A Generic Humidification-Ironing Strategy for Highly Aligned 2D Nanosheet Assemblies

Constructing macroscopic films from 2D nanosheets that retain their intrinsic properties is fundamentally limited by structural defects formed during solvent evaporation. Here, inspired by the ironing of fabrics, we develop a generic humidification-ironing strategy to reconstruct wrinkled nanosheet assemblies into highly aligned and dense films. In this process, controlled hydration plasticizes the interlayer interfaces, while the applied thermal-mechanical field promotes nanosheet sliding, wrinkle removal, and structural fixation. Using graphene oxide (GO) as a model system, the processed film exhibits a 2.4-fold increase in orientation order and a nearly twofold increase in bulk density compared with the conventionally dried film. After chemical reduction, the resulting reduced GO (rGO) film achieves an in-plane thermal conductivity of 814 W m⁻¹ K⁻¹, corresponding to an 86% improvement over the untreated counterpart, together with a nearly doubled tensile strength. The same strategy is further extended to MoS₂, MXene, and vermiculite (VMT) films, demonstrating its robustness across different wet-assembled 2D materials. As a thermal spreader in a smartphone, the optimized rGO film reduces the peak chip temperature by 5.3°C and suppresses thermal throttling. This work establishes a scalable and material-adaptable route for manufacturing high-performance 2D nanosheet assemblies for thermal management and flexible electronics.