Ultrasonic-Excited Ultrafast Seamless Integration of Heterostructured Liquid Crystalline Elastomers for Multi-responsive Soft Actuators

Abstract

Multicomponent/heterostructured liquid crystalline elastomers (LCEs) have recently garnered extensive attention for the design of soft robots with high dexterity and flexibility. However, the reported integration strategies of LCEs seriously suffer from high welding temperature, long processing time, and poor joint quality. Herein, the high-efficiency seamless ultrasonic welding (UW) of reprogrammable silver nanowire−LCE composites (AgNW−LCEs) have been realized without any auxiliary reagents based on the dynamic silver− disulfide coordination interactions. The elaborate combination of silver− disulfide coordination interactions and UW technology establishes an effective double-network welding mechanism of AgNWs and dynamic LC networks due to the high-frequency vibration at the welding interface. During the UW process, monolithic AgNW−LCEs can be integrated into heterostructured actuators at room temperature for 0.68 s. Furthermore, the welded AgNW−LCEs demonstrate an exceptional strain healing efficiency of ∼100%, a stress healing efficiency of ∼85%, and a maintained orientation of the LC alignment. Taking advantage of the high-efficiency UW technology, the heterostructured AgNW−LCE actuators with different LC alignments or LC monomers have been successfully implemented for a multi-degree-of-freedom soft robotic arm and a time-modulated flower-mimic actuator. This work provides an efficient approach toward the development of multi-responsive entirely soft actuators based on smart polymers.

Programming Liquid Crystalline Elastomer Networks with Dynamic Covalent Bonds

“…prepared an LCE network via thiol‐Michael addition reactions (Figure 3E), where the disulfide groups in the non‐mesogenic chain extender can undergo bond exchange reactions upon heating or UV irradiation. [ 24 ] The other strategy is to form DCBs during the LCE network formation. For example, Yang et al.…”

“…Reproduced with permission. [ 24 ] Copyright 2023, American Chemical Society. F) In situ generating DCBs during the LCE synthesis.…”

“…This subtle difference can be further recognized from a network perspective when DCBs are served as network linkages (Figure 3C,D). More specifically, the cross-link density of an "addition" DCB-LCE network decreases Transesterification Heat [11,15,23,25,30,31,32,35] Transcarbamoylation Heat [42] Boronic ester Heat [27] Siloxane exchange Heat [26,28] Disulfide metathesis Heat/Light [12,13,16,24,36,40] Diselenide metathesis Heat/Light [14] Ally sulfide exchange Light [29,37,38] Imine exchange Heat [33] Thiol-urea exchange Heat (Continued).…”

“…For instance, Zheng et al prepared an LCE network via thiol-Michael addition reactions (Figure 3E), where the disulfide groups in the non-mesogenic chain extender can undergo bond exchange reactions upon heating or UV irradiation. [24] The other strategy is to form DCBs during the LCE network formation. For example, Yang et al prepared an LCE network via a ring-opening reaction between epoxy-terminated biphenyl mesogens and sebacic acid, forming ample hydroxyl and esters groups that are capable of transesterification for network rearrangement (Figure 3F).…”