Manipulating mechanical strength of isoreticular two-dimensional polyamide materials via multiple interactions

Anisotropic two-dimensional (2D) materials exhibit huge difference in the directions parallel and vertical to the plane, especially in mechanical properties, and the connecting interactions among 2D nanosheets dominates the bulk mechanical strength owing to the challenge to prepare continuous, single-crystal 2D material film at macroscopic scale. Herein, we report a series of isoreticular 2D polyamide materials and reveal that smaller structural units result in higher Young's modulus, while multiple weak forces including the hydrogen-bond, π-π and mismatched electrostatic interactions endows the bulk 2D materials superior elasticity, hardness and yield strength. Specifically, The Young's modulus and hardness of 2D polyamide film (GH-TMC) reach 35.6 GPa and 2.0 GPa, and the elastic recovery rate is as high as 60%, overwhelming the most polymer, metal and metal-organic framework (MOF)/covalent organic framework (COF) materials. The synergy of rigid small-ring units, high-density H-bond networks, and π-π/electrostatic interactions enable these films to bridge the gap between inorganic and polymeric materials, making them ideal for flexible electronics, high-performance protective coatings, and energy devices. The strategy via designing molecular structure and interactions among nanosheets in 2D materials enable us fabricate super 2D materials with overall mechanical strength.