Dependence Of Modulus Research Articles

Molecular dynamics analysis of iPP-polymorphs; Investigating thermal expansion and elastic properties

The elastic properties of α and β crystals of isotactic polypropylene are obtained by molecular dynamics simulations of a crystalline domain resembling an infinite crystal. The helical polymer chains are modeled with an all-atom force-field. The assessment of the pristine α2 lattice agreed with published results of structure, density, thermal expansion, and stiffness. Monoclinic α systems with particular imperfections are sampled to assess the effect of defects on conformational stability and elastic properties. The sensitivity of elastic moduli with temperature correlates with the helicity disruption: the more chain-conformational defects, the stronger the decrease in elastic modulus. The non-perfect chiral up-down α1 lattice and the arrangement with one vacancy also display a lower stiffness than α2, which can be attributed to a less dense crystal and decreased inter-chain cooperative forces due to periodicity disruption.Two variations of the metastable β modification were sampled to assess the most energetically favorable configurations. Then, both were subjected to the same procedure, validated first for α. A trigonal mono-chiral system, β2, and a stable bi-chiral one with a four-chain frustrated orthorhombic cell, β1, were found, both presenting novel characteristics. Both β structures display a less stable conformation than α2, observed by a higher specific volume, a lower transition temperature, and a more significant dependence of the elastic moduli with temperature. Remarkably, the mono-chiral β2 crystal showed higher elastic modulus than any other crystal below room temperature, related to a more efficient global methyl interlocking between chains. The fact that the experimental value for the density of the β-kind of crystal is in between the values that we obtained from the simulations of β2 and β1 implies that the experimental observations consist of both of these β crystals, where β1 might work as an interface between monochiral β2 layers.

Thermophysical modeling of niobium alloys informs materials selection and design for high-temperature applications

There is renewed interest in refractory alloys that possess higher service temperatures than incumbent Ni-based superalloys (⪆1100 °C). Thermophysical property data for six Nb-alloys are gathered from the literature and reviewed, and new data are provided for two Hf-containing Nb-alloys; elastic modulus, thermal expansion, thermal conductivity, and heat capacity are presented for C103, and new thermal conductivity data are provided for a higher strength alloy, WC-3009. Comparisons with Ni-superalloys and other refractory-metal based alloys provide context. Physics-based models are provided that describe the temperature dependencies of the Young’s modulus, coefficient of thermal expansion and density, and thermal conductivity; such that fair comparisons can be made across alloys for any given condition. The results suggest a need for improved understanding of the temperature dependence of the elastic modulus. A performance index is introduced for making informed materials selection decisions in the context of lightweight, panel-shaped applications subjected to sharp thermal transients or steep thermal gradients, and the significant strain rate sensitivity of Nb-alloys is highlighted. Ultimately, the relative value of current commercial alloy, C103, as well as the promise of specific Nb-W-Zr alloys are highlighted.

A low copper content alloy Al(1-x)Cux, x≤0.1: A joint computational and experimental study

Atomistic simulation of Al1-xCux (x ≤ 0.1) alloy is performed and the mechanical properties are calculated within the framework of the density functional theory (DFT) by using of the virtual crystal approximation (VCA). The elastic matrix is calculated within the DFT using the CASTEP code and the dependences of Young's, shear and bulk moduli, Vickers hardness, Poisson's ratio, plasticity coefficient and anisotropy indices on the amount of copper are obtained. Al0.9Cu0.1 alloy was synthesized by spark plasma sintering (SPS) method. As a result, the aluminum and intermetallic CuAl2 phases were identified in the obtained sample by X-ray diffraction patterns. The microstructure (SEM) and Vickers microhardness of the sample were studied. The results of the work compensate for the lack of data for the Al-Cu alloys with a low copper content.

Coherent Acoustic Phonons in Plasmonic Nanoparticles: Elastic Properties and Dissipation at Low Temperatures.

We studied the frequency and quality factor of mechanical plasmonic nanoresonators as a function of temperature, ranging from ambient to 4 K. Our investigation focused on individual gold nanorods and nanodisks of various sizes. We observed that oscillation frequencies increase linearly as temperature decreases until saturation is reached at cryogenic temperatures. This behavior is explained by the temperature dependence of the elastic modulus, with a Debye temperature compatible with reported bulk values for gold. To describe the behavior of the quality factor, we developed a model considering the nanostructures as anelastic solids, identifying a dissipation peak around 150 K due to a thermally activated process, likely of the Niblett-Wilks mechanism type. Importantly, our findings suggest that external dissipation factors are more critical to improving quality factors than internal friction, which can be increased by modifying the nanoresonator's environment. Our results enable the future design of structures with high vibration frequencies and quality factors by effectively controlling external losses.

Estimation of local variation in Young's modulus over a gold nanocontact using microscopic nanomechanical measurement method.

Nanoscale materials tend to have a single crystal domain, leading to not only size dependence but also orientation dependence of their mechanical properties. Recently, we developed a microscopic nanomechanical measurement method (MNMM), which enabled us to obtain equivalent spring constants (force gradients) of nanocontacts while observing their atomic structures by transmission electron microscopy (TEM). Therein, we evaluated Young's modulus based on a model that a newly introduced layer at the thinnest section of a nanocontact determined the change in the measured equivalent spring constant, and discussed their size dependence. However, this model is not general for other nanomaterials that do not exhibit the introduction of a new atomic layer while stretching. In this study, using MNMM, we propose a new analytical method to directly retrieve the local Young's modulus of nanomaterials by measuring initial lattice spacing and its displacement of a local region in the TEM image during the stretching of the nanocontact. This reveals the size dependence of local Young's modulus at various positions of the nanocontact at once. As a result, our estimated Young's modulus for a gold [111] nanocontact showed a size dependence similar to the one previously reported. This indicates that this analytical method benefits in revealing the mechanical properties of not only nanomaterials but also structurally heterogeneous materials such as high-entropy alloys.&#xD.

Identification of the Payne effect in a viscoelastic material coupling Bayesian identification and digital twin

The Payne or Fletcher-Gent effect is a particular behavior occurring in viscoelastic materials containing fillers. It induces a nonlinear dependency of the viscoelastic storage modulus on the amplitude of the applied strain. This amplitude dependency must be taken into account in engineering applications as it does change the elastodynamic behavior of the overall structure integrating the material. A methodology is developed in the proposed work to identify this nonlinear effect. The approach first starts with the identification by Bayesian inference of the frequency and damping properties of a viscoelastic sample. The input data are obtained from a modified Oberst test, conducted for different displacement load amplitudes. A digital twin of the experimental set-up is then used to evaluate the stiffness behavior, and in particular the Young's modulus of the material, at the measured frequencies, and to deduce the strain level within the sample. This work shows that the Payne effect, which leads to the decrease with the amplitude of the Young's modulus, can thus be estimated in terms of mean and standard deviation by combining experiments and numerical simulations.

Characterization and modelling of the damping properties of composite structures based on flax fibers

In this paper, an experimental-numerical modelling is proposed to determine the damping properties of composite structures based on flax fibers. Assuming that these properties are due to a viscoelastic behavior of each layer and each direction of these structures, three viscoelastic models were considered : the Maxwell-type Zener (ZM) model, the generalized Maxwell (GM) model, and the fractional derivative Zener (ZF) model. As well known, the viscoelastic models involve complex modulus and frequency dependence. So, the free vibration problem of these composite structures is complex and non-linear one. This nonlinear problem is solved by an high order Newton method (HON method) which permits to determine damping properties (damped frequency and the structural loss factor). Using experimental tests, an identification method, based on the HON and the Nelder–Mead methods, is applied to identify the rheological parameters of the proposed viscoelastic models. The comparison between experimental and numerical results demonstrates the efficiency of the proposed experimental–numerical method : all parameters for the three models are successfully identified. From, the results, only the GM or ZF models seem to be suitable for representing the viscoelastic behavior of flax/epoxy composite structures.

Stress-strain state of ceramic shell mold during formation of spherical steel casting in it. Part 2

The paper presents the results of numerical calculations of the solution to the problem of modeling the process of possible cracking in a spherical shell mold when pouring liquid steel into it and cooling the solidifying casting. The numerical scheme of the axisymmetric problem and the algorithm for its solution were given in Part 1. The crack resistance is estimated by magnitude of the normal stresses in the ceramic shell during its co-cooling with a solidifying casting. The results detailed analysis considered: fields of displacement, stresses, and temperatures both on spherical surface and in growing crust of solidified metal. The solution took into account the change in the shear modulus of the mold material from temperature, and an assessment of this refinement was given. The problem was solved in two ways. The first – with a constant shift modulus of the shell mold; the second – with its temperature-dependent shift modulus. There is a significant difference between these variants in terms of magnitude of the normal stresses arising in the shell mold. The authors analyzed resistance of the shell mold spherical geometry to external influences from its support filler and filling funnel. The problem of determining the contact and free surfaces at the boundary of the shell mold and support filler was solved. The results are presented graphically in the form of diagrams of stresses and temperatures over the studied area in its different sections and time intervals for cooling of the growing metal crust. The role of compressive normal stresses σ22 , σ33 on the surface of contact of the shell mold with liquid metal at the initial moment of cooling on probability of cracking in a spherical mold is shown. The level of strain-stress state in a spherical shell mold when cooling a steel casting in it is significantly determined by dependence of shift modulus of the shell mold on temperature.

Synergistic Effects of Pea Protein on the Viscoelastic Properties of Sodium Alginate Gels: Findings from Fourier Transform Infrared and Large-Amplitude Oscillatory Shear Analysis

The rheological characteristics of pea protein (PP100%) and alginate (AG100%) as pure and mixed gels with different levels of pea protein (AP90:10, AP80:20, and AP70:30) were investigated via large-amplitude oscillatory shear (LAOS) and Fourier transform infrared (FTIR). Small-angle oscillatory shear (SAOS) was carried out for the samples, and a slight frequency dependence of the storage modulus (G′) and the loss modulus (G″) was observed for the pastes and gels, indicating the formation of a weak network, which is crucial for understanding the gel’s mechanical stability under small levels of deformation. Elastic and viscous Lissajous curves from the LAOS measurement at different levels of strain (1 to 1000%) elucidated that the mixed gels formed a strong network, which showed breakdown at high deformation (>100% strain). The synergistic strengthening of the network of the mixture was noticeable in the Fourier transform and Chevyshev harmonic analyses. This analysis indicated that the nonlinearity of e3/e1 and v3/v1 started at higher levels of strain for the mixed gels. The FTIR spectra revealed that there was no strong interconnection by crosslinking between pea protein and sodium alginate, indicating that the synergistic effect mainly came from electrostatic interactions. These findings suggest that combining alginate with pea protein can enhance the mechanical properties of gels, making them suitable for various food applications.

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.

Revealing the displacive and diffusional phase transformations in a low-modulus Ti-12Nb alloy

Non-toxic and biocompatible Ti alloys with low modulus are promising biomaterials for implants. Except from the intensely studied metastable β Ti-Nb-based alloys, the α′-type Ti alloys could also present low modulus. But due to the low β stability, the microstructures of these α′ Ti alloys are sensitive to the heat-treatments especially to the cooling rates, which could lead to very different deformation mechanisms and mechanical properties. Thus, the phase transformations and the ‘microstructure–mechanical property’ correlation in the α′ Ti alloys need to be established. In this study, a novel Ti-12Nb wt% alloy was prepared and cooled from the β region temperature to obtain the water-quenched (WQ), air-cooled (AC), and furnace-cooled (FC) samples. Systematic investigations revealed the displacive β → α′ martensitic transformation in the WQ and diffusional β → β + α transformation in the AC and FC samples, in which the α′/α show evident variant selections. The inter-variant orientation relationships (ORs) among the α′/α variants and their ORs with the retained β phase, were found to be agree well with the classical Burgers OR. The high-resolution transmission electron microscope (HRTEM) studies show coherent α′/α′ interfaces in the WQ samples and α/β phase boundaries in the AC and FC samples, the abnormal β nanodomains inside the α′ martensites in WQ samples and the ω nanoparticles in the β phase of AC and FC samples were also presented. The tensile tests show increasing Young's modulus of 61.8 GPa, 77.1 GPa and 108.6GPa in the WQ, AC and FC samples, respectively. The difference in the modulus of these samples was explained by the Nb dependency of Young's modulus in the Ti-Nb alloy. The correlations between the microstructures, deformation mechanisms and mechanical properties were established. The {101¯1}α′ and {101¯2}α′ deformation twins inside the α′ martensites are believed to contribute to the good plasticity in the WQ samples, while the fine α + β structures and severely piled-up dislocations should account for the high yield strength and the poor plasticity in the AC samples. The abundant mobile dislocations in the α bands and deformation-induced ω needles in the surrounding β phase led to the best plasticity in the FC samples among all Ti-12Nb samples. This study systematically studied the displacive and diffusional transformations and the plastic deformation in a Ti-12Nb alloy, the results might pave the way for designing low-modulus biomedical α′ Ti alloy with low content of β stabilizing elements and provide insights into tailoring of the phase transformations and mechanical properties in these Ti alloys.

One-step light-induced hierarchical surface wrinkles on photodegradable polymer films

Photodegradable polymers have become an emerging class of stimulus-sensitive materials for advanced applications, in which using the photolysis characteristic for patterning surface is a key but still a notable challenge. Herein, we report a simple, facile, green and high-efficiency strategy to induce and further tune surface wrinkling only relying on one-step ultraviolet (UV) irradiation of a photodegradable polymer-based film/substrate composite system. Interestingly, a series of intriguing wrinkling states from no wrinkling to surface wrinkling and final no wrinkling with UV exposure take place on the photodegradable polymer film. This wrinkling behavior is intimately related to the competition between the stress accumulation from the heating effect of UV lamp itself and the stress release from the UV-induced molecular chain breakage. Meanwhile, the dependence of photodegradable polymer film modulus and photodegradation-induced stress release on the exposure time has been characterized by taking advantage of surface wrinkling metrology, which is not easily accessible to other systems and methods. This one-step light irradiation strategy has enabled the fabrication of diverse hierarchical surface wrinkling on photodegradable polymer film by simply controlling the UV exposure time. As demonstrated, these hierarchical surface wrinkles with tunable features have been applied for optical information display/storage and optical gratings. Notably, this simple flexible light control strategy not only provides new insights into the photo-induced change in mechanical properties and stress release of photodegradable polymers in molecular level, but also paves new avenues for advanced wrinkle-based applications by incorporating desirable functional materials into the photodegradable polymer-based systems.

Nonlinear vibration characteristics of thermo-viscoelastic coupling of moving PET films with temperature-dependent elastic modulus

In order to improve the transport stability of roll-to-roll produced polyethylene terephthalate films (PET films) in high temperature environments, this paper investigates the nonlinear vibrational properties of moving PET films under a uniform temperature field by considering the temperature dependence of the elastic modulus. Firstly, constant tensile tests were conducted to test the elastic modulus values of PET films at different hot air temperatures, and the Wachtman model was improved to establish a temperature-dependent elastic modulus model for PET films. Secondly, based on the Kelvin-Voigt model, the nonlinear vibrational equilibrium differential equations of the system were established by applying the Bubnov-Galerkin method of discretization according to D’Alembert’s principle. Finally, numerical simulations based on the 4th-order Runge-Kutta method were carried out to analyze the effects of films width, external excitation frequency, external excitation amplitude, transfer velocity, ambient temperature, damping coefficient and viscoelasticity coefficient on the nonlinear vibration of the system. This provides a theoretical basis for the commissioning of stabilized transfer parameters for roll-to-roll production of PET films.

Photoinduced Reversible Disentanglement-Entanglement Transition in partially miscible azobenzene polymer blends

Entanglements, an intrinsic feature of long chains, are critical to the rheological and mechanical properties of polymers. Adding low molecular weight solvents or oligomers into entangled polymers can reduce the entanglements, but the entanglement cannot recover without removing the solvents. Reversible control of the entanglement degree is still a big challenge. In this work, we introduce the azobenzene polymer (Pazo) with reversible photoswitchable side-chain conformation as dynamic diluent into entangled poly(butyl methacrylate) (PBMA) to form a partially miscible blend system. The reduction of entanglement of PBMA by trans-Pazo is similar to a typical solvent, while an unexpectedly stronger tube dilation effect was found for cis-Pazo. Cis-Pazo/PBMA blends exhibit a stronger dependence of plateau modulus on PBMA content, GN(φ)∼φ4.5, which is significantly different from the well-established relation GN(φ)∼φ2 for polymer solutions and blends. The cis-Pazo can disentangle PBMA at a much lower concentration (∼55 %) than the trans-Pazo (>70 %). Pazo content of 55 %–70 % can induce a completely unentangled state of PBMA in Pazo/PBMA blends when Pazo is in the cis state after UV light irradiation, and the entanglement can recover when it is transformed to the trans state. Adding azobenzene polymer does not alter the activation energy of the re-entanglement process.

2-Cyanopropan-2-yl versus 1-Cyanocyclohex-1-yl Leaving Group: Comparing Reactivities of Symmetrical Trithiocarbonates in RAFT Polymerization.

This study introduces bis(1-cyanocyclohex-1-yl)trithiocarbonate (TTC-bCCH) as a novel trithiocarbonate chain transfer agent and compares its reactivity with the previously described bis(2-cyanopropan-2-yl)trithiocarbonate (TTC-bCP) for the reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (St), n-butyl acrylate (nBA), and methyl methacrylate (MMA). Significant findings include the effective control of Mn and low dispersities from the onset of polymerization of St and nBA showing swift addition-fragmentation kinetics, leading to similar behaviors between the two RAFT agents. In contrast, a fourfold decrease of the chain transfer constant to MMA is established for TTC-bCCH over TTC-bCP. This trend is confirmed through density functional theory (DFT) calculations. Finally, the study compares thermoplastic elastomer properties of all-(meth)acrylic ABA block copolymers produced with both RAFT agents. The impact of dispersity of PMMA blocks on thermomechanical properties evaluated via rheological analysis reveals a more pronounced temperature dependence of the storage modulus (G') for the triblock copolymer synthesized with TTC-bCCH, indicating potential alteration of the phase separation.

Two-phase model for inverse Hall–Petch effect in nanocrystalline thin film: Atomistic simulation study

This work presents two methods to improve the understanding of the mechanical behavior of nanocrystalline thin films. Firstly, a simple two-phase model is proposed to explain the inverse Hall–Petch effect. The model suggests that the nanocrystalline material consists of the grain-boundary and the grain interior with different mechanical properties. Secondly, a computational method is developed to create more realistic grain boundaries in simulations of polycrystals. Traditionally created grain boundaries by Voronoi tessellation are too dense and do not accurately reflect the reality and the experimental results. The strength of the nanocrystalline aluminum thin film is simulated using molecular dynamics. The grain size dependence of the elastic modulus, ultimate tensile stress, and engineering yield strength is demonstrated. The experimental values of modulus and strength are approximately 6 times smaller probably due to the presence of porosity in the real sample. An approach is developed to introduce porosity in the simulated samples at the grain boundaries and in the grain interior to reduce this discrepancy. The modeled value of modulus for a grain size of 40 nm without porosity is 67GPa, whereas, with 50% grain-boundary porosity and 20% intra-granular porosity it is 30GPa. For the ultimate tensile strength, we get 3GPa and 1.4GPa for samples without porosity and with porosity, respectively. The simulated values of modulus with porosity are still 4 times higher and the values of strength are about 2 times higher than the experimental ones. The amount of porosity in our method can be adjusted to fit the experimental values; however, high values of porosity cause the mechanical instability of the simulated samples.

Biopolymer networks packed with microgels combine strain stiffening and shape programmability

Biomaterials that can be reversibly stiffened and shaped could be useful in broad biomedical applications where form-fitting scaffolds are needed. Here we investigate the combination of strong non-linear elasticity in biopolymer networks with the reconfigurability of packed hydrogel particles within a composite biomaterial. By packing microgels into collagen-1 networks and characterizing their linear and non-linear material properties, we empirically determine a scaling relationship that describes the synergistic dependence of the material's linear elastic shear modulus on the concentration of both components. We perform high-strain rheological tests and find that the materials strain stiffen and also exhibit a form of programmability, where no applied stress is required to maintain stiffened states of deformation after large strains are applied. We demonstrate that this non-linear rheological behavior can be used to shape samples that do not spontaneously relax large-scale bends, holding their deformed shapes for days. Detailed analysis of the frequency-dependent rheology reveals an unexpected connection to the rheology of living cells, where models of soft glasses capture their low-frequency behaviors and polymer elasticity models capture their high-frequency behaviors.

The study of the dependence of dielectric properties, electric modulus, and ac conductivity on the frequency and voltage in the Au/(CdTe:PVA)/n-Si (MPS) structures

The dielectric properties, electric modulus, loss tangent (tanδ), and ac conductivity of the fabricated Au/(CdTe:PVA)/n-Si (MPS) structures were investigated in wide-range frequency. By using the capacitance/conductance–voltage–frequency (C/G-V-f) measurements, the real/imaginary components of complex dielectric constant (εʹ, εʺ)/electrical modulus (M′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M{\\prime}$$\\end{document}, M′′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M{\\prime}{\\prime}$$\\end{document}), loss tangent (tanδ), and σac were calculated in wide-range frequency (2 kHz–0.7 MHZ) and voltage (± 2.5 V), and all results show that these parameters are a strong function of voltage and frequency. The observed decreases of εʹ and εʺ with increasing frequency were attributed to the existence of Nss, interlayer, and dipole polarizations. The value of εʹ was calculated as 128.38 (at 2 kHz and 2.5 V), which is quite higher than the maximum value of traditional SiO2. ln(σac)–ln(f) plot for 0.7 V shows three linear parts, indicating three different conduction mechanisms at low, intermediate, and high frequencies. These results show that the fabricated MPS structures can be successfully used instead of traditional metal–insulator–semiconductor as ultra-capacitors, which can use more electronic charges or energy.

Novel soft food gels using beta-lactoglobulin via enzymatic crosslinking as agar gel alternatives

Soft food gels are of high interest for food innovation that can cater to the specific needs of various populations. This study explores the innovative development of soft beta-lactoglobulin (β-LG) gels through a green process that combines heat treatment and transglutaminase (TGase)-catalyzed crosslinking at a moderate pH. The optimal procedure involves heating β-LG solutions, pH 7.5 at 80 °C for 30 min to facilitate protein unfolding and aggregation, followed by TGase catalysis at 50 U TGase/g β-LG. This process produced soft and moist β-LG gels at a low concentration of 5% (w/v). The softness of β-LG gels was characterized through rheological measurements, suggesting a low storage modulus and high frequency dependence. Morphological observations of β-LG gels using TEM showed a loosely arranged network. SDS-PAGE and FTIR analyses indicated the formation of covalent disulfide bonds and isopeptide bonds in β-LG gels through the heat and TGase treatments. The potential of the novel β-LG gels as traditional agar gel substitutes was comparatively analyzed on their textural properties. Both gels showed distinctive jelly-like characteristics, whereas β-LG gels exhibited superior softness and reduced brittleness, positioning them as viable protein-based alternatives to agar gels for various applications in both food and nonfood sectors.

Fast relaxation in metallic glasses studied by measurements of the internal friction at high frequencies

We performed high-frequency (0.4–1.7 MHz) measurements of the internal friction (IF) on 14 bulk metallic glasses (MGs). It is found that 12 of these MGs display relaxation IF peaks at temperatures ≈ 400–500 K, which are weakly affected by heat treatment within the amorphous state. The corresponding relaxation time is about 0.3 μs. This fast relaxation is reported for the first time in the literature. The apparent activation enthalpy for 4 MGs is determined. It is shown that if measured at a low frequency of 1 Hz, these IF peaks would appear near room temperature or by 30–50 K below it. Thus, the IF peaks found in the present investigation are direct analogues of low-temperature/low-frequency β′- and/or γ-relaxations described in the literature. It is argued that the origin of these IF peaks is related to the relaxation of structural defects similar to dumbbell interstitials, which are frozen in solid glass from the liquid state upon melt quenching. These defects can be considered as elastic dipoles and their re-orientation in the applied stress provides anelastic deformation and corresponding IF peak. After correction for temperature dependence of the shear modulus, the true activation enthalpy (0.62–1.08 eV) and activation entropy (4 ≤ΔS∕kB≤15) for defect re-orientation are determined.