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.

Four-point probe stand for magnetoresistance measurement of unpatterned sample

An experimental stand for express diagnostics of multilayer spin tunnel structures has been developed. The current-in-plane tunnelling method (CIPT) requires no processing, is fast, and provides reliable data which are reflective of the deposition only. The stand is based on the four-probe method for measuring resistance at external alternating magnetic field. This technique can be applied after only a short processing route, thereby saving time and resources, and reducing the potential for damaging the junction.

Measurement of volume fraction of air in water: experimental Study

In multi phase mixing of flow streams, the measurement of fraction of individual components with consideration of proportion of volume need to be analyzed considering the serious issues in many chemical and other processing industries. Even though, quantifiable measurements technique are exist for the calculation of solubility, partial pressure, molar fraction and VOF, the VOF measurement is the meaningful measure of percentage fraction of air in water. In this experimental procedure, the method to resolve the Volume fraction (VOF) is discussed and the same is achieved by impedance probe method.

Evaluation of the influence of the degree of saturation, measuring time and use of a conductive paste on the determination of thermal conductivity of normal and lightweight concrete using the hot-wire method

The determination of thermal conductivity of cement-based materials is relevant from the perspective of buildings’ energy efficiency. The absence of unified tests for its measurement in mortars and concrete results in a heterogeneity of the data available in the literature. This work’s purpose is to determine the relevant influence from a a statistical viewpoint that three factors; degree of saturation, measuring time and use of a conductive paste, have in the measurement of the conductivity using the hot-wire needle probe method in two concretes with different thermal behavior: standard-weight concrete and lightweight concrete. The results obtained allow for the establishment of recommendations for future researchers on the minimum information to be included in their reports of thermal conductivity of cement-based materials by the needle probe method, the need to treat outliers, the most favorable saturation conditions and measuring times, as well as the possible benefits of using conductive pastes.

G-Doping-Based Metal-Semiconductor Junction

Geometry-induced doping (G-doping) has been realized in semiconductors nanograting layers. G-doping-based p-p(v) junction has been fabricated and demonstrated with extremely low forward voltage and reduced reverse current. The formation mechanism of p-p(v) junction has been proposed. To obtain G-doping, the surfaces of p-type and p+-type silicon substrates were patterned with nanograting indents of depth d = 30 nm. The Ti/Ag contacts were deposited on top of G-doped layers to form metal-semiconductor junctions. The two-probe method has been used to record the I–V characteristics and the four-probe method has been deployed to exclude the contribution of metal-semiconductor interface. The collected data show a considerably lower reverse current in p-type substrates with nanograting pattern. In the case of p+-type substrate, nanograting reduced the reverse current dramatically (by 1–2 orders of magnitude). However, the forward currents are not affected in both substrates. We explained these unusual I–V characteristics with G-doping theory and p-p(v) junction formation mechanism. The decrease of reverse current is explained by the drop of carrier generation rate which resulted from reduced density of quantum states within the G-doped region. Analysis of energy-band diagrams suggested that the magnitude of reverse current reduction depends on the relationship between G-doping depth and depletion width.