A wide variety of biological materials (e.g. Dionaea muscipula and Mimosa pudica) can react to external stimulation with movements and changes of shape in order to fulfill diverse biological functions. The unique behavior observed for biological systems inspires the development of synthetic materials with unusual combination of shape changing properties for various applications. In particular, photoresponsive soft liquid crystalline elastomers (LCE) are considered promising candidates for production of sensors, actuators, and soft robots or muscle-like devices. With the advent of 3D printing of such materials, it has been possible to elaborate geometries with controlled and predetermined photoactuated movements, getting one step closer to the astonishing complexity and efficiency found in natural systems. However, the development of such materials is still in its infancy and only a limited choice of printable LCE is yet available. In this context, we propose to combine cellulose nanocrystals (CNC) from renewable resources into a LCE in order to enable the printing process by direct ink writing (DIW). The rheological influence of CNC allows the production of freestanding structures, while the printed part benefits from the anisotropic mechanical properties resulting from the extrusion-induced alignment of such nanoparticles. After printing, azobenzene photo-switches are introduced in the composite, conferring photomechanical behaviors to the printed material. This approach results in soft composites, with an elastic modulus of 20 – 30 MPa, that present fully reversible photosoftening of 35% and photomechanical actuation occurring in less than 3 seconds. The presence of CNC as reinforcement allows precise tailoring of mechanical properties of the composites. This renders such phototriggered materials suitable candidates for the production of actuators and 3D structures with particular and dynamic load cases.

Photo-responsive movement in 3D printed cellulose nanocomposites

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.