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Made available in DSpace on 2014-12-17T15:41:55Z (GMT). No. of bitstreams: 1 WildsonAM_DISSERTPPGQ.pdf: 2126383 bytes, checksum: 6a1a9e8b2c55caac2fbd3fb938bff756 (MD5) Previous issue date: 2011-07-20 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Gels consist of soft materials with vast use in several activities, such as in pharmaceutical industry, food science, and coatings/textile applications. In order to obtain these materials, the process of gelification, that can be physical (based on physical interactions) and/or chemical (based on covalent crosslinking), has to be carried out. In this work we used dynamic light scattering (DLS) and rheometry to monitor the covalent gelification of chitosan solutions by glutaraldehyde. Intensity correlation function (ICF) data was obtained from DLS and the exponential stretched Kohrausch-William-Watts function (KWW) was fitted to them. The parameters of the KWW equation, β, Γ and C were evaluated. These methods were effective in clarifying the process of sol-gel transition, with the emergence of non-ergodicity, and determining the range of gelation observed in about 10-20 minutes. The dependence between apparent viscosity on reaction time was used to support the discussion proposed. / G?is s?o materiais que possuem aplica??es em v?rias ?reas, tais quais, na ind?stria de tintas, alimentos e farmac?utica. Os m?todos empregados para obten??o dos g?is podem ser f?sicos (intera??es f?sicas) e/ou qu?micos (baseado em intera??es covalentes), tal processo, ? denominado gelifica??o. Neste trabalho, o processo de gelifica??o de quitosana/glutaralde?do foi monitorado utilizando reometria e espalhamento da luz (DLS). As fun??es de correla??o de intensidade (ICF) foram obtidas atrav?s de DLS e a equa??o de Kohrausch-William-Watts (KWW) foi ajustada com os dados experimentais. Os par?metros da equa??o KWW, β, Γ e C foram avaliados. Estes m?todos foram eficazes na clarifica??o do processo que compreende a transi??o sol-gel, com o surgimento da n?o-ergodicidade, e na determina??o da faixa de gelifica??o, observada em torno de 10-20 minutos. A depend?ncia da viscosidade aparente em fun??o do tempo foi utilizada para comprovar o tempo de gelifica??o observado no DLS.

Photopolymerization is the basis of several multi-million dollar industries including films and coating, inks, adhesives, fiber optics, and biomaterials. The fundamentals of the photopolymerization process, however, are not well understood. As a result, spatial variations of photopolymerization impose significant limitations on applications in which a high spatial resolution is required. To address these issues, microrheology was implemented to study the spatial and temporal effects of free-radical photopolymerization. In this work a photosensitive, acrylate resin was exposed to ultraviolet light, while the Brownian motion of micron sized, inert fluorescent tracer particles was tracked using optical videomicroscopy. Statistical analysis of particle motion yielded data that could then be used to extract rheological information about the embedding medium as a function of time and space, thereby relating UV exposure to the polymerization and gelation of monomeric resins. The effects of varying depth, initiator concentration, inhibitor concentration, composition of the monomer, and light intensity on the gelation process were studied. The most striking result is the measured difference in gelation time observed as a function of UV penetration depth. The observed trend was found to be independent of UV light intensity and monomer composition. The intensity results were used to test the accuracy of energy threshold model, which is used to empirically predict photo-induced polymerization. The results of this research affirm the ability of microrheology to provide the high spatial and temporal resolution necessary to accurately monitor the photopolymerization process. The experimental data provide a better understanding of the photo-induced polymerization, which could lead to expanded use and improved industrial process optimization. The use of microrheology to monitor photopolymerization can also aid in the development of predictive models and offer the ability to perform in-situ quality control of the process.