Cation Exchange Capacity Controlled Exfoliation of Monolayer Montmorillonite as Inorganic Liquid Crystals

Clays, pivotal in human civilization for millennia, are re-emerging as promising candidates in applications such as liquid crystals (LCs) after 2D delamination. However, the scalable exfoliation of monolayer clays with high geometric anisotropy remains challenging, hindering fundamental investigations and applications of 2D clay LCs. Here, a cation exchange capacity (CEC)-controlled exfoliation to achieve monolayer production of montmorillonite (MMT), a typical aluminosilicate clay, is developed. The optimized exchange ratios based on the CEC of MMT enable stepwise swelling and delamination, thus achieving 2D MMT with a record-high aspect ratio of ≈600. Then, lyotropic liquid crystalline behavior in 2D MMT is observed, and its electro-birefringence Kerr effect with a high sensitivity of ≈1.0 × 10⁻³ m V⁻² is discovered. By leveraging the interference from electro-birefringence, electrochromic devices capable of reversible electro-optical switching and dynamic coloration are demonstrated. This work provides an effective strategy to prepare monolayer clays and bridges natural resources with novel 2D LCs, advancing sustainable materials in smart optics and beyond.