité de l'hydroxyde de nickel ainsi que les propriétés de conduction du carbone. Ce projet de doctorat vise à concevoir et à fabriquer de nouvelles classes d'électrodes composites hybrides basées sur des assemblages de graphène (pour la capacitance renforcée à double couche) et d'oxydes poreux de métaux de transition (pour une capacité faradique supplémentaire due à de multiples processus rédox réversibles). Les avantages combinés du graphène et des oxydes de métaux de transition permettront aux supercondensateurs à haute densité d'énergie de travailler dans des électrolytes aqueux respectueux de l'environnement ce qui est, aujourd’hui, un besoin reconnu. / Supercapacitors are the focus of much research at the present time. They offer a potential solution for reversible energy storage in the fields of space, aircrafts or transportation (hybrid vehicles). An important research line, aiming at increasing both energy and power densities, is devoted to asymmetric transition metal oxides / activated carbon (C) systems. RuO2-based devices exhibit the highest capacitance, more than 700 F/g, but their cost limits the applications to small electronic devices. Less expensive oxides such as cobalt oxides (especially Co3O4), MnO2, V2O5, Fe3O4, NiO, Ni(OH)2, as well as electrically conducting polymers, have been extensively studied in the past decades, or used in commercial devices; they EACH exhibit each drawbacks and advantages with regard to applications. But no system has been investigated as much as the C/MnO2 one, which is particularly interesting because it can work in aqueous media at tensions up to 2 V, and high stability in ageing has been demonstrated. Nevertheless, the performances of the system, especially in terms of power density, are limited by the poor electronic conductivity of MnO2. This problem is usually solved by simply mixing conductive carbon materials (carbon black, CNTs…) with MnO2 or by developing more elaborated grafting or decoration strategies. The combination of oxide and carbonaceous species is widely reported in the literature, whereas combining oxides with different natures is less frequently encountered. We propose in this project to synthesize and develop original materials enhancing, through a synergistic effect, the interesting properties of manganese, cobalt and nickel oxide/hydroxide, the drawbacks of each component being overbalanced by the good complementary properties of the other components. We aim at gathering in one single material (or composite), the good pseudocapacitive behavior of manganese, the good electronic conductivity associated to cobalt oxides, the high capacity of nickel hydroxide, as well as the enhanced conduction properties of carbon. The present PhD project aims at designing and manufacturing new classes of hybrid composite electrodes based on assemblies of graphene (for enhanced double layer capacitance) and porous transition metals oxides (for additional faradaic capacitance due to multiple reversible redox processes) directly applied on metallic current collectors. The combined advantages of graphene with those of transition metals oxides will enable supercapacitors with high energy density, working in environmentally friendly aqueous electrolytes, which are an acknowledged need. / A procura crescente de energia em setores distintos, como residencial, transporte e industrial, bem como a proliferação de fontes renováveis de produção de energia, exigem novos e mais eficientes dispositivos de armazenamento de energia. Consequentemente, tem-se observado um interesse crescente na produção e engenharia de materiais para armazenamento de energia. Muito dos esforços de R&D estão centrados no desenvolvimento de materiais nanoestruturados que possam responder aos requisitos da aplicação, tais como densidade de energia, densidade de potência e estabilidade face à ciclagem do dispositivo. Presentemente são muitos os materiais investigados como potenciais candidatos para elétrodos para dispositivos de armazenamento de energia por via eletroquímia, nomeadamente baterias, condensadores, pseudocondensadores ou supercondensadores. O objetivo do presente trabalho é produzir e estudar novos materiais com uma resposta eletroquímica intermédia entre um elétrodo típico de supercondensador e um elétrodo típico de bateria, também conhecidos como elétrodos híbridos. Por essa razão, selecionaram-se hidróxidos e óxidos de níquel e cobalto devido à sua elevada atividade eletroquímica e baixo custo. Estes materiais foram combinados com derivados de grafeno, que exibem alta condutividade e elevada área superficial ativa. Portanto, este trabalho foca a síntese e caracterização fisico química e eletroquímica de hidróxidos e óxidos de níquel-cobalto nanoestruturados e sua combinação com óxido de grafeno reduzido para aplicações de armazenamento de energia. A síntese foi efectuada por duas vias distintas: eletrodeposição e exfoliação. A eletrodeposição é usada para obter hidróxidos e óxidos de níquel-cobalto em combinação com óxido de grafeno reduzido. Os resultados evidenciam um efeito sinérgico quando o óxido de grafeno reduzido é combinado com o (hidr)óxido de níquel- cobalto, isto é, um aumento na capacidade, condutividade e estabilidade do compósito quando comparado com o (hidr)óxido de níquel-cobalto. Neste trabalho é dada especial atenção à espectroscopia de impedância eletroquímica que foi utilizada para avaliar os fenômenos que ocorrem durante a carga e descarga contínua e compreender os processos que ocorrem no material ativo e que resultam na sua degradação. O hidróxido de níquel-cobalto é também preparado por exfoliação, em meio aquoso, por meio da intercalação de lactato, enquanto o tetra-butilamónio é utilizado na exfoliação do óxido de níquel-cobalto. A resposta eletroquímica é avaliada em diferentes eletrólitos após reconstrução. Os resultados revelam a influência das espécies intercaladas durante o processo de exfoliação: quando a exfoliação é realizada para fins de armazenamento de energia, as espécies intercaladas e a força da interação com o material ativo devem ser consideradas de antemão para evitar o bloqueio superficial ou inibição da interação elétrodo-eletrólito. Os resultados mostraram que a exfoliação é uma rota promissora para aumentar a área de superfície ativa dos materiais, um parâmetro crítico no desempenho eletroquímico dos materiais dos eletrodos. Nesta dissertação é também estudado o mecanismo de carga-descarga do hidróxido de níquel-cobalto, que ainda não está completamente entendido. Assim, compreender esse mecanismo é um passo crítico para otimizar a morfologia e o desempenho do material e para projetar futuros dispositivos de armazenamento de energia. Para esclarecer os processos que ocorrem durante a carga, aplica-se o modelo de Mott-Schottky foi aplicado parade modo a avaliar a variação da conductividade do material e da sua capacidade na interface elétrodo-eletrólito. [...]

Η παρούσα προοπτική ελεγχόμενη κλινική μελέτη διεξήχθη για να ερευνήσει τη συσχέτιση του συνδρόμου αποφολίδωσης με τη νευροαισθητήρια απώλεια ακοής. Τα άτομα της ομάδας μελέτης εμφάνιζαν το σύνδρομο στον ένα ή αμφοτέρους τους οφθαλμούς, ενώ τα άτομα της ομάδας ελέγχου δεν εμφάνιζαν το σύνδρομο σε κανένα οφθαλμό. Κριτήρια αποκλεισμού από τη μελέτη ήταν: προηγηθείσα ωτολογική επέμβαση, οξείες ή χρόνιες ωτολογικές παθήσεις, τραύμα κεφαλής ή ωτός, έκθεση σε θόρυβο, λήψη ωτοτοξικών φαρμάκων, λοίμωξη ανωτέρου αναπνευστικού συστήματος, γλαύκωμα, οφθαλμική υπερτονία και διάφορες συστηματικές παθήσεις. Οι συμμετέχοντες υπεβλήθησαν σε μέτρηση οπτικής οξύτητας, βιομικροσκόπηση, τονομέτρηση, γωνιοσκοπία, βυθοσκόπηση μετά από μυδρίαση, εξέταση οπτικών πεδίων, επισκόπηση και ψηλάφηση ώτων, ωτοσκόπηση, εξέταση ρινοφάρυγγα, εξέταση με τονοδότες και ακοομετρία καθαρών τόνων. Κατά την ακοομετρία υπολογίστηκε για κάθε ους ο ουδός ακοής, για την αέρινη και την οστέινη αγωγή, στις συχνότητες των 0.25, 0.5, 1, 2, 4 και 8kHz. Συνολικά έλαβαν μέρος στη μελέτη 69 άτομα (47 στην ομάδα μελέτης και 22 στην ομάδα ελέγχου). Η μέση ηλικία των συμμετεχόντων ήταν 74,7 ετών και στις δύο ομάδες. Δεν υπήρξαν στατιστικά σημαντικές διαφορές στην κατανομή ηλικιών και φύλων ανάμεσα στις δύο ομάδες. Σε όλους τους εξετασθέντες οι ουδοί ακοής αέρινης και οστέινης αγωγής ήταν ταυτόσημοι για κάθε συχνότητα, γεγονός που υποδήλωνε αμιγή νευροαισθητήρια απώλεια ακοής ή φυσιολογική ακοή. Δεν προέκυψαν κλινικά σημαντικές διαφορές, μεταξύ ουδών ακοής δεξιού και αριστερού ωτός, σε κανένα άτομο. Τα άτομα της ομάδας μελέτης, σε σύγκριση με εκείνα της ομάδας ελέγχου, παρουσίασαν: Α) Σημαντικά υψηλότερα ποσοστά επιπολασμού απώλειας ακοής στις συχνότητες των 1, 2, 4 και 8kHz. Β) Σημαντικά υψηλότερους μέσους ουδούς ακοής και σοβαρότερη απώλεια ακοής στις συχνότητες των 4 και 8kHz. Η μεγαλύτερη διαφορά στη σύγκριση των μέσων ουδών ακοής παρατηρήθηκε στα 8kHz. Τα ανωτέρω αποτελέσματα συνηγορούν υπέρ πολλαπλής συσχέτισης του συνδρόμου αποφολίδωσης με τη νευροαισθητήρια απώλεια ακοής και αφενός επιβεβαιώνουν μαρτυρίες από προηγούμενες έρευνες, αφετέρου παρέχουν ένα εντελώς νέο εύρημα που είναι η στατιστικά σημαντική επίδραση του συνδρόμου στη σοβαρότητα απώλειας ακοής στις υψηλές συχνότητες. Σε σύγκριση με προηγούμενες μελέτες, η παρούσα μελέτη πλεονεκτεί διότι η διερεύνηση της επίδρασης του συνδρόμου στον επιπολασμό και στη σοβαρότητα απώλειας ακοής έγινε με πιο αναλυτική διαδικασία, ετέθησαν λεπτομερέστερα κριτήρια αποκλεισμού υποψηφίων, o ακοομετρικός έλεγχος αφορούσε σε μεγαλύτερο αριθμό συχνοτήτων και αποκλείστηκαν γλαυκωματικοί ασθενείς, ώστε η σχέση μεταξύ συνδρόμου αποφολίδωσης και απώλειας ακοής να εξεταστεί με πιο αντικειμενικό τρόπο. Τα ευρήματα της παρούσας μελέτης επαληθεύουν τη θεωρία ότι το σύνδρομο αποφολίδωσης δεν αποτελεί μόνο οφθαλμολογική πάθηση, αλλά συστηματική διαταραχή με πολυάριθμες επιπλοκές, μία εκ των οποίων αφορά το έσω ους. Συνεπώς, στους ασθενείς με σύνδρομο αποφολίδωσης, εκτός από την οφθαλμολογική εξέταση, συνιστάται η εκτίμηση της ακουστικής ικανότητας με ακοομετρική δοκιμασία. / The present prospective case control clinical study was conducted to investigate the relationship between exfoliation syndrome and sensorineural hearing loss. Study group subjects manifested the syndrome in one or both eyes, whereas control group subjects didn’t manifest the syndrome in either eye. Exclusion criteria from the study were: previous ear surgery, acute or chronic ear diseases, ear or head trauma, noise exposure, oto-toxic drug intake, upper respiratory system infection, glaucoma, ocular hypertension and various systemic diseases. All participants underwent visual acuity measurement, biomicroscopy, tonometry, gonioscopy, dilated fundoscopy, visual field testing, ear inspection and palpation, otoscopy, nasopharyngeal examination, tuning fork testing and pure-tone audiometry. During audiometry the hearing threshold was calculated for every ear, using air and bone conduction, at frequencies of 0.25, 0.5, 1, 2, 4 and 8kHz. A total of 69 subjects participated in the study (47 in study group and 22 in control group). Mean age of participants was 74.7 years in both groups. Differences in age and gender distribution between the two groups were not statistically significant. Hearing thresholds were identical for both air and bone conduction, in all examined subjects at each frequency, signifying pure sensorineural hearing loss or normal hearing. No clinically significant differences were found, between hearing thresholds of left and right ear, in any subject. Compared to control group, study group subjects displayed: A) Significantly higher prevalence rates of hearing loss at frequencies of 1, 2, 4 and 8kHz. B) Significantly higher mean hearing thresholds and more severe hearing loss at frequencies of 4 and 8kHz. The greatest difference in the comparison of mean hearing thresholds was observed at 8kHz. The above results advocate for a multiple association between exfoliation syndrome and sensorineural hearing loss and on the one hand support evidence from previous research, on the other hand provide a totally new finding, that is the statistically significant effect of the syndrome on severity of hearing loss at high frequencies. Compared to previous studies, the present study has advantages because the syndrome effect on prevalence and severity of hearing loss was investigated in a more thorough manner, the candidate exclusion criteria were more detailed, audiometric testing involved a greater number of frequencies and glaucomatous patients were excluded, in order the relationship between exfoliation syndrome and hearing loss to be examined in a more objective way. The findings of the present study verify the theory that exfoliation syndrome is not only an ocular disease, but also a systemic disorder with numerous complications, one of which concerns the inner ear. Consequently, in patients with exfoliation syndrome, besides the ophthalmologic examination, an assessment of hearing ability with audiometric testing is recommended.