Stimuli-Responsive Polymers for Soft Robotics

This article reviews recent progress in the use of stimuli-responsive polymers for soft robotics. First, we introduce different types of representative stimuli-responsive polymers, which include liquid crystal polymers and elastomers, hydrogels, shape memory polymers, magnetic elastomers, electroactive polymers, and thermal expansion actuators. We focus on the mechanisms of actuation and the evaluation of performance and discuss strategies for improvements. We then present examples of soft robotic applications based on stimuli-responsive polymers for bending, grasping, walking, swimming, flying, and sensing control. Finally, we discuss current opportunities and challenges of stimuli-responsive soft robots for future study. Expected final online publication date for the Annual Review of Control, Robotics, and Autonomous Systems, Volume 5 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Engineering Achiral Liquid Crystalline Polymers for Chiral Self-Recovery

Flexible construction of permanently stored supramolecular chirality with stimulus-responsiveness remains a big challenge. Herein, we describe an efficient method to realize the transfer and storage of chirality in intrinsically achiral films of a side-chain polymeric liquid crystal system by combining chiral doping and cross-linking strategy. Even the helical structure was destroyed by UV light irradiation, the memorized chiral information in the covalent network enabled complete self-recovery of the original chiral superstructure. These results allowed the building of a novel chiroptical switch without any additional chiral source in multiple types of liquid crystal polymers, which may be one of the competitive candidates for use in stimulus-responsive chiro-optical devices.

Polarization Imaging of Liquid Crystal Polymer Using Terahertz Difference-Frequency Generation Source

We performed the polarization imaging of a liquid crystal polymer with a terahertz difference-frequency generation (THz DFG) source. The DFG source is an easy-to-operate and practical THz source. Liquid crystal polymers (LCPs) are suitable for applications such as fuel cell components, aircraft parts, and next-generation wireless communication materials. Accordingly, the demand for evaluating the orientation of liquid crystals, which affects the properties of the polymers, is set to increase. Since LCPs exhibit birefringence in the THz range due to the orientation of the liquid crystal molecules, we can determine the alignment of the molecules from the direction of the optical axis.