(734g) Light-Responsive Shape Memory Polymer Photonic Crystals Enabled By Photothermal Heating
Here we report a strategy for fabricating smart shape memory polymers (SMPs) which exhibit nontraditional shape manipulation in response to laser illumination. While previous work has explored light-responsive SMPs which are enabled by photofixing and photocleaving of cinnamic acid type molecules, this method of shape memory is slow, requiring ~60 minutes of laser illumination. The method reported here relies on the photothermal effect, where light is absorbed and converted into heat. This allows for indirect heating of a local region within the SMP system. In this work, macroporous SMP photonic crystals membranes with three-dimensional ordered macropores and microscopic thickness (~ 3 mm) are templated using self-assembled colloidal crystals as sacrificial templates. The SMP system is either doped with graphene nanoplatelets or coumarin 522 laser dye. Deformation of the permanent periodic structure into temporary disordered configurations can be achieved by heating the membrane above its glass transition temperature and applying pressure in a hydraulic press. Laser illumination can trigger rapid recovery of the 3-D ordered structure (in seconds), leading to strong Bragg diffraction of the incident laser. The graphite-doped SMP allows for broadband light absorption and strong mechanical properties of the SMP system, such as an increase in glass transition temperature as measured by differential scanning calorimetry. The dye-doped SMP maintains a high level of transparency, allowing for use in various applications that require transparency. The durable graphene-loaded SMP system can find applications in protecting military vehicles from high-energy laser weapons, while the transparent dye-doped SMP can be used to protect pilots from hazardous flash blinding laser light.