Papers by Author: L. A. S. de A. Prado

Abstract: In the present work we report that the addition of inorganic nanoparticles to MWCNT epoxy composites leads to the formation of a hybrid structures which cause different states of dispersion for the multiphase nanocomposites containing either MWCNTs and titania or MWCNTs and silica. The microstructure is characterised by titania nanoparticles attached to the surface of MWCNTs leading to an enhanced dispersion of MWCNTs. The hydrophilic surface of fumed silica nanoparticles causes the formation of independent networks of silica and MWCNTs. Therefore, the change of the state of dispersion is less pronounced compared to the MWCNT/titania structures. Changes in the state of dispersion lead to a decrease in electrical conductivity for the MWCNT/titania systems. Conversely, an almost independent behaviour was found for the MWCNT/silica nanocomposites due to their interpenetrating networks. Besides the altered state of dispersion, the hybrid structure leads synergistic effects in terms of the glass transition of the nanocomposites. Although a decrease of the glass transition temperature (Tg) is observed for the nanocomposites containing only one kind of filler, the combination of nanoparticles can reduce the decrease of Tg.

Abstract: Given their unique set of properties, carbon nanotubes are rapidly gaining importance as stress/damage sensors in addition to as mere reinforcing elements in polymer composites. In this work, single-walled carbon nanotubes (SWCNT) are used to monitor internal stresses developing during the curing process of thermoset materials. SWCNT-epoxy composites with high dispersion quality were obtained via calandering. In situ Raman spectroscopy was used to identify chemical and thermal induced stresses by following the changes in the G’-band versus time and temperature. Thermal shrinkage prompts a pronounced effect on the spectral shifts of the composite, pointing at its dominant role (over chemical shrinkage) on the development of the internal stress field. Above Tg, Raman shifts due to temperature increase are found to be negligible, confirming the existence of a stress releasing mechanism. Shift rate of the composites cooling from their processing temperatures depended on the combination of matrix/SWCNT type, pointing at the role of interfacial strength on the load transfer efficiency.