Entropy-driven liquid-phase exfoliation of non-Van-Der-Waals crystals into nanoplatelets

Abstract

Liquid-phase exfoliation (LPE) methods have revolutionized the production of two-dimensional (2D) materials from layered crystals, employing techniques such as ultrasonic degradation, mechanical exfoliation, and electrochemical exfoliation. However, the exfoliation of three-dimensional (3D) crystals that are nonlayered and non-Van-Der-Waals presents both challenges and opportunities. This study introduces an atomistic biaxial shear-normal strain entropy analysis to comprehend and design the LPE process specifically for such materials. By analysing the atomistic compressive biaxial shear-normal strain induced during LPE in 3D crystals, we establish a strain–stress-entropy relationship and derive a general exfoliation rate equation. We validate our model by comparing it to literature-based alloy exfoliation tests and conducting new Mg(OH)2 LPE (ball milling) experiments. The results not only confirm the applicability of the derived equation but also provide valuable insights into the exfoliation process. The implications of these findings are substantial, as they open new possibilities in various applications by informing the selection of 3D crystals and facilitating the design and optimization of LPE processes.