Reconfigurable assemblies of shape-changing nanorods.

Reconfigurable nanostructures represent an exciting new direction for materials. Applications of reversible transformations between nanostructures induced by molecular conformations under external fields can be found in a broad range of advanced technologies including smart materials, electromagnetic sensors, and drug delivery. With recent breakthroughs in synthesis and fabrication techniques, shape-changing nanoparticles are now possible. Such novel building blocks provide a conceptually new and exciting approach to self-assembly and phase transformations by providing tunable parameters fundamentally different from the usual thermodynamic parameters. Here we investigate via molecular simulation a transformation between two thermodynamically stable structures self-assembled by laterally tethered nanorods whose rod length is switched between two values. Building blocks with longer rods assemble into a square grid structure, while those with short rods form bilayer sheets with internal smectic A ordering at the same thermodynamic conditions. By shortening or lengthening the rods over a short time scale relative to the system equilibration time, we observe a transformation from the square grid structure into bilayer sheets, and vice versa. We also observe honeycomb grid and pentagonal grid structures for intermediate rod lengths. The reconfiguration between morphologically distinct nanostructures induced by dynamically switching the building block shape serves to motivate the fabrication of shape-changing nanoscale building blocks as a new approach to the self-assembly of reconfigurable materials.