resumo
Oscillatory and steady-shear rheological methods as well as scanning electron microscopy were used to characterize silica (SiO(2))/galactomannan dispersions. Particle loading and surface charge are found to strongly influence the composite structure and dynamics. When the particles were added above a minimum concentration, a sol-gel transition was induced. The SiO(2)/polysaccharide dispersions exhibited significant non-linearities, especially under ionic conditions that favor interparticle and particle-polysaccharide interactions, characterized by strong shear-thinning, diverging viscosities at low shear rates, apparent yield stress and high strain sensitivity. The mechanical spectra for the composite systems suggest that stress relaxation of these composites is effectively arrested by the presence of silica nanoparticles. Microstructural analysis revealed an ordering of the silica particles around the polymer chains. Polysaccharide chains act as templates for particle clustering leading to the formation of a particle-mediated transient biopolymer network, with particle clusters hindering polymer mobility and enhancing junction zones within the network. (C) 2010 Elsevier Ltd. All rights reserved.
palavras-chave
VISCOELASTIC PROPERTIES; NANOTUBE NETWORKS; NANOCOMPOSITES; BEHAVIOR; SUSPENSIONS; GELATION; SHEAR
categoria
Chemistry; Polymer Science
autores
Oliveira, F; Monteiro, SR; Barros-Timmons, A; Lopes-da-Silva, JA
nossos autores
Ana Margarida Madeira Viegas de Barros Timmons
Professor associadoagradecimentos
F.C. Oliveira thanks the Portuguese Foundation for Science and Technology (FCT) for a PhD grant (SFRH/BD/23396/2005).