Ion exchange engineering of 2D mica for tunable mechanical and dielectric properties

Mica, a well-known natural mineral, combines chemical stability, electrical insulation, and atomically flat surfaces, enabling applications ranging from ornaments to capacitors and device substrates, supporting the stepwise progress in human civilization. However, the extreme chemical inertness is a double-edged sword: While it preserves stability, it restricts functionalization to aggressive, defect-inducing activation, severely impeding functional improvement and expansion. Consequently, mild, mechanistically informed strategies remain exceedingly scarce. Here, we demonstrate a gentle ion exchange process via simple solution immersion to reprogram the surface chemistry of atomically flat two-dimensional (2D) mica by exchanging native cations K⁺ for H⁺, Na⁺, and Cs⁺. This surface-selective modification preserves the intrinsic Young’s modulus of the mica, while allowing systematic control over surface adhesion and friction (H⁺ > cleaved > Cs⁺ >Na⁺), with a fivefold difference between the maximum and minimum. Moreover, the exceptional dielectric response of H⁺-exchanged mica originates from a uniquely dense interfacial water layer, which elevates both the intrinsic permittivity and ion mobility. This non-invasive surface engineering strategy not only precisely tunes mica’s mechanical and dielectric properties but also provides insights into developing high-performance 2D dielectrics in advanced electronics and bio-integrated systems.