Photocured Liquid-Crystalline Polymer Electrolytes with 3D Ion Transport Pathways for Electromechanical Actuators

Abstract

Self-assembly of ionic molecules into hierarchical ordered structures is a promising route to new types of solid electrolytes with enhanced ion transport. Herein, we report a liquid-crystalline polymer electrolyte membrane that contains three-dimensionally (3D) interconnected ionic pathways. To build this membrane, we used wedge-shaped amphiphilic molecules that have two ionic heads and a lipophilic tail. These molecules were combined with a low content of ionic liquid (5.6 wt %) to form a hexagonal columnar phase, where the selfassembled lipophilic cylinders were surrounded by the ionic shell. Photopolymerization of this phase produced flexible nanostructured films with 3D ionic pathways, which can serve as an electrolyte layer in soft robotic actuators. Ionic transport in the 3D pathways leads to shape memory capability as well as durable bending actuation with a voltage-controllable blocking force. Furthermore, we find a significant enhancement of actuation for the nanostructured electrolyte compared with the corresponding amorphous electrolyte.

Nanostructured liquid-crystalline polymer films for ionic actuators: self-assembly of photopolymerizable ionic itaconate with an ionic liquid

“…Each of these properties is superior to those of other ionic liquid-based actuators including block polymers and polyimides and is comparable to our recent columnar LC polymer actuator with 3D ion-transport pathways. 28 In addition, we have observed the biodegradability of the nanostructured polymer electrolyte film. This sustainable design of polymerizable liquid crystals using itaconate offers exciting opportunities for electromechanical energy conversion in the development of next-generation soft robotic and haptic technologies.…”

“…25,26 In our recent report, we discussed the development of ionic actuators composed of photopolymerized ionic columnar liquid crystals and conductive polymer electrodes made of poly (3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS). 27,28 These innovative actuators exhibit larger strain and higher force, despite having a lower ion content compared to conventional gel electrolytes. In addition, we recently reported high frequency actuators using a randomly oriented twodimensional (2D) lithium-ion-conductive phosphate liquid crystal/vinyl polymer composite.…”

Ion‐Conducting Non‐Flammable Liquid Crystal–Polymer Composites for High‐Frequency Soft Actuators

“…[9][10][11][12][13][14][15][16][17][18][19] For example, 3D nanoarchitectured materials with high surface-area such as carbon nanotube/ graphitic carbon nitride hybrids, [20] laserscribed reduced graphene oxides, [21] and conductive metal-organic frameworks, have been developed as flexible, highly conductive, and crack-free electrodes. [22] On the other hand, novel block copolymers, [23] liquid-crystalline polymers, [24][25][26] and ionic covalent organic frameworks [27] were designed as promising ion-conductive membranes to achieve large and fast displacement owing to the formation of ion-transport pathways. However, most iEAP actuators cannot simultaneously achieve large deformation, fast response, and high output force.…”

“…[12] We have recently reported on the iEAP actuators based on ionic liquid-containing photo-cross-linked liquid-crystalline (LC) polymers, which were sandwiched between poly (3,4-ethylenedioxythiophene):pol y(styrenesulfonic acid) (PEDOT:PSS) electrodes. [25,26] These actuators exhibited large strain (0.30-0.35% strain at an AC voltage of 1 V and 0.1 Hz) and high force (0.3-1.1 mN at a DC voltage of 2 V) resulting from efficient ion-migration in macroscopically oriented anisotropic structures. These liquid crystal-based iEAP actuators are superior to other iEAP actuators owing to their lower content of ionic liquids (6-8 wt%), high mechanical moduli, facile large-area alignment of ion-transport pathways, and stable electrode-electrolyte interfaces.…”

“…These liquid crystal-based iEAP actuators are superior to other iEAP actuators owing to their lower content of ionic liquids (6-8 wt%), high mechanical moduli, facile large-area alignment of ion-transport pathways, and stable electrode-electrolyte interfaces. [25,26] Despite promising results from these LC polymer actuators, improving the frequency response and mechanical robustness remains an important challenge. In particular, actuators for tactile feedback need to show a fast vibrational displacement over human perceivable frequency range of 0-250 Hz.…”