Thermo-responsive shape and optical memories of photonic composite films enabled by glassy liquid crystalline polymer networks.

We propose a novel shape and optical memories of a photonic composite film based on a silica opal photonic crystal (PC) template and a liquid crystal polymer network (LCN). Here, the photonic composite film was fabricated by introducing a LCN precursor into a silica opal PC template, followed by UV photo-polymerization and then by the removal of the template. The obtained bilayer-structure photonic film was found to spontaneously form a three-dimensional (3D) temporary bending shape in response to heating, and thus the corresponding reflection color of the photonic composite film shows a blue shift during bending deformation. The inherent mechanisms of these two observations could be attributed to the variations of the LC molecule orientation and the light reflection in the photonic composite film during the thermal process. More intriguingly, the resulting temporary bending shape was fixed by applying mechanical force during slowly cooling down to the room temperature or autonomously fixed by a rapid cooling in liquid nitrogen. Additionally, this temporary state could restore back to the permanent flat shape when the film is cooled from the heat source without an external force. Finally, more complex 3D shape-memory samples could also be achieved by simply controlling the LC alignment or designing the sample geometry. This work opens up a new way to develop a novel shape-memory polymer photonic film.