Nonlinear dielectric effect near the critical point of binary mixtures

The nonlinear dielectric effect (NDE) was measured in two binary systems near the critical point. The effect of independent of specific dipole-dipole interactions in contrast with previous conceptions. Its singular part is proportional to (T ? T_c)^{?$\text{1}\text{2}$} in agreement with Snider's theory as applied to NDE.     

Nonlinear dielectric effect in benzonitrile and lauronitrile solutions

The nonlinear dielectric effect, NDE, and the calculated correlation factors R^p and R^s are reported for binary solutions of benzonitrile and lauronitrile in benzene and cyclohexane. Substantial differences found for solutions in these two solvents have been explained in terms of critical phenomena in cyclohexane solution.     

Nonlinear dielectric effect in carbon tetrachloride solutions of iodobenzene

The results of measurements of Δ/E² as a function of concentration for CCl₄ solutions of iodobenzene are given and compared with earlier results for CCl₄ solutions of fluoro-, chloro- and bromo-benzene. Terms contributing to the molar saturation constant for pure halogeno-derivatives of benzene have been calculated, using Kielich's theory. The change of sign of Δ/E² for bromo- and iodo-benzene is explained.     

Nonlinear dielectric effect fortert-nitrobutane andtert-butylnitrile in hexane and benzene solutions

A nonlinear dielectric effect, and the calculated correlation factors R _p and R _s are reported for binary solutions of tert-nitrobutane and tert-butylnitrile in hexane and benzene. The results are discussed in terms of the three main mechanism: association of polar molecules, fluctuations in concentration and density, and intermolecular processes due to a strong electric field. The dipolar part of the cohesion energy is also accounted for.     

Nonlinear dielectric effect (NDE) and molecular orbital study of the conformational equilibrium in 1,4-dimethoxybenzene in benzene solution

The conformational equilibrium in 1,4-dimethoxybenzene (1,4-DMB) in benzene solutions has been studied. On the basis of experimental values of the nonlinear dielectric effect (NDE) parameter, electric permittivity and density, determined in this work, and applying the general statistical theory of NDE, the contributions of the syn-anti and syn-syn conformers and the electric dipole moment of the polar syn-syn conformer were calculated. The molecular orbital method (PM3) has also been applied for calculation of the dipole moments and energies of particular conformers. The results of the NDE study and PM3 calculations are consistent and they reveal the existence of two conformers (syn-anti and syn-syn) of comparable energy values, but different values of dipole moments, and the predominance of the polar form (syn-syn) of the mole fraction in benzene. Moreover, the energies of intermolecular interactions have been determined from the concentration dependence of linear and nonlinear polarisability.     

Nonlinear dielectric effect of phenyl and methyl isothiocyanates in benzene and carbon tetrachloride

The nonlinear dielectric effect (NDE) of phenyl isothiocyanate and methyl isothiocyanate in benzene and carbon tetrachloride as solvents has been investigated. A different NDE dependence on the concentration for both investigated isothiocyanates and a significant solvent effect in the case of methyl isothiocyanate were observed.     

Nonlinear depression of the lower critical solution temperatures in aqueous solutions of thermo-sensitive random copolymers

We develop a theoretical model of cooperative hydration to clarify the molecular origin of the observed nonlinear depression of the lower critical solution temperature (LCST) in the aqueous solutions of thermosensitive random copolymers and find the monomer composition at which LCST shows a minimum. Phase diagrams of poly(N-isopropylacrylamide-co-N,N-diethylacrylamide) copolymer solutions are theoretically derived on the basis of the theory of cooperative hydration by introducing the microscopic structure parameter η which characterizes the distribution of the monomer sequences along the chains. We compared them with the experimental data of LCST of random copolymers with various monomer compositions and also of the diblock copolymers with equimolar monomer composition. The transition temperature shifts to lower than those of homopolymer counterparts when the monomer sequence of the chains has an alternative tendency. On the contrary, for the blocky polymers such as diblock copolymers, the transition temperature remains almost the same as those of the homopolymers. Thus, the nonlinear effect in phase separation appears when the average block length of the copolymers is shorter than the average sequence length of the cooperative hydration. The degree of hydration is calculated as a function of the temperature and polymer concentration for varied distribution of the copolymer compositions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1112–1123     

Nonlinear electrophoresis of dielectric particles in Newtonian fluids

In classical electrokinetics, the electrophoretic velocity of a dielectric particle is a linear function of the applied electric field. Theoretical studies have predicted the onset of nonlinear electrophoresis at high electric fields because of the nonuniform surface conduction over the curved particle. However, experimental studies have been left behind and are insufficient for a fundamental understanding of the parametric effects on nonlinear electrophoresis. We present in this work a systematic experimental study of the effects of buffer concentration, particle size, and particle zeta potential on the electrophoretic velocity of polystyrene particles in a straight rectangular microchannel for electric fields of up to 3 kV/cm. The measured nonlinear electrophoretic particle velocity is found to exhibit a 2(±0.5)-order dependence on the applied electric field, which appears to be within the theoretically predicted 3- and 3/2-order dependences for low and high electric fields, respectively. Moreover, the obtained nonlinear electrophoretic particle mobility increases with decreasing buffer concentration (for the same particle) and particle size (for particles with similar zeta potentials) or increasing particle zeta potential (for particles with similar sizes). These observations are all consistent with the theoretical predictions for high electric fields.     

Nonlinear actuation of non-prismatic dielectric elastomeric membrane

ABSTRACT

Nowadays, the soft material, dielectric elastomers (DEs) are being used for many engineering applications due to their exceptional properties like high strain rate sensitivity, low power consumption, capable of static force measurement and capability of changing dimensions when subjected to voltage. They have the ability of converting mechanical energy to electrical energy and vice versa. In this article, nonlinear dynamic behavior of viscoelastic tapered DE under mechanical and electromechanical loading is studied. A dynamic model based on standard linear solid model is incorporated for viscoelasticity. Strain energy density of the system is derived from Gent model of hyperelasticity. The tapered DE is analyzed with different values of damping coefficients, ratio of shear moduli of springs, width and height tapers. The effects of tapers greatly put an impact on the dynamic responses of the system. The tapered DEs exhibits damped vibration and weak nonlinearity with an increase in damping force. The dynamic stability of tapered DEs is also studied using phase diagrams, and the results indicated that with an increase in damping force, the dynamic stability changes from a state of aperiodic vibration to quasi-periodic vibration. It is also found that the resonant frequency and peak amplitude reduce with an increase in the damping force.     

The effect of external orienting electric field on dielectric relaxation of segmented polyesters in dilute solution

A comparative study of dipole polarization relaxation in the absence and in the presence of an external orienting electric field was performed for linear segmented polyesters with alternating rigid (oxyfumaroylbis-4-oxybenzoates) and flexible (methylene-CH₂-, ethylene oxide-CH₂CH₂-O-, and dimethylsiloxane-Si(CH₃)₂-O-Si(CH₃)₂-) fragments in dilute solutions. Polyesters that do not display mesomorphic properties in the bulk show several regions of dielectric absorption with relaxation character. These regions are associated with the motions via the local mobility mechanisms of different polar fragments of the macromolecule. In solutions of polyesters that possess LC properties in the bulk, large-scale dipole polarization relaxation with long relaxation times and high activation energies was revealed along with local dielectric relaxation transitions. This process is associated with the cooperative motion of mesogenic fragments in their associates. In an external orienting electric field, the intensity of dielectric absorption usually increases for all types of dielectric transition; relaxation times and activation energies experience changes only for large-scale processes.     

Efficient evaluation of the effective dielectric function of a macromolecule in aqueous solution

We propose an analytical approach to calculate the effective dielectric function of proteins in aqueous solution. The screening effect if quantified by a measure of enclosure which is based on the distribution of solute atomic volumes around a pair of charges in a macromolecule. For protein conformations that vary significantly in size and shape, a comparison with finite difference Poisson calculations shows that pair interaction energies, their sums and solvation energies are well reproduced. The approach rivals the speed of simple distance dependent dielectric functions and the accuracy of the generalized Born model.     

Polystyrene in cyclopentane: Dilute solution properties from the upper critical to the lower critical solution temperature

Dilute solutions of polystyrene in cyclopentane are studied with four narrow-distribution polymer fractions ranging in molecular weight from 1.6 × 10⁵ to 1.8 × 10⁶. Light scattering (total intensity) and viscosity measurements cover a temperature range spanning both “theta” temperatures: the limiting upper critical solution temperature (19.6°C) and the limiting lower critical temperature (154.5°C). Within experimental uncertainty, chain dimensions are the same at the two theta temperatures. Correlations among second virial coefficients, mean-square molecular radii of gyration, and intrinsic viscosities, are analyzed. Temperature and molecular-weight dependences are correlated satisfactorily in terms of the excluded-volume parameter z that is central to the “two-parameter” theories of dilute solution behavior. The data can also be correlated in the framework of the newer renormalization theories.     

Electric potential distributions around discrete charges in a dielectric membrane—electrolyte solution system

Within the framework of the linearized Debye-Hückel theory an exact solution of the problem of calculating the electric potential caused by discrete fixed charges located at arbitrary positions with respect to a dielectric membrane-solution interface is presented. It takes into account the existence of an electrolyte solution on both sides of the membrane. Asymmetric ionic conditions are allowed for. For some interesting typical cases of fixed charge locations and electrolyte ionic strengths electric potential distributions were calculated and discussed. It is shown that, if the fixed charges were at or in front of the membrane surface, the characteristic distance of the electric potential decay was comparable to the Debye-Hückel length. At the opposite membrane surface only very small electric potentials can be observed. If, however, the fixed charge was placed below the membrane surface the electric potential in lateral direction and towards the other membrane surface largely increased. This effect was very sensitive to the position of the fixed charge with respect to the membrane surface.     

Effective charge of polyelectrolytes as a function of the dielectric constant of a solution

The combination of diffusion and electrophoresis NMR is applied to determine the effective charge of poly(styrene sulfonate) in solution. While electrophoresis NMR yields the electrophoretic mobility of the molecules in solution, the hydrodynamic friction is determined from diffusion NMR. From the force balance between electrostatic force and hydrodynamic friction, the effective charge of the molecule is determined free of any model. In the present study poly(styrene sulfonate) has been investigated in mixtures of water and methanol of varying composition. The lower dielectric constant in the mixtures with high methanol content results in a drastically reduced effective charge of the polyelectrolytes. The reduced effective charge along the polymer chain is the reason for a much more compact conformation of the polyelectrolyte, which is seen in a smaller hydrodynamic size of the molecule.     

Scandium sulfate complexation in aqueous solution by dielectric relaxation spectroscopy

Ion association in aqueous solutions of scandium sulfate has been investigated at 25 degrees C and at concentrations from 0.01 to 0.8 M by broadband dielectric spectroscopy over the frequency range 0.2 相似文献   

The non-linear dielectric effect in liquid xenon

The non-linear dielectric effect (NLDE), that is the increase in the dielectric constant divided by the square of the applied field, is measured for a number of non-polar molecular liquids and for liquid xenon. The values of the NLDE are compared with results in the literature and with values predicted by theory. The agreement with other experiments is quite good, but with theory is very poor, the only exception being Liquid xenon, where agreement is good. A possible explanation is given. The prediction that the NLDE should increase strongly near the critical point due to the divergence of the isothermal compressibility could not be established by experiment. The conclusion is drawn that this failure is due to the reduction by the theory of second-order effects to first-order thermodynamic and molecular properties.     

High frequency dielectric behaviour of critical binary solutions of benzonitrile-isooctane

The high frequency dielectric behaviour of critical binary mixtures of benzonitrile-isooctane is described, as a function of temperature, for two concentrations and for a frequency coverage comprising several discrete values between 3 and 112 GHz and a continuous range between 600 and 3600 GHz. For the first time, the precritical region is explored using far infrared spectroscopy and the temperature dependence of the refractive index and the absorption is reported. As the temperature approaches the critical value, the Cole-Davidson diagrams are found to show a progressive flattening, which can be characterised by a decrease in β, the Cole-Davidson coefficient. Both the microwave and the far-infrared properties are strongly anomalous near the consolute temperature and this could be consistent with the assumption of growing microscopic regions within the liquid, near this temperature.     

The determination of the critical concentration of a binary mixture containing a polar component by dielectric measurements

The step in the dielectric constant that occurs upon cooling a binary liquid mixture below its phase separation is further investigated and explained. It is shown that this phenomenon can be used to determine the critical concentration (x_c).     

Phase diagrams with critical and tricritical liquid phase solution points in a ternary system

Critical phenomena of liquid phase stratification in ternary systems are considered. Models of the T-x ₁-x ₂ phase diagrams with critical and tricritical liquid solution points and isothermal diagrams over the corresponding interinvariant intervals are given.