Estudo das propriedades térmicas, estruturais e fotocrômicas do acetato de celulose contendo ácido fosfotungstico
Arquivos
Data
2022-06-20
Autores
Pacheco, Camila de Castro 
Orientadores
Molina, Celso
Tipo
Trabalho de conclusão de curso
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ISSN da Revista
Título de Volume
Resumo
Materiais fotocrômicos são aqueles capazes de mudar de cor reversivelmente quando submetidos a certas radiações eletromagnéticas, como o ultravioleta (UV). Derivados de celulose tais como o acetato de celulose (AC) são interessantes devido as boas propriedades mecânicas, alta transparência na região do visível, são biodegradáveis e solúveis em diversos solventes, sendo matrizes interessantes para a incorporação de espécies ativas de interesse como o ácido fosfotungstico (PWA). Neste trabalho foram estudadas as propriedades térmicas, estruturais e fotocrômicas de filmes fotocrômicos baseados na matriz de AC contendo diferentes concentrações de PWA (0, 10, 20, 40, 50%) (m:v) em mistura de solventes (N,N-dimetilformamida:Acetona). Os filmes foram obtidos pela técnica de deposição por casting. As caracterizações foram realizadas pelas técnicas de termogravimetria e calorimetria exploratória diferencial, espectroscópicas de UV-Vis, infravermelho e raman. Os resultados mostraram que os filmes obtidos são estáveis termicamente até aproximadamente 200oC e apresentam alta transparência na região do visível tanto para o filme puro de AC quanto para os contendo PWA. Além disso, todas as composições apresentaram efeito fotocrômico, apresentam coloração azul quando expostos a radiação ultravioleta e esse efeito é reversível. A intensidade da cor azul aumenta em função da concentração de PWA. O filme de maior concentração que apresentou a maior absorbância, 50% de PWA, foi escolhido para o estudo fotocrômico. Foi exposto à radiação ultravioleta com lâmpada de mercúrio e seus espectros UV-Vis mostram bandas de transição d-d e de transferência de carga intervalência (TCIV) devido à redução de W6+ para W5+. A reversibilidade foi acompanhada monitorando as bandas de transição d-d em 485 nm e de TCIV em 745 nm até retorno da cor transparente original. Estes filmes apresentaram fotosensibilidade à radiação UV com potencial para aplicações como materiais fotocrômicos.
Photochromic materials are those capable of reversibly changing color when certain electromagnetic radiation is applied, such as ultraviolet (UV). Cellulose derivatives such as cellulose acetate (CA) are interesting due to their good mechanical properties, high transparency in the visible region, biodegradable and soluble in several solvents, being interesting matrices for the incorporation of active species of interest such as phosphotungstic acid (PWA). In this investigation, thermal, structural and photochromic properties of photochromic materials based on AC matrix containing different concentrations of PWA (0, 10, 20, 40, 50%) (m:v) in solvent mixture (N,N-dimethylformamide:Acetone) were studied. The films were obtained by casting deposition method. These were characterized by thermogravimetric techniques thermogravimetry and differential scanning calorimetry, UV-Vis, infrared and Raman. Films are thermally stable up to approximately 200°C and show high transparency in the visible range for both AC and AC-PWA based. Moreover, all composition showed photochromic and effect after ultraviolet exposition and they change their color from transparent to blue. Taking these properties into account, the film with the highest concentration was chosen for the studies of photochromic properties. The film containing the highest concentration that showed the highest absorbance, 50% of PWA was exposed to ultraviolet radiation with a mercury lamp. The color changed from transparent to blue and the d-d transition and charge transfer intervalence (TCIV) bands were observed due to the reduction from W6+ to W5+. Photobleaching process was monitored in the d-d transition at 485nm and from TCIV at 745nm bands until the original transparent color be reached. These films showed photosensitivity to UV radiation with potential for applications such as photochromic materials.
Photochromic materials are those capable of reversibly changing color when certain electromagnetic radiation is applied, such as ultraviolet (UV). Cellulose derivatives such as cellulose acetate (CA) are interesting due to their good mechanical properties, high transparency in the visible region, biodegradable and soluble in several solvents, being interesting matrices for the incorporation of active species of interest such as phosphotungstic acid (PWA). In this investigation, thermal, structural and photochromic properties of photochromic materials based on AC matrix containing different concentrations of PWA (0, 10, 20, 40, 50%) (m:v) in solvent mixture (N,N-dimethylformamide:Acetone) were studied. The films were obtained by casting deposition method. These were characterized by thermogravimetric techniques thermogravimetry and differential scanning calorimetry, UV-Vis, infrared and Raman. Films are thermally stable up to approximately 200°C and show high transparency in the visible range for both AC and AC-PWA based. Moreover, all composition showed photochromic and effect after ultraviolet exposition and they change their color from transparent to blue. Taking these properties into account, the film with the highest concentration was chosen for the studies of photochromic properties. The film containing the highest concentration that showed the highest absorbance, 50% of PWA was exposed to ultraviolet radiation with a mercury lamp. The color changed from transparent to blue and the d-d transition and charge transfer intervalence (TCIV) bands were observed due to the reduction from W6+ to W5+. Photobleaching process was monitored in the d-d transition at 485nm and from TCIV at 745nm bands until the original transparent color be reached. These films showed photosensitivity to UV radiation with potential for applications such as photochromic materials.