Jan Sumfleth

Time and temperature dependent piezoresistance of carbon nanofiller/polymer composites under dynamic load

In this study, the behaviour of carbon nanotube/epoxy and carbon black/epoxy composites under dynamic load is studied via dynamic mechanical thermal analysis (DMTA) in combination with DC electrical resistivity measurements. DMTA measurements are carried out at fixed temperature whilst the dynamic loading frequency is varied. With this procedure, a loading frequency-dependence of the phase shift between DC electrical resistance and mechanical elongation (δR–ε) is observed, although the force and elongation of the sample are still in phase. Moreover, the magnitude of this phase shift, as well as the amplitude of the DC electrical resistance change shows a clear dependence on the initial electrical conductivity of the samples. In addition, temperature sweeps are carried out to investigate the temperature dependency of the piezoresistance of the samples. An abrupt change in their sensitivity is observed as soon as the glass transition of the polymer is reached. However, the trend of the resistance change beyond the glass transition is substantially different between the nanocomposites containing carbon black and carbon nanotubes, revealing a strong influence of the network characteristics on the piezoresistive behaviour of these novel materials.

Enhanced Dispersion of MWCNTs and Synergistic Properties in Multiphase Epoxy Nanocomposites by Incorporation of Inorganic Nanoparticles

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.