Ion-Conducting Flexible Thin Films of Composites from Poly(ethylene oxide) and Nematic Liquid Crystals E8—Characterization by Impedance and Dielectric Relaxation Spectroscopy

Abstract

Complex electrical impedance and dielectric spectroscopy were applied to study the dielectric relaxations and their thermal behavior in ion-conducting composites/complexes from polymer poly(ethylene oxide) (PEO) and E8 nematic liquid crystals (LCs), at the compositional ratio PEO:E8 = 70:30 wt%. Flexible thin films of PEO/E8 with a thickness of 150 μm were inspected, as well as such films from Na+ ion-conducting electrolyte PEO/E8/NaIO4 with the same PEO:E8 compositional ratio, but additionally containing 10 wt.% from the salt sodium metaperiodate (NaIO4) as a dopant of Na+ ions. The molecular dynamics, namely the dielectric relaxation of PEO/E8 and PEO/E8/NaIO4, were characterized through analyses of complex impedance and dielectric spectra measured in the frequency range of 1 Hz–1 MHz, under variation of temperature from below to above the glass-transition temperature of these composites. The relaxation and polarization of dipole formations in PEO/E8 and PEO/E8/NaIO4 were evidenced and compared in terms of both electrical impedance and dielectric response depending on temperature. The results obtained for molecular organization, molecular relaxation dynamics, and electric polarization in the studied ion-conducting polymer/LC composites/complexes can be helpful in the optimization of their structure and performance, and are attractive for applications in flexible organic electronics, energy storage devices, and mechatronics.

Ion-Conducting Composites of Polymers and Nematic Liquid Crystals

“…The oscillating electric field can cause the dipoles in such complex dielectric material to align, resulting in polarization. As recently reported, this can be evidenced by analyses of the thermodynamical behaviors of the PNLCCs …”

“…For such ion-conducting PNLCCs where metal ions are active for the ion transport, the same conclusions from impedance studies may be drawn, regarding the presence of molecular dipoles, dipole polarization (dipolar reorganization), and dipole relaxation (dielectric relaxation of dipoles) driven by an external AC electric field. Significantly, in this case the value of f max Z″ is higher, and the characteristic dielectric relaxation time is shorter, as compared to the corresponding undoped (base) ion-conducting PNLCCs (Figure b and c) . This is explained with the structural changes induced by the ion donor, mainly the increase of the amorphous portion in the PNLCC material and, thereby, the increase in the segmental motion of polymer chains due to the addition of the salt. , …”

“…The polarity of PEO favors formation of PEO-based ion-conducting electrolyte materials. Efficient and reliable PEO–NLC ion-conducting systems have been reported. ,, …”

“…The plot of Δε against the NLC content shows that the dispersion of NLCs E8 in the polymer PEO leads to enhanced dielectric properties of the composite dielectric material PEO/E8. The increasing Δε implies an increase of polarization, a presence of molecular dipoles, a dipole contribution to the polarization, and an enhanced electrodipolar character of PNLCCs . Reasonably, the change in the dipolar character (and dipole–dipole interaction) of PNLCCs depends on their composition.…”

Achieving synergistic improvement in dielectric constant and energy storage properties of all-organic liquid crystal molecule/PVDF composites

“…In addition, it has been reported that 5CB can greatly improve the e r of a polymer matrix such as PMMA, 31 PS 32 and PEO. 33 Moreover, the average dielectric constant of 5CB in the liquid crystal state is 10.8, 34 and the dielectric constant is 10.5 when the temperature is above 40 1C. 35 As a consequence, the dielectric constant difference between 5CB and PVDF (e r is around 8) is small, thus avoiding the large local electric field difference between the components.…”