K. Orzechowski

Electric field effect on the upper critical solution temperature

Abstract Using a non-linear dielectric effect apparatus the influence of electric fields on the upper critical mixing temperature of nitrobenzene+2,2,4-trimethylpentane was investigated. A downward shift of the critical temperature proportional to the square of the electric field was found. The d T c /d E 2 derivative was estimated as −0.85±0.2×10 −15 K m 2 V −2 .

Electrical properties of an ethanol–dodecane mixture near the upper critical solution point

The electric permittivity and conductivity of an ethanol–dodecane critical mixture have been investigated as a function of frequency (100 Hz–1 MHz) and temperature. Dispersion of the electric permittivity and conductivity were found and these phenomena were interpreted in terms of Maxwell–Wagner polarization. The temperature dependence of Iµ for high frequencies was described according to Sengers model and the theoretically predicted critical exponent (0.89) agrees with the experimental results. The temperature dependence of the conductivity was analysed both for low (f fr) frequencies. The non-linear temperature dependence of the background term makes the estimation of the conductivity critical exponent very difficult, but for low frequencies the exponent ϕ= 1 –α is the most probable one. The Maxwell–Wagner permittivity increment defined as ΔIµMW=Iµf fr diverges in the vicinity of Tc with an exponent of –0.39. The conductivity increment defined as ΔσMW=σf>fr–σf<fr diverges in the vicinity of Tc with an exponent of 0.22, close to the value predicted on the basis of the Wagner model, β-exponent value.

Nonlinear dielectric effect in ethanol-dodecane critical mixture

Abstract The nonlinear dielectric effect in ethanol + dodecane critical mixture ( T c = 13.6±0.03° C , x c = 0.68±0.005 mole fraction of EtOH) as a function of temperature and concentration was investigated. The strong increase of Δe/ E 2 in the vicinity of the critical solution point was found. The critical anomaly was expressed by the power law equation: Δe / E 2 = ( Δe / E 2 ) B + Ct - Θ and the obtained critical exponent value Θ was 0.57±0.07.

Complex formation in binary propionic acid-triethylamine mixtures: A dielectric relaxation and titration study

Complex (dielectric) permittivity spectra of propionic acid-triethylamine mixtures have been measured using four different frequency domain methods to cover the frequency range from 1 MHz to 40 GHz. At 20 °C spectra have been determined at eight mole fractions xb of base between 0.11 and 0.8. For one mixture (xb=0.3) measurements have been performed at ten temperatures between −20 °C and 25 °C. Additionally, the extrapolated low frequency (static) permittivity of the propionic acid triethylamine system has been obtained at 0⩽xb⩽1 from titration measurements in the frequency range between 1 MHz and 1 GHz. The spectra exhibit a dielectric relaxation in the microwave region, subject to a small unsymmetric relaxation time distribution, and an extrapolated high frequency permittivity e(∞) which noticeably exceeds the squared optical refractive index nD2. The microwave relaxation is discussed in terms of acid–base complexes in the liquid, including proton transfer complexes. The dielectric spectra do not eviden...

Shift of the critical mixing temperature in strong electric fields. Theory and experiment.

We study the shift in the critical temperature T(c) in binary mixtures in strong electric fields. In experiments we measure the nonlinear dielectric effect (NDE) in a mixture of nitrobenze and n-octane and calculate Piekaras factor. We find that the critical anomaly of Piekaras factor is a function of an electric field strength. We propose to explain this observation as a result of a downward shift of T(c), and this allows us to calculate (∂T(c)/∂E(2)) = (-22 ± 10) × 10(-16) (K m(2))/V(2). In the theoretical part we amend Landau and Lifshitzs formula and show that the downward shift of Tc can be estimated from a simple mean-field theory taking into account the linear and quadratic terms in an expansion of the constitutive relation ε(x) between the electric constant ε and mixture composition x.

Investigation of the structure of aqueous solutions of 1,2-and 1,4-butanediol by positron annihilation and ultrasonic methods

The structure of aqueous solutions of 1,2-butanediol and 1,4-butanediol was investigated using adiabatic compressibility measurements and positron annihilation methods. In the case of 1,2-butanediol the experimental results are very similar to those obtained earlier for systems where hydrophobic hydration dominates. In both cases there are evidences for increased rigidity of the water network, which arises from the formation of hydrogen bonds between diols and water. The usefulness of both the methods applied in investigating the structure of liquid solutions was proved.

DIELECTRIC PROPERTIES OF METHANOL + HEXANE CRITICAL MIXTURES WITHOUT AND WITH IONIC ADDITIVES

Abstract The electric permittivity and conductivity of methanol + hexane and methanol + hexane + (CH3)4NCl mixtures were investigated in the vicinity of consolute critical point. The properties of the investigated system are similar to those of others phase separating mixtures. The observed low frequency dispersion was explained in terms of Maxwell-Wagner phenomena in a mixture with large concentration fluctuations. The generalised equations describing e(t) and σ(t) (e — is the electric permittivity, σ — is the specific conductivity, t — is the reduced temperature) both in low and high frequencies were proposed and tested for the title systems. Critical mixtures and microemulsions were found to be similar. The permittivity dispersion both for x xc, the dispersion is negligible — as in “oil-in-water” ones.

Comparison studies of the influence of an electric field on permittivity close to ferroelectric-paraelectric phase transition in TGS, DMACA and DMABA crystals

Abstract The non-linear dielectric effect (NDE) technique was applied to the studies of the ferro-paraelectric phase transition in TGS, [(CH3)2NH2]Sb2Br9 (DMABA) and [(CH3)2NH2]3Sb2Cl9 (DMACA) crystals. The NDE response for these three crystals was explained in terms of the reversed polarization process. The critical exponents were estimated for TGS and DMACA.

Non-linear dielectric effect in an ethanol + dodecane critical mixture with minor amounts of ions

A critical binary mixture with a low concentration of ions (tetramethylamonium chloride) was investigated by the non-linear dielectric method. It was observed that the addition of ions increases the critical anomaly of the non-linear dielectric effect. The increase was only observable at low frequencies of the measuring field. Possible explanations are presented and discussed. In spite of the very low concentration of ions, some evidence of crossover from Ising-like to the mean field behaviour was found.

Dielectric, acoustic, densimetric and viscosimetric investigations of the tributylamine + propionic acid system

Data obtained at 293 K and atmospheric pressure by different experimental techniques, dielectric, acoustic, densimetric and viscosimetric, give an almost uniform picture of the structure of the investigated binary mixture. The extrema observed at the concentration range 70–75 mol% of propionic acid are explained as a result of the formation of amine–acid associates of composition 1:n where n≈3. Analysis of the dielectric relaxation parameters suggests a high flexibility of these associates.