Modeling Static Electric Field Effect on Nematic Liquid Crystal Director Orientation in Side-Electrode Cell

A two-dimensional model of Fredericks effect was used for the investigation of the static electric field influence on nematic liquid crystal director orientation in the side-electrode cell. The solutions of the equations describing the model were obtained by finite-difference methods. Fredericks transition threshold for the central part of the cell, as well as dependencies of the distribution of the director orientation patterns on the electric field and location, were obtained. The numerical results are found to agree qualitatively with the experiment. Further investigations are needed to elucidate completely the Fredericks effect

Photoluminescent Thin Films of Room-Temperature Glassy Tris(keto-hydrozone) Discotic Liquid Crystals and Their Nanocomposites with Single-Walled Carbon Nanotubes for Optoelectronics

This study addresses the photoresponse of liquid-crystalline tris(keto-hydrozone) discotic (TKHD)a star-shaped molecular structure with three branches. Object of our research interest was also TKHD filled with single-walled carbon nanotubes (SWCNTs) at a concentration of 1 wt %. At room temperature, the discotic liquid crystals in thin films (thickness 3 μm) of both TKHD and nanocomposite SWCNT/TKHD were in a glassy state. Such glassy thin films exhibited photoluminescence ranging from the deep-red to the near-infrared spectral region, being attractive for organic optoelectronics. The addition of SWCNTs to TKHD was found to stabilize the photoluminescence of TKHD, which is of significance for optoelectronic device applications. The photothermoelectrical response of highly conductive SWCNT/TKHD nanocomposite films was characterized by electrical impedance spectroscopy in the frequency range from 1 Hz to 1 MHz of the applied electric field. It was elucidated that the reversible photothermoelectrical effect in SWCNT/TKHD films occurs through SWCNTs and their network

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

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

SODIUM-ION-CONDUCTING POLYMER NANOCOMPOSITE ELECTROLYTE OF TIO2/PEO/PVP COMPLEXED WITH NАIO4

Investigation on Sodium-ion-conducting polymer nanocomposite electrolyte system based on the polymer blend of poly(ethylene oxide) and polyvinyl pyrrolidone (PEO/PVP), complexed with NaIO4 salt and nanofilled with TiO2 of average size ~10 nm, are presented in this report. The salt complexed polymer blend electrolytes were prepared in the form of dimensionally stable and free-standing thin films (150 μm) by conventional solution cast technique. In the polymer blend, the PEO proportion was 70 weight percent (wt%). In PEO/PVP polymer matrix, the salt NaIO4 and the TiO2 nanofiller were at concentration of 10 wt% and 1 wt%, respectively. Micro Raman and XRD studies confirmed the miscibility between PEO and PVP and the complexation of the salt with PEO/PVP polymer host. TEM measurements were carried out to evaluate the size and distribution of the dispersed TiO2 nanofillers. The complex impedance spectroscopy in the frequency range 1 Hz – 1 MHz at room temperature shows an enhanced ionic conductivity of the four-component PEO/PVP/NaIO4/TiO2 nanocomposite Sodium-ion-conducting polymer electrolyte system

First Direct Gravimetric Detection of Perfluorooctane Sulfonic Acid (PFOS) Water Contaminants, Combination with Electrical Measurements on the Same Device—Proof of Concepts

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are pollutants of concern due to their long-term persistence in the environment and human health effects. Among them, perfluorooctane sulfonic acid (PFOS) is very ubiquitous and dangerous for health. Currently, the detection levels required by the legislation can be achieved only with expensive laboratory equipment. Hence, there is a need for portable, in-field, and possibly real-time detection. Optical and electrochemical transduction mechanisms are mainly used for the chemical sensors. Here, we report the first gravimetric detection of small-sized molecules like PFOS (MW 500) dissolved in water. A 100 MHz quartz crystal microbalance (QCM) measured at the third harmonic and an even more sensitive 434 MHz two-port surface acoustic wave (SAW) resonator with gold electrodes were used as transducers. The PFOS selective sensing layer was prepared from the metal organic framework (MOF) MIL-101(Cr). Its nano-sized thickness and structure were optimized using the discreet Langmuir–Blodgett (LB) film deposition method. This is the first time that LB multilayers from bulk MOFs have been prepared. The measured frequency downshifts of around 220 kHz per 1 µmol/L of PFOS, a SAW resonator-loaded QL-factor above 2000, and reaction times in the minutes’ range are highly promising for an in-field sensor reaching the water safety directives. Additionally, we use the micrometer-sized interdigitated electrodes of the SAW resonator to strongly enhance the electrochemical impedance spectroscopy (EIS) of the PFOS contamination. Thus, for the first time, we combine the ultra-sensitive gravimetry of small molecules in a water environment with electrical measurements on a single device. This combination provides additional sensor selectivity. Control tests against a bare resonator and two similar compounds prove the concept’s viability. All measurements were performed with pocket-sized tablet-powered devices, thus making the system highly portable and field-deployable. While here we focus on one of the emerging water contaminants, this concept with a different selective coating can be used for other new contaminants

PHOTO-ELECTRICAL RESPONSE OF DONORACCEPTOR COMPLEX WITH CARBONYL VIOLOGEN ACCEPTOR

<div>The photo-electrical response of donor-acceptor complex formed by carbonyl viologen 1,1'-bis[2-(4-methoxyphenyl)-2-oxoethyl]-4,4'-bipyridine-1,1'-diium bromide (as electron acceptor), and 1-Aminonaphthalene (electron donor), is studied in acetonitrile solutions under illumination close to solar irradiation conditions. The effect of the donor-to-acceptor molar ratio on the photo-electrical properties of the molecular complex is established. The molecular system containing carbonyl viologen acceptor exhibits an efficient photo-electrical response that may be of interest for solar energy conversion.</div><div><br></div

Modeling Static Electric Field Effect on Nematic Liquid Crystal Director Orientation in Side-Electrode Cell

A two-dimensional model of Fredericks effect was used for the investigation of the static electric field influence on nematic liquid crystal director orientation in the side-electrode cell. The solutions of the equations describing the model were obtained by finite-difference methods. Fredericks transition threshold for the central part of the cell, as well as dependencies of the distribution of the director orientation patterns on the electric field and location, were obtained. The numerical results are found to agree qualitatively with the experiment. Further investigations are needed to elucidate completely the Fredericks effect

Modeling Static Electric Field Effect on Nematic Liquid Crystal Director Orientation in Side-Electrode Cell

A two-dimensional model of Fredericks effect was used for the investigation of the static electric field influence on nematic liquid crystal director orientation in the side-electrode cell. The solutions of the equations describing the model were obtained by finite-difference methods. Fredericks transition threshold for the central part of the cell, as well as dependencies of the distribution of the director orientation patterns on the electric field and location, were obtained. The numerical results are found to agree qualitatively with the experiment. Further investigations are needed to elucidate completely the Fredericks effect