Prolonged Thermal Relaxation of the Thermosetting Polymers

The rigidity of structures made of polymer composite materials, operated at elevated temperatures, is mainly determined by the residual rigidity of the polymer binder (which is very sensitive to elevated temperatures); therefore, the study of ways to increase the rigidity of polymer materials under heating (including prolonged heating) is relevant. In the previous research, cured thermosetting polymer structure’s non-stability, especially under heating, is determined by its supra-molecular structure domain’s conglomerate character and the high entropy of such structures. The polymer elasticity modeling proved the significance of the entropy factor and layer (EPL) model application. The prolonged heating makes it possible to release adsorptive inter-layer bonds and volatile groups. As a result, the polymer structure is changing, and inner stress relaxation occurs due to this thermo-process, called thermo-relaxation. The present study suggests researching thermo-relaxation’s influence on polymers’ deformability under load and heating. The research results prove the significant polymer structure modification due to thermo-relaxation, with the polymer entropy parameter decreasing, the glassing onset temperature point (Tg) increasing by 1.3–1.7 times, and the modulus of elasticity under heating increasing by 1.5–2 times.

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Thermal stability and diffusion characteristics of ultrathin amorphous carbon films grown on crystalline and nitrogenated silicon substrates by filtered cathodic vacuum arc deposition

Scientific Reports ◽

10.1038/s41598-021-91903-y ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Shengxi Wang ◽

Anurag Roy ◽

Kyriakos Komvopoulos

Keyword(s):

Thermal Stability ◽

Amorphous Carbon ◽

Silicon Substrate ◽

Elevated Temperatures ◽

Carbon Films ◽

Vacuum Arc ◽

Cross Sectional ◽

Prolonged Heating ◽

Filtered Cathodic Vacuum Arc ◽

Thermal Stability Of

AbstractAmorphous carbon (a-C) films are widely used as protective overcoats in many technology sectors, principally due to their excellent thermophysical properties and chemical inertness. The growth and thermal stability of sub-5-nm-thick a-C films synthesized by filtered cathodic vacuum arc on pure (crystalline) and nitrogenated (amorphous) silicon substrate surfaces were investigated in this study. Samples of a-C/Si and a-C/SiNx/Si stacks were thermally annealed for various durations and subsequently characterized by high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The TEM images confirmed the continuity and uniformity of the a-C films and the 5-nm-thick SiNx underlayer formed by silicon nitrogenation using radio-frequency sputtering. The EELS analysis of cross-sectional samples revealed the thermal stability of the a-C films and the efficacy of the SiNx underlayer to prevent carbon migration into the silicon substrate, even after prolonged heating. The obtained results provide insight into the important attributes of an underlayer in heated multilayered media for preventing elemental intermixing with the substrate, while preserving the structural stability of the a-C film at the stack surface. An important contribution of this investigation is the establishment of an experimental framework for accurately assessing the thermal stability and elemental diffusion in layered microstructures exposed to elevated temperatures.

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2000 Macromolecular Science and Engineering Award LectureThe versatility of azobenzene polymers

Canadian Journal of Chemistry ◽

10.1139/v01-098 ◽

2001 ◽

Vol 79 (7) ◽

pp. 1093-1100 ◽

Cited By ~ 13

Author(s):

Almeria Natansohn ◽

Paul Rochon

Keyword(s):

Liquid Crystalline ◽

Surface Deformation ◽

Polymer Structure ◽

Light Polarization ◽

Polymer Materials ◽

Science And Engineering ◽

Crystalline Polymers ◽

The Third ◽

Macroscopic Motion ◽

Azobenzene Groups

The well-known transcistrans photoisomerization of azobenzenes produces at least three different kinds of motion in the polymer materials to which the azobenzenes are bound. The first is a photoinduced motion of the azobenzene groups only, and they can align in a selected position with respect to the light polarization. The second is a macroscopic motion of huge amounts of polymeric material, producing surface deformation, and the third is a reorganization of smectic domains in liquid crystalline polymers. These motions and their consequences are briefly discussed in relation to the polymer structure and some possible photonic applications are mentioned.Key words: photoinduced orientation, azobenzene polymers, surface gratings, photonics, thermochromism, photochromism, photorefractivity, photoinduced chirality and switching.

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Laser Beam Welding of a Low Density Refractory High Entropy Alloy

Metals ◽

10.3390/met9121351 ◽

2019 ◽

Vol 9 (12) ◽

pp. 1351 ◽

Cited By ~ 2

Author(s):

Evgeniya Panina ◽

Nikita Yurchenko ◽

Sergey Zherebtsov ◽

Nikita Stepanov ◽

Gennady Salishchev ◽

...

Keyword(s):

Laser Beam ◽

Room Temperature ◽

Elevated Temperatures ◽

Laser Beam Welding ◽

Base Material ◽

Laves Phase ◽

High Entropy Alloy ◽

High Entropy ◽

Grains Refinement ◽

Cast Condition

The effect of laser beam welding on the structure and properties of a Ti1.89NbCrV0.56 refractory high entropy alloy was studied. In particular, the effect of different pre-heating temperatures was examined. Due to the low ductility of the material, laser beam welding at room temperature resulted in the formations of hot cracks. Sound butt joints without cracks were produced using pre-heating to T ≥ 600 °C. In the initial as-cast condition, the alloy consisted of coarse bcc grains with a small amount of lens-shaped C15 Laves phase particles. A columnar microstructure was formed in the welds; the thickness of the grains increased with the temperature of pre-heating before welding. The Laves phase particles were formed in the seams after welding at 600 °C or 800 °C, however, these particles were not observed after welding at room temperature or at 400 °C. Soaking at elevated temperatures did not change the microstructure of the base material considerably, however, “additional” small Laves particles formed at 600 °C or 800 °C. Tensile test of welded specimens performed at 750 °C resulted in the fracture of the base material because of the higher hardness of the welds. The latter can be associated with the bcc grains refinement in the seams.

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Design of Polymer Blends Based on Chitosan:POZ with Improved Dielectric Constant for Application in Polymer Electrolytes and Flexible Electronics

Advances in Polymer Technology ◽

10.1155/2020/8586136 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10 ◽

Cited By ~ 11

Author(s):

Shujahadeen B. Aziz ◽

M. H. Hamsan ◽

M. F. Z. Kadir ◽

H. J. Woo

Keyword(s):

Dielectric Constant ◽

Dielectric Loss ◽

Loss Tangent ◽

Flexible Electronics ◽

Elevated Temperatures ◽

Electric Modulus ◽

Polymer Materials ◽

Blend Films ◽

Optical Micrograph ◽

Peak Broadening

There is a considerable demand for the development and application of polymer materials in the flexible electronic- and polymer-based electrolyte technologies. Chitosan (CS) and poly(2-ethyl-2-oxazoline) (POZ) materials were blended with different ratios to obtain CS:POZ blend films using a straightforward solution cast technique. The work was involved a range of characteristic techniques, such as impedance spectroscopy, X-ray diffraction (XRD), and optical microscopy. From the XRD spectra, an enhancement in the amorphous nature in CS:POZ blend films was revealed when compared to the pure state of CS. The enhancement was verified from the peak broadening in CS:POZ blend films in relative to the one in crystalline peaks of the CS polymer. The optical micrograph study was used to designate the amorphous and crystalline regions by assigning dark and brilliant phases, respectively. Upon increasing POZ concentration, the dielectric constant was found to increase up to ɛ′ = 6.48 (at 1 MHz) at 15 wt.% of POZ, and then a drop was observed beyond this amount. The relatively high dielectric constant and dielectric loss were found at elevated temperatures. The increase of POZ concentration up to 45 wt.% made the loss tangent to shift to the lower frequency side, which is related to increasing resistivity. The increases of dielectric constant and dielectric loss with temperature were attributed to the increase of polarisation. The loss tangent peaks were found to shift to the higher frequency side as temperature elevated. Obvious relaxation peaks were observed in the imaginary part of electric modulus, and no peaks were found in the dielectric loss spectra. The concentration dependent of M″ peaks was found to follow the same trend of loss tangent peaks versus POZ content. The relaxation process was studied in terms of electric modulus parameters.

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Element Effects on High-Entropy Alloy Vacancy and Heterogeneous Lattice Distortion Subjected to Quasi-equilibrium Heating

Scientific Reports ◽

10.1038/s41598-019-51297-4 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 8

Author(s):

E-Wen Huang ◽

Hung-Sheng Chou ◽

K. N. Tu ◽

Wei-Song Hung ◽

Tu-Ngoc Lam ◽

...

Keyword(s):

Elevated Temperatures ◽

Lattice Structure ◽

High Entropy Alloy ◽

Quasi Equilibrium ◽

X Ray ◽

Structure Relaxation ◽

High Entropy ◽

Spatially Resolved ◽

Formation Enthalpies ◽

Different Characteristics

Abstract We applied Simmons–Balluffi methods, positron measurements, and neutron diffraction to estimate the vacancy of CoCrFeNi and CoCrFeMnNi high-entropy alloys (HEAs) using Cu as a benchmark. The corresponding formation enthalpies and associated entropies of the HEAs and Cu were calculated. The vacancy-dependent effective free volumes in both CoCrFeNi and CoCrFeMnNi alloys are greater than those in Cu, implying the easier formation of vacancies by lattice structure relaxation of HEAs at elevated temperatures. Spatially resolved synchrotron X-ray measurements revealed different characteristics of CoCrFeNi and CoCrFeMnNi HEAs subjected to quasi-equilibrium conditions at high temperatures. Element-dependent behavior revealed by X-ray fluorescence (XRF) mapping indicates the effect of Mn on the Cantor Alloy.

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Effect of thermal relaxation on residual stress and microstructure in the near-surface layers of dual shot peened Inconel 625

Advances in Mechanical Engineering ◽

10.1177/1687814018800530 ◽

2018 ◽

Vol 10 (10) ◽

pp. 168781401880053

Author(s):

Lihong Wu ◽

Chuanhai Jiang

Keyword(s):

Residual Stress ◽

Compressive Residual Stress ◽

Elevated Temperatures ◽

Thermal Relaxation ◽

Diffraction Method ◽

Relaxation Behavior ◽

Inconel 625 ◽

Surface Layers ◽

Near Surface ◽

Subsurface Layers

Thermal relaxation behavior of residual stress and microstructure in the near-surface layers of dual shot peened Inconel alloy 625 was investigated by X-ray diffraction method. Residual stress on the top surface layer was significantly relaxed in the first 15 min at the elevated temperatures of 500°C, 600°C, and 700°C. However, there was still high maximum compressive residual stress in subsurface layers. The relaxation behavior of residual stress has contributed to the thermally activated process. The activation enthalpy Δ H and m were calculated according to the Zener–Wert–Avrami method, the values of which were 1.59 eV and 0.4934, respectively. Microstructural evaluation revealed that it was slightly changed in the near-surface layers after various isothermal treatments. Accordingly, high level of compressive residual stress and dislocation density resulted in the retained mechanical properties of dual shot peened Inconel 625, which was discussed based on the relaxation of microstructure and microhardness.

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A novel equiaxed eutectic high-entropy alloy with excellent mechanical properties at elevated temperatures

Materials Research Letters ◽

10.1080/21663831.2020.1772395 ◽

2020 ◽

Vol 8 (10) ◽

pp. 373-382 ◽

Cited By ~ 2

Author(s):

Liuliu Han ◽

Xiandong Xu ◽

Zhiming Li ◽

Bin Liu ◽

C. T. Liu ◽

...

Keyword(s):

Mechanical Properties ◽

Elevated Temperatures ◽

High Entropy Alloy ◽

High Entropy

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Identifying the high entropy effect on plastic dynamics in bulk metallic glasses: A nanoindentation study at room and elevated temperatures

Materials & Design ◽

10.1016/j.matdes.2020.108500 ◽

2020 ◽

Vol 189 ◽

pp. 108500

Author(s):

Qing Zhou ◽

Yin Du ◽

Weichao Han ◽

Qian Jia ◽

Yuyu Deng ◽

...

Keyword(s):

Metallic Glasses ◽

Elevated Temperatures ◽

Bulk Metallic Glasses ◽

High Entropy ◽

Entropy Effect

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2D-IR spectroscopy for oil paint conservation: Elucidating the water-sensitive structure of zinc carboxylate clusters in ionomers

Science Advances ◽

10.1126/sciadv.aaw3592 ◽

2019 ◽

Vol 5 (6) ◽

pp. eaaw3592 ◽

Cited By ~ 9

Author(s):

Joen. J. Hermans ◽

Lambert Baij ◽

Mark Koenis ◽

Katrien Keune ◽

Piet D. Iedema ◽

...

Keyword(s):

Ir Spectroscopy ◽

Metal Ions ◽

Relative Concentration ◽

Cluster Structure ◽

Polymer Structure ◽

Polymer Materials ◽

White Pigment ◽

Metal Soap ◽

2D Ir ◽

Degradation Reactions

The molecular structure around metal ions in polymer materials has puzzled researchers for decades. This question has acquired new relevance with the discovery that aged oil paint binders can adopt an ionomer structure when metal ions leached from pigments bind to carboxylate groups on the polymerized oil network. The characteristics of the metal-polymer structure are expected to have important consequences for the rate of oil paint degradation reactions such as metal soap formation and oil hydrolysis. Here, we use two-dimensional infrared (2D-IR) spectroscopy to demonstrate that zinc carboxylates formed in paint films containing zinc white pigment adopt either a coordination chain– or an oxo-type cluster structure. Moreover, it was found that the presence of water governs the relative concentration of these two types of zinc carboxylate coordination. The results pave the way for a molecular approach to paintings conservation and the application of 2D-IR spectroscopy to the study of polymer structure.

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