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The dielectric function of a dipolar liquid exhibits a strong wavenumber dependence in the bulk homogeneous state. Such a behavior seems to suggest the possibility of a strong system size dependence of the dielectric constant (DC) of a nanoconfined liquid, although details have been revealed only recently. The dielectric properties of nanoconfined water, indeed, show a marked sensitivity not only to the size and shape (dielectric boundaries) of confinement but also to the nature of surface–water interactions. For geometries widely studied, namely, water confined in a narrow slit, nanocylinder, and nanospherical cavity, the asymptotic approach to the bulk value of the DC with the increase in confinement size is found to be surprisingly slow. This seems to imply the appearance of a dipolar cross correlation length, much larger than the molecular length-scale of water. In narrow slits and narrow cylinders, the dielectric function becomes both inhomogeneous and anisotropic, and the longitudinal and transverse components display markedly different system size dependencies. This sensitivity can be traced back to the dependence of the DC on the ratio of the mean square dipole moment fluctuation to the volume of the system. The observed sensitivity of collective dipole moment fluctuations to the length scale of confinement points to the possibility of using DC to estimate the orientational correlation length scale, which has been an elusive quantity. Furthermore, the determination of volume also requires special consideration when the system size is in nanoscale. We discuss these and several other interesting issues along with several applications that have emerged in recent years. [ABSTRACT FROM AUTHOR]

When using metal–organic frameworks (MOFs) as electric field-dependent sensor devices, understanding their dielectric response is crucial as the orientation of polar groups is largely affected by confinement. To shed light on this at the molecular level, the response to a static field was computationally investigated for two structurally related MOFs, depending on their loading with guest molecules. The pillared-layer MOFs differ in their pillar moiety, with one bearing a rotatable permanent dipole moment and the other being non-polar. Two guest molecules with and without polarity, namely, methanol and methane, were considered. A comprehensive picture of the response of the guest molecules could be achieved with respect to both the amount and polarity of the confined species. For both MOFs, the dielectric response is very sensitive to the introduction of methanol, showing an anisotropic and non-linear increase in the system's relative permittivity expressed by a strongly increasing polarization response to external electric fields scaling with the number of confined methanol molecules. As expected, the effect of methane in the non-dipolar MOF is negligible, whereas subtle differences can be observed for the dipolar response of the MOF with rotatable dipolar linker groups. Taking advantage of these anisotropic and guest-molecule-specific confinement effects may open pathways for future sensing applications. Finally, methanol-induced global framework dynamics were observed in both MOFs. [ABSTRACT FROM AUTHOR]

The paper presents a method for determining the mutual impedance of two dipoles located on a multilayer dielectric structure. Determining the mutual impedance of linear antennas is a complex issue and it is impossible to obtain an exact solution, it is influenced by many elements (location, dimensions, electrical parameters of the earth, thickness of the substrate, thickness and antenna conductivity, etc.) In the case of antennas on a dielectric substrate, the coupling analysis is even more complicated, because the operation of these antennas is significantly influenced by the occurrence of surface waves conducted through an open dielectric structure. The problem was solved by the method of moments using the Galerkin method as its special case. The work uses a method developed by Richmond for obtaining the elements of the impedance matrix, based on the concept of reaction between sections of the base and testing functions. Their mutual interaction was described by the reaction of the electric field caused by the current flowing through one dipole with the current flowing through the other dipole. Based on this analysis, the mutual impedance of two arbitrarily oriented dipoles located on a multilayer dielectric was determined, where the current distribution and antenna lengths are arbitrary. A computer program was developed that allowed to determine the mutual impedance for freely oriented dipoles. [ABSTRACT FROM AUTHOR]

We present a rigorous framework for fully quantum calculation of the third dielectric virial coefficient Cɛ(T) of noble gases, including exchange effects. The quantum effects are taken into account with the path-integral Monte Carlo method. Calculations employing state-of-the-art pair and three-body potentials and pair polarizabilities yield results generally consistent with the few scattered experimental data available for helium, neon, and argon, but rigorous calculations with well-described uncertainties will require the development of surfaces for the three-body nonadditive polarizability and the three-body dipole moment. The framework, developed here for the first time, will enable new approaches to primary temperature and pressure metrology based on first-principles calculations of gas properties. [ABSTRACT FROM AUTHOR]

The nano-graphite (NG) and acid modified nano-graphite (ANG) have been synthesized from graphite powder via mixture of strong acid (sulphuric acid and nitric acid) respectively by a soft chemistry route involving microwave, ultrasonic method and characterized by high-resolution electron microscopy (HR-TEM), scanning electron microscopy (SEM), fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD), clearly demonstrated the successful synthesis of acid modified NG. SEM images confirmed the surface morphology of NG, and ANG and HR-TEM study shows the nanoparticles size of NG and ANG. FTIR data confirmed the presence of acid functional groups on the surface of synthesized NG powder. XRD data of NG and ANG shows that 2θ is at 26.43° and 0.336 nm is an interlayer distance (d). NG and ANG pellets have been prepared for their dielectric analysis with frequency for different thickness. The dielectric loss tangent (tanδ) spectra show relaxation peak with frequency and peak shifts due to presence of polar groups in the ANG. The capacitance values of NG and ANG decrease with frequency and increase with thicknesses due to the capacitive nature of nanoparticles. The dielectric permittivity decreases with frequency and increases with thickness due to the charge orientation and dipole moment change of functional groups of synthesized NG, and ANG. The electrical conductivity of NG and ANG nanoparticles increases with frequency and thickness of NG and ANG pellets due to the conductive nature. Electrical conductivity and dielectric permittivity of NG and ANG are found to highly rely on thickness, according to the dielectric evaluation. [ABSTRACT FROM AUTHOR]

The use of sulfur hexafluoride (SF6) as an electrical insulator and arc‐quenching gas in high‐voltage equipment raises serious environmental concerns. The search of a replacement gas for SF6 is hindered by a priori assessment on its interruption performance. The routine fluid or mathematic magneto‐hydrodynamic models for arc burning and extinguishing are too complex to be practical for virtual screening. Herein a state‐of‐the‐art quantum chemical model to predict the interruption capability of the dielectric gases straightforwardly has been established in terms of the rate of rise of the recovery voltage (RRRV). On the basis of the molecular electrostatic potentials, five sets of descriptors, including the global statistical parameters vσ2 and Π, the site‐specific parameter ΔVs, the total positive surface area As+, augmented with the product of polarizability and dipole moment αμ, were optimized to reveal the inherent mechanisms for interruption and thus a viable structure–activity relationship mode for RRRV has been developed with the correlation coefficient 0.975. Theoretical RRRV relative to SF6 = 100 for all the known dielectric gases are in good agreement with the experimental data by a mean absolute deviation of 3.6. Accordingly, the perfluorinated cycloalkenes and alkynes, in particular, 1,3,3,3‐tetrafluoropropyne, are found to be the promising candidates as the replacement dielectric gases for SF6. [ABSTRACT FROM AUTHOR]

A series of new liquid crystal compounds with negative dielectric anisotropy was synthesised by regulating the orientation of the substituents on the benzoxazole ring, namely, 5–4-(2-(4-(alkoxy)phenyl)-2,3-difluorophenyl)benzo[d]oxazole derivatives (nPP(2,3)FO). These compounds mainly display enantiotropic nematic mesophases in the ranges of 8.62–16.09°C (heating process) and 23.98–30.32°C (cooling process), moderate birefringence (Δn) ranging from 0.25–0.32 (DFT theoretical calculation) and 0.22–0.28 (experimental measurement), as well as negative dielectric anisotropy (Δɛ) ranging from −2.77 to −2.94. These characterises are ascribed to the larger perpendicular dipole moments and orientation angles of benzoxazole. This work provides new ideas for the rational design of negative dielectric anisotropy liquid crystals. [ABSTRACT FROM AUTHOR]

Structural and dynamical properties of heterocyclic organic compound isatin in the solution state with DMSO has been studied in the frequency region of 10 MHz to 50 GHz over the temperature range of 273.15–298.15 K using time domain reflectometry. High- and low-frequency relaxation has been observed for Isatin + DMSO. The high-frequency relaxation peak is due to free DMSO molecules while low-frequency relaxation peak is attributed to isatin. Dielectric permittivity, static dielectric constant, relaxation time, dipole moment, correlation factor along with thermodynamical parameters have been calculated. Molecular interaction has been discussed broadly under solute–solute, solute–solvent, and solvent–solvent category. [ABSTRACT FROM AUTHOR]

In order to develop a microscopic level understanding of the anomalous dielectric properties of nanoconfined water (NCW), we study and compare three different systems, namely, (i) NCW between parallel graphene sheets (NCW–GSs), (ii) NCW inside graphene covered nanosphere (NCW–Sph), and (iii) a collection of one- and two-dimensional constrained Ising spins with fixed orientations at the termini. We evaluate the dielectric constant and study the scaling of ε with size by using linear response theory and computer simulations. We find that the perpendicular component remains anomalously low at smaller inter-plate separations (d) over a relatively wide range of d. For NCW–Sph, we could evaluate the dielectric constant exactly and again find a low value and a slow convergence to the bulk. To obtain a measure of surface influence into the bulk, we introduce and calculate correlation lengths to find values of ∼9 nm for NCW–GS and ∼5 nm for NCW–Sph, which are surprisingly large, especially for water. We discover that the dipole moment autocorrelations exhibit an unexpected ultrafast decay. We observe the presence of a ubiquitous frequency of ∼1000 cm−1, associated only with the perpendicular component for NCW–GS. This (caging) frequency seems to play a pivotal role in controlling both static and dynamic dielectric responses in the perpendicular direction. It disappears with an increase in d in a manner that corroborates with the estimated correlation length. A similar observation is obtained for NCW–Sph. Interestingly, one- and two-dimensional Ising model systems that follow Glauber spin-flip dynamics reproduce the general characteristics. [ABSTRACT FROM AUTHOR]

We present a new effective medium theory for the dielectric response of mixtures of molecules with molecular polarizability and a permanent dipole moment. This model includes the interaction of each local dipole moment with the dipolar reaction fields of neighboring dipolar molecules. This interaction leads to an enhancement of the dielectric response of the mixture and constitutes an alternative method to describe the correlated motion of dipoles in liquids compared to the models of Fröhlich and Kirkwood. The model requires as input parameters the volume fractions of the components contained in the mixture and the dielectric parameters of the pure components. The results of the model are compared with experimental data and with the results of previous effective-medium theories. [ABSTRACT FROM AUTHOR]

In this work, we develop a method for simulating polar species in the dissipative particle dynamics (DPD) method. The main idea behind the method is to treat each bead as a dumb-bell, i.e., two sub-beads kept at a fixed distance, instead of a point-like particle. The relation between the bead dipole moment and the bulk dielectric permittivity was obtained. The interaction force of single charges in polar liquid showed that the effective dielectric permittivity is somewhat smaller than that obtained for the bulk case at large separation between the charges. In order to understand the reasons behind the observed drop in the dielectric permittivity, we calculate the electric field of an isolated charge in a polar liquid; no permittivity drop is observed for this case. We can assume that the behavior observed for the force is due to the fact that the probing point is always associated with the charged bead, which is a force center, which essentially leads to a non-homogeneous density distribution around it on average; this is not the case when the field is measured. The interaction of a single charge with an interface between two liquids with different permittivities was studied after that; the model is found to correctly reproduce the "mirror image" effects. Finally, we show why it is necessary to treat the polar species in DPD explicitly by investigating the behavior of a charged colloidal particle at a liquid–liquid interface. [ABSTRACT FROM AUTHOR]

The dielectric properties of a composite obtained by embedding a ferroelectric salt Rb2ZnCl4 into a porous glass matrix with an average size of through pores of about 46 nm have been studied within the temperature range of 100–350 K at frequencies of 5–500 kHz. An increase in the dielectric permittivity dispersion depth Δε upon sample cooling, due to an increase in the concentration of "relaxers" and an increase in their dipole moment, was found. An analysis of the dielectric response features showed that a domain structure is formed in the ferroelectric phase of Rb2ZnCl4 particles, the mobility of which in the vicinity of the freezing temperature Tf obeys the empirical Vogel–Fulcher relation. [ABSTRACT FROM AUTHOR]

The dielectric properties of a composite obtained by embedding a ferroelectric salt Rb2ZnCl4 into a porous glass matrix with an average size of through pores of about 46 nm have been studied within the temperature range of 100–350 K at frequencies of 5–500 kHz. An increase in the dielectric permittivity dispersion depth Δε upon sample cooling, due to an increase in the concentration of "relaxers" and an increase in their dipole moment, was found. An analysis of the dielectric response features showed that a domain structure is formed in the ferroelectric phase of Rb2ZnCl4 particles, the mobility of which in the vicinity of the freezing temperature Tf obeys the empirical Vogel–Fulcher relation. [ABSTRACT FROM AUTHOR]

Wide band dielectric spectroscopy of bent-shaped achiral liquid-crystal dimers 1″-n″-bis(4-cyanobiphenyl-4′-yl) n-alkanes (CBnCB n = 7, 9, 11) has been investigated in a frequency range 0.1 Hz–100 MHz using planar-aligned cells of sample thicknesses ranging from 2 to 10 (μm) over a temperature range that covers both nematic and twist bend nematic phases. Two peaks in the dielectric spectrum in the higher frequency range are assigned to the molecular relaxation processes. The peak at the highest frequency, ∼40 to 80 MHz, is assigned to an internal precessional rotation of a single unit of the dimer around the director. The mode in the next lower frequency range of 2–10 MHz is assigned to the spinning rotation of the dimer around its long axis. This involves fluctuations of the dipole moment of the bent-shaped conformation that is directed along its arrow direction of the bow shape formed by the dimer. The peak in the frequency range 100 kHz–1 MHz can be assigned to the collective fluctuations of the local director with reference to the helical axis of the NTB structure. The dependence of its frequency on temperature is reminiscent of the soft mode observed at the SmA* to SmC* phase transition. This result clearly corresponds to the electro-clinic effect—the response of the director to the applied electric field in an electro-optic experiment. The lowest frequency mode, observed in the frequency range of 0.1 Hz–100 Hz, is identified with the Goldstone mode. This mode is concerned with the long range azimuthal angle fluctuations of the local director. This leads to an alternating compression and expansion of the periodic structure of the NTB phase. [ABSTRACT FROM AUTHOR]

Organic crystalline dielectric materials are attractive target in the field of materials chemistry. In their designing strategy, the molecular motion induced by the external dielectric field is required to maximize the polarization effect in the materials to realize a large dielectric constant. Especially, the molecular motion of curved-π aromatics such as C60 and their supramolecular complexes are the known to show characteristic smoothness in the solid state. In this context, we focused on the in-plane motion of the one of the representative buckybowl, sumanene (Sum) in its curve-to-curve-contacted columnar structure as the new platform of the motion for the emergence of dielectric response. The newly designed and synthesized fluorinated sumanene, 1,1-difluorosumanene (F2-Sum), which possesses two fluorine atoms on the same benzylic carbon of pristine sumanene showed a large dipole moment along the in-plane direction. Thermal analyses, variable temperature X-ray diffraction and IR measurements indicated the presence of in-plane motion of F2-Sum although no clear phase transition was involved. This thermal property of F2-Sum realized an anisotropic dielectric response with a Debye-type dielectric relaxation in the single crystalline state. Further trials to form the solid solution of Sum and F2-Sum in various mixing ratio realized the tuning of the dielectric property. [ABSTRACT FROM AUTHOR]

We investigated the effect of gate bias stress (GBS) on the electrical characteristics of ferroelectric oxide thin-film transistors (FeOxTFTs) with poly(vinylidenefluoride-trifluoroethylene). Generally, conventional oxide thin-film transistors (OxTFTs) with dielectric gate insulators exhibit a small negative shift under negative gate bias stress (NBS) and a large positive shift under positive gate bias stress (PBS) in transfer characteristic curves. In contrast, the FeOxTFTs show a small positive shift and a large negative shift under NBS and PBS, respectively. It was confirmed that sufficient changes in the electrical characteristics are obtained by 10 min NBS and PBS. The changed electrical characteristics such as threshold voltage shift, memory on- and memory off-current were maintained for more than 168 h after NBS and 24 h after PBS. It is deduced that, since the dipole alignment of the ferroelectric layer is maximized during GBS, these changes in electrical properties are caused by the remnant dipole moments still being retained during the gate sweep. The memory on- and memory off-current are controlled by GBS and the best on/off current ratio at 107 was obtained after NBS. By repeatedly alternating NBS and PBS, the electrical characteristics were reversibly changed. Our results provide the scientific and technological basis for the development of stability and performance optimization of FeOxTFTs. [ABSTRACT FROM AUTHOR]

High‐electrical‐strength polymer dielectrics are essential for advanced devices with high power and/or high integration densities and film capacitors with high energy‐storage densities. Key factors affecting the polymer dielectric electrical strength are deep‐level defect states, which lead to electron and hole accumulation. Numerous deep‐level defect states lead to charge accumulation in the polymer dielectric during operation, contributing to local electric field distortion and resulting in flashover or breakdown. In this work, first‐principles calculations and experiments reveal that VH (i.e., H vacancies) in the polymer dielectric molecular chain can create defect states deep in the bandgap. RCl (R = Li, Na, K) can be used for passivating the deep‐level polymer dielectric defect states. In addition, the passivation mechanisms are analyzed. The RCl cations can passivate deep‐level defect states into shallow‐level acceptor defect states because the RCl dipole moment regulates the deep‐level defect state energy. The RCl anions can passivate deep‐level defect states into shallow‐level donor defect states by forming a stable covalent bond between carbon and lone‐pair electrons. This work supports the design of high‐electrical‐strength polymer dielectrics. [ABSTRACT FROM AUTHOR]

We present high-level, coupled-mode calculations of the infrared spectrum of the cyclic formic acid dimer. The calculations make use of full-dimensional, ab initio potential energy and dipole moment surfaces. The potential is a linear least-squares fit to 13 475 CCSD(T)-F12a/haTZ (haTZ means aug-cc-pVTZ basis set for O and C, and cc-pVTZ for H) energies, and the dipole moment surface is a fit to the dipole components, calculated at the MP2/haTZ level of theory. The variables of both fits are all (45) internuclear distances (actually Morse variables). The potential, which is fully permutationally invariant, is the one published recently and the dipole moment surface is newly reported here. Details of the fits, especially the dipole moment, and the database of configurations are given. The infrared spectrum of the dimer is calculated by solving the nuclear Schrödinger equation using a vibrational self-consistent field and virtual-state configuration interaction method, with subsets of the 24 normal modes, up to 15 modes. The calculations indicate strong mode-coupling in the C—H and O—H stretching region of the spectrum. Comparisons are made with experiments and the complexity of the experimental spectrum in the C—H and O—H stretching region is successfully reproduced. [ABSTRACT FROM AUTHOR]

Double hybrid (DH) density functionals are amongst the most accurate density functional approximations developed so far, largely due to the incorporation of correlation effects from unoccupied orbitals via second order perturbation theory (PT2). The xDH family of DH functionals calculate energy directly from orbitals optimized by a lower level approach like B3LYP, without self-consistent optimization. XYG3 and XYGJ-OS are two widely used xDH functionals that are known to be quite accurate at equilibrium geometries. Here, we show that the XYG3 and XYGJ-OS functionals can be ill behaved for stretched bonds well beyond the Coulson-Fischer point, predicting unphysical dipole moments and humps in potential energy curves for some simple systems like the hydrogen fluoride molecule. Numerical experiments and analysis show that these failures are not due to PT2. Instead, a large mismatch at stretched bond-lengths between the reference B3LYP orbitals and the optimized orbitals associated with the non-PT2 part of XYG3 leads to an unphysically large non-Hellman- Feynman contribution to first order properties like forces and electron densities. [ABSTRACT FROM AUTHOR]

Hydrogen-bonded liquid crystals (HBLC) formed by mixing 4-alcyloxy-2-fluorobenzoic acid (nOBAF) and the 4-pentyl-4-biphenylcarbonitrile (5CB) at (1:1), (1:3) and (3:1) (mol/mol) ratios have been investigated. Four HBLC series are prepared by changing the carbon chain length from 7 to 10 designated 5CB/nOBAF. The fluorobenzoic acids (nOBAF) are the proton donors while the pyridine unit (5CB) is the proton acceptors. Thermal behaviour and phase diagrams of the individual series have been established using differential scanning Calorimetry (DSC) and polarising optical microscopy (POM). It was found that all complexes exhibit nematic (N) and smectic G (SmG) phases. For the nematic phase, the dielectric anisotropy was increased while the thresholds voltage was decreased. This can be explained by the strong longitudinal dipole moment of the nematic phase compared to the nOBAF compounds. Furthermore, as the alkoxy chain length increases, the birefringence, response time, rotational viscosity, and splay elastic constant all decrease by the way of the reduction of the order parameter for the longer chains. In addition, hydrogen-bonded proton transfer between cyano and carboxylic acid groups have been explored by Fourier transform infrared spectroscopy (FTIR) for the first time. [ABSTRACT FROM AUTHOR]

The report shows the temperature behavior of the real part of dielectric permittivity in the static (dielectric constant) and low-frequency (LF) domains in bulk samples of 11CB and its BaTiO3-based nanocolloids. The study covers the isotropic liquid (I), nematic (N), smectic A (SmA), and solid crystal (Cr) phases. For each phase, the dominance of pretransitional fluctuations, significantly moderated by nanoparticles, is shown. The authors consider separate focuses on the dielectric constant ε T evolution in the static domain, yielding mainly response from permanent dipole moment and its arrangement, and in the low-frequency (LF) domain Δ ε ′ f = ε ′ f - ε (where ε ′ f is for the real part of dielectric permittivity in the LF domain), which is associated solely with ionic-related polarization mechanisms. All of these led to new experimental evidence concerning I–N, N–SmA, and SmA–solid transitions, focusing on the strength and extent of pretransitional effects, critical exponents, and phase transitions discontinuities. The strong evidence for pretransitional effects near the SmA–Cr transition is notable, particularly regarding Δ ε ′ f , T . Studies are supplemented by the discussion of DC electric conductivity—a parameter also related to the LF domain. Finally, the validity of the relation ε ′ f = Af - 3 / 2 + ε (where f stands for frequency, and A is a constant parameter), often used for discussing dielectric spectra in LC compound and its nanocolloids in the LF domain, is examined. [ABSTRACT FROM AUTHOR]

In this work, we report results for the static second hyperpolarizability of magnesium oxide clusters including electronic and vibrational contributions. The comparison between second-order Møller-Plesset (MP2) perturbation theory and coupled cluster results to the electronic contribution points out that MP2 is a suitable method to compute this property. When computed at the MP2 level, the electronic contribution per atom converges to approximately 5000 a.u. Vibrational corrections were computed at the MP2 level through the perturbation theoretical method of Bishop and Kirtman. Results obtained showed that the term [α2]0,0 represents around 20% of the electronic counterpart while the term [μβ]0,0 is comparable to it. Modes that contribute significantly to [α2]0,0 are those in which all or part of the bond lengths simultaneously increase and decrease, leading to large polarizability derivatives. In turn, modes that provide relevant contributions to [μβ]0,0 are those in which oxygen anions move in opposite directions to the magnesium cations yielding large derivatives of the dipole moment and first hyperpolarizability. [ABSTRACT FROM AUTHOR]

In this work, poly(N-isopropylacrylamide) (PNIPAM) was used as a research object to explore the feasibility of molecular dynamics (MD) simulations to study the dielectric properties of polymers. A comparison of the static dielectric constants for two different calculation schemes, the applied electric field method and the dipole moment fluctuation method, has been conducted. The dielectric properties of PNIPAM aqueous solutions with different concentrations were studied as a function of temperature. The static dielectric constants derived from dipole moment fluctuation method at different temperatures can accurately describe the phase transition process. The concentration does not affect the lower critical solution temperature, but significantly affects the relaxation process of the system. According to the frequency-dependent dielectric constants, two relaxation processes are observed, namely, the dielectric relaxation process in the region of frequency less than 30 terahertz (THz) determined by the synergistic interaction of PNIPAM and water molecules, and that in the region of frequency higher than 30 THz mainly determined by water molecules beyond the solvation shell of the polymer. The calculation results suggest that the dielectric behaviour is concentration and temperature independent, similar to Debye behaviour of bulk water. This method of calculating dielectric properties using MD simulations can be used in detecting the dynamic processes of soft condensed matter and in aiding the design of materials with excellent dielectric properties. [ABSTRACT FROM AUTHOR]

Results of an analysis of our and literature data devoted to the study of the effect of a homogeneous dielectric medium on the rate constant of the 1 Δ g → 3 Σ g − radiative transition in singlet oxygen are presented. It is shown that the influence of the refractive index n on the radiative rate constant is due to the change of the density of photon states and the local field factor. At the same time, in a dielectric medium, the transition dipole moment increases significantly as a result of contact of singlet oxygen with solvent molecules. Only taking into account all of the above factors will provide a consistent explanation of the influence of the medium on the rate constant of the luminescence of singlet oxygen. [ABSTRACT FROM AUTHOR]

Hyper-Rayleigh scattering (HRS) is sensitive to long-range molecular orientation correlation in isotropic liquids composed of dipolar molecules. Measurements of the polarization, angle, and spectral dependence for HRS from liquid nitrobenzene (NB) are analyzed to determine the NB molecular orientation correlations at long range. The longitudinal and transverse orientation correlation functions for r > 3 nm are BL(r) = (a/r)³ and BT(r) = −BL(r)/2, where a = 0.20 ± 0.01 nm. Measurements of HRS induced by dissolved ions are also analyzed and combined with molecular dynamics simulation and dielectric response results, to determine the molecular dipole moment μ = 3.90 ± 0.04 D, Kirkwood orientation correlation factor gK = 0.68 ± 0.02, and local field factor f(0) = 0.85 ± 0.04 × Onsager local field factor in liquid nitrobenzene. [ABSTRACT FROM AUTHOR]

The present work reported the synthesis and characterisation of β-cyclodextrin (βCD) grafted into silica (SiO2@βCD) nanoparticles (NPs). Morphology analysis shows that the prepared NPs have a spherical shape with 170 nm of size. The electro-optic, dielectric and viscoelastic properties of SiO2@βCD doped nematic 5CB were examined in different concentrations of the NPs. A decrease in clearing temperature, birefringence and the order of the nanocomposite systems as compared to the pure system was observed. Dielectric parameters of pure and doped samples were measured in the frequency range of 1–2 MHz. Ionic conductivity and dielectric anisotropy increase significantly with NPs concentration due to the strong dipole moment and polarisability of SiO2@βCD. The advantage of dopedSiO2@βCDnematic 5CB is attributed to the significant decrements in threshold voltage by 32% and strong additional coupling of the electrical dipole moments in the spherical NPs with the nematic director field. On the other hand, it is found that the NPs exhibit a decreasing effect on the response time of the nematic liquid crystal, which is demonstrated by the decrement in the viscosity. The results indicate that doping SiO2@βCD is appropriate to fabricate a fast response LC device. [ABSTRACT FROM AUTHOR]

We are presenting the non-aqueous emulsions comprising of liquid crystal 8CB (4′-Octyl-4-biphenylcarbonitrile) and silicone oil in varying ratios (5:95, 10:90, 25:75 and 50:50 wt./wt.%). Emulsions are self-stabilised via dipolar interactions, alignment and anchoring without the use of any surfactant. The formation of distinct defects geometries over the studied concentration range of silicone oil in the liquid crystal matrix has been discussed. The dielectric dynamics of the non-aqueous emulsions have been studied in the smectic (30°C) and nematic (38°C) phases over the continuous broadband of frequency 50Hz–1MHz. In both cases (smectic and nematic regions), dielectric permittivity decreases with a rise in the content of the silicone oil in the emulsion systems. The proposed mechanism for such dielectric behaviour has been discussed considering charge/defects boundary interactions and decrement of resultant dipole moment. A relaxation mode in the lower frequency range has been observed for all the emulsion systems. In addition, the emulsion systems have shown significant optical transmission behaviour. A significant enhancement in optical transmission about 82% has been noticed for 25 wt% comparing to 5 wt% emulsion system. Such self-stabilised systems could pave a way to develop dual-frequency LCs systems for progressive technological applications, tunable polarisation filters, and adaptive optics. [ABSTRACT FROM AUTHOR]

New benzoxazole-terminated mesogenic compounds containing tolane moiety with high birefringence and large dielectric anisotropy, namely, 2-[4-[2-[4-alkoxyphenyl]ethynyl]-2,6-difluoro-phenyl]-benzoxazole derivatives (nPEDFPBx), were synthesised and investigated. Among them, the ones bearing methyl and nitro substituents at 5-position of benzoxazole moiety exhibit stable mesophase ranges of 30–71°C and 55–81°C during heating and cooling processes, respectively, while the non-substituted compounds exhibit no mesophase except the ones with long terminal alkoxy chain (n = 10, 12). Birefringence of nPEDFPBx is obtained from DFT theoretical calculation (0.446–0.583) and experimental measurement (0.395–0.499), respectively, where high birefringence is ascribed to their large π-conjugated molecule composed of benzene ring, acetylene linkage and benzoxazole moiety. Meanwhile, it is found that nPEDFPBx displays large dielectric anisotropy because of their high dipole moment. As an example, the compound 5PEDFPBM is doped into the liquid crystalline mixture as an additive, the properties of the resulting mixture, such as birefringence, dielectric anisotropy, clearing point and response time, are improved obviously, indicating high potential application for liquid crystalline mixture. [ABSTRACT FROM AUTHOR]

Far-field directional radiation of a single dipole in a cuboid slot is investigated in the presence of a dielectric substrate. Due to strong near field coupling between the dipole source and the surfaces of the slot and the dielectric, the far-field radiation shows strongly anisotropic pattern depending on the dipole radiation energy. By tuning local resonances within the air-slot interface or the substrate-slot interface, highly directional radiation either to free space or to the substrate space can be obtained. In the visible spectrum ranging from 1.2 eV to 3.5 eV, up to 18 fold directivity can be obtained. The up-to-down ratio can be tuned from -7.5 dB to 10 dB. We identify induced eigenmodes responsible for highly unidirectional radiations as a function of the emitter spectrum and slot thickness to assess controllability of radiation power and direction. [ABSTRACT FROM AUTHOR]

Through symmetry breaking, an electric dipole moment is generated out of the fundamental magnetic dipole mode of dielectric resonator antennas (DRAs). Unidirectional radiation is then achieved based on the concept of complementary antennas by disturbing the modal field distribution. The eigenmode method and Cartesian multipole analysis are utilized to analyze the modified DRA and quantitatively monitor the amplitude and phase of the dipole moments. The characteristic mode analysis and scattering spectrum method are also applied for further validation. It is found that the unidirectional radiation pattern is obtained by a modified eigenmode instead of the superposition of two adjacent ones. Based on the proposed mechanism, several different design examples are presented. High front-to-back ratios (FBRs) are observed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two series of dibenzofuran- and dibenzothiophene-based liquid crystals were designed and synthesised respectively. • All of the obtained mesogens possessed large negative dielectric anisotropy values. • The calculated orientation of the dipole moment in these compounds was almost perpendicular to their long molecular axis. • A new negative LC mixture with excellent low-temperature stability was formulated. Two series of dibenzofuran- and dibenzothiophene-based liquid crystals were designed and synthesised respectively. The structures of the intermediates and the target mesogens were confirmed by nuclear magnetic resonance and mass spectrometry. The melting points of dibenzofuran-based liquid crystals were lower than dibenzothiophene-based ones if the 3-position was long-chain alkoxy while a reversed result was obtained when cyclohexyl and tetrahydropyran were introduced. All of the designed dibenzofuran- and dibenzothiophene-based liquid crystals possessed large negative dielectric anisotropy (Δ ε) values when compared with the reference compounds, which proved the effectiveness of these two heterocycle core units in the improvement of the negative Δ ε. The DFT calculations found that the elevation of the negative Δ ε values might be owed to the orientation of the dipole moment in these new compounds was almost perpendicular to their long molecular axis. A new liquid crystal mixture LTNLCM-1 was finally formulated, which could be stored at −20 °C (−40 °C when filled in liquid crystal cell) for two weeks without any obvious precipitation, illustrating the vital function of the dibenzothiophene-based compounds in improvement of the low-temperature stability of liquid crystal mixtures. [ABSTRACT FROM AUTHOR]

We propose a two-sublattice proton ordering model for the quasi-one-dimensional CsH2PO4 ferroelectric with hydrogen bonds, which takes into account contributions to the energy of the proton subsystem that are linear in the lattice strains ε1, ε2, ε3, and ε5. The model also takes into account the dependence of the effective dipole moments of pseudospins on the order parameters, which enables us to coordinate the values of the effective dipole moments in the paraelectric and ferroelectric phases. Within this model in the two-particle cluster approximation for the short-range interactions and in the mean field approximation for the long-range interactions, the behavior of spontaneous polarization, longitudinal dielectric permittivity, piezoelectric and elastic characteristics, and molar heat capacity under the influence of uniaxial and hydrostatic pressure and a longitudinal electric field are investigated. [ABSTRACT FROM AUTHOR]

We propose a two-sublattice proton ordering model for the quasi-one-dimensional CsH2PO4 ferroelectric with hydrogen bonds, which takes into account contributions to the energy of the proton subsystem that are linear in the lattice strains ε1, ε2, ε3, and ε5. The model also takes into account the dependence of the effective dipole moments of pseudospins on the order parameters, which enables us to coordinate the values of the effective dipole moments in the paraelectric and ferroelectric phases. Within this model in the two-particle cluster approximation for the short-range interactions and in the mean field approximation for the long-range interactions, the behavior of spontaneous polarization, longitudinal dielectric permittivity, piezoelectric and elastic characteristics, and molar heat capacity under the influence of uniaxial and hydrostatic pressure and a longitudinal electric field are investigated. [ABSTRACT FROM AUTHOR]

Electrohydrodynamics of drops is a classic fluid mechanical problem where deformations and microscale flows are generated by application of an external electric field. In weak fields, electric stresses acting on the drop surface drive quadrupolar flows inside and outside and cause the drop to adopt a steady axisymmetric shape. This phenomenon is best explained by the leaky-dielectric model under the premise that a net surface charge is present at the interface while the bulk fluids are electroneutral. In the case of dielectric drops, increasing the electric field beyond a critical value can cause the drop to start rotating spontaneously and assume a steady tilted shape. This symmetry-breaking phenomenon, called Quincke rotation, arises due to the action of the interfacial electric torque countering the viscous torque on the drop, giving rise to steady rotation in sufficiently strong fields. Here, we present a small-deformation theory for the electrohydrodynamics of dielectric drops for the complete Melcher–Taylor leaky-dielectric model in three dimensions. Our theory is valid in the limits of strong capillary forces and highly viscous drops and is able to capture the transition to Quincke rotation. A coupled set of nonlinear ordinary differential equations for the induced dipole moments and shape functions are derived whose solution matches well with experimental results in the appropriate small-deformation regime. Retention of both the straining and rotational components of the flow in the governing equation for charge transport enables us to perform a linear stability analysis and derive a criterion for the applied electric field strength that must be overcome for the onset of Quincke rotation of a viscous drop. [ABSTRACT FROM AUTHOR]

The response to an electrostatic field is determined through simple model calculations, within both the restricted Hartree-Fock and density functional theory methods, for long, finite as well as infinite, periodic chains. The permanent dipole moment, μ0, the polarizability, α, and the hyperpolarizabilities β and γ , calculated using a finite-field approach, are extensively analyzed. Our simple model allows for treatment of large systems and for separation of the properties into atomic and unit-cell contributions. That part of the response properties attributable to the terminations of the finite system change into delocalized current contributions in the corresponding infinite periodic system. Special emphasis is placed on analyzing the reasons behind the dramatic overestimation of the response properties found with density functional theory methods presently in common use. [ABSTRACT FROM AUTHOR]

We present (far-infrared) Collision Induced Absorption (CIA) spectra calculations for pure gaseous N2 made for the first time, from first-principles. They were carried out using classical molecular dynamics simulations based on ab initio predictions of both the intermolecular potential and the induced-dipole moment. These calculations reproduce satisfactory well the experimental values (intensity and band profile) with agreement within 3% at 149 K. With respect to results obtained with only the long range (asymptotic) dipole moment (DM), including the short range overlap contribution improves the band intensity and profile at 149 K, but it deteriorates them at 296 K. The results show that the relative contribution of the short range DM to the band intensity is typically around 10%.We have also examined the sensitivity of the calculated CIA to the intermolecular potential anisotropy, providing a test of the so-called isotropic approximation used up to now in all N2 CIA calculations. As all these effects interfere simultaneously with quantitatively similar influences (around 10%), it is rather difficult to assert which one could explain remaining deviations with the experimental results. Furthermore, the rather large uncertainties and sometimes inconsistencies of the available measurements forbid any definitive conclusion, stressing the need for new experiments. [ABSTRACT FROM AUTHOR]

We study to what extent dielectric nanoparticles prefer to self-assemble into linear chains or into more compact structures. To calculate the Van der Waals (VdW) attraction between the clusters we use the Coupled Dipole Method (CDM), which treats each atom in the nanoparticle as an inducible oscillating point dipole. The VdW attraction then results from the full many-body interactions between the dipoles. For non-capped nanoparticles, we calculate in which configuration the VdW attraction is maximal. We find that in virtually all cases we studied, many-body effects only result in local potential minima at the linear configuration, as opposed to global ones, and that these metastable minima are in most cases rather shallow compared to the thermal energy. In this work, we also compare the CDM results with those from Hamaker-de Boer and Axilrod-Teller theory to investigate the influence of the many-body effects and the accuracy of these two approximate methods. [ABSTRACT FROM AUTHOR]

New liquid crystal compounds with 5,6-difluorobenzofuran core were synthesised by palladium catalysed coupling and ring-closing reaction. Their structures were identified using 1HNMR, 13CNMR and MS. Thermo analysis show that these compounds exhibit a broad nematic range and high clearing points. Physical property test revealed that the dielectric anisotropies of these compounds are about 11 ~ 17, which is twice of that of the 3, 4-difluorinated benzene analogues. DFT calculation results show that the 5, 6-difluorobenzofuran-based compounds have much larger polarisation and dipole moments compared with the common 3,4-difluorobenzene compounds, which leads to a significant increase in dielectric anisotropy and birefringence. As a new fluorinated building block, 5, 6-difluorobenzofuran shows a good prospect for display device. [ABSTRACT FROM AUTHOR]

We are reporting on the interaction of zinc oxide (ZnO) nanoparticles (NPs) with the lyotropic phase comprises of Polyoxyethylene (20) sorbitan monolaurate and protic solvent ethylene glycol. The concentration of the NPs has been varying from 0.05 to 0.5 wt%. Multiwall lamellar and inverse phases have been observed at lower and higher concentration of ZnO NPs doping. Interestingly, the organization of ZnO NPs on the periphery and inside the periphery of ring-like structures has been observed at lower and higher concentration of the dopant, respectively. Such organization of the NPs can be explained considering interfacial interaction amid host and dopant and may also attribute to the adsorption mechanisms of surfactant. Effects of NPs doping on the dielectric dynamics has also been examined. About 32.6% decrease in the dielectric permittivity has been noticed at higher NPs doping. Such decrement in permittivity could be a result of the screening of the ZnO NPs dipole moment by the adsorption of surfactant molecules on their surface. Relaxation and optical parameters of the non-doped and doped mixtures have also been discussed. [ABSTRACT FROM AUTHOR]

In this paper, we perform molecular dynamics simulations of a dielectric fluidic material composed of permanent molecular dipoles. The dielectric spectrum features two peaks at lower frequencies than the system phonon frequency. The primary peak is observed at all temperatures studied and shifts toward lower frequencies as the temperature decreases. During this shift, the secondary peak emerges with a higher peak frequency than the primary peak. The secondary peak amplitude increases as the temperature decreases. Both peaks are dependent on the wavevector; in the small wavevector regime, the primary peak is shifted to higher frequencies as the wavevector squared and the secondary peak amplitude increases as the wavevector increases, but shows no shift in frequency. From the polarisation balance equation, we propose a model for the dielectric spectrum. This captures the spectrum features, and we conjecture that the primary peak is due to dipole moment correlations (Debye-type) and the secondary peak is due to the correlation between the dipole moment and a microscopic local field. [ABSTRACT FROM AUTHOR]

Glasslike dielectrics are investigated by methods of plasmon dispersion and asymmetry of the number of localized electrons in the region in which total external reflection of X-rays is formed and excitation of plasmon oscillations takes place. The internal mechanical stress and the related polarization of the studied dielectrics are determined. It is discovered that a lithium fluoride crystal lacks an internal mechanical stress and that the observed polarization in this single crystal is caused by a large macroscopic dipole moment. [ABSTRACT FROM AUTHOR]

Here we present a general approach for the description for the frequency dependent dielectric tensor coefficients for optically anisotropic materials. Based on symmetry arguments we show that the components of the dielectric tensor are in general not independent of each other. For each excitation there exists an eigensystem, where its contribution to the dielectric tensor can be described by a diagonal susceptibility tensor. From the orientation of the eigensystem and the relative magnitude of the tensor elements, the dipole interaction distribution in real space can be deduced. In the limiting cases, the oriented dipole approach as well as the tensor of isotropic and uniaxial materials are obtained. The application of this model is demonstrated exemplarily on triclinic K2Cr2O7 and the orientation and directional distribution of the corresponding dipole moments in real space are determined. [ABSTRACT FROM AUTHOR]

Here we present a general approach for the description for the frequency dependent dielectric tensor coefficients for optically anisotropic materials. Based on symmetry arguments we show that the components of the dielectric tensor are in general not independent of each other. For each excitation there exists an eigensystem, where its contribution to the dielectric tensor can be described by a diagonal susceptibility tensor. From the orientation of the eigensystem and the relative magnitude of the tensor elements, the dipole interaction distribution in real space can be deduced. In the limiting cases, the oriented dipole approach as well as the tensor of isotropic and uniaxial materials are obtained. The application of this model is demonstrated exemplarily on triclinic K2Cr2O7 and the orientation and directional distribution of the corresponding dipole moments in real space are determined. [ABSTRACT FROM AUTHOR]

Structure with the asymmetric environment of cation has a large effect on the polarization mechanism and dielectric response. In this study d0 cation, Ti4+ is introduced into asymmetric α-TeO 2 to prepare Ti x Te (1-x) O 2 (x = 0 to 0.25) by conventional solid-state method. In all the samples, it is found that the dielectric response increases relative to the parent α-TeO 2. Sample with x = 0.25 forms cubic TiTe 3 O 8 phase and shows maximum dielectric permittivity of 77. The remaining samples show biphasic nature comprising cubic (TiTe 3 O 8) and tetragonal (α-TeO 2) phase and their dielectric behaviour follows the Lichtenecker logarithmic mixing rule of composites. Structural analysis reveals that the cubic TiTe 3 O 8 phase consists of TeO 4 and TeO 6 framework structure with locally strained TeO 4 units compared to α-TeO 2 and the Raman study complements this observation. The local strain enhances the dipolar polarizability of TeO 4 unit; additionally, ionic polarizability of TiO 6 unit also contributes to high dielectric permittivity in TiTe 3 O 8. [ABSTRACT FROM AUTHOR]

In the framework of dipole approximation, it is shown that the oscillator strengths of transitions as well as the dipole moments for transitions for one-particle electron quantum-confined states emerging above the spherical surface quantum dot of aluminum oxide assume giant values considerably (by two orders of magnitude) exceeding the typical values of the corresponding quantities for dielectrics. It has been established that the giant values of the light absorption cross section in the nanosystems under investigation make it possible to use such nanosystems as strongly absorbing nanomaterials in a wide range of infrared waves with a wavelength that can be varied in a wide range depending in the type of contacting materials. [ABSTRACT FROM AUTHOR]

A low-frequency dielectric relaxation mode in deformed helix ferroelectric liquid crystal (DHFLC) has been observed at the interface of strongly rubbed substrates and DHFLC material which may find applications in low power consumption FLC devices. The surface-induced dielectric relaxation process at the interface of DHFLC and substrate is called the partially unwound helical mode (p-UHM) due to the unwinding of the helical structure at this interface. After investigation of the material under various parameters such as temperature, variation of the amplitude of probing ac voltage and dc bias voltage, the relaxation frequency of p-UHM is found to be shifted towards Goldstone mode and merged with it. The relaxation frequency of Goldstone mode is found to decrease, whereas the relaxation frequency of p-UHM process increases with the increase in temperature of DHFLC. Finally, both the modes merge and the resultant relaxation frequency is found to be lower than Goldstone mode in SmC* phase. It seems that phason mode and partial helical unwinding mode are coupled together due to dipole moment that is resulting in a new relaxation frequency. p-UHM process is significant for low-power displays and non-displays applications like a part of sensor where weak electric signal is required to be realized without pre-amplification. [ABSTRACT FROM AUTHOR]

Dielectric spectroscopy of CaCu3Ti4O12 was performed spanning broad ranges of temperature (10-300 K) and frequency (0.5 Hz-2 MHz). We attribute the permittivity step-fall to the evolution of Kirkwood-Fröehlich dipole-correlations, reducing the moment-density due to anti-parallel orienting dipoles, with decreasing temperature. Unambiguous sub-Arrhenic dispersion of the associated loss-peak reveals the prime role of strange kinetics, used to describe nonlinearity-governed meso-confined/fractal systems, witnessed here for the first time in a bulk material. Effective energy-scale is seen to follow the thermal evolution of the moment density, and the maidenly estimated correlation-length achieves mesoscopic scale below ∼100 K. Temperature dependence of correlations reveals emergence of a new, parallel-dipole-orientation branch below 85 K. Novel features observed define a crossover temperature window connecting the single-dipoles regime and the correlated moments. We suggest a fractal-like self-similar configuration of Ca/Cu-rich sub-phases; resultant heterogeneity endowing CaCu3Ti4O12 its peculiar electrical behaviour. [ABSTRACT FROM AUTHOR]

Understanding the effect of inhomogeneity on the charge regulation and dielectric properties, and how it depends on the conformational characteristics of the macromolecules is a long-standing problem. In order to address this problem, we have developed a field-theory to study charge regulation and local dielectric function in planar polyelectrolyte brushes. The theory is used to study a polyacid brush, which is comprised of chains end-grafted at the solid-fluid interface, in equilibrium with a bulk solution containing monovalent salt ions, solvent molecules, and pH controlling acid. In particular, we focus on the effects of the concentration of added salt and pH of the bulk in determining the local charge and dielectric function. Our theoretical investigations reveal that the dipole moment of the ion-pairs formed as a result of counterion adsorption on the chain backbones play a key role in affecting the local dielectric function. For polyelectrolytes made of monomers having dipole moments lower than the solvent molecules, dielectric decrement is predicted inside the brush region. However, the formation of ion-pairs (due to adsorption of counterions coming from the dissociation of added salt) more polar than the solvent molecules is shown to increase the magnitude of the dielectric function with respect to its bulk value. Furthermore, an increase in the bulk salt concentration is shown to increase the local charge inside the brush region. [ABSTRACT FROM AUTHOR]