Flexoelectricity in Flexoionic Polymer Electrolyte Membranes: Effect of Thiosiloxane Modification on Poly(ethylene glycol) Diacrylate and Ionic Liquid Electrolyte Composites

Abstract

The present article entails the generation of flexoelectricity during cantilever bending of a solid polymer electrolyte membrane (PEM), composed of poly­(ethylene glycol) diacrylate (PEGDA) precursor and ionic liquid (hexylmethyl­imidazolium hexafluorophosphate). The effects of thiosiloxane modification of PEGDA precursor on glass transition, ionic conductivity, and flexoelectric performance have been explored as a function of PEM composition. The glass transition temperature (T g) of the PEM declines with increasing thiosiloxane amount in the PEGDA co-network, while the ionic conductivity improves. The PEM/compliant carbonaceous electrodes assemblies were assembled to determine the flexoelectric coefficients by monitoring electrical voltage/current outputs for various PEM compositions under the intermittent square-wave and dynamic oscillatory sine-wave deformation modes. Of particular interest is that the room temperature flexoelectric coefficient exhibits strong frequency dependence in the vicinity of 0.01–10 Hz, suggesting that ion polarization and ion transport through the ion-dipole complexed networks can still be affected by the mobile side chain branches even in the elastic regime of the covalently bonded PEGDA network. The in-depth understanding of the effect of thiosiloxane side chain on flexoelectricity generation is anticipated to have impact on the development of mechano­electrical energy conversion devices for energy harvesting applications from natural and dynamical environment.

Flexo-Ionic Effect of Ionic Liquid Crystal Elastomers

“…It appears that the cells cross-linked in the isotropic phase, and those that are cross-linked in the nematic phase between planar alignment substrates, give the largest response with flexo-ionic coefficients . Such coefficients are comparable to the well-developed iEAPs (see Table 1 ) [ 6 , 9 ]. It is interesting to discern that the flexo-ionic coefficients of iLCEs outperform the flexoelectric (polarization mechanism is different) coefficients of ceramics (PZT [ 12 ] and Ba 0.67 Sr 0.33 TiO 3 [ 40 ]), crystalline polymers (PVDF) [ 41 ], and bent-core liquid crystals [ 18 , 19 ] as indicated in Table 1 .…”

“…The past few decades have witnessed a flourishing development of electro-mechanical transducers for use in soft robotics [1][2][3], sensors [4,5] and micropower generations [6][7][8][9]. Piezoelectricity and flexoelectricity are the two major physical mechanisms for linear electro-mechanical transduction for insulating materials.…”

“…In appearance, this effect is similar to the flexo-electric effect. However, instead of the displacement of bound charges, here, positive and negative ions move in opposite directions due to mechanical bending [ 6 , 7 , 8 , 9 , 26 ]. To express this difference, we shall call this the flexo-ionic effect.…”

Solid state polymer ionogel electrolyte for use in Li‐ion batteries

“…Several recent studies also reported the benefits of solidstate electrolyte membranes in LIBs [34,35] and energy harvesting from mechanical deformation. [36][37][38] The present work is built on the early concepts of Raut et al [33] to alleviate the concerns of loss of IL from the ionogel membranes at high temperature due to differences in thermal expansion coefficient of solid strands in sPS gel and the liquid state IL. In this context, the threedimensional δ-form sPS porous gels [39,40] offered higher melting temperature (275 C C) and dimensional stability at high temperature compared to commercial polyolefin membranes, such as polyethylene and polypropylene, with melting temperature, respectively, 135 and 160 C. [41,42] The loss of IL from the ionogel membrane at high temperature was avoided in this work by using a polymerizable IL (PIL) and 1-ethyl-3-vinylimidazolium bis (trifluoromethylsulfonyl) imide (VI-TFSI).…”

“…Several recent studies also reported the benefits of solid‐state electrolyte membranes in LIBs [ 34,35 ] and energy harvesting from mechanical deformation. [ 36–38 ]…”