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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.
11

Filmes de Langmuir e Langmuir-Blodgett (LB) de azopolímeros com controle do tamanho da cadeia e posição dos cromóforos / Langmuir and Langmuir-Blodgett (LB) films of azopolymers with controlled chain-length and chromophores position

Felippe José Pavinatto 08 March 2006 (has links)
Azopolímeros apresentam propriedades de fotoisomerização, úteis para confecção de memórias ópticas, que dependem da arquitetura molecular do azopolímero e do filme formado a partir dele. Neste trabalho foram sintetizados polímeros com arquitetura molecular controlada, usando os azomonômeros [4-(N-etil-N-2-(metacriloxietil)) amino-2\'-cloro-4\'-nitroazobenzeno] (DR13MA) e [4-(N-etil-N-2-(metacriloxietil)) aminoazobenzeno] (MAEAMA). Para a síntese de homopolímeros e copolímeros em bloco foram utilizados dois métodos: NMRP - polimerização radicalar mediada por nitróxidos e ATRP - polimerização radicalar por transferência de átomo. Foram produzidos copolímeros dibloco, com um dos blocos contendo azocorantes, pela reação do monômero DR13MA com macroiniciadores poliestireno (PS) no método NMRP, e poli(metacrilato de metila) (PMMA) via ATRP. Homopolímeros de ambos os azomonômeros foram sintetizados por ATRP, e assim como os copolímeros em bloco mostraram cadeias com baixa polidispersividade. Complementando o trabalho de síntese, foram estudadas as propriedades dos materiais na interface ar-água, utilizando filmes de Langmuir, e procedeu-se a transferência dos mesmos para substratos sólidos formando filmes Langmuir-Blodgett (LB). Nos filmes de Langmuir foi observada a conformação e as interações (agregação) das moléculas dos materiais, destacadamente, no caso do homopolímero HPMAEA, foi observado um patamar próximo a 8 mN/m na isoterma de pressão de superfície, indicando haver reorganização do material no filme. Os filmes LB serviram como objeto de estudo das propriedades ópticas dos compostos, e no caso do homopolímero HPDR13 sintetizado via ATRP, pela primeira vez foi possível a realização de medidas em filmes puros do material. Medidas de armazenamento óptico foram realizadas para comprovar a aplicabilidade dos materiais em memórias ópticas. No caso do terpolímero PS-b-[MMA-co-DR13] sintetizado por NMRP, os resultados de armazenamento foram semelhantes aos obtidos com blendas. Para o homopolímero HPMAEA, uma grande influência do tipo de filme empregado (cast ou LB) foi observada no tempo de escrita das memórias, com o tempo para o filme LB sendo 26 vezes menor. Copolímeros em bloco PMMA-b-DR13 podem ser vantajosos por aliarem as propriedades ópticas do homopolímero HPDR13 à maior estabilidade térmica e mecânica do PMMA. / Azopolymers display photoisomerization properties, which can be exploited in optical memories, and depend strongly on the molecular architecture of the polymer chain and kind of film employed. In this work, azopolymers with controlled molecular architecture were synthesized using the azomonomers [4-(N-ethyl-N-2(methacryloxyethyl))amino-2\'-chloro-4\'-nitroazobenzene](DR13MA)and[4-(N-ethyl-N-2-(methacryloxyethyl))aminoazobenzene] (MAEAMA). Two methods were used to synthesize homopolymers and block-copolymers: NMRP - Nitroxide-mediated radical polymerization and ATRP - Atom transfer radical polymerization. Diblock-copolymers were produced, with one block composed by azodyes units, by reacting the monomer DR13MA with a polystyrene (PS) macroinitiator via NMRP, or with poly(methyl methacrylate) (PMMA) macroinitiator via ATRP. Homopolymers of both azomonomers were synthesized by ATRP, and - analogously to the blockcopolymers - exhibited controlled structure with a small polydispersity. The synthesized polymers were then used in the formation of Langmuir films at the air-water interface, which could be transferred onto solid substrates forming Langmuir-Blodgett (LB) films. In Langmuir films, an investigation was made of the conformation and interactions (aggregation) of the film-forming molecules. Interestingly, a plateau was observed at 8 mN/m in the surface pressure isotherm for the HPMAEA homopolymer, pointing to a reorganization of the polymer during compression. For HPDR13 produced by ATRP, it was possible to deposit LB films with no need to use surfactants, unlike the case of HPDR13 synthesized by conventional methods. Optical storage measurements were performed to demonstrate the applicability of the azo-containing materials in optical memories. For the terpolymer PS-b-[MMA-co-DR13] made by NMRP, the storage results were similar to those obtained with blends. In the case of the homopolymer HPMAEA, a large influence of the kind of film used (cast or LB) was observed in the writing time of the memories, with the writing time for the LB film being 26 times faster. PMMA-b-DR13 block-copolymers may be advantageous in combining the optical properties of the homopolymer HPDR13 with the thermal and mechanical stability of PMMA.
12

Design and engineering of light-driven dynamic films for bioelectronic interfacing / Design och konstruktion av ljusdrivna dynamiska filmer för bioelektroniska gränssnitt

Terenzi, Luca January 2023 (has links)
In the realm of neuroelectronics, the challenge lies in achieving finer observations of physiological processes to comprehend neuronal interactions and computations. This necessitates the development of more compliant and biomimetic interfaces for improved integration with biological tissues, enabling finer physiological process observations. Commonly used flat and static electrode interfaces contrast sharply with the dynamic, complex, and three dimensional (3D) extracellular matrix (ECM) in which cells reside. Introducing 3D patterns on electrode surfaces enhances cell-chip coupling, improving the signal recording. Moreover, inorganic electrodes are stiff and rigid, creating mechanical mismatches with softer biological tissues, and they fail to fully capture ionic conduction.This thesis addresses these challenges by focusing on designing and engineering a multi-layer dynamic and stimuli-responsive bioelectronic interface. The system combines light-responsive, deformable polymers like Poly(Disperse Red 1-methacrylate) (pDR1m) with conductive polymers such as Poly(3,4-ethylenedioxythiophene): poly(stirensulfonate) (PEDOT:PSS). pDR1m responds to light, exhibiting 3D surface topography deformation, while PEDOT:PSS facilitates electrical recording and stimulation of cells, offering mixed electronic and ionic conduction as well as good mechanical properties. The potential use of an intermediate Polydimethylsiloxane (PDMS) film to improve layer adhesion is also explored. The individual and multi-layer samples were first optimized for spin coating manufacturing, and then thoroughly characterized to investigate their thickness, morphology, optical and electrochemical properties. Patterning of pDR1m-based samples was carried out using laser scanning confocal microscopy and a Lloyd’s mirror interferometer.The pDR1m\PEDOT:PSS sample demonstrates promising morphological and conductive properties, and the presence of PEDOT:PSS does not alter the absorption spectra of pDR1m. The multi-layer approach also supports efficient inscription of 3D surface reliefs without damaging the conductive layer. In conclusion, this work successfully designs conductive and dynamic light-driven films, which showcase good potential for bioelectronics and neuroelectronic interfaces. These interfaces could lead to enhanced investigations into combined electromechanical stimulation on cells and provide a more biomimetic coupling with biological tissues. / Inom neuroelektronikens område ligger utmaningen i att uppnå finare observationer av fysiologiska processer för att förstå neuronala interaktioner och beräkningar. Detta kräver utveckling av mer följsamma och biomimetiska gränssnitt för förbättrad integration med biologiska vävnader, vilket möjliggör finare fysiologiska processobservationer. Vanligt använda platta och statiska elektrodgränssnitt står i skarp kontrast till den dynamiska, komplexa och tredimensionella (3D) extracellulära matrisen (ECM) i vilken celler finns. Att introducera 3D-mönster på elektrodytor förbättrar cell-chip-kopplingen, vilket förbättrar signalinspelningen. Dessutom är oorganiska elektroder styva och stela, vilket skapar mekaniska felmatchningar med mjukare biologiska vävnader, och de lyckas inte helt fånga jonledning.Den här avhandlingen tar upp dessa utmaningar genom att fokusera på att designa och konstruera ett flerlagers dynamiskt och stimuli-responsivt bioelektroniskt gränssnitt. Systemet kombinerar ljuskänsliga, deformerbara polymerer som Poly(Disperse Red 1-methacrylate) (pDR1m) med ledande polymerer som Poly(3,4-etylendioxitiofen): poly(stirensulfonat) (PEDOT:PSS). pDR1m reagerar på ljus och uppvisar 3D-yttopografideformation, medan PEDOT:PSS underlättar elektrisk inspelning och stimulering av celler, erbjuder blandad elektronisk och jonledning samt goda mekaniska egenskaper. Den potentiella användningen av en mellanliggande polydimetylsiloxan (PDMS) film för att förbättra skiktvidhäftningen undersöks också. De individuella och flerskiktiga proverna optimerades först för spinnbeläggningstillverkning och karakteriserades sedan grundligt för att undersöka deras tjocklek, morfologi, optiska och elektrokemiska egenskaper. Mönster av pDR1m-baserade prover utfördes med laserskanning konfokalmikroskopi och en Lloyds spegelinterferometer.pDR1m\PEDOT:PSS-provet visar lovande morfologiska och ledande egenskaper, och närvaron av PEDOT:PSS förändrar inte absorptionsspektra för pDR1m. Flerskiktsmetoden stöder också effektiv inskription av 3D-ytreliefer utan att skada det ledande lagret. Sammanfattningsvis designar detta arbete framgångsrikt ledande och dynamiska ljusdrivna filmer, som visar upp god potential för bioelektronik och neuroelektroniska gränssnitt. Dessa gränssnitt kan leda till förbättrade undersökningar av kombinerad elektromekanisk stimulering på celler och ge en mer biomimetisk koppling med biologiska vävnader.

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