Tuning Spatially Resolved Shape Memory Effects of Stimuli‐Responsive Macroporous Photonic Crystals

Abstract

Stimuli‐responsive photonic crystals with patterned microstructures are of great interest in developing reconfigurable nano‐optical devices. Leveraging unconventional all‐room‐temperature shape memory efforts and spatially resolved photopolymerization, herein, a facile method for micropatterning stimuli‐responsive photonic crystals is reported. Macroporous shape memory polymer (SMP) photonic crystals fabricated by colloidal templating can be deformed by cold programming, triggering the disappearance of their original structural colors. Exposure of the deformed samples to UV light through a photomask selectively disables the shape memory capabilities in the UV‐exposed regions. Hidden micropatterns defined by the photomask can be revealed by exposing the colorless SMP films to ethanol vapor, which triggers the shape memory recovery of the “memorized” ordered microstructures and the corresponding structural colors. Extensive nanoindentation experiments indicate that the exposure to UV light increases the crosslinking density and enhances the elastic modulus and toughness of the exposed regions by a factor of ≈2.0 and ≈5.2, respectively. Due to the formation of these extra crosslinks in the deformed configuration, they prevent normal shape memory behavior where the strained polymer chains rearrange from the temporary to permanent configuration when triggered by an external stimulus. This simple micropatterning technology can enable multistimuli‐responsive reconfigurable nanophotonic devices and chromogenic anticounterfeiting labels.