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Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 462
Author(s):  
Josef Bartoš ◽  
Bożena Zgardzińska ◽  
Helena Švajdlenková ◽  
Barbara Charmas ◽  
Miroslava Lukešová ◽  
...  

A combined study of one of the simplest aromatic hydrocarbons, i.e., methylbenzene (toluene) (TOL), via the annihilation of an ortho-positronium (o-Ps) probe via positron annihilation lifetime spectroscopy (PALS) and the rotation dynamics of nitroxide spin probe 2,2,6,6-tetramethyl-piperidinyl-1-oxy (TEMPO) using electron spin resonance (ESR) over a wide temperature range, 10–300 K, is reported. The o-Ps lifetime, τ3, and the relative o-Ps intensity, I3, as a function of temperature exhibit changes defining several characteristic PALS temperatures in the slowly and rapidly cooled samples. Similarly, the spectral parameter of TEMPO mobility in TOL, 2Azz‘, and its correlation time, τc, reveal several effects at a set of the characteristic ESR temperatures, which were determined and compared with the PALS results. Finally, the physical origins of the changes in free volume expansion and spin probe mobility are revealed. They are reflected in a series of the mutual coincidences between the characteristic PALS and ESR temperatures and appropriate complementary thermodynamic and dynamic techniques.


Author(s):  
Арсен Мухамедович Хараев ◽  
Рима Чамаловна Бажева

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.


Polymers ◽  
2021 ◽  
Vol 13 (21) ◽  
pp. 3829
Author(s):  
Ekaterina M. Zubanova ◽  
Sergei V. Kostjuk ◽  
Peter S. Timashev ◽  
Yury A. Rochev ◽  
Alexander I. Kokorin ◽  
...  

Coil to globule transition in poly(N-isopropylacrylamide) aqueous solutions was studied using spin probe continuous-wave electronic paramagnetic resonance (CW EPR) spectroscopy with an amphiphilic TEMPO radical as a guest molecule. Using Cu(II) ions as the “quencher” for fast-moving radicals in the liquid phase allowed obtaining the individual spectra of TEMPO radicals in polymer globule and observing inhomogeneities in solutions before globule collapsing. EPR spectra simulations confirm the formation of molten globules at the first step with further collapsing and water molecules coming out of the globule, making it denser.


Author(s):  
Artem S. Poryvaev ◽  
Anastasiya A. Yazikova ◽  
Daniil M. Polyukhov ◽  
Matvey V. Fedin
Keyword(s):  

Author(s):  
Pin Dong ◽  
Christian Teutloff ◽  
Jürgen Lademann ◽  
Alexa Patzelt ◽  
Monika Schäfer-Korting ◽  
...  

Polymers ◽  
2021 ◽  
Vol 13 (18) ◽  
pp. 3059
Author(s):  
Oleg I. Gromov ◽  
Mikhail O. Kostenko ◽  
Alexander V. Petrunin ◽  
Anastasia A. Popova ◽  
Olga O. Parenago ◽  
...  

High-pressure electron paramagnetic resonance (EPR) was used to measure translational diffusion coefficients (Dtr) of a TEMPONE spin probe in poly(D,L-lactide) (PDLLA) and swollen in supercritical CO2. Dtr was measured on two scales: macroscopic scale (>1 μm), by measuring spin probe uptake by the sample; and microscopic scale (<10 nm), by using concentration-dependent spectrum broadening. Both methods yield similar translational diffusion coefficients (in the range 5–10 × 10−12 m2/s at 40–60 °C and 8–10 MPa). Swollen PDLLA was found to be homogeneous on the nanometer scale, although the TEMPONE spin probe in the polymer exhibited higher rotational mobility (τcorr = 6 × 10−11 s) than expected, based on its Dtr. To measure distribution coefficients of the solute between the swollen polymer and the supercritical medium, supercritical chromatography with sampling directly from the high-pressure vessel was used. A distinct difference between powder and bulk polymer samples was only observed at the start of the impregnation process.


2021 ◽  
Vol 14 (7) ◽  
pp. 665
Author(s):  
Zsolt Preisz ◽  
Nóra Hartvig ◽  
Balázs Bognár ◽  
Tamás Kálai ◽  
Sándor Kunsági-Máté

The scavenging effect of the antimetabolite dihydrofolate reductase inhibitor methotrexate (MTX) and the isomers of its photoswitchable derivate, cis- and trans-phototrexate (PHX), have been compared by ESR spectroscopy, with the application of a cyclic hydroxylamine spin probe. The results showed the most pronounced scavenging effect in the presence of trans-phototrexate (trans-PHX). At a low concentration (100 µM) cis-PHX also showed a greater scavenging effect than the parent molecule MTX. Direct antioxidant properties of the investigated molecules were measured by ABTS scavenging assay, which showed no significant difference between trans-PHX and cis-PHX, but both of the isomers of PHX showed a higher antioxidant capacity than MTX. These findings imply that trans-PHX may have more pronounced anti-inflammatory and tissue-protective effects than MTX, despite the lack of its cytotoxic, antineoplastic effect.


Author(s):  
Jakov Slade ◽  
Dalibor Merunka ◽  
Ezequiel Huerta ◽  
Miroslav Peric

2021 ◽  
Vol 57 (6) ◽  
pp. 905-913
Author(s):  
O. Yu. Rogozhnikova ◽  
D. V. Trukhin ◽  
N. B. Asanbaeva ◽  
V. M. Tormyshev

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