Abstract
Carbon nanotubes (CNTs) which have high stability, specific surface area, and conductivity are suitable for conductive composite. This research discuss the application of carbon nanotubes composite as thermoelectric (multi-walled CNTs (MWCNTs)/TiO2) and electromagnetic shielding (porous composite of MWCNTs/ ethylcellulose) materials. Seebeck coefficient, according to Ioffe’s approximation, is inversely proportional to carrier density and decreases with doping. Here we find that incorporation of multi-walled carbon nanotubes into rutile TiO2 improves electrical conductivity and Seebeck coefficient at low filling fraction of tubes; the former is owing to lengthening of mean free path and doping modified effective mass for the latter. Tube-oxide mixing also causes significant phonon scattering at interfaces and reduced thermal conductivity is verified by promoted figure of merit. In contrast to conductive bulk materials, ethylcellulose porous composite with high MWCNTs weight percentage, which is synthesized by freeze-drying, exhibits low reflectance and high absorbance. The contribution of porous structure can be sorted into three mechanisms. First, electromagnetic wave is able to penetrate into porous structure. It decreases the reflectance. Second, the increase of diffuse reflection expands the transport path. Third, the increment of specific surface area enlarges the interfacial polarizations. The latter two are contributed to the enhancement of absorbance.