Precise Network Polymerized Ionic Liquids for Low‐Voltage, Dopant‐Free Soft Actuators

Abstract

Next‐generation material applications require electroactive materials for actuation which are light weight, operate at low voltages (<5 V), exhibit cyclability, and are compatible with a range of environments. Here, a class of network polymerized ionic liquid (n‐PIL) actuators is reported, synthesized via a facile step growth polymerization, which not only have comparable actuation strains (≈0.9%) to other state‐of‐the‐art ionic polymer systems at ±3 V, but also exhibit 85% performance preservation after 1000 testing cycles and operate with no additives such as solvent or free ionic liquid. Molecular engineering of the n‐PILs by controlling crosslinking density and linker polarity leads to an order‐of‐magnitude increase in tip displacement which provides insights on future materials development.

Electroresponsive Ionic Liquid Crystal Elastomers

“…Here d is the tip displacement in horizontal direction, L is the free length of the film and w is the thickness of the strip with electrodes . As plotted on the right axis of Figure c, the overall bending strain in our hybrid aligned iLCE is about 0.3%, comparable to iEAPs …”

A comprehensive review of the structures and properties of ionic polymeric materials

“…For instance, Shen et al synthesized a crosslinked poly(ionic liquid) with an imidazolium backbone and bis(trifluoromethane sulfonimide) counterions. 163 An electro-responsive actuator was further designed by implementing this as-synthesized poly(ionic liquid) between two carbon nanotube sheets. The resulting actuator bent on applying a voltage as a result of charge accumulation on one of the carbon nanotube sheets due to ion transport.…”

Conductivity–modulus–Tg relationships in solvent‐free, single lithium ion conducting network electrolytes

“…[ 72,73 ] Similar trends have been observed in TFSI − single anion conducting network systems. [ 16,74 ] At 8 mol% crosslinking and below, the conductivity is essentially invariant, while a 24 mol% crosslinker sample begins to show a reduction. A normalized plot superposes the data as shown in Figure S7 indicating this is primarily a T g effect.…”

“…Polymer networks containing ionic species have received attention as functional materials in liquid/gas separations, [9][10][11][12][13][14][15] soft actuators, [16][17][18][19][20] ion exchange membranes, [21][22][23][24][25] and electrolytes for energy storage. [26][27][28][29][30][31][32][33][34][35] In the context of lithium conduction, polyethylene oxide (PEO) networks with added lithium salts have been investigated and it was shown that covalent crosslinking can significantly reduce the crystallinity and increase the ionic conductivity.…”

“…High T g PILs have greater mechanical stability but lower ionic conductivity due to lower segmental mobility. [57] Many groups have noted the important roles of polarity, ion concentration, polymer morphology, and segmental dynamics on conductivity in linear single-ion conducting systems.. [21,[57][58][59][60] Prior works on single anion conducting network polymers have investigated the roles of network versus linear architecture, [35] precise length of carbon spacers between network junctions, [61] crosslinking density, [16,62,63] ionic interactions, [55,63,64] and ion concentration [55] on ion transport through changes in T g and mechanical properties. However, there is still a need for systematic studies of Li + single-ion conducting networks with controlled architecture, charge density, and mechanical properties to understand how performance is related to molecular structure.…”