A Highly Robust Ionotronic Fiber with Unprecedented Mechanomodulation of Ionic Conduction

Abstract

unlike human tissues with rather complex and hierarchical structures, most of currently reported artificial ionic conductors, involving hydrogels, organohydrogels, ionogels, and ionic elastomers, were synthesized on the basis of a homogeneous solvent-swollen or salt-plasticized soft chain network. [4,[7][8][9][10][11] Despite high stretchability and optical transparency, such a soft network shows negligible or very small modulating effect on ion transportation; as a result, the ionic conductivity does not change or only slightly increases as stretched due to the preferential orientation of elastic chains. Generally, the mechanoelectric response of the current ionic conductors is just between conductivityconstant conductors (e.g., ionic liquids, [12] liquid metals, [13] viscoelastic gels, [11] etc.; conductivity change, σ/σ 0 = 1) and resistance-constant conductors (e.g., buckling sheath-core fibers, [14] liquid metal-elastomer composites, [15] etc.; σ/σ 0 = λ 2 , λ is the deformation ratio) (Figure 1a). It is well-known that the output resistance (R) is governed by Pouillet's Law (R = L/(σ•A)), with A designating the cross-sectional area and L the length (during stretch, L increases while A is reduced). Understandably, the moderate electrical response of ionic conductors not only limits their strain sensing applications toward high gauge factors as do percolating electronic conductors with strain-induced deteriorated conductivity, [16] but also goes against interconnect applications that require straininsensitive resistance to maintain stable electrical transmission. So far, it remains a formidable challenge for stretchable ionic conductors to overcome the seemingly inherent yet tardy mechanoelectric response arising from the poor modulating ability of soft chain network for ionic conduction.It is reported that the network topology of ionic conductors at nanometer scales is of paramount importance in altering the mobility of ionic species. [17,18] In nanofluidics, tortuosity is defined as the ratio of actual ion pathway length to the straight end-to-end distance. Highly ordered or longitudinally aligned ion-insulating nanostructures can afford low-tortuosity pathways to promote ion transport and thus significantly reduce apparent resistance. [19] Therefore, it could be feasible to introduce large amounts of ion-insulating rigid molecular units into the elastic network of ionic conductors to modulate ion transport via tortuosity changes. We consider that, liquid crystal elastomers (LCEs) might be one of the best candidate materials for this purpose, as they encompass the properties of polymeric Stretchable ionic conductors are appealing for tissue-like soft electronics, yet suffer from a tardy mechanoelectric response due to their poor modulation of ionic conduction arising from intrinsic homogeneous soft chain network. Here, a highly robust ionotronic fiber is designed by synergizing ionic liquid and liquid crystal elastomer with alternate rigid mesogen units and soft chain spacers, which shows an unprecedented s...

Robust and Reprocessable Artificial Muscles Based on Liquid Crystal Elastomers with Dynamic Thiourea Bonds

“…[10][11][12] Moreover, the anisotropic mechanical properties of the LCEs can be harnessed to program their shape changes, enabling complex deformations including bending, coiling, twisting, and helixing. [3,13,14] Recently, significant progress has been achieved in the field of LCEs for materials synthesis, [15][16][17][18][19] fabrication, [16,[20][21][22][23][24] and expansion of LCE applications., [25][26][27][28][29][30][31] which has led to the renaissance of LCEs from both scientific and engineering aspects. However, the preparation of LCEs as actuators typically requires mesogen alignment prior to cross-linking, which leads to complicated fabrication processes unlike those required for fabricating conventional elastomers.…”

Fatigue-free artificial ionic skin toughened by self-healable elastic nanomesh

“…; Δ R / R 0 = ε 2 + 2 ε ; Δ R is the resistance change (= R − R 0 ), R and R 0 the strain-dependent and initial resistances) at large strains. This is quite unusual, as most reported ionic conductors show only a moderate mechanoelectrical response (i.e., always lower than the conductivity-constant curve) 39 . The calculated gauge factor (GF = ∂(Δ R / R 0 )/∂ ε ) of hybrid ionic skin can reach as high as 66.8 at 630% strain, significantly higher than the ionic matrix (GF = 4.0) and conductivity-constant conductors (GF = 14.6) at the same strain (Fig.…”

“…To clarify the mechanism of the substantially enhanced strain sensation of hybrid ionic skin, we first transformed the resistance changing curves in Fig. 4a to conductivity changes via the equation ( σ c / σ c,0 = λ 2 /( R / R 0 ); σ c and σ c,0 are the strain-dependent and initial conductivities, respectively) 39 , which reflect intrinsic structural changes without considering shape parameters. As shown in Fig.…”

Materials development in stretchable iontronics

“…Wu et al reported a robust iontronic fibre (IonoLCE) consisting of a rigid mesogen of RM257, a soft chain spacer of 2,2ethylenedioxy diethanethiol (EDDET), a crosslinker of pentaerythritol tetrakis (3-mercaptopropionate) (PETMP), and an ionic liquid of [BMIM + ][PF 6 À ]. 137 The diacrylate mesogens were reacted with the dithiol chain spacer and the tetrathiol crosslinkers via click Michael-addition reactions, in the presence of the IL (Fig. 13e).…”