STUDY OF RELAXATION TRANSITIONS IN SOME AROMATIC POLYESTERS

Методом спинового зонда проведено систематическое изучение основных релаксационных переходов жесткоцепных стеклообразных полимеров в широком интервале температур с применением спиновых зондов разного размера на примере полисульфона. В главной области релаксации ароматических полиэфиров с помощью метода спинового зонда обнаружены два перегиба. Два перегиба, обнаруженные на температурной зависимости времени корреляции вращения, являются следствием размораживания сегментальной подвижности в областях с различной упаковкой сегментов. Показано, что высокотемпературный перегиб соответствует размораживанию сегментальной подвижности кооперативного типа (а -переходу), а перегиб при более низкой температуре р -размораживанию сегментальной подвижности локального типа (а'-процессу). Для объяснения природы данного перехода была использована теоретическая модель полимера, где предполагается, что в аморфных полимерах возможны разные уровни надмолекулярной организации, т.е. существование более упорядоченных и более плотно упакованных областей, которые чередуются с более «рыхлыми» и менее упорядоченными областями. Исследовано влияние различных факторов на положение а’-перехода на температурной шкале. Выбор объема зонда на основе строго обоснованной модели его движения позволил выявить взаимосвязь между вращательным движением зонда и движением отдельных сегментов аморфного полимера ниже температуры стеклования. The spin probe method was used to systematically study the main relaxation transitions of rigid-chain glassy polymers in a wide temperature range using spin probes of different sizes using polysulfone as an example. In the main relaxation region of aromatic polyesters, two inflections were found using the spin probe method. The two inflections found in the temperature dependence of the rotation correlation time are the result of unfreezing of segmental mobility in regions with different packing of segments. It was shown that the high-temperature inflection corresponds to the defrosting of the cooperative-type segmental mobility (a -transition), and the inflection at a lower temperature corresponds to the / -defrosting of the segmental mobility of the local type (the a' -process). To explain the nature of this transition, a theoretical model of the polymer was used, where it is assumed that different levels of supramolecular organization are possible in amorphous polymers, i.e. the existence of more ordered and more densely packed regions, which alternate with looser and less ordered regions. The influence of various factors on the position of the a' -transition on the temperature scale is investigated. The choice of the probe volume on the basis of a strictly substantiated model of its motion made it possible to reveal the relationship between the rotational motion of the probe and the motion of individual segments of the amorphous polymer below the glass transition temperature.

Development of a machine vision system for recording experimental data in the study of torsional stiffness by dynamic mechanical analysis

A machine vision system has been developed for recording data obtained on an experimental installation for studying relaxation transitions of polymers, as well as studying the dynamic shear modulus during phase transformations in alloys based on titanium nickelide. The computer vision system is based on simple algorithms implemented in the Java language in the IDE “Processing”. The conditions for the experiment and the procedure for processing the experimental data obtained on the basis of the machine vision system are determined.

Study of the effect of the reinforcement direction on the identification of relaxation transitions of moisture-saturated carbon fiber VKU-25

Thermodilatometric methods of analysis are used to study the structural parameters of polymer materials, however, when studying moisture-saturated compositions certain difficulties arise in their identification. The results of thermophysical tests of VKU-25 carbon fiber samples in the initial state and after moisture saturation are presented. It is shown that heat treatment of materials affects the recorded values of the glass transition temperature of the epoxy matrix. When the samples are exposed in water or above the water surface, the sorbate penetrates into the polymer at the same rate, which is confirmed by almost identical values of water absorption at the same exposure time. The estimates of the thermal coefficient of linear expansion (TCLE) of the samples in the range of 20 - 250°C are given. Moreover, it is shown that the glass transition temperature of the plasticized polymer matrix depends on the direction of fiber reinforcement. In the case of moisture-saturated carbon fiber (CF)heated to 210°C, the formation of main cracks occurs mainly at the fiber-matrix interface. The glass transition temperature (GTT) of the material in the dry state (176 - 177°C), appeared almost independent on the heating rate, whereas for water-saturated samples, GTT changes significantly and can be described by a polynomial of the 2nd order. After exposure of the carbon fiber under conditions of high temperature and humidity, two relaxation transitions corresponding to the systems occur in the polymer matrix: epoxidian oligomer— amine hardener and polyfunctional resin— amine hardener. The glass transition temperature is 132 and 159°C in the first and in the second, respectively. The results obtained can be used in the development of new polymer composite materials.

Miscibility of poly(urethane-urea) elastomers with chlorinated poly(vinyl chloride)

Effect of a chemical structure of poly(ether-urethane-urea) (PUU) elastomers on a miscibility of their blends with chlorinated poly(vinyl chloride) (cPVC) has been studied by FTIR and DSC. The segmented PUU were synthesized by prepolymer approach in N,N-dimethylformamide (DMF) solution. PUU-1 was synthesized using poly(propylene glycol) (PPG) of Mn = 1000, mixture of 2,4- and 2,6-isomers of tolylenediisocyanate (TDI) in a ratio of 65:35 (by weight) and 4,4´-methylenedianiline as a chain extender at a molar ratio of 1:2:1. PUU-2 was prepared based on poly(tetramethylene glycol) (PTMG) of Mn = 1000, TDI and cyanoethylated ethylene diamine at a molar ratio of 2:3:1. The polymer-polymer blends were obtained via solution casting technique using DMF as a solvent. It was found a miscibility of the polymers enhances due to a formation of hydrogen or donor-acceptor bonding between polar NH urethane-urea or nitrile groups of hard PUU segments and chlorine of cPVC. According to DSC results the polymer-polymer systems stabilized by stronger donor-acceptor bonding are characterized by single glass transition temperature, Tg, a position of which is higher than that of the theoretical one, TFg, calculated in full composition range via Fox’s equation. When stabilization of polymer-polymer blend with 30 % (by weight) of cPVC performs by weaker hydrogen bonding we observed a formation of mixed phase and the composite is characterized by appearance of three relaxation transitions. Increasing cPVC content reduces a miscibility of the components and biphasic structure of the composites forms. Comparative analysis of experimental and theoretical (additive) tensile strength vs composition dependencies demonstrates an impact of donor-acceptor interface interactions on strength of the polymer composites obtained.

Solution-Based Deposition of Transparent Eu-Doped Titanium Oxide Thin Films for Potential Security Labeling and UV Screening

Transparent titanium oxide thin films attract enormous attention from the scientific community because of their prominent properties, such as low-cost, chemical stability, and optical transparency in the visible region. In this study, we developed an easy and scalable solution-based process for the deposition of transparent TiOx thin films on glass substrates. We showed that the proposed method is also suitable for the fabrication of metal-doped TiOx thin films. As proof-of-the-concept, europium Eu(III) ions were introduced into TiOx film. A photoluminescence (PL) study revealed that Eu-doped TiOx thin films showed strong red luminescence associated with 5D0→7Fj relaxation transitions in Eu (III). We found that prepared TiOx thin films significantly reduce the transmittance of destructive UV radiation; a feature that can be useful for the protection of photovoltaic devices. In addition, transparent and luminescent TiOx thin films can be utilized for potential security labeling.