  Reconfigurable metamaterials require constituent nanostructures to
demonstrate switching of shapes with external stimuli. For generality, such
nanostructures would touch and stick to other surfaces in one of its
configurations. Yet, a longstanding challenge is in overcoming this stiction
caused by Van der Waals forces, which impedes shape recovery. Here, we
introduce a stiff yet self-recovering material system based on acrylic acid,
and tested it in high-aspect ratio structures, where recovery is weak. This
designer material has a storage modulus of ~5.2 GPa at room temperature and ~90
MPa in the rubbery state at 150 Celsius, an order of magnitude higher than
previous reports. A high-resolution resin for two-photon lithography was
developed based on this polymer system, enabling 3D printing of nanopillars
with diameters of ~400 nm and aspect ratio as high as ~10. Experimentally, we
observed self-recovery as collapsed and touching structures overcome stiction
to stand back up. We developed a theoretical model to explain the
recoverability of these sub-micron structures. Reconfigurable structural colour
prints and holograms were demonstrated, indicating potential applications of
the material system as a shape memory polymer suitable for sub-micron
reconfigurable metamaterials.
