Dielectric Spectroscopy Technique Research Articles

Preparation and Structural-Thermodynamical Investigation of Renewable Copolyesters Based on Poly (Ethylene Succinate) and Polyisosorbide

A series of novel renewable copolymers based on poly(ethylene succinate) (PESu) and poly(isosorbide succinate) (PISSu), with the Isosorbide (Is)/PESu molar ratio varying from 5/95 to 75/25, were synthesized in-situ and studied in this work. A sum of characterization techniques was employed here for the structural and thermo-dynamical characterization. The sophisticated technique of dielectric spectroscopy, along with proper analysis, enabled the molecular dynamics mapping of both the local and segmental types, which is presented for such materials for the first time. With increasing the Is fraction, shorter copolymeric entities were gradually formed. Based on the overall findings, the systems were found to be homogeneous, e.g., exhibiting single glass transitions, with the two polymer segments being found to be excellently distributed. The latter is indirect, although strong, evidence for the successful copolymerization. The thermal degradation mechanism for the copolymers was exhaustingly explored employing analytical pyrolysis. The systems exhibited, in general, good thermal stability, according to the thermogravimetric analysis. Confirming one of the initial scopes for the present systems, isosorbide plays here the role of hardener (PISSu) over the soft polymer (PESu), and this is reflected in the monotonic increase of the glass transition temperature, Tg, from −16 to ~56 °C. The introduction of Is results in an increase in constraints (hardening of the matrix), while there seems to be an overall densification of the polymer (decrease of the free volume).

Segmental mobility in linear polylactides of various molecular weights

In this work we synthesized and studied a series of linear polylactides (PLA) with a fixed L/d -lactide stereoisomer ratio, covering together the wide range of molecular weights, Mn, from ∼6 to ∼80 kg/mol. The basic aims are the segmental mobility mapping, in terms of time scale and fragility, the recording of the Mn dependences of the glass transition temperature and fragility, and, finally, the comparison with corresponding findings from the literature. Obviously, the direct Mn effects on Tg are assessed by preserving PLA at the amorphous state, i.e., via melting and relatively fast cooling. The segmental mobility is studied by conventional and temperature modulated calorimetry, whereas the molecular dynamics is assessed employing the technique of broadband dielectric spectroscopy in combination with proper critical analysis and evaluation routes. The calorimetric and dielectric Tg(Mn) trends were found consistent between each other as well as with previous findings in similar systems, both with respect to experimental findings and theoretic predictions for PLAs of similar L/D ratio. The Mn threshold of entanglements seems to lay between 13 and 28 kg/mol. The fragility index of the α relaxation, i.e., the dielectric analogue of the glass transition, exhibits a similar dependence to that of Tg(Mn). When decreasing Mn to very low values, the high fragility (∼150) drops down to 0 (Mñ6 kg/mol), denoting the vanishing of the polymer chains’ cooperativity. Qualitatively interesting alternations are recorded in the dielectric strength of the α relaxation and the relaxation times width. The effects are discussed in terms of the various parameters co-affecting the polymer dynamics, namely, chain lengths, free volume and dynamical heterogeneities.

Noncontact In Situ Multidiagnostic NMR/Dielectric Spectroscopy.

Introduction of a dielectric material in a nuclear magnetic resonance (NMR) probe head modifies the frequency response of the probe circuit, a phenomenon revealed by detuning of the probe. For NMR spectroscopy, this detuning is corrected for by tuning and matching the probe head prior to the NMR measurement. The magnitude of the probe detuning, "the dielectric shift", provides direct access to the dielectric properties of the sample, enabling NMR spectrometers to simultaneously perform both dielectric and NMR spectroscopy. By measuring sample dielectric permittivity as a function of frequency, dielectric permittivity spectroscopy can be performed using the new methodology. As a proof of concept, this was evaluated on methanol, ethanol, 1-propanol, 1-pentanol, and 1-octanol using a commercial cross-polarization magic angle spinning (CPMAS) NMR probe head. The results accurately match the literature data collected by standard dielectric spectroscopy techniques. Subsequently, the method was also applied to investigate the solvent-surface interactions of water confined in the micropores of an MFI-type, hydrophilic zeolite with a Si/Al ratio of 11.5. In the micropores, water adsorbs to Bro̷nsted acid sites and defect sites, resulting in a drastically decreased dielectric permittivity of the nanoconfined water. Theoretical background for the new methodology is provided using an effective electric circuit model of a CPMAS probe head with a solenoid coil, describing the detuning resulting from the insertion of dielectric samples in the probe head.

Development of long-range conductivity mechanisms in glass-like carbon

The conductivity mechanisms in glass-like carbon synthesised from SU-8 3005 photoresist are explored as a function of pyrolysis temperature (between 700–750 °C) utilising microwave dielectric spectroscopy techniques. Broadband measurements using an open-ended coaxial probe (BCP) are used to investigate the complex permittivity and conductivity as a function of frequency and show the development of long range conduction and sp2 carbon chain formation. Fixed frequency resonance measurements using microwave cavity perturbation (MCP) methods are shown as a way of measuring this transition and change in Q-factor without requiring contacts and therefore acting as a effective method for non-destructive and non-invasive measurements. Using these methods we show a clear change in the AC conductivity of glass-like carbon at a pyrolysis temperature of ∼730 °C and demonstrate how microwave cavity perturbation (MCP) can be used as a non-contact method of dielectric spectroscopy for determining the transition of conductivity mechanisms in glass-like carbon from short to long range and therefore as a method for non-destructive material quality control. We demonstrate that both BCP and MCP dielectric spectroscopy methods are effective at clearly detecting changes in the structure and conductivity mechanisms of glass-like carbon over a small pyrolysis temperature range.

Resilience of the Aurivillius structure upon La and Cr doping in a Bi5Ti3FeO15 multiferroic.

Combining the experimental techniques of high-resolution X-ray diffraction, magnetometry, specific heat measurement, and X-ray photoelectron, Raman and dielectric spectroscopy techniques, we have studied the influence of La and Cr doping on the crystal structure and magnetism of the room temperature Aurivillius multiferroic Bi5Ti3FeO15 by investigating the physical properties of (Bi4La)Ti3FeO15 and Bi5Ti3 (Fe0.5Cr0.5)O15. The parent (Bi5Ti3FeO15) and the doped ((Bi4La)Ti3FeO15 and Bi5Ti3(Fe0.5Cr0.5)O15) compounds crystallize in the A21am space group, which is confirmed through our analysis of high-resolution synchrotron X-ray diffraction data obtained on phase-pure polycrystalline powders. We determined the oxidation states of the metal atoms in the studied compounds as Fe3+, Ti4+, Cr3+, and La3+ through the analysis of X-ray photoelectron spectroscopy data. The magnetic susceptibilities of the three compounds are marked by the absence of a long-range ordered ground state, but dominated by superparamagnetic clusters with dominant antiferromagnetic interactions. This signature of short-range magnetism is also seen in specific heat as a low temperature enhancement which is suppressed upon the application of external magnetic fields up to 8 T. Our dielectric spectroscopy experiments showed that the three studied compounds display similar features in the dielectric constant measured as a function of frequency. However, upon doping La at the Bi site, the width of the ferroelectric hysteresis loop increases for (Bi4La)Ti3FeO15 compared to that of the parent compound Bi5Ti3FeO15, and with Cr doping, Bi5Ti3(Fe0.5Cr0.5)O15 becomes a leaky dielectric. The resilience of the Aurivillius crystal structure towards doping of La at the Bi site and Cr at the Fe site is clearly seen in the bulk properties of magnetic susceptibility, specific heat and the average crystal structure. The relevance of changes in the local structure is evident from our Raman spectroscopy and X-ray pair distribution function studies.

Molecular mobility and thermal transitions study in renewable PLA-polyols star-like copolymers

The molecular dynamics mapping in poly(lactic acid) (PLA)-based star-like copolymers is performed herein, employing dielectric spectroscopy techniques supplemented by calorimetry and other structure characterization methods. Next to the neat linear PLA, three star-like copolymers, with 3, 4 and 5 branches were synthesized via ring opening polymerization at the presence of, respectively, glycerol, pentaerythritol and sorbitol (initiators). When increasing the branch number, consequently, the overall molar mass drops, from 55 kg/mol (neat PLA) to 17k (PLA@glycerol), 25k (PLA@pentaerythritol), and 14k (PLA@sorbitol) and, thus, the branch length decreases to ∼6k, ∼6k, and ∼3 k g/mol in the stars. The latter leads to faster segmental mobility, documented by the accelerated α relaxation and the drop in the calorimetric and dielectric glass transition temperatures. Simultaneously, the cooperativity (chains’ fragility) drops. Together these results suggest possibly the increase in free volume, a factor that can potentially favour the physical biodegradability. Next to the segmental dynamics, the local beta relaxation is recorded to have a mild dependence on the type of star (mainly decelerates), while the rare case of Normal Mode relaxation is recorded here only in the stars, providing additional support for the quite short branches. The overall data suggest the co-implementation of two antagonistic effects on mobility, i.e., the chain length changes in parallel to the constraints imposed by the star-like structure. Moreover, the in general low crystallizability of linear PLA further drops in the stars in terms of both suppressed crystalline fraction and nucleation, as well as lower quality of crystals. The materials exhibit single thermal transitions, indicating a homogeneous character, whereas a variety of semicrystalline morphologies can be achieved via both the composition and the thermal treatment. This provides a tool for tuning various properties and, consequently, the manipulation of the macroscopic performance.

Smectic layers reorientation with stripes and heliconical structure in surface stabilised ferroelectric liquid crystal

ABSTRACT High-tilt angle ferroelectric liquid crystal material in surface stabilised geometry (SSFLC) is investigated for the smectic layer reorientation and its molecular dynamics by electro-optical and dielectric spectroscopy techniques. Smectic layer reorientation (5 o to 45 o ) is obtained by controlled cooling rate and applying electric field in the vicinity of transition temperature from chiral nematic ( N ∗ ) to chiral smectic C ( Sm C ∗ ) phase. After slow cooling down to room temperature, the stripe domain textures along the rubbing are observed with quasi-bistable states. Dielectric spectroscopy has revealed the unusual increment in the dielectric permittivity. A dielectric relaxation process at lower frequency than Goldstone mode with the increase in DC bias up to 2 V is observed in the sample cooled without any bias. This increment is found to be originated by the heliconical structure within the stripes which is seen in the optical textures recorded at the time of dielectric scan. However, this increment is not observed in the sample cooled under DC bias. Thus, there exist different phenomena in the high tilt angle SSFLC sample cooled in different conditions of DC bias; stripe domains, smectic layers reorientation, heliconical stricture and twisted structure within stripes which are significant to explore deeply in high-tilt angle ferroelectric liquid crystals.

Ultra-broadband direct dielectric spectroscopy of liquids using a calibrated Microwave-Fluidic vertical Two-Wire sensor with Bi-Material 3D printed chamber

A novel ultra-broadband dielectric spectroscopy technique for liquids is introduced. A two-wire transmission line sensor is employed in which the liquid-under-test comprises fully the propagation medium ensuring high sensitivity and direct permittivity measurement. A vertical wire arrangement is exploited fed by a double-sided parallel stripline with a microstrip interface and no bandwidth-limiting impedance transformation. A seal-integrated flex-rigid 3D-printed liquid container is developed for robust assembly. A raw measured propagation constant correction is proposed through setup calibration using only one reference liquid, which can be air. Sensor operation and design aspects are discussed in detail and an exemplary sensing setup is developed for experimental validation. A set of liquids is characterized within a three-decade bandwidth up to 42 GHz and fitted into a relaxation model along with a comparison against industry-standard broadband open-coax sensor captured data. The conducted study and error analysis certified the performance of the proposed setup.

Enhancement of electro-optical properties and phase transition temperature of thermotropic liquid crystal 5CB by doping with 4-n-pentylbenzoic acid

ABSTRACT Liquid crystalline materials that have been used in the display industry need to have a wide temperature-range nematic phase while remaining functioning in different climate conditions. In this work, a new binary mixture of thermotropic liquid crystal materials, particularly the nematic phase, has been studied. A widely used material 5CB (4-Cyano-4’−pentyl biphenyl), exhibiting nematics phase, and PA (4-Phenylbenzoic acid) were preferred. Mixtures of different concentrations of 5CB-PA were prepared and investigated using dielectric spectroscopy, phase transition and electro-optical responses techniques. It was found that not only was an improvement to the dielectric anisotropic achieved but also the nematic temperature range extended from 35 ºC to just above 50°C by adding 10 wt.%. On the other hand, the threshold voltage is increased by 10% for the same sample. In addition, elastic constants and response time showed similar behaviours upon increasing the loading concentration of PA, whereas the visco-elastic coefficient significantly declined. All the estimated values for the pure 5CB are in good agreement with the literature. This improvement in the operating temperature range is unique and suggests that the doping can lead to cheap and mass production of a stable liquid crystalline material for their application in the display industry.

Structural, optical, and electrical properties of Mn0.9La0.1Fe2O4 nanocrystalline ferrites and its synthesis through sol-gel method

This work reports the formation of La-doped nano-crystalline manganese ferrite Mn0.9La0.1Fe2O4 through sol–gel route and examined using XRD and dielectric spectroscopy techniques. The single-phased cubic spinel structure of the ferrite is supported by X-ray diffraction (XRD). The mean crystallite dimension appraised from XRD data has been found to be 21 nm and 11 nm for un-doped and La3+ doped MnFe2O4, respectively, along with a significant rebate in the optical band gap. At room temperature, the frequency-dependent dielectric properties were studied in the frequency range (42 Hz − 5 MHz). The dielectric constant of both the samples narrowly lowers with enhancing frequency and, consequently, shows exemplary dielectric dispersion. The AC-conductivity of the un-doped samples enhances with increasing frequency while it decreases with doping. The dispersion in ac-conductivity (σac) and dielectric properties imply the ordinary dispersion of Maxwell-Wagner type due to the process of hopping of electrons between the Fe2+ and Fe3+ ions and interfacial polarization. The band gap of energy is evaluated with the help of the UV–visible spectra and found to be decreased when La3+ doped with MnFe2O4 ferrite.

Temperature and frequency dependence on dielectric permittivity and electrical conductivity of recycled Liquid Crystals

The dielectric behavior and the electrical conductivity response of recycled nematic Liquid Crystals (LCs) were studied over a wide range of frequencies (0.1 to 106 Hz) and temperatures (100 to −20 °C) with a broadband dielectric spectroscopy technique. These LC mixtures were extracted from a total of 65700 End-Of-Life (EOL)-Liquid Crystals Displays (LCD) such as computers, tablets and TVs of various sizes, brands, and production years. After a stage of purification, the recycled LC blends seemed to possess similar physical properties as conventional nematic LCs. In this report, two types of anchoring of LC molecules, obtained with homeotropic or homogeneous alignment cells, were investigated. All dielectric data were analyzed with adapted models: Havriliak-Negami and Almond West formalisms for the frequency dependence of the data, as well as Arrhenius and Vogel-Fulcher-Tammann models for their temperature dependence. In this article, it is demonstrated that despite the wide variety of EOL-LCD devices used leading to a large number of LC molecules, the frequency and temperature evolution of the recorded spectra are comparable to those of commercial LC mixtures as reported in the literature. Therefore, their future reuse could be envisaged for display applications.

INVESTIGATION OF DIELECTRIC PROPERTIES OF MBBA-5CB NEMATIC LIQUID CRYSTAL STRUCTURES

The dielectric anisotropy (Δε') is the response of the LC molecules to an applied electric field. In this study, the dielectric properties of 4-pentyl-4'-cyanobiphenyl (5CB) and N-(4-methoxybenzylidene)-4-butylaniline (MBBA) nematic liquid crystals with positive and negative dielectric anisotropy were investigated in detail. In addition, a structure with zero dielectric anisotropy was obtained by mixing MBBA and 5CB liquid crystals in certain rate (1:0.02). The behavior of the samples under 0V and 20V voltages was investigated in detail. Dielectric measurements were made with dielectric spectroscopy technique, which is a powerful method to investigate the molecular interaction mechanisms of liquid crystal materials, at a frequency of 1 kHz-10 MHz and a voltage of 0-20 V at room temperature. Some important parameters such as dielectric anisotropy (Δε'), relaxation frequency (fR), relaxation time (τ) were determined for the samples. When electric field is applied to nematic liquid crystals, it is seen that, depending on the voltage, the relaxation frequency decreases, and the relaxation time increases.

Tunable dielectric and memory features of ferroelectric layered perovskite Bi4Ti3O12 nanoparticles doped nematic liquid crystal composite

Herein, we report the synthesis of ferroelectric layered perovskite Bi4Ti3O12 (BT4) nanoparticles (NPs) and the temperature-dependent dielectric and electro-optical (especially memory effect) properties of 4-pentyl-4′-cyanobiphenyl (5CB) nematic liquid crystal (NLC) doped with 1 wt% BT4 NPs (i.e. 5CB-BT4 composite) using polarising optical microscopy and frequency-dependent dielectric spectroscopy techniques. BT4 NPs were synthesised via a microwave-assisted chemical method and characterised using various instrumental techniques, which confirmed the formation of a non-stoichiometric and oxygen-deficient orthorhombic crystal phase. The agglomeration-free and uniform dispersion of BT4 NPs in the 5CB matrix was confirmed by optical textures. The optical memory studied by bias voltage-dependent (ON-OFF) optical textures is decreased by ∼ 2.6 times in the 5CB-BT4 composite compared with 5CB. Moreover, dielectric parameters such as dielectric permittivity, dielectric loss, loss tangent, conductivity, and activation energy of 5CB and composite (5CB-BT4) are estimated using dielectric spectroscopy. The dielectric anisotropy is decreased, whereas no shift in the clearing temperature is observed in the 5CB-BT4 composite compared to the 5CB sample. Also, the DC conductivity of 5CB-BT4 composite is found to be increased by approximately four times compared to the 5CB. Our studies clearly demonstrate the tunability of the dielectric and optical memory features of NLC (5CB) matrix by dopant BT4 NPs, without significantly affecting the molecular alignment of the NLC molecules. Such composites would certainly be useful in the fabrication of NLC based tunable devices such as optical memory and conductivity switches.

Dielectric and calorimetric study in renewable polymer blends based on poly(ethylene adipate) and poly(lactic acid) with microphase separation

A series of sustainable polymeric blends based on poly(lactic acid) (PLA) and poly(ethylene adipate) (PEAd), are studied herein, from the point of view of thermal transitions, crystallization and molecular mobility. The blending aims at the manipulation of the chains' mobility and crystallization of PLA, as PEAd exhibits quite lower glass transition temperature and is expected to act as plasticizer. In a next step, such systems are envisaged for use as patches for transdermal administration of antimicrobial drugs, formed as fibril-systems via the electrospinning technique. For the present work, we have employed calorimetry and the advanced technique of dielectric spectroscopy as main investigation tools, which are supplemented by polarized microscopy. Regarding molecular mobility, the overall dynamics (local and segmental) map was constructed for these systems, for the first time. The presence of PEAd imposed plasticization on the PLA chains, as manifested by the lowering of Tg and acceleration of segmental dynamics. On the other hand, PEAd is deplasticized at the presence of PLA. In addition, the fragility of PLA chains drops at the presence of PEAd, suggesting increasing in the cooperativity length, or else, a chain-chain detaching. The overall data are also indicative of the partially miscible polymers. Regarding crystallization, neat PLA exhibits neither hot nor cold crystallization, whereas, strikingly, with the addition of PEAd, the nucleation of PLA is facilitated and strong cold crystallization is systematically recorded. The phenomenon seems to be connected with both the plasticization of the PLA chains along with the homogeneous microphase separation of the two polymers (partial immiscibility), overall, with size-effects. Local dynamics, originating from more localized molecular motions, exhibit systematic alternation in the blends in both the time scale and dielectric strength. Our results show that the PLA/PEAd blends are ‘phase change materials’ with potentials to tune the materials performance, connected, among others, with the semicrystalline morphology and the interchain distances.

Antipolar transitions in GaNb4Se8 and GaTa4Se8

We present dielectric, polarization, resistivity, specific heat, and magnetic susceptibility data on single crystals of the lacunar spinels GaNb4Se8 and GaTa4Se8, tetrahedral cluster-based materials with substantial spin-orbit coupling. We concentrate on the possible occurrence of antipolar order in these compounds, as previously reported for the isoelectronic GaNb4S8, where spin-orbit coupling plays a less important role. Our broadband dielectric-spectroscopy investigations reveal clear anomalies of the intrinsic dielectric constant at the magneto-structural transitions in both systems that are in accord with the expectations for antipolar transitions. A similar anomaly is also observed at the cubic-cubic transition of the Nb compound leading to an intermediate phase. Similar to other polar and antipolar lacunar spinels, we find indications for dipolar relaxation dynamics at low temperatures. Polarization measurements on GaNb4Se8 reveal weak ferroelectric ordering below the magneto-structural transition, either superimposed to antipolar order or emerging at structural domain walls. The temperature-dependent dc resistivity evidences essentially thermally-activated charge transport with different activation energies in the different phases. A huge step-like increase of the resistivity at the magneto-structural transition of the Ta compound points to a fundamental change in the electronic structure or the mechanism of the charge transport. At low temperatures, charge transport is governed by in-gap impurity states, as also invoked to explain the resistive switching in these compounds.

Phase diagram, dielectric and electro optic properties of binary liquid crystals mixtures

ABSTRACT Nematic phase at room temperature with wide stability and high birefringence is particularly desirable for functional devices. Two thermotropic liquid crystals (tolane and the 4-pentyl-4-biphenylcarbonitrile nematic also known as 5CB) are mixed by varying the weight fraction (wt%) in order to investigate the phase sequences and their physical properties using differential scanning calorimetry (DSC), polarised optical microscopy (POM) and dielectric spectroscopy techniques. Phase coexistence was observed for a concentrations 20 ≤ C ≤ 60 wt% of tolane in 5CB and the phase diagram was established. In addition, the nematic-isotropic temperature TNI increases with increasing the concentration of tolane LCs. A eutectic mixture at room temperature with large nematic range and high birefringence is obtained for C = 10 wt%. The increase in the nematic range is due to an enhancement of the nematic order induced by the LCs. It is found that the electro optical parameters like the threshold voltage, the response time were relatively increased. This increment can be attributed to an increase in the viscoelastic properties of the mixture.

Significant Interfacial Dielectric Relaxation of Covalently Bonded Ice-Hydrogels.

Hydrogels are composed of a three-dimensional network of cross-linked hydrophilic polymer chains and large amounts of water. The physicochemical properties of the polymer-water interface in hydrogels draw our attention. Due to the complex structure of hydrogel systems, it is still a challenge to investigate the interfacial layer properties of hydrogels through experiments. In this work, we investigate the properties of the covalently bonded chitosan-based ice-hydrogels interfacial layer by dielectric relaxation spectroscopy (DRS) techniques in the presence of avoided electrode polarization. The DRS data exhibit that the polymer-water interfacial layer has a strong dielectric signal response, which indicates that a large number of polar electric dipoles or polar molecules may be contained in the interfacial layer. The variable temperature dielectric relaxation behavior of a series of chitosan-base ice-hydrogels showed that the value of dielectric activation energy for different water contents is about 180 kJ/mol, which is much larger than that of the polymer and ice phases, suggesting a strong coupling of polar electric dipoles within the interfacial layer. This work demonstrates the important role of the polymer-water interface in covalently bonded hydrogels, which will provide assistance in the design and application of covalently bonded hydrogels.

Multiple glassy dynamics of a homologous series of triphenylene-based columnar liquid crystals – A study by broadband dielectric spectroscopy and advanced calorimetry

Hexakis(n-alkyloxy)triphenylene) (HATn) consisting of an aromatic triphenylene core and alkyl side chains are model discotic liquid crystal (DLC) systems forming a columnar mesophase. In the mesophase, the molecules of HATn self-assemble in columns, which has one-dimensional high charge carrier mobility along the columns. Here, a homologous series of HATn with different length of the alkyl chain (n = 5,6,8,10,12) is investigated using differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS) and advanced calorimetric techniques including fast scanning calorimetry (FSC) and specific heat spectroscopy (SHS). The investigation of the phase behavior was done utilizing DSC experiments and the influence of the alkyl chain length on the phase behavior was revealed. By the dielectric investigations probing the molecular mobility, a γ-relaxation due to localized fluctuations as well as two glassy dynamics, the αcore- and αalkyl-relaxation, were observed in the temperature range of the plastic crystalline phase. Moreover, the observed glassy dynamics were further studied employing advanced calorimetry. All observed relaxation processes are attributed to the possible specific molecular fluctuations and discussed in detail. From the results a transition at around n = 8 from a rigid constrained (n = 5,6) to a softer system (n = 10,12) was revealed with increasing alkyl chain length. A counterbalance of two competing effects of a polyethylene-like behavior of the alkyl chains in the intercolumnar domains and self-organized confinement is discussed in the context of a hindered glass transition.

Electrical properties and heavy ions removal ability of graphitic carbon nitride/polypyrrole composite

A composite of graphitic carbon nitride (g-C3N4) and polypyrrole (PPy) is synthesized in a ratio of 1:1 by in situ oxidation polymerization technique as a novel heavy-ions removal composite. The structure of the prepared material compared with g-C3N4 pure is characterized using FTIR and XRD. Investigation of electric and dielectric properties of the composite using Broadband dielectric spectroscopy technique is carried out to explore the conductivity change and charge carriers' density of the composite. The results showed that the electrical conductivity of the composite is unexpectedly nearly the same as that of pure PPy despite having such a high ratio of g-C3N4. Moreover, a significant increase in the density of charge carriers is realized and considered the origin of conductivity enhancement. Adsorption of Pb (II) and Cd (II) from their solution is performed under different conditions of pH, time, ions concentration, and temperature. The results confirmed increasing in ions uptake in case of using composite compared with pure (g-C3N4) owing to the increase in the density of charge carriers. Determination of the kinetics of g-C3N4 and g-C3N4/PPy to understand their adsorption property is carried out using various kinetic models namely, Pseudo-first order (PFORE), pseudo-second order (PSORE) and Elovich, to fit the experimental data. The obtained data showed that pseudo-second-order kinetic model is the best model for the adsorption process and chemisorption might be the rate-determining step. Regeneration efficiencies of g-C3N4 and g-C3N4/PPy were found to be 95% and 98% respectively. The results demonstrated that presence of PPy not only increased ions uptake from wastewater but also enhanced the workability and efficiency for three repeated cycles of sorption–desorption.

Significantly improved dielectric performance of bio-inspired gelatin/single-walled carbon nanotube nanocomposite

In this study, the dielectric properties of gelatin/single-walled carbon nanotube (Gel/SWCNT) nanocomposite were evaluated. The nanocomposites were synthesized by a simple solution casting method. The electron transport properties of the nanocomposites were studied by the dielectric and impedance spectroscopy techniques. A dielectric constant as high as 104 and a loss tangent of 0.91 were obtained for the Gel/SWCNT nanocomposite material at 100 Hz. The dielectric permittivity data of the nanocomposites were fitted by the modified Cole–Cole model to estimate the dielectric strength and the relaxation time. The addition of SWCNT into the gelatin reduces the relaxation time of the nanocomposite from 3.03 to 1.01 μs. The complex impedance spectra analyses show an increase in alternating current conductivity due to the incorporation of SWCNT and can be attributed to the change in bulk resistance together with a reduction in relaxation time of the nanocomposite. A quantitative analysis from the fitting of the Cole–Cole plot also reveals that the incorporation of SWCNT into the nanocomposite decreases the grain boundary resistance from 16 950 to 53 kΩ and increases the capacitive element from 67 to 275 nF. The mechanism behind the improved dielectric performance of the Gel/SWCNT nanocomposites has been elucidated in this study.