Structural Relaxation Processes Research Articles

On the dependence of the thermal module of elasticity of a two-component magnetic fluid on frequency, concentration and magnetic field

Purpose. Study of the dependence of the thermal modulus of elasticity of a two-component magnetic fluid on the magnitude of the magnetic field strength, the frequency of external disturbance and the volumetric concentration of magnetic particles.Method. The research method is based on the kinetic theory of liquid systems. Based on previously constructed kinetic equations for one-particle and two-particle distribution functions and a microscopic expression for the heat flux vector, an explicit dynamic expression for the thermal modulus of elasticity of magnetic fluids is obtained. In fast processes in liquids, heat transfer occurs in waves and their propagation is similar to the propagation of second sound in helium II. The thermal modulus of elasticity in liquids appears at high frequencies and ensures the propagation of second sound. The expression for the thermal modulus of elasticity consists of potential and kinetic parts, taking into account structural and translational relaxation processes, respectively. To study the thermoelastic properties of magnetic fluids, appropriate expressions of potential interaction energies were selected for each subsystem, allowing for numerical calculations.Results. Numerical calculations of the frequency and concentration dependence of the dynamic thermal modulus of elasticity in the presence of an external magnetic field in a kerosene-based magnetic fluid were carried out. The calculation results show that an increase in the influence of external disturbances leads to a nonlinear increase in the thermal modulus of elasticity in the magnetic fluid. An increase in the volume concentration of magnetic particles and an increase in the magnetic field strength also led to a nonlinear increase in the thermal modulus of elasticity in the magnetic fluid.Conclusion. It has been established that, due to taking into account translational and structural relaxation processes, the region of frequency dispersion of the thermal elastic modulus is wide. Numerical calculations carried out at different values of the external magnetic field and the volume concentration of magnetic particles showed that although an increase in the magnetic field and concentration of magnetic particles leads to an increase in the thermal modulus of elasticity, their increase does not affect the change in the frequency dispersion region.

Microstructural stability and mechanical property of AlCrFeMoTi high-entropy amorphous alloy thin films under He+ ions irradiation

High-entropy amorphous materials have recently proved exceptional radiation resistance, showing potential as a candidate materials for nuclear industry applications. This study synthesized nearly equi-atomic AlCrFeMoTi high-entropy amorphous thin films with a thickness of about 499 nm using magnetron sputtering. The prepared films were subjected to low dose, 0.5 MeV He+ ion irradiation, with varying irradiation damage ranging from 0.01 to 0.1 displacement per atom (dpa). Increasing the irradiation dose led to a decrease in the radius of the inner diffraction halo (r) and an increase in the crystal-like order, indicating an irradiation-induced structural relaxation process within the amorphous matrix. This relaxation results in more efficient atomic packing, yielding a denser amorphous structure and enhanced hardness of AlCrFeMoTi high-entropy amorphous thin films. This study demonstrates that AlCrFeMoTi high-entropy amorphous thin films exhibit remarkable radiation resistance, with stable microstructure and mechanical properties under He+ irradiation, making them promising candidates for applications in the nuclear industry.

Mechanical Properties of an Ultrahard In Situ Amorphous Steel Matrix Composite

We report compression tests on micropillars manufactured from bulk specimens of partially devitrified SAM2×5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4). Yield strength values of ≈6 GPa are obtained. Such a high strength can be attributed to the higher glass transition temperature (883 K) of this material, which impedes the multiplication of shear bands under loading, and to the presence of hard crystalline domains that result from devitrification of the amorphous powders during powder consolidation. The Vickers hardness of the specimens is found to be strongly correlated to the processing temperature and, hence to the volume of crystalline phases present in the specimens. As the processing temperature is increased, there is a reduction in free volume from the structural relaxation process in the amorphous alloy, leading to the eventual nucleation of crystalline phases of BCC Fe, Cr2B, Cr21.30Fe1.7C6, or Fe23B2C4, during the densification process. These results shed light on the relationship between nanocrystalline domains and the mechanical behavior of Fe‐based amorphous/crystalline composites.

Thermo-Structural Characterization of Phase Transitions in Amorphous Griseofulvin: From Sub-Tg Relaxation and Crystal Growth to High-Temperature Decomposition.

The processes of structural relaxation, crystal growth, and thermal decomposition were studied for amorphous griseofulvin (GSF) by means of thermo-analytical, microscopic, spectroscopic, and diffraction techniques. The activation energy of ~395 kJ·mol-1 can be attributed to the structural relaxation motions described in terms of the Tool-Narayanaswamy-Moynihan model. Whereas the bulk amorphous GSF is very stable, the presence of mechanical defects and micro-cracks results in partial crystallization initiated by the transition from the glassy to the under-cooled liquid state (at ~80 °C). A key aspect of this crystal growth mode is the presence of a sufficiently nucleated vicinity of the disrupted amorphous phase; the crystal growth itself is a rate-determining step. The main macroscopic (calorimetrically observed) crystallization process occurs in amorphous GSF at 115-135 °C. In both cases, the common polymorph I is dominantly formed. Whereas the macroscopic crystallization of coarse GSF powder exhibits similar activation energy (~235 kJ·mol-1) as that of microscopically observed growth in bulk material, the activation energy of the fine GSF powder macroscopic crystallization gradually changes (as temperature and/or heating rate increase) from the activation energy of microscopic surface growth (~105 kJ·mol-1) to that observed for the growth in bulk GSF. The macroscopic crystal growth kinetics can be accurately described in terms of the complex mechanism, utilizing two independent autocatalytic Šesták-Berggren processes. Thermal decomposition of GSF proceeds identically in N2 and in air atmospheres with the activation energy of ~105 kJ·mol-1. The coincidence of the GSF melting temperature and the onset of decomposition (both at 200 °C) indicates that evaporation may initiate or compete with the decomposition process.

Mechano-Synthesis, Structure, and Thermal and Magnetic Behaviors of the New Compound Mn1.2Co0.05Fe0.7P0.45Si0.5B0.05

The Mn1.2Co0.05Fe0.7P0.45Si0.5B0.05 compound has been systematically synthesized by mechanical alloying for 15 h, followed by annealing with two heating cycles at 1373 K for 2 h and 1073 K for 24 h. The powder that was milled for 15 h revealed the main hexagonal-Mn2P-type phase and the minor cubic-Mn3Fe2Si phase through X-ray diffraction examination. After annealing the same powder at 1373 K for 2 h and again at 1073 K for 24 h, the refined phase was the unique (Mn, Fe)2(P, Si) type with a hexagonal structure. For the mechanically alloyed powder, the final crystallite size was approximately 20 nm, and it rose to 95 nm during the annealing process. Further, a large amount of lattice microstrain was achieved as a result of high-energy milling (about 0.75%). Over the whole temperature range of 373 to 923 K, the thermal analysis showed several overlapping exothermic peaks, which indicated the improvement of the microstructure after the structural relaxation and reordering process. Moreover, the Curie temperature of the alloy was retrieved at approximately 675 K. According to an analysis of the magnetic properties, the mechanically alloyed powder exhibited an exceptional soft ferromagnetic state after 15 h of milling, and the annealed alloy showed superparamagnetic characteristics.

Direct Observation of Solid-Phase Crystallization of an Amorphous Complex Oxide in the Transmission Electron Microscope

Many complex metal oxides possess intricate structure-function relations, resulting in a wide range of tunable functional properties. The introduction of disorder through amorphization provides additional opportunities for tuning the properties, particularly in the area of electrochemical energy storage and conversion [1]. Consequently, amorphous and partly crystalline complex oxides have garnered growing interest in recent years, with two primary goals: to harness their unique functional properties or to employ them as a chemically-flexible, far-from-equilibrium, thin-film processing platform that offers novel synthesis opportunities [2] due to the minimal energy input required to initiate crystallization and other structural relaxation processes.Relevant to both these aims, the processing-structure-function relationship for amorphous complex oxides is examined by in situ solid-phase crystallization (SPC) in the (scanning) transmission electron microscope ((S)TEM), focusing on perovskite-like (ABO3) mixed ion-electron conducting (MIEC) amorphous complex oxides which make promising low-temperature solid-oxide cell (SOC) electrodes [3] due to the widely observed disorder-mediated oxygen surface-exchange [4]. Key aspects of MIEC amorphous complex oxide processing, such as the evolution of structure and chemistry with temperature and the corresponding effect on conductivity are detailed in the amorphous La0.8Sr0.2MnO3-δ (LSM) system. Further, approaches to direct amorphous complex oxide processing towards desirable synthesis products based on these insights are discussed.Here, we elucidate down to the atomic scale the development of structural characteristics such as porosity, crystallized fraction, crystallite tension, size, curvature, and surface termination, with the aim to establish approaches to tune surface functionality in partly crystalline MIECs by heating or electron beam irradiation [5]. In situ electrical measurements are used to correlate these changes with electrical behavior, revealing that the onset of crystallization is correlated with an increase in electronic conductivity by small polaron hopping, attributed to oxygen-metal-oxygen bond alignment. Further, in the absence of epitaxial constraints, an immiscibility-driven self-organization of amorphous heterointerfacial structures manifests by spinodal decomposition, that is likely to be broadly relevant in low-temperature processing of amorphous complex oxides [6]. Thus, processing from an amorphous complex oxide precursor could be a method to establish uniformly-dispersed nanoscale heterointerfaces of tunable characteristic length scale throughout a thin film volume, while also enabling direct tuning of the porous mesostructure by electron beam irradiation. Overall, case studies of amorphous complex oxide crystallization are limited to relatively few chemical systems and processing conditions. Thus, extending this body of work to explore a broader processing space, and extracting fundamental insights to establish process-structure-function relationships are prerequisites to realizing the full potential of partly crystallineMIEC systems, and provides guidance for processing amorphous complex oxides generally. Acknowledgments The authors acknowledge the UC Irvine School of Engineering new faculty setup funds, the National Science Foundation CAREER award (DMR-2042638) and the UC Irvine Materials Research Institute (IMRI). References S. Yan ... H. Xia, Small (2019)D. Prakash, ... F. Cavallo, Small (2022).J. Zhang ... Y. Chen, Advanced Functional Materials (2022)T. Chen ... N. Perry, ACS Applied Materials & Interfaces (2019)J. Wardini ... W. Bowman (submitted)J. MacManus-Driscoll, Advanced Functional Materials (2010)

Tailoring Vacancy Defects in Isolated Atomically Precise Silver Clusters through Mercury-Doped Intermediates.

Vacancy defects are known to have significant effects on the physical and chemical properties of nanomaterials. However, the formation and structural dynamics of vacancy defects in atomically precise coinage metal clusters have hardly been explored due to the challenges associated with isolation of such defected clusters. Herein, we isolate [Ag28(BDT)12]2- (BDT is 1,3-benzenedithiol), a cluster with a "missing atom" site compared to [Ag29(BDT)12]3-, whose precise structure is known from X-ray diffraction. [Ag28(BDT)12]2- was formed in the gas-phase by collisional heating of [Ag28Hg(BDT)12]2-, a Hg-doped analogue of the parent cluster. The structural changes resulting from the loss of the Hg heteroatom were investigated by trapped ion mobility mass spectrometry. Density functional theory calculations were performed to provide further insights into the defect structures, and molecular dynamics simulations revealed defect site-dependent structural relaxation processes.

Dielectric relaxations and the phenomena of glass transition in supercooled D-xylose aqueous mixtures

D-xylose aqueous solutions at various concentrations of water (0 ≤ x ≤ 40 %) were investigated using broadband dielectric spectroscopy and differential scanning calorimeter in the wide temperature range (150–300 K). Two resolvable relaxations were observed in all studied D-xylose aqueous solutions. The slower relaxation process (process-I) observed above the glass transition temperature (Tg), usually referred to as the structural relaxation process, is responsible for the collective movement of the D-xylose and water mixture. The faster one (process-II) observed below Tg is mainly related to the water molecular relaxation inside the D-xylose matrix. The temperature dependence of the average dielectric relaxation time and dielectric strength of both observed processes (I & II) were analyzed for all concentrations of water (x) in D-xylose. It was observed that the dielectric strength of process-II in the D-xylose water mixture increased sharply above critical concentration, x = 25 % shows moderate characteristics as compared to its isomers viz. D-ribose, D-arabinose and D-lyxose. Also the activation energies were found to be almost water content independent above critical concentration, x = 25 %. This suggests that this dynamic process was dominated by water-water interaction. Moreover, the Tg of bulk water was estimated at 133 ± 1 K and 138 ± 1.2 K from the extrapolation of DSC Tg and dielectric Tg, respectively of the D-xylose aqueous mixture using the Gordon-Taylor equation. This gives further support to the commonly accepted Tg value of bulk water.

How temperature-induced depolymerization and plasticization affect the process of structural relaxation

The self-plasticization, i.e., the increase in the polymer segmental mobility by the inclusion of its own monomer, has a major impact on the structural, thermal, and mechanical properties of the polymer. Differential scanning calorimetry (DSC) was used to investigate the influence of thermally induced self-plasticization on the structural relaxation of polydioxanone (PDX). Depolymerization (based dominantly on the end-chain scission mechanism) was found to be controlled by the depolymerization temperature Td as well as the actual number of re-melting cycles (while keeping the time spent at Td constant). PDX samples with the glass transition temperature (Tg) ranging from −52 (highly plasticized) to −13 °C (virgin) were prepared. The DSC data were described in terms of the Tool-Narayanaswamy model; a consistent structural relaxation behavior associating the degree of plasticization with Tg was identified. The activation energy first decreased with plasticization from 430 kJ mol−1 to 210 kJ mol−1 in the Tg range of −40 to −13C, which is consistent with the plasticization-caused spacing-apart of the polymer chains resulting in larger free volume and increased freedom for the relaxation movements. For the highly plasticized PDX samples, the activation energy increased from 210 kJ mol−1 to 310 kJ mol−1, which appears to be associated with the possible segregation of the portion of the plasticizer into a discrete phase. The width of the relaxation times distribution increased with plasticization as a consequence of the plasticizer loosening the polymeric chains and enabling a wider variety of the segmental movement. The plasticization also leads to a higher dependence of the segmental relaxation movements on their current physico-chemical and steric surrounding.

Unveiling the Synergy of Polymer–Salt Compositions for Properties Enhancement of Solid Polymer Electrolytes Based on PEO/PVP Blend Polymer Matrix and LiTFSI Dopant Salt

Solid polymer electrolytes (SPEs) are ion-dipole complexes credited to their use in the design and development of widespread solid-state ion conducting innovative devices. Accordingly, herein, two sets of highly flexible, stretchable, and sticky type SPE films based on poly(ethylene oxide) (PEO)/ poly(vinyl pyrrolidone) (PVP) blend as host matrix of different compositional ratios (i.e., 25/75, 50/50, and 75/25 wt/wt%) with 30 and 50 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as ionic dopant salt, and also one sample of polymer-in-salt (PiS) comprised the 50/50 wt/wt% polymer blend matrix and 60 wt% salt, are prepared and characterized in detail. These SPEs are predominantly amorphous having substantial absorbance for ultraviolet-visible radiations and tunable wide range energy band gaps. The 20 Hz—1 GHz broadband dielectric permittivity, loss angle tangent, and electrical conductivity spectra explained a variety of polarization and structural relaxation processes and the mechanism of ion transport ruled by the compositional synergy of polymer and salt in these SPEs. The highest ionic conductivity with appreciable electrochemical performance of the SPE is found for the PEO-rich blend matrix with 50 wt% of LiTFSI dopant. We conclude the suitability of these enhanced promising propertiesSPEs for the development of futuristic ion-conducting energy storage as well as revolutionary iontronic devices.

Physical aging of lithium disilicate glass

Refractive index measurements were used to probe the structural relaxation behavior during the physical aging of a lithium disilicate glass at temperatures below the glass transition. The structural relaxation process was recorded using a single sample, starting from 5 K below the initial fictive temperature (Tf) of 720 K and gradually lowering it by 5 K increments until reaching an impractical experimental time to obtain complete relaxation at Tf − 35 K. The aging curves exhibited a stretched exponential relaxation behavior characteristic of glassy systems and showed good reproducibility in relaxation kinetics at three temperatures. A long continuous aging experiment conducted at 705 K demonstrated that the interruptions between isothermal treatments and property determinations did not affect the results. Finally, it was impossible to complete all experiments with the same sample, as after several cycles of cumulative relaxation experiments, the glass began to crystallize with the appearance of a small fraction of lithium disilicate crystals. This result indicates a relationship between structural relaxation and crystallization, corroborating recent studies in the literature.

Broadband dielectric behaviour and structural characterization of PVDF/PMMA/OMMT polymer nanocomposites for promising performance nanodielectrics in flexible technology advances

Characterization of broadband dielectric behaviour of polymer nanocomposites (PNCs) is vital for the exploration of efficient nanodielectrics as energy storage, flexible dielectric substrates, and insulators in a wide range of advanced electronic device technologies. Accordingly, herein, PNC films based on poly(vinylidene fluoride) (PVDF)/ poly(methyl methacrylate) (PMMA) blend matrix (80/20 wt/wt%) dispersed with 0, 2.5, 5, and 10 wt% organo-modified montmorillonite (OMMT) nanoclay are developed by state-of-the-art homogenized solution casting method. These PVDF/PMMA/OMMT compositions based flexible PNC films are characterized in detail by employing a scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) device, x-ray diffractometer (XRD), Fourier transform infrared (FTIR) spectrometer, differential scanning calorimeter (DSC), inductance-capacitance-resistance (LCR) meter, and impedance/material analyzer (IMA). The SEM microimages, XRD traces, and FTIR spectra evidenced appreciable homogeneity and surface morphology, intercalated and exfoliated OMMT structures, and the α, β and γ-phase crystallites of the PVDF in these complex semicrystalline PNCs. The DSC thermograms confirmed a significant alteration in the melting temperature and degree of crystallinity of the PVDF crystallites with the increased amount of OMMT in the 80PVDF/20PMMA blend host matrix. The broadband dielectric dispersion spectra over the frequency range of 20 Hz−1 GHz explained the contribution of interfacial polarization in the complex dielectric permittivity at lower experimental frequencies, whereas at higher frequencies permittivity is ruled by dipolar polarization in these composites at 27 °C. The dielectric loss angle tangent and electric modulus spectra revealed an intense structural dynamics relaxation process in the upper radio frequency region. The influence of OMMT concentration on the dielectric permittivity and electrical conductivity is explored. The detailed dielectric and electrical characterization of these innovative semicrystalline composites with important structural and thermal properties revealed their immense potential as high-performance nanodielectrics for highlighting current applications of broadband frequency range electrical and electronic device technologies.

Johari–Goldstein β relaxation in glassy dynamics originates from two-scale energy landscape

Supercooled liquids undergo complicated structural relaxation processes, which have been a long-standing problem in both experimental and theoretical aspects of condensed matter physics. In particular, past experiments widely observed for many types of molecular liquids that relaxation dynamics separated into two distinct processes at low temperatures. One of the possible interpretations is that this separation originates from the two-scale hierarchical topography of the potential energy landscape; however, it has never been verified. Molecular dynamics simulations are a promising approach to tackle this issue, but we must overcome laborious difficulties. First, we must handle a model of molecular liquids that is computationally demanding compared to simple spherical models, which have been intensively studied but show only a slower process: α relaxation. Second, we must reach a sufficiently low-temperature regime where the two processes become well-separated. Here, we handle an asymmetric dimer system that exhibits a faster process: Johari-Goldstein β relaxation. Then, we employ the parallel tempering method to access the low-temperature regime. These laborious efforts enable us to investigate the potential energy landscape in detail and unveil the first direct evidence of the topographic hierarchy that induces the β relaxation. We also successfully characterize the microscopic motions of particles during each relaxation process. Finally, we study the correlation between low-frequency modes and two relaxation processes. Our results establish a fundamental and comprehensive understanding of experimentally observed relaxation dynamics in supercooled liquids.

Issue Information

International Journal of Applied Glass ScienceVolume 14, Issue 2 p. 165-166 ISSUE INFORMATIONFree Access Issue Information First published: 10 March 2023 https://doi.org/10.1111/ijag.16587AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract Cover Photograph: Top) Optimization of the electric heatings for the annealing lehr's zones bottom left and bottom right; (Bottom left) Original and optimized temperature distribution in the UTG ribbon's side at 400 mm to the edge; (Bottom right) Original and optimized residual stresses calculated from FEM and measured via VI at different distances to the UTG ribbon edge. Residual stress seriously affects the quality of ultra-thin glass (UTG); therefore, it is of great scientific interest and technological significance to precisely regulate the annealing process for controlling residual stress. In the past, many studies point out that the residual stress formation process is the comprehensive result of the stress accumulation and release of viscoelastic in the macro. However, we consider that it is caused by the glass atoms structure relaxation process in the micro based on our molecular dynamics (MD) calculation results. The precise regulation of UTG residual stress is realized by revealing the relationship between residual stress with annealing temperature schedule from the micro-scale and combining it with the relevant measurement and calculation means. Volume14, Issue2April 2023Pages 165-166 RelatedInformation

Viscosity and structure relaxation in Zr60Cu20Al10Ni10 metallic glass

This work reports the estimation of the viscosity, relaxation time and free volume of Zr60Cu20Al10Ni10 metallic glass (MG) by extrapolating differential scanning calorimetry (DSC), thermo-mechanical analyzer (TMA), and nanoindentation measurement data. The structural relaxation process of Zr60Cu20Al10Ni10 MG is shown through the study of viscosity and relaxation behavior also displayed by these measurements. It has the ability to exhibit strong fluid behavior near the glass transition temperature and exhibits a large strength parameter of 26.9 and a Vogel-Fulcher-Tamman temperature of 378 K. At the same time its stress relaxation exhibits sensitivity to strain rate and paused load. Finally, we estimated the residual free volume from melt freezing inside the Zr60Cu20Al10Ni10 MG by DSC technique as 0.041. These results indicate that the Zr60Cu20Al10Ni10 MG has a large free volume and exhibits both strong fluidic properties and significant stress relaxation behavior.

The role of free volume, hydrogen bonds, and crosslinks on physical aging in polymers of intrinsic microporosity (PIMs)

Physical aging rates strongly correlate with the initial free volume of microporous polymers. Introducing hydrogen bonds and crosslinks can reduce the initial free volume and significantly impact gas separation selectivity over time.

Structural, Thermal and Magnetic Analysis of Two Fe-X-B (X = Nb, NiZr) Nanocrystalline Alloy.

High-energy ball milling was used to produce two Fe-X-B (X = Nb, NiZr) nanocrystalline alloys. X-ray diffraction (XRD), differential scanning calorimetry (DSC), and vibrating sample magnetometry (VSM) were used to analyze the microstructure, thermal, and magnetic characteristics of the milled powders, the agglomerated particles (also generated during the milling process), and the compacted specimens of both alloys. The main crystallographic phase is always a bcc Fe-rich solid solution; whereas a minor Nb(B) phase is detected on powders and agglomerated particles in the Fe80Nb8B12 alloy. The crystalline size of the Fe80(NiZr)8B12 alloy is between 11 and 14 nm, whereas in the Fe80Nb8B12 alloy, it ranges between 8 and 12 nm. Microstrain and dislocation density are higher in agglomerated samples for both alloys than in milled powders. Thermal analysis detects structural relaxation and crystal growth exothermic processes with high dispersion in the temperature intervals and in the calculated apparent activation energy of the main crystallization process. Regarding magnetic behavior, the coercivity values of all powdered-agglomerated specimens were around 800 A/m. The coercivity is higher in compacted sample, but controlled annealing favors enhanced soft behavior.

Volumetric, Compressibility and Viscometric Approach to Study the Interactional Behaviour of Sodium Cholate and Sodium Deoxycholate in Aqueous Glycyl Glycine.

Viscosity, speed of sound (u), and density (ρ) have been measured in aqueous glycyl glycine solution over a temperature range from 293.15 to 313.15 K with a 5 K interlude to evaluate the volumetric and compressibility properties of bio-surfactants, namely sodium cholate (NaC; 1-20 mmol∙kg-1) and sodium deoxycholate (NaDC; 1-10 mmol∙kg-1). Density and viscosity findings provide information on both solute-solute and solute-solvent types of interactions. Many other metrics, such as apparent molar adiabatic compression (κS,φ), isentropic compressibility (κS), and apparent molar volume (Vφ), have been calculated from speed of sound and density measurements, utilising experimental data. The results show that the zwitterionic end group in the glycyl glycine strongly interacts with NaDC and NaC, promoting its micellization. Since the addition of glycyl glycine causes the bio-surfactant molecules to lose their hydrophobic hydration, the observed concentration-dependent changes in apparent molar volume and apparent molar adiabatic compression are likely attributable to changes in water-water interactions. Viscous relaxation time (τ) increases significantly with a rise in bio-surfactant concentration and decreases with increasing temperature, which may be because of structural relaxation processes resulting from molecular rearrangement. All of the estimated parameters have been analysed for their trends with regard to the different patterns of intermolecular interaction present in an aqueous glycyl glycine solution and bio-surfactant system.

Nanostructured metallic glass contributing to efficient catalytic degradation of dye wastewater

The effects of annealing temperature on the catalytic degradation capacity of Fe75P15C10 amorphous ribbons in the photo-enhanced Fenton-like reactions are studied using reactive red 195 (RR195) solution. The order of catalytic degradation capacity of the ribbons is AN722 ≥ AN662 ≥ AS ≥ AN542 ≥ AN602, the AN722 ribbon has the highest k (0.349 min−1), the lowest tη≥95% (10 min) values, and compared with AS ribbon has good reusability (9 times). Firstly, isothermal annealing is a process of metastable structural relaxation, in which the energy stored in AS ribbon is gradually released, and the high thermodynamic enthalpy and residual stress decrease, which jointly lead to the decline of the catalytic degradation capacity of the ribbons. Secondly, the precipitation of Fe3P nanocrystal/nanophase and amorphous matrix, identified by TEM, induces the formation of galvanic cells effect increase the electron donation rate in the reaction, thus restoring/improving its catalytic degradation capacity.

Indomethacin: The Interplay between Structural Relaxation, Viscous Flow and Crystal Growth.

Non-isothermal differential scanning calorimetry (DSC) was used to study the influences of particle size (daver) and heating rate (q+) on the structural relaxation, crystal growth and decomposition kinetics of amorphous indomethacin. The structural relaxation and decomposition processes exhibited daver-independent kinetics, with the q+ dependences based on the apparent activation energies of 342 and 106 kJ·mol−1, respectively. The DSC-measured crystal growth kinetics played a dominant role in the nucleation throughout the total macroscopic amorphous-to-crystalline transformation: the change from the zero-order to the autocatalytic mechanism with increasing q+, the significant alteration of kinetics, with the storage below the glass transition temperature, and the accelerated crystallization due to mechanically induced defects. Whereas slow q+ led to the formation of the thermodynamically stable γ polymorph, fast q+ produced a significant amount of the metastable α polymorph. Mutual correlations between the macroscopic and microscopic crystal growth processes, and between the viscous flow and structural relaxation motions, were discussed based on the values of the corresponding activation energies. Notably, this approach helped us to distinguish between particular crystal growth modes in the case of the powdered indomethacin materials. Ediger’s decoupling parameter was used to quantify the relationship between the viscosity and crystal growth. The link between the cooperativity of structural domains, parameters of the Tool-Narayanaswamy-Moynihan relaxation model and microscopic crystal growth was proposed.