Aerogels are extremely high surface area, low density materials with applications including thermal and acoustic insulators, radiation detectors and cometary dust particle traps. However, their low density and aggregate structure makes them extremely fragile and practically impossible to machine or handle without breaking. This has led to the development of aerogel composites with enhanced mechanical properties through the addition of polymers or surface modifiers. To date, attempts to strengthen aerogels have come with significant increases in density and processing time. Here I will describe our search for a solution to these problems with our invention using methyl cyanoacrylate chemical vapor deposition (CVD) to strengthen silica, aminated silica and bridged polysilsesquioxane aerogels. This approach led to a strength improvement of the composites within hours and the strongest composite prepared had a 100x strength improvement over the precursor aerogel. We also developed the first approach to control the molecular weight of the polymers that reinforce silica aerogels using surface-initiated atom transfer radical polymerization (SI-ATRP). Although PMMA reinforcement of silica aerogels improved the mechanical properties, further strength improvements were achieved by cross-linking the grafted PMMA. Additionally, we developed the first silica aerogels reinforced with polyaniline nanofibers that were strong and electrically conductive. Reinforcing silica aerogels with polyaniline allowed them to be used as a sensor for the detection of protonating and deprotonating gaseous species. Finally we developed a new approach for the synthesis of silica and bridged polysilsesquioxane spheres using a surfactant free synthesis. This approach allowed for the first in-situ incorporation of base sensitive functionalities during the sol-gel polymerization.

This paper analyses the effect of polypropylenglycol and potential-sweep rates on the form of polarization curves and polyaniline electrosynthesis speed by polarizing Pt and Ti electrodes through the potentiodynamic method. It has been found out that the polypropylenglycol’s effect accelerates formation of polyaniline on the surface of the Pt electrode at the initial stages of electrosynthesis grows up with the increase of concentration. By calculating the electric charge that has accumulated during the anode cycle we have established that the greatest effect is produced by small concentrations of polypropylenglycol. Further increase of polypropyleneglycol has had no marked effect. Polypropylenglycol reduces in the direction of positive potentials of the first anode spike. By synthesizing polyaniline on the surface of the Ti electrode, the effect accelerates the polypropylenglycol process is observed only at slow potential sweep rates velocities, whereas at the same time the increase in the speed results in the noticeable slowdown of the process. Polypropylenglycol penetrates indelibly into the polyaniline coating apparently forming a composite.

Conductive polymers are promising pseudo capacitive materials as they feature both good conductivity and high capacitance. Formation of composite between conductive polymers and carbon nanotubes is a proven technique in enhancing the material electroactivity. In-situ polymerization of conductive polymers includes polyaniline, polypyrrole and PEDOT: PSS and composite with MWCNT has been successfully achieved. Composites fabricated by using different dopants and their performance were studied. Excellent achieved capacitive performance is due to the combination of pseudo capacitance and double layer capacitance. The MWCNTs content has significant influence on the morphology and structure of the polymerized ECP in the composite. And therefore affects the material conductivity and the charge storage performance. Two electrodes cell performance shows that Ppy/MWCNT composite shows a more promising performance as electrode materials for EC applications in contrast to PANI/MWCNT and PEDOT: PSS/MWCNT composites.

Conductive polymers are promising pseudo capacitive materials as they feature both good conductivity and high capacitance. Formation of composite between conductive polymers and carbon nanotubes is a proven technique in enhancing the material electroactivity. In-situ polymerization of conductive polymers includes polyaniline, polypyrrole and PEDOT: PSS and composite with MWCNT has been successfully achieved. Composites fabricated by using different dopants and their performance were studied. Excellent achieved capacitive performance is due to the combination of pseudo capacitance and double layer capacitance. The MWCNTs content has significant influence on the morphology and structure of the polymerized ECP in the composite. And therefore affects the material conductivity and the charge storage performance. Two electrodes cell performance shows that Ppy/MWCNT composite shows a more promising performance as electrode materials for EC applications in contrast to PANI/MWCNT and PEDOT: PSS/MWCNT composites.

Because of its high theoretical specific capacity (4200mAh/g) and natural abundance (2nd most abundant element on earth), silicon is considered a promising anode candidate for high energy density lithium-ion batteries. However, the dramatic volume changes (up to 400%) that occur during lithiation/delithiation and the relative low electrical conductivity of silicon prevent the implementation of this material. In this work, a nano-silicon/polyaniline/reduced graphene oxide composite was synthesized via a two-step process: in-situ polymerization of polyaniline (PANi) in the presence of nano-silicon followed by combination of the prepared n-Si/PANi binary composite with reduced graphene oxide (RGO), to form a n-Si/PANi/RGO composite. Electron microscopy reveals the unique nano-architecture of the n-Si/PANi/RGO composite: silicon nanoparticles are well dispersed within a PANi matrix, which in turn is anchored to the surface of RGO sheets. The n-Si/PANi/RGO ternary composite delivered an initial capacity of 3259 mAh/g and 83.5% Coulombic efficiency. The new composite displayed better rate performance and capacity recovery than either nano-Si or n-Si/PANi. Structural and morphological studies combined with AC impedance analysis suggest that the n-Si/PANi/RGO composite has higher electrical conductivity than the other two component materials, yielding better performance at high current densities or C rates. The good rate performance, high initial specific capacity and stable Coulombic efficiency of n-Si/PANi/RGO make it a promising anode material for high energy density lithium-ion batteries.

Because of its high theoretical specific capacity (4200mAh/g) and natural abundance (2nd most abundant element on earth), silicon is considered a promising anode candidate for high energy density lithium-ion batteries. However, the dramatic volume changes (up to 400%) that occur during lithiation/delithiation and the relative low electrical conductivity of silicon prevent the implementation of this material. In this work, a nano-silicon/polyaniline/reduced graphene oxide composite was synthesized via a two-step process: in-situ polymerization of polyaniline (PANi) in the presence of nano-silicon followed by combination of the prepared n-Si/PANi binary composite with reduced graphene oxide (RGO), to form a n-Si/PANi/RGO composite. Electron microscopy reveals the unique nano-architecture of the n-Si/PANi/RGO composite: silicon nanoparticles are well dispersed within a PANi matrix, which in turn is anchored to the surface of RGO sheets. The n-Si/PANi/RGO ternary composite delivered an initial capacity of 3259 mAh/g and 83.5% Coulombic efficiency. The new composite displayed better rate performance and capacity recovery than either nano-Si or n-Si/PANi. Structural and morphological studies combined with AC impedance analysis suggest that the n-Si/PANi/RGO composite has higher electrical conductivity than the other two component materials, yielding better performance at high current densities or C rates. The good rate performance, high initial specific capacity and stable Coulombic efficiency of n-Si/PANi/RGO make it a promising anode material for high energy density lithium-ion batteries.

Electroactive polymers (EAP) are an emerging branch of smart materials that possess the capability to change shape in the presence of an electric field. Opportunities for the advancement of knowledge were identified in the branch of EAP consisting of inherently electrically conductive polymers. This dissertation explores methods by which the unique properties of composite materials having conductive polymers as a constituent may be exploited. Chapter 3 describes the blending of polyaniline with conventional thermoplastics. Processing these polyblends into foams yielded a porous conductive material. The effect of blend composition and processing parameters on the resulting porous morphology and electrical conductivity was investigated. These findings represent the first systematic study of porous conductive polymer blends. In Chapter 4, multilayer electroactive polymer actuators consisting of polypyrrole films electropolymerized on a passive polymer membrane core were harnessed as actuators. The membrane is vital in the transport of ionic species and largely dictates the stiffness of the layered configuration. The impact of the mechanical properties of the membrane on the actuation response of polypyrrole-based trilayer bending actuators was investigated. Candidate materials with distinct morphologies were identified and their mechanical properties were evaluated. These results indicated that polyvinylidene difluoride membranes were superior to the other candidates. An electrochemical synthesis procedure was proposed, and the design of a novel polymerization vessel was reported. These facilities were utilized to prepare actuators under a variety of synthesis conditions to investigate the impact of conductive polymer morphology on the electromechanical response. Characterization techniques were implemented to quantitatively assess physical and electrochemical properties of the layered composite. Chapter 5 proposes a new unified multiphysics model that captures the electroactive actuation response inherent to conductive polymer trilayer actuators. The main contribution of this investigation was the proposal and development of a new hybrid model that unifies concepts from charge transport and electrochemomechanical models. The output of the proposed model was compared with published data and shown to be accurate to within 10%. Finally, Chapter 6 demonstrated the application of these materials for use as precision mirror positioners in adaptive optical systems.

Dissertation (Ph.D.)--Auburn University, 2006. / Abstract. Includes bibliographic references.

Este trabalho de tese versa sobre o estudo espectroscópico da polianilina (PANI) formada em solução e nas cavidades de sólidos inorgânicos porosos e, também, sobre o monitoramento da interação entre a PANI e íons metálicos, através das técnicas espectroscópicas Raman ressonante, espectroscopia no infravermelho (IR), espectroscopia eletrônica no UV-VIS-NIR, ressonância paramagnética eletrônica (EPR) e absorção de raios X (XANES). Na síntese em solução, empregou-se o Cu(II) como agente oxidante em dois meios: (i) aquoso ácido e (ii) acetonitrila/água. As matrizes inorgânicas utilizadas foram a MCM-41, Cu(II)-MCM-41, Cu(II)-Montmorilonita e alfa-Zr(HOPO3)2.H2O. A espectroscopia Raman ressonante, utilizando diferentes radiações excitantes, demonstrou-se uma importante ferramenta no estudo dos diversos segmentos poliméricos nos diferentes ambientes químicos. Verificou-se a importância do meio reacional na natureza do polímero obtido. Usando Cu(II) em meio aquoso ácido, forma-se o de sal de esmeraldina enquanto em meio de acetonitrila/água, obteve-se um polímero contendo anéis fenazínicos e segmentos quinonadiimina e/ou fenilenodiamina. Os polímeros obtidos na sílica mesoporosa Cu(II)-MCM-41, na argila Cu(II)-MMT e no fosfato lamelar alfa-Zr(HPO4)2.H2O (alfa-ZrP) também apresentam novos segmentos provenientes de mecanismos de polimerização que diferem do usual acoplamento cabeça-cauda. Através da técnica \"layer-by-layer\" foi possível obter filmes de alfa-ZrP/PANI com a PANI na forma sal de esmeraldina e conformação estendida. Foi observado que complexação da esmeraldina base (EB) com Cu(II), Fe(III) e Zn(II) leva à formação de radicais cátions. O monitoramento do comportamento espectroscópico de soluções de EB e íons metálicos em solução de N-metil-pirrolidona demonstrou que as espécies presentes dependem da natureza dos íons metálicos, da proporção Metal/EB e das concentrações do polímero e do íon metálico. / This work presents the spectroscopic study of polyaniline (PANI) formed in solution and inside inorganic porous materials, and also the monitoring of the interaction of PANI and metallic ions through resonance Raman, infrared spectroscopy (IR), electronic UV-VIR-NIR spectroscopy, electronic paramagnetic resonance (EPR) and X-ray absorption near edge structure (XANES). In the polymerization of aniline in solution, Cu(II) ions were used as oxidizing in two different media: (i) acidic aqueous medium and (ii) acetonitrile/water. The inorganic hosts employed were MCM-41, Cu(II)-MCM-41, Cu(II)-Montmorillonite and alpha-Zr(HOPO3)2.H2O. Resonance Raman scattering by using exciting laser lines in a wide spectral range is an important technique for the structural investigation of the polymeric segments in different environments. It was verified the important role of the synthetic parameters in the structure of the polymeric material obtained. Using Cu(II) ions in acidic aqueous medium, emeraldine salt (ES) is formed while in acetonitrile/water medium it was observed a polymer having phenazine-like rings, quinonediimine and/or phenylenediamine segments. The obtained polymers into mesoporous silica Cu(II)-MCM-41, into Cu(II)-MMT clay and into the lamellar phosphate alpha-Zr(HPO4)2.H2O (alpha-ZrP) also present new segments resulted from distinct polymerization mechanisms from the usual head-to-tail coupling. Through the layer-by-layer technique it was possible to obtain alpha-ZrP/PANI films with PANI in the ES form and with extended conformation. It was observed that complexation of emeraldine base (EB) with Cu(II), Fe(III), and Zn(II) ions gives rise to radical cations formation. The monitoring of spectroscopic behavior of EB and metallic ions in NMP solution showed that the species present depend on the nature of metallic ion, on the Metal/EB ratio, and on the metallic ion and polymer concentrations.

Neste trabalho, foram adicionadas diferentes concentrações de polianilina (PANI) a uma solução polimérica de poliétersulfona (PES) e N-metil-pirrolidona (NMP), com o intuito de sintetizar membranas de ultrafiltração a partir do método de inversão de fases. O desafio consistem em combinar alta condutividade elétrica, boas propriedades mecânicas e oxidação eletroquímica, permitindo assim que a oxidação de possíveis contaminantes ocorra ao mesmo tempo em que a membrana atua como uma barreira de filtração seletiva. O efeito da adição de PANI foi avaliado quanto à morfologia da membrana, capacidade de separação e desempenho, em termos de permeabilidade e condutividade. As membranas modificadas apresentaram uma morfologia muito singular quando analisadas pelo Microscópio Eletrônico de Varredura (MEV), poros maiores foram identificados, ausência da camada seletiva, diminuição da camada inferior e grandes fases aglomeradas ao longo da seção transversal. Devido ao aumento do tamanho dos poros, a seletividade das membranas modificadas foi comprometida. Os resultados de porosidade para as membranas modificadas variaram entre 53 e 66%. A permeabilidade e a condutividade das membranas modificadas aumentaram à medida que a concentração de PANI também aumentou. O fluxo mediano obtido para a membrana com concentração de 40% de PANI foi de 835 L.m-2.h-1, cerca de 5 vezes maior do que o fluxo mediano obtido para a membrana controle. Já a condutividade mediana obtida para a mesma membrana modificada foi de 1,7x10-6 S, cerca de 15 vezes maior do que a membrana controle. Durante o teste de voltametria cíclica não foram observadas reações de oxidação-redução, nem da solução de ferro-cianeto nem da própria polianilina, ao aplicar uma tensão variando entre -0,2 V e 0,8 V. Desta forma, a partir dos resultados, pode-se afirmar que a adição de Polianilina alterou a morfologia e o desempenho das membranas modificadas, destacando o incremento na permeabilidade, hidrofilicidade e condutividade, mantendo sua característica de ser uma barreira de filtração seletiva. / In this work, different concentrations of Polyaniline (PANI) were added to a polymer solution made of Polyethersulfone (PES) and N-methylpyrrolidone (NMP), in order to synthesize ultrafiltration membranes by the phase inversion method and the challenge of combine high electrical conductivity, good mechanical properties and electrochemical oxidation, thus allowing the oxidation of matter to occur at the same time that the membrane acts as a selective and reliable filtration barrier. The effect of PANI addition was evaluated regarding the membrane morphology, separation capacity and performance in terms of permeability and conductivity. The modified membranes presented a very unique morphology when analyzed by the Scanning Electron Microscope (SEM), larger pores were identified, absence of the selective layer, decrease of the lower layer and large agglomerated phases with phase contour characterization along the cross section. Due to the increase in pore size, the selectivity of the modified membranes was compromised. The porosity results for the modified membranes are only reflections of the morphology obtained, and the median porosities varied between 53 and 66%. The permeability and conductivity of the modified membranes increased as the PANI concentration also increased. The median flow obtained for the membrane with 40% PANI concentration was 835 L.m-2.h-1, about 5 times higher than the median flow obtained for the control membrane. The median conductivity obtained for the same modified membrane was 1.7x10-6 S, about 15 times higher than the control membrane. During the cyclic voltammetry test, no oxidation-reduction reactions were observed, neither the iron-cyanide solution nor the polyaniline itself, when applying a voltage ranging from -0.2 V to 0.8 V. From the results, it can be affirmed that the addition of polyaniline particles altered the morphology and performance of the modified membranes, highlighting the increase in permeability, hydrophilicity and conductivity, maintaining its characteristics of being a selective filtration barrier.