ABSTRACT
The first study of the flexo-ionic effect, i.e., mechanical deformation-induced electric signal, of the recently discovered ionic liquid crystal elastomers (iLCEs) is reported. The measured flexo-ionic coefficients were found to strongly depend on the director alignment of the iLCE films and can be over 200 µC/m. This value is orders of magnitude higher than the flexo-electric coefficient found in insulating liquid crystals and is comparable to the well-developed ionic polymers (iEAPs). The shortest response times, i.e., the largest bandwidth of the flexo-ionic responses, is achieved in planar alignment, when the director is uniformly parallel to the substrates. These results render high potential for iLCE-based devices for applications in sensors and wearable micropower generators.
ABSTRACT
The role of side-chain branching in flexoelectric properties of a flexible, ionic solid polymer electrolyte membrane (PEM) has been investigated subjected to mechanical bending. These PEMs were synthesized via photopolymerization of the bifunctional poly(ethylene glycol) diacrylate (PEGDA) network attached with monofunctional poly(ethylene glycol) methyl ether acrylate (PEGMEA) branches in their ternary mixtures with lithium bis(tri-fluoromethane sulfonyl) imide (LiTFSI) salt. Both the PEGDA polymer precursor and PEGDMA side branches are capable of ionizing the lithium salt, but the dissociated lithium cations can also form the complexation with ether oxygen of PEGDA. With increasing PEGMEA content, not only the glass transition temperature is lowered, but also the ionic conductivity increases with temperature, which may be attributed to plasticization by dangling PEGMEA side chains. The flexoelectric responses of PEMs were investigated under various intermittent and oscillatory cantilever bending modes as a function of PEM composition and frequency. Last but not the least, the mechanoelectrical energy conversion was evaluated for various PEGDA/PEGMEA compositions and discussed its potential applications in energy harvesting from natural resources such as wind and wave motions.
