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.
Highlights
Solid-state and flexible composites from polymers and liquid crystals (LCs) are multifunctional materials with great potential and are of current interest for advanced applications, e.g., for the realization of flexible displays and smart windows [1,2,3,4,5,6]
Temperature-dependent frequency spectra of the complex electrical impedance (Z) for both poly(ethylene oxide) (PEO)/E8 and PEO/E8/NaIO4 composite films were obtained under identical experimental conditions by varying the temperature (T) from ambient temperature, Troom, to values slightly above their melting temperatures (Tm )
The dielectric relaxation in the PEO/E8 and PEO/E8/NaIO4 polymer/LC composites/complexes was investigated on a temperature scale in the range of their glass transition temperature (Tg )
Summary
Solid-state and flexible composites from polymers and liquid crystals (LCs) are multifunctional materials with great potential and are of current interest for advanced applications, e.g., for the realization of flexible displays and smart windows [1,2,3,4,5,6]. Electrical, dielectric, thermal, and other properties, as well as relatively easy preparation, stable chemical properties, and film-forming behaviors, and providing high mobility of charge carriers, such all-organic soft-solid composite materials can be ionic conductors that combine the advantages of solid polymer electrolytes with the unique properties of the LC soft matter included in plastic materials For this reason, promising polymer-LC combinations are developed for alternative electrical energy storage systems, for thin-film devices, such as dry-state mini-batteries, electromechanical actuators, solar cells, solar-energy harvesting, and electrochromic displays, as well as for sensorics, mechatronics, and soft electronics applications [7,8,9,10,11,12,13,14,15]. The low glass transition temperature (Tg ) of PEO, as well as its flexibility and other valuable properties, are well suited for engineering composite materials made from PEO and mesogens
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