Aiming at better understanding the properties of the near-surface nano-layers of UHMWPE reactorpowders (RP) used for manufacturing high-performance fibers by solvent-free processing, acomparative study of the molecular mobility in the nano-layers of two different UHMWPE RP andits change after compaction and sintering is carried out with the help of thermoluminescence method.The dependence of the intensity of light quanta emitted by heated samples (previously evacuated,cooled to 77 K, and activated by low-temperature argon plasma) on the heating temperature (glowcurves) is analyzed. The glow curves were recorded using a unique Nanoluminograph device, whichexists in a single copy at Ioffe Institute. It was found that all the glow curves observed had thecomplicate profiles, which evidenced the overlapping of a number of relaxation processes. The Fityksoftware was used for deconvolution the experimental curves into elementary peaks. The length ofthe so-called kinetic unit of motion (the mobility of which is defreezing in the temperature intervalof each elementary peak) was calculated. The influence of the behavior of the near-surface RPnano-layer during compaction/sintering on the achieved strength of the oriented final film threads isdemonstrated.

To clarify the influence of processing conditions on the structure of the ultra-high-molecular-weight polyethylene (UHMWPE) nascent reactor powder, its change in the course of sintering at various temperatures and pressures has been studied with the help of DSC technique. The basic morphological units of the UHMWPE reactor powder studied, as evidenced by scanning electron microscopy, are crystalline lamellae. An analysis of the shape of the polymer melting peak on the DSC curves made it possible to obtain the data on the thickness distribution of the lamellae since the heat flux dH/dT (where \(\Delta H\) is the melting enthalpy and T is the sample temperature) is proportional to the mass fraction of lamellae melting at a certain temperature. Such an analysis of the UHMWPE structure has not been carried out yet. It has been found that the percentage of the thick (>15 nm) and the thin (<10 nm) lamellae in the compacted samples and in those sintered at a temperature of 130oC (lower than the equilibrium melting temperature of an infinitely long polyethylene crystal T0 = 142oC), remains nearly the same. However, in the samples sintered at temperatures above the T0 of PE with subsequent cooling under different conditions, significant changes in the content of the lamellae of different thicknesses have been observed. At the same time, their melting points remained unchanged, provided that heating from 130°C to 145°C has been carried out when the samples were kept under pressure.

The ultra-high-molecular-weight polyethylene reactor powders are widely used for the actively developing solvent-free method for producing high-strength high-modulus PE filaments, which includes the compaction and sintering of a powder followed by orientational hardening. To find an appropriate regime of the technological process, it is important to know how the nanostructure changes when transforming from a powder to a precursor for hardening. Nanocrystalline lamellae are characteristics of the powder structure. For the first time, the DSC technique was used to follow changes in the thickness distribution of lamellae in ultra-high-molecular-weight polyethylene reactor powder on its way to a precursor for orientation hardening. It was found that the percentage of thick (>15 nm) and thin (10 nm) lamellae in compacted samples and those sintered at temperatures lower than the melting temperature of PE (140°C) remains nearly the same. However, significant changes in the content of lamellae of different thicknesses were observed in the samples sintered at 145°C with subsequent cooling under different conditions. The influence of the lamellae thickness distribution in precursors on the mechanical characteristics of oriented filaments was discussed.

Aiming at finding the proper UHMWPE reactor powders convenient for solvent-free technology producing high-strength fibers, the comparative study of the near-surface layers of the commercial and lab-scale UHMWPE reactor powders was carried out with the help of the thermoluminiscence method. The difference in the powder glow curves and changes in them after subjecting the powders to various processing (compaction and sintering) were observed. Decomposition of the curves was carried out using Fityk program. The energy activation of the electron trap erosion, and the relative content of the shallow and deep traps in the samples investigated were calculated. The association of these observations with the mechanical propeties of the end sintered oriented product is discussed.

For the first time, the statistical distribution of Young’s modulus and of strain at break of ultra-high-molecular-weight polyethylene (UHMWPE) gel-cast highly oriented film threads have been investigated by employing the Weibull model. These have been produced by the multi-stage hot-zone drawing technique. It has been shown that the results of a large number of mechanical measurements for the two series of UHMWPE film threads drawn to an ultimate draw ratio (λ) of 120 from xerogels formed from 1.5% solutions of UHMWPE in decalin or paraffin oil (50 samples in each case) can be satisfactorily described in the framework of the standard Weibull distribution. The values of Weibull modulus and scale factor have been estimated for the two film threads series investigated. It has been found that the scatter in the experimental data depends on the solvent nature and the mechanical characteristic analysed.

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

Studies of the potentials of the multi-stage hot-zone drawing technique for enhancing the tensile strength (σ) of ultra-high-molecular-weight polyethylene (UHMWPE) gel-cast highly oriented film threads, the applicability of the Weibull statistics to the σ distribution, and the solvent role in the film thread strength are presented. It is shown that the results of a large number of mechanical measurements for two series of UHMWPE film threads drawn to an ultimate draw ratio (λ) of 120 from xerogels formed from 1.5 % solutions of UHMWPE in decalin or paraffin oil are satisfactorily described by the Weibull model. It is shown that the threads produced are characterised by an average strength σ av = 4.7 GPa and 20 % of the samples have σ = 5.2–6.5 GPa. This is higher than the strength of the commercially available gel-spun oriented UHMWPE fibres of σ = 3.5 GPa. It is found that the solvent nature does not affect the tensile strength of the film threads but exerts a considerable influence on the long-term characteristics.

Xerogel reactor powders and supramolecular polyethylene fibers with various degrees of hood have been studied via differential scanning calorimetry. A higher strength of laboratory fibers in comparison with industrial ones is found to be achieved due to a multistage band high-temperature hood that causes the thermodynamic parameters of supramolecular polymer structure.

A statistical analysis of the distribution of the tensile strength σ of ultra-oriented ultra-high-molecular-weight polyethylene (UHMWPE) film filaments has been performed in the framework of the Weibull model using the results obtained from a large number (50) of measurements. The UHMWPE film filaments have been produced by means of high-temperature multistage zone drawing of xerogels prepared from 1.5% UHMWPE solutions in decalin. The Weibull modulus has been determined for this type of materials. It has been shown that, for the ultimate draw ratio λ = 120, the average tensile strength is equal to 4.7 GPa, which is significantly higher than the tensile strength σ = 3.5 GPa for commercial gel-spun UHMWPE fibers manufactured by the DSM Company (The Netherlands) and the Honeywell International Incorporation (United States). It has been demonstrated that, for 20% of the specimens thus prepared, the tensile strength reaches record-high values σ = 5.2–5.9 GPa.

The method of plasma-induced thermoluminescence for the first time has been used to investigate the molecular mobility in near-surface nanolayers of molecular crystals (paraffins) with different chain lengths. The investigations have been performed using a NanoLuminograph device (PlasmaChem, GmbH, Germany) under conditions excluding the modifying effect of gas discharge plasma emission on the surface structure under study. The origin of charge stabilization sites on the surface of molecular crystals as well as the influence of the chain length of paraffins and the purity of their chemical composition on the thermoluminescence intensity and the shape of the glow curves have been discussed.

A comparative investigation of the surface structure of ultrahigh molecular weight polyethylene film filaments obtained with different draw ratios from xerogels prepared from 1.5 wt % polymer solutions in decaline and mineral oil has been performed using a SUPRA-55V scanning electron microscope and a nanoluminograph for recording thermoluminescence of ultrathin near-surface layers of solids. It has been found that, with an increase in the draw ratio, the luminescence intensity decreases, and the peaks responsible for the segmental mobility are shifted toward higher temperatures. It has been assumed that this is associated with the improvement of the structure of near-surface layers of the polymer (with a decrease in the number of microcavities and segments of molecules with a high degree of coiling). It has also been revealed that the peaks observed in glow curves of the oriented gel samples from polymer solutions in decaline are shifted more significantly than those of the gel samples from polymer solutions in mineral oil, and the extremely oriented films are characterized by a large discretization of kinetic units of motion.

AbstractRelaxation properties of polymer near‐surface layers were investigated with the help of thermoluminescent method using Nanoluminograph (PlasmaChem GMbH, Germany). The gel‐ and melt‐crystallized films from PE of different molecular weight were studied. The light sum of thermoluminescence in the temperature range of various relaxation transitions was compared. It is found that it is primarily controlled by the type of morphology forming during crystallization and the arrangement of the structural units on a surface. The glass transition temperature in near‐surface layers appeared to be lower that that in the bulk. Bulk glass transition temperature was determined by radiothermoluminescence, DMA and DSC techniques.

С целью выявления особенностей структуры реакторных порошков сверхвысокомолекулярного полимера в зависимости от каталитической системы, на которой проводится синтез, осуществлено сравнительное исследование серии лабораторных и коммерческого порошков сверхвысокомолекулярного ПЭ, синтезированных на разных катализаторах в суспензионном процессе в различных условиях. Использован целый комплекс современных физических методик, таких как просвечивающая и сканирующая электронная микроскопия, рентгеноструктурный анализ, спектроскопия комбинационного рассеяния, дифференциальная сканирующая калориметрия, ядерный магнитный резонанс и термолюминесценция. Найдено, что все насцентные частицы имеют сложную иерархическую структуру. Элементарной структурной единицей во всех реакторных порошках являются кристаллические ламели, размер и взаимная ориентация которых определяются типом каталитической системы. При синтезе на нанесенных катализаторах характер образующейся структуры зависит от свойств подложки. При разрушении подложки во время синтеза образуются фибриллы. Коллоидные размеры частиц катализатора обусловливают более однородную ламелярную структуру реакторных порошков. Дана оценка конформационного состава сегментов молекул в межламелярных областях реакторных порошков.

To reveal the features of the structure of UHMWPE that depend on the catalytic system used for synthesis, a comparative study of the sets of laboratory and commercial powders of UHMWPE synthesized on different catalysts in the slurry process under different conditions is conducted. This study includes the use of various modern physical methods, such as transmission and scanning electron microscopy, X-ray analysis, Raman scattering spectroscopy, differential scanning calorimetry, nuclear magnetic resonance, and thermoluminescence. All nascent particles are shown to have a complex hierarchical structure. In all reactor powders, the elementary structural unit is crystalline lamellas, whose dimensions and mutual orientation are dependent on the type of catalytic system. In the synthesis on the supported catalysts, the character of the formed structure depends on the characteristics of the substrate. During the breakdown of the substrate in the course of the synthesis, fibrils form. The colloidal dimensions of the catalyst particles are responsible for a more uniform lamellar structure of the reactor powders. The conformational composition of the segments of molecules in the interlamellar regions of the reactor powders is characterized.

The effect of crystallization conditions on the relaxation properties of ultra-thin surface layers in the meltgrown ultra-high molecular weight polyethylene samples was studied using a novel Nanoluminograph device. The device can record thermoluminescence generated upon heating the sample preactivated by high-frequency low-temperature low-power glow-discharge plasma. The glow curves were analyzed, and activation energy of thermoluminescence for the observed glow maxima was calculated. The effect of crystallization conditions on the formation of a lamellar structure on the surface of ultra-high molecular weight polyethylene was examined. The possibility of structural characterization of disordered interlamellar regions using thermoluminescence data is discussed. The estimated activation energy of thermoluminescence was used to calculate the apparent dimensions of kinetic units of motion in the region of β transition, which are supposed to characterize the cooperativeness in the motion of molecular segments.

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 vibrational spectra of 2-cyclooctylamino-5-nitropyridine (COANP) solutions and the evolution of the spectra upon changing over from the solutions to solid-phase COANP are investigated. The bands observed in the spectra are assigned to the corresponding vibrational modes. The nature of the interaction of COANP with C60 and C70 fullerenes is elucidated by analyzing the transmission spectra of these compounds. No interaction of the COANP compound with C60 and C70 fullerenes is revealed under the studied conditions. It is assumed that the physical nature of this phenomenon can be associated with the formation of liquid-crystal clusters consisting of fullerene molecules.

We report on two-photon absorption and two-photon excited fluorescence of a selected group of new derivatives of cyclohexanone and piperidone with regard to their molecular structure. The molecular cross-section of the two-photon absorption of these compounds, as high as 3000 × 10-50 cm4 s/photon at nanosecond pumping, makes then promising nonlinear materials for optical limiting in the near-infrared region. They also exhibit an intense two-photon exciting fluorescence. Similar compounds have previously demonstrated strong anticancer effect. Both features combined in a single compound thus open the way for more efficient treatment of cancer, when biochemical destruction of malignant cells is accompanied by their two-photon fluorescent imaging.