Evidence of a liquid–liquid transition in a glass-forming ionic liquid

A liquid–liquid transition (LLT) is a transformation from one liquid to another through a first-order transition. The LLT is fundamental to the understanding of the liquid state and has been reported in a few materials such as silicon, phosphorus, triphenyl phosphite, and water. Furthermore, it has been suggested that the unique properties of materials such as water, which is critical for life on the planet, are linked to the existence of the LLT. However, the experimental evidence for the existence of an LLT in many molecular liquids remains controversial, due to the prevalence and high propensity of the materials to crystallize. Here, we show evidence of an LLT in a glass-forming trihexyltetradecylphosphonium borohydride ionic liquid that shows no tendency to crystallize under normal laboratory conditions. We observe a step-like increase in the static dielectric permittivity at the transition. Furthermore, the sizes of nonpolar local domains and ion-coordination numbers deduced from wide-angle X-ray scattering also change abruptly at the LLT. We independently corroborate these changes in local organization using Raman spectroscopy. The experimental access to the evolution of local order and structural dynamics across a liquid–liquid transition opens up unprecedented possibilities to understand the nature of the liquid state.

Influence of the uniaxial stress $p_2$ and transverse fields $E_1$ and $E_3$ on the phase transitions and thermodynamic characteristics of GPI ferroelectric materials

A modified GPI model that accounts for the piezoelectric coupling between the ordered structural elements and the strains $\varepsilon_j$ has been used for studing of effects arising in GPI ferroelectrics under the action of the uniaxial stress $p_{2}$ and electric fields $E_1$ and $E_3$. The polarization vectors and components of static dielectric permittivity are calcucated in the two-particle cluster approximation for mechanically clamped crystal, and piezoelectric and thermal parameters are also determined. The influence of the simultaneous action of the stress $p_{2}$ and fields $E_1$ and $E_3$ on the phase transition and physical characteristics of GPI crystal has been studied.

Dielectric spectroscopy and hydrogen bonding studies of 1-chloropropane–ethanol mixture using TDR technique

The time-domain reflectometry technique was exercised to assess the complex permittivities of 1-chloropropane and ethanol along with their binary mixture in the frequency range of 10[Formula: see text]MHz–50[Formula: see text]GHz and in the temperature range of 10–[Formula: see text]C. Dielectric parameters like static dielectric permittivity ([Formula: see text] and relaxation time ([Formula: see text] have been acquired by the least-square-fit method. The obtained assessments of static permittivity and relaxation time were used to compute various dielectric parameters like excess dielectric constant, excess relaxation time, Kirkwood correlation factor and thermodynamic parameters. The experimental outcome illustrates the nonlinear variations in dielectric permittivity, relaxation time and authenticates the structural formation due to intermolecular interaction between 1-chloropropane and ethanol. Molecular rotary motion and dipole reorientation movements of these complex systems are presented in agreement with the molar entropy and enthalpy.

Применение электростатической силовой микроскопии для определения статической диэлектрической проницаемости индивидуальных молекул гемоглобина

The technique for determination the dielectric permittivity of individual hemoglobin molecules based on modeling the profiles of their images obtained by electrostatic force microscopy is presented. The obtained values of static dielectric permittivity are in agreement with the literature data. The proposed technique can be adapted to determination the dielectric characteristics of individual molecules of various proteins.

Influence of Longitudinal Electric Field on Thermodynamic Properties of NH3CH2COOH·H2PO3 Ferroelectric

Using a modified model of ferroelectric glycine phosphite by considering the piezoelectric coupling with strains e1 within the two-particle cluster approximation, the expressions for the polarization vector, static dielectric permittivity tensor, piezoelectric coefficients, and elastic constants of the crystal in the presence of a longitudinal electric field E2 are calculated. An analysis of the influence of this field on thermodynamic characteristics of the crystal is carried out. The dependence of effective dipole moments on order parameters is taken into account. This allowed us to agree the effective dipole moments in the ferro- and paraelectricphases and to describe the smearing of phase transition under the influence of an electric field. The satisfactory quantitative description of the available experimental data for these characteristics has been obtained at the proper choice of the model parameters.

Fluctuation-induced dielectric permittivity in the isotropic phase of cholesteric liquid crystals

The temperature and pressure dependence of the static dielectric permittivity in the isotropic phase of the isotropic to cholesteric phase transition is calculated using Landau–de Gennes’s fluctuation theory, allowing spatial variation of the orientational order parameter. A comparison is made with experimental data available in the isotropic phase of the isotropic to cholesteric phase transition.

Theoretical investigation of dielectric properties of rare earth stillwellite compounds

Ab initio density functional calculations are performed to investigate the dielectric properties of LnBSiO 5 (Ln = Ce, Pr, Nd) with the stillwellite structure. The calculated structural parameters are found to agree well with existing experimental results. The three compounds possess insulating electronic structure with nearly isotropic high frequency dielectric permittivity tensors. On the other hand, the static dielectric permittivity tensors are found to be less isotropic. The anisotropy of static dielectric tensors are found to increase as the atomic number of the lanthanide increases.

Influence of External Pressures of Different Symmetry on the Phase Transitions and Thermodynamic of the RbHSO4 Ferroelectrics

We use the four-sublattice model of the RbHSO4 crystal modified by taking into account the piezoelectric coupling to the strains , . Within the mean field approximation we calculate the components of the polarization vector and static dielectric permittivity tensor of mechanically clamped and free crystals, as well as their piezoelectric characteristics. We study the influence of hydrostatic pressure and uniaxial stresses on the phase transition and physical characteristics of the crystal. A good quantitative description of the experimental data is obtained.