Parameters of LC molecules’ movement measured by dielectric spectroscopy in wide temperature range

Dielectric properties of a nematic liquid crystal (NLC) mixture ZhK-1282 were investigated in the frequency range of 10²–10⁶Hz and a temperature range of ?20 to 80?°С. On the basis of the Debye’s relaxation polarization model dielectric spectra of temperature dependence of the orientational relaxation time τ and the dielectric strength δe were numerically approximated at the parallel orientation of a molecular director relative to alternating electric field. Influence of ester components in the mixture plays crucial role in relaxation processes at low temperature and external field frequency. The activation energy of the relaxation process of a rotation of molecules around their short axis was measured in a temperature interval of ?20 to ?+15?°С in which the dispersion of a longitudinal component of the dielectric constant takes place. The energy of potential barrier for polar molecules rotation in the mesophase was calculated. The value of the transition entropy from the nematic to isotropic phase was obtained from this calculation. The values of the coefficient of molecular friction and rotational diffusion were obtained by different methods. The experimental data obtained are in a satisfactory agreement with the existing theoretical models.     

Mesomorphic behaviors of a series of heterocyclic thiophene-imine-ester-based liquid crystals

The synthesis and characterization of a series of heterocyclic liquid crystal, 4-{[(thiophen-2-yl)methylidene]amino}phenyl 4-alkoxybenzoates possessing even number of carbon atoms at the alkoxy chain (C_nH_2n+1O-, n = 6, 8, 10, 12, 14, 16, 18) are reported. The molecular structures of title compounds were elucidated using Fourier-transform infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopic techniques along with mass spectrometric analysis. The phase behavior of these compounds was characterized and studied by differential scanning calorimetry and polarizing optical microscopy. All members exhibited enantiotropic nematic phase except for the highest member (n = 18) which is a non-mesogen. Influence of alkoxy chain length on the transition temperatures of crystal-to-nematic (melting point) and nematic-to-isotropic (clearing point) was studied. Nematic phase range was found to increase from n = 6 to n = 10, then it started to descend from n = 12 to n = 16 and finally the nematic phase disappeared when n changed to 18.     

Finite deformation analysis of slip-induced crystalline rotations during tensile and compressive tests on bcc iron crystals

This work compares slip-induced lattice rotations calculated from double-slip, finite-deformation analytical solutions to electron-back-scattering-diffraction (EBSD) rotation measurements from SEM in situ, room temperature straining of bcc iron crystals. The finite-deformation modelling assumes slip proportionality between the two dominant active systems. Four experimental cases from a recently published work (2015) are examined, two in axial tension and two in axial compression. They correspond to mixed double-slip on {110} and {112} planes, with slip on the latter in both ‘easy’ and ‘hard’ orientations. In the experiments, EBSD rotation measurements were made on three faces of the iron samples and the dominant active systems were identified from slip traces. Here the relative contributions of the two systems for the best match with available rotation data are determined for each case, and the results discussed in relation to initial shear stress and (probable) critical shear-strength ratios. The analyses provide insight into achievable accuracy in crystal-slip quantification, based on slip-trace observations and rotation measurements of a sample’s load and lateral axes, and some assessment of the relative hardening of active slip systems.     

Optical damage resistance of Hf:Fe:LiNbO3 crystals with various [Li]/[Nb] ratios

Hf:Fe:LiNbO₃ crystals were grown in air by the Czochralski technique with various [Li]/[Nb] ratios ([Li]/[Nb]=0.94, 1.05, 1.20) in melt. The defect structure and location of doped ions were analyzed by the UV‐visible absorption spectra. The optical damage resistance of Hf:Fe:LiNbO₃ crystals was investigated by the photoinduced birefringence change and the transmitted light spot distortion method. The results show that the optical damage resistance ability of Hf:Fe:LiNbO₃ crystals decreases with the increase of the [Li]/[Nb] ratio. The dependence of the optical damage resistance of Hf:Fe:LiNbO₃ crystals on the defect structure is discussed in detail. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Acoustic-electromagnetic slow waves in a periodical defective piezoelectric slab

Coupled slow waves, slow acoustic waves, and electromagnetic waves are simultaneously achieved based on a piezoelectric material, in which a line defect is created within a honeycomb lattice array of cylindrical holes etched in a LiNbO_3 slab. Finite element simulations in frequency domain and time domain demonstrate that a highly localized slow mode is obtained in the defect. Owing to the piezoelectricity of LiNbO_3, acoustic and electromagnetic waves are coupled with each other and transmit along the line defect. Therefore, in addition to a slow acoustic wave, an electromagnetic wave with a group velocity even lower than conventional acoustic waves is achieved.     

Transmission and radiation of acoustic oblique incident through tube arrays based on phononic crystals theory

In a utility boiler, the heat exchanger’s structure is similar to a two-dimensional phononic crystal. Based on the phononic crystal theory, this paper studies sound propagation through tube arrays as a function of the incident sound direction and the surroundings temperature. We carried out both the computational and experimental work for particular values of the pitch and diameters in the tube arrays and studied the band-gap diagram and insertion loss spectra for different angles of incidence. The first band gap is found to correspond to Bragg’s Law while the second band gap moves to lower frequencies as the angle increases. Simulations indicate also that the uneven temperature field influences the insertion loss spectrum. Results of experiments and calculations confirm that, for a particular tube array, the most important factors influencing sound propagation are incidence angle and the surrounding temperature. For the acoustic source in tube arrays, the acoustic radiation have relation with the frequency whether in the acoustic bang gap or not. The results should provide a basis for further work: both on sound source localization and low frequency sonic cleaning in large tube arrays.     

Synthesis and study of mesomorphic properties in rod-like chalconyl compounds

In order to investigate the influence of the central linking group and effect on flexibility on mesophase behavior of liquid crystal we have synthesized newly homologous series viz. 3-(4-Octyloxyphenyl)-1-(4′-n-alkoxy phenyl) prop-2-en-1-one (Series-l) consists of thirteen homologues (C₁ to C₈, C₁₀, C₁₂, C₁₄, C₁₆, C₁₈). Textures of a nematic phases are threaded or Schlieren type. The textures of smectic and nematic phase are directly judged from the heating and cooling condition. Group efficiency order for mesophases is derived on the basis of thermal stabilities from the comparative study of thermometric data determined from structurally analogous series. A transition curve as depicted in a phase diagram behaves in normal manner. Structural and conformational characterization of these new compounds had achieved by ¹H NMR, ¹³C NMR, IR, and elemental analysis.