The kinetics of the first-order solid-state structural transition in monodisperse n-alkanes samples of even tetracosane C 24 H 50 was studied by FTIR spectroscopy. The existence of many irregular conformers in solid phases of tetracosane, the concentration of which reaches a maximum when approaching the melting temperature, has been demonstrated. The existence of these defective molecules promotes transitions between different rotator phases in the solid state.

The kinetics of the first-order solid-state structural transition in monodisperse n-alkanes samples of odd tricosane C23H48 and even tetracosane C24H50 was studied by FTIR spectroscopy. The initial nuclei location of the new phase was revealed. The process of crystal structure rearrangement is initiated in the interlayers between neighboring lamellar for odd tricosane, while the nanonuclei in even tetracosane arise in the crystalline lamellas cores. Thus, the influence of the number evenness of carbon atoms in the n-alkanes chains on the first-order structural phase transition has been proved.

The kinetics of the structural first order phase transition in the tetracosane С24Н50 monodisperse samples is studied with the help of FTIR spectroscopy. The temperature dependencies of the frequency and intensity of rocking (ν~ 720 cm-1) and bending (ν~ 1470 cm-1) vibrations of СН2-groupes in the methylene trans-sequences in the crystalline cores of the elementary lamellae are investigated. It is shown that the first order solid phase transition is developing on a heterogeneous mechanism in the narrow temperature interval (T~ 2 K) according to the theory of the diffused first order phase transitions and is due to the crystalline cell symmetry change.

The dependence of the IR absorption spectrum on the type of symmetry of crystallographic cells allowed us to investigate the kinetics of phase transitions. It is confirmed that the first order solid-phase transition develops by a heterogeneous mechanism in a narrow temperature range Delta T >= 1 K.

The kinetics of the development of the structural phase transition of the first order in monodisperse samples of tetracosane C24H50 has been studied using Fourier-transform IR spectroscopy. Temperature dependences of frequencies and intensities of rocking (in the region of  ν ~ 720 cm–1) and bending (in the region of  ν ~ 1470 cm–1) vibration modes of CH2 groups in trans methylene sequences in crystalline cores of elementary lamellae has been analyzed. It has been shown that the solid-phase transition of the first order develops by the heterogeneous mechanism in a narrow temperature interval ΔT ~ 2 K according to the theory of diffuse phase transitions of the first order and is caused by changes in the symmetry of crystallographic cells.

The structural changes in crystalline lamella cores of tridecanoic acid CH 3 (CH 2 ) 11 COOH during heating in the range from the temperature T 1 = 13.5°C to T 2 > T m = 41.6°C have been investigated using Fourier transform infrared spectroscopy. The behavior of the bands of rocking (in the region of 720 cm –1 ) and bending (in the region of 1470 cm –1 ) vibrations of CH 2 groups in tridecanoic acid methylene segments has been analyzed. It has been shown that, in the first-order phase transition region ( T s–s ~ 36°C) within a narrow temperature range (Δ T 1 ≤ 1 K), there is a gradual transformation of the initial triclinic subcell into the hexagonal subcell. The mechanism of this transition has been considered in terms of the theory of diffuse first-order phase transitions.

Методом ИК-Фурье спектроскопии изучены структурные изменения в кристаллических сердечниках ламелей тридекановой кислоты СН3(СН2)11СООН при нагревании от T1=13.5oC до T2>Tm=41.6oC. Анализировалось поведение полос маятниковых (область 720 cm-1) и деформационных (область 1470 cm-1) колебаний СН2-групп в метиленовых отрезках тридекановой кислоты. Показано, что в области фазового перехода I рода (Ts-s~36oC) в узком температурном интервале (Delta T1≤1 K) происходит постепенная трансформация исходной триклинной субъячейки в гексагональную субъячейку. Рассмотрен механизм этого перехода с позиции теории диффузионных фазовых переходов I рода. Работа выполнена при финансовой поддержке Российского фонда фундаментальных исследований (код проекта 16-03-00493). DOI: 10.21883/FTT.2017.02.44056.285

The IR absorption spectra of α,ω-alkanediols with different chain lengths, HO(CH 2 ) 22 OH and HO(CH 2 ) 44 OH, in the spectral range of 400–5000 cm −1 are analyzed. The assignment of numerous absorption bands to vibration modes in short methylene sequences and terminal hydroxyl groups is suggested. The splitting of IR absorption bands into doublets at 720–730 cm −1 (rocking vibrations of CH 2 groups) and 1463–1473 cm −1 (bending vibrations of CH 2 groups) testifies that the crystal unit subcells in the lamellae of alkanediols are orthorhombic with parameters typical of normal hydrocarbons. The specific features of absorption bands due to O-H stretching and C-O-H bending vibrations have been analyzed. These bands appear during formation of lengthy associates from hydrogen bonds formed by hydroxyl groups on the surface of elementary lamellae. A sharp increase in the intensity of the absorption bands in progression of C-C stretching and CH 2 wagging vibrations due to the anharmonic Fermi resonance with the stretching vibrations of C-O groups in the terminal hydroxyl groups has been detected.

The formation of cellulose-nickel nanocomposites has been studied by WAXS, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and scanning electron spectroscopy. Changes in the experimental conditions make it possible to widely vary the size of nickel and its oxide nanoparticles in the bulk and on the surface of cellulose fibers and to monitor the localization of these nanoparticles with the structure of cellulose remaining unchanged. The use of cellulose allowed preparation of nickel nanoparticles stabilized in the matrix.

A matrix of microcrystalline cellulose was used as a nanoreactor for the reduction of Ni(II) ions with hydrazine dihydrochloride.

Conformation, orientation, and thermodynamic characteristics of a series of random copolymers containing highly asymmetric mesogenic fragments and flexible spacers with various lengths and chemical structures were studied by methods of IR spectroscopy, X-ray diffraction, and calorimetry. The molecular ordering of a smectic type observed in the polymers studied is explained by complete of partial segregation of the mesogenic chain fragments without change in the conformations of flexible spacers characteristic of the corresponding homopolymers. The structural order of these copolymers in the liquid-crystalline state is similar to the order observed in rigid-chain thermotropic random polymers in the same state.

Thermotropic main-chain LC polyesters have been studied with the aid of IR and NMR spectroscopy. Rigid mesogens and mesogens with a possibility of conformational isomerism were examined. The dependence of the order parameters of the mesogens and spacers on the chemical structure of the polymer has been determined. The IR spectroscopy data and the data of the calculation of the possible conformations of the mesogen and the spacer confirm the theoretical predictions about the straightening of macromolecules in the anisotropic melt. Solid-state H-2 NMR spectra show that p-oxybenzoic rings adjacent to a flexible spacer are more mobile than inner terphthalic rings. In decamethylene spacer the contrary holds true: the mobility of inner methylene groups is more marked than that of the alpha-methylene groups bound to the mesogen.