Unveiling the deposition mechanism of ultra-thin graphene oxide flakes in an aqueous colloidal phase

• Simple drop-casting enables to fabricate various structured graphene oxide films. • The transport/aggregation of graphene oxide flakes affect the contact line dynamics. • The deposition mechanism of graphene oxide flakes is comprehensively demonstrated. • The contact line dynamics and deposition behavior determine final film structures. The ability to control the structures of deposited films after the solution evaporation is critical to use the solution process to simply fabricate large-area micro-nanomaterial films utilized in various function devices such as sensors, flexible electronics and biomaterials. In this work, we experimentally demonstrate the deposition mechanism of the high-aspect ratio graphene oxide flakes dispersed within the evaporating sessile droplet by observing/analyzing the change in overall structures and the surface wrinkles of the graphene oxide films deposited by the simple drop-casting under various evaporation conditions (evaporation temperature, solution concentration, and initial contact angle). Variations in internal flows (capillary flow vs. Marangoni flow) and interaction forces between dispersed graphene oxide flakes depending on the evaporation conditions affected contact line dynamics of the evaporating droplet and the deposition behavior of the dispersed flakes, resulting in different deposition patterns, maximum diameters of the films and surface structures. The detailed deposition mechanism was revealed from the perspective of the transport and aggregation of the dispersed graphene oxide flakes during the evaporation process, which can be foundational to understand and control the deposition pattern of other functional two-dimensional nanomaterials deposited by the solution process.