Broadband Dielectric Spectroscopy Technique Research Articles

Hydration effects on thermal transitions and molecular mobility in Xanthan gum polysaccharides.

In this work, the xanthan gum (XG) polysaccharide is studied over a wide range of temperatures and water fractions 0 ≤ hw ≤ 0.70 (on a wet basis) by employing differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The investigation reveals that the critical water fraction for ice formation is about 0.35. Glass transition temperature (Tg) was determined through calorimetry experiments for all the samples studied. Water acts as a strong plasticizer, i.e., decreasing Tg, for water fractions up to about 0.35. A secondary (local) relaxation process is recorded in both dry and hydrated samples, which is sensitive to the presence of water molecules. This fact indicates that this process originates due to the orientation of small polar groups of the side chain, or/and due to the local main chain dynamics. Two types of long-range charge transport processes were resolved. The first is related to the conductive paths being formed via bulk-like ice structures (at high hydration levels), whereas the second can be attributed to proton mobility via the hydrogen bond (HB) network of non-freezing water existing in XG. Interestingly, this process is exactly the same in all the hydrated samples with hw > 0.25. With respect to the sample with hw = 0.27, a Vogel-Tammann-Fulcher (VTF)-like polarization process has also been recorded which seems to be related to long-range charge mobility via interconnected water clusters. As far as we are aware, this is the first time that XG is studied in terms of glass transition and molecular mobility over a wide range of hydration levels combining DSC and BDS techniques.

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.

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.

Study of Relaxations in Epoxy/Rubber Composites by Thermally Stimulated Depolarization Current and Dielectric Spectroscopy

Liquid rubber toughened epoxy resins are widely used in electrical equipment and electronic packaging. Previous studies have only investigated the relaxation process of epoxy resins through dielectric spectroscopy. The trap characteristics of the relaxation process by thermally stimulated depolarization current (TSDC) analysis are less studied. In this work, TSDC and broadband dielectric spectroscopy techniques were used to complementarily characterize the dielectric relaxation process of hydroxyl-terminated liquid nitrile-butadiene rubber (HTBN) toughened epoxy resin polymers. The experimental results show that HTBN introduces two new relaxation processes in the epoxy matrix, which are attributed to the α polarization of the rubber molecule and the interfacial polarization based on the correlation between the TSDC and the dielectric spectroscopy data, respectively. The trap parameters of each TSDC current peak were obtained using the multi-peak fitting method. The addition of rubber increases the trap density in epoxy composites significantly, especially for traps with energy levels in the range of 0.5–0.9 eV. The trap energy level of the DC conductivity process increases with increasing rubber concentration. The above results provide analytical ideas for rubber-toughened epoxy resins’ polarization and trap characteristics and theoretical guidance for formulation improvement.

Breakdown Performance and Partial Discharge Development in Transformer Oil-Based Metal Carbide Nanofluids.

In this work, the influence of semi-conductive SiC nanoparticles on the AC breakdown voltage and partial discharge development in natural ester oil FR3 is examined. Primarily, the dielectric constant and the electrical conductivity of the nanoparticles are measured following the broadband dielectric spectroscopy technique. The nanoparticles are added into the matrix following the ultrasonication process in three weight percentage ratios in order for their effect to be evaluated as a function of their concentration inside the base oil. The processing of the results reveals that the nanofluid containing SiC nanoparticles at 0.004% w/w demonstrates the highest AC dielectric strength improvement and shows the greatest resistance to the appearance of partial discharge activity. The mechanisms behind the aforementioned results are discussed in detail and confirmed by the broadband dielectric spectroscopy technique, which reveals that this particular nanofluid sample is characterized by lower dielectric constant and electrical conductivity than the one with double the weight percentage ratio.

Dynamic processes and charge carriers transport in polyvinyl acetate–polyaniline composites

This work studies the effect of composite formation between polyvinyl acetate (PVAc) and conductive polyaniline (PAni) on its conductivity mechanism. To achieve this goal, different concentrations of PAni in mini-emulsion of PVAc are prepared. The dynamic relaxation and electric conductivity are evaluated using broadband dielectric spectroscopy technique. The relaxation rate of the local reorientations (β-process) of ester group follows an Arrhenius relation with activation energy 39 kJ/mole. The coupling of the segmental dynamic (α-process) and terminal fluctuation (β′-process) occurs just above the calorimetric glass transition temperatures, Tg, of pure PVAc. This is reasonable since α-process that originated from a structural rearrangement became very slow below Tg which takes the polymer toward its equilibrium state. There is also decoupling of the charge carriers transport, and the segmental motion, the concept concluded in this manuscript, sounds reasonable if one thinks about the ion motion at T < Tg. This conclusion is straightforwardly deduced from the experimental data, as explained in more detail. The study also confirms that PAni electrical conductivity mechanism is conserved.

Interfacial interactions and interfacial polarization in polyazomethine/MWCNTs nanocomposites

We prepared the polyazomethine/MWCNTs nanocomposites varying in the nanofiller loading (from 0 to 1.5 wt%). Taking into account an upshift of the characteristic D and G bands of MWCNTs in the Raman spectrum of the nanocomposite, we confirmed the interfacial interactions between MWCNTs and polymer chains. When we studied the nanocomposites morphology, we concluded that both disentanglement and dispersion of MWCNTs in the polymer matrix are provided by interfacial interactions. Using broadband dielectric spectroscopy technique, we investigated the interfacial polarization in the nanocomposites. We found that this phenomenon is valuable for electrical conductivity of the nanocomposites with high MWCNTs loading, particularly, at high temperatures and low frequencies.

Synthesis and Characterization of Polyaniline/Mn3O4/Reduced Graphene Oxide Nanocomposite

The present work is concerned with the synthesis and studying the electrical and dielectric properties of Polyaniline (PANI)/Mn3O4/Reduced Graphene Oxide (RGO) nanocomposites using the Broadband Dielectric Spectroscopy technique. Polyaniline/Mn3O4 and polyaniline/Mn3O4/RGO nanocomposites were prepared using in-situ polymerization. To investigate the structural and morphology of the prepared samples, XRD, FTIR, HRTEM and SEM techniques were used. XRD results of pure Mn3O4 and PANI showed that PANI has crystallinity to some extent and the formation of Mn3O4 as a major phase with crystallite size ~20 nm is obtained. In case of nanocomposite samples, PANI/Mn3O4 and PANI /Mn3O4/RGO revealed a slight disappearance of the characteristic peaks of Mn3O4, which may be attributed to the covering of Mn3O4 surface by PANI. FTIR analysis of the nanocomposite samples indicated that the characteristic absorption peaks are shifted to higher wavenumbers compared with that of pure PANI confirming the interaction between PANI, graphene and Mn3O4. The morphological study of the samples revealed a porous surface of micro aggregates of Mn3O4 and PANI enveloped by RGO sheets and showed the distribution of Mn3O4 nanoparticle and PANI nanofibers on and between the thin sheets of RGO. The value of dc conductivity is rather high, and the prepared nanocomposites could be considered as synthetic metals from the conductivity point of view of such plastic electrode materials.

(Invited) Multiscale Morphological and Electrical Characterization of Charge Transport and Charge Transfer Limitations to Power Performance of Positive Electrode for Li-Ion Batteries

Composite materials consisting of several interpenetrated and percolating phases are widely used as electrodes for a variety of electrochemical cells. Such electrodes are generally mixed ionic−electronic conductors, in which ions and electrons are confined to transport within the specific conducting network. In particular, for electrochemical storage and energy transformation devices, the transport properties play critical roles in determining their performance, which is pivotal to improve them for service as power sources. To reach this goal, an increased fundamental understanding of the factors that play on the transport properties within such composite materials is still required. The transport of the electrons and ions through Li-ion battery electrode and their transfer to the active matter depend on the electrode architecture (nano- and microstructure) through the interfacial areas, materials connectivity, and the transport length scales. Novel opportunity for progressing in this direction and exploring relationships between electrode architecture, charge transport and electrochemical performance is implementation of X-ray computed tomography (XRCT) and focused ion beam in combination with scanning electron microscopy (FIB-SEM) techniques to characterize and quantify the 3D architecture of composite electrodes. In particular, tortuosity, a critical parameter with respect to ionic transport, has been exhaustively studied. Comparatively, factors that play on the electrons transport and wiring to the active mass have been much less considered. Moreover, attempts to correlate quantified 3D geometries with measured electrochemical power performance or electrical transport properties of same real electrodes remain rare. We intend to fill this gap in this presentation. We have undertaken exhaustive characterizations of 3D geometries of LiNi1/3Mn1/3Co1/3O2 (NMC), LiFePO4 (LFP), and NMC/LFP blended electrodes and rationally interpreted their measured electrical properties and electrochemical performance. A combination of X-Ray tomography and FIB-SEM tomography are used for a multiscale analysis of electrodes 3D geometries, in particular the distribution of the conductive additive and the binder that perform as electronic wires, the tortuous pores distribution, which after electrolyte impregnation perform as ionic wires, and the inter-connectivity between the active matter phase and the electronic and the ionic wires [1]. The electrical properties (permittivity and conductivity) are measured from low (a few Hz) to microwave (a few GHz) frequencies by the broadband dielectric spectroscopy technique [2]. This one is very sensitive to the different scales of the electrode architecture involved in electronic transport, from interatomic distances to macroscopic sizes, as well as to the morphology at these scales, coarse or fine distribution of the constituents [2,3]. In addition to the geometry of the electrode architecture, the interfaces (adsorption of ions to the surface of active material and carbon nanoparticles), and interactions at such interfaces lead to a reciprocal influence of ionic and electronic transfers at the different scales of the electrode [4]. Finally, discharge rate performance is analyzed by simple, yet efficient methods. This approach allows discriminating between the contributions of the electronic and ionic wiring networks as the performance limiting factors, depending on the electrode geometry and discharge rate. [5] Acknowledgements Financial funding from the ANR Program No. ANR-15-CE05-0001-01 (PEPITE) is acknowledged. We also thank the CLYM (Centre Lyonnais de Microscopie) supported by the CNRS, the “Grand Lyon” and the Rhône-Alpes Region for use of the Zeiss NVision40 FIB/SEM. The IMD (Institut de la Mobilité Durable – Sustainable Mobility Institute) is also acknowledged for financial support.

Atorvastatin as a Promising Crystallization Inhibitor of Amorphous Probucol: Dielectric Studies at Ambient and Elevated Pressure.

The aim of this article was to check the physical stability of the amorphous form of probucol at both standard storage and manufacturing conditions. Our studies clearly show that disordered form of the examined, cholesterol lowering, agent stored at ambient pressure does not reveal any tendency toward recrystallization. The physical stability of neat probucol stored at ambient pressure has been investigated (i) at room temperature by means of X-ray diffraction technique (XRD) as well as (ii) at T = 333 K by means of broadband dielectric spectroscopy (BDS). Due to the fact that compression is an important stage of drugs manufacturing we additionally performed physical stability tests of amorphous probucol at elevated pressure. The recrystallization tendency of the examined pharmaceutical has been tracked online from the initial and further up to a few hours after compression by means of the high pressure BDS technique. These experiments indicate that even very small pressure applied during the sample compression immediately induce its recrystallization. Since, the sensitivity on pressure eliminates probucol from the group of physically stable amorphous APIs, its stabilization is required. Taking into account that there are many scientific reports describing the positive effect of coadministration of probucol with the drug atorvastatin, we used the latter as probucol's crystallization inhibitor.

Anisotropic charge transport in ion-conductive photoresponsive polyethylene oxide-based mesomorphic materials.

The mechanism of charge motion in conductive and photosensitive mesogenic block copolymers containing polyethylene oxide (PEO) segments is investigated over a wide frequency and temperature range with the broadband dielectric spectroscopy technique. It is found that the ultraviolet (UV) irradiation, the UV intensity, and the anchoring conditions of mesogenic unit in the cells produce changes in conductivity properties and in the molecular arrangement. The anisotropic nature of the conductivity is established.

Molecular dynamics, conductivity and morphology of sodium deoxycholate-based poly(ester ether)urethane ionomer biomaterials

Broad-band dielectric spectroscopy technique was used to investigate the molecular dynamics of new sodium deoxycholate-based poly(ester ether)urethane ionomers of particular interest in biomedical devices. These polyurethane ionomers have identical hard segment containing bile salt moiety but with different soft segment chemistries. Poly(ethylene oxide)-rich soft segment promotes stronger ionic interactions and solvation capacity of ions and higher ionic conductivity in these polyurethane ionomers. The universal power law was employed to study the evolution of alternating conductivity (AC) with frequency and temperature. The calculated values of fractional exponent ranged between 0 and 1 which indicate AC conduction through hopping mechanism. Direct current conductivity evidences Arrhenius behaviour in the function of temperature and the estimated values of activation energy for poly(ethylene oxide)-rich soft segment polyurethane ionomers are found higher. The increase in the conductivity with temperature can be interpreted as a hopping mechanism assisted by chain relaxation. AFM and SAXS investigations evidence lamellar arrangement at the sub-micron scale and the nanophase-separated morphology for these polyurethane ionomers. The tensile tests evidenced that the polyurethane with highest molecular weight exhibits the highest values of mechanical properties and ductile behaviour.

Interest in broadband dielectric spectroscopy to study the electronic transport in materials for lithium batteries

Broadband dielectric spectroscopy (BDS) is used to measure complex permittivity and conductivity of conducting materials for lithium batteries at frequencies from a few Hz to several GHz with network and impedance analysers. Under the influence of an electric field, there will be charge density fluctuations in the conductor mainly due to electronic transfer. These fluctuations result in dielectric relaxations for frequencies below 100GHz. The materials are compacted powders in which each element (particles, agglomerates of particles) can have different sizes and morphologies. In the present review, studies are reported on the influence of surface states in LiNiO2 (ageing and degradation in air) and LiFePO4 (carbon coating thin layer), and on a composite electrode based on the lithium trivanadate (Li1.1V3O8) active material. The results have shown that the BDS technique is very sensitive to the different scales of materials architectures involved in electronic transport, from interatomic distances to macroscopic sizes.

Secondary chain motion and mechanical properties of γ‐irradiated‐regenerated cellulose films

Regenerated cellulose films prepared using NaOH/urea solvent system were exposed to different doses of γ‐radiation, ranging from 5 to 50 kGy to modify their properties. Change in relative crystallinity as a function of absorbed dose was studied using XRD. The tensile and dynamic mechanical properties were tested and it was found that exposure to 10 kGy imparted maximum improvement in these properties, that is 10% improvement in tensile strength, 43% increase in Young's modulus, and 22% increase in storage modulus. Broadband dielectric spectroscopy technique was used to investigate effect of absorbed dose on the secondary chain motions of the regenerated cellulose and the results were in line with findings of the tensile and dynamic mechanical tests.

Influence of Electrolytes on the Electronic Transfer in Electrode Materials: Ex- and In-Situ Dielectric Spectroscopy Study between 103 and 1010 Hz

The fruitful contribution of Broadband Dielectric Spectroscopy (BDS) to study hierarchical materials applied to batteries electrodes has been previously shown [1-5]. The results demonstrate that the broadband dielectric spectroscopy technique is very sensitive to the different scales of the electrode architecture involved in the electronic transport, from interatomic distances to macroscopic sizes, as well as to the morphology at these scales, coarse or fine distribution of the constituents. When the frequency increases, different kinds of polarizations appear from interatomic distances to macroscopic sizes (Fig. 1) and give rise to dielectric relaxations in the following order: (a) space-charge polarization (low-frequency range) due to the interface sample/current collector; (b) polarization of clusters of particles (micronic scale) and (c) polarization of particles due to the existence of resistive junctions between them; d) electron transfers (nanometric or interatomic scale).The BDS measurement was up to now ex situ measurement, on dry electrode. They provide a fundamental insight into the conduction properties at all scales of the materials before being integrated in a real battery. An innovative device (measurement cell) has been developed to make synchronized BDS measurements and electrochemical cycling. The frequency range is about 103 - 1010 Hz. In this work, data acquisitions were made on dry electrode (LiNi1/3Co1/3Mn1/3O2 / Carbon black / PVdF) and then on the same electrode wetted with an electrolyte. Short- and long-range motions of ions are evidenced in the low-frequency region. At higher frequencies, the study shows for the first time the influence of the ions of the electrolyte on the transfer of the electronic charges (holes) in LiNi1/3Co1/3Mn1/3O2at the micronic scale. Acknowledgements Financial funding from CNRS, Université de Nantes, UMICORE, and the ANR program n° ANR-09-STOCK-E-02-01 is acknowledged.

In Situ Synthesis and Properties of Epoxy Nanocomposites

Abstractsilver‐epoxy nanocomposite films based on diepoxide of Mn = 450, silver tetradecanoate and triethylamine were synthesized by in situ method. The mean diameter of AgNPs in nanocomposite films as defined by SEM technique has been found within the range of 15–20 nm. Ag NPs narrow size distribution was found independent on silver tetradecanoate concentration as shown by UV‐vis spectroscopy analysis. Dielectric properties of silver‐epoxy nanocomposite films were investigated also by Broadband dielectric spectroscopy technique.

Influence of adsorbed polar molecules on the electronic transport in a composite material Li1.1V3O8–PMMA for lithium batteries

The broadband dielectric spectroscopy (BDS) technique (40 to 10(10) Hz) is used here to measure the electronic transport across all observed size scales of a Li(1.1)V(3)O(8)-polymer-gel composite material for lithium batteries. Different electrical relaxations are evidenced, resulting from the polarizations at the different scales of the architecture: (i) atomic lattice (small-polaron hopping), (ii) particles, (iii) clusters of particles, and finally (iv) sample-current collector interface. A very good agreement with dc-conductivity measurements on a single macro-crystal [M. Onoda and I. Amemiya, J. Phys.: Condens. Matter, 2003, 15, 3079.] shows that the BDS technique does allow probing the bulk (intrinsic) electrical properties of a material in the form of a network of particles separated by boundaries in a composite. Moreover, this study highlights a lowering of the surface electronic conductivity of Li(1.1)V(3)O(8) particles upon adsorption of polar ethylene carbonate (EC) and propylene carbonate (PC) that trap surface polarons. This result is meaningful as EC and PC are typical constituents of a liquid electrolyte of lithium batteries. It is thus suggested that interactions between active material particles and the liquid electrolyte play a role in the electronic transport within composite electrodes used in a lithium battery.

Systematic Dielectric Relaxation Study of Solid-Like Polyelectrolyte−Surfactant Complexes formed between Poly(styrenesulfonate) and Cationic Surfactants

The dielectric relaxation behavior of polyelectrolyte−surfactant complexes with ordered lamellar microstructure were studied using broadband dielectric spectroscopy technique in the frequency range...

A Multiscale Description of the Electronic Transport within the Hierarchical Architecture of a Composite Electrode for Lithium Batteries

AbstractThe broadband dielectric spectroscopy technique is applied, for the first time, to a composite material used as an electrode for lithium battery. The electrical properties (permittivity and conductivity) are measured from low (a few Hz) to microwave (a few GHz) frequencies. The results demonstrate that the broadband dielectric spectroscopy technique is very sensitive to the different scales of the electrode architecture involved in electronic transport, from interatomic distances to macroscopic sizes, as well as to the morphology at these scales, coarse or fine distribution of the constituents. This work opens up new prospects for a more fundamental understanding and more rational optimization of the electronic transport in composite electrodes for lithium batteries and other electrochemical energy storage technologies (including other batteries, supercapacitors, low‐ and medium‐temperature fuel cells), electrochemical sensors and conductor–insulator composite materials.