Lightweight conductive foam: An ultralight conductive nanocomposite foam with a density of 0.05 g cm−3 (see SEM image) was successfully prepared based on multi‐walled carbon nanotubes and rigid polyurethane. An interesting density‐dependent conductor–insulator transition was observed in this ultralight composite, which reveals the weight‐lightening limit of a conductive polymer composite.

The carbon nanotubes (CNTs)/rigid polyurethane (PU) foam composites with a low percolation threshold of $ 1.2 wt % were prepared by constructing effective conductive paths with homogeneous dispersion of the CNTs in both the cell walls and struts of the PU foam. The conductive foam presented excellent electrical stability under various temperature fields, highlighting the potential applications for a long-term use over a wide temperature range from 20 to 180 C. Compression measurements and dynamical mechanical analysis indicated 31% improvement in compression properties and 50% increase in storage modulus at room temperature in the presence of CNTs (2.0 wt %). Additionally, the incorporation of only 0.5 wt % CNTs induced remarkable thermal stabilization of the matrix, with the degradation temperature increasing from 450 to 499 C at the 50% weight loss.

It is particularly difficult to prepare a foam CPC material because its porous structure makes it hard to form a conductive network. We utilized acetone‐assisted dispersion to disperse CNTs into PU foam and successfully prepared a lightweight conductive CNT/assembled PU foam composite. The NTC effect, which exclusively exists in the melt state CPC materials, has unexpectedly been observed in the solid‐state lightweight conductive CNT/sPU composite. Higher gas fraction and lower matrix modulus could result in stronger NTC effect. The mechanism that thermal expansion of gas wrapped in the cellular structure induces more perfect conductive paths has been proposed to satisfactorily elucidate the NTC effect and its gas fraction and matrix modulus dependence.magnified image

Cover: The cover picture summarizes the study of the negative temperature coefficient (NTC) of resistivity in lightweight conductive carbon nanotube-polymer composites. The SEM images show the typical microstructure consisting of walls and struts. The bottom images show the gas fraction-dependence of the NTC effect (right), and the gas expansion-induced NTC schematic (left). Further details can be found in the article by

The variations of electrical property of an ultralight conductive carbon nanotube/polymer composite foam upon compression were investigated. It was found the sharp increase of volume resistivity and strain was generated by the same microstructural change, i.e., the damage of foam struts. Even the strain was increased to as high as 50%, the ultimate resistivity remained stable. Volume resistivity of the foam kept almost changeless under an invariant external mechanical field. The stable microstructure of the conductive network formed by contact of CNTs and the high endurance of samples' core regions endow the ultralight conductive foam with much stable electrical properties.