Amorphous Fraction Research Articles

Distinct dynamics of structural relaxation in the amorphous phase of poly(l-lactic acid) revealed by quiescent crystallization.

Fast scanning calorimetry (FSC) experiments were performed to investigate physical aging in amorphous and semi-crystalline poly(l-lactic acid)s (PLLAs) that were thermally crystallized under conditions leading to the α'- or α-crystalline form, and either favouring or inhibiting the development of a rigid amorphous fraction (RAF). The enthalpy of recovery was calculated after two procedures of rescaling to the content of the whole amorphous phase and also to the only content of the mobile amorphous fraction (MAF), which helped in clarifying the contribution of the RAF. From the dependence of the structural relaxation rate on the aging temperature, two regimes were evidenced for all samples. In the aging temperature domain situated close to the glass transition, the structural relaxation occurs significantly faster in the MAF. Its rate is independent of the aging temperature and is not influenced by the microstructure. However, the distance to equilibrium is higher in samples for which the coupling is strong between crystal and amorphous, implying that the time to reach equilibrium is also higher. In contrast, at low aging temperatures, for which the whole amorphous phase can be considered as solid, MAF and RAF exhibit the same structrural relaxation rate. This convergence in the relaxation kinetics by decreasing the temperature of physical aging was interpreted as the evolution of relaxation dynamics in the MAF from segmental to local. This change is highlighted by the comparison between MAF and RAF relaxation kinetics, but it occurs similarly in a pure amorphous system.

Immersion corrosion and electrochemical performances of laser cladded FeSiB, FeSiBCr and FeSiBCrMo coatings in 3.5 wt% NaCl solution

FeSiB, FeSiBCr and FeSiBCrMo coatings were laser cladded on S355 steel using a pre–placed powder method. The surface and cross–section morphologies, chemical elements and phases of obtained coatings was analyzed using a scanning electron microscope (SEM), energy dispersive spectroscope (EDS), and X–ray diffraction (XRD), respectively, and the effects of Cr and Mo additions on the immersion corrosion and electrochemical performances of obtained coatings in 3.5 wt% NaCl solution for 720 h were analyzed. The result shows that the amorphous area fractions of FeSiB, FeSiBCr and FeSiBCrMo coatings are 7.27, 10.51, and 10.07%, respectively. The immersion corrosion rates of FeSiB, FeSiBCr and FeSiBCrMo coatings are 68.4, 31.6 and 27.6 μm/year, respectively, and the corresponding polarization resistances are 5464, 12,645, and 19,016 Ω·cm2, respectively. The Cr2O3 passivation film is formed and further improved by the additions of Cr and Mo, respectively, which inhibits the occurrences of immersion and electrochemical corrosions.

A Novel Class of Cost Effective and High Performance Composites Based on Terephthalate Salts Reinforced Polyether Ether Ketone.

Poly(ether ether ketone) (PEEK)-based nanocomposites have been realized with incorporation (0–30 wt %) of anhydrous calcium terephthalate salts (CATAS), synthetized by reaction of terephtalic acid with the metal (Ca) oxide, by means of a melt processing. Their structure, morphology, thermal, and mechanical properties have been investigated. Scanning electron microscopy observations confirmed homogeneous dispersion of nanometer-sized fillers and a toughened fracture morphology even at the higher content, while thermal characterization confirmed an unvaried thermal stability and unmodified crystalline structure of the reference PEEK matrix. A negligible nucleating effect was evidenced, while a blocking effect of the amorphous phase fraction provide composites with increased stiffness, confirmed by enhanced values of G’ and shifts of glass transition peak to higher temperatures, for restriction in chain mobility imposed by CATAS. The proposed solutions aimed to enlarge the application range of high performance costly PEEK-based composites, by using thermally stable nanofillers with limited costs and easily controllable synthesis phase.

Temperature-dependent orientation of poly(ether ether ketone) under uniaxial tensile and its correlation with mechanical properties

Poly(ether ether ketone) (PEEK) is a high-performance thermoplastics with outstanding mechanical properties and thermal resistance (serving temperature up to 250 °C). Although many studies have been performed on the stress–strain behavior and related modeling, less attention has been paid on the structural and orientational evolution of PEEK during tensile deformation. In this work, the orientational and structural evolution during tensile deformation at a wide range of temperatures from 30 to 170 °C was probed ex situ by wide-angle X-ray diffraction and differential scanning calorimetry. The enthalpy of cold crystallization of PEEK as a function of strain, which reflects the content of amorphous fraction and the disorder degree of crystals, presents an interesting dependence on tensile temperature. The evolution of orientation with strain is strongly dependent on the tensile temperature. Oriented PEEK presents much improved modulus and tensile strength compared to that of undrawn PEEK. This finding demonstrated that pre-stretching especially at temperatures above Tg is an effective way to improve the mechanical property of PEEK.

Molecular dynamics, crystallization and hydration study of Poly(Propylene succinate) based Poly(Ester amide)s

Poly(ester amide)s, PEA, based on poly(propylene succinate), PPS, improved by the addition of a new symmetrical amido diol, AD, at various molar fractions are investigated in this article. The emphasis is given on the effect of AD (hard segment) on crystallization and molecular mobility of the polymer. To that aim, we employed differential scanning calorimetry, DSC, and broadband dielectric spectroscopy, BDS. AD was found to systematically facilitate crystallization, both with respect to the rate and the fraction (CF increases from 0 up to ~50 wt%), which is desirable for industrial processing and applications. In agreement with previous findings on the same systems, our results suggest that the crystallites consist mainly of the hard AD segments, whereas soft segments (PPS-related) are the main contributors to the glass transition. AD was found to increase the glass transition temperature, Tg, of the soft segments both calorimetric and dielectric, indirectly via the increase in the CF. The rigid amorphous fraction, RAF, of the polymer existing in the vicinity of the formed crystals was estimated and is proposed to consist mainly of soft segments without, however, excluding a minor contribution of non-crystallized AD. RAF exhibits non-systematic alternations with CF, most probably due to the expected variations in the semicrystalline morphology. BDS allowed the full-temperature range dynamics mapping and, subsequently, revealing of effects of the polymer composition in combination with CF and the involved traces of water on the local (β and βw relaxations) and segmental (α relaxation) dynamics. Upon addition of AD, the ester bond-related local β relaxation of PPS accelerates, exhibiting, however, unchanged activation energy (Eact~39 kJ/mol). Simultaneously, α relaxation, related to the glass transition, slows down (in agreement with calorimetry) and exhibits a worth noting decrease in cooperativity. These results indicate severe effects on molecular dynamics and suggest possible changes in the polymer free volume/density in the PEAs. βw relaxation with Eact~58 kJ/mol is recorded for the first time in PPS and is related with the same ester group as β, moreover, with water molecule(s) attached.

Monocationic porphyrin dyads with fullerene as the electron-accepting material

Dyad compounds in which a fullerene [Formula: see text] was covalently linked to a monocationic porphyrin at a N,N[Formula: see text]-bridge substituent, were synthesized by condensation reaction. The low solubility of a dyad containing tetraphenylporphyrin (TPP) derivative was improved by using octaethylporphyrin (OEP) derivatives and introduction of an alkyl substituent to the porphyrin derivatives. The energy levels of the frontier orbitals, estimated experimentally using potentiometric data and the optical energy band gaps obtained by the UV-vis spectra, were sufficiently low to be comparable to acceptor materials. They varied depending on the peripheral substituents on the porphyrin unit. DSC analysis of the drop-cast films of the P3HT/dyad blends showed that the film containing the OEP dyad, annealed at a higher temperature, had more amorphous fractions than the films containing the TPP dyad.

Selective laser melting vitrification of amorphous soft magnetic alloys with help of double-scanning-induced compositional homogeneity

Recently, selective laser melting (SLM) of Fe-based soft magnetic bulk metallic glass (BMG) is garnering great attention because it can yield both superior magnetic properties such as high permeability and low core loss and near-net shaping of 3-dimensional complex components. However, full vitrification of BMGs with high saturation magnetization above 1.2 T has never been realized because cooling rates are limited and compositional inhomogeneity induced by rapid laser processing causes severe undesirable crystallization. In this work, a double scan strategy has been employed with the aim of amorphous phase fraction enhancement as well as densification. We have shown that double scanning effectively fills voids generated due to partial melting of powders, and leads to relative density of up to 96% and corresponding saturated magnetization of 1.22 T. More importantly, the double scan strategy stimulates reflow in the melt pool, securing compositional uniformity, and eventually enhances amorphous phase fraction to a value as high as 47%. As a consequence, coercivity has been significantly decreased, which in turn reduces core loss and increases permeability.

Application of chemical and biological tests for estimation of current state of a tailing dump and surrounding soil from the region of Tarniţa, Suceava, Romania.

This paper presents the results from a study on the current state of tailing dump, surrounding soil and water in the region of Tarniţa-Suceava, Romania. A number of chemical analyses and germination tests were applied in an attempt to estimate the ability of soil to maintain the plants growing, the bioavailability, and heavy metals uptake. Total heavy metals, exchangeable metals, acidity, and carbon and nitrogen content were determined. A modified sequential extraction method was used to determine geochemical phase distribution of heavy metals. The most abundant heavy metals in the studied samples were Cu, Zn, and Pb. Elevated concentrations of As were also found. The results from sequential extraction revealed that up to 51% of copper was retained by amorphous and crystalline iron oxides in soil. Higher content of lead was noticed in amorphous iron oxide fraction. The heavy metal concentration in river water during dry season varied from 0.13 mg/L (Fe) to 4.2 mg/L (Zn) and was below the maximum contamination level for drinking water. The soil toxicity and heavy metal bioavailability of tailing dump material and surrounding soils were studied by germination tests. The germinated plantlets on the studied soils were found to accumulate elevated concentrations of heavy metals thus indicating the bioavailability of soil contaminants. Soil decontamination by distilled water or magnesium nitrate solution was found to be efficient enough to improve the capability of the studied soils to support the germination process.

Constrained Amorphous Interphase and Mechanical Properties of Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate)

In the present study, for the first time the evolution of tensile mechanical properties of different poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymers (PHBV8 and PHBV12, with 8 mol% and 12 mol% of HV co-units, respectively) as a function of the storage time at room temperature has been investigated in parallel with the quantification of the crystalline, mobile amorphous, and rigid amorphous fractions. A comparison with the evolution of the crystalline and amorphous fractions in the homopolymer poly(3-hydroxybutyrate) (PHB) was also performed. For all the samples, the crystallinity was found to slightly increase during storage. In parallel, the mobile amorphous fraction (MAF) decreased markedly, with the result that a relevant increase in the rigid amorphous fraction (RAF) was detected. The RAF content in the copolymers was lower than that of PHB. For all the samples, the RAF formation during aging was ascribed to the growth of secondary crystals in geometrically restricted areas. It was demonstrated that the storage at Troom leads in PHB, PHBV8, and PHBV12 to a progressive increase in the total solid fraction (crystal phase + rigid amorphous fraction) and to a simultaneous physical aging of the rigid amorphous fraction. The two different processes cannot be separated and distinguished, so that only the resulting effect on the mechanical properties was considered. The experimental elastic modulus of both PHBV8 and PHBV12 was found to increase regularly with the total solid fraction, as well as the tensile strength. Conversely, the elongation at break turned out to be an increasing function of the mobile amorphous fraction. The elastic moduli of the crystalline, mobile amorphous, and rigid amorphous fractions of PHBV8 and PHBV12 were estimated by means of a three-phase modified Takayanagi's model, to take into account also the contribution of the rigid amorphous fraction. The calculated values were found in agreement with theoretical expectations.

Ion beam induced transient amorphous nucleation in silicon

Ion-beam amorphization of crystalline silicon is reviewed. All the peculiar features of the process (temperature effect, incubation fluence, superlinear behavior of the amorphous fraction as a function of the ion fluence, dose–rate effects, ion mass/energy dependence, doping influence, etc.) can be explained within the classical theory of nucleation and growth based on capillarity. Nucleation and growth rates depend on the free energy of the amorphous clusters and on the kinetics balance between damage creation at the prompt stage of each ion collision cascade and competitive re–crystallization induced by atomic jumps of long living defects at the cluster surface. The model explains the damage accumulation kinetics either in dilute or dense collision cascade. It is an extension of the theoretical approach describing the reverse process, i.e. the ion–beam assisted nucleation and growth of crystalline clusters in the amorphous material. The description is independent on the atomistic nature of the involved defects.

Effect of surface modification of colloidal silica nanoparticles on the rigid amorphous fraction and mechanical properties of amorphous polyurethane–urea–silica nanocomposites

ABSTRACTColloidal silica nanoparticles (NPs) modified with eight different silane coupling agents were incorporated into an amorphous poly(tetramethylene oxide)‐based polyurethane–urea copolymer matrix at a concentration of 10 wt % (4.4 vol %) in order to investigate the effect of their surface chemistry on the structure–property behavior of the resulting nanocomposites. The rigid amorphous fraction (RAF) of the nanocomposite matrix as determined by differential scanning calorimetry and dynamic mechanical analysis was confirmed to vary significantly with the surface chemistry of the NPs and to be strongly correlated with the bulk mechanical properties in simple tension. Hence, nanocomposites with an RAF of about 30 wt % showed a 120% increase in Young's modulus, a 25% increase in tensile strength, a 15% decrease in elongation at break with respect to the neat matrix, which had no detectable RAF, whereas nanocomposites with an RAF of less than 5% showed a 60% increase in Young's modulus, a 10% increase in tensile strength and a 5% decrease in the elongation at break. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2543–2556

Glass forming ability and continuous-cooling-transformation (CCT) diagrams of Vitreloy 105 as function of cooling rate and oxygen concentration

A design of experiments was used to investigate the effects of oxygen concentrations and cooling rates during solidification of Vitreloy 105. The cooling rates of different copper molds were estimated by measuring the interlamellar spacing of an Al-33Cu (wt.%) eutectic alloy cast into these molds. Rietveld refinements of synchrotron X-ray diffraction (XRD) patterns were used to identify and quantify the phases and the results were used to construct a phase map for the Vitreloy 105. Differential scanning calorimetry (DSC) was used to determine the glass stability, transformation temperatures and to quantify the amorphous fractions. Amorphous quantification by image analysis in light optical microscopy (LOM) micrographs was performed in the same samples for comparison. Finally, continuous-cooling-transformation diagrams for Vitreloy 105, with different oxygen contents, were attempted for the first time.

Impact of the solidification path of FeOx–SiO2 slags on the resultant inorganic polymers

AbstractAiming to reduce the carbon dioxide emissions associated with cement production, alternative binders such as inorganic polymers currently receive substantial attention and slags from the non‐ferrous metallurgy are promising precursors. However, studies that correlate their chemistry and crystallinity with the newly formed binder remain limited. In this work, the effect of three different solidification methods on glass formation and reactivity of FeOx–SiO2 slags, as well as on the molecular structure of the resultant Fe‐rich inorganic polymers, was investigated. The inorganic polymers were synthesized by mixing the slags (approximate molar ratio FeO/SiO2 = 1.6) with an alkali silicate solution (molar ratios SiO2/Na2O = 1.6 and H2O/Na2O = 25). Results demonstrated that higher cooling rates promoted higher glass formation and faster reaction kinetics when the slags were activated. 57Fe Mössbauer spectroscopy indicated that all the slags consisted predominantly of Fe2+ ions with a minor amount of Fe3+ ions, regardless of the variability in glass content. The binder phase of all inorganic polymers consisted of iron in both Fe2+ and Fe3+ states, after 28 days of curing. After pulverizing the inorganic polymer pastes and exposing the powder to air for 28 additional days, the Fe2+ state in the binder transformed to Fe3+. The compressive strength evolution of the three slags showed that the 2‐day strength was higher for the samples with a higher amorphous fraction, while after 28 days, this influence was less pronounced.

Whiskers of Iron(II) (1-Hydroxyethylidene)diphosphonate and Its Complex with Morpholine

The interaction of an aqueous suspension of fine-grained iron with one equivalent of (1-hydroxy-ethylidene)diphosphonic acid (H4L) leads to the formation of poorly soluble iron(II) (1-hydroxy-ethylidene)diphosphonate (FeH2L · H2O), which precipitates from the solution in the form of whiskers. A compound consisting of crystalline and X-ray amorphous fractions, whose structure is based on stacked sheets of whiskers, linked by amorphous phase, was selected from the FeH2L · H2O reaction mixture with morpholine. The compounds have been studied by methods of elemental analysis, scanning electron microscopy, optical microscopy, atomic force microscopy (AFM), and X-ray diffraction (XRD) analysis.

Structure of photo-damaged white and naturally pigmented human hair

The effect of photo-degradation processes on the morphology and ultrastructure of pigmented and non-pigmented hair was evaluated in this work by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). Samples consisted of three types of grey hair (separated out into subsamples of totally white and totally black strands) and one type of dark-brown hair exposed to solar irradiation for 75 h or to a mercury lamp for 600 h.SAXS patterns showed that irradiation mainly damaged the amorphous regions of hair, and in some types of hair, an ordered structure appeared, with spaces of ca. 4.5 nm. This structure occurred independently of the presence of pigments and its scattering intensity increased after irradiation. Layers of lipids present in the cuticle may be responsible for this scattering around 4.5 nm, as indicated by TEM images. TEM also showed morphological changes in the outermost cuticle layers, such as the degradation of endocuticle and the detachment of the cell membrane complex. Therefore, the results presented herewith showed that irradiation caused different damages to the hair amorphous fractions, especially in the cuticle layers, which are the most exposed areas of the hair strands.

Mixtures of m-fluoroaniline with apolar aromatic molecules: Phase behaviour, suppression of H-bonded clusters, and local H-bond relaxation dynamics

We employ differential scanning calorimetry, IR spectroscopy, X-ray powder diffraction and dielectric spectroscopy to characterize binary mixtures of m-fluoroaniline (mFA), a rigid-molecule glass former, with two non-self-associating molecules containing benzene rings, namely m-xylene (mX) and a distyrene derivative (DS). The addition of mX suppresses the formation of H-bonded mFA clusters. While both mX and DS dilute the H-bond density of mFA, they have opposite effects on the glass transition temperature (Tg) and structural relaxation time of mFA, with mX acting as a plasticiser and DS as an antiplasticiser. While the mFA-DS mixtures can be studied in the supercooled liquid regime at DS molar mass fraction as high as 0.9 without undergoing phase separation, the mFA-mX mixtures remain homogeneous at low temperatures only up to a mX molar fraction of 0.5. All homogeneous mixtures display a structural relaxation which shifts according to the Tg of the mixture, and a secondary relaxation which remains virtually invariant with respect to that of pure mFA. For mX molar fraction higher than 0.5, the mixtures phase-separate into almost pure crystalline mX domains and a mFA-rich amorphous phase. Upon partial crystallization the structural relaxation time and Tg of the remaining amorphous fraction shift to larger values, consistent with the increased effective mFA concentration. At the same time, the secondary relaxation time undergoes a dramatic shift of more than two decades. These findings allow identifying the secondary relaxation in the rigid-molecule mFA glass former as a local reorientational motion of a m-fluoroaniline moiety around one of its H-bonds, a rotation that is strongly affected if the mobility of the H-bond sharing species is quenched by crystallization.

Influence of interfaces on the crystallization behavior and the rigid amorphous phase of poly(l-lactide)-based nanocomposites with different layered doubled hydroxides as nanofiller

Based on the three-phase model of semi-crystalline polymers, we determined all phase fractions of the NiAl-LDH/PLLA nanocomposite in dependence on the concentration of the nanofiller. Moreover, the rigid amorphous fraction (RAF) was separated into the RAFcrystal and the RAFfiller unbiasedly. A detailed comparison to the related nanocomposite system MgAl-LDH/PLLA was made considering that Mg and Ni have different atomic weights. As a first result is was found that NiAl-LDH/PLLA displays a higher crystallization rate compared to MgAl-LDH/PLLA, which is related to the different morphologies of the two nanocomposite systems. For both systems RAFcrystal devided by the degree of crystallization increases with increasing concentration of the nanofiller. This means in the case of the nanocomposites investigated here not each crystal produces the same amount of RAF, as often assumed. Also, RAFfiller increases with the concentration for both systems but in a different way. This is discussed considering again the different morphologies of both nanocomposites.

Crystal self-nucleation in polyamide 11 of different semicrystalline morphology

Self-nuclei supported recrystallization of the crystal-free melt of polyamide 11 (PA 11) of qualitatively different initial semicrystalline morphology, either containing nodular crystals or spherulitically grown lamellar crystals, has been investigated by fast scanning chip calorimetry, optical microscopy and atomic force microscopy. Melt-recrystallization of PA 11 initially containing a large number of nodules of high surface-to-volume ratio and strong coupling to the surrounding amorphous structure, as confirmed with the detection of significant amount of rigid amorphous fraction, is distinctly faster than melt-recrystallization of PA 11 initially containing lamellae and spherulites, caused by a lower number of self-nuclei in the latter system. Moreover, the temperature range of survival of self-nuclei above the respective melting temperature of nodular and lamellar crystals is larger for PA 11 initially containing nodules. The melt-residence time, within the assessable time-range before onset of melt-recrystallization, has no effect on the self-nuclei number. Enhanced self-nucleation in PA 11 containing nodules, compared to spherulitically crystallized PA 11, is suggested being caused by the distinctly larger initial number of individually grown crystals. A possible effect of the rigid amorphous fraction, forming during nodular crystallization, on hindering relaxation of the melt is discussed.

Denitration of simulated radioactive liquid waste

Radioactive liquid wastes containing large amounts of nitric acid (approx. 4–7 M) generated in the nuclear fuel cycle are very undesirable by-products. Denitration of highly acidic radioactive liquid wastes with organic reducing agents has several advantages, such as a significant pH increase, possibility of separation of radioisotopes which can be utilized in other technologies, reduction of volatility of radioisotopes and fixation of certain mono- and divalent radioisotopes with zeolite. In the present work some aspects of denitration of simulated radioactive liquid wastes at laboratory level were investigated. Denitration of HNO3 with formic acid was investigated for different [HCOOH]/[HNO3] ratios. The changes in the induction time, pH increase and volume reduction were determined. It was shown that by the denitration of simulated radioactive liquid waste high pH values could be achieved which in real systems would create more possibilities in radioactive waste management. Analysis of solid phases formed after the oxidation of excess HCOOH with H2O2 showed the presence of amorphous fraction as well as goethite and hematite phases, which could remove different radioactive cations from the liquid phase. The immobilization of simulated solid radioactive waste with borosilicate glass matrix was also shown.

Citric acid enhances Ce uptake and accumulation in rice seedlings exposed to CeO2 nanoparticles and iron plaque attenuates the enhancement

To assess the role of citric acid, as a typical low-molecular-weight organic acid from root exudates, on cerium (Ce) uptake, accumulation and translocation in rice seedlings (Oryza sativa L.) exposed to two CeO2 nanoparticles (NPs) (14 nm and 25 nm). A hydroponic experiment was performed under two citric acid levels (0.01 and 0.04 mmol L−1) combined with iron plaque presence. Citric acid significantly enhanced surface-Ce, root-Ce and shoot-Ce accumulation, irrespective of NPs size and iron plaque presence. The increased surface-Ce was associated with the promoted interactive attraction between NPs and root surface, and the enhanced NPs dissolution. Surface-Ce (containing crystalline and amorphous fractions of iron plaque) accumulation increased with the increase of citric acid concentrations. However, the enhancement influence of 0.01 mmol L−1 citric acid on root-Ce, shoot-Ce accumulations, rice-Ce distribution and TFroot-shoot was more remarkable than citric acid (0.04 mmol L−1), which suggested higher food security risk for human health with environment-level citric acid. Iron plaque presence attenuated the enhancement effect of citric acid on rice-Ce accumulation and distribution (containing surface-Ce, root-Ce and shoot-Ce) due to the reduced attractive interaction between NPs and root surface from the effect of Fe2+ being dissolved by iron plaque. Above effect of citric acid and iron plaque was more remarkable in 25 nm NP than 14 nm NP.