Changes In Amorphous Structure Research Articles

Changes in amorphous structure and reaction acceleration during bulk polymerization of methacrylates

Changes in amorphous structure and reaction acceleration during bulk polymerization of methacrylates

Simulation and experimental evaluation of laser-induced graphene on the cellulose and lignin substrates

In this article, the formation of laser-induced graphene on the two natural polymers, cellulose, and lignin, as precursors was investigated with molecular dynamics simulations and some experiments. These eco-friendly polymers provide significant industrial advantages due to their low cost, biodegradability, and recyclable aspects. It was discovered during the simulation that LIG has numerous defects and a porous structure. Carbon monoxide, H2, and water vapor are gases released by cellulose and lignin substrates. H2O and CO are released when the polymer transforms into an amorphous structure. Later on, as the amorphous structure changes into an ordered graphitic structure, H2 is released continuously. Since cellulose monomer has a higher mass proportion of oxygen (49%) than lignin monomer (29%), it emits more CO. The LIG structure contains many 5- and 7-carbon rings, which cause the structure to have bends and undulations that go out of the plane. In addition, to verify the molecular dynamics simulation results with experimental tests, we used a carbon dioxide laser to transform filter paper, as a cellulose material, and coconut shell, as a lignin material, into graphene. Surprisingly, empirical experiments confirmed the simulation results.

Relationship between Dynamic Viscoelasticity and Amorphous Structural Changes Associated with Enthalpy Relaxation in Polystyrene Injection Moldings

Relationship between Dynamic Viscoelasticity and Amorphous Structural Changes Associated with Enthalpy Relaxation in Polystyrene Injection Moldings

Crosslinking agents effect on gelatins from carp and tilapia skins and in their biopolymeric films

The extracted gelatins from carp and tilapia skins were chemically crosslinked by electrolytes (NaCl and MgSO4) and nonelectrolytes (gallic acid and citric acid) agents and, the fish gelatins films were produced by casting. Rheological, chemical and physicochemical properties were evaluated. All crosslinked films showed a significant increase in tensile strength and a slight reduction in elongation compared to non–crosslinked films. The crosslinked films with nonelectrolytes presented the highest reductions in water vapor permeability. Fourier Transform Infrared spectra, X–Ray Diffraction and Scanning Electron Microscopy showed the interactions between protein/agents and the changes in amorphous structure of the films, which presented surfaces in chains of twisted shape. Differential Scanning Calorimetry demonstrated that the incorporations of gallic acid and citric acid improved the films thermal stability. The results showed that the chemical crosslinking can be used to improve the quality of fish skin gelatin films and, thus, these films can be an alternative to food packaging, as well to improve added value of the fish waste.

Thermophysical Properties and X-Ray Structure Investigations of Polyurethane Ureas, Containing Folate Derivative of Ferrocene

Thermophysical properties of polyurethane ureas by thermogravimetry and differential scanning calorimetry were studied. It was shown, that investigated polyurethane ureas are heat-resistant up to 523 K. The structure of polyurethane ureas, containing folate derivative of ferrocene, by wide-angle and small angle X-ray method for different content of folate-derivative of ferrocene was investigated. Wide-angle X-ray diffraction data revealed that the introduction of 0.01 mole of folate derivative of ferrocene to the PUU structure leads to the change of period alternating arrangement of flexible and rigid blocks of PUU, significant degradation of heterogeneous structure, but does not cause changes in amorphous structure of the polymer.

Thermally induced structural modifications and O2 trapping in highly porous silica nanoparticles

In this work we investigate by Raman spectroscopy the effect of isochronal (2 h) thermal treatments in air in the temperature range 200–1000 °C of amorphous silicon dioxide porous nanoparticles with diameters ranging from 5 up to 15 nm and specific surface 590–690 m2/g. Our results indicate that the amorphous structure changes similarly to other porous systems previously investigated, in fact superficial SiOH groups are removed, Si–O–Si linkages are created and the ring statistic is modified, furthermore these data evidence that the three membered rings do not contribute significantly to the Raman signal detected at about 495 cm−1. In addition, after annealing at 900 and 1000 °C we noted the appearance of the O2 emission at 1272 nm, absent in the not treated samples. The measure of the O2 emission has been combined with electron paramagnetic resonance measurements of the γ irradiation induced HO2 radicals to investigate the O2 content per mass unit of thin layers of silica. Our data reveal that the porous nanoparticles have a much lower ability to trap O2 molecules per mass units than nonporous silica supporting a model by which O2 trapping inside a surface layer of about 1 nm of silica is always limited.

Structural Transformations in Metallic Glasses

Structural transformations that are taking place in metallic glasses have severe impact upon their performance in variety of practical applications. Their originally amorphous structure changes under elevated temperature. Eventually, partial crystallization occurs. In order to follow the development of crystallization, the investigation of heat treatment of Fe-based metallic glasses was performed. Modifications in structure were studied by employing in-situ techniques of synchrotron radiation. Namely, diffraction experiments and nuclear forward scattering of synchrotron radiation are reported. Both methods of study were performed on-fly providing information about the state of the samples in real time.

Nanovoid formation by change in amorphous structure through the annealing of amorphous Al 2O 3 thin films

The formation mechanism of a high density of nanovoids by annealing amorphous Al 2O 3 thin films prepared by an electron beam deposition method was investigated. Transmission electron microscopy observations revealed that nanovoids ∼1–2 nm in size were formed by annealing amorphous Al 2O 3 thin films at 973 K for 1–12 h, where the amorphous state was retained. The elastic stiffness, measured by a picosecond laser ultrasound method, and the density, measured by X-ray reflectivity, increased drastically after the annealing process, despite nanovoid formation. These increases indicate a change in the amorphous structure during the annealing process. Molecular dynamics simulations indicated that an increase in stable AlO 6 basic units and the change in the ring distribution lead to a drastic increase in both the elastic stiffness and the density. It is probable that a pre-annealed Al 2O 3 amorphous film consists of unstable low-density regions containing a low fraction of stable AlO 6 units and stable high-density regions containing a high fraction of stable AlO 6 units. Thus, local density growth in the unstable low-density regions during annealing leads to nanovoid formation (i.e., local volume shrinkage).

Structural studies and polymorphism in amorphous solids and liquids at high pressure

When amorphous materials are compressed their structures are expected to change in response to densification. In some cases, the changes in amorphous structure can be discontinuous and they can even have the character of first-order phase transitions. This is a phenomenon referred to as polyamorphism. Most evidence for polyamorphic transitions between low and high density liquids or analogous transformations between amorphous forms of the same substance to date has been indirect and based on the changes in thermodynamic and other structure-related properties with pressure. Recent studies using advanced X-ray and neutron scattering methods combined with molecular dynamics simulations are now revealing the details of structural changes in polyamorphic systems as a function of pressure. Various "two state" or "two species" models are used to understand the anomalous densification behaviour of liquids with melting curve maxima or regions of negative melting slope. Thermodynamic analysis of the two state model leads to the possibility of low- to high-density liquid transitions caused by differences in bulk thermodynamic properties between different amorphous forms and on the degree of cooperativity between low- and high-density structural configurations. The potential occurrence of first-order transitions between supercooled liquids is identified as a critical-like phenomenon. In this tutorial review we discuss the background to polyamorphism, incorporating the experimental observations, simulation studies and the two-state models. We also describe work carried on several systems that are considered to be polyamorphic.

Annealing Temperature Dependence of the Amorphous Structure of Amorphous Si–Ge–Au Thin Films

The amorphous Si–Ge–Au thin films were consecutively annealed to determine annealing effects on the amorphous structures. Electrical resistivities were measured to investigate the amorphous structural changes. The electrical resistivies of the specimen annealed up to 1000 K were changed with hysteresis at high temperatures, but returned to same values of electrical resistivity at room temperature. Increasing of the upper limit of thermal annealing temperature from 1000 K to 1100 K made the electrical resistivity change irreversibly over the entire temperature range. Therefore, the expected transition temperature of the amorphous phase is considered to be between 1000 K and 1100 K.

Amorphous structure changes in poly(ethylene terephthalate) induced by annealing under dry and wet conditions and its dye uptake properties

The amorphous structure changes in poly(ethylene terephthalate) (PET) induced by annealing under dry and wet conditions were discussed in terms of amorphous density ( ρ a) and dye uptake properties. The ρ a value of PET decreased with increasing annealing temperature, but it conversely increased at annealing temperatures above 210°C for the dry treatment and above 170°C for the wet treatment. With decreasing ρ a from 1.35 to 1.31 g cm −3, the conformation of amorphous molecules changed from the gauche to trans form. The ρ a value conversely increased on annealing at higher temperatures; however, the dye exhaustion continuously increased. The ratio of the absorbance of the α band to that of the β band of the basic dye crystal violet ( α β ratio), indicating the degree of dye aggregation, in PET decreased with a decrease in ρ a. The degree of dye aggregation further increased when ρ a conversely increased on high temperature annealing. These results suggested that the free volume content of PET increased as a result of conformational change from the gauche to trans form in amorphous molecules with increasing annealing temperature, and finally the increased free volume converted to microvoids around 1.31 g cm −3 of ρ a. The dye exhaustion increased with increasing annealing temperature according to microvoid formation.

Effect of γ-irradiation on the optical and electrical properties of amorphous InSe thin films

Abstract The influence of γ-irradiation on the optical and electrical properties of amorphous InSe thin films was investigated. Optical absorption coefficient (α) of amorphous InSe thin films was represented as a function of photon energy (hμ) and the data were used to deduce the value of the optical energy gap (Eg opt), the refractive index (n) and the valence band density of states (gi) of the films. The analysis of the absorption coefficient data revealed the existence of indirect transition with optical energy gap Eg opt = 0.98 eV for as-deposited (unirradiated) amorphous InSe films, which increases to 1.15 eV with increasing the γ-doses to 2.5 Mrad. It was found that the activation energy ΔE obtained form the temperature dependence of conductivity for unirradiated and irradiated amorphous InSe films increases and the conductivity decreases with increasing γ-doses. Also it was found that the degree of disorder and defects in the amorphous structure changes due to γ-irradiation.

Structural changes of amorphous cellulose by thermal and hydrothermal treatments.

Structural changes of cellulose molecules in non-crystalline region of cellulosic materials by thermal and hydrothermal treatments were studied by using new amorphous cellulose samples, which were prepared from cellulose/SO2-diethylamine-dimethylsulfoxide solutions. Dry-thermal treatments led to depolymerization of amorphous cellulose and a decrease in moisture contents by forming irreversible hydrogen bonds, and these changes depended on molecular weight of original amorphous samples, heating temperature, and heating time. However, no crystallization was detected by X-ray diffraction analyses. In the case of thermal treatments of amorphous cellulose samples at 80°C and 80% relative humidity for 1-14 days, no change in amorphous structure, molecular weight, or moisture contents was observed. Hydrothermal treatments of amorphous cellulose samples in water at temperature higher than 100°C brought about crystallization to cellulose IV, together with depolymerization and a decrease in moisture contents. These structural changes depended on molecular weight of original amorphous celluloses, heating temperature, and heating time. In comparison with the results of dry-thermal treatments, it was shown that the presence of water remarkably enhanced depolymerization and crystallization to cellulose IV.

無電解Ni-Pめっき膜の構造と諸性質におよぼす繰返し応力の影響

The microstructure of electroless deposited Ni-P alloys in the composition ranging from 5.3 to 7.9 mass%P has been studied by a large angle X-ray scattering method. The changes of microstructure and mechanical properties by cyclic stressing at various stress levels were examined by a X-ray scattering technique and also by a static bend test.The results obtained are as follows;(1) The microstructure of electroless Ni-P alloys containing less than about 7 mass%P is a supersaturated solid solution of fcc Ni in which an excess of P dissolves. On the other hand, the electroless Ni-P alloys containing more than about 7 mass%P are completely amorphous structure. This structure is quite similar to that of the amorphous alloys obtained by other methods such as rapid quenching and electrodeposition.(2) The amorphous Ni-P alloys prepared by the present method have some excellent properties such as good ductility and high corrosion resistance. But, these excellent properties deteriorate by cyclic stressing, particularly by tensile stressing, because of a changes in amorphous structure due to structural relaxation and local crystallization.

Structure of amorphous Fe80-P13-C7 alloy by X-ray diffraction

X-ray diffraction patterns have been obtained from Fe80-P13-C7 alloy in both amorphous and liquid states. Using the common Fourier analysis, the atomic radial distribution function was evaluated from which interatomic distance and coordination number were obtained. The essential feature of the structure in the amorphous state was similar to that in the liquid state. The crystallization process of this alloy during isothermal aging at 330°C was also studied by the same procedures. The results indicated that the initial amorphous structure changes to a second amorphous structure, which in turn, transforms to the stable crystalline phase. This crystallization product was single phase of bcc structure (a0=2.864 A). By means of the Fourier analysis, these results led to the conclusion that the initial amorphous structure re-arranges to relax the stress or anisotropic configuration of atoms arising from the rapid quenching and subsequently the crystallization of this alloy occurs by a nucleation and growth mechanism during isothermal aging.