The rapidly increasing device densities in electronics dictate the need for efficient thermal management. If successfully exploited, graphene, which possesses extraordinary thermal properties, can be commercially utilized in polymer composites with ultrahigh thermal conductivity (TC). The total potential of graphene to enhance TC, however, is restricted by the large interfacial thermal resistance between the polymer mediated graphene boundaries. We report a facile and scalable dispersion of commercially available graphene nanoplatelets (GnPs) in a polymer matrix, which formed composite with an ultrahigh TC of 12.4 W/m K (vs 0.2 W/m K for neat polymer). This ultrahigh TC was achieved by applying high compression forces during the dispersion that resulted in the closure of gaps between adjacent GnPs with large lateral dimensions and low defect densities. We also found strong evidence for the existence of a thermal percolation threshold. Finally, the addition of electrically insulating boron-nitride nanoparticles to the thermally conductive GnP-polymer composite significantly reduces its electrical conductivity (to avoid short circuit) and synergistically increases the TC. The efficient dispersion of commercially available GnPs in polymer matrix provides the ideal framework for substantial progress toward the large-scale production and commercialization of GnP-based thermally conductive composites.

The rush to develop graphene applications mandates mass production of graphene sheets. However, the currently available complex and expensive production technologies are limiting the graphene commercialization. The addition of a protective diluent to graphite during ball-milling is demonstrated to result in a game-changer yield (>90%) of defect-free graphene, whose size is controlled by the milling energy and the diluent type.

Thermal management has become a critical aspect in next-generation miniaturized electronic devices. Efficient heat dissipation reduces their operating temperatures and insures optimal performance, service life, and efficacy. Shielding against shocks, vibrations, and moisture is also imperative when the electronic circuits are located outdoors. Potting (or encapsulating) them in polymer-based composites with enhanced thermal conductivity (TC) may provide a solution for both thermal management and shielding challenges. In the current study, graphene is employed as a filler to fabricate composites with isotropic ultrahigh TC (>12 W m(-1) K(-1)) and good mechanical properties (>30 MPa flexural and compressive strength). To avoid short-circuiting the electronic assemblies, a dispersion of secondary ceramic-based filler reduces the electrical conductivity and synergistically enhances the TC of composites. When utilized as potting materials, these novel hybrid composites effectively dissipate the heat from electronic devices; their operating temperatures decrease from 110 to 37 °C, and their effective thermal resistances are drastically reduced, by up to 90%. The simple filler dispersion method and the precise manipulation of the composite transport properties via hybrid filling offer a universal approach to the large-scale production of novel materials for thermal management and other applications.

A fundamental understanding of the mechanisms involved in the surfactant-assisted exfoliation and dispersion of carbon nanotubes (CNTs) in water calls for well-controlled experimental methodologies and reliable comparative metrics. We have assessed the ability of several ionic surfactants to disperse single and multiwalled carbon nanotubes, resorting to a stringently controlled sonication-centrifugation method for the preparation of the dispersions. The CNT concentration was accurately measured for a wide range of surfactant concentration, using combined thermogravimetric analysis and UV-vis spectroscopy. The obtained dispersibility curves yield several quantitative parameters, which in turn allow for the effects of nanotube morphology and surfactant properties (aromatic rings, chain length, headgroup charge, and cmc) to be assessed and rationalized, both in terms of dispersed nanotube mass and surface area. The data also indicate that the CNT-surfactant association follows patterns that are markedly different from other equilibrium processes governed by hydrophobicity (such as micellization); in particular, the surfactant concentration needed for maximum dispersibility, c(s,max), and the number of surfactant molecules per unit CNT area at c(s,max) are shown to depend linearly on chain length. The results further suggest that the presence of micelles in the exfoliation process is not a key factor either for starting CNT dispersibility or attaining its saturation value.

Dispersing graphite into few-layers graphene sheets (GS) in water is very appealing as an environmental-friendly, low-cost, low-energy method of obtaining graphene. Very high GS concentrations in water (0.7 mg mL(-1)) were obtained by optimizing the nature of dispersant and the type of ultra-sonic generator. We find that a multi-step sonication procedure involving both tip and bath sources considerably enhances the yield of exfoliated GS. Raman and transmission electron microscopy indicate few-layers graphene patches with typical size of ∼0.65 μm in one dimension and ∼0.35 μm in the other. These were further employed in combination with water-dispersed CNTs to fabricate conductive transparent electrodes for a molecularly-controlled solar-cell with an open-circuit voltage of 0.53 V.