Dipolar Relaxation Research Articles

Electrical properties of 0.7Na0.5Bi0.5TiO3-0.2SrTiO3-0.1BaTiO3 lead free ceramic: An Off-Morphotropic phase boundary composition

Probing in to the electrical behavior of ceramics is very essential for casting them in to real life applications. In this work, we report the temperature dependence of dielectric permittivity and impedance spectroscopic studies of 0.7Na0.5Bi0.5TiO3-0.2SrTiO3-0.1BaTiO3 to investigate its electrical properties. A Lorentz type law was found to well describe the diffused permittivity peak by two independent fitting processes. Such a peculiarity was related to the temperature response of the PNRs. This was ascertained from the temperature and frequency dependent Z* and M′′ spectra respectively. Combined graphs of normalized Z′′(f) and M′′(f) in the range 50 – 200 °C predict short ranged dipolar relaxations within the grains.

Elucidation of the Mechanism of Phase Transition in a Zinc Formate Framework Templated by a Diammonium Cation—Structural, Phonon and Dielectric Studies

In this paper we present the synthesis method and a detailed description of the crystal structure, as well as thermal, dielectric and phonon properties, of the [CH3NH2CH2CH2NH2CH3][Zn2(HCOO)6] (dmenH2-Zn) metal organic framework. The negative charge of the anionic framework ([Zn2(HCOO)6]2-) is balanced by N,N′-dimethylethylenediamine (dmenH22+) ions located in the voids of the framework. Thermal analysis revealed that dmenH2-Zn underwent a reversible structural phase transition at around room temperature (Tc~300 K). The single-crystal X-ray diffraction showed that dmenH22+ templates were dynamically disordered at 295 K, since N-H…O bonds were too weak to surmount their thermally activated motions. Reduction in the temperature resulted in ordering of the dmenH22+ cations as a consequence of freezing of their reorientational movements. This behavior caused a symmetry change from P-31c (trigonal) to C 2/c (monoclinic). The mechanism of the observed phase transition of dmenH2-Zn compound was also investigated by temperature-dependent IR measurements. These spectroscopic studies showed that the ordering of the dmenH22+ ions also resulted in the distortion of the anionic framework. Dielectric investigations revealed the occurrence of the dipolar relaxation process clearly defined in the monoclinic phase. The asymmetric shape of the studied process, which indicated a non-Debye-like relaxation, was analyzed using the Havriliak–Negami relaxation function, leading to an Ea value of approximately 0.36 eV.

Dielectric properties of fresh rabbit meat in the microwave range.

Dielectric properties (DPs) of fresh rabbit meat in the microwave range (0.5 to 20GHz) were determined. Three different muscles (Biceps femoris, Tensor fasciae latae, and Longissimus thoracis) from California rabbits (male and female) were measured with the open-ended coaxial probe method at temperatures of 20, 40, and 60 °C. To assess the possible effect of age, females of 100 and 180 days old were analyzed. DPs were affected by frequency, muscle type, age, gender, and temperature (p<0.05). Dielectric constant decreased with increasing frequency. Loss factor decreased from 0.5 to 2.5GHz due to ionic conduction, followed by an increase up to 20GHz, dominated by dipolar relaxation. PRACTICAL APPLICATION: These results are key parameters for further quality sensing applications and for heating processes of meat rabbit using microwaves. Longer penetration depths were achieved at 915MHz; this frequency is recommended for further applications. Besides, dielectric properties have potential to be a tool for identification of gender and age for slaughtered rabbits.

Sulfur‐doped biomass‐derived hollow carbon microtubes toward excellent microwave absorption performance

Micro/nanocarbon materials have been regarded as one of the most desirable microwave absorbents due to their unique physical and chemical properties, whereas their unsatisfactory intrinsic complex permittivity and poor impedance matching severely hinder the further application in microwave adsorption. Herein, novel sulfur-doped hollow carbon microtubes (S-HCMTs) are successfully prepared through a facile one-step pyrolysis process using poplar catkin as a carbon precursor and sulfur powder as a doping agent. The poplar catkin-derived carbon materials exhibit a novel hollow microtubular structure, which is hard to be realized by the conventional chemical synthesis, and meanwhile the one-dimensional hollow structure can be well preserved after the sulfur doping treatment. Note that the introduction of sulfur atoms is beneficial to the adjustment of the electrical conductivity, thereby leading to superior impedance matching characteristics and dipolar relaxation loss capacity in comparison with pure hollow carbon microtubes (HCMTs). The as-obtained S-HCMTs exhibit excellent microwave absorption performance. The minimum reflection loss (RLmin) of S-HCMTs is as high as − 37.4 dB at 6.72 GHz, and the broadest effective absorption bandwidth reaches 8.0 GHz. The high-efficiency microwave absorption is mainly originated from the unique hollow structures, enhanced dipolar/interfacial polarization, multiple scatterings, as well as the excellent impedance match. The results demonstrate that the S-HCMTs can be considered as a promising candidate in high-performance microwave absorbers integrating lightweight and strong absorption intensity.

Ferroelectric columnar assemblies from the bowl-to-bowl inversion of aromatic cores

Organic ferroelectrics, in which the constituent molecules retain remanent polarization, represent an important topic in condensed-matter science, and their attractive properties, which include lightness, flexibility, and non-toxicity, are of potential use in state-of-the-art ferroelectric devices. However, the mechanisms for the generation of ferroelectricity in such organic compounds remain limited to a few representative concepts, which has hitherto severely hampered progress in this area. Here, we demonstrate that a bowl-to-bowl inversion of a relatively small organic molecule with a bowl-shaped π-aromatic core generates ferroelectric dipole relaxation. The present results thus reveal an unprecedented concept to produce ferroelectricity in small organic molecules, which can be expected to strongly impact materials science.

Quantitative Examination of Changes in Fluidity and Cholesterol Content in Bovine Aortic Endothelial Cells using Phasor Analysis of Laurdan Fluorescence Lifetime

Cholesterol is important for maintaining cell membrane integrity and is known to have an effect on the function of ion channels in endothelial cells. Here, we use the properties of Laurdan to investigate how various cellular cholesterol manipulations, altering membrane fluidity and adding a cholesterol analog affect physical properties of bovine aortic endothelial cells (BAEC). Laurdan, a solvatochromic dye, has a spectral red shift in its emission when in a more liquid disordered (Ld) phase compared to a liquid ordered phase (LO). BAECs labeled with Laurdan were treated with methyl-ß-cyclodextrin (MßCD) to remove cholesterol, MßCD saturated with cholesterol to enrich cholesterol content, the cholesterol analog epicholesterol, or fluidizing alcohols benzyl alcohol (BA) or dodecanol and compared to BAECs treated with PBS+Ca2+ as a control. Two-photon excitation was used to excite Laurdan and lifetime measurements were compared at two emission channels (‘blue channel’ and ‘green channel’) in order to differentiate between changes in membrane fluidity and cholesterol content using two methods: traditional phasor analysis and a multiparametric distance analysis using phasor data. Treatment with MßCD, BA and dodecanol resulted in a shift to shorter lifetimes in the blue channel, indicative a more polar (Ld) environment, while enriching cells with cholesterol shifted phasors to longer lifetimes. In the green channel, the phasors of cholesterol enriched cells were shifted in the direction that corresponds to an increase in dipolar relaxation. Only treatment with a higher concentration of MßCD caused a shift in the opposite direction. Using Laurdan and phasor analysis to distinguish changes in fluidity from changes in cholesterol gives us the ability to manipulate these parameters to assist in determining the mechanisms by which cholesterol can impair cell signaling processes.

Investigation of Temperature Dependence of Protein Solutions by NMR Spectroscopy

In this work, the proton spin–lattice (T1) and spin–spin (T2) relaxation times of aqueous solutions of bovine serum albumin (BSA) were investigated as a function of temperature. The T1 relaxation times were measured versus temperature (T) for five H2O solutions containing different BSA concentrations. The sample temperature was varied from 304 to 253 K for each concentration. T2 measurements were carried out versus the BSA concentrations only. The least-square fitting of ln(T1) versus T−1 yields a linear correlation. The effective correlation times $$\tau_{1}$$ for T1 and $$\tau_{2}$$ for T2 were calculated by using experimental data and the related theory. The data suggest that surface water is responsible for the dipolar relaxation mechanisms. Both T1 and T2 mechanisms are caused by overall tumbling of albumin molecule causing the rotational correlation time. However, some slow motions may contribute to the T2 mechanism.

LAURDAN since Weber: The Quest for Visualizing Membrane Heterogeneity.

Any chemist studying the interaction of molecules with lipid assemblies will eventually be confronted by the topic of membrane bilayer heterogeneity and may ultimately encounter the heterogeneity of natural membranes. In artificial bilayers, heterogeneity is defined by phase segregation that can be in the nano- and micrometer range. In biological bilayers, heterogeneity is considered in the context of small (10-200 nm) sterol and sphingolipid-enriched heterogeneous and highly dynamic domains. Several techniques can be used to assess membrane heterogeneity in living systems. Our approach is to use a fluorescent reporter molecule immersed in the bilayer, which, by changes in its spectroscopic properties, senses physical-chemistry aspects of the membrane. This dye in combination with microscopy and fluctuation techniques can give information about membrane heterogeneity at different temporal and spatial levels: going from average fluidity to number and diffusion coefficient of nanodomains. LAURDAN (6-dodecanoyl-2-(dimethylamino) naphthalene), is a fluorescent probe designed and synthesized in 1979 by Gregorio Weber with the purpose to study the phenomenon of dipolar relaxation. The spectral displacement observed when LAURDAN is either in fluid or gel phase permitted the use of the technique in the field of membrane dynamics. The quantitation of the spectral displacement was first addressed by the generalized polarization (GP) function in the cuvette, a ratio of the difference in intensity at two wavelengths divided by their sum. In 1997, GP measurements were done for the first time in the microscope, adding to the technique the spatial resolution and allowing the visualization of lipid segregation both in liposomes and cells. A new prospective to the membrane heterogeneity was obtained when LAURDAN fluorescent lifetime measurements were done in the microscope. Two channel lifetime imaging provides information on membrane polarity and dipole relaxation (the two parameters responsible for the spectral shift of LAURDAN), and the application of phasor analysis allows pixel by pixel understanding of these two parameters in the membrane. To increase temporal resolution, LAURDAN GP was combined with fluctuation correlation spectroscopy (FCS) and the motility of nanometric highly packed structures in biological membranes was registered. Lately the application of phasor analysis to spectral images from membranes labeled with LAURDAN allows us to study the full spectra pixel by pixel in an image. All these methodologies, using LAURDAN, offer the possibility to address different properties of membranes depending on the question being asked. In this Account, we will focus on the principles, advantages, and limitations of different approaches to orient the reader to select the most appropriate technique for their research.

Achieving super-broad effective absorption bandwidth with low filler loading for graphene aerogels/raspberry-like CoFe2O4 clusters by N doping

A unique three-dimension (3D) porous network structure where N-doped reduced graphene oxide aerogels (N-rGA) are decorated by raspberry-like CoFe2O4 (CFO) clusters. Super-broad effective microwave absorption bandwidth (7.28 GHz) of the CFO/N-rGA composite is obtained at 2.53 mm by changing N contents. Here, the dipolar relaxation loss and conduction loss are highly sensitive to the presence of pyridinic, pyrrolic and graphitic N in the CFO/N-rGA composites. A minimum reflection loss of the CFO/N-rGA composites reaches up to −55.43 dB at 15.36 GHz with a matching thickness (2.3 mm) and low filler loading (10 wt%). Its effective absorption bandwidth completely covers X-band from 7.76 to 12.72 GHz at 3.3 mm. The high-efficiency microwave absorption of the composites mainly results from the enhanced polarization relaxation, the specific design of conductive network and the superior impedance matching. This study offers a promising technical route to explore new N-doped magnetic/dielectric composites as ideal microwave absorbers.

Dipolar relaxation in thin films of supramolecular stacks of benzenecarboxamides and insights to enhance their ferroelectric characteristics.

The relationship between molecular structure and ferroelectric behaviour of thin films is explored in an all-organic supramolecular polymer material based on benzenecarboxamides, using atomistic molecular dynamics simulations. While increasing the number of amide groups around the phenyl core increases the dipole density of a molecule, increasing the length of the corresponding alkyl groups decreases the same. The interplay between these two contributions displays a rich behaviour on key material characteristics, in particular, the polarisation retention time. The latter is shown to be inversely proportional to the alkyl chain length, a consequence of weaker interactions between macrodipoles of stacks. Polarisation retention time was observed to be the highest in a molecule with five amide groups around the aromatic phenyl core which is explained as due to the large barrier for amide group rotation, which is one of the crucial channels for dipolar relaxation. Simulations also demonstrate that the barrier, however, does not affect the switchability of polarization, upon field reversal.

Dielectric and thermal stability studies on high density polyethylene – Chitosan composites plasticized with palm oil

HDPE-chitosan composites (HC) prepared using maleic anhydride as compatibilizer and palm oil as plasticizer have been subjected to dielectric characterization and thermal studies. At a lower frequency HC films were seen to exhibit an increasing dielectric constant due to interfacial polarization of the chitosan. This increase in dielectric loss with increasing concentration of chitosan indicated the presence of relaxing dipoles in the system. The addition of palm oil to the optimised HC5 system showed improved segmental mobility due to the interaction of polar amine group in chitosan with HDPE. The thermal stability and activation energy of the composites were computed using Coats- Redfern model.

Dipole relaxation process and giant dielectric permittivity in Eu3+-doped CdMoO4 single crystal

Single crystal of Eu3+-doped cadmium molybdate (Cd0.9268▯0.0244Eu0.0488MoO4, where ▯ denotes cationic vacancies) has been successfully grown by the Czochralski method in air and under 1 MPa. X-ray diffraction analysis indicates that as-grown single crystal exhibits tetragonal scheelite-type structure (a = b = 5.16188(14) Å; c = 11.2080(5) Å; space group I41/a). Eu3+ ions do not show long-range order and they are randomly distributed in CdMoO4 framework substituting Cd2+ ones. UV–vis diffuse reflectance measurements revealed very close optical band gap (Eg) values, i.e. ∼1.74 eV along [100] and [001] crystallographic directions that are twice smaller than Eg of microcrystalline pure CdMoO4 as well as powder Eu3+-doped single crystal. Magnetic and electrical studies of Eu3+-doped cadmium molybdate single crystal showed a paramagnetic and n-type semiconducting behaviour with the metal-insulator transition above 350 K along both crystallographic directions. Dielectric results analysis using the Cole-Cole fit function revealed that the dipole relaxation process has different time scale depending on the crystallographic direction and exhibits Arrhenius temperature dependence for both studied directions. This fact is accompanied by the colossal dielectric permittivity with εr > 8⋅103. The above results are considered in the framework of narrow europium multiplets of energy comparable to thermal energy.

Low cost 3D bio-carbon foams obtained from wheat straw with broadened bandwidth electromagnetic wave absorption performance

Bio-derived dielectrics have drawn extensive attention for microwave absorption and shielding because of renewability and environmental friendliness. In this work, foam-like bio-carbon has been obtained from wheat straw waste and its microwave absorption performance has been studied. By controlling the precursor ratio of KOH, the optimized morphology of bio-carbon has been realized. The 3D carbon foam obtained at 600 °C with KOH and biomass ratio 1:1 (AC-600 (1:1), presents decent microwave reflection loss. Especially, with a low absorber ratio (10 wt%), the effective absorption bandwidth (RL < -10 dB) can reach 8.8 GHz (7.2–16 GHz) at a matching thickness of 2.5 mm. 3D porous network, interface effect, defects in carbon network, and dipolar relaxation make a good contribution towards broadband and excellent reflection loss. The eco-friendly, lightweight, and low-cost bio-carbon foam has great application prospects of microwave absorption.

Efficient generation of triangular optical pulses in an erbium-doped chalcogenide fiber amplifier by exploiting the time transformation technique.

The time transformation (TT) technique is used to study the nonlinear pulse reshaping towards triangular pulse (TP) generation by efficiently optimizing the pulse parameters in an erbium-doped chalcogenide fiber amplifier (EDCFA), for the first time, to the best of our knowledge. The effects of input chirp parameter, optical gain, and dipole relaxation time are also depicted in the context of TP generation. The results obtained from the TT approach when compared with that from the nonlinear Schrodinger equation show excellent agreement. The study also reveals that spectral pulse doubling can be achieved at a shorter length when a pre-chirped Gaussian pulse is propagated through the proposed EDCFA.

Calmodulin binds to Drosophila TRP with an unexpected mode

Drosophila TRP is a calcium-permeable cation channel essential for fly visual signal transduction. During phototransduction, Ca2+ mediates both positive and negative feedback regulation on TRP channel activity, possibly via binding to calmodulin (CaM). However, the molecular mechanism underlying Ca2+ modulated CaM/TRP interaction is poorly understood. Here, we discover an unexpected, Ca2+-dependent binding mode between CaM and TRP. The TRP tail contains two CaM binding sites (CBS1 and CBS2) separated by an ∼70-residue linker. CBS1 binds to the CaM N-lobe and CBS2 recognizes the CaM C-lobe. Structural studies reveal the lobe-specific binding of CaM to CBS1&2. Mutations introduced in both CBS1 and CBS2 eliminated CaM binding in full-length TRP, but surprisingly had no effect on the response to light under physiological conditions, suggesting alternative mechanisms governing Ca2+-mediated feedback on the channel activity. Finally, we discover that TRPC4, the closest mammalian paralog of Drosophila TRP, adopts a similar CaM binding mode.

High dielectric permittivity and low temperature ferroelectric-phase-transition in Bi1-x(Sr0·5Pb0.5)xFeO3

Bi1-x(Sr0·5Pb0.5)xFeO3 with x = 0.1 and 0.3 were synthesized by solid-state reaction method. The dielectric properties of the samples have been investigated in the temperature range from −100 to 300 °C. The colossal dielectric constant (CDC) behavior was observed in temperature range from 50 to 200 °C and frequency range from 102 Hz to 103 Hz. The CDC behavior is composed of two relaxation processes with the lower temperature relaxation being a dipolar relaxation caused by the hopping of oxygen vacancies and the higher temperature one being a Maxwell-Wagner relaxation caused by hopping oxygen vacancies blocked by grain boundaries. In the temperature range beyond 200 °C, a ferroelectric-phase-transition-induced dielectric anomaly with an extremely huge intensity over 106 was observed in both samples. (Sr, Pb) co-doping in the place of Bi significantly shift the Curie temperature towards a low temperature of 263 and 243 °C for the samples with x = 0.1 and 0.3, respectively.

Unique Dynamics of Water Confined on the Surface of Metal Oxide Clusters.

Water confined on metal oxide surface plays significant roles in heterogeneous catalysis. Heteropolyacid, a 1.2 nm-metal oxide cluster with well-defined structure, is applied as a model to understand the dynamics of water on its surface. The surface water strongly associates with heteropolyacid cluster and form the so-called 'pseudoliquid phase' where catalytic reactions are conducted. Broadband dielectric spectroscopy and differential scanning calorimetry have been applied to probe the dynamics of water in this pseudoliquid phase. A supercooling phase transition of water below its normal melting temperature and a dipolar glassy relaxation behaviour due to the hindered dynamics of water have been observed. The rich dynamic behavior on the surface of such well-defined metal clusters provide new perspectives to understand the properties of surface water and their relation to catalytic performance of heteropolyacid.

Electrical and magnetic properties of ZnCr2S4 – nanoparticles

The results of magnetic and electrical measurements of ZnCr2S4 – nanoparticles (NPs) synthesized by mechanical alloying method showed an almost ideal paramagnetic state with the weak ferromagnetic short-range interactions derived from a small positive paramagnetic Curie-Weiss temperature of θ = 0.9 K and the presence of magnetic NPs confirmed by the significantly lower value of the effective magnetic moment (μeff = 2.089 μB/f.u.) compared to the μeff = 5.215 μB/f.u. for bulk spinel as well as n-type semiconducting behavior with an extrinsic region not thermally activated and with an intrinsic region with an activation energy of 0.253 eV. Broadband dielectric spectroscopy measurements showed the relaxation processes only in the intrinsic region of the electrical conductivity, i.e. above 170 K, in which the dipole relaxation becomes faster as temperature rise. These results are interpreted in the framework of the Cole-Cole function and a hopping variable range model including structural defects.

Role of Chain Polarity on Ion and Polymer Dynamics: Molecular Volume-Based Analysis of the Dielectric Constant for Polymerized Norbornene-Based Ionic Liquids

Norbornene-based polymerized ionic liquids (PILs) were systematically prepared to understand the role of PIL architecture and linker on the ionic conductivity (σDC), segmental dynamics, and dielectric constant. In PILs with two- or one-armed imidazolium (Im⁺)-bis(trifluoromethanesulfonyl)imide (Tf₂N–) pendants, their dynamics and polarity were tuned by incorporating either oxyethylene [(OCH₂CH₂)ₓ = (OE)ₓ, x = 1 or 3] or alkylene [(CH₂)₂] moieties as linkers between the norbornene and imidazolium cation moieties and ethyleneoxy [(CH₂CH₂O)y = (EO)y, y = 2 or 3] terminal units on the imidazolium. All PILs exhibit three dipolar relaxations; the local chain β motions of the PIL pendants were observed below the glass transition temperature (Tg), while above Tg, the segmental α and slower ionic rearranging α₂ relaxations were observed. Unlike the alkylene linker, the OE linker incorporation speeds up the α and α₂ relaxations (consistent with the decrease in Tg), increases the relaxation strengths [leading to an increase in the static and Coulombic dielectric constants (eₛ and eC)], imparts a higher number density of simultaneously conducting ions (p), and boosts their mobility (μ). This is directly reflected in the OE-containing PILs having 10 times higher ionic conductivities (σDC) than the PIL with the alkylene linker. The Tg, eₛ, and σDC are significantly influenced by the repeat unit molecular volume (Vₘ), polarizability volume (Vₚ), and Keesom volume (VK), suggesting that the OE linker not only facilitates ion dissociation of Im⁺Tf₂N– but also promotes segmental motion, thereby leading to a strong correlation of ionic conductivity with the dielectric constant and glass transition temperature.

NMR Intermolecular Dipolar Cross-Relaxation in Nanoconfined Fluids.

Spin relaxation, a defining mechanism of nuclear magnetic resonance (NMR), has been a prime method for determining three-dimensional molecular structures and their dynamics in solution. It also plays key roles for contrast enhancement in magnetic resonance imaging (MRI). In bulk solutions, rapid Brownian molecular diffusion modulates dipolar interactions between a spin pair from different molecules, resulting in very weak intermolecular relaxations. We show that in fluids confined in nanospace or nanopores (nanoconfined fluids) the correlation of dipolar coupling between spin pairs of different molecules is greatly enhanced by the nanopore constraint boundaries on the molecular diffusion, giving rise to an enhanced correlation for the spin pair. As a result, the intermolecular dipolar interaction behaves cooperatively, which leads to a large intermolecular dipolar relaxation rate and opposite in sign to the bulk solution. We found that the classical NMR relaxation theory fails to capture these observations in a nanoconfined fluid environment. Hence, we developed a formal theory and experimentally confirmed that enhanced correlation and cooperated relaxation are ubiquitous in nanoconfined fluids. The newly discovered phenomenon and the developed NMR method reveal new applications in a broad range of synthesized and naturally occurring materials in the field of nanofluidics to study molecular dynamics and structure as well as for MRI image enhancement.