Liquid–crystalline properties of aqueous suspensions of natural clay nanosheets

Clay minerals, like beidellite or nontronite, spontaneously exfoliate in water and form colloidal suspensions of nanosheets. In a given range of concentration, these suspensions display a nematic liquid–crystalline phase whose structure and properties can be conveniently studied in detail by polarized-light microscopy and small-angle X-ray scattering (SAXS). Moreover, in situ SAXS investigations of sheared clay suspensions provide information about their flow properties, both in the isotropic and nematic phases. The colloidal nematic phase shows the classical properties of usual nematics, such as surface anchoring and electric-field and magnetic-field alignment. Thus, nematic single domains can be produced. The isotropic phase also displays strong electro-optic effects in moderate electric fields. Finally, we describe a few examples of applications of such systems and we show how these studies could be extended to suspensions of other types of nanosheets.