Dispersion and Sorting of Nanomaterials

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In the past two decades, a significant share of the activities in today’s nanoscience and nanotechnology has been devoted to synthetic carbon allotropes (0-dimensional fullerenes, 1D carbon nanotubes and 2D graphene), as they exhibit outstanding and unique mechanical and electronic properties. However, despite overwhelming progress in the dispersion, functionalization, sorting, characterization and processing of this family of materials, large scale industrial applications are still lacking, underlining the need of constantly identifying new, highly potent classes of materials. Currently, layered inorganic materials (e.g. BN, transition metal chalcogenides or oxides) exhibit a renaissance, as these materials cover the whole spectrum of metallic, semiconducting and insulating properties. As already partly documented in literature, they bear great potential for both electronic applications (metallic materials as transparent electrodes, semiconducting materials as transistors or insulating materials as dielectrics in capacitors) and energy harvesting and storage - especially as components in hybrid materials with carbon nanotubes as thermoelectric devices, supercapacitors or cathodes in Li ion batteries. Up to now, the insolubility and polydispersity of the layered inorganic materials rendered solution phase processing - a prerequisite for convenient thin film applications - virtually impossible. Thus, the first step in the process chain towards high performance devices has been the bottleneck for these layered nanomaterials that exhibit extraordinary properties from a physicist’s point of view. In 2011, Coleman and co-workers have shown that, in analogy to carbon allotropes, wet chemical exfoliation is an accessible route towards bulk production of monolayers and thus solution-phase processing. This certainly calls for chemists now, in order to further elaborate and improve wet chemical exfoliation, as the full potential of dispersion and sorting techniques is yet to be explored. This proposal is part of this work and targets unifying concepts in dispersion and exfoliation of nanomaterials, especially in aqueous solution by the choice of clever stabilizers and preparation conditions. Furthermore, efficient sorting scenarios to separate individual flakes from bi- and multilayers, as well as flakes of different sizes by centrifugation-based techniques are to be developed for the first time.