Programmable Self-assembly from Two-dimensional Nanosheets to Spiral, Twisted and Branched Nanostructures

Self-assembly of nanomaterials into hierarchical structure is of great interest to fabricate functional materials. However, programmable design of the assembled structures remains a great challenge. Herein, we reported a programmable self-assembly strategy to customize the assembled structure. The self-assembly strategy is designed to orderly transform the two-dimensional (2D) Ca ions assembled F127 nanosheets (Ca-F127 NSs) into spiral nanosheet structures (S-Ca-F127 NSs), branched nanosheet structures (B-Ca-F127 NSs), branched-spiral nanosheet structures (B-S-Ca-F127 NSs), and twisted-branched structures (T-Ca-F127 NBs). Wide-angle X-ray scattering (WAXS) and X-ray absorption spectroscopy (XAS) indicate that these different structures maintain the same orthorhombic phase and Ca-O octahedral coordination structure. Selected area electron diffraction (SAED) in the double-tilt liquid nitrogen cooling holder identifies the Eshelby twist in the twisted structures, demonstrating the spiral structure are formed by screw dislocation growth. Cryo-electron microscopy (cryo-EM) proves the oriented epitaxial growth in the B-Ca-F127 NSs. Furthermore, the formation mechanisms of spiral structure and branched structure can be recombined to form complex hierarchical structures. The epitaxial growth along screw dislocation can lead to the formation of B-S-Ca-F127 NSs, while the twisted epitaxial growth in the screw dislocation can lead to the formation of T-Ca F127 NBs.