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Multiwalled carbon nanotubes (CNTs) as produced are usually entangled and not ready to be dispersed into fluids. We treated CNTs by using a concentrated nitric acid to disentangle CNT aggregates for producing CNT nanofluids. Oxygen-containing functional groups have been introduced on the CNT surfaces and more hydrophilic surfaces have been formed during this treatment, which enabled to make stable and homogeneous CNT nanofluids. Treated CNTs were successfully dispersed into polar liquids like distilled water, ethylene glycol without the need of surfactant and into nonpolar fluid like decene with oleylamine as surfactant. We measured the thermal conductivities of these nanotube suspensions using a transient hot wire apparatus. Nanotube suspensions, containing a small amount of CNTs, have substantially higher thermal conductivities than the base fluids, with the enhancement increasing with the volume fraction of CNTs. For the suspensions with the same loading, the enhanced thermal conductivity ratios are reduced with the increasing thermal conductivity of the base fluid. Comparison between the experimental data and the theoretical model indicates that the thermal conductivities of nanotube suspensions seem to be very dependent on the interfacial layer that exists between the nanotube and the liquid.

The recent achievement of the high thermoelectric figure of merit in nanograined materials is attributed to the successful optimization of the consolidation process. Despite a thermal conductivity reduction, it has been experimentally observed that the porous nanograined materials have lower thermoelectric figure of merit than their bulk counterpart due to significant reduction in the electrical conductivity. In this paper, nanoscale porosity effects on electron and phonon transport are modeled to predict and explain thermoelectric properties in porous nanograined materials. Electron scattering at the pores is treated quantum mechanically while phonon transport is treated using a classical picture. The modeling results show that the charge carriers are scattered more severely in nanograined materials than the macroscale porous materials, due to a higher number density of scattering sites. Porous nanograined materials have enhanced Seebeck coefficient due to energy filtering effect and low thermal conductivity, which are favorable for thermoelectric applications. However, the benefit is not large enough to overcome the deficit in the electrical conductivity, so that a high sample density is necessary for nanograined SiGe.

Current studies investigating properties of nanoparticle-reinforced polymers have shown that nanocomposites often exhibit improved properties compared to neat polymers. However, over two decades of research, using both experimental studies and modeling analyses, has not fully elucidated the mechanistic underpinnings behind these enhancements. Moreover, few studies have focused on developing an understanding among two or more polymer properties affected by incorporation of nanomaterials. In our study, we investigated the elastic and thermal properties of poly(acrylamide) hydrogels containing silica nanoparticles. Both nanoparticle concentration and size affected hydrogel properties, with similar trends in enhancements observed for elastic modulus and thermal diffusivity. We also observed significantly lower swellability for hydrogel nanocomposites relative to neat hydrogels, consistent with previous work suggesting that nanoparticles can mediate pseudo crosslinking within polymer networks. Collectively, these results indicate the ability to develop next-generation composite materials with enhanced mechanical and thermal properties by increasing the average crosslinking density using nanoparticles.

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