Dielectric Relaxation of Some Rigid Molecules in Viscous Media

Abstract

The dielectric relaxation times(τ) have been evaluated from the measured values of dielectric constant(?′) and loss (?′′) of four rigid molecules in paraffin oil + benzene mixtures of varying viscosity extending from moderate to high values. Two of the rigid systems are nearly spherical in nature. An attempt has been made to find out the suitable viscosity term describing the dipolar rotation by applying the measured parameters to the earlier models as proposed by Debye, Hill and Kalman. Hill's model which describes the motion by a mutual viscosity (η_AB) term has been found to yield negative values showing its inadequacy for the systems rotating in high viscosity media. A comparison of Kalman's equation with Debye shows that the former gives better results for the region investigated both in high and low viscosity media. Even the systems having spherical symmetry give more satisfactory results when applied to Kalman's equation. In the process, the thermodynamical parameters and dipole moments of the molecules have also been evaluated and discussed.     

Dielectric Study of Charge-transfer Complexes in Binary and Ternary Systems at 35°C

Abstract

The measurements of dielectric constant of a number of binary and ternary mixtures of butyl acetate, butyl alcohol, quinoline, pyridine and o-cresol in carbon tetrachloride and benzene have been made at 35°C. Molecular interaction of these aromatic compounds have been studied in terms of variations in parameters; ‘dipole moment’ (μ), ‘interaction dielectric constant’ (δ?), ‘molecular polarisation’ (P) and ‘excess polarisation’ (P_E ). The dipole moment has been calculated using Hysken's method, the interaction dielectric constant utilizing the equation of ideal mole fraction law and excess polarisation using the theory of Erap and Glasstone. The positive values of δ?₁₂ for binary mixtures of quinoline and butyl acetate in carbon tetrachloride and benzene have been attributed to the formation of charge transfer complexes. The negative values of δ?₁₂ and δ?₁₂₃ with pyridine suggest that charge transfer interaction is weakened by pyridine in its binary and ternary mixtures. The plot between the excess polarisation value and the product of mole fractions yielded a straight line passing through the origin showing the formation of charge transfer complexes.     

Densities and Viscosities of the Ternary Mixture (Benzene + 1-Propanol + Ethyl Acetate) at 298.15 K

Abstract

Densities and viscosities of the ternary mixture (benzene + 1-propanol + ethyl acetate) and the corresponding binary mixtures (benzene + 1-propanol, benzene + ethyl acetate and 1-propanol + ethyl acetate) have been measured at the temperature 298.15 K. From these measurements excess volumes, V^E , excess viscosities, η^E, and excess Gibbs energies of activation for viscous flow, G*^E , have been determined. The equation of Redlich-Kister has been used for fitting the excess properties of binary mixtures. The excess properties of the ternary system were fitted to Cibulka's equation.     

Mechanism of the oxidation of some substituted acetophenones byN-Bromosuccinimide in acidic media

The kinetics of the reaction of three substituted acetophenones withN-Bromosuccinimide was studied in perchloric acid media in presence of mercuric acetate. The reactions were found to be zero order with respect toNBS while the order with respect to ketones and [H⁺] was found to be unity. The addition of succinimide mercuric acetate and sodium perchlorate has no effect on the rate of oxidation and the rate increases with the decrease in dielectric constant of the medium. Kinetic investigations have revealed that the order of reactivity ism-nitroacetophenone > p-chloroacetophenone > p-methylacetophenone. TheArrhenius equation has been found to be valid in the temperature range 35–55°. Thermodynamic parameters have been calculated. Mechanistic pathways of the reactions are discussed and a rate equation is derived.Hammett's plot gives a ? value of +0.60 for methyl-aryl-ketones.     

Influence of Intramolecular Interactions on Some Parameters in Adsorption Thin-Layer Chromatography

Abstract

Using the equation connecting the R_M values with the appropriate data of the adsorption process from solutions the values of the parameters characterizing substance ? mobile phase interactions have been calculated for the systems: silica gel-benzene+acetone and silica gel-acetone+methanol.Quinoline, aniline, nitrobenzene, phenol and their derivatives were the chromatographed substances. An influence of the structure of the substance on the parameter values has been examined, special attention being paid to intramolecular effects, mainly those of hydrogen bonds.     

Kinetics of the oxidation of cyclohexene by thallium(III) acetate

The kinetics of the reaction by which thallium(III) acetate oxidizes cyclohexene in glacial acetic acid medium, has been studied by UV spectrophotometric observation at 30°C. The consumption of thallium(III) acetate follows a second-order rate law exhibiting first-order dependence on each of thallium(III) acetate and cyclohexene; however, the first-order dependence on cyclohexene disappears at high cyclohexene concentrations as pseudo-first-order conditions prevail above 0.2 M cyclohexene. A steady-state model of the following form is proposed: where Tl, Cy, and Com are units of Thallium(III) acetate, cyclohexene, and a reaction complex. The value of k₂ has been evaluated as 0.00027 and (k_?1 + k₂) as 0.0385k₁. For low thallium(III) acetate concentrations the reaction kinetics follow the rate law: where α = the excess concentration of cyclohexene over thallium(III) triacetate. For thallium(III) acetate concentrations above 0.02 M, double salt formation of thallium(III) acetate with product thallium(I) acetate removes thallium(III) acetate from the reaction and a modified rate law is observed. Runge–Kutta numerical solutions to the differential equations provide confirmation that the rate expressions are valid in predicting the observed concentrations of thallium(III) acetate.     

Phase Equilibria in the Systems Oxolane + Vinyl Acetate,Oxolane + Ethyl 1,1-Dimethylethyl Ether and Vinyl Acetate + Ethyl 1,1-Dimethylethyl Ether

Abstract

Vapor-liquid equilibrium at 94kPa has been determined for the binary systems oxolane (THF) + vinyl acetate, oxolane + ethyl 1,1-dimethylethyl ether (ETBE) and vinyl acetate + ethyl 1,1-dimethylethyl ether. The three systems present slight to moderate positive deviations from ideal behavior and, to a first approximation, can be considered to behave like regular solutions. An azeotrope is present in the system vinyl acetate + ETBE that boils at 340.40 K and contains 49.8% mol vinyl acetate. The activity coefficients of the systems were correlated reasonable well with its composition by the Wohl, Wilson, UNIQUAC and NRTL models. The boiling points of the binary systems were correlated with the Wisniak-Tamir equation.     

Study of the influence of isomerism on the curing properties of the epoxy system DGEBA (n=0)/1,2 DCH by DEA and MDSC

Summary Modulated differential scanning calorimetry (MDSC) and dielectric analysis (DEA) have been used to characterize the cure process of the system diglycidyl ether of bisphenol A (DGEBA(n=0)/1,2 diaminocyclohexane (1,2 DCH). The trans isomer and a mixture cis/trans(30-70% respectively) of 1,2 DCH were used to find their different behaviour. The study allowed to check the influence of the cisisomer on the thermoset curing process. Gelation times were obtained through the equation proposed by Johari and vitrification times from the point of inflection of the complex calorific capacity modulus.     

The Goldstone mode in mixtures containing ferroelectric liquid crystals

Abstract

Measurements of complex electric permittivity of room temperature ferroelectric liquid crystal mixtures have been made on aligned samples with the electric measuring field being parallel to the layer planes. The spontaneous polarization, the tilt angles and pitch have been measured in these mixtures. By theoretical fitting of the experimental points of electric permittivity for the Cole–Cole modification of the Debye equation dielectric parameters, the dielectric strength, relaxation frequency, and distribution parameter for the Goldstone mode have been computed. The dielectrically observed Goldstone mode in our mixtures is shown to have both DC bias field and AC field dependences.     

Evaluation of Excess Molar Polarization in Binary Mixtures of Amines in Nonpolar Solvents

Abstract

A new expression for the excess molar polarization in binary mixture of polar and nonpolar liquids has been proposed. An experimental assessment of the proposed equation has been made by comparison with an earlier equation in the binary mixtures of amines in nonpolar liquids. The proposed equation for excess molar polarization is found to be more appropriate for detailed study of molecular association in the liquid mixtures.     

A new microwave dielectric method for studying photoinitiated chain radical polymerization processes

Measurements of both real and imaginary parts of the dielectric constant at a fixed microwave frequency have been performed on n-butyl acrylate/poly(n-butyl acrylate) mixtures. The dielectric constant of the mixtures has been compared with that of neat n-butyl acrylate during UV photoinitiated polymerization. The values of the imaginary part of the dielectric constant thus obtained have allowed determination of the instantaneous monomer concentration and verified the kinetic equation for the photoinitiated polymerization process. The limits of validity of the method as well as its capability of providing detailed kinetic information are also discussed.     

Effects of diluent on molecular motion and glass transitions in polymers. III. The system poly(vinyl acetate)–toluene

Dielectric measurements, differential thermal analyses (DTA), and broad-line proton magnetic resonance (NMR) measurements are reported on the system poly(vinyl acetate)–toluene. Four dielectric relaxations were observed between 80 and 400°K. From proton NMR measurements on solutions in toluene and in deuterated toluene, the relaxation processes can be assigned, respectively, to segmental motion of poly(vinyl acetate), α; motion of side group, β′ rotation of toluene, β; local motions of poly(vinyl acetate) and toluene, γ, in order of appearance with decreasing temperature. Two stepwise changes in DTA traces have been observed and can be assigned as glass transition points T_gI and T_gII. Comparison of these glass transition points with temperatures at which dielectric relaxation times for the α and β processes are 100 sec, indicate that segmental motion of poly(vinyl acetate) and rotation of toluene are frozen-in at T_gI and T_gII, respectively. Activation plots for the α process conform to the Vogel–Tamman equation. In terms of the parameters A, B, and T₀ of the equation, T_gI can be represented by an expression of the form T_gI ≈ T₀ + B/(A + 3). In the range of concentration above 50% by weight, A and B are almost independent of concentration but T₀ varies strongly. The nature of the secondary dispersions is also discussed.     

Pressure dependence of the β molecular relaxation process and dielectric properties of polyvinylidene fluoride

The effects of hydrostatic pressure to 20 kbar on the β molecular relaxation process of polyvinylidene fluoride (PVDF) and on the dielectric properties in the neighborhood of this relaxation have been investigated. This relaxation has a strong influence on the electrical and mechanical properties of PVDF. Pressure causes a large shift to higher temperatures (～ 10K/kbar) of the dielectric relaxation peak and a decrease in the width of the distribution of relaxation times. This slowing down of the relaxation process is discussed in terms of the Vogel–Fulcher equation and related models, and it results from an increase in both the energy barrier to dipolar motion and the reference temperature (T₀) for the kinetic relaxation process which represents the “static” dipolar freezing temperature for the process. The general applicability of the Vogel–Fulcher equation to relaxional processes in polymers and other systems is briefly discussed. The pressure dependence of the dielectric constant both above and below the relaxation peak temperature (T_max) is found to be dominated by the change in polarizability. The effect is larger above T_max because of the relatively large decrease in the dipolar orientational polarizability with pressure.     

Kinetics and mechanism of the oxidation of glycine by N-bromosuccinimide

A systematic kinetic study on the oxidation of glycine by N-bromosuccinimide (NBS) in presence of mercuric acetate in acetic acid—water media has been made. Near first order dependence inNBS and glycine and near inverse first order dependence in hydrogen ion concentrations have been observed. A negligible ionic strength effect and a positive dielectric effect have been observed. Various rate parameters have been computed and hydrocyanic acid identified as the end product. On the basis of the kinetic data, a mechanism of the reaction has been proposed.With 3 Figures     

Characterization of the electroclinic effect of smectic LCs in terms of the transitional dielectric constant in the SA phase

Abstract

The electric-field dependence of the dielectric constant of some materials which show a strong electroclinic effect in the S_A phase, has been studied by measurement of the transitional dielectric constant. We suggest that the observed variation of the dielectric constant may originate from the electric field induced dielectric biaxiality; this is inherent in a material that exhibits the electroclinic effect.     

Dielectric relaxation study of binary mixture of sulfolane and N,N-dimethylformamide in benzene solution using microwave absorption data

The dielectric constant (???) and dielectric loss (???) for dilute solutions of the binary mixture of different molar concentrations of sulfolane and DMF in benzene solution has been measured at 9.885 GHz and different temperatures (25, 30, 35, 40°C) by using standard microwave techniques. Following the single frequency concentration variational method, the dielectric relaxation time (??) and dipole moment (??) have been calculated. It is found that dielectric relaxation process can be treated as the rate process, just like the viscous flow. The presence of solute-solute molecular associations in benzene solution has been proposed. Energy parameters (??H _?, ??F _?, ??S _?) for dielectric relaxation process of binary mixture at 50% mole fraction in benzene at 25, 30, 35, and 40°C have been calculated and compared with the corresponding energy parameters (??H _??, ??F _??, ??S _??) for the viscous flow.     

Partition Coefficients at Infinite Dilution from Flory-Huggins Theory

Abstract

An expression relating partition coefficients at infinite dilution to Flory-Huggins interaction parameters has been derived. The equation has been successfully applied to the partitioning of alcohols between water and cellulose acetate. The solvent-solute interaction parameter has a dominant effect on partition coefficients. For the systems studied, solvent-polymer interactions appear to be negligible.     

Dielectric and raman spectroscopic studies on the rotational isomerism of t-butyl formate

Static dielectric constants, refractive indices and densities have been measured for t-butyl formate and acetate in cyclohexane at increasing concentrations and at two temperatures, 20°C and 60°C. The ΔH value for the cis-trans equilibrium of t-butyl formate and the dipole moment of the trans conformation has been calculated from the dielectric measurements taking the ΔS value calculated from the sum-over-states for the cis and trans conformations and assuming the dipole moment of the cis conformation to be equal to 1.94 D as found for t-butyl acetate, which has the cis conformation only.The relative intensities of the Raman bands corresponding to specific vibrations modes of the cis and trans conformations of t-butyl formate are measured in cyclohexane and acetonitrile at various concentrations. The enthalpy difference ΔH is also measured in the liquid state and in acetonitrile by variation of the intensity ratio of the bands with temperature.All thermodynamic quantities obtained from dielectric or Raman intensity measurements are compared with each other and with the theoretical values. The solvation energy difference between cis and trans conformations in cyclohexane and acetonitrile as well as in the liquid state are also compared with theoretical values. The large deviation of solvation energy difference between the experimental value and Onsager's model value are well described by an additional term, which considers dipole-dipole interaction.     

一种电荷转移晶体的磁和介电弛豫性质

在外加电场下,利用分子的旋转和取向运动是组装分子介电马达以及弛豫型分子介电体的一个主要策略。在本论文中,我们制备并表征了一个新的电荷转移晶体[C₁₀-DMPy][Ni(mnt)₂](1)(C₁₀-DMPy⁺=1-decanel-N, N-dimethylpyridinium, mnt^2-=马来二氰基二硫烯)。在一定的频率范围内,该化合物展现了介电弛豫行为,我们将此归于平衡阳离子的动力学位置取向和阴、阳离子间的电荷转移。该化合物的介电弛豫过程遵循Cole-Cole方程,偏离理想的Debye模型。单晶X-射线衍射表明该化合物的阴、阳离子分别独立堆积成柱状,柔性的有机阳离子与刚性的磁性阴离子构筑块间存在电荷协助氢键作用。此外,该化合物的磁行为展现为弱的铁磁耦合作用。