H NMR study of hydrogen bonding and molecular dynamics of 5CB confined to molecular sieves

It has been found that the main mechanism of ¹H protons spin–lattice relaxation of bulk 5CB at 200 MHz is its intramolecular motion, namely, the reorientation of CH₂ and CH₃ groups of its alkyl chain. Activation parameters of such motions have been estimated.

Drastic decrease in proton spin–lattice relaxation times at the nematic-to-isotropic phase transition can be explained by the activation of molecular translational diffusion and reorientations around long and short molecular axes of bulk 5CB.

Our NMR analysis revealed the slowing-down of molecular dynamics of confined 5CB molecules and their fragments. This can be explained by the interaction of some part of 5CB molecules with the surface active Si(Al)–OH centers of MCM matrix via hydrogen bonds of Si(Al)–OHN≡C-type.     

Investigation of the structure of the flow in an axisymmetric dead-end

The results of an experimental investigation of the structure of the flow in an axisymmetrical dead-end, with central flow of the liquid, are presented.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza., No. 2, pp. 16–23, March–April, 1977.     

Polymorphic transformations and thermal deformations of monoclinic n-paraffins C30H62 and C32H66

Thermal deformations and polymorphic transformations of even long chain monoclinic normal paraffins C₃₀H₆₂ and C₃₂H₆₆ (homological purity 97–99%) are studied. Thermal deformations and temperature limits of the existence of crystalline (1M _cryst and 2M _cryst ), low-temperature rotationally crystalline triclinic (Tc _rot.1), monoclinic (M _rot.1), and orthorhombic (Or _rot.1) and high-temperature rotationally crystalline hexagonal (H _rot.2) phases of these n-paraffins are estimated by the character of changes in their diffraction patterns and unit cell parameters (thermal X-ray diffraction). The molecular structure and conformational composition of these n-paraffins in different phase states are determined (IR spectroscopy). In order to determine the temperatures of phase transitions differential scanning calorimetry is also applied. The data of all three methods are in good agreement with each other. The initial sample of C₃₀H₆₂ n-paraffin at room temperature is characterized by a two-layer monoclinic 2M crystalline modification. When the melt is rapidly cooled, it crystallizes in monolayer monoclinic 1M and orthorhombic Or modifications (two-phase mixture 1M+Or). The initial sample of C₃₂H₆₆ n-paraffin at room temperature is characterized by the monolayer monoclinic modification 1M. When the melt is rapidly cooled, as well as C₃₀H₆₂ n-paraffin, it crystallizes in monolayer monoclinic 1M and orthorhombic Or modifications (two-phase mixture 1M+Or). It is found that both n-paraffin undergo irreversible polymorphic transformations from the crystalline state cryst to the low-temperature rotationally crystalline state rot.1. For C₃₀H₆₂ n-paraffin the transition is performed by the scheme 2M _cryst → M _rot.1 → Or _rot.1, and for C₃₂H₆₆ n-paraffin it is performed by the scheme 1M _cryst → Tc _rot.1. Both paraffins do not undergo the transition to the high-temperature rotationally crystalline state rot.2 (hexagonal phase H _rot.2), similarly to monoclinic C₂₈H₅₈ n-paraffin studied previously. These and previously obtained data allow us to consider that as the molecular chain length increases, differences in the polymorphic modification of initial crystalline phases cease to be significant and the sequence of polymorphic transformations is mainly determined by the length of the molecule.     

Basic properties of the problem of the best simultaneous approximation of several elements

For the problem of the best approximation of several elements with respect to the maximum of convex-concave fractional functions with additional restrictions, we establish duality relations and criteria for the element of the best approximation. Kamenets-Podol'skii Pedagogical Institute, Kamenets-Podol'sk. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 48, No. 9, pp. 1183–1193, September, 1996.     

Mass transfer of indium in the In-CdTe structure under nanosecond laser irradiation

The features of mass transfer of indium in high-resistance CdTe crystals under nanosecond irradiation of the In-CdTe structure by laser pulses have been studied and analyzed. The mass transfer coefficients are determined and the average transfer rate of the indium atoms in CdTe under irradiation is evaluated. It is assumed that the concentration diffusion of indium in CdTe and the transfer of impurity atoms by the front of the laser-induced shock wave are not dominant mechanisms of mass transfer under dynamic doping. The most probable process, which provides the formation of the inverse layer in the surface region of the CdTe crystal under nanosecond laser irradiation of the In film, is an transfer of interstitial In atoms due to the thermal fluctuation jumps under the action of the driving force of the thermoelastic stresses and temperature gradient.     

Influence of Confinement on The Phase Transition And Spectral Characteristics of Nematic Liquid Crystals

The results of nematic liquid crystal - isotropic liquid phase transition study by the method of differential scanning calorimetry for inclusion compounds - mesoporous aluminosilicate molecular sieves of MCM-41 type (including Cu-exchanged samples) with encapsulated in inner-crystalline space nematic liquid crystal (5CB), as well as IR spectroscopic data for such compounds were represented. It was shown, that the 5CB molecules are able to interact with the active centers in the MCM-41 channels forming strong enough bonds of -C≡N⋅⋅⋅H-O- type. The relative amount of 5CB molecules interacting with the walls of channels and those retaining ‘liquid crystalline’ state in binary systems of molecular sieves MCM-41 and CuMCM-41 was estimated. This conclusion was confirmed by the data obtained from differential scanning calorimetry measurements. This revised version was published online in August 2006 with corrections to the Cover Date.     

Correlation between the structure and magnetic and strength properties in high-carbon alloys alloyed by aluminium

Using the method of magnetic analyses and the measurements of hardness investigation of changes of the mechanical and magnetic properties of high-carbon Fe?Al?C alloys in the beginning of a low-temperature tempering has been conducted. Along with X-ray diffraction data these technics gave a possibility to make some conclusions on the processes which take place during the first stage of the martensite structure decay.     

Polymorphic transformations of C26H54 and C28H58 n-paraffins as typical rotator substances

Thermal deformations and polymorphic transformations of two long-chain evennumbered normal paraffins C₂₆H₅₄ and C₂₈H₅₈ were studied by thermal X-ray diffraction (temperature step is tenths of a degree), infrared spectroscopy (temperature step is 1–5°), and differential scanning calorimetry (temperature step is 2° in a sample heating melt cooling mode. The samples are characterized by high homologous purity (99.0%) and belong to so-called “boundary” n-paraffins. The starting C₂₆H₅₄ n-paraffin sample is a triclinic modification at room temperature (Tc _cryst). When quickly cooled, the melt crystallizes as the triclinic Tc _cryst and monoclinic monolayer 1M _cryst forms (two-phase mixture Tc _cryst + 1M _cryst). The starting C₂₈H₅₈ n-paraffin sample is a double-layer monoclinic modification 2M _cryst at room temperature. Crystallization from hexane or slow cooling of a melt leads to a monolayer monoclinic form 1M _cryst. Thermal deformations and temperature ranges of existence of the crystalline forms (Tc _cryst, 1M _cryst, and 2M _cryst), low-temperature rotator crystalline orthorhombic form (Or _rot.1), and high-temperature rotator crystalline hexagonal (H _rot.2) phases of these n-paraffins were evaluated from changes in their diffraction patterns and unit cell parameters. The molecular structure and the conformational composition of these n-paraffins in different states were found from their IR spectra. Differential scanning calorimetry (DSC) was used to determine the phase transition temperature. Thermal X-ray diffraction, IR, and DSC data agree well with one another.     

Peculiarities of the structure and intermolecular interactons in 4-n-ALKYL-4′-cyanobiphenyls studied by IR spectroscopy

Experimental and theoretical methods of IR spectroscopy have been used to study the peculiarities of the structure and of intermolecular interactions in the homologous series of 4-n-alkyl-4′-cyanobiphenyls (abbreviated to nCBs, where n is the number of carbon atoms in the alkyl radical). IR absorption spectra of nCBs (n = 4, 8, 9) were measured in the frequency range from 400 cm^?1 to 4000 cm^?1 and in the temperature range from 26° to 100°C, which corresponded to the crystalline, liquid crystalline and liquid states of the samples. The analysis of the measured spectra was performed with regard to available X-ray data on the structures of crystalline phases and to the theoretical modeling of IR spectra; a comparison with previously studied spectra of nCBs with n = 2 and 5 was made. Characteristic differences between the spectra of higher and lower homologues of nCBs were found. Changes in the conformation of nCB molecules with the change of temperature and the length of the alkyl radical are discussed.