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Glycolipids prepared from palm kernel oil, PKO, in tropical regions represent an excellent opportunity to develop new surfactant formulations for cosmeceutical and pharmaceutical applications while contributing to sustainable economies. Here we report the synthesis of a new mannoside obtained from palm kernel oil, aManPKO, and we characterise its thermotropic properties by using DSC, POM, SAXS, WAXS, FT-IR and broadband dielectric spectroscopy. aManPKO exhibits a monotropic smectic phase with a partially interdigitated bilayer structure, similar to its major unsaturated component, the oleyl mannoside with a C18:1 monounsaturated alkyl chain. The smectic phase of aManPKO vitrifies below room temperature, which is associated to the C18:1 component, but also to the activation of short-range motions, ~4 Å, by cleavage of strong hydrogen bonding between the polar heads of the mannosides. The stability of the liquid crystal phase, on the other hand, is linked to the presence of weak hydrogen bonding, whose breakage leads to the activation of long rate motions in the range of the layer distances, ~39 Å. [ABSTRACT FROM AUTHOR]

In this paper, the study of relaxation processes in ferroelectric ceramics under the influence of a dc electric field has been performed. To measure the field and time dependences of the complex elastic, dielectric, and piezoelectric parameters of ferroelectric ceramics, the impedance spectroscopy method and piezoelectric resonance analysis program were used. A comparative analysis of various characterization methods was carried out, and a physical interpretation of the results has been proposed. [ABSTRACT FROM AUTHOR]

In the past decades, para-terphenyls have been attracting tremendous attention due to their polymorphism and conformational diversity. In this work we report the synthesis, crystal structure, polymorphism and dielectric properties of two 2,2′′-bis-substituted para-terphenyls: 2,2′′-bis(hydroxymethyl)-para-terphenyl and 2,2′′-bis(acetyloxymethyl)-para-terphenyl. On the basis of calorimetric and X-ray studies, we showed that the latter compound occurs in at least four polymorphic forms with melting points equal to 364, 345, 341 and 326 K, differentiated also in terms of thermodynamic stability and crystal symmetry. The most stable polymorph I is characterized by the P21/n space group. 2,2′′-Bis(hydroxymethyl)-para-terphenyl crystallizes in the monoclinic P21/c space group. Both 2,2′′-bis-substituted para-terphenyls can undergo vitrification, which is a highly exceptional feature for this class of chemical compounds and has not been reported before. Consequently, the molecular dynamics and conformational changes in the glassy and supercooled liquid states were analyzed by means of IR and broadband dielectric spectroscopy. Two relaxation processes were observed for both compounds: structural α-relaxation, connected with reorientational motions of molecules in supercooled liquid, and intermolecular γ-relaxation, ascribed to rotational motions of substituents of the para-terphenyl skeleton. Taking into account the ongoing discussion about the conformational diversity of the para-terphenyl skeleton, we showed that although free rotation of benzene rings is suppressed, the molecules in the glassy and liquid states can adopt both twisted and helical conformations, which results in diversity of the polymorphic forms. [ABSTRACT FROM AUTHOR]

Different polymorphs of niobium pentoxide (Nb 2 O 5) were synthesized using niobium ethoxide as a precursor by varying the pyrolyzing temperature. The room temperature X-ray diffractograms revealed the irreversible phase evolution from amorphous to pseudohexagonal (823 K) to orthorhombic (1023 K) and to monoclinic crystal structure (1223 K). While phase evolution was also confirmed by thermogravimetry and dilatometry, Raman spectroscopy clearly suggested complete elimination of free carbon in the pyrolysed ceramics. The sintering conditions were optimized to produce a highly dense (>95%) thermodynamically stable monoclinic Nb 2 O 5. The electrical properties of stable monoclinic Nb 2 O 5 sample were thoroughly studied. The monoclinic Nb 2 O 5 was found to have a dielectric constant of around 28 with a dielectric loss of 0.008 at room temperature and at 100 kHz. At low measurement frequencies, an anomalous increase in the effective dielectric permittivity with increasing temperature was observed. Large values of the ε ' are associated with polarization due to the accumulation of free electrons at the grain boundaries. An analysis of the dispersion curves of Nb 2 O 5 revealed that two relaxation processes are responsible for the observed anomalies, and the temperature dependencies of their parameters (dielectric strength, relaxation time and spectrum broadening parameter) were determined. The low-frequency process (relaxation time τ 0 ~ 0.45 s), which makes the largest contribution to the dielectric constant, was apparently due to the inhomogeneous conductivity of ceramics. It was revealed that the DC conductivity of ceramics has thermoactivation character with activation energy of about 660 meV and was determined by the oxygen vacancies. [ABSTRACT FROM AUTHOR]

Molecular mobility of cyanophenyl alkylbenzoates (CPnBs) (n = 2, 3, 7 – number of carbon atoms in the alkyl chain) in the bulk and in composites with aerosil A380 is investigated by broadband dielectric spectroscopy, while thermal analysis and infrared spectroscopy were applied to characterise the molecular species. The work completes preliminary results obtained for the members with n = 4 ... 6. An interaction by hydrogen bonding, between aerosil surface – OH groups and – CN or ester groups of the CPnB molecules takes place. It slows down the relaxation process as observed for related composites in comparison to the pure materials. The existence of two types of bonding might be the reason that Vogel temperature for the relaxation process in the surface layer does not show the odd-even effect. Temperature dependence of the relaxation rates for composites shows a crossover behaviour from a high to a low temperature regime. Moreover, the temperature dependence of the dielectric strength is unusual. As the loading degree is similar, comparison of the dielectric, spectroscopic and thermal data obtained here and with the results obtained for the composites with n = 4 ... 6 can be directly done. Increasing the number of the members of the homologous series confirms and hardens the preliminary conclusions. [ABSTRACT FROM AUTHOR]

Temperature-dependent dielectric spectroscopy was used to observe multiple dielectric responses involving four sets of dielectric relaxations (DRs) in molecular beam epitaxy-deposited ultrathin (001) SrMnO3/Nb:SrTiO3 heterojunctions. Two sets of oxygen-vacancy (OV)-related DRs, which were sensitive to oxygen annealing, were attributed to short-range OV hopping and localized Jahn–Teller (JT)-polaron hopping-induced dipolar-type relaxations. Arising from electron-phonon coupling between eg electrons and JT-distortion in Mn3+ ions, the appearance of JT-polarons was closely related to the presence of oxygen vacancies, which leads to transitions from Mn4+ to Mn3+. [ABSTRACT FROM AUTHOR]

Despite the widespread use of aqueous electrolytes as conductors, the molecular mechanism of ionic conductivity at moderate to high electrolyte concentrations remains largely unresolved. Using a combination of dielectric spectroscopy and molecular dynamics simulations, we show that the absorption of electrolytes at ~0.3 THz sensitively reports on the local environment of ions. The magnitude of these high-frequency ionic motions scales linearly with conductivity for a wide range of ions and concentrations. This scaling is rationalized within a harmonic oscillator model based on the potential of mean force extracted from simulations. Our results thus suggest that long-ranged ionic transport is intimately related to the local energy landscape and to the friction for short-ranged ion dynamics: a high macroscopic electrolyte conductivity is thereby shown to be related to large-amplitude motions at a molecular scale. The ionic conductivity of an aqueous electrolyte has a great impact on the performance of devices such as batteries. Here, the authors advance our understanding by showing that a high macroscopic conductivity originates from the large-amplitude sub-picosecond motions of ions on a molecular scale. [ABSTRACT FROM AUTHOR]

The Ba0.85Ca0.15Zr0.1Ti0.9O3 (referred to as BCZT) ceramic powders were synthesized by the sol–gel method followed by calcining, and then the ceramics were obtained by sintering at different temperatures varied from 1200 to 1350 °C. The effects of sintering temperature on the microstructure, impedance spectroscopy, dielectric, and ferroelectric properties for BCZT ceramics have been thoroughly investigated. The pure perovskite structure and homogenous microstructure with high relative density (> 90%) for all BCZT ceramics are identified by XRD analysis and SEM measurement, and the stability is identified by the variable-temperature dielectric characterization. The impedance spectroscopy and well-defined polarization–electric field hysteresis loops for BCZT samples were detected at room temperature. In particular, the BCZT ceramic sintered at 1300 °C resulted the highest dielectric constant (εr ~ 2170), the lowest dielectric loss (tan δ ~ 0.027), and the highest grain boundary resistance (Rgb ~ 8.9 × 107 Ω cm). [ABSTRACT FROM AUTHOR]

Herein, X‐ray diffraction, energy dispersive X‐ray spectroscopy, and spectral ellipsometry techniques are used to investigate the structural, pseudo‐optical, and pseudodielectric properties of arsenic selenide thin films. The stoichiometric films which are prepared by the thermal evaporation technique are found to prefer the amorphous nature of growth. While the pseudoabsorption coefficient spectra display strong absorption bands at 1.84, 1.81, 1.41, and 1.13 eV, the preferred pseudo‐optical transitions happen within a direct forbidden energy bandgap of 1.80 eV. In addition, the real part of the pseudodielectric spectra displays three strong resonance peaks at critical energy values of 2.33, 1.90, and 1.29 eV. Modeling of the imaginary part of the pseudodielectric constant spectra in accordance with the Drude–Lorentz approach results in the existence of six linear oscillators. The response of arsenic selenide to elliptically polarized light signals shows that the films exhibit drift mobility, free electron concentration, and plasmon frequency values in the ranges of 0.21–43.96 cm2 V−1s−1, 1.90–58.0 × 1019 cm−3, and 5.8–32.0 GHz, respectively. The optical conductivity parameters for As2Se3 film nominate it as a promising candidate for the fabrication of tunneling diodes suitable for microwaves filtering up to 32.0 GHz and as thin‐film transistors. [ABSTRACT FROM AUTHOR]

Single-phase Ba 1-x Sr x TiO 3 (BST) perovskite ceramics with 0.3 ≤ x ≤ 0.4 were prepared from powders synthesized via sol-gel route. The compositions have the ferroelectric-paraelectric phase transition close to room temperature. At 20 °C the BST ceramics are ferroelectric for 0.3 ≤ x ≤ 0.35 and paraelectric for x = 0.375 and x = 0.40. The study follows the relation between the structural changes produced when increasing the Sr content and the dielectric properties at low intensity electric fields. It is found that the grain size and tetragonality decreases as the Sr content increases. Analyses of complex permittivity and impedance spectroscopy reveal the temperature and frequency dependencies of the dielectric properties. The phase transitions seem to be of first order for all compositions, with a thermal hysteresis that decreases with increasing the Sr content, fact attributed to the corresponding increase of the grain boundaries weight allowing a more efficient stress relaxation in the structure during the change of the symmetry from cubic to tetragonal. The diffusiveness degree during the phase transition is increasing with Sr content, suggesting some relaxor-type contribution attributed to smaller grain size. The ac conductivity follows the universal Jonscher law, with an ac component having the power parameter s independent of Sr content, and a dc component that it is thermally activated with an activation energy of about 0.7–0.77 eV attributed to oxygen vacancies acting as donor-like defects. The fit of impedance spectra at different temperatures and frequencies is obtained by using an equivalent circuit accounting the grains, grain boundaries, electrode interfaces and the local contributions produced by reorientation of defect dipoles or defect clusters. All the component circuits have significant variations around phase transitions. These are discussed in relation to structural changes occurring during transition and considering the changes in the distribution of various charges when polarization vanishes. [ABSTRACT FROM AUTHOR]

Polyimides (PIs) and their composites hold promise as low-cost alternatives to conventional ceramic-based dielectrics. Nevertheless, they are far unsatisfactory for practice applications, mainly resulting from the low interfacial compatibility between PI matrices and inorganic fillers. Herein, black phosphorous (BP) nanoflakes/PI composite films with outstanding dielectric and mechanical properties were fabricated via an in situ polymerization pathway. Owing to the hydrophilic surface of BP nanoflakes resulting from slight oxidation during fabrication, the robust noncovalent interaction between BP and PI can be formed, leading to good interfacial compatibility between the two domains and thus well dispersion of BP in PI. Even with a low BP content of 2 wt%, the composite can reach a high-permittivity value of 8.6 at 102 Hz and a low dielectric loss value of 0.02. Moreover, the BP/PI composite films inherited the good mechanical performance of PI matrix due to homogeneous dispersion and low loading of BP. [ABSTRACT FROM AUTHOR]

The crystals of pure [(CH3)3NH]2[KFe(CN)6] (TrMAFe) and [(CH3)3NH]2[KCo(CN)6] (TrMACo) as well as their mixed crystals (TrMAFexCo1−x), with different ratios of x = 0, 0.12, 0.18, 0.49, 0.56, 0.73, 0.81, 1.0, have been grown from aqueous solutions. The structure of TrMACo has been determined at 360 K to be cubic (Fm3¯m). In phase II (100 K), the TrMACo crystal is monoclinic (C2/c). The thermal stability of the pure and mixed crystals has been determined by using both DTA and TGA. Based on the DSC results, we have found a single phase transition (PT) for both pure and mixed crystals. The Fe(III) concentration was estimated by using the SEM technique. We have found a linear relationship between the PT temperature (Tc) and the molar concentration of Fe(III). Based on the obtained results, a phase diagram has been constructed. The mechanism of the structural PT has been discussed based on the results of dielectric relaxation and 1H NMR and X-ray spectroscopy measurements. The results confirmed that the PT mechanism of both pure and mixed crystals is related to the change in the dynamic state of the TrMA+ cations. The dielectric activation energy changes linearly with the mole fraction ranking from 35 to 38 kJ mol−1, for the mixed crystals. [ABSTRACT FROM AUTHOR]

The current study investigated the dielectric and electrical properties of BaAl (2−2 x) (Zn 0.5 Ti 0.5) 2 x O 4 ceramics, with x = 0, 0.4%, 0.8%, 1.2% and 1.6%, via impedance spectroscopy. The co-doping of Zn and Ti improved the temperature stability over −100 °C–700 °C of ε r and lowered tan δ due to the electron-pinned defect-dipoles. Effects of oxygen partial pressure on the electrical, dielectric and ferroelectric properties of x = 1.6% ceramic were studied as well. The bulk conductivity of the N 2 –H 2 -sintered and O 2 -sintered samples was attributed to the e ' and h • , respectively. [ABSTRACT FROM AUTHOR]

Mg doping effects on the dielectric response and relaxation behavior in Ba 2 Co 2- x Mg x Fe 12 O 22 are experimentally studied for doping range of 0 ≤ x ≤ 1 through measurements of dielectric constant, loss and impedance spectroscopy as functions of temperature and frequency. It is shown that a colossal dielectric response with dielectric constant higher than 103 near room temperature for a wide range of frequency up to ~1 MHz can be realized by Mg doping at Co sites. Our results demonstrate that Mg doping can cause three obvious effects, namely, (i) to decrease Co3+ ions and in turn increase Fe ions in octahedrons, (ii) to raise the activation energy of relaxation and (iii) to increase resistance and capacitance of grain boundary. Our results also demonstrate that the dielectric relaxation is gradually changed from the intragranular- to the intergranular-dominated relaxation with increasing Mg doping content, perhaps due to the doping-caused increase in both resistance and capacitance of grain boundary. [ABSTRACT FROM AUTHOR]

Heat-resistant polymer nanocomposites based on polyimide matrix and mixture of ethoxysilanes have been synthesized and investigated. Using the sol-gel method, samples were obtained based on pyromellitic acid dianhydride and 4,4'-diaminodiphenyl ether and mixtures of tetraethoxysilane and methyltriethoxysilane in the ratio (1: 1, 1: 2) in the amount (5, 20, 50% by weight of the original PACK).  e in􀄘 uence of the ratio and content of ethoxysilanes on the structure and properties of nanocomposites was studied by the methods of X-ray structural analysis, dielectric spectroscopy and thermogravimetric analysis.  e established structural dependences for these composites allow us to conclude that there is no signi􀄕 cant eff ect of the ratio and amount of ethoxysilane introduced into the system to form the inorganic component on the structure.  e obtained materials are characterized by high thermal stability, low dielectric constant.  e greatest decrease in dielectric constant compared to the original polyimide is observed for samples with diff erent ethoxysilane ratio at 20% content.  e resulting nanocomposites are characterized by high thermal stability and can be used in high temperature conditions. [ABSTRACT FROM AUTHOR]

For conducting comparative research, samples of cross‐linked polyethylene (XLPE), made exactly in the same manner as those used in nuclear power plants, were aged in two ways: purely thermally, and concurrently with heat and γ‐irradiation, for long periods up to 2000 h. They were then examined by an indenter, mid‐infrared absorption spectroscopy, broadband dielectric spectroscopy, and measuring the electrical conductivity. As a result, it became clear that the effect of radiation is more dominant than that of heat on the oxidation or carbonyl formation in XLPE. However, heat is a more determining factor on the surface hardness of XLPE. In addition, the complex permittivity of XLPE increases as a result of the appearance of abundant carbonyl groups. Both the carbonyl index and indenter modulus can be indicators of aging. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [ABSTRACT FROM AUTHOR]

This paper reports the effect of interlayer species on the electrical and dielectric behaviours of a lamellar structure. The successful intercalation of three oxyanions ( CO 3 2 - , NO 3 - and H 2 PO 4 -) in the interlayer space of NiAl-layered double hydroxide (LDH) was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis and inductively coupled plasma. Using complex impedance spectroscopy measurements, equivalent circuit consisting of three serially connected R-CPE units was established for each sample. Each unit contains a resistance and a constant phase element representing contributions of grain, grain boundary and electrode interface, which allowed the determination of their electrical parameters. The adjustment of experimental data of conductivity by the double power law allowed the determination of σ dc and other conductivity parameters, and therefore, the investigation of the effect of intercalated anions on NiAl LDH electrical behaviour. Indeed, dihydrogenophosphates intercalated sample was found to decrease σ ac over the frequency range of measure, comparing to the other anions. The intercalation of this anion has also an effect on dielectric properties, it reduces the value of dielectric constant of NiAl LDH, and shifts the maximum of tan δ towards medium frequencies with a decrease in the value of loss tangent above 10 5 Hz. Carbonate and nitrate intercalated LDH showed a similarity in their effect on electrical and dielectric properties of NiAl LDH. [ABSTRACT FROM AUTHOR]

We report on the synthesis and characterization of carbon nanotube (CNT)-doped polyaniline (PANI) composites for enhanced corrosion protection of steel with improved electrical properties. PANI–CNT nanocomposites were prepared through in situ polymerization of aniline in the presence of CNTs. Synthesized nanocomposites were characterized by several analytical methods such as Fourier transform infrared spectroscopy, x-ray diffraction, micro-Raman spectroscopy, and scanning electron microscopy in order to understand the structural, morphological, and molecular aspects of the composites. The doping of CNTs in PANI matrix drastically enhanced the alternating current/direct current (AC/DC) conductivities as well as the dielectric attributes and impedance spectroscopy of the composites. The anticorrosion studies of the prepared composites were performed by using open-circuit potential analysis and potentiodynamic measurements. Compared to stainless steel, PANI–CNT nanocomposites demonstrated excellent anticorrosion behavior. The obtained results showed that 25 wt.% of CNT-doped PANI composite exhibits excellent anticorrosion properties due to electron transmission and passive catalysis. [ABSTRACT FROM AUTHOR]

Magnetoelectric composites combining ferromagnetic cobalt ferrite (CFO) and ferroelectric barium titanate (BT) are prepared using conventional solid-state reaction. Dielectric measurements reveal that CFO and CFO-BT composites exhibit Maxwell–Wagner polarization and temperature-dependent relaxation originating due to the presence of ions/defects vacancies. Prominently, CFO-30%BT composite showed an unexpected low dielectric loss ≈ 0.5 above 1 kHz and has potential for device application. Impedance spectroscopy confirms the thermally activated relaxation mechanism and high impedance behavior in the samples. Modulus analysis affirms the statistically distributed non-Debye-type behavior existing in CFO-BT composites. The electric conductivity takes place via correlated barrier hopping in CFO and CFO-10BT composite and overlapping large polaron tunneling in CFO-30BT composite. The addition of BT in CFO initiates the structural modification and results in conductivity cross-over with improved conductivity. These results are useful for exploring devices based on CFO-BT composites. [ABSTRACT FROM AUTHOR]

Dielectric relaxation and conductivity mechanism in (100 − x)(Li0.12Na0.88)NbO3 − xBaTiO3 (0 ≤ x ≤ 40) ferroelectric ceramics were investigated using impedance spectroscopy over a broad temperature (− 100 °C to 500 °C) and frequency (0.1 Hz to 1 MHz) range. The dielectric relaxation and conductivity mechanism is considered to be associated with oxygen-defect-related complexes (VO··, ((TiNb′ − VO··)·) and ionization of oxygen vacancies (VO··), respectively. The hopping of VO·· in the lattice is considered to be equivalent to a dipolar reorientation contributing to the dielectric relaxation, whereas ionization of VO·· provides some localized electrons (e′) which further contribute to conduction mechanism at higher temperatures. Furthermore, a low-frequency dispersion in dielectric permittivity is observed, which is recognized as a quasi-DC process where the bipolar orientation or the charge carrier transition occurs naturally through discrete movements and that every orientation or transition contributes to ε′ makes a proportional contribution to ε″. The activation energies of DC conduction (0.64–1.24 eV) and the range of activation energies associated with the grain boundary conduction (0.72–1.22 eV) also indicate that the conduction mechanism is regulated by hopping of electrons through the grain boundary that could be associated to the oxygen vacancies. [ABSTRACT FROM AUTHOR]

Dangling bond defects (DBs) in silicon-passivated (1- or 3-nm thick Si cap) strained-(100)Si1−xGex (x = 0.25–0.55) layers at interfaces with 1.8-nm thick HfO2 gate dielectric are studied by means of Electron Spin Resonance (ESR) spectroscopy. The results suggest a dominant contribution of Si DBs (Pb0 centers), a considerable fraction of which is located at the interface between the Si substrate crystal and the pseudomorphic Si1−xGex film. The density of Si DBs in the Ge containing samples is significantly lower than at the reference (100)Si/ HfO2 interface and decreases below the ESR detection limit (≈ 0.8 × 1011cm−2) with increasing thickness and Ge concentration in the Si1−xGex layer. However, the beneficial effect of Ge becomes less pronounced when the thickness of the Si cap is reduced to 1 nm or in the case of direct deposition of HfO2 on top of uncapped Si1−xGex. From these observations we conclude that DBs are eliminated due to in-diffusion of Ge from the Si1−xGex channel into interfacial Si layers, bringing the concentration of Ge to the range in which generation of Si DBs becomes energetically unfavourable, in agreement with previous observations on condensation-grown Si1−xGex layers. [ABSTRACT FROM AUTHOR]

Ultralight and ultrathin dielectric materials with high dielectric permittivity and power densities are required to meet the ever-increasing demands of microelectronic and energy storage devices. In the present study, we demonstrate the feasibility of achieving giant dielectric performance of light weight, highly porous three-dimensional architectures of insulating graphene oxide (GO) foams by saturating the pores with liquid containing mobile ions. Dielectric behavior of GO foam is investigated over a range of frequencies (1 kHz–10 kHz) by employing electrochemical impedance spectroscopy. The relative permittivity of pristine GO foam is shown to improve by five orders upon saturating the pores with different concentrations of aqueous NaCl solutions. Dielectric constants of foams saturated with aqueous NaCl solutions are measured to be of the order of 106 at high frequencies (1 kHz–10 kHz) and are observed to enhance to 108 at lower frequencies down to 0.01 Hz. Various contributions to the measured capacitance are deciphered by modelling the impedance data to an equivalent circuit in order to evaluate the exact contribution from dipole orientation. The plausible reasons for the enhanced dielectric behavior are emphasized. Image 1 [ABSTRACT FROM AUTHOR]

We studied conformational transition of poly(acrylic acid)‐graft‐dodecyl (PAA‐g‐dodecyl), and PAA‐graft‐poly(ethylene oxide)‐graft‐dodecyl (PAA‐g‐PEO‐g‐dodecyl) molecules in DMF/H2O solvent by dielectric analysis method utilizing a double‐layer polarization theory. In addition to the hydrophobic interaction which has been demonstrated to be vital for their conformational transition with water content, it is confirmed that the electrostatic interaction is crucial. For PAA‐g‐dodecyl molecules, at a critical value of water content, a peak value of correlation length is reached originating from the delicate balance between electrostatic and hydrophobic interactions. For PAA‐g‐PEO‐g‐dodecyl molecules, chains conformation is mainly determined by electrostatic interaction over the entire range of water content due to the low content of dodecyl groups. Meanwhile, H‐bond associative interaction prevents the dissociation of free carboxyl groups over the range of lower water content, thus their stretched transition moves to higher water content. Our results provide the underlying insights needed to understand solvent effect on the conformational transition for polyelectrolytes with hydrophobic groups. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 1716–1724 [ABSTRACT FROM AUTHOR]

The results of Broadband Dielectric Spectroscopy and Differential Scanning Calorimetry of the 4-ethyl-4′-octylazoxybenzene (4EOB) liquid crystal are presented. Numerical analysis of the dielectric spectra results points to complex dynamics of the liquid crystal molecules in isotropic liquid, nematic and conformationally disordered crystalline phases. Two well-separated maxima on the imaginary part of electric permittivity were detected and described in liquid-like and crystalline phases. A third relaxation process, hidden in the conductivity region, describing conformational disorder of alkyl chains has been found in some plastic crystal phases. Temperature dependences of mean relaxation times characterising conformational disorder, flip-flop motions and rotation around long axis are of the Arrhenius type in liquid-like phases and conformationally disordered crystalline phases, and of the Vogel–Fulcher–Tammann type in the low-temperature crystalline phases for relaxation processes around short and long axis. [ABSTRACT FROM AUTHOR]

The dielectric behavior of the Ba(Ti0.8Ce0.2)O3 ceramics was studied by broadband dielectric spectroscopy in a temperature interval 140–500 K. The broad dielectric relaxation was analyzed by the Havriliak–Negami relationship and the distribution of relaxation times formalism. It was found that the Havriliak–Negami average relaxation time, longest and most probable relaxation times from the distribution of relaxation times follow the Vogel–Fulcher law. The freezing temperature of the longest relaxation time is substantially higher than the freezing temperature of the most probable relaxation time, indicating the distribution of freezing temperatures. The dielectric dispersion has all features inherent to relaxor ferroelectrics and the relaxation is assigned to the dynamics of polar nanoregions. [ABSTRACT FROM AUTHOR]

We have analyzed the dielectric spectra of thin (1200 Å) films of vanadium dioxide, a material with strong electron–electron correlations. We have tested both undoped and germanium-doped VO2 : Ge films. The latter exhibits an additional peak in the frequency spectrum of the tangent of the dielectric loss angle. We have analyzed the fine structure of the spectra and provided physical interpretation of two peaks on the frequency dependence of the tangent of dielectric loss angle and two semi-circles on the Cole–Cole diagram. Analysis of results has been performed based on equivalent electric circuit diagrams of samples, viz., one-loop RC circuit for the undoped VO2 film and two-loop circuit for VO2 : Ge film. The numerical values of parameters of model systems have been determined. [ABSTRACT FROM AUTHOR]

The polyazomethine/hybrid carbon nanofillers composites were fabricated. The nanofilles were comprised of thermally reduced graphene oxide (rGO) and multi‐walled carbon nanotubes (MWCNTs) varying in rGO:MWCNTs ratio; the total nanofillers loading was 1 wt%. The scanning electron miscroscopy images revealed uniform distribution of the hybrid nanofillers and formation of 3D networks between rGO and MWCNTs. Molecular dynamics of the polymer chains in these nanocomposites was investigated with broadband dielectric spectroscopy. The polymer fragility, the dielectric glass transition temperature, and the dielectric relaxation strength of the nanocomposites were evaluated and analyzed depending on the rGO:MWCNTs ratio. The thermal glass transition temperature and the thermal relaxation strength evaluated from the differential scanning calorimetry data were shown to behave in other manner. This behavior was interpreted in terms of a fraction of polymer being immobilized in an interfacial layer around the nanoparticles. [ABSTRACT FROM AUTHOR]

Water plays a key role in the functioning of natural and synthetic molecular systems. Despite several hydration studies, different techniques are employed individually for monitoring different physical features such as kinetics, dynamics, and absorption. This study describes a compact hydration cell that enables simultaneous dielectric relaxation spectroscopy (DRS) and mass loss/uptake measurements in thin organic layers under controlled humidity conditions and in a wide temperature range. This approach enabled us to correlate the physical quantities obtained during the same experiment by complementary techniques. To demonstrate the performance of this device, a 200 nm thick poly(methyl methacrylate) (PMMA) layer was measured at various relative humidity levels (0%–75%), temperatures (25–75 °C), and frequencies (DRS: 0.1 Hz–1 MHz) to study how hydration and dehydration processes affect its molecular dynamics. The results show the capability of this setup to study the changes in the PMMA film regarding the kinetics and molecular dynamics upon variation of the water content. [ABSTRACT FROM AUTHOR]

This article presents an integrated time-domain (TD) microwave broadband dielectric spectroscopy (MBDS) system in the 3–10-GHz frequency span divided into nine subbands. The generated multitone input pulse with 1-GHz bandwidth is upconverted to RF frequencies in the transmitter using a broadband single-sideband (SSB) mixer to suppress the lower sideband of the excited signal and prevent the signal distortion at the configured dc-free direct conversion receiver with the center frequency of 500 MHz at the baseband. The upconverted pulse is passed through a contactless sensor in TD where the material under test (MUT) is placed in the middle of the two ultra-wideband (UWB) Vivaldi antennas coupled in their radiative near field. To identify both the real ($\epsilon _{r}'$) and imaginary ($\epsilon _{r}''$) parts of the MUT’s permittivity, the impact of the entire system on MUT characterization is alleviated by designing the system subblocks and the sensor with flat gain and constant group delay over the entire frequency range. The proposed MBDS system is fabricated in 65-nm CMOS and occupies an active area of 1.24 mm2 while consuming 64~69 mW from a 1-V supply. As a proof of concept, the complex dielectric permittivity of different pure organic chemical liquids has been detected within the desired frequency range with a customized quartz-glass cuvette with the MUT volume of ~ 5 mL by calibrating the sensor using the variations in the phase and the magnitude after FFT with respect to the reference material (air). The system results in an rms error of less than 0.2% and 0.4% for $\epsilon _{r}'$ and $\epsilon _{r}''$ , respectively, compared with theory. To the best of our knowledge, this is the first CMOS TD MBDS system with a homodyne RF transceiver architecture including an on-chip UWB excitation pulse generation and the contactless sensor. [ABSTRACT FROM AUTHOR]

Novel chiral three-ring compounds with the –CH2O group close to chirality centre were synthesised and their properties were studied. The phase transitions and phase sequences were observed using a polarising optical microscope. The phase transition temperatures and enthalpies were checked by differential scanning calorimetry. A broad-frequency dielectric spectroscopy was also used to confirm the phase transition temperatures as well as the phase sequence. The helical pitch was measured by the spectrophotometry method. It was found that the compounds differing only in one lateral substituted fluorine atom create two different chiral tilted smectic phases, one a ferroelectric phase (SmC*) and the other an antiferroelectric phase (SmCA*). [ABSTRACT FROM AUTHOR]

The mixed ferrite sample Ni0.5−xMgxCu0.2Cd0.3Fe2O4 (0.0 ≤ x ≤ 0.5, in the steps 0.1) has been synthesized employing sol–gel auto-combustion process. From XRD diffractograms, it has been observed the simple cubic spinel structure of the ferrite samples. With the substitution of Mg ion, both the experimental and theoretical lattice constant increased. For x = 0.0, the value of experimental lattice constant has been found 8.459 Å, which increases to a value 8.490 Å for x = 0.5. The surface morphology has been studied by FESEM images. Besides, the chemical composition and the elemental distribution of the sample have been revealed by EDS study. From the vibration band, the formation of spinel ferrite has been confirmed from the FT-IR spectra. It is seen that the samples exhibit ferrimagnetic behavior at room temperature, which has been shown by the magnetic measurement done by VSM. Dielectric constant, dielectric loss tangent, ac conductivity, and impedance Spectroscopy have been analyzed within the range 20 Hz–15 MHz. In the lower frequency region, a typical dielectric dispersion based on Maxwell–Wagner type interfacial polarization has been observed. Dielectric loss tangent exhibits an analogous sort of behavior as that of dielectric constant. The grain and grain boundary effect on electric properties have been studied from the complex impedance analysis. It has been seen that both the grain resistance and grain boundary resistance increase with the substitution of Mg2+ content. A rise in ac conductivity has been observed with the increase in frequency. [ABSTRACT FROM AUTHOR]

The dielectric behavior of the Ba(Ti0.8Ce0.2)O3 ceramics was studied by broadband dielectric spectroscopy in a temperature interval 140–500 K. The broad dielectric relaxation was analyzed by the Havriliak–Negami relationship and the distribution of relaxation times formalism. It was found that the Havriliak–Negami average relaxation time, longest and most probable relaxation times from the distribution of relaxation times follow the Vogel–Fulcher law. The freezing temperature of the longest relaxation time is substantially higher than the freezing temperature of the most probable relaxation time, indicating the distribution of freezing temperatures. The dielectric dispersion has all features inherent to relaxor ferroelectrics and the relaxation is assigned to the dynamics of polar nanoregions. [ABSTRACT FROM AUTHOR]

In this, the third part of our series on the dielectric spectrum symmetrical broadening of water, we consider the nucleotide aqueous solutions. Where in Parts I [E. Levy et al., J. Chem. Phys. 136, 114502 (2012)] and II [E. Levy et al., J. Chem. Phys. 136, 114503 (2012)], the dipole-dipole or ion-dipole interaction had a dominant feature, now the interplay between these two types of dipole-matrix interactions will be considered. We present the results of high frequency dielectric measurements of different concentrations of adenosine monophosphate/adenosine-5′-triphosphate aqueous solutions. We observed the Cole-Cole broadening of the main relaxation peak of the solvent in the solutions. Moreover, depending on the nucleotide concentration, we observed both types of dipole-matrix interaction. The 3D trajectory approach (described in detail in Part I) is applied in order to highlight the differences between the two types of interaction. [ABSTRACT FROM AUTHOR]

2H-nuclear magnetic resonance (NMR) and neutron scattering (NS) on isotopically labelled samples have been combined to investigate the structure and dynamics of polyvinylpyrrolidone (PVP) aqueous solutions (4 water molecules/monomeric unit). Neutron diffraction evidences the nanosegregation of polymer main-chains and water molecules leading to the presence of water clusters. NMR reveals the same characteristic times and spectral shape as those of the slower process observed by broadband dielectric spectroscopy in this system [S. Cerveny et al., J. Chem. Phys. 128, 044901 (2008)]. The temperature dependence of such relaxation time crosses over from a cooperative-like behavior at high temperatures to an Arrhenius behavior at lower temperatures. Below the crossover, NMR features the spectral shape as due to a symmetric distribution of relaxation times and the underlying motions as isotropic. NS results on the structural relaxation of both components-isolated via H/D labeling-show (i) anomalously stretched and non-Gaussian functional forms of the intermediate scattering functions and (ii) a strong dynamic asymmetry between the components that increases with decreasing temperature. Strong heterogeneities associated to the nanosegregated structure and the dynamic asymmetry are invoked to explain the observed anomalies. On the other hand, at short times the atomic displacements are strongly coupled for PVP and water, presumably due to H-bond formation and densification of the sample upon hydration. [ABSTRACT FROM AUTHOR]

Propylene carbonate and a mixture of two secondary amides, N-methylformamide and N-ethylacetamide, are investigated by means of broadband dielectric and mechanical shear spectroscopy. The similarities between the rheological and the dielectric responses of these liquids and of the previously investigated tripropylene glycol are discussed within a simple approach that employs an electrical circuit for describing the frequency-dependent behavior of viscous materials. The circuit is equivalent to the Gemant-DiMarzio-Bishop model, but allows for a negative capacitive element. The circuit can be used to calculate the dielectric from the mechanical response and vice versa. Using a single parameter for a given system, good agreement between model calculations and experimental data is achieved for the entire relaxation spectra, including secondary relaxations and the Debye-like dielectric peak in the secondary amides. In addition, the predictions of the shoving model are confirmed for the investigated liquids. [ABSTRACT FROM AUTHOR]

We report here a broadband dielectric spectroscopy study on an ionic liquid microemulsion (ILM) composed of water, Triton X-100 (TX-100), and 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6). It is found that the phase behavior of this ILM can be easily identified by its dielectric response. The dielectric behavior of the ILM in the GHz range is consistent with that of TX-100/water mixtures with comparable water-to-TX-100 weight ratio. It consists of the relaxations due to ethylene oxide (EO) unit relaxation, hydration water dynamics, and/or free water dynamics. The water content dependence of the EO unit relaxation suggests that this relaxation involves dynamics of hydration water molecules. In the IL-in-water microemulsion phase, it is found that bmimPF6 molecules are preferentially dissolved in water when their concentration in water is lower than the solubility. An additional dielectric relaxation that is absent in the TX-100/water mixtures is observed in the frequency range of 107-108 Hz for this ILM. This low-frequency relaxation is found closely related to the bmimPF6 molecule and could be attributed to the hopping of its cations/anions between the anionic/cationic sites. [ABSTRACT FROM AUTHOR]

Dynamics of water, especially in the temperature range of the 'no man's land', remain a mystery. We present detailed study of dynamics in aqueous LiCl solution that is often considered as a model for bulk water. We employ broadband dielectric and light scattering spectroscopy in a broad frequency and temperature range. Our analysis reveals no sign of the fragile-to-strong crossover (FSC) neither in structural relaxation nor in translational motions. Our experimental results combined with a large selection of literature data lead to the clear conclusion-there is no FSC in dynamics of aqueous solutions at T ∼ 200-230 K. Instead, our analysis reveals appearance of the so-called excess wing at the high frequency tail of the structural relaxation peak. We discuss the localized nature of the relaxation process that contributes to the excess wing. [ABSTRACT FROM AUTHOR]

We present the first broadband dielectric spectroscopy (BDS) and differential scanning calorimetry study of supercooled xylitol-water mixtures in the whole concentration range and in wide frequency (10-2-106 Hz) and temperature (120-365 K) ranges. The calorimetric glass transition, Tg, decreases from 247 K for pure xylitol to about 181 K at a water concentration of approximately 37 wt. %. At water concentrations in the range 29-35 wt. % a plentiful calorimetric behaviour is observed. In addition to the glass transition, almost simultaneous crystallization and melting events occurring around 230-240 K. At higher water concentrations ice is formed during cooling and the glass transition temperature increases to a steady value of about 200 K for all higher water concentrations. This Tg corresponds to an unfrozen xylitol-water solution containing 20 wt. % water. In addition to the true glass transition we also observed a glass transition-like feature at 220 K for all the ice containing samples. However, this feature is more likely due to ice dissolution [A. Inaba and O. Andersson, Thermochim. Acta, 461, 44 (2007)]. In the case of the BDS measurements the presence of water clearly has an effect on both the cooperative α-relaxation and the secondary β-relaxation. The α-relaxation shows a non-Arrhenius temperature dependence and becomes faster with increasing concentration of water. The fragility of the solutions, determined by the temperature dependence of the α-relaxation close to the dynamic glass transition, decreases with increasing water content up to about 26 wt. % water, where ice starts to form. This decrease in fragility with increasing water content is most likely caused by the increasing density of hydrogen bonds, forming a network-like structure in the deeply supercooled regime. The intensity of the secondary β-relaxation of xylitol decreases noticeably already at a water content of 2 wt. %, and at a water content above 5 wt. % it has been replaced by a considerably stronger water (w) relaxation at about the same frequency. However, the similarities in time scale and activation energy between the w-relaxation and the β-relaxation of xylitol at water contents below 13 wt. % suggest that the w-relaxation is governed, in some way, by the β-relaxation of xylitol, since clusters of water molecules are rare at these water concentrations. At higher water concentrations the intensity and relaxation rate of the w-relaxation increase rapidly with increasing water content (up to the concentration where ice starts to form), most likely due to a rapid increase of small water clusters where an increasing number of water molecules interacting with other water molecules. [ABSTRACT FROM AUTHOR]

Recently, we have studied the mutarotation kinetics in D-fructose by means of dielectric spectroscopy. In the present work we investigate density behavior of D-fructose during mutarotation process. By performing volume measurements at temperature T = 303 K and pressure p = 10 MPa we are able to monitor kinetics of this process. As a result we found nearly the same value of the rate constant as previously determined from dielectric measurements. However, these two experimental methods monitor different molecular aspects of mutarotation phenomenon in D-fructose. Dielectric spectroscopy is sensitive to the decay of former ring as well as to the forming of another, while specific volume measurements are sensitive to the forming of new tautomers only. Calculations of activation energy of mutarotation in D-fructose led us to the conclusion, that mechanism of this reaction in amorphous phase could be based on internal proton transfer. Moreover it was found that the main mutarotation path in quenched D-fructose melt is transformation of α,β-furanose to β-pyranose. [ABSTRACT FROM AUTHOR]

We present the experimental realization and characterization of a broadband acoustic metamaterial with strongly anisotropic effective mass density. The metamaterial is composed of arrays of solid inclusions in an air background, and the anisotropy is controlled by the rotational asymmetry of these inclusions. Transmission and reflection measurements inside a one-dimensional waveguide are used to extract the relevant components of the effective density tensor together with the effective bulk modulus of the metamaterial. Its broadband anisotropy is demonstrated by measurements that span 500-3000 Hz. Excellent agreement between these measurements and numerical simulations confirms the accuracy of the design approach. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy as a function of temperature and pressure was used to study the secondary relaxation in poly [(phenyl glycidyl ether)-co-formaldehyde] at hydrostatic pressure up to 600 MPa and at different temperatures between 315 and 243 K. From the analysis of the isothermal measurements, we observe that the activation volume of the secondary relaxation has nonmonotonic temperature dependence with a maximum at the temperature of the glass transition at ambient pressure. An interpretation in terms of mean hole volume dispersion is proposed based on literature data. Moreover, from isobaric data, we studied the effect of pressure on activation entropy and enthalpy of the secondary relaxation evidencing its local nature but also the presence of a certain complexity of the motion, which supports the idea that this process reflects the motion of a large part of the molecule. [ABSTRACT FROM AUTHOR]

Broadband dielectric spectroscopy was employed to investigate the relaxation dynamics of supercooled and glassy nonivamide-the synthetic form of capsaicin being the most spicy-hot substance known to man. The material is of great importance in the pharmaceutical industry because it has wide usage in the medical field for relief of pain, and more recently it has been shown to be effective in fighting cancers. Dielectric measurements carried out at various isobaric and isothermal conditions (pressure up to 400 MPa) revealed very narrow α-loss peak and unresolved secondary relaxations appearing in the form of an excess wing on the high frequency flank. Moreover, our studies have shown the shape of dielectric loss spectrum at any fixed loss peak frequency is invariant to different combinations of temperature and pressure, i.e., validity of the time-temperature-pressure superpositioning. We also found the fragility index is nearly constant on varying pressure. This property is likely due to the unusual structure of nonivamide, which has a part characteristic of van der Waals glass-former and another part characteristic of hydrogen-bonded glass-former. [ABSTRACT FROM AUTHOR]

The behavior of water dynamics confined in hydrated calcium silicate hydrate (C-S-H) gel has been investigated using broadband dielectric spectroscopy (BDS; 10-2-106 Hz) in the low-temperature range (110-250 K). Different water contents in C-S-H gel were explored (from 6 to 15 wt%) where water remains amorphous for all the studied temperatures. Three relaxation processes were found by BDS (labeled 1 to 3 from the fastest to the slowest), two of them reported here for the first time. We show that a strong change in the dielectric relaxation of C-S-H gel occurs with increasing hydration, especially at a hydration level in which a monolayer of water around the basic units of cement materials is predicted by different structural models. Below this hydration level both processes 2 and 3 have an Arrhenius temperature dependence. However, at higher hydration level, a non-Arrhenius behavior temperature dependence for process 3 over the whole accessible temperature range and, a crossover from low-temperature Arrhenius to high-temperature non-Arrhenius behavior for process 2 are observed. Characteristics of these processes will be discussed in this work. [ABSTRACT FROM AUTHOR]

There are a number of chemical compounds that readily convert to other isomers when their crystalline structure is lost (e.g., during melting or dissolution). This phenomenon, commonly known as tautomerism, is a subject of intense research. It is an important problem especially in pharmaceutical industry because various isomers of a drug may have different pharmacological activity. Therefore, it is important to find appropriate experimental technique which enables the determination of the isomerization ability of compounds. In this communication, we demonstrate that broadband dielectric spectroscopy (BDS) method has the potential of detection and monitoring of tautomerism of drugs. To investigate the tautomerism phenomenon we have chosen one of the hypoglycemic agents that belong to the class II of sulfonylurea drugs. Based on density functional theory (DFT) calculations we have analyzed two possible tautomerization pathways of glibenclamide. By using BDS as a tool, we show it can detect the conversion between the isomeric forms through time dependence in the dielectric properties. The activation energy (Ea) of this process is in good agreement with that obtained from DFT analysis. Finally, we discuss the possible effects of tautomerism on basic pharmaceutical parameters such as biological activity or bioavailability in the case of the glibenclamide drug. [ABSTRACT FROM AUTHOR]

The nematic liquid crystalline mixture E7 was confined with similar filling degrees to molecular sieves with constant composition but different pore diameters (from 2.8 to 6.8 nm). Fourier transform infrared analysis proved that the E7 molecules interact via the cyanogroup with the pore walls of the molecular sieves. The molecular dynamics of the system was investigated by broadband dielectric spectroscopy (10-2–109 Hz) covering a wide temperature range of ∼200 K from temperatures well above the isotropic-nematic transition down to the glass transition of bulk E7. A variety of relaxation processes is observed including two modes that are located close to the bulk behavior in its temperature dependence. For all confined samples, two relaxation processes, at frequencies lower than the processes observed for the bulk, were detected. At lower temperatures, their relaxation rates have different temperature dependencies whereas at higher temperatures, they seem to collapse into one chart. The temperature dependence of the slowest process (S-process) obeys the Vogel–Fulcher–Tammann law indicating a glassy dynamics of the E7 molecules anchored to the pore surface. The pore size dependence of both the Vogel temperature and fragility revealed a steplike transition around 4 nm pore size, which indicates a transition from a strong to a fragile behavior. The process with a relaxation rate in between the bulklike and the S-process (I-process) shows no dependence on the pore size. The agreement of the I-process with the behavior of a 5CB surface layer adsorbed on nonporous silica leads to the assignment of E7 molecules anchored at the outer surface of the microcrystals of the molecular sieves. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy has been recently used to monitor mutarotation in undercooled D-fructose. This method can be viewed as a universal method to study mutarotation phenomenon in the whole family of monosaccharides. In this paper, we studied kinetics of mutaration of anhydrous D-ribose at ambient pressure as well as pressure effect on the rate constant of this process. Ribose mutarotation behavior is compared to the one obtained for D-fructose. In addition, we attempted to determine the “direction” of mutarotation in undercooled monosaccharides after quenching the melted sample. To this end, analysis of dipole moments of different tautomers of D-fructose and D-ribose have been performed. Conformational analysis of studied carbohydrates was done with use of density functional theory. Geometry optimizations as well as calculations of dipole moments were done on the 6-311++G(d,p)/B3LYP level. Finally, it turned out that data obtained from the mutarotation experiment might be helpful in understanding the origin of γ-process occurring in the whole family of carbohydrates. [ABSTRACT FROM AUTHOR]

The α-relaxation dynamics of 1-cyano-adamantane (CNA) and its mixtures with 1-chloro-adamantane (ClA) has been studied by means of broadband dielectric spectroscopy. The existence of orientationally disordered (OD) face centered cubic mixed crystals (ClA1-XCNAX) for 0.5≤X≤1 has been put in evidence by thermodynamics and structural analyses. In addition to the OD phase of CNA, mixed crystals with compositions higher than the equimolar one exhibit a freezing of the orientational degrees of freedom into a glassy state, which involves also a strong increase of the antiferroelectric order at temperatures higher than the dielectric glass transition temperature. This experimental evidence is revealed by a stairlike effect in the variation of the Kirkwood factor with the temperature as a consequence of a twin effect in the dielectric strength without any anomaly in the temperature-density curves. The characteristic relaxation times are analyzed as a function of temperature and mole fraction. By setting a common temporal origin (“isochronal origin”) at τ(Tg)=100 s for each mole fraction, it emerges that the substitution of ClA molecules by those of CNA (diminution of X) gives rise to a slow down in the dynamics, despite that the molecular volume of ClA molecules are smaller than those of CNA. This fact goes along and is accompanied by a diminution of the lattice packing with the decrease of composition. It is also shown that the heterogeneities produced by the concentration fluctuations due to the chemical disorder are the main contribution to the non-exponential character of the α-relaxation peaks. [ABSTRACT FROM AUTHOR]