Poly(vinyl alcohol) (PVA)-based membranes have gathered significant interest because of their film forming ability and low cost. These films are usually crosslinked to provide a macromolecular network with high dimensional stability. PVA can be modified by introduction of sulfonic acid groups (sPVA) contributing to increase its proton conductivity. In addition, the preparation of hybrid organic-inorganic composite membranes by the addition of graphene oxide (GO) as nano-filler not only reinforces the matrix but also decreases the permeability of solvents. All this has motivated the use of these materials for the preparation of proton exchange membranes (PEMs) for direct methanol fuel cell (DMFC) applications. Contribution I presents the chemical schemes followed for the bi-sulfonation of the PVA, the synthesis of GO and the preparation of PVA/GO and sPVA/GO composite membranes. In addition, a structural, morphological, thermal, and mechanical characterization of the starting materials and the composite membranes were performed. Finally, in order to evaluate the suitability of the prepared PEMs in fuel cells, the prot cond. was evaluated at room temperature. The results showed that the addition of GO (1 wt.%) into the sPVA matrix, 30sPVA/GO membrane, enhance by 89% the prot cond. compared to its homologue membrane, 30sPVA, free-standing of GO. In Contribution II, the proton conductive properties of the previously prepared membranes were investigated as a function of the structural (bi-sulfonation) and morphological (crosslinking and addition of GO) modifications. The bi-sulfonated membrane reinforced with GO, 30sPVA/GO, stands out over the rest. The addition of GO improves considerably its prot cond. (20.96 mS/cm at 90 °C) and its maximum power density (Pmax) in the H2-O2 fuel cell test (13.9 mW/cm2 at 25 ºC). In Contribution III was studied the effect of a new variable, the sufonation of the GO (sGO), on the functional properties of the composites PVA/sGO and sPVA/sGO for DMFC applications. In addition, the results were compared to that obtained for the previously described PVA/GO and sPVA/GO composites. The results conclude that, contrary to expectations, the multiple sulfonation of the 30sPVA/sGO composite strongly reduces the prot cond. (5.22 mS/cm at 50 °C) compared to its homologue 30sPVA/GO (8.42 mS/cm at 50 °C), despite its higher values of ion exchange capacity (IEC). Finally, the 30PVA/sGO composite (1.85 mW/cm2) shows a significant improvement of the DMFC performance (50 °C, 4M methanol solution) compared to the 30sPVA/GO composite (1.00 mW/cm2). The Layer-by-Layer (LbL) assembly method was used in Contribution IV for the preparation of composite membranes assembled via hydrogen bonding interactions. To do this, GO/PVA and GO/sPVA bilayers were deposited on the surface of 15PVA and 15sPVA substrate membranes, respectively. The composites were denoted as 15PVA(GO/PVA)n and 15sPVA(GO/sPVA)n where n is the number of deposited bilayers, in our case n ranges between 1 and 3. Finally, the potential of the composite membranes for DMFC applications were evaluated, showing the best performance the 15sPVA(GO/sPVA)1 composite. Finally, the Contribution V was focused on the preparation of composite membranes by LbL Assembly method, but in this case the assembly forces were electrostatic interactions. The GO was dispersed in a poly(allyl amine hydrochloride) solution (GO-PAH) in order to obtain a positively charged solution. The composites were assembled by alternate deposition of GO-PAH and sPVA layers on the surface of 15PVA and 15sPVA substrates, obtaining as a result the composites 15PVA(GO-PAH/sPVA)n and 15sPVA(GO-PAH/sPVA)n. The best value of prot cond. (8.26 mS/cm at 90 °C) was obtained for the 15PVA(GO-PAH/sPVA)1 composite, almost twice that the value obtained for its homologue sulfonated composite 15sPVA(GO-PAH/sPVA)1 (4.96 mS/cm a 90 °C). / Membranas constituidas básicamente por alcohol polivinílico (PVA) han despertado un gran interés debido a su bajo coste y su fácil procesado para conformarlas en forma de films. Estos films frecuentemente son sometidos a entrecruzamiento para disponer de una red macromolecular con una elevada estabilidad dimensional. La modificación del PVA por introducción de grupos sulfónicos (sPVA) cambia la estructura del polímero contribuyendo a aumentar su conductividad protónica. Además, la preparación de membranas híbridas orgánico-inorgánicas (composites) mediante la adición de óxido de grafeno (GO) refuerza la matriz, a la vez que disminuye su permeabilidad frente a disolventes. Todo ello ha motivado el uso de estos materiales para la preparación de membranas de intercambio protónico (PEMs) empleadas en pilas de combustible de metanol (DMFCs). En la Contribución I se presentan los esquemas químicos conducentes a la bi-sulfonación del PVA, la síntesis del GO y la preparación de las membranas composite PVA/GO y sPVA/GO. Además, se realizó la caracterización estructural, morfológica, térmica y mecánica de cada uno de los materiales de partida y de los composite. Finalmente, con el fin de evaluar su idoneidad como PEMs en pilas de combustible, se evaluó su cond. prot a temperatura ambiente. Los resultados obtenidos mostraron que la adición de GO (1 wt.%) como nano-carga a la matriz de sPVA genera un composite, 30sPVA/GO, cuya cond. prot supera en un 89 % a la de su membrana homóloga sin carga, 30sPVA. La Contribución II trata de explorar las propiedades conductoras de las membranas preparadas previamente en función de la modificación estructural (bi-sulfonación) y la morfológica (reticulación y adición de GO). La membrana bi-sulfonada y reforzada con GO, 30sPVA/GO, destaca sobre el resto. La adición de GO mejora considerablemente tanto la cond. prot (20.96 mS/cm a 90 ºC) como la densidad de potencia máxima (Pmax) en pila de combustible de hidrógeno (13.9 mW/cm2 a temperatura ambiente). En la Contribución III se estudió el efecto de una nueva variable, la sulfonación del GO (sGO), sobre las propiedades funcionales de los composites PVA/sGO y sPVA/sGO en aplicaciones de DMFC. Además, se llevó a cabo un estudio comparativo con los composite PVA/GO y sPVA/GO previamente descritos. Los resultados concluyeron que, en contra a lo esperado, la múltiple sulfonación de la membrana 30sPVA/sGO reduce fuertemente su cond. prot (5.22 mS/cm a 50 ºC) en comparación con su homóloga 30sPVA/GO (8.42 mS/cm a 50 ºC), aun mostrando valores superiores de IEC. Finalmente, el rendimiento de la composite 30PVA/sGO (1.85 mW/cm2) en una DMFC (50 ºC, disolución de metanol 4M) mostró una mejora significativa en comparación con la composite 30sPVA/GO (1.00 mW/cm2). El método de LbL assembly se empleó en la Contribución IV para la preparación de composites ensamblados mediante enlaces por puente de hidrógeno. Para ello, se llevó a cabo la deposición de bicapas de GO/PVA y GO/sPVA sobre los substratos 15PVA y 15sPVA, respectivamente. Los composites se codificaron como 15PVA(GO/PVA)n y 15sPVA(GO/sPVA)n siendo n el número de bicapas depositadas, en nuestro caso n varía entre 1 y 3. Por último, se evaluó su potencial para aplicaciones en DMFC, presentando el mejor comportamiento el composite 15sPVA(GO/sPVA)1. Finalmente, la Contribución V va dedicada a la fabricación de composites mediante el método de LbL Assembly, pero en este caso a través de interacciones electrostáticas. El GO se dispersó en una disolución de hidrocloruro de polialilamina (GO-PAH), con el fin de dotarlo de carga positiva. El ensamblaje se realizó por deposición alterna de capas de GO-PAH y sPVA, obteniéndose los composites 15PVA(GO-PAH/sPVA)n y 15sPVA(GO-PAH/sPVA)n. El mejor valor de cond. prot (8.26 mS/cm a 90 ºC) se obtuvo para el composite 15PVA(GO-PAH/sPVA)1, siendo casi el doble que el obtenido para su homólogo s / Membranes constituïdes a base PVA han despertat un gran interès a causa del seu baix cost i el seu fàcil processament per conformar-les en forma de films. Aquests films freqüentment són sotmesos a entrecreuament per disposar d'una xarxa macromolecular amb una elevada estabilitat dimensional. La modificació del PVA per introducció de grups sulfònics (sPVA) canvia l'estructura del polímer contribuint a augmentar la seua conductivitat protònica. A més, la preparació de membranes híbrides orgànic-inorgànics (composites) mitjançant addició d'òxid de grafè (GO) reforça la matriu, alhora que disminueix la seua permeabilitat enfront de dissolvents. Tot això ha motivat l'ús d'aquestos materials per a la preparació de membranes d'intercanvi protònic (PEMs) emprades en piles de combustible de metanol (DMFCs). En la Contribució I es presenten els esquemes químics conduents a la bi-sulfonació del PVA, la síntesi del GO i la preparació de les membranes composite PVA/GO i sPVA/GO. A més, es va realitzar la caracterització estructural, morfològica, tèrmica i mecànica de cada un dels materials de partida i de les membranes composite. Finalment, per tal d'avaluar la seua idoneïtat com a PEMs en piles de combustible, es va mesurar la seua cond. prot a temperatura ambient. Els resultats obtinguts van mostrar que l¿addició de GO (1 wt.%) com a nano-càrrega en la matriu de sPVA genera un composite, 30sPVA/GO, amb una cond. prot que supera en un 89% a la de la seua membrana homòloga sense càrrega, 30sPVA. La Contribució II tracta d'explorar les propietats conductores de les membranes composite preparades prèviament en funció de la modificació estructural (bi-sulfonació) i morfològica (reticulació i addició de GO). La membrana bi-sulfonada i reforçada amb GO, 30sPVA/GO, destaca sobre la resta. L'addició de GO millora considerablement tant la cond. prot (20.96 mS/cm a 90 ºC) com la densitat de potència màxima (Pmax) a la pila de combustible d'hidrogen (13.9 mW/cm2 a temperatura ambient). En la Contribució III es va estudiar l'efecte d'una nova variable, la sulfonació del GO (sGO), sobre les propietats funcionals dels composites PVA/sGO i sPVA/sGO per aplicacions en DMFC. A més, es va dur a terme un estudi comparatiu amb els composites PVA/GO i sPVA/GO prèviament descrits. Els resultats van concloure que en contra del que s'esperava, la múltiple sulfonació de la membrana 30sPVA/sGO redueix fortament la seua cond. prot (5.22 mS/cm a 50 ºC) en comparació amb la seua homòloga 30sPVA/GO (8.42 mS/cm a 50 ºC), tot i que mostra valors superiors de IEC. Finalment, el rendiment de la membrana 30PVA/sGO (1.85 mW/cm2) en una DMFC (50 ºC, dissolució de metanol 4M) va mostrar una millora significativa en comparació amb la membrana 30sPVA/GO (1.00 mW/cm2). El mètode de LBL assembly es va emprar en la Contribució IV per a la preparació de composites acoblats mitjançant enllaços per pont d'hidrogen. Amb aquest fi, es va dur a terme la deposició de bicapes de GO/PVA i GO/sPVA sobre els substrats 15PVA i 15sPVA, respectivament. Els composites es van codificar com a 15PVA(GO/PVA)n i 15sPVA(GO/sPVA)n on n és el nombre de bicapes dipositades, en el nostre cas n varia entre 1 i 3. Finalment, es va avaluar el seu potencial per a aplicacions en DMFC, presentant el millor comportament el composite 15sPVA(GO/sPVA)1. Finalment, la Contribució V va dedicada a la fabricació de composites mitjançant el mètode de LBL Assembly, però en aquest cas acoblats a través d'interaccions electrostàtiques. El GO es va dispersar en una dissolució de hidroclorur de polialilamina (GO-PAH), per tal de dotar-lo de càrrega positiva. L'acoblament es va realitzar per deposició alterna de capes de GO-PAH i sPVA, obtenint-se els composites 15PVA(GO-PAH/sPVA)n i 15sPVA(GO-PAH/sPVA)n. El millor valor de cond. prot (8.26 mS/cm a 90 ºC) es va obtenir per al composite 15PVA(GO-PAH/sPVA)1, sent gairebé el doble que l'obtingut / Sánchez Ballester, SC. (2017). Synthesis and characterization of new polymer electrolytes to use in fuel cells fed with bio-alcohols [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86198 / TESIS

Content: Graphene oxide (GO) is one of the most interesting nanomaterials in recent years. In order to explore its potential application in leather making process, a study on evaluating the effects of GO on the thermal stability and decomposition kinetics of bovine hide powders (HP) was performed by thermogravimetry. It was shown that the GO-doped hide powders (GO-HP) exhibit better thermal stability than those of raw hide powders. The kinetic and mechanism analysis of the decomposition stage used an integrated procedure involving model-free methods and universal master-plots method. Various methods were employed to calculate the activation energy of the fibers, including the Flynn-Wall-Ozawa (FWO), Modified Kissinger-Akahira-Sunose (MKAS) and Friedman methods. The activation energy values of GO-HP and raw hide powder were found to be 240.5 and 184.7 kJ/mol, respectively. Comparison of the experimental and theoretical master plots of various reaction mechanisms showed that when the conversion values are below 0.5, the most probable decomposition mechanism for HP and GO-HP is D1. Above 0.5, the decomposition mechanisms of HP and GO-HP are most probably described by A3 and R3 models, respectively. Take-Away: Graphene oxide (GO) doped hide powders (GO-HP) exhibit better thermal stability than those of raw hide powders. The activation energy values of GO-HP and raw hide powder were found to be 240.5 and 184.7 kJ/mol, respectively.

Sulfur dioxide (SO₂), a well-known pollutant emitted from fossil fuel combustion, has major adverse health and environmental impacts. It is harmful at low concentration with a permissible exposure limit of two ppm for the eight-hour time-weighted average (TWA) value. Fortunately, its atmospheric concentration, like other air pollutants, has gradually reduced in Canada in the past years. However, despite the well-established flue gas desulfurization technologies, they have the disadvantages of being energy-intensive, not very efficient to achieve very low concentrations (at ppm level) and they operate at high temperatures. Moreover, emission standards are becoming more stringent. Novel methods are therefore investigated to capture SO₂, such as adsorption processes using zeolites and metal oxides (e.g., Iron (Fe) and Vanadium (V) based) which tend to sustain wide ranges of temperatures and pressures. Graphene oxide (GO) was also shown to physisorb SO₂ at low temperatures. In this work, we propose to metal functionalize GO as a step forward on the path for efficient SO₂ capture, by promoting the SO₂ oxidation reaction into sulfur trioxide (SO₃) for increased capacity due to a possible higher affinity with the surface. The GO has a high surface area, high porosity, and controllable surface chemistry. The aim is to achieve outlet concentration of SO₂ as low as 1 ppm through combined physisorption and reaction promoted that the presence of GO and metal, at low operating temperature. Iron oxide functionalized GO was synthesized using two different techniques: a polyol process (GO-FeₓOᵧ-P) and using a hydrolysis method (GO-FeₓOᵧ-H). The characterization analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), performed on the materials before and after SO₂ reaction show changes on the surface due to metal adding and to the sulfur capture. The breakthrough curves and the capacity calculations of the performed experiments have shown that with the addition of FeₓOᵧ on the surface of GO, the capturing capacity increases by a factor of three to four, indicating a possible change in the capturing mechanism. The evaluation of the temperature effect (from room temperature to 100℃) showed an increasing trend in the capture capacity for SO₂ with an increase in temperature, for both functionalized and non-functionalized GO, indicating it is not driven only by surface adsorption. The presence of sulfur species captured from the gas stream has been confirmed by energy-dispersive X-ray (EDXS) analysis. The future work would be focused on the investigation of the mechanisms and capturing phenomenon and the regeneration step for the materials in order to further improve the capturing capacity and process applicability.

Orientador: Diogo Paschoalini Volanti / Resumo: O avanço na ciência e tecnologia de sensores de compostos orgânicos voláteis (VOCs) é importante para o desenvolvimento sustentável de materiais funcionais. A dissertação de mestrado refere-se à avaliação do uso de óxido de grafeno (GO, sigla em inglês) em óxido metálicos (OM) tipo-n (V2O5) e tipo-p (Co3O4) para melhorar a sensibilidade, a seletividade e o tempo de resposta dos sensores. O GO teve uma modificação sendo submetido a um processo oxidativo. Os OMs nano ou microestrurados foram preparados a partir de seus sais ou por processos de ressolubilização dos óxidos. Por fim, os compósitos GO-OM foram preparados após os percursores ficarem em suspensão com o GO por 24 horas. O GO aumentou a adsorção gasosa dos compostos resultando em maior seletividade e sensibilidade. Por outro lado, os principais benefícios das estruturas nano e microestrutruradas dos OMs seriam a maior área superficial do material resultando em melhores propriedades gasosas, resultando em mais sítios ativos para adsorção do oxigênio e das moléculas do gás analito. As respostas sensoras foram avaliadas na presença de diferentes concentrações (nas faixas de ppm e ppb) de VOCs (ex.: acetona, acetaldeído, etanol, metanol, benzeno, xileno e tolueno) em atmosfera seca. / Abstract: The advancement in science and technology of volatile organic compounds (VOCs) sensors is essential for the sustainable development of functional materials. The master's thesis refers to the evaluation of the use of graphene oxide (GO) in metallic oxides (OM) type-n (V2O5) and type-p (Co3O4) to improve sensitivity, selectivity and the response time of the sensors. The GO had a modification being subjected to an oxidative process. The nano or microstructured OMs were prepared from its precursors. Finally, the GO-OM composites were prepared after the precursors were in suspension with the GO for 24 hours. The GO increased the gaseous adsorption of the compounds resulting in greater selectivity and sensitivity. On the other hand, the main benefits of the nanostructured and micro-structured structures of OMs would be the greater surface area of the material resulting in better gaseous properties, resulting in more active sites for adsorption of oxygen and analyte gas molecules. The sensory responses were evaluated in the presence of different concentrations (in the ppm and ppb ranges) of VOCs (e.g., acetone, acetaldehyde, ethanol, methanol, benzene, xylene and toluene) in a dry atmosphere. / Mestre

[pt] O grafeno é formado por uma monocamada de átomos de cabono ligados entre si formando uma rede hexagonal. Ele tem sido bastante estudado por pesquisadores e atraído investimentos de vários setores da economia por apresentar excelentes propriedades mecânicas, térmicas, elétricas e ópticas. O presente trabalho tem como objetivo principal a caracterização reológica das suspensões de óxido de grafeno (GO) dispersas em polietileno glicol (PEG 400), com diferentes tempos de oxidação (2 e 96 horas), através do uso da reometria rotacional. O óxido de grafeno foi obtido pelo método de Hummers e caracterizado por várias técnicas. Este método é baseado na esfoliação química do grafite através de ácidos fortes, como o ácido sulfúrico. Uma vez que o óxido de grafite (GrO) é obtido, ele é esfoliado em um banho ultrassônico em PEG para a formação da suspensão com óxido de grafeno. A caracterização reológica foi realizada através de medições em escoamento de cisalhamento em regime permanente, transiente e oscilatório. A caracterização do GO foi realizada utilizando técnicas como: Difração de Raios-X (DRX), Espectroscopia Raman, Infravermelho por Transformada de Fourier (FTIR), Microscopia de Força Atômica (AFM) e Análise Termogravimétrica (TGA). Os resultados servirão de base para a compreensão da interação entre o GO e o polímero, e o comportamento reológico dos nanofluidos de polímeros à base de GO. / [en] Graphene is formed by a monolayer of cabon atoms linked together forming a hexagonal network. It has been extensively studied by researchers and attracted investment from various sectors of the economy, because it presents excellent mechanical, thermal, electrical and optical properties. The present work has as main objective the rheological characterization of the suspensions of graphene oxide (GO) dispersed in poly(ethylene) glycol (PEG 400), with different oxidation times (2 and 96 hours), through the use of rotational rheometry. Graphene oxide was obtained by Hummers method and characterized by various techniques. This method is based on the chemical exfoliation of graphite using strong acids such as sulfuric acid. Once the graphite oxide (GrO) is obtained, it is exfoliated in an ultrasonic bath in PEG to form the suspension with graphene oxide. The rheological characterization is fulfilled through measurements in steady shear flow, transient shear flow and oscillatory shear flow. The characterization of GO was performed using techniques such as: X-Ray Diffraction (XRD), Raman Spectroscopy, Fourier Transform Infrared (FTIR), Atomic Force Microscopy (AFM) and Thermogravimetric Analysis (TGA). The results will serve as a basis for understanding the interaction between the GO and the polymer, and the rheological behavior of GO-based polymer nanofluids.

The development of a new deposition technique called evaporative vapor deposition (EVD) is reported, allowing deposition and formation of atomically-thin, large area materials on arbitrary substrates. This work focuses on the highly popular monolayer material – graphene oxide (GO). A droplet of a GO solution is formed on a heated polymer substrate, and maintained at steady-state evaporation (all droplet parameters are held constant over time). The polymer substrate is laser patterned to control the droplet's contact line dynamics and the droplet's contact angle is maintained using a computer controlled syringe pump. A room temperature silicon wafer is translated through the vapor field of the evaporating GO droplet using a computer controlled translation stage. Dropwise condensation formed on the silicon wafer is monitored using both optical and infrared cameras. The condensation rate is measured to be ~50pL/mm2?s – 500 pL/mm2?s and dependent on the substrate translation speed and height difference between the droplet's apex and substrate surface. Nano-sized GO flakes carried through the vapor phase are captured in the condensate, depositing on the translating wafer. Deposition rate is dependent on the stability of the solution and droplet condensate size. Characterization with Raman spectroscopy show expected shifts for graphene/graphite. The presented EVD technique is promising toward formation of large scale 2D materials with applications to developing new technologies.

No description available.

Ag is a widely used electrical contact material due to its excellent electrical properties. The problems with Ag are that it is soft and has poor tribological properties (high friction and wear in Ag/Ag sliding contacts). For smart grid applications, friction and wear became increasingly important issues to be improved, due to much higher sliding frequency in the harsh operation environment. The aim of this thesis is to explore several different concepts to improve the properties of Ag electrical contacts for smart grid applications. Bulk Ag-X (X=Al, Sn In) alloys were synthesized by melting of metals. An important result was that the presence of a hcp phase in the alloys significantly reduced friction coefficients and wear rates compared to Ag. This was explained by a sliding-induced reorientation of easy-shearing planes in the hexagonal structure. The Ag-In system showed the best combination of properties for potential use in future contact applications.  This thesis has also demonstrated the strength of a combinatorial approach as a high-throughput method to rapidly screen Ag-based alloy coatings. It was also used for a rapid identification of optimal deposition parameters for reactive sputtering of a complex AgFeO2 oxide with narrow synthesis window. A new and rapid process was developed to grow low frictional AgI coatings and a novel designed microstructure of nanoporous Ag filled with AgI (n-porous Ag/AgI) using a solution chemical method was also explored. The AgI coatings exhibited low friction coefficient and acceptable contact resistance. However, under very harsh conditions, their lifetime is too short. The initial tribotests showed high friction coefficient of the n-porous Ag/AgI coating, indicating an issue regarding its mechanical integrity. The use of graphene as a solid lubricant in sliding electrical contacts was investigated as well. The results show that graphene is an excellent solid lubricant in Ag-based contacts. Furthermore, the lubricating effect was found to be dependent on chemical composition of the counter surface. As an alternative lubricant, graphene oxide is cheaper and easier to produce. Preliminary tests with graphene oxide showed a similar frictional behavior as graphene suggesting a potential use of this material as lubricant in Ag contacts.

Pour mieux comprendre leurs propriétés, diverses nanostructures individuelles ont été étudiées à l’aide d’une technique couplant microscopie à force atomique et spectroscopie Raman confocale. Sous excitation lumineuse polarisée, la composition chimique, la structure et la présence de défauts a pu être précisée dans des nanobâtonnets d’oxydes métalliques (ZnO et α-Fe2O3). Sous irradiation laser résonnante, les spectres de nanotubes de carbone monoparoi enrobés de polymères ont révélé notamment l’absence de transfert de charge polymère-nanotube et un effet de désolvatation. Finalement, des feuillets de graphène oxydé et des ADNs double-brin peignés ont pu être préparés et caractérisés par spectroscopie Raman exaltée par effet de pointe en atteignant une résolution spatiale latérale voisine du rayon de courbure de l’apex de la pointe utilisée (12 nm), bien plus faible que la limite de diffraction, ce qui ouvre la voie à de nouveaux travaux spectroscopiques à l’échelle nanométrique. / To better understand their properties, various nanostructures have been studied using a technique combining atomic force microscopy and confocal Raman spectroscopy. Under polarized light excitation, the chemical composition, the structure and the presence of defects has been described in metal oxides nanorods (ZnO et α-Fe2O3). Under resonant laser excitation, Raman spectra of polymer-wrapped single-walled carbon nanotubes have revealed the absence of polymer-nanotube charge transfer and an effect due to desolvation. Finally, graphene oxide sheets and combed double-stranded DNAs have been prepared and characterized using tip-enhanced Raman spectroscopy with a lateral spatial resolution down to the curvature radius of the apex of the used tip (12 nm), well below the diffraction limit, which opens new opportunities for spectroscopic works at the nanometer scale.

Cette thèse est dédiée à l'étude d'une nouvelle méthode de formation de films ultra-minces de nanomatériaux carbonés sur surface. Basée sur le transfert d'un film d'eau stabilisé par des tensioactifs, elle permet notamment la réalisation et l'étude de films de nanotubes de carbone et d'oxyde de graphène (GO) aux propriétés remarquables. L’efficacité de l’approche développée est prouvée au travers de l’ajustement précis des caractéristiques des films. Pour l’assemblage d’objets bidimensionnels cette approche est particulièrement pertinente puisque la planéité des feuillets de GO est conservée quelle que soit leur taille. Les avantages de l’approche ne se limitent pas à la réalisation de monocouches à morphologie contrôlée mais s’étendent à la réalisation de films multicouches d’épaisseur ajustée et de très faible rugosité. De plus, cette approche est modulable et permet le transfert de films de nano-objets sur des surfaces de différentes mouillabilités et de grandes dimensions (transfert à l’échelle de wafers). L’intérêt du graphène oxydé en tant qu’analogue du graphene ne se justifie que par une désoxygénation (réduction) efficace du matériau idéalement complétée par une réparation de sa structure sp². Cette thèse aborde ces deux aspects. Les électrodes transparentes à base d'oxyde de graphène réduit (rGO) réalisées au cours de cette thèse sont parmi les plus performantes du domaine. Les résultats présentés incluent également un travail important sur les caractérisations électriques des feuillets individuels et des films de GO et de rGO. Ainsi, nous avons prouvé qu’il est possible de mesurer leur conductivité sans contact, par voie électrochimique (Scanning Electrochemical Microscopy). Même si les performances des électrodes en rGO n'atteignent pas celles des électrodes en graphène, les films réalisés peuvent d’ores et déjà être intégrés dans des dispositifs photovoltaïques. Nos travaux permettent de contribuer au domaine émergeant des cellules basées sur l’hétérojonction entre film de nano-objets carbonés et silicium. Dans le cadre de cette thèse nous montrons en particulier que les analyses par Time Resolved Microwave Conductivity sont complémentaires des mesures effectuées à l’échelle des cellules photovoltaïques, chacune permettant de caractériser, sous des angles différents, l’efficacité de séparation des charges photo-induites. Les travaux réalisés au cours de cette thèse contribuent aux problématiques dépendantes d’assemblage et d’intégration des nano-objets carbonés dans des dispositifs en ouvrant de nombreuses perspectives dans ces domaines en rapide évolution. / This thesis concerns the study of a new solution-based deposition method for the formation of ultrathin carbon nano-object films on surfaces. Based on the transfer of a surfactant-stabilized water film, this method enables the formation and the study of carbon nanotubes and graphene oxide (GO) films with remarkable properties. The efficiency of the developed approach is proven through the fine-tuning of the film properties. This method is particularly well-suited for the assembly of bidimensional nano-objects such as GO sheets, the flatness of which is preserved whatever their dimensions. The advantages of the approach are not limited to the morphological control of monolayer assemblies but extend to the realization of multilayer films of adjustable thickness and extremely low roughness. Besides, it enables the transfer of nano-object films on large (wafer-scale) surfaces of various wettability. The use of graphene oxide as an intermediate step toward graphene only makes sense if it is efficiently deoxygenated (reduced) and, ideally, repaired at the level of sp² domains. This thesis addresses these aspects. The realized transparent electrodes made of reduced graphene oxide (rGO) are among the most efficient in this field. The presented results also include an important work on the electrical characterization of graphene oxide sheets and films. We notably prove that conductivity can be measured without contact by an electrochemical way using Scanning Electrochemical Microscopy. While the performances of rGO electrodes are below those of graphene electrodes, the studied films can already be integrated into photovoltaic devices allowing to contribute to the emerging field of solar cells based on carbon/silicon heterojunctions. We particularly demonstrate that Time Resolved Microwave Conductivity analysis and photovoltaic cell measurements are complementary. Each of these techniques allows evaluating the efficiency of the separation of photo-induced charges. This thesis contributes to the dependent problematics of nano-object assembly and nano-object integration into devices, which are central for the development of nanotechnologies based on the bottom-up strategy.