Microstructural evaluation of poly(vinyl alcohol)‐based hydrogels obtained by freezing‐thawing technique: Thermal analysis and positron annihilation |
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| Authors: | Caio M Paranhos Bluma G Soares Renata N Oliveira Luiz A Pessan Daniela S de Freitas Dario Windmöller José C Machado |
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| Affiliation: | 1. Instituto de Macromoléculas, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bloco J, Ilha do Fund?o, Rio de Janeiro RJ 21945‐970, Brasil;2. Departamento de Engenharia de Materiais, Universidade Federal de S?o Carlos, Rodovia Washington Luiz km 235, S?o Carlos SP 13565‐905, Brasil;3. Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, Av. Ant?nio Carlos 6627, Belo Horizonte MG 31270‐901, Brasil |
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| Abstract: | In this work, semi‐interpenetrating polymer network (s‐IPN) hydrogels of poly(vinyl alcohol) (PVA) with different contents of water‐soluble sulfonated polyester (PES) were obtained by freezing and thawing cycles. The samples were characterized by positron annihilation lifetime spectroscopy (PALS) and differential scanning calorimetry (DSC). PALS was used to determine the average free volume radius through lifetime measures of the ortho‐positronium (o‐Ps). Degree of crystallinity of the PVA/PES hydrogels was evaluated using the melting enthalpy ratios between the samples and the 100% crystalline PVA. The results show that an increase on the PES content leads to a decrease on the degree of crystallinity of the samples, reflecting an increase on the lifetimes (τ3). These structural changes could be interpreted as a result of different polymer‐polymer interactions between PVA and PES in the hydrogels. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 |
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| Keywords: | differential scanning calorimetry (DSC) free volume hydrogel positron lifetime water‐soluble polymers polymer– polymer interactions |
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