In-Depth Insights into the Key Steps of Delamination of Charged 2D Nanomaterials

Delamination is a key step to obtain individual layers from inorganic layered materials needed for fundamental studies and applications. For layered van der Waals materials such as graphene, the adhesion forces are small, allowing for mechanical exfoliation, whereas for ionic layered materials such as layered silicates, the energy to separate adjacent layers is considerably higher. Quite counterintuitively, we show for a synthetic layered silicate (Na_0.5-hectorite) that a scalable and quantitative delamination by simple hydration is possible for high and homogeneous charge density, even for aspect ratios as large as 20000. A general requirement is the separation of adjacent layers by solvation to a distance where layer interactions become repulsive (Gouy-Chapman length). Further hydration up to 34 nm leads to the formation of a highly ordered lamellar liquid crystalline phase (Wigner crystal). Up to eight higher-order reflections indicate excellent positional order of individual layers. The Wigner crystal melts when the interlayer separation reaches the Debye length, where electrostatic interactions between adjacent layers are screened. The layers become weakly charge-correlated. This is indicated by fulfilling the classical Hansen-Verlet and Lindeman criteria for melting. We provide insight into the requirements for layer separation and controlling the layer distances for a broad range of materials and outline an important pathway for the integration of layers into devices for advanced applications.