Nonlinear Dielectric Effect Research Articles

Are Critical Fluctuations Responsible for Glass Formation?

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 Tg. 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 Tg 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.

Influence of the presence of ions on the dielectric properties of reverse micelle systems

AOT/isooctane/water reverse micelle solution was doped with ionic salts solutions: sodium chloride, potassium chloride, tetramethylammonium chloride, tetramethylammonium bromide, sodium butyrate and sodium benzoate. Each system was investigated for the influence of ionic additives on dielectric properties: electric permittivity, conductivity and nonlinear dielectric effect (NDE). Studies showed that addition of salts noticeably changes the dielectric parameters. Based on the salts used in this research, the most common effect is a decrease of electric permittivity, conductivity and NDE effect. However, addition of some ions can lead to their increase, which was proved in the case of sodium benzoate. The registered changes were explained based on the percolation effect and changes in rigidity of the micellar surfactant shell due to the incorporation of the dissolved ions into the micellar structure.

Linear and Nonlinear Dielectric Response of Intrinsically Disordered Proteins.

Linear and nonlinear dielectric responses of solutions of intrinsically disordered proteins (IDPs) were analyzed by combining molecular dynamics simulations with formal theories. A large increment of the linear dielectric function over that of the solvent is found and related to large dipole moments of IDPs. The nonlinear dielectric effect (NDE) of the IDP far exceeds that of the bulk electrolyte, offering a route to interrogate protein conformational and rotational statistics and dynamics. Conformational flexibility of the IDP makes the dipole moment statistics consistent with the gamma/log-normal distributions and contributes to the NDE through the dipole moment's non-Gaussian parameter. The intrinsic non-Gaussian parameter of the dipole moment combines with the protein osmotic compressibility in the nonlinear dielectric susceptibility when dipolar correlations are screened by the electrolyte. The NDE is dominated by dipolar correlations when electrolyte screening is reduced.

Phase Equilibria and Critical Behavior in Nematogenic MBBA-Isooctane Monotectic-Type Mixtures.

The transition from the isotropic (I) liquid to the nematic-type (N) uniaxial phase appearing as the consequence of the elongated geometry of elements seems to be a universal phenomenon for many types of suspensions, from solid nano-rods to biological particles based colloids. Rod-like thermotropic nematogenic liquid crystalline (LC) compounds and their mixtures with a molecular solvent (Sol) can be a significant reference for this category, enabling insights into universal features. The report presents studies in 4'-methoxybenzylidene-4-n-butylaniline (MBBA) and isooctane (Sol) mixtures, for which the monotectic-type phase diagram was found. There are two biphasic regions (i) for the low (TP1, isotropic liquid-nematic coexistence), and (ii) high (TP2, liquid-liquid coexistence) concentrations of isooctane. For both domains, biphasic coexistence curves' have been discussed and parameterized. For TP2 it is related to the order parameter and diameter tests. Notable is the anomalous mean-field type behavior near the critical consolute temperature. Regarding the isotropic liquid phase, critical opalescence has been detected above both biphasic regions. For TP2 it starts ca. 20 K above the critical consolute temperature. The nature of pretransitional fluctuations in the isotropic liquid phase was tested via nonlinear dielectric effect (NDE) measurements. It is classic (mean-field) above TP1 and non-classic above the TP2 domain. The long-standing problem regarding the non-critical background effect was solved to reach this result.

Multiparticle orientational correlations are responsible for the nonlinear dielectric effect: Analysis of temperature-dependent measurements for glycerol.

The nonlinear dielectric effect (NDE) is traditionally viewed as originating from saturation of the response of individual dipoles in a strong electric field. This mean-field view, mathematically described by the Langevin saturation function, predicts enhanced dielectric saturation at lower temperatures. In contrast, recent experiments for glycerol have shown a sharp increase of the NDE with increasing temperature. The formalism presented here splits the NDE into a sum of a term representing binary correlations of dipolar orientations and terms referring to three- and four-particle orientational correlations. Analysis of experimental data shows that the contribution of three- and four-particle correlations strongly increases at elevated temperatures. The mean-field picture of dielectric saturation as the origin of the NDE is inconsistent with observations. A positive NDE (increment of the field-dependent dielectric constant) is predicted for low-concentration solutions of polar molecules in nonpolar solvents. The dependence of the NDE on the concentration of the polar component is polynomial.

Improving the comprehensive energy storage performance of composite materials through the coupling effect of AgNbO3/PVDF nanocomposite

AbstractCeramic‐polymer nanocomposites with high energy storage density can achieve excellent energy storage performance and have a wide range of application prospects. Currently, it has been shown that the coupling effects have a great impact on improving the performance of dielectric composites, but increasing the breakdown strength of polymer nanocomposite is still a tremendous challenge to the achievement of high energy density under high voltages. The aim of this paper is to further investigate this problem and obtain AgNbO3/PVDF flexible composites by introducing a small amount of AgNbO3 ultrafine powder prepared by hydrothermal method into poly(vinylidene fluoride) (PVDF). The interfacial coupling effect within this nanocomposite with the coupling effects of nonlinear dielectric materials improves its energy storage capacity and electrical strength resistance. The energy density of the 2 wt% AgNbO3/PVDF composite film was raised to 16.5 J/cm3 at the electric breakdown strength of 391.7 MV/m, and its energy storage capacity is two to three times that of AgNbO3 lead‐free antiferroelectric ceramics. Finite element simulations showed the further enhancement of breakdown strength was ascribed to the local electric field and to the AgNbO3 ultrafine powder which blocked the breakdown path in the nanocomposites and coupling effects occurred with PVDF. Hence, the AgNbO3 ultrafine powder has a positive effect on improving the energy storage performance of flexible composites. The effects of nonlinear dielectric material coupling effects and interfacial coupling effects on the dielectric properties of composite dielectric materials are further investigated, which are important for the development of flexible high energy storage capacitors.

Inside out Approach to Rotator State in Hydrogen-Bonded System-Experimental and Theoretical Cross-Examination in n-Octanol.

The experimental and theoretical description of premelting behavior is one of the most challenging tasks in contemporary material science. In this paper, n-octanol was studied using a multi-method approach to investigate it at macroscopic and molecular levels. The experimental infrared (IR) spectra were collected in the solid state and liquid phase at temperature range from C to −15 C to detect temperature-related indicators of pretransitional phenomena. Next, the nonlinear dielectric effect (NDE) was measured at various temperatures (from −30 C to −15 C) to provide insight into macroscopic effects of premelting. As a result, a two-step mechanism of premelting in n-octanol was established based on experimental data. It was postulated that it consists of a rotator state formation followed by the surface premelting. In order to shed light onto molecular-level processes, classical molecular dynamics (MD) was performed to investigate the time evolution of the changes in metric parameters as a function of simulation temperature. The applied protocol enabled simulations in the solid state as well as in the liquid (the collapse of the ordered crystal structure). The exact molecular motions contributing to the rotator state formation were obtained, revealing an enabling of the rotational freedom of the terminal parts of the chains. The Car–Parrinello molecular dynamics (CPMD) was applied to support and interpret experimental spectroscopic findings. The vibrational properties of the stretching of OH within the intermolecular hydrogen bond were studied using Fourier transformation of the autocorrelation function of both dipole moments and atomic velocity. Finally, path integral molecular dynamics (PIMD) was carried out to analyze the quantum effect’s influence on the bridged proton position in the hydrogen bridge. On the basis of the combined experimental and theoretical conclusions, a novel mechanism of the bridged protons dynamics has been postulated—the interlamellar hydrogen bonding pattern, resulting in an additional OH stretching band, visible in the solid-state experimental IR spectra.

Pretransitional and premelting effects in menthol

To canonic features of melting/freezing discontinuous phase transitions, one can encounter the lack of pretransitional effects in the liquids state and weak premelting effects with non-defined temperature evolutions in the crystalline state. This report shows the evidence for long-range and critical-like pretransitional effects in liquid menthol for electrooptic Kerr effect (EKE) and nonlinear dielectric effect (NDE). These methods are inherently associated with a strong electric field.The premelting effect, with well-defined temperature evolution, was evidenced in the crystalline state. Model explanations of these phenomena are proposed. For the premelting effect, the ‘reversed’ Mossotti-Catastrophe behavior is suggested.

Indicators of premelting in 1-decanol and 1-nonanol studied by FTIR spectroscopy

In this paper, the use of FTIR spectroscopy as a way of studying the premelting behavior of n-nonanol and n-decanol is discussed. The OH and CH stretching vibrations were analyzed, and compared with the results obtained from the CH2 rocking vibrations band (frequently employed in the detection of rotator state and surface premelting), and the previous results of the authors from the nonlinear dielectric effect method. It was determined that the selected regions of IR spectra were sensitive to pretransitional changes. In n-decanol, a wider range of pretransitional changes was observed, consistent with the formation of rotator state followed by surface premelting. It was confirmed by the changes in the CH2 rocking band. In nonanol, no signs of rotator state formation were found, with only surface premelting present.

Supercritical anomalies in liquid ODIC-forming cyclooctanol under the strong electric field

The evidence for long-range pretransitional effects in the liquid phase of ODIC-forming cycloctanol is presented. ODIC means ‘orientationally disordered crystal’, i.e. the plastic crystalline material in which translation freezing in a crystalline network coexists with the orientational freedom. The mentioned result was obtained using two methods inherently associated with the strong electric field: Electrooptic Kerr Effect (EKE) and Nonlinear Dielectric Effect (NDE). The model-analysis revealed the weakly discontinuous character of ODIC←Liquid phase transition and the possibility of a unified description with the isotropic – nematic/smectic transitions in rod-like liquid crystalline compounds. The extension to precritical effects near the critical consolute point and the gas–liquid critical point is indicated. Results obtained can be considered a potential base for the new generation of supercritical technologies, using ODIC- forming liquids with properties controlled by the electric field.

Long-Range Static and Dynamic Previtreous Effects in Supercooled Squalene—Impact of Strong Electric Field

This article presents evidence for the long-range previtreous changes of two static properties: the dielectric constant (ε) and its strong electric field related counterpart, the nonlinear dielectric effect (NDE). Important evidence is provided for the functional characterizations of ε(T) temperature changes by the ‘Mossotti Catastrophe’ formula, as well as for the NDE vs. T evolution by the relations resembling those developed for critical liquids. The analysis of the dynamic properties, based on the activation energy index, excluded the Vogel–Fulcher–Tammann (VFT) relation as a validated tool for portraying the evolution of the primary relaxation time. This result questions the commonly applied ‘Stickel operator’ routine as the most reliable tool for determining the dynamic crossover temperature. In particular, the strong electric field radically affects the distribution of the relaxation times, the form of the evolution of the primary relaxation time, and the fragility. The results obtained in this paper support the concept of a possible semi-continuous phase transition hidden below Tg. The studies were carried out in supercooled squalene, a material with an extremely low electric conductivity, a strongly elongated molecule, and which is vitally important for biology and medicine related issues.

New experimental approach to nonlinear dielectric effects in the static limit

We present a nonlinear dielectric technique that measures the real and imaginary component of permittivity in a time resolved fashion for a sequence of high field amplitudes. Data is recorded within a few milliseconds of exposing the sample to sinusoidal fields without dc-bias. This short exposure time and a sample thickness of only 10 μm greatly reduces heating effects. The Piekara factor quantifying the nonlinear dielectric effect can be derived from analyzing the response at both the fundamental and the third harmonic frequency, and for both quantities the near quadratic field dependence is verified. The small deviations from the expected field dependence are ascribed to a resolved fifth harmonic response. In this manner, the nonlinear dielectric effect of the polar glass-forming liquid propylene glycol is determined in the static limit, and it is found that the Piekara factor changes from −2.9 × 10−16 V−2 m2 to −1.4 × 10−16 V−2 m2 when the temperature is raised from 204 K to 235 K.

Quantifying dielectric permittivities in the nonlinear regime

In contrast to the static dielectric permittivity, ε, associated with linear response, its high-field counterpart, ε E , is not a material specific quantity, but rather depends on the experimental method used to determine the nonlinear dielectric effect (NDE). Here, we define ε E in a manner consistent with how high field permittivities are typically derived from a capacitance measurement using high voltages. Based upon characterizing the materials nonlinear behavior via its third order susceptibility, χ 3, the relations between a given χ 3 and the observable ε E is calculated for six different experimental or theoretical approaches to NDEs in the static limit. It is argued that the quantity χ 3 is superior over ε E or the Piekara factor, (ε E − ε)/E 2, because it facilitates an unambiguous comparison among different experimental techniques and it provides a more robust connection between experiment and theory.

Interfacial, Electroviscous, and Nonlinear Dielectric Effects on Electrokinetics at Highly Charged Surfaces.

The dielectric constant and the viscosity of water at the interface of hydrophilic surfaces differ from their bulk values, and it has been proposed that the deviation is caused by the strong electric field and the high ion concentration in the interfacial layer. We calculate the dependence of the dielectric constant and the viscosity of bulk electrolytes on the electric field and the salt concentration. Incorporating the concentration and field-dependent dielectric constant and viscosity in the extended Poisson–Boltzmann and Stokes equations, we calculate the electro-osmotic mobility. We compare the results to literature experimental data and explicit molecular dynamics simulations of OH-terminated surfaces and show that it is necessary to additionally include the presence of a subnanometer wide interfacial water layer, the properties of which are drastically transformed by the sheer presence of the interface. We conclude that the origin of the anomalous behavior of aqueous interfacial layers cannot be found in electrostriction or electroviscous effects caused by the interfacial electric field and ion concentration. Instead, it is primarily caused by the intrinsic ordering and orientation of the interfacial water layer.

Characterization of isooctane/AOT/water reverse micelles by dielectric spectroscopy, dynamic light scattering and acoustic methods

Reverse micelles are complex systems, where polar phase is enclosed in surfactant shell surrounded by non-polar solvent (water-in-oil microemulsion). Our previous studies proved their large sensibility to an external electric field and revealed a presence of pronounced maximum in the non-linear dielectric effect measured in function of concentration of water. The results obtained previously do not allow for an unequivocal explanation of the observed maximum. In this paper the micellar system of isooctane/sodium docusate (AOT)/water was investigated by dielectric spectroscopy, non-linear dielectric effect, dynamic light scattering and acoustic methods. The measurements were performed along pathways of constant AOT-to-isooctane ratios. The existence of maximum of the nonlinear dielectric effect investigated in function of water content was confirmed. It was shown that the maximum occurs for mixtures for which the molar ratio of water to surfactant (w0) is 10. Strong maxima were also observed in the measurements of electric permittivity and conductivity. The maxima were found for the same concentrations as those for non-linear dielectric effect. Sound velocity and dynamic light scattering studies do not evince any anomalies in the mixtures under discussion. No convincing evidence has been found that the maxima noticed in dielectric studies are related to critical phenomena. They were interpreted basing on the percolation effect, but not all the observed properties can be explained in this way.

Premelting Phenomena in n-Alcohols from Nonanol to Dodecanol

The nonlinear dielectric effect (NDE) measurements of nonanol, undecanol, and dodecanol in the vicinity of the melting point were performed to examine and to develop the hypothesis on pretransition...

Mechanical and dielectric response within and beyond the linear regime

In this work a comparison of dielectric and mechanical data is presented based on experiments within the linear response limit and beyond that limit. The linear dynamic and shear-mechanical response is discussed in terms of the molecular supercooled liquid tetramethyl-tetraphenyl-trisiloxane. As the dynamics measured by the two methods depict the same temperature-dependence, the underlying cause for the observed responses is assumed to be identical for both methods, namely structural relaxation. The comparison of dielectric and mechanical measurements under high excitation amplitudes reveals that this cannot be assumed for the nonlinear response: Mechanical experiments on metallic glasses suggest that involved energies are clearly beyond kBT, with observed nonlinear effects based on the activation of microstructural plastic rearrangements. In contrast, nonlinear dielectric measurements on another molecular glass-former involve energies clearly below kBT, so that nonlinear dielectric effects occur due to energy uptake from the electric field or entropy-based changes in the dynamics, but are very unlikely connected to the triggering of plastic rearrangements by the applied electric field.

Impact of Pressure on Low-Molecular Weight Near-Critical Mixtures of Limited Miscibility.

Near-critical mixtures of limited miscibility are significant for chemical physics, soft matter physics, and a variety of challenging applications. Their basic properties can be tuned by compressing or a systematic change of one of the components. This report addresses these issues, based on experimental studies in nitro-compound (nitrobenzene, o-nitrotoluene, and 1-nitropropane) and n-alkane (from pentane to eicosane) critical mixtures. Studies reveal new patterns for the evolution of the critical consolute temperature (TC) and concentration (xC, mole fraction) within the tested homologous series: TC(n) ∼ n2 and xC(n) ∼ n1/2. They also show two paths of the high-pressure impact: (i) dTC(P)/dP > 0 and overlapping of normalized TC(P) dependences and (ii) the crossover dTC(P)/dP < 0 → dTC(P)/dP > 0 with increasing n-alkane length. The consistent parameterization of all TC(P) dependencies is introduced. Supplementary nonlinear dielectric effect studies indicate a possible molecular origin of the phenomenon. The coexistence curve under high pressure is in the agreement with the isomorphism postulate for critical phenomena but with a surprisingly strong distortion from the Cailletet–Mathias law of the rectilinear diameter. The new and reliable method for estimating the critical concentration and temperature is proposed. It explores the analysis of relative volumes occupied by coexisting phases.

‘Quasi-Tricritical’ and Glassy Dielectric Properties of a Nematic Liquid Crystalline Material

Results of dielectric studies in the nematic and isotropic liquid phases of pentylcyanobiphenyl (5CB), a model rod-like liquid crystalline material, are shown. They are based on the discussion of the evolution of dielectric constant ( ε ), its changes under the strong electric field (nonlinear dielectric effect, NDE), and finally, the primary relaxation time. It is shown that changes in ε T and NDE are entirely dominated by the impact of pretransitional fluctuations (pre-nematic and pre-isotropic, respectively) which are associated with the weakly discontinuous character of the isotropic–nematic phase transition. This influence also extends for the low-frequency, ionic species dominated, region. Notable, that the derivative-based and distortions sensitive analysis revealed the tricritical nature of the I-N transition. Although the glass transition in 5CB occurs in the deeply supercooled state at T g ≈ − 68 ° C , the dynamics (changes of the primary relaxation time) follow a previtreous pattern both in the isotropic and in the nematic phase. Finally, the discussion of the ’molecular’ vs. ‘quasi-critical’ characterizations of the isotropic and nematic phases is presented. It shows the evident prevalence of the ‘quasi-critical-picture’, which offers the consistent temperature parameterization in the total tested temperature range.

Non-linear dielectric effect in reverse micelles system

Reverse micelles are macromolecular systems consisting of highly polar and non-polar components. External electric field should significantly affect their structure and properties. The non-linear dielectric effect (NDE) measurements of the isooctane/water/AOT ternary system were carried out. Extremely large positive response was noted. A mechanism describing the response of the system on a strong electric field is connected with a movement of ions inside the micelles. A pronounced maximum of the NDE effect was also found in a region of stability of reverse micelles. It was explained by precritical phenomena.