Tiling characteristics of water-surfactant stabilized graphene nanosheets by self-assembly at liquid-air interface

Direct liquid phase exfoliation of pristine 3D graphite into ultra-thin graphene nanosheets has been recognized as a simple and effective method for developing solution-processed techniques to produce high-quality samples. However, transforming such dispersions into functional and continuous thin films of graphene remains challenging due to limitations of conventional coating techniques such as spray coating, spin coating, drop casting, Langmuir-Blodgett deposition and printing. These methods often result random orientation and aggregation of nanosheets leading to thicker films and requiring sophisticated processing. Although graphene possesses exceptional physical properties arising from its unique structure, its full potential has yet to be realized, largely due to the absence of efficient and cost-effective thin film preparation methods. In this work, we report a self-assembly approach at the liquid-air interface that utilizes a volatile solvent to guide the dispersed nanosheets from random motion in the liquid phase into an orderly, tiled thin-film. Capillary forces during the drying process, driven by the Marangoni effect, result in the rapid formation of a distinct monolayer at the interface within 2 min as the volatile solvent evaporates. Sub-micron graphene thin films with different aspect ratios, multilayers and controlled film thicknesses in the range of ∼65 nm to ∼1 μm are successfully prepared. These self-assembled graphene films demonstrate an electrical conductivity of ≥ 10⁴ S/m and a negative temperature coefficient of resistance of −8 × 10⁻⁴/°C. The formation of densely packed graphene nanosheet films through the self-assembly approach opens promising opportunities for lightweight applications.