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Layered materials1 are in the centre of interest since the discovery of graphene. One of the methods used for producing thin, 2-dimensional (2D) sheets from those materials is liquid exfoliation2, which enables production of thin layers and layered metamaterial composites. Many layered compounds can be exfoliated using ion intercalation, often resulting in structural deformation, thus sonication in organic solvents has become very much used2,3. However; efficient exfoliation by exposure of a layered material to ultrasonic waves usually requires use of long sonication times and relatively high power4, which together with the toxicity of the organic solvents make the method environmentally unfriendly and this triggers interests for procedures adopted for aqueous solutions3.
Here we present an example of a layered material which naturally exfoliates after immersion into water, namely nanolayered clay5,6, which generally does not require any of the procedures described above. We discuss swelling and exfoliation potential7 of several types of clay (hectorite, laponite, natural vermiculite) and the quality of exfoliated 2D sheets that can be obtained. Perspectives for inclusion of 2D clays in Van der Waals heterostructure devices is discussed.
References:
1. Geim, A. K. & Grigorieva, I. V. Van der Waals heterostructures. Nature 499, 419–425 (2014).
2. Nicolosi, V. et al. Liquid Exfoliation of Layered Materials. Science 340, (2013).
3. Smith, R. J. et al. Large-scale exfoliation of inorganic layered compounds in aqueous surfactant solutions. Adv. Mater. 23, 3944–3948 (2011).
4. Kouroupis-Agalou, K. et al. Fragmentation and exfoliation of 2-dimensional materials: a statistical approach. Nanoscale 6, 5926–33 (2014).
5. Mukherjee, S. Classification and Composition of Clay Constituents. The Science of Clays: Applications in Industry, Engineering and Environment (Springer Netherlands, 2013). doi:10.1007/978-94-007-6683-9_2
6. E. L. Hansen, H. Hemmen, D. M. Fonseca, C. Coutant, K. D. Knudsen, T. S. Plivelic, D. Bonn & J. O. Fossum, Swelling transition of a clay induced by heating. Scientific Reports 2, 618 (2012).
7. Rosenfeldt, S. et al. In-Depth Insights into the Key Steps of Delamination of Charged 2D Nanomaterials. Langmuir 32, 10582–10588 (2016).