Orientational order parameter estimated from molecular polarizabilities – an optical study

A mechanism of dyes molecules orientation by laser radiation is proposed that takes into account anisotropy of molecular optical polarizability. A dependence of dye molecules energy on polarizability anisotropy, order parameter, quantity of molecules in a cluster, strength of light wave electrical field, light beam incidence angle is derived.

The refractive indices, densities and ultrasonic velocities of binary liquid mixtures of tetrahydrofuran (THF) with methanol and o-cresol over the entire composition range have been measured at 293, 303 and 313 K. Refractive index, density and ultrasonic velocity data have been used to evaluate the molar refraction deviation ∆Rm, deviation in ultrasonic velocity ∆u, excess internal pressure π i , excess molar enthalpy H m and excess free volume V E f . The computed results of ∆Rm, ∆u, π E i , H m and V E f were fitted to the Redlich–Kister polynomial equation. These results suggest that specific strong interactions are taking place in THF + o-cresol mixture while dispersive forces seem to be responsible for behaviour of THF + methanol mixture. Further, experimental refractive index and density data of these mixtures were also used to test the validity of the empirical/semi-empirical relations and models for refractive index and density, respectively.

ABSTRACTOrientational order parameter is one of the important parameter of the liquid crystalline mesogens. This parameter governs nearly all physical properties of mesogens. Many methods are known for the estimation of orientational order parameter in liquid crystalline phase. In the present investigation the birefringence and dilatometric techniques have been exploited on some liquid crystalline CBOnO.m compounds with spacer n = 7, 10, 8, 5, and terminal group m = 10. Using density and birefringence data, the molecular polarizability and the orientational order parameter by Vuks and Neugebauer methods were evaluated and discussed the results with available data on number of liquid crystalline compounds.

Birefringence, polarizability order parameters and DFT calculations in the nematic phase of two bent-core liquid crystals and their correlation

The refractive indices, optical anisotropies, polarisabilities and order parameters of a number of phenylthiophenes and the parent dithienyl and biphenyl compounds with butylsulfanyl and cyano substituents have been measured. The presence of a thiophene ring leads to: (i) increased values of n∥ and n⊥ with the latter values normally being increased more so that the optical anisotropies are typically reduced, and (ii) increased molecular polarisabilities with the 2,5substituted thiophene compounds having higher values than the 2,4-substituted compounds. The dithienyl compound has the lowest order parameter and the highest molecular polarisability. The results are discussed in terms of the structural differences of the compounds, including differences in the pattern of substitution in the thiophene ring and in linearity, inter-annular torsion angle and the distribution of the permanent dipoles.

Recently, several studies have shown that the addition of a secondary element likes Al, Si, etc. to nitride and carbide binary systems such as Ti–N and Cr–N improved their structural and mechanical properties and also their thermal stability. In this study, we realized a comparison between the effects of aluminium or molybdenum addition on the properties of the Cr–N system. The (Cr,Al)N and (Cr,Mo)N films were deposited by RF dual magnetron sputtering. To control the aluminium and molybdenum contents in (Cr,Al)N and in (Cr,Mo)N films, respectively, we modified the Cr, Al and Mo target bias. The structural, morphological and composition analyses of the deposited films were carried out using X‐ray diffraction (XRD) and SEM equipped with an energy dispersive spectroscopy (EDS) microanalysis. The variation of the residual stresses with the Al and Mo contents has been studied using the Newton's rings method. The obtained Al contents in (Cr,Al)N deposited films varied between 0 and 51 at.% while the Mo contents in (Cr,Mo)N layers varied between 0 and 42 at.%. A morphological change from amorphous to columnar films has been observed with the addition of Al in the case of (Cr,Al)N coatings, while all the (Cr,Mo)N films presented a columnar structure. The residual stresses of the (Cr,Mo)N coatings are higher than the (Cr,Al)N ones but they exhibited a similar behaviour for both coatings.

Experimental and correlation of viscosity and refractive index of non-aqueous system of diethanolamine (DEA) and dimethylformamide (DMF) for CO2 capture

The experimental densities, ρ, relative permittivities, ε, and refractive indices, nD, of binary mixtures of dihydrofuran-2(3H)-one + butan-1-ol and + butan-2-ol have been measured at T = (293.15 to 313.15) K and atmospheric pressure over the whole mole fraction range. From density data, excess molar volumes, VE, were calculated at various temperatures. VE is negative for all systems investigated. The experimental results have been correlated using the Redlich−Kister polynomial equation, and parameters from least-squares analysis have been reported.

The tri critical point (TCP), where the second-order transition transforms to first order has been located in nO.m homologous series. The order parameter has been estimated from the birefringence δn, from the refractive indices and from birefringence data available in literature and from those obtained at our laboratory on a number of nO.m compounds. The compounds in the nO.m series exhibit both second and first-order nematic/smectic-A (NSA) transition depending on the McMillan ratio (TNA/TIN) which in turn depends on the nematic and smectic-A thermal ranges. The data presented are compared with the body of the data available on this homologous series obtained with other techniques.

Reaction pathways of biochemical processes are influenced by the dissipative electrostatic interaction of the reagents with solvent water molecules. The simulation of these interactions requires a parametrization of the permanent and induced dipole moments. However, the underlying molecular polarizability of water and its dependence on ions are partially unknown. Here, we apply intense terahertz pulses to liquid water, whose oscillations match the timescale of orientational relaxation. Using a combination of terahertz pump / optical probe experiments, molecular dynamics simulations, and a Langevin dynamics model, we demonstrate a transient orientation of their dipole moments, not possible by optical excitation. The resulting birefringence reveals that the polarizability of water is lower along its dipole moment than the average value perpendicular to it. This anisotropy, also observed in heavy water and alcohols, increases with the concentration of sodium iodide dissolved in water. Our results enable a more accurate parametrization and a benchmarking of existing and future water models.

Simultaneous viscosity and density measurements and modeling of 2-alcohols at temperatures between (291 and 353) K and pressures up to 50 MPa

The relative intensities of O and S branch lines in the v=1←v=0 Stokes Raman spectrum of gaseous H2, D2, N2, O2, and CO have been measured in order to obtain a parameter χ= (α∥−α⊥)e/{re[∂ (α∥−α⊥)/∂r]e}. Values for χ reflect the detailed molecular electronic structure and are needed in various scattering theories and to correct rotational and vibrational–rotational Raman intensities for molecular nonrigidity and vibrational-rotational interaction. The values of χ obtained are +0.38±0.01 (H2), +0.38±0.01 (D2), +0.45±0.09 (N2), +0.23±0.07 (O2), and +0.27±0.13 (CO). By combining the measured values of χ with experimental values for 〈α∥−α⊥〉v=0 in the literature, the following values of the polarizability anisotropy and its first derivative at re are obtained: (α∥−α⊥)e=0.288 (H2), 0.282 (D2), 0.691 (N2), 1.080 (O2), and 0.525 (CO) Å3; [∂ (α∥−α⊥)/∂r]e=1.02 (H2), 1.00 (D2), 1.40 (N2) 3.89 (O2), and 1.72 (CO) Å2. These values are compared with literature theoretical values. Molecular polarizability is an experimentally accessible quantity which reflects in a rather direct way the electronic structure of simple molecules. For this reason the orientational anisotropy of molecular polarizability and its variation with internuclear distance are of fundamental interest in developing understanding of the detailed electronic structure of diatomic molecules. Polarizability anistropies and their derivatives are directly related to both absolute and relative intensities of vibrational and rotational Raman transitions.

The densities and refractive indices of two binary systems (water + MEA and water + MDEA) and three ternary systems (water + MEA + CO2, water + MDEA + CO2, and water + MEA + MDEA) used for carbon dioxide (CO2) capture were measured over the range of compositions of the aqueous alkanolamine(s) used for CO2 absorption at temperatures from 295 to 338 K. Experimental densities were modeled empirically, while the experimental refractive indices were modeled using well-established models from the known values of their pure-component densities and refractive indices. The density and Gladstone−Dale refractive index models were then used to obtain the compositions of unknown samples of the binary and ternary systems by simultaneous solution of the density and refractive index equations. The results from this technique have been compared with HPLC (high-performance liquid chromatography) results, while a third independent technique (acid−base titration) was used to verify the results. The results show that the systems' compositions obtained from the simple and easy-to-use refractive index/density technique were very comparable to the expensive and laborious HPLC/titration techniques, suggesting that the refractive index/density technique can be used to replace existing methods for analysis of fresh or nondegraded, CO2-loaded, single and mixed alkanolamine solutions.

In this paper, we present the application of transmissive terahertz (THz) time-domain spectroscopy for determining molecular polarizability for three widely applied solvents: water, ethanol, and acetone. Molecular polarizabilities of those solvents are obtained from the refractive index by using the Lorentz-Lorenz equation. The measured THz molecular polarizabilities are comparable with theoretical values estimated with both the first principle calculation and the atomic polarizability additive model. The THz spectra are presented over frequencies ranging from 0.3 to 1.2 THz (10-40cm-1). The molecular polarizability at 1.0 THz is determined as 3.81±0.03, 7.04±0.07, and 7.9±0.2Å3 for water, ethanol, and acetone, respectively.

Molecular dynamics simulation is used to study the relaxation of the polarizability anisotropy in liquid ethanol at temperatures of 298 and 348 K. Ethanol molecules are represented by a four-site semi-flexible model in which the internal degree of freedom, corresponding to the torsional motion around the C–O bond, is taken into consideration. The molecular polarizability is calculated using an interaction-site model, based on the modified dipole-induced dipole model developed by Thole. The collective polarizability induced by intermolecular interactions is included using first-order perturbation theory and calculated considering both center–center and site–site models. Results are analyzed in terms of projected variables that allow the decomposition of the total relaxation into orientational and collision-induced components, both of which are influenced by molecular flexibility. We compare our data with the results of low-frequency depolarized Rayleigh light scattering experiments, examining the possibility of separating different relaxation processes from spectroscopic signals in the time and frequency domains. We find that even though the largest contributor to polarizability anisotropy dynamics is orientational relaxation, collision-induced contributions are important, especially at shorter times. Moreover, we show that torsional motion also plays a significant role in the fast decay of the polarizability anisotropy of the system. Although liquid ethanol is strongly associated and its dipolar relaxation is highly collective, we find orientational pair correlation effects on polarizability relaxation to be negligible. A comparison with simulation data previously obtained for methanol suggests that increasing the alcohol chain length decreases the relative importance of OH dynamics in polarizability relaxation. We further show that, as expected for such a structured liquid composed of strongly asymmetric molecules, polarizability and dipole relaxation processes exhibit marked differences.