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For both dielectric spectroscopy and light scattering spectra, the relaxation modes in the microwave region have been characterized by the Debye relaxation model, which is determined by the peak frequency, or by an empirically extended model (e.g., Cole–Davidson and Kohlrausch–Williams–Watts), which has the appropriate line shape. For light scattering from glass-forming liquids, the general line shape is a broader high frequency side in comparison with Debye relaxation. However, for triethylene glycol (TEG) in liquid form at room temperature, the lowest frequency Raman scattering (LFR) mode shows a peak at about 3.0 GHz, which is narrower than that expected for the Debye relaxation. With increasing temperature, this peak exhibits a significant blueshift and begins to resemble the Debye relaxation shape, indicating that the LFR mode of TEG is also a relaxation mode. The narrowing of the LFR mode of TEG is suggested to be caused from the increased non-whiteness of the fluctuation correlations due to increased hydrogen bonding. This is a consequence of breaking the Debye relaxation model's approximation of the overdamping and narrowing limits in the GHz region, which was found in this study by analyzing the relaxation modes of Raman scattering using the multiple random telegraph model for evaluating thermal bath correlation. The analysis results show that the LFR relaxation times of TEG and the main dielectric relaxation overlap only by 333 K. However, the second LFR mode and β-relaxation at higher frequencies coincide over a wide temperature range, suggesting that they are corresponding modes. [ABSTRACT FROM AUTHOR]

In this work, we present an experimental study of the primary and secondary relaxations of the semi-crystalline polymer polyethylene naphthalate by modulated differential scanning calorimetry, Thermally Stimulated Depolarization Currents (TSDCs), and Broadband Dielectric Spectroscopy (BDS) and how they are affected by physical aging. Three dipolar relaxation modes can be observed: from slowest to fastest: the primary α relaxation, which vitrifies at the glass transition temperature, Tgα, and two secondary relaxations, named β* and β. Modulated differential scanning calorimetry results show how the secondary β* relaxation also vitrifies, giving rise to an additional glass transition at Tgβ* < Tgα. In fact, the α and β* relaxations can be considered as part of a very broad and distributed relaxation. Its main part is the primary α relaxation with a shoulder at the high-frequency region corresponding to a complex secondary β* relaxation. BDS results about β* can be modeled by a main contribution (β3*) and two additional ones (β1* and β2*) with a weaker dielectric strength. TSDC results show that each single mode of the relaxation has its own glass transition temperature and they are compatible with the structure inferred by BDS. This scenario gives rise to an extended glass transition dually centered in the Tgβ* ∼ 305 K and Tgα ∼ 387 K temperatures. [ABSTRACT FROM AUTHOR]

We investigate water dynamics in mesoporous silica across partial crystallization by combining broadband dielectric spectroscopy (BDS), nuclear magnetic resonance (NMR), and molecular dynamics simulations (MDS). Exploiting the fact that not only BDS but also NMR field-cycling relaxometry and stimulated-echo experiments provide access to dynamical susceptibilities in broad frequency and temperature ranges, we study both the fully liquid state above the melting point Tm and the dynamics of coexisting water and ice phases below this temperature. It is found that partial crystallization leads to a change in the temperature dependence of rotational correlation times τ, which occurs in addition to previously reported dynamical crossovers of confined water and depends on the pore diameter. Furthermore, we observe that dynamical susceptibilities of water are strongly asymmetric in the fully liquid state, whereas they are much broader and nearly symmetric in the partially frozen state. Finally, water in the nonfreezable interfacial layer below Tm does not exhibit a much debated dynamical crossover at ∼220 K. We argue that its dynamics is governed by a static energy landscape, which results from the interaction with the bordering silica and ice surfaces and features a Gaussian-like barrier distribution. Consistently, our MDS analysis of the motional mechanism reveals a hopping motion of water in thin interfacial layers. The rotational correlation times of the confined ice phases follow Arrhenius laws. While the values of τ depend on the pore diameter, freezable water in various types of confinements and mixtures shows similar activation energies of Ea ≈ 0.43 eV. [ABSTRACT FROM AUTHOR]

The glass formation and the dipolar reorientational motions in deep eutectic solvents (DESs) are frequently overlooked, despite their crucial role in defining the room-temperature physiochemical properties. To understand the effects of these dynamics on the ionic conductivity and their relation to the mechanical properties of the DES, we conducted broadband dielectric and rheological spectroscopy over a wide temperature range on three well-established carboxylic acid-based natural DESs. These are the eutectic mixtures of choline chloride with oxalic acid (oxaline), malonic acid (maline), and phenylacetic acid (phenylaceline). In all three DESs, we observe signs of a glass transition in the temperature dependence of their dipolar reorientational and structural dynamics, as well as varying degrees of motional decoupling between the different observed dynamics. Maline and oxaline display a breaking of the Walden rule near the glass-transition temperature, while the relation between the dc conductivity and dipolar relaxation time in both maline and phenylaceline is best described by a power law. The glass-forming properties of the investigated systems not only govern the orientational dipolar motions and rheological properties, which are of interest from a fundamental point of view, but they also affect the dc conductivity, even at room temperature, which is of high technical relevance. [ABSTRACT FROM AUTHOR]

Chirped-Pulse Fourier-Transform millimeter wave (CP-FTmmW) spectroscopy is a powerful method that enables detection of quantum state specific reactants and products in mixtures. We have successfully coupled this technique with a pulsed uniform Laval flow system to study photodissociation and reactions at low temperature, which we refer to as CPUF ("Chirped-Pulse/Uniform flow"). Detection by CPUF requires monitoring the free induction decay (FID) of the rotational coherence. However, the high collision frequency in high-density uniform supersonic flows can interfere with the FID and attenuate the signal. One way to overcome this is to sample the flow, but this can cause interference from shocks in the sampling region. This led us to develop an extended Laval nozzle that creates a uniform flow within the nozzle itself, after which the gas undergoes a shock-free secondary expansion to cold, low pressure conditions ideal for CP-FTmmW detection. Impact pressure measurements, commonly used to characterize Laval flows, cannot be used to monitor the flow within the nozzle. Therefore, we implemented a REMPI (resonance-enhanced multiphoton ionization) detection scheme that allows the interrogation of the conditions of the flow directly inside the extended nozzle, confirming the fluid dynamics simulations of the flow environment. We describe the development of the new 20 K extended flow, along with its characterization using REMPI and computational fluid dynamics. Finally, we demonstrate its application to the first low temperature measurement of the reaction kinetics of HCO with O2 and obtain a rate coefficient at 20 K of 6.66 ± 0.47 × 10−11 cm3 molec−1 s−1. [ABSTRACT FROM AUTHOR]

A great deal of effort has been recently devoted to the study of dielectric relaxation processes in ferroelectric nematic liquid crystals, yet their interpretation remains unclear. In this work, we present the results of broadband dielectric spectroscopy experiments of a prototypical ferroelectric nematogen in the frequency range 10 Hz–110 MHz at different electrode separations and under the application of DC bias fields. The results evidence a complex behavior in all phases due to the magnitude of polar correlations in these systems. The observed modes have been assigned to different relaxation mechanisms based on existing theoretical frameworks. [ABSTRACT FROM AUTHOR]

Highly acidic protic ionic liquids (PILs) are promising materials for potential electrochemical applications due to their high proton conductivity and excellent thermal stability. Still, little is known about the correlation between charge transport and structural dynamics as well as the proton transport mechanism despite the large body of literature on this topic. Here, we have examined the charge transport and structural dynamics by employing broadband dielectric spectroscopy in two highly acidic PILs in their supercooled liquid and glassy states, which included the same anion [TfO]− and different cations, [Tau]+ vs [Ahs]+. Unlike many other ionic liquids, the conductivity relaxation time τe of two studied PILs is substantially faster than the structural relaxation time τα. The decoupling behavior between charge transport and structural dynamics of two materials, which is manifested by a decoupling index Rτ, varies between 0.3 and 2.3 over the temperature range above Tg. Moreover, "Walden" plots of the molar conductivity vs the viscosity qualify both compounds as "Super ILs." All findings support the physical picture of large, polar, and orientationally correlated ion clusters, where the slow α-relaxation can be identified as structural relaxation associated with cooperative reorientations of the cluster macrodipole. In contrast, the shortest timescale for diffusive charge transport, τe, is 1–2 decades shorter than τα, implying that proton hopping is triggered by "single particle" (ions or ion pair) rotations and jumps on a sub-length scale of the cluster size, a dynamics being present even in the glassy state as indicated by a strong β-relaxation. These results demonstrate the practicality of employing highly acidic PILs in electrochemical fields. [ABSTRACT FROM AUTHOR]

The electrical conductivity of Na2O substituted zinc borate glasses has been studied in the frequency range of 10 mHz to 1 MHz and in the temperature range from 313 to 573 K. The conduction mechanism has been ascertained using the values of the frequency exponent (s) extracted from the fitting of experimental data of the real part of electric conductivity in light of the Almond–West equation. Depending on the glass composition, the ac conduction in the glasses happened via correlated barrier hopping and non-overlapping small polaron tunneling conduction models. The electric modulus studies support the assertion of composition dependent conduction mechanisms. Furthermore, electronic conduction and ionic conduction have been studied from impedance investigations. Equivalent circuit models were used to fit the Nyquist and Bode plots of each sample at the temperatures under consideration. It has been found that the activation energy values calculated from conductivity, electric modulus, and impedance measurements are more or less the same. [ABSTRACT FROM AUTHOR]

Investigating the effect of nanoparticle dispersion morphology on the properties of the interfacial layer of polymer nanocomposites (PNCs) provides an important theoretical basis for designing and regulating the macroscopic properties of PNCs. Differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS) were used to investigate the characteristic parameters of the interfacial area, segmental dynamics and enthalpy relaxation of PNCs with nanoparticle agglomerates and uniformly dispersed morphology. The volume fraction of the interfacial area (φint) and the extent of influence of the interfacial area on the enthalpy hysteresis reduction (χint) in PNCs with agglomerated nanoparticles are lower than that of PNCs with uniformly dispersed nanoparticles for the same nanoparticle loading. Because of the irregular structure of the nanoparticle aggregate morphology, the linear relationships between φint and nanoparticle content is not valid in PNCs with agglomerated nanoparticles. Interestingly, φint obtained by BDS and χint have a clearly linear relationship in all PNCs, independent of nanoparticle dispersion morphology. Such universal quantitative relationship provides a new research methodology for investigating the characteristic parameters of the interfacial area in PNCs, and facilitates the construction of a correspondence between the microscopic parameters of interfacial area and the macroscopic properties of PNCs. Highlights: The linear relationships between φint and nanoparticle content are not valid in PNCs with agglomerated nanoparticles.The linear relationships between φint and the decreased degree of ΔHR can be noted in all PNCs, independent of nanoparticle dispersion morphology.The universal correspondence provides a new research methodology for investigating the characteristic parameters of the interface layer in PNCs. [ABSTRACT FROM AUTHOR]

The present study aims to improve the mechanical strength of hydrogels via a simplified method, involving the creation of a nanocomposite hydrogel using polyvinyl alcohol (PVA) incorporated with un‐modified multiwalled carbon nanotubes (um‐MWCNTs). Departing from conventional freezing–thawing cycles, our research employs a facile approach, in which high‐shear mixing along with solvent exchange with deionized water was utilized. Morphological analysis unveiled a compact and dense microstructure within the nanocomposite hydrogel in correlation with MWCNT concentration. Attenuated total reflection‐Fourier transform infrared spectroscopy (ATR‐FTIR) elucidated the chemical structure of PVA/um‐MWCNTs hydrogel nanocomposite. Rheological studies on the viscoelastic properties indicated the formation of more "solid‐like" structure in the developed hydrogel nanocomposite. Broadband dielectric spectroscopy revealed alterations in dielectric properties of the fabricated PVA/um‐MWCNTs hydrogel nanocomposite corresponding to MWCNTs content in the PVA matrix. This comprehensive investigation highlights the impact of minimal MWCNTs concentration on the rheology, mechanical, and dielectric properties of developed PVA/um‐MWCNTs hydrogel nanocomposite. [ABSTRACT FROM AUTHOR]

We have studied the molecular properties of water in physically and chemically cross-linked gelatin hydrogels by FTIR-spectroscopy, NMR relaxation, and diffusivity and broadband dielectric spectroscopy, which are sensitive to dynamical properties of water, being a structural marker of polymer network. All experiments demonstrated definite reinforcement of the hydrogel net structure and an increase in the amount of hydrate water. FTIR experiments have shown that the chemical cross-linking of gelatin molecules initiates an increase in the collagen-like triple helices "strength", as a result of infused restriction on protein molecular mobility. The "strengthening" of protein chains hinders the mobility of protein fragments, introducing complex modifications into the structural properties of water which are remained practically unchanged up to up to 30–40 °C. [ABSTRACT FROM AUTHOR]

Potential applications of known compounds from the V2O‐Y2O3 system, i. e. YVO4, Y8V2O17 and Y10V2O20, were the inspiration to undertake research, the main goal of which was to determine whether unknown phases of the solid solution type are formed in this system. Solid solutions are still sought‐after phases because their properties depend on their chemical composition. In this work it was experimentally demonstrated that a new substitute solid solution with the formula Y2‐xVxO3+x (0.00<×<0.60) is formed from mixtures of V2O5 with Y2O3 as a result of mechanochemical synthesis. Its properties were examined by using, i.a. XRD (X‐ray diffraction) and UV‐Vis‐DRS (ultraviolet‐visible light spectroscopy with diffusion reflectance) methods. It was found among other things, that it crystallizes in a regular system, exhibits a Y2O3 structure and is thermally stable up to at least 800 °C (for x=0.40). Moreover, the estimated value of the band gap width indicated that the solid solution Y2‐xVxO3+x belongs to the class of semiconductors. The study of dielectric properties of new phase was performed by means of broadband dielectric spectroscopy. The obtained measurement data showed the presence of relaxation type dielectric mechanisms. The thermally activation energies of the relaxation processes related to the electric conductivity were calculated. [ABSTRACT FROM AUTHOR]

The possibility of reusing ceramic roller waste to produce cordierite and mullite refractories was investigated. Five batches were designed using wastes representing ceramic roller waste, magnesite, and silica sand, shaped and fired at 1300 °C/2 h, and one batch was selected at 1200 °C. The chemical composition and precipitated phases of the used raw materials and the fired batches were analyzed using XRF and XRD techniques, respectively. Densification parameters, morphology, microstructure and electrical properties were also studied to evaluate the effect of the formed phases on the properties of fired materials. Bulk density increases with an increase in mullite and a decrease in cordierite, and it also increases with increasing temperature, whereas porosity and water absorption show a opposite behavior to density (it decreases with an increase in mullite and temperature). The main phases developed after firing at 1300 °C/2 h were cordierite, mullite, corundum, baddeleyite, and spinel. Bending strength increases with increasing mullite percentage and density, and decreasing grain size and porosity. The microstructure develops and becomes finer with increasing mullite percentage and density. The grain size of the crystals was very fine at 1200 °C/2 h and increased at 1300 °C/2 h. Broadband dielectric spectroscopy was employed to study the electrical and dielectric behavior of the investigated samples. The increase in mullite concentration shows a remarkable increase in ε', especially at lower frequencies, as it is three times higher than that of M10. At f > 103 Hz ε', frequency independence is accompanied by an increase in mullite concentrations due to the lag of dynamics fluctuations after the alteration of the electric field. The generation of new free ions leads to the enhancement of conductivity as the mullite concentration increases. [ABSTRACT FROM AUTHOR]

The ability of vitrification when crossing the glass transition temperature (Tg) of confined and bulk water is crucial for myriad phenomena in diverse fields, ranging from the cryopreservation of organs and food to the development of cryoenzymatic reactions, frost damage to buildings, and atmospheric water. However, determining water's Tg remains a major challenge. Here, we elucidate the glass transition of water by analyzing the calorimetric behavior of nano-confined water across various pore topologies (diameters: 0.3 to 2.5 nm). Our approach involves subjecting confined water to annealing protocols to identify the temperature and time evolution of nonequilibrium glass kinetics. Furthermore, we complement this calorimetric approach with the dynamics of confined water, as seen by broadband dielectric spectroscopy and linear calorimetric measurements, including the fast scanning technique. This study demonstrated that confined water undergoes a glass transition in the temperature range of 170 to 200 K, depending on the confinement size and the interaction with the confinement walls. Moreover, we also show that the thermal event observed at ~136 K must be interpreted as an annealing prepeak, also referred to as the "shadow glass transition." Calorimetric measurements also allow the detection of a specific heat step above 200 K, which is insensitive to annealing and, thereby, interpreted as a true thermodynamic transition. Finally, by connecting our results to bulk water behavior, we offer a comprehensive understanding of confined water vitrification with potential implications for numerous applications. [ABSTRACT FROM AUTHOR]

Recent studies have hypothesized that the reinforcing effects of boehmite nanoparticles (BNPs) in polymer nanocomposites (PNCs) are partly related to the particles themselves and partly to the water released from the BNP during curing. In this work, PNCs made from dried BNP (dBNP) with concentrations up to 15 wt% are investigated to differentiate particle and water related effects. The observed trend of the storage modulus in dynamic mechanical thermal analysis measurements was found to be independent of the drying procedure. Stiffness maps from intermodulation atomic force microscopy showed that dBNP leads to a stiffening of the interphase surrounding the particles compared with the unaffected epoxy matrix, while a softer interphase was reported for PNCs with as received BNP. A slight decrease in the glass transition temperature was observed by broadband dielectric spectroscopy related to a lowered crosslink density due to the particles. A significantly higher decrease was reported for PNCs with BNP, attributed to water influencing the curing process. In conclusion, the stiffening of PNC with BNP is related to the particles themselves, while the release of water causes the formation of a soft interphase in the vicinity of the particles and a significant decrease in crosslink density. [ABSTRACT FROM AUTHOR]

A polymer nanocomposite based on sulfonated polyphenylene oxide with amino-functionalized mesoporous silica was designed, synthesized, and tested as a new material for proton exchange membrane (PEM preparation. Characterization of the intermediate and final products of synthesis was realized by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and thermal analysis. Broadband Dielectric Spectroscopy (BDS) was used to determine dielectric properties including ionic conductivity. Thermogravimetric analysis has provided important information regarding the composition and thermal stability of the three compounds, subject to thermal degradation: 1) the amino-silica with cetyltrimethylammonium bromide (CTAB) template inside the pores (MS-NH2I), 2) the mesoporous amino-silica after removing the template (MS-NH2II) and 3) the polymer nanocomposite (sPPO-MS-NH2). The thermal decomposition of the composite samples occurs in three stages: in the first, up to 150 °C, water and organic solvents were lost; the second stage, between 200-300 °C, was due to breaking the organic functionalities (-NH2, amino and -SO3H, sulfonic acid), and the third stage, above 400 °C was due to polymer chain degradation. The final residue at 700 °C reflects the contribution of inorganic silica. The proton conductivity, for polymeric (sPPO) and composite (sPPO-MS-NH2) membranes was determined from BDS dates, both in dry and hydrated states. For dried samples, the higher values of proton conductivities were: 0.16 mS cm−1 (sPPO, 70 °C) and 0.03 mS cm−1 (sPPO-MS-NH2, 120 °C), and the higher values of proton conductivity increased for the hydrated samples with two orders of magnitude: 36.5 mS cm−1 (sPPO, 40 °C) and 22.4 mS cm−1 (sPPO-MS-NH2, 50 °C). However, the proton conductivity is still dependent on the hydration state, even for the composite membrane. [ABSTRACT FROM AUTHOR]

By using broadband dielectric spectroscopy over a wide frequency and temperature range, the effect of the chain extender and cross‐linkers on molecular dynamics of polyurethanes based on piperazine as a heterocyclic compound was assessed. Three relaxations attributed to local motions of polar side groups and small segments of the polyurethane chain (β, γ‐mode) and glass transition (α‐mode) were detected with the increase in temperature from −120 to 100 °C, along with the conductivity process at high temperatures and low frequencies. Experimental data were examined using the impedance and electric modulus for the conductivity study. Due to the presence of dipole polarization of functional groups in the hard segments, cross‐linked polyurethanes are characterized by higher dielectric constant value (≈11 at 1 kHz and 25 °C) compared to the linear ones (≈6–7 at 1 kHz and 25 °C). High conductivity was achieved for the Tween 20‐cross‐linked polyurethanes. The activation energy for the secondary γ relaxation was in the range of 34–37 kJ mol−1 for all polyurethanes, regardless of the chain extender or cross‐linker used. Piperazine‐based polyurethanes had lower activation energies for α relaxation and high conductivity compared to cyclohexane‐based polyurethanes. This indicates that α relaxation is more vulnerable to structural alterations. [ABSTRACT FROM AUTHOR]

The combination of PbHfO3 and PbSnO3 in perovskite solid solutions presents valuable opportunities to study the formation mechanisms of incommensurate phases. Crystals of PbHf1-xSnxO3 with 8% Sn were grown and measured using broadband dielectric spectroscopy to investigate the nature of relaxation and the effects of phase transitions. Our findings reveal significant alterations in the dielectric response of the PbHf0.92Sn0.08O3 solid solution, shedding light on the influence of Sn doping on lattice dynamics during the phase transition. [ABSTRACT FROM AUTHOR]

The molecular dynamics, with an emphasis on the calorimetric and dynamic glass transitions, of non-isocyanate polyhydroxyurethanes (PHUs) produced by the equimolar polyaddition of polyether-based dicyclic carbonates (P-CCs) and various short diamines was studied. The diamine component consisted of a short aliphatic diamine (1,4-diaminobutane, DAB) and a more complex 'characteristic' diamine. The study was conducted to investigate (i) the chemical structure of the characteristic amine, (ii) its molar ratio, and (iii) the structure and molar mass of the P-CC. Infrared spectroscopy, differential scanning calorimetry, and broadband dielectric spectroscopy were employed. The P-CC, constituting the bulk of the systems, was the most crucial component for the glass transition. The characteristic amine influenced the glass transition as a result of its bulky structure, but also presumably as a result of the introduction of free volume and the formation of hydrogen bonds. The dynamic glass transition (α relaxation) trace in the Arrhenius plots showed a subtle change at a certain temperature that merits further study in the future. The charge mobility was fully coupled with the molecular mobility, as evidenced by dc conductivity being directly proportional to the characteristic frequency of α relaxation. The fluctuation in carbonyl units (β relaxation) was mildly affected by changes in their immediate environment. [ABSTRACT FROM AUTHOR]

Phase-change alloy Ge 2 Sb 2 Te 5 (GST) forms a favorable material platform for modern optics, photonics, and electronics thanks to a pronounced increase in conductivity with thermally induced phase transitions from amorphous (a-GST) into cubic (c-GST) and then hexagonal (h-GST) crystalline states at the temperatures of ≃ 150 and ≃ 300 ° C, respectively. Nevertheless, the data on broadband electrodynamic response of distinct GST phases are still missing, which hamper the design and implementation of related devices and technologies. In this paper, a-, c-, and h-GST films on a sapphire substrate are studied using broadband dielectric spectroscopy. For all GST phases, complex dielectric permittivity is retrieved using Drude and Lorentz models in the frequency range of 0.06 – 50 THz or the wavelength range of ≃ 5000 – 6 μ m. A contribution from the free charge-carriers conductivity and vibrational modes to the broadband response of an analyte is quantified. In this way, the Drude model allows for estimation of the static (direct current—DC) and dynamic (at 1.0 THz) conductivity values, caused by motions of free charges only, which are as high as σ DC ≃ 15 and 40 S/cm and σ 1.0 THz ≃ 8.8 and 28.6 S/cm for the c- and h-GSTs, respectively. This overall agrees with the results of electrical measurements of GST conductivity using the four-point probe technique. The broadband electrodynamic response models obtained for the three GST phases are important for further research and developments of GST-based devices and technologies. [ABSTRACT FROM AUTHOR]

We investigate the reorientation dynamics of four octanol isomers with very different characteristics regarding the formation of hydrogen-bonded structures by means of photon-correlation spectroscopy (PCS) and broadband dielectric spectroscopy. PCS is largely insensitive to orientational cross-correlations and straightforwardly probes the α-process dynamics, thus allowing us to disentangle the complex dielectric relaxation spectra. The analysis reveals an additional dielectric relaxation contribution on time scales between the structural α-process and the Debye process. In line with nuclear magnetic resonance results from the literature and recent findings from rheology experiments, we attribute this intermediate contribution to the dielectric signature of the O–H bond reorientation. Due to being incorporated into hydrogen-bonded suprastructures, the O–H bond dynamically decouples from the rest of the molecule. The relative relaxation strength of the resulting intermediate contribution depends on the respective position of the hydroxy group within the molecule and seems to vanish at sufficiently high temperatures, i.e., exactly when the overall tendency to form hydrogen bonded structures decreases. Furthermore, the fact that different octanol isomers share the same dipole density allows us to perform an in-depth analysis of how dipolar cross-correlations appear in dielectric loss spectra. We find that dipolar cross-correlations are not solely manifested by the presence of the slow Debye process but also scale the relaxation strength of the self-correlation contribution depending on the Kirkwood factor. [ABSTRACT FROM AUTHOR]

We use 2H nuclear magnetic resonance (NMR) to study water (D2O) reorientation and diffusion in the metal–organic framework MFU-4l, which features a regular three-dimensional network of nearly spherical pores with diameters of 1.2 and 1.9 nm. We observe that the rotational correlation times follow Vogel–Fulcher–Tammann and Arrhenius (Ea = 0.48 eV) relations above ∼225 K and below ∼170 K, respectively, whereas the temperature dependence continuously evolves from one to the other behavior in the broad crossover zone in between. In the common temperature range, the present NMR results are fully consistent with previous broadband dielectric spectroscopy (BDS) data on water (H2O) in a very similar framework. Several of our observations, e.g., rotational–translational coupling, indicate that a bulk-like structural (α) relaxation is observed above the crossover region. When cooling through the crossover zone, a quasi-isotropic reorientation mechanism is retained, while 2H spin-lattice relaxation evolves from exponential to nonexponential, implying that the water dynamics probed at low temperatures does no longer fully restore ergodicity on the time scale of this experiment. We discuss that the latter effect may result from bulk-like and/or confinement-imposed spatially heterogeneous water properties. Comparison with previous NMR and BDS results for water in other confinements reveals that, for confinement sizes around 2 nm, water reorientation depends more on the pore diameter than on the pore chemistry, while water diffusion is strongly affected by the connectivity and topology of the pores. [ABSTRACT FROM AUTHOR]

The correction of chromatic aberration and achievement of high numerical aperture (NA) are two main issues for the realistic application of metalenses in imaging and display systems. In this work, we design a broadband achromatic metalens (BAM) with high NA, which is composed of hybrid all-dielectric meta-atoms in the visible region. By simultaneously and independently manipulating the geometric phase and propagation phase, meta-atoms can focus the incident lights on the same spot. Besides, a large phase compensation can be obtained through the variation in structural parameters of the hybrid meta-atom, which is essential to achieve high-NA BAM. For demonstration, the achromatic metalens with NA of 0.68 over the spectrum from 420 to 700 nm is numerically simulated. The metalens possessing high NA, broad bandwidth, and diffraction-limited achromatic focusing performance can be potentially applied in the field of imaging, spectroscopy, display, etc. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multicomponent polymer materials offer superior and adaptable properties. • Single chain nanoparticles represent an intermediate state between polymers and colloids. • Internal cross-linking impacts the structure and dynamics of SCNPs. • QENS studies show different atomic motions based on the SCNP chemical composition. The industrial sector has made significant strides in the development of multicomponent and multiphasic polymer materials, including polymer blends, composites (such as nanocomposites), and various copolymers. Random copolymers, characterized by their statistical arrangement of repeating units, are particularly noteworthy due to their tunability from amorphous to semicrystalline states. In this study, we focus on poly(tetrahydrofuran- ran -epichlorohydrin) (P(THF- ran -ECH)) copolymers, which serve as precursors for single-chain nanoparticles (SCNPs). These SCNP-based materials are of particular interest as they bridge the gap between traditional polymers and colloids. This research comprehensively investigates how the type and degree of internal cross-linking influence the structure and dynamics of P(THF- ran -ECH) copolymers and their SCNPs. Techniques such as quasielastic neutron scattering (QENS), differential scanning calorimetry (DSC), and broadband dielectric spectroscopy (BDS) were employed to study copolymers with varying compositions and levels of cross-linking. By analyzing two samples with different epichlorohydrin (ECH) contents (13 mol% and 27 mol%), we aim to control crystallization and explore its effects on dynamic behavior. Our results show that both the composition and the degree of cross-linking significantly impact the dynamics of the SCNPs, with SCNPs exhibiting slower dynamics compared to their precursor copolymers. Furthermore, semicrystalline samples display faster dynamics in SCNPs than amorphous samples. These findings provide valuable insights for the design and optimization of advanced multicomponent polymer systems. [ABSTRACT FROM AUTHOR]

Power electronic conversion systems introduce different types of voltage stresses on high-voltage epoxy cast insulation in medium-frequency transformers (MFTs), which challenges the reliability of MFTs. The endurance of epoxy insulation at different voltages (AC, DC and pulse) and environmental (thermal and humidity) stresses was studied using encapsulated electrodes in the absence of partial discharge. To assess aging processes and select aging state indicators, various tests including AC breakdown strength (BDE), broadband dielectric spectroscopy, small-angle x-ray scattering (SAXS), Fourier-transform infrared spectroscopy and differential scanning calorimetry (DSC) were first conducted on aged flat samples. The increase of mesoscopic free volume from the SAXS result and local densification (physical aging) of epoxy network from the DSC result were both found. BDE is proved to be sensitive to various aging conditions and thus determined as a test method for encapsulated samples. It is found that the physical aging effect under thermal stress at early aging stages can cause a reversible increase in BDE compared to non-aged samples. This effect can be erased by coupled medium-low electrical stress during aging. In contrast, a sufficiently high electric field will deepen the physical aging extent. Occasional sample failures were observed simultaneously within this process. According to the SAXS and DSC results on flat samples, the failure of encapsulated samples is possibly attributed to the chain fracture around increased mesoscopic free volume during electron bombardment and microcracks generated by interfacial stress release during physical aging. At longer aging periods, the volumetric absorption and diffusion of chemical reactants (oxygen and water) in epoxy networks at high temperatures determines the eventual decrease in BDE, which can be accelerated by the electric field. Ages with different voltage types were gauged by the reduction of BDE compared to pure environmental stress. Bipolar pulses bring heavier aging effects than ACs at the same RMS value. However, the DC component has opposite effects on the BDE with and without thermal stress. [ABSTRACT FROM AUTHOR]

Frequency-dependent dielectric relaxation in three deep eutectic solvents (DESs), (acetamide+LiClO4/NO3/Br), was investigated in the temperature range, 329 ≤ T/K ≤ 358, via molecular dynamics simulations. Subsequently, decomposition of the real and the imaginary components of the simulated dielectric spectra was carried out to separate the rotational (dipole–dipole), translational (ion–ion), and ro-translational (dipole–ion) contributions. The dipolar contribution, as expected, was found to dominate all the frequency-dependent dielectric spectra over the entire frequency regime, while the other two components together made tiny contributions only. The translational (ion–ion) and the cross ro-translational contributions appeared in the THz regime in contrast to the viscosity-dependent dipolar relaxations that dominated the MHz–GHz frequency window. Our simulations predicted, in agreement with experiments, anion-dependent decrement of the static dielectric constant (ɛs ∼ 20 to 30) for acetamide (ɛs ∼ 66) in these ionic DESs. Simulated dipole-correlations (Kirkwood g factor) indicated significant orientational frustrations. The frustrated orientational structure was found to be associated with the anion-dependent damage of the acetamide H-bond network. Single dipole reorientation time distributions suggested slowed down acetamide rotations but did not indicate presence of any "rotationally frozen" molecule. The dielectric decrement is, therefore, largely static in origin. This provides a new insight into the ion dependence of the dielectric behavior of these ionic DESs. A good agreement between the simulated and the experimental timescales was also noticed. [ABSTRACT FROM AUTHOR]

Vibration and noise severely affect the operation of mechanical equipment and is also detrimental to human health. Therefore, the development of high performance damping materials is crucial. However, current methods to improve damping properties often come at the expense of mechanical properties, resulting in inferior mechanical performance of materials. In order to address the issue of imbalance between damping properties and mechanical properties in polyurethane damping elastomers. In this study, polyester dangling chains containing polar groups are synthesized and introduced into polyurethane. The obtained polyurethane exhibited an effective damping temperature range of 154 °C (−54 °C to 100 °C) and a tensile strength of 15.82 MPa. Furthermore, dynamic mechanical analysis and broadband dielectric relaxation spectroscopy are combined to investigate the influence of polar dangling chains on the structure and properties of polyurethane. The degree of microphase separation increases after the introduction of polar dangling chains, indicating enhances intermolecular interaction forces, facilitating the formation of hydrogen bond between the main chain and dangling chains, thereby increasing molecular chain friction and energy dissipation. This work overcomes the challenge of balancing the damping and mechanical properties of polyurethane, providing a new strategy for designing high performance polyurethane damping elastomers. [ABSTRACT FROM AUTHOR]

This report presents the low-frequency (LF), static, and dynamic dielectric properties of neopentyl glycol (NPG), an orientationally disordered crystal (ODIC)-forming material important for the barocaloric effect applications. High-resolution tests were carried out for 173 K < T < 440 K , in liquid, ODIC, and solid crystal phases. The support of the innovative distortion-sensitive analysis revealed a set of novel characterizations important for NPG and any ODIC-forming material. First, the dielectric constant in the liquid and ODIC phase follows the Mossotti Catastrophe-like pattern, linked to the Clausius–Mossotti local field. It challenges the heuristic paradigm forbidding such behavior for dipolar liquid dielectrics. For DC electric conductivity, the prevalence of the 'critical and activated' scaling relation is evidenced. It indicates that commonly applied VFT scaling might have only an effective parameterization meaning. The discussion of dielectric behavior in the low-frequency (LF) domain is worth stressing. It is significant for applications but hardly discussed due to the cognitive gap, making an analysis puzzling. For the contribution to the real part of dielectric permittivity in the LF domain, associated with translational processes, exponential changes in the liquid phase and hyperbolic changes in the ODIC phase are evidenced. The novelty also constitutes t g δ temperature dependence, related to energy dissipation. The results presented also reveal the strong postfreezing/pre-melting-type effects on the solid crystal side of the strongly discontinuous ODIC–solid crystal transition. So far, such a phenomenon has been observed only for the liquid–solid crystal melting transition. The discussion of a possible universal picture of the behavior in the liquid phase of liquid crystalline materials and in the liquid and ODIC phases of NPG is particularly worth stressing. [ABSTRACT FROM AUTHOR]

In this work, the effect of etching the surface of polymer matrix nanocomposites with atmospheric pressure plasma targeting to achieve enhanced dielectric properties was investigated. Polymer nanocomposites, with varying reinforcing phase content, were modified by atmospheric-pressure plasma resulting in an increase in the surface filler's concentration. Polymethyl methacrylate (PMMA) matrix nanocomposites reinforced with zinc oxide (ZnO) nanoparticles were prepared and dielectrically studied as a function of the nanoparticle content and the plasma modified surfaces. The electrical response of the composite systems was studied by means of Broadband Dielectric Spectroscopy (BDS) over a wide range of temperatures and frequencies. The dielectric permittivity increased with the embedded phase content and with plasma surface treatment. Energy density followed the same trend as dielectric permittivity, and the plasma-treated nanocomposite with the higher ZnO content exhibited approximately 27% higher energy density compared to the unreinforced matrix. [ABSTRACT FROM AUTHOR]

Nanocomposites of poly(ε‐caprolactone) (PCL) reinforced by an organomodified beidellite (BDT) with 3% of cetyltrimethylammonium bromide (CTAB) (labeled PCL/3CTA‐BDT) were prepared by varying the content of filler (1, 2, 3, and 5 wt%). Their molecular dynamics were investigated by broadband dielectric spectroscopy at temperatures ranging from 0 to 40°C and a frequency window from 10−1 to 106 Hz. Three relaxation processes were detected for unfilled PCL: electrode polarization (EP), the Maxwell–Wagner–Sillars (MWS) polarization, and the α‐relaxation. The incorporation of the filler induced the emergence of a fourth process at high frequency of dipolar origin labeled as interfacial polarization (IP). Fitting the data with the Havriliak–Negami model as well as a study of the relaxation time variation with temperature demonstrated the noncooperative nature of the IP process. Activation energy and dielectric strength values demonstrated that the PCL/3CTA‐BDT with 3 wt% of filler showed a higher quality of dispersion and better interfacial features compared to those with other filler contents (2 and 5 wt%). This work highlights the challenges of dielectric green nanocomposites used for capacitors (storage energy) and cable/wire insulation. Highlights: The various samples were analyzed using broadband dielectric spectroscopy.Relaxation processes in pure matrix: EP, MWS, and α‐relaxation.Incorporation of the filler induced the emergence of interfacial polarization (IP).Noncooperative behavior of the IP process.3 wt% loading showed a higher quality of dispersion and interfacial features. [ABSTRACT FROM AUTHOR]

Amorphous solid phases can be represented by shallow basins in the potential energy hypersurface. Glasses formed by substances with prolific crystal polymorphism, such as nateglinide, an anti-diabetes drug, are susceptible to greater kinetical instability. Their energy landscape is characterized by deep pits in an accessible range, into which the supramolecular configuration can fall, when the amorphous solid relaxes to some crystalline polymorph. Alternative co-amorphization strategies are explored in this work to overcome the crystallization of nateglinide amorphous phases, namely by comparing two synthetic approaches, cryo-milling and quench-cooling, for a dual-drug system in combination with ranolazine. An alternative co-former, the essential amino-acid tryptophan, was also used for the synthesis of a cryo-milled nateglinide co-amorphous system. Enhanced kinetical stability for up to 8 months is achieved with both multicomponent systems. Their physico-chemical characterization in 3 molar ratios is accompanied by the study of their relaxation processes by broadband dielectric spectroscopy. Despite the higher glass transition temperatures obtained for the cryo-milled co-amorphous system with tryptophan, the co-amorphous salt system with ranolazine was found to have higher kinetical stability upon heating or ageing. [ABSTRACT FROM AUTHOR]

The present work explores a systematic investigation of the microstructural, optical, and dielectric properties of W1−xNixO3 (x = 0, 0.02, 0.04, and 0.06) samples and their application in supercapacitors. The sol–gel auto-combustion process was used to synthesize these samples, and a number of analytical techniques such as x-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, Raman, Scanning Electron Microscopy (SEM), UV–visible spectroscopy, dielectric measurements, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were used to characterize them. The Rietveld refined XRD patterns confirm the monoclinic phase with space group P21/n in a single phase. FTIR spectroscopy confirms the functional groups associated with stretching and bending vibrational modes at various wavenumbers. Raman spectroscopy ensures the phase purity of the materials and shows a blue shift with Ni doping. SEM microscopy reveals a uniform surface morphology as well as particle agglomeration at the surface. UV–visible studies reveal a significant decrease in the bandgap (2.13–1.81 eV) as the Ni concentration is increased. Dielectric studies show that as the frequency rises, the dielectric constant decreases and becomes saturated at higher frequencies. The highest value of the dielectric constant (ε') is observed for the 4% Ni-doped WO3 sample. The electrochemical and capacitive properties have been characterized and studied using CV and EIS analysis. Cyclic voltammetry tests were carried out in the range of − 0.2 to 0.8 V with varying scan rates (5–100 mVs−1), exhibiting a significantly large area under the CV curve, hence higher values of specific capacitance. The maximum specific capacitance at a scan rate of 5 mVs−1 for each sample of W1−xNixO3 (x = 0, 0.02, 0.04, and 0.06) is found to be 126.671, 192.31, 278.52, and 128.58 Fg−1, respectively, in 2M KOH electrolyte. Thus, the synthesized samples exhibit potential for application as electrode materials for supercapacitors. [ABSTRACT FROM AUTHOR]

The dynamic heterogeneities occurring just before the transition to the glassy phase have been named as the cause of amorphization in supercooled systems. Numerous studies conducted so far have confirmed this hypothesis, and based on it, a widely accepted solution to the puzzle of glass transition has been developed. This report focuses on verifying the existence of a strong pretransitional anomaly near the glass transition T g . For this purpose, supercooled liquid-crystalline systems with a strong rod-like structure were selected. Based on the obtained experimental data, we demonstrate in this article that the previously postulated dynamic heterogeneities exhibit a critical characteristic, meaning a strong pretransitional anomaly can be observed with the described critical exponent α = 0.5 . Due to this property, it can be concluded that these heterogeneities are critical fluctuations, and consequently, the transition to the glassy state can be described based on the theory of critical phenomena. To measure the pretransitional anomaly near T g in supercooled liquid-crystalline systems, broadband dielectric spectroscopy (BDS) and nonlinear dielectric effect (NDE) methods were applied. The exponent α provides insight into the nature and intensity of critical fluctuations in the system. A value of α = 0.5 suggests that the fluctuations become increasingly intense as the system approaches the critical point, contributing to the divergence in specific heat. Understanding the role of critical fluctuations in the glass transition is crucial for innovating and improving a wide range of materials for energy storage, materials design, biomedical applications, food preservation, and environmental sustainability. These advancements can lead to materials with superior properties, optimized manufacturing processes, and applications that meet the demands of modern technology and sustainability challenges. [ABSTRACT FROM AUTHOR]

Zirconium (Zr)-doped ZnO samples (ZZO) have been successfully prepared by the solid-state reaction (SSR) method at different doping levels. Thermal stability and weight changes were studied using thermogravimetric analysis. A negligible weight loss of 0.0894 mg/wt% was observed during degradation. X-ray diffraction (XRD) measurements confirmed the hexagonal structure of ZZO samples. Zr ions were well doped into ZnO lattices, with no secondary phases detected. Doping Zr resulted in a slight shift toward smaller angles and lattice parameter expansion. High doping leads to crystal disorder and reduced crystallite size. Scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray analysis (EDX) confirmed that Zr content follows the stoichiometric ratio. Particle size decreases with increasing doping concentration. Increasing Zr content enhances optical transmittance in the visible range; a 9 wt% doping level produced the highest average optical transmittance at 69%. An empirical law for band gap variation has been proposed and compared to the literature. Electrical impedance spectroscopy data with frequencies varying between 1 Hz and 1 MHz were measured at 300 K. The Nyquist diagram shows the impedance response, with semi-circles at different frequencies corresponding to bulk, electrode, and grain boundary contributions. The Randles equivalent circuit has been successfully used to reconcile impedance measurements with the theoretical model. Impedance spectroscopy analysis reveals dielectric behavior deviation from ideal Debye, and both dielectric constant and dielectric loss decreased with frequency. Dielectric parameters increased with Zr doping while the loss values were in the order of 10−1. It was demonstrated that ZZO's structural properties greatly influence its electrical conductivity. At room temperature, the Zr doping element enhanced AC conductivity in the mid- and high-frequency domains, with a significant change of around 5 wt%. The observed results proved a significant correlation between the physiochemical and electrical properties of ZZO samples synthesized by SSR. [ABSTRACT FROM AUTHOR]

The study of marine lubricants using modern methods for quality control and diagnostics of engine conditions is an important task. The solution to this task determines the technical condition of ships, their performance, and accident-free operation in maritime transport. In this study, the properties of several marine motor oils were studied using broadband dielectric spectroscopy. The complex dielectric constant, conductivity, and loss tangent of base oil, Shell Rimula 15W40 oil fresh and used for 250 and 500 h were studied. The influence of the test voltage frequency and temperature on the selected electrical parameters was determined. In used oils, the DC conductivity decreases slightly, which is apparently due to the depletion of additives. The increase in the conductivity of all studied oils with increasing current frequency is caused by the displacement current. It is shown that dielectric losses increase with frequency as long as the polarization has time to follow the change in the field. A shift in the frequency at which the maximum loss occurs with a change in temperature was discovered. The activation energies of polarization and conductivity were determined. The thermal activation energies obtained from the conductivity and dielectric constant are not significantly different. For the first time, the distributions of the dielectric constant relaxation times for the studied lubricating oils have been obtained. The dielectric relaxation time distribution function depends on the composition of additives in the oil, wear particles, contaminants, and the chemical degradation of the oil during operation. For the first time, correlations have been established between conductivity and dielectric constant at different temperatures and frequencies. These correlations can be used to select frequency ranges that provide stable parameter values and maximum diagnostic ability. [ABSTRACT FROM AUTHOR]

We report an experimental work on the liquid crystal dimer 1",7'-bis(4-cyanobiphenyl-4'-yl) heptane (CB7CB) confined to Anopore membranes. We have studied the behaviour of the dielectric relaxation modes in the isotropic (I), nematic (N) and twist-bend nematic (NTB) phases by broadband dielectric spectroscopy and compared to the results of the bulk sample. We have found that the strength of the components of the static dielectric permittivity for bulk and confined samples diminishes when cooling but, once in the NTB phase, those of the confined CB7CB tend to decrease in a slower rate compared to the ones of bulk CB7CB. This work is meant to play a humble tribute to the first report on a cyanobiphenyl-based LC in its 50th anniversary. [ABSTRACT FROM AUTHOR]

In the present work, hybrid nanocomposites of an epoxy resin reinforced with ZnTiO3 and BaTiO3 nanoparticles, at various filler contents, were fabricated and studied. The successful integration of ceramic nanofillers and the fine distribution of nanoparticles were confirmed via X-ray Diffraction patterns and Scanning Electron Microscopy images, respectively. Dielectric properties and related relaxation phenomena were investigated via Broadband Dielectric Spectroscopy in a wide range of frequencies and temperatures. Data analysis showed that dielectric permittivity increases with filler content, although optimum performance does not correspond to the maximum ZnTiO3 content. Four relaxation processes were observed and attributed to interfacial polarization (IP) (at low frequencies and high temperatures), glass-to-rubber transition (α-relaxation) of the epoxy matrix (at intermediate frequencies and temperatures), and local rearrangements of polar side groups of the macromolecules (β-relaxation) and small flexible groups of the main polymer chain (γ-relaxation) occurring at low temperatures and high frequencies. The ability of hybrid nanocomposites to store and retrieve energy was studied under dc conditions by employing a charging/discharging sequence. The stored and retrieved energy increases with filler content and charging voltage. The optimum ability of energy recovering, shown by the epoxy/7 phr ZnTiO3/7 phr BaTiO3 nanocomposite, ranges between 30 and 50 times more than the matrix, depending on the time instant. The employed nanoparticles induce piezoelectric properties in the nanocomposites, as found by the increase in the piezoelectric coefficient with filler content. [ABSTRACT FROM AUTHOR]

Renewable dielectric materials have attracted the attention of industries and stakeholders, but such materials possess limited properties. This research focused on studying polylactic acid (PLA)/cellulose acetate (CA) blends produced by 3D printing to facilitate their integration into the electrical insulation field. The dielectric findings showed that a blend containing 40% of CA by weight had a dielectric constant of 2.9 and an electrical conductivity of 1.26 × 10−11 S·cm−1 at 100 Hz and 20 °C while exhibiting better mechanical rigidity in the rubbery state than neat PLA. In addition, it was possible to increase the electrical insulating effect by reducing the infill ratio at the cost of reduced mechanical properties. The differential scanning calorimetry, broadband dielectric spectroscopy, and dynamic mechanical analysis results showed that the PLA plasticizer reduced the energy required for PLA relaxations. These preliminary results demonstrated the benefits of using a combination of PLA, CA, and 3D printing for electrical insulation applications. [ABSTRACT FROM AUTHOR]

In this study, two polymorphs of the [1,1′-dibutyl-4,4′-bipyridinium][Ni(mnt)2] salt (1) were synthesized. The dark-green polymorph (designated as 1-g) was prepared under ambient conditions by the rapid precipitation method in aqueous solutions. Subsequently, the red polymorph (labeled as 1-r) was obtained by subjecting 1-g to ultrasonication in MeOH at room temperature. Microanalysis, infrared spectroscopy, thermogravimetry (TG), differential scanning calorimetry (DSC), and powder X-ray diffraction (PXRD) techniques were used to characterize the two polymorphs. Both 1-g and 1-r exhibit structural phase transitions: a reversible phase transition at ∼403 K (∼268 K) upon heating and 384 K (∼252 K) upon cooling for 1-g (1-r) within the temperature range below 473 K. Interestingly, on heating 1-r to 523 K, an irreversible phase transition occurred at about 494 K, resulting in the conversion of 1-r into 1-g. Relative to 1-r, 1-g represents a thermodynamically metastable phase wherein numerous high-energy conformations in butyl chains of cations are confined within the lattice owing to quick precipitation or rapid annealing from higher temperatures. Through variable-temperature single crystal and powder X-ray diffractions, UV-visible spectroscopy, dielectric spectroscopy, and DSC analyses, this study delves into the mechanism underlying phase transitions for each polymorph and the manual transformation between 1-g and 1-r as well. [ABSTRACT FROM AUTHOR]

In this paper, a novel polylactide-based nanocomposite with the addition of bentonite as a filler, Fusabond, and glycerine as a compatibilizer and plasticizer, were prepared and investigated. Four samples with different contents of bentonite (1, 5, 10, and 15 wt.%), as well as three samples without fillers, were prepared with an easily scalable method: melt blending. The electrical properties of all prepared samples were investigated with broadband dielectric spectroscopy in the frequency range between 0.1 Hz and 1 MHz. Measurements were conducted at nine temperatures between 293.15 and 333.15 K (20 to 60 °C) with steps of 5 K. It was found that the increase in the content of bentonite in polylactide has a significant effect on the electrical properties of the prepared nanocomposites. [ABSTRACT FROM AUTHOR]

A tetra(ethylene glycol)‐based 1,3,4,5‐tetrasubstituted poly(1,2,3‐triazolium) is synthesized in two steps including: i) the catalyst‐free polyaddition of a diazide and an activated internal dialkyne and ii) the N‐alkylation of the resulting 1,2,3‐triazole groups. In order to provide detailed structure/properties correlations different analogs are also synthesized. First, parent poly(1,2,3‐triazole)s are obtained via AA+BB polyaddition using copper(I)‐catalyzed alkyne‐azide cycloaddition or metal‐free thermal alkyne‐azide cycloaddition (TAAC). Poly(1,2,3‐triazole)s with higher molar masses are obtained in higher yields by TAAC polyaddition. A 1,3,4‐trisubstituted poly(1,2,3‐triazolium) structural analog obtained by TAAC polyaddition using a terminal activated dialkyne and subsequent N‐alkylation of the 1,2,3‐triazole groups enables discussing the influence of the methyl group in the C‐4 or C‐5 position on thermal and ion conducting properties. Obtained polymers are characterized by 1H, 13C, and 19F NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, size exclusion chromatography, and broadband dielectric spectroscopy. The targeted 1,3,4,5‐tetrasubstituted poly(1,2,3‐triazolium) exhibits a glass transition temperature of −23 °C and a direct current ionic conductivity of 2.0 × 10−6 S cm−1 at 30 °C under anhydrous conditions. The developed strategy offers opportunities to further tune the electron delocalization of the 1,2,3‐triazolium cation and the properties of poly(1,2,3‐triazolium)s using this additional substituent as structural handle. [ABSTRACT FROM AUTHOR]

We report the effect of titanium doping on the structure, morphology, dielectric and electrical properties of zirconium ferrite Zr1−xTixFe2O4 (x = 0.0, 0.01, 0.03, 0.05) nanocrystalline ceramics prepared via sol–gel method. X-ray diffraction (XRD) technique confirmed the spinel structure of all samples and that the average crystallite size decreased with Ti doping. Scanning electron microscopy (SEM) confirmed the spherical-shaped morphology with an average grain size of 300 and 200 nm for x = 0 and 0.05, respectively. The Raman study revealed that Ti4+ substitution slightly shifts the Raman modes towards the lower wavenumber. The dielectric studies analyzed using Impedance analyzer show the increase in dielectric parameters such as dielectric constant and dielectric loss with Ti concentration. The complex impedance analysis in the frequency range (10–106 Hz) is analyzed to understand the interactions from the grain and grain boundary phases. The dielectric feedback and impedance analysis studied the electrical properties in the 300–700 K temperature range and frequency range of 20–106 Hz. The AC conductivity increases with applied frequency and decreases with doping concentration. It is found that the Ti concentration increases the activation energy determined using the Arrhenius equation of AC conductivity and is a characteristic of polaron conduction. The Universal power law dependency of AC conductivity indicates charge transport made possible by hopping or tunneling. The temperature-dependent frequency exponent n's observed minimal implies that the major transport mode is significant polaron tunneling. [ABSTRACT FROM AUTHOR]

The inherently weak chiroptical responses of natural materials limit their usage for controlling and enhancing chiral light-matter interactions. Recently, several nanostructures with subwavelength scale dimensions were demonstrated, mainly due to the advent of nanofabrication technologies, as a potential alternative to efficiently enhance chirality. However, the intrinsic lossy nature of metals and the inherent narrowband response of dielectric planar thin films or metasurface structures pose severe limitations toward the practical realization of broadband and tailorable chiral systems. Here, we tackle these problems by designing all-dielectric silicon-based L-shaped optical metamaterials based on tilted nanopillars that exhibit broadband and enhanced chiroptical response in transmission operation. We use an emerging bottom-up fabrication approach, named glancing angle deposition, to assemble these dielectric metamaterials on a wafer scale. The reported strong chirality and optical anisotropic properties are controllable in terms of both amplitude and operating frequency by simply varying the shape and dimensions of the nanopillars. The presented nanostructures can be used in a plethora of emerging nanophotonic applications, such as chiral sensors, polarization filters, and spin-locked nanowaveguides. L-shaped silicon metamaterials are realized exhibiting broadband and enhanced chirality. The current work sets new benchmarks in the assembly of ultrathin dielectric chiral metamaterials that can efficiently control chiral light-matter interactions. [ABSTRACT FROM AUTHOR]

Polymers are essential in several sectors, yet some applications necessitate surface modification. One practical and eco-friendly option is non-thermal plasma exposure. The present research endeavors to examine the impacts of dielectric barrier discharge atmospheric pressure plasma on the chemical composition and wettability properties of acrylonitrile butadiene styrene surfaces subject to the action of additive manufacturing. The plasma source was produced by igniting either helium or argon and then adjusted to maximize the operational conditions for exposing polymers. The drop in contact angle and the improvement in wettability after plasma exposure can be due to the increased oxygen-containing groups onto the surface, together with a reduction in carbon content. The research findings indicated that plasma treatment significantly improved the wettability of the polymer surface, with an increase of up to 60% for both working gases, while the polar index increased from 0.01 up to 0.99 after plasma treatment. XPS measurements showed an increase of up to 10% in oxygen groups at the surface of He–plasma-treated samples and up to 13% after Ar–plasma treatment. Significant modifications were observed in the structure that led to a reduction of its roughness by 50% and also caused a leveling effect after plasma treatment. A slight decrease in the glass and melting temperature after plasma treatment was pointed out by differential scanning calorimetry and broadband dielectric spectroscopy. Up to a 15% crystallinity index was determined after plasma treatment, and the 3D printing process was measured through X-ray diffraction. The empirical findings encourage the implementation of atmospheric pressure plasma-based techniques for the environmentally sustainable manipulation of polymers for applications necessitating higher levels of adhesion and specific prerequisites. [ABSTRACT FROM AUTHOR]

The report presents static, low-frequency, and dynamic dielectric properties in the isotropic liquid, nematic, and solid phases of MBBA and related nanocolloids with paraelectric BaTiO3 nanoparticles (spherical, d = 50 nm). MBBA (4-methoxybenzylidene-4′–butylaniline) is a liquid crystalline compound with a permanent dipole moment transverse to the long molecular axis. The distortions-sensitive analysis of the dielectric constant revealed its hidden pretransitional anomaly, strongly influenced by the addition of nanoparticles. The evolution of the dielectric constant in the nematic phase shows the split into two regions, with the crossover coinciding with the standard melting temperature. The 'universal' exponential-type behavior of the low-frequency contribution to the real part of the dielectric permittivity is found. The critical-like pretransitional behavior in the solid phase is also evidenced. This is explained by linking the Lipovsky model to the Mossotti catastrophe concept under quasi-negative pressure conditions. The explicit preference for the 'critical-like' evolution of the apparent activation enthalpy is worth stressing for dynamics. Finally, the long-range, 'critical-like' behavior of the dissipation factor (D = tgδ), covering the isotropic liquid and nematic phases, is shown. [ABSTRACT FROM AUTHOR]

The development of efficient and sustainable composites remains a primary objective of both research and industry. In this study, the use of biochar, an eco-friendly reinforcing material, in additive manufacturing (AM) is investigated. A high-density Polyethylene (HDPE) thermoplastic was used as the matrix, and the material extrusion (MEX) technique was applied for composite production. Biochar was produced from olive tree prunings via conventional pyrolysis at 500 °C. Composite samples were created using biochar loadings in the range of 2.0–10.0 wt. %. The 3D-printed samples were mechanically tested in accordance with international standards. Thermogravimetric analysis (TGA) and Raman spectroscopy were used to evaluate the thermal and structural properties of the composites. Scanning electron microscopy was used to examine the fractographic and morphological characteristics of the materials. The electrical/dielectric properties of HDPE/biochar composites were studied over a broad frequency range (10–2 Hz–4 MHz) at room temperature. Overall, a laborious effort with 12 different tests was implemented to fully characterize the developed composites and investigate the correlations between the different qualities. This investigation demonstrated that biochar in the MEX process can be a satisfactory reinforcement agent. Notably, compared to the control samples of pure HDPE, biochar increased the tensile strength by over 20% and flexural strength by 35.9% when added at a loading of 4.0 wt. %. The impact strength and microhardness were also significantly improved. Furthermore, the Direct current (DC) conductivity of insulating HDPE increased by five orders of magnitude at 8.0 wt. % of biochar content, suggesting a percolation threshold. These results highlight the potential of C-based composites for the use in additive manufacturing to further exploit their applicability by providing parts with improved mechanical performance and eco-friendly profiles. Highlights: The reinforcement of MEX 3D printed parts with eco-friendly biochar. Biochar was obtained from olive trees. Popular high-density polyethylene (HDPE) was the polymeric matrix in the study. biochar increased the tensile strength by over 20% and the flexural strength by 35.9% at a loading of 4 wt. %. The DC conductivity of the insulating HDPE increased by five orders of magnitude at 8 wt. % biochar loading. [ABSTRACT FROM AUTHOR]

Nickel copper ferrite nanoparticles (NPs) in the form Ni0.65Cu0.35Fe2O4 were synthesized by the sol–gel method while PVA-CMC blend films were manufactured by cast method. The prepared films of PVA-CMC/(Ni0.65Cu0.35Fe2O4)x, where x = 2,4,6, and 8 wt%, were characterized using X-ray diffractometer (XRD) and Raman spectroscopy. The transmission and absorption spectra were investigated for PVA-CMC/Ni0.65Cu0.35Fe2O4 films using UV–visible spectrophotometer. The assessment of dielectric characteristics of the prepared PVA-CMC blend films was done by using broadband dielectric spectroscopy (BDS). XRD verified the production of face-centered cubic spinel structure of space group Fd3m with the lattice parameters a = 8.3310 Å for Ni0.65Cu0.35Fe2O4 NPs and the amorphous characteristics of blend films. Furthermore, XRD verified that Ni0.65Cu0.35Fe2O4 NPs were included in the blend matrix. The Raman spectra of the PVA-CMC blend films showed several strong characteristic scattering peaks. The optical bandgaps were evaluated via the Tauc's model. The optical bandgap decreases from 5.50 to 5.05 eV and the Urbach energy increases from 1.35 to 2.99 eV, gradually, with increasing NPs' concentrations. Moreover, the index of refraction rises from 1.776 (pure PVA-CMC) to 2.881 (PVA-CMC/8%Ni0.65Cu0.35Fe2O4). Also, it was discovered that as Ni0.65Cu0.35Fe2O4 NPs were added to the PVA-CMC blend matrix, optical conductivity increased as well. The results showed that the PVA/CMC blend films can be tailored by Ni0.65Cu0.35Fe2O4 additives which nominate it for optical devices applications. Three remarkable trends were investigated on the dielectric spectra of the investigated samples. The low frequency range shows a linear increase with decreasing frequency indicating the transport of the free charge carriers. Nano-confinement phenomenon affected in reducing the conductivity of the blend, even the conductivity of the nano-ferrite is higher in conductivity than the blend. [ABSTRACT FROM AUTHOR]

Poly(ethylene furanoate) (PEF)-based nanocomposites were fabricated with silver (Ag) and titanium dioxide (TiO2) nanoparticles by the in-situ polymerization method. The importance of this research work is to extend the usage of PEF-based nanocomposites with improved material properties. The PEF-Ag and PEF-TiO2 nanocomposites showed a significant improvement in color concentration, as determined by the color colorimeter. Scanning electron microscopy (SEM) photographs revealed the appearance of small aggregates on the surface of nanocomposites. According to crystallinity investigations, neat PEF and nanocomposites exhibit crystalline fraction between 0–6%, whereas annealed samples showed a degree of crystallinity value above 25%. Combining the structural and molecular dynamics observations from broadband dielectric spectroscopy (BDS) measurements found strong interactions between polymer chains and nanoparticles. Contact angle results exhibited a decrease in the wetting angle of nanocomposites compared to neat PEF. Finally, antimicrobial studies have been conducted, reporting a significant rise in inhibition of over 15% for both nanocomposite films against gram-positive and gram-negative bacteria. From the overall results, the synthesized PEF-based nanocomposites with enhanced thermal and antimicrobial properties may be optimized and utilized for the secondary packaging (unintended food-contact) materials. [ABSTRACT FROM AUTHOR]

In the electric discharge machining process, the material is separated from the surface of the work piece by an electric spark, and in the presence of the dielectric material and tool electrode, changes are made on the surface of the work piece. In this project, we investigated the effect of dielectric material and brass tool electrode diffusion on the surface of carbon steel workpiece by means of quantmetric analysis, X-ray diffraction and electrochemical impedance spectroscopy. The effect of the parameters such as electric current intensity (I), pulse on time (ton), pulse off time (toff) and machining time (τ) on the composition of work peace, microstructure and electrochemical corrosion of machined work peace, were investigated. The results of quantmetric analysis showed that with the increase of machining parameters, the amount of diffused copper (from brass tool electrode) and carbon (from pyrolysis of flashing dielectric material) on the surface of machined carbon steel was increased. X-ray diffraction results confirmed that the formation of different phases such as Fe1.92C0.08, Cu4, Cu2 and Fe2 on the surface of workpiece, which was accordance with the quantmetric results. Electrochemical studies showed that during the EDM process, the electrochemical corrosion resistance was increased. [ABSTRACT FROM AUTHOR]

The present study was designed to investigate the physical stability of three organic materials with similar chemical structures. The examined compounds revealed completely different crystallization tendencies in their supercooled liquid states and were classified into three distinct classes based on their tendency to crystallize. (S)-4-Benzyl-2-oxazolidinone easily crystallizes during cooling from the melt; (S)-4-Benzylthiazolidine-2-thione does not crystallize during cooling from the melt, but crystallizes easily during subsequent reheating above Tg; and (S)-4-Benzyloxazolidine-2-thione does not crystallize either during cooling from the melt or during reheating. Such different tendencies to crystallize are observed despite the very similar chemical structures of the compounds, which only differ in oxide or sulfur atoms in one of their rings. We also studied the isothermal crystallization kinetics of the materials that were shown to transform into a crystalline state. Molecular dynamics and thermal properties were thoroughly investigated using broadband dielectric spectroscopy, as well as conventional and temperature-modulated differential scanning calorimetry in the wide temperature range. It was found that all three glass formers have the same dynamic fragility (m = 93), calculated directly from dielectric structural relaxation times. This result verifies that dynamic fragility is not related to the tendency to crystallize. In addition, thermodynamic fragility predictions were also made using calorimetric data. It was found that the thermodynamic fragility evaluated based on the width of the glass transition, observed in the temperature dependence of heat capacity, correlates best with the tendency to crystallize. [ABSTRACT FROM AUTHOR]