Liquid-Evaporation-Assisted Self-Folding of One-Dimensional Nanomaterials

When one-dimensional (1-D) nanomaterials (e.g., nano-tubes, nanowires, nanofibers, nanoribbons) are suspended in a liquid droplet, once the liquid evaporation occurs at elevated temperatures, the system equilibrium will break, leading to large deformation, instability, and self-assembly of the 1-D nanomaterials. In the present study, we develop a theoretical framework that can describe the liquid evaporation-driven deformation and self-folding of one single 1-D nanofiber. An energy-based criterion is proposed by taking account of the mutual energy competitions of liquid surface tension and interaction and deformation of nanofibers. Both the critical elastocapillary length beyond which the self-folding will occur by liquid evaporation and the critical self-folding length beyond which the ultimate stable self-folded patterns can arrive after a complete evaporation of liquid are extracted and incorporated with properties of both nanofiber and liquid. Besides, the size and configuration of folded stable patterns are well predicted. Coarse-grained molecular dynamics simulations are conducted and show agreement with the theoretical predictions in both deformation configuration and self-folded patterns of 1-D nanofibers. The effect of bending-induced stretching and buckling deformation of nanofibers with various geometric features such as hollow fibers on self-folding is also discussed. The quantitative framework established herein is expected to shed an immediate guidance on the evaporation-assisted manufacturing technique by assembling low-dimensional nanomaterials into large-scale superstructures.