Shape-programmable liquid crystal elastomers with arbitrary 3D director fields and geometries
Programmable shape-morphing is vital for devices in various applications, such as robot locomotion, drug delivery and tunable surface wetting. Liquid crystal elastomer structures can have programmable complex shape transformations, depending on the programmed geometries and molecular orientations.
Capability to arbitrarily program three-dimensional (3D) director fields and 3D geometries of liquid crystal elastomer (LCE) structures, which allows for traditionally non-achievable morphing modes, is highly demanded. We report a strategy to fabricate liquid crystal elastomers (LCEs) with uncoupled programmable arbitrary 3D geometries and arbitrary 3D director fields by 3D-assembling microscale heterogeneous LCE voxel building blocks. This strategy is realized in a two-stage process presented in Figure 1. First, LCE voxels with arbitrarily selected uniform director field are fabricated via two-photon polymerization. The selected director field is realized via a two-step rotation of LCE voxels around predefined axis (Figure 1a). Second, these voxels with arbitrary director fields are 3D assembled together to form arbitrary geometries with any desired heterogeneous profiles of the director fields (Figure 1b).
Figure 1. Schematic of the fabrication process.
Programmed complex, large, and reversible shape-morphing is one characteristic advantage of LCEs compared with other stimuli-responsive materials. Since the morphing modes depend on both the geometry and the director fields of the LCE, our strategy of fabricating LCEs with both arbitrary geometries and arbitrary director fields enables various shape-morphing modes. We present one-dimensional (1D), two-dimensional (2D) and 3D (Figure 2) LCEs with traditionally non-achievable director fields and demonstrate the enabled exotic morphing modes. By significantly enriching 3D morphing modes, we hope that this work can inspire more research effort in exploring the possibility of 3D shape-morphing between two arbitrary shapes.
Figure 2. Programmed thermal 3D-to-3D shape-morphing of the fabricated 3D LCE.
Additionally, LCEs are anisotropic, where almost all physical properties are different along the directions parallel and perpendicular to their local director fields. In this work, we demonstrated the anisotropic optical properties of the assembled LCE structures. We expect that the proposed versatile approach to fabricate LCE structures with arbitrarily programmable 3D geometries and 3D director fields would enable a wide range of applications in constructing 3D LCE devices with programmable heterogeneous physical properties.
Our future research will improve the reported approach by addressing three challenges. First, the manual assembly employed at this stage is a serial process with relatively low throughput, requiring a longer time to fabricate larger or more complex structures with more voxels. Second, the voxel size need to be larger than 50 μm for effective assembly, which limits the LCE’s resolution. Third, the surface anchoring strength of the LC monomer in the LC cells limits the maximal voxel size to 100 μm, which set the maximal assembled structure size to be a few millimeters considering the serial assembly process speed. We will employ advanced automated robotic micromanipulation systems to address such challenges in the future.
For more information, please read our recent publication in Nature Communications:
Yubing Guo, Jiachen Zhang, Wenqi Hu, Muhammad Turab Ali Khan & Metin Sitti. Shape-programmable liquid crystal elastomer structures with arbitrary three-dimensional director fields and geometries. Nature Communications (2021).
Lab website: http://pi.is.mpg.de