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To date, the orientational birefringence and the photoelastic birefringence of alternating copolymers have not been studied in detail. We focused on N-substituted maleimide (RMI) and styrene (St) as alternating copolymers and analyzed the birefringence, refractive index, and glass transition temperature (Tg) of the alternating copolymers. It was found that the photoelastic coefficient and Tg exhibit a nonlinear relationship with the composition ratio of RMI and St. It is considered that the alternating copolymerization of RMI and St confirms that the conformation is inhibited by interacting with each other. A zero–zero-birefringence polymer that exhibits no birefringence was obtained by using N-ethylmaleimide and St and adjusting the composition ratio. This polymer showed a high Tg, low haze, and a low temperature dependence of birefringence. [ABSTRACT FROM AUTHOR]

The viscosity of silicate melts is one of the most important physical properties for understanding high-temperature phenomena in magmatic systems and material processing. The effects of composition and temperature on viscosity have long been elucidated. Although iron ions are the main components of magmatic systems, their influence on viscosity remains unclear because the behavior of iron is complicated; iron ions have two redox states, Fe3+ and Fe2+. Here, we elucidate the viscosity of an iron-sodium-silicate system with a variety of iron redox states at temperatures close to its glass transition temperature (Tg). The redox states and structures of the samples were characterized using x-ray absorption near-edge structure (XANES) spectroscopy, Raman spectroscopy, synchrotron x-ray total scattering, and density (molar volume) measurements. The viscosity increased (by more than four orders of magnitude) with an increase in the ratio of Fe3+ to total Fe (Fe3+/Fetot), whereas the temperature dependence of the viscosity was larger for glasses with a higher Fe3+/Fetot ratio at temperatures close to the glass transition temperature. The tendencies in viscosity and structural variation against the Fe3+/Fetot ratio support the consensus on the structural roles of Fe3+ and Fe2+ from previous studies: Fe3+ ions have a stronger tendency to behave as network formers than Fe2+ ions. [ABSTRACT FROM AUTHOR]

The glass transition dynamics and conductivity relaxation are studied for a series of non-stoichiometric protic ionic liquids (PILs) based on 2-aminoethyl hydrogen sulfate and triflic acid with varying molar ratios (denoted as AT-55, AT-46, AT-37, AT-28, and AT-19) by broadband dielectric spectroscopy in a wide frequency (10−1–107 Hz) and temperature range (173–353 K). The results indicate that the addition of acid lowers the glass transition temperature, as confirmed by the activation energy fine structure analysis and a crossover in the conductivity relaxation time. Notably, samples with higher acid content deliver markedly increased conductivity. In addition, detailed analysis of the permittivity and modulus spectra reveals enhanced decoupling between the structural (α-process) and conductivity relaxation in samples with a higher acid content. Remarkably, nano-phase separation in AT-28 and AT-19 samples is observed, resulting in a second glass transition temperature indicating a more mobile phase. Based on the above-mentioned findings, we infer that increased acid content disrupts strong ionic interactions within the IL fraction, resulting in a decrease in the glass transition temperature and leading to nano-phase separation into distinct acid-rich and IL-rich phases with varying Tg values. This phase separation alters the long-range ionic pathways, shifting from being solely governed by IL cluster dynamics to a scenario where charge transport becomes largely decoupled from the dynamics of IL-rich clusters. Hence, modulating the stoichiometry of PILs appears a promising approach to enhance the conductivity together with widening the usable temperature range for applications. [ABSTRACT FROM AUTHOR]

Glass and crystal are inherently different material states in terms of their structural and physical features; consequently, the direct quantitative connection between crystal and glass is lacking. Herein, we first show that the liquid fragility m, which is featured by the negative departure degree of viscosity with the temperature at the glass transition temperature (Tg), has a direct exponential correlation with the ratio of the average longest metal–oxygen and the average phosphorus, silicon, or boron–oxygen bond lengths of the crystal in various oxides including phosphates, silicates, and borates. Such a result can be rationalized by the fact that the fragility m in these glass-formers is associated with the total network rigidity determined by the weakest bond due to the "bucket effect" and the bond pair inheritance of glass from that of the crystal. Our work connects direct features between glass and crystal with identical composition, providing a new viewpoint bridging glass and crystal. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations of a small redox-active protein plastocyanin address two questions. (i) Do protein electrostatics equilibrate to the Gibbsian ensemble? (ii) Do the electrostatic potential and electric field inside proteins follow the Gaussian distribution? The statistics of electrostatic potential and electric field are probed by applying small charge and dipole perturbations to different sites within the protein. Nonergodic (non-Gibbsian) sampling is detectable through violations of exact statistical rules constraining the first and second statistical moments (fluctuation–dissipation relations) and the linear relation between free-energy surfaces of the collective coordinate representing the Hamiltonian electrostatic perturbation. We find weakly nonergodic statistics of the electrostatic potential (simulation time of 0.4–1.0 μs) and non-Gibbsian and non-Gaussian statistics of the electric field. A small dipolar perturbation of the protein results in structural instabilities of the protein–water interface and multi-modal distributions of the Hamiltonian energy gap. The variance of the electrostatic potential passes through a crossover at the glass transition temperature Ttr ≃ 170 K. The dipolar susceptibility, reflecting the variance of the electric field inside the protein, strongly increases, with lowering temperature, followed by a sharp drop at Ttr. The linear relation between free-energy surfaces can be directly tested by combining absorption and emission spectra of optical dyes. It was found that the statistics of the electrostatic potential perturbation are nearly Gibbsian/Gaussian, with little deviations from the prescribed statistical rules. On the contrary, the (nonergodic) statistics of dipolar perturbations are strongly non-Gibbsian/non-Gaussian due to structural instabilities of the protein hydration shell. [ABSTRACT FROM AUTHOR]

Lithium-ion conducting borate glasses are suitable for solid-state batteries as an interfacial material between a crystalline electrolyte and an electrode, thanks to their superior formability. Chlorine has been known to improve the electron conductivity of borate glasses as a secondary anion. To examine the impact of chlorine on lithium dynamics, molecular dynamics (MD) simulations were performed with a machine-learning interatomic potential (MLIP). The accuracy of the MLIP in modeling chlorine-doped lithium borate (LBCl) and borosilicate (LBSCl) glasses was verified by comparing with available experimental data on density, neutron diffraction S(q), and glass transition temperatures (Tg). While the MLIP-MD simulations underestimated the density when an isobaric–isothermal (NPT) ensemble was used, the glass models relaxed using the NPT ensemble after a melt-quench simulation employing a canonical (NVT) ensemble possessed reasonable density. The LBCl and LBSCl glass models exhibited increased lithium ion diffusion, and the ions were found to travel longer distances with an increase in the chlorine content. According to the structural analyses, it was observed that chlorine ions primarily interacted with lithium ions rather than the network formers. Consequently, lithium ions that interacted with a higher amount of chlorine showed a moderate increase in mobility. In summary, the MLIP demonstrated reasonable accuracy in modeling chlorine-containing borate glasses and enabled the investigation of the effect of chlorine on electron conductivity. In contrast, the first sharp diffraction peaks in S(q) deviated from the experimental diffractions, suggesting that additional efforts are required to accurately model the middle-range structure of the glasses. [ABSTRACT FROM AUTHOR]

Rolling friction is of great importance for many applications, such as tires and conveyor belts. We study the rolling friction for hard cylinders rolling on flat rubber sheets. The rolling friction depends on the number of rolling cycles, the rolling speed, and the temperature. We show that when the rubber is cooled down below the glass transition temperature, the deformations of the rubber surface are frozen-in, resulting in a non-flat rolling track where uphill and downhill rolling movements strongly affect the rolling force. The experimental data are analyzed using the Persson rolling friction theory; good agreement with the experiments is obtained when the non-linear (strain-softening) properties of the viscoelastic modulus are taken into account. [ABSTRACT FROM AUTHOR]

This work studies the influence of the adsorbed layer on the glass transition of thin films of polysulfone. Therefore, the growth kinetics of the irreversibly adsorbed layer of polysulfone on silicon substrates was first investigated using the solvent leaching approach, and the thickness of the remaining layer was measured with atomic force microscopy. Annealing conditions before leaching were varied in temperature and time (0–336 h). The growth kinetics showed three distinct regions: a pre-growth step where it was assumed that phenyl rings align parallel to the substrate at the shortest annealing times, a linear growth region, and a crossover from linear to logarithmic growth observed at higher temperatures for the longest annealing times. No signs of desorption were observed, pointing to the formation of a strongly adsorbed layer. Second, the glass transition of thin polysulfone films was studied in dependence on the film thickness using spectroscopic ellipsometry. Three annealing conditions were compared: two with only a tightly bound layer formed in the linear growth regime and one with both tightly bound and loosely adsorbed layers formed in the logarithmic growth regime. The onset thickness and increase in the glass transition temperature increases with annealing time and temperature. These differences were attributed to the distinct conformations of the formed adsorbed layers. [ABSTRACT FROM AUTHOR]

Strong changes in bulk properties, such as modulus and viscosity, are observed near the glass transition temperature, Tg, of amorphous materials. For more than a century, intense efforts have been made to define a microscopic origin for these macroscopic changes in properties. Using transition state theory (TST), we delve into the atomic/molecular level picture of how microscopic localized unit relaxations, or "cage rattles," evolve to macroscopic structural relaxations above Tg. Unit motion is broken down into two populations: (1) simultaneous rearrangement occurs among a critical number of units, nα, which ranges from 1 to 4, allowing a systematic classification of glass formers, GFs, that is compared to fragility; and (2) near Tg, adjacent units provide additional free volume for rearrangement, not simultaneously, but within the "primitive" lifetime, τ1, of one unit rattling in its cage. Relaxation maps illustrate how Johari–Goldstein β-relaxations stem from the rattle of nα units. We analyzed a wide variety of glassy materials and materials with a glassy response using literature data. Our four-parameter equation fits "strong" and "weak" GFs over the entire range of temperatures and also extends to other glassy systems, such as ion-transporting polymers and ferroelectric relaxors. The role of activation entropy in boosting preexponential factors to high "unphysical" apparent frequencies is discussed. Enthalpy–entropy compensation is clearly illustrated using the TST approach. [ABSTRACT FROM AUTHOR]

In many fields, from semiconductors for opto-electronic applications to ionic liquids (ILs) for separations, the glass transition temperature (Tg) of a material is a useful gauge for its potential use in practical settings. As a result, there is a great deal of interest in predicting Tg using molecular simulations. However, the uncertainty and variation in the trend shift method, a common approach in simulations to predict Tg, can be high. This is due to the need for human intervention in defining a fitting range for linear fits of density with temperature assumed for the liquid and glass phases across the simulated cooling. The definition of such fitting ranges then defines the estimate for the Tg as the intersection of linear fits. We eliminate this need for human intervention by leveraging the Shapiro–Wilk normality test and proposing an algorithm to define the fitting ranges and, consequently, Tg. Through this integration, we incorporate into our automated methodology that residuals must be normally distributed around zero for any fit, a requirement that must be met for any regression problem. Consequently, fitting ranges for realizing linear fits for each phase are statistically defined rather than visually inferred, obtaining an estimate for Tg without any human intervention. The method is also capable of finding multiple linear regimes across density vs temperature curves. We compare the predictions of our proposed method across multiple IL and semiconductor molecular dynamics simulation results from the literature and compare other proposed methods for automatically detecting Tg from density–temperature data. We believe that our proposed method would allow for more consistent predictions of Tg. We make this methodology available and open source through GitHub. [ABSTRACT FROM AUTHOR]

In experimental and theoretical studies of glass transition phenomena, one often finds a sharp crossover in dynamical properties at a temperature Tcr. A bifurcation of a relaxation spectrum is also observed at a temperature TB ≈ Tcr; both lie significantly above the glass transition temperature. In order to better understand these phenomena, we introduce a new model of glass-forming liquids, a binary mixture of prolate and oblate ellipsoids. This model system exhibits sharp thermodynamic and dynamic anomalies, such as the specific heat jump during heating and a sharp variation in the thermal expansion coefficient around a temperature identified as the glass transition temperature, Tg. The same temperature is obtained from the fit of the calculated relaxation times to the Vogel–Fulcher–Tammann (VFT) form. As the temperature is lowered, the calculated single peak rotational relaxation spectrum splits into two peaks at TB above the estimated Tg. Similar bifurcation is also observed in the distribution of short-to-intermediate time translational diffusion. Interrogation of the two peaks reveals a lower extent of dynamic heterogeneity in the population of the faster mode. We observe an unexpected appearance of a sharp peak in the product of rotational relaxation time τ2 and diffusion constant D at a temperature Tcr, close to TB, but above the glass transition temperature. Additionally, we coarse-grain the system into cubic boxes, each containing, on average, ∼62 particles, to study the average dynamical properties. Clear evidence of large-scale sudden changes in the diffusion coefficient and rotational correlation time signals first-order transitions between low and high-mobility domains. [ABSTRACT FROM AUTHOR]

It is highly demanded to understand the confinement effect on nanoconfined polymers. Recent studies reported a strong perturbation of local dynamics and substantial alteration of glass transition temperature Tg at nanoscale. However, how confinement affects the mechanical properties of polymers is not fully understood. Here, we show that the modulus of thin polymer films could be remarkedly altered through a polymer–polymer interface. The modulus of a thin polystyrene (PS) film next to a polydimethylsiloxane (PDMS) was determined from the PS–PDMS bilayer bulging test. A series of experiments show that the modulus of PS can be increased up to 37%, when the modulus of the neighboring PDMS varies from 1.04 to 4.88 MPa. The results demonstrate a strong sensitivity of mechanical properties of thin polymers to the hard/soft environment, which we attribute to the change of high-mobility layer by the polymer–polymer interface. [ABSTRACT FROM AUTHOR]

Metallic glasses (MGs) are of high strength but limited plasticity at room temperature (RT) due to localized shear in the intrinsically heterogeneous structure. Here, we investigate the variation of structural heterogeneity and plasticity of a Zr-based MG after high-temperature (T) tension under different stresses (σ) at 579 K (0.9Tg, where Tg is the glass transition temperature). The correlation length (ξ) of the heterogeneous structure and the average Young's modulus ( E ¯ ) increase with σ when σ is below 160 MPa; when σ exceeds 160 MPa, both ξ and E ¯ decrease with σ, leading to the improvement of the plasticity. This research could be enlightening for improving the plasticity of MGs at RT through tuning their structural heterogeneity with high-T deformation. [ABSTRACT FROM AUTHOR]

This study investigated the segmental dynamics of polymers near polymer–polymer interfaces by probing the rotation of polymer-tethered fluorescent molecules using imaging rotational fluorescence correlation microscopy. Multilayered films were utilized to provide spatial selectivity relative to different polymer–polymer interfaces. In the experimental setup, for the overlayer polymer, polystyrene (PS) was employed and a 15 nm-thick probe-containing layer was placed ≈25 nm apart from different underlayer polymers with glass transition temperatures (Tg) either lower or higher than that of PS. The underlayer of poly-n-butyl methacrylate had 72 K lower Tg than that of PS, whereas polymethyl methacrylate and polysulfone had 22 and 81 K higher Tg, respectively, than that of PS. Two key dynamic features of the glass transition, the non-Arrhenius temperature dependence and stretched relaxation, were examined to study the influence of soft and hard confinements on the segmental dynamics of the overlayer polymer near the polymer–polymer interfaces. Although complications exist in the probing location owing to the diffusion of the polymer-tethered probe during the annealing protocol to consolidate the multilayers, the results suggest that either the segmental dynamics of the polymer near the polymer–polymer interface do not change owing to the soft and hard confinements or the interfacial perturbation is very short ranged. [ABSTRACT FROM AUTHOR]

To develop special insulating paper is of great significance to promote the service life of transformers. Using molecular simulation to guide the development of special insulating paper can greatly reduce the trial-and-error rate and waste of resources in traditional experiments. The effect of different types of polysilsesquioxane (POSS) on cellulose insulating paper was investigated by using molecular simulation. This paper investigated the thermal stability and mechanical properties and electrical characteristics of caged POSS, semi-caged POSS, and ladder-like POSS doped cellulose insulating paper. The results show that POSS with all types can enhance the performance of cellulose insulating paper, and ladder-like POSS possess the best modification effect. The glass transition temperature was increased by 58 K, and the bulk modulus, shear modulus, and elastic modulus of cellulose insulating paper doped with ladder-like POSS can improve up to 27.07%, 45.67%, and 41.28%, respectively. Meanwhile, the dielectric properties of ladder-like POSS modified insulating paper are also significantly improved. The findings of this paper propose a method for the preparation of ladder-like POSS modified insulating paper, which provides theoretical guidance for the experimental preparation of special insulating paper. [ABSTRACT FROM AUTHOR]

The present work describes the preparation of a new series of chalcogenide glasses in an As14Sb26S(60−x) (AgI)x system intending to explore its thermal, structural, optical, mechanical, and electrical properties. The differential scanning calorimetry results of the studied glasses show the sharp decrease in glass transition temperature (Tg) with the successive incremental inclusion of AgI in the composition, implying the structural changes in the glass network. A thorough Raman analysis corroborates the occurrence of changes in the glass network due to the formation of AsI3 units and Ag–S–As bonds with increasing AgI content. Also, structural changes can be reflected with the change in the optical bandgap (Eg) that was calculated using Tauc equations where it was found that Eg is in harmony with the observed structural variations of glasses. The studied glasses possess a transmittance window (∼0.68–12 μm) with transmittance above 60% in the mid-infrared region. These structural changes are closely related to the significant enhancement of conductivity of the present glasses from 10−8 to 10−6 S/cm at 373 K with a decrease in activation energies. Impedance spectra for the glass with highest AgI revealed the presence of two different relaxation processes. AC conductivity data followed an Arrhenius behavior as well as Jonscher's power law. The present work provides insights into glass network modifications due to silver iodide inclusion and its role in the enhancement of conductivity. [ABSTRACT FROM AUTHOR]

In order to prepare highly heat-resistant packaging insulation materials, in this paper, bismaleimide/epoxy resin (BMI/EP55) composites with different contents of BMI were prepared by melt blending BMI into amino tetrafunctional and phenolic epoxy resin (at a ratio of 5:5). The microstructures and thermal and electrical properties of the composites were tested. The electrostatic potential distribution, energy level distribution, and molecular orbitals of BMI were calculated using Gaussian. The results showed that the carbonyl group in BMI is highly electronegative, implying that the carbonyl group has a strong electron trapping ability. The thermal decomposition temperature of the composites gradually increased with the increase of BMI content, and the 20% BMI/EP55 composites had the highest heat-resistance index, along with a glass transition temperature (Tg) of >250 °C. At different test temperatures, with increase in the BMI content, the conductivity of epoxy resin composites showed a tendency to first decrease and then increase, the breakdown field strength showed a tendency to first increase and then decrease, and the dielectric constant was gradually decreased. Two trap centers were present simultaneously in the composites, where the shallow trap energy level is the deepest in 20% BMI/EP composites and the deep trap energy level is the deepest in 10% BMI/EP55 composites. Correspondingly, the 10% BMI/EP55 composite had a slower charge decay rate, while the 20% BMI/EP55 had a faster charge decay rate. In summary, the BMI/EP55 composites with high heat resistance and insulating properties were prepared in this study, which provided ideas for preparing high-temperature packaging insulating materials. [ABSTRACT FROM AUTHOR]

The impact of successive replacement of K+ by Na+ on the megahertz–gigahertz polarization response of 0.25[fKSCN + (1 − f)NaSCN] + 0.75CH3CONH2 deep eutectic solvents (DESs) was explored via temperature-dependent (303 ≤ T/K ≤ 343) dielectric relaxation (DR) measurements and computer simulations. Both the DR measurements (0.2 ≤ ν/GHz ≤ 50) and the simulations revealed multi-Debye relaxations accompanied by a decrease in the solution static dielectric constant (ɛs) upon the replacement of K+ by Na+. Accurate measurements of the DR response of DESs below 100 MHz were limited by the well-known one-over-frequency divergence for conducting solutions. This problem was tackled in simulations by removing the zero frequency contributions arising from the ion current to the total simulated DR response. The temperature-dependent measurements revealed a much stronger viscosity decoupling of DR times for Na+-containing DES than for the corresponding K+ system. The differential scanning calorimetry measurements indicated a higher glass transition temperature for Na+-DES (∼220 K) than K+-DES (∼200 K), implying more fragility and cooperativity for the former (Na+-DES) than the latter. The computer simulations revealed a gradual decrease in the average number of H bonds (⟨nHB⟩) per acetamide molecule and increased frustrations in the average orientational order upon the replacement of K+ by Na+. Both the measured and simulated ɛs values were found to decrease linearly with ⟨nHB⟩. Decompositions of the simulated DR spectra revealed that the cation-dependent cross interaction (dipole-ion) term contributes negligibly to ɛs and appears in the terahertz regime. Finally, the simulated collective single-particle reorientational relaxations and the structural H-bond fluctuation dynamics revealed the microscopic origin of the cation identity dependence shown by the measured DR relaxation times. [ABSTRACT FROM AUTHOR]

Glutaronitrile (GN) doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) at concentrations below and above the room-temperature conductivity optimum near 1M of Li salt is investigated using dielectric spectroscopy and shear rheology. The experiments are carried out from ambient down to the glass transition temperature Tg, which increases considerably as LiTFSI is admixed to GN. As the temperature is lowered, the conductivity optimum shifts to lower salt concentrations, while the power-law exponents connecting resistivity and molecular reorientation time remain smallest for the 1M composition. By contrast, the rheologically detected time constants, as well as those obtained using dielectric spectroscopy, increase monotonically with increasing Li salt concentration for all temperatures. It is demonstrated that the shear mechanical measurements are, nevertheless, sensitive to the 1M conductivity optimum, thus elucidating the interplay of the dinitrile matrix with the mobile species. The data for the Li doped GN and other nitrile solvents all follow about the same Walden line, in harmony with their highly conductive character. The composition dependent relation between the ionic and the reorientational dynamics is also elucidated. [ABSTRACT FROM AUTHOR]

We extend the force-level elastically collective nonlinear Langevin equation theory to treat the spatial gradients of the alpha relaxation time and glass transition temperature, and the corresponding film-averaged quantities, to the geometrically asymmetric case of finite thickness supported films with variable fluid–substrate coupling. The latter typically nonuniversally slows down motion near the solid–liquid interface as modeled via modification of the surface dynamic free energy caging constraints that are spatially transferred into the film and which compete with the accelerated relaxation gradient induced by the vapor interface. Quantitative applications to the foundational hard sphere fluid and a polymer melt are presented. The strength of the effective fluid–substrate coupling has very large consequences for the dynamical gradients and film-averaged quantities in a film thickness and thermodynamic state dependent manner. The interference of the dynamical gradients of opposite nature emanating from the vapor and solid interfaces is determined, including the conditions for the disappearance of a bulk-like region in the film center. The relative importance of surface-induced modification of local caging vs the generic truncation of the long range collective elastic component of the activation barrier is studied. The conditions for the accuracy and failure of a simple superposition approximation for dynamical gradients in thin films are also determined. The emergence of near substrate dead layers, large gradient effects on film-averaged response functions, and a weak non-monotonic evolution of dynamic gradients in thick and cold films are briefly discussed. The connection of our theoretical results to simulations and experiments is briefly discussed, as is the extension to treat more complex glass-forming systems under nanoconfinement. [ABSTRACT FROM AUTHOR]

The glass formation and the dipolar reorientational motions in deep eutectic solvents (DESs) are frequently overlooked, despite their crucial role in defining the room-temperature physiochemical properties. To understand the effects of these dynamics on the ionic conductivity and their relation to the mechanical properties of the DES, we conducted broadband dielectric and rheological spectroscopy over a wide temperature range on three well-established carboxylic acid-based natural DESs. These are the eutectic mixtures of choline chloride with oxalic acid (oxaline), malonic acid (maline), and phenylacetic acid (phenylaceline). In all three DESs, we observe signs of a glass transition in the temperature dependence of their dipolar reorientational and structural dynamics, as well as varying degrees of motional decoupling between the different observed dynamics. Maline and oxaline display a breaking of the Walden rule near the glass-transition temperature, while the relation between the dc conductivity and dipolar relaxation time in both maline and phenylaceline is best described by a power law. The glass-forming properties of the investigated systems not only govern the orientational dipolar motions and rheological properties, which are of interest from a fundamental point of view, but they also affect the dc conductivity, even at room temperature, which is of high technical relevance. [ABSTRACT FROM AUTHOR]

In this work, we propose a linear machine learning force matching approach that can directly extract pair atomic interactions from ab initio calculations in amorphous structures. The local feature representation is specifically chosen to make the linear weights a force field as a force/potential function of the atom pair distance. Consequently, this set of functions is the closest representation of the ab initio forces, given the two-body approximation and finite scanning in the configurational space. We validate this approach in amorphous silica. Potentials in the new force field (consisting of tabulated Si–Si, Si–O, and O–O potentials) are significantly different than existing potentials that are commonly used for silica, even though all of them produce the tetrahedral network structure and roughly similar glass properties. This suggests that the commonly used classical force fields do not offer fundamentally accurate representations of the atomic interaction in silica. The new force field furthermore produces a lower glass transition temperature (Tg ∼ 1800 K) and a positive liquid thermal expansion coefficient, suggesting the extraordinarily high Tg and negative liquid thermal expansion of simulated silica could be artifacts of previously developed classical potentials. Overall, the proposed approach provides a fundamental yet intuitive way to evaluate two-body potentials against ab initio calculations, thereby offering an efficient way to guide the development of classical force fields. [ABSTRACT FROM AUTHOR]

Nanoconfined poly(4-methylstyrene) [P(4-MS)] films exhibit reductions in glass transition temperature (Tg) relative to bulk Tg (Tg,bulk). Ellipsometry reveals that 15-nm-thick P(4-MS) films supported on silicon exhibit Tg − Tg,bulk = − 15 °C. P(4-MS) films also exhibit fragility-confinement effects; fragility decreases ∼60% in going from bulk to a 20-nm-thick film. Previous research found that incorporating 2–6 mol % 2-ethylhexyl acrylate (EHA) comonomer in styrene-based random copolymers eliminates Tg- and fragility-confinement effects in polystyrene. Here, we demonstrate that incorporating 3 mol % EHA in a 4-MS-based random copolymer, 97/3 P(4-MS/EHA), eliminates the Tg- and fragility-confinement effects. The invariance of fragility with nanoconfinement of 97/3 P(4-MS/EHA) films, hypothesized to originate from the interdigitation of ethylhexyl groups, indicates that the presence of EHA prevents the free surface from perturbing chain packing and the cooperative mobility associated with Tg. This method of eliminating confinement effects is advantageous as it relies on the simplest of polymerization methods and neat copolymer only slightly altered in composition from homopolymer. We also investigated whether we could eliminate the Tg-confinement effect with low levels of 2-ethylhexyl methacrylate (EHMA) in 4-MS-based or styrene-based copolymers. Although EHMA is structurally nearly identical to EHA, 4-MS-based and styrene-based copolymers incorporating 4 mol % EHMA exhibit Tg-confinement effects similar to P(4-MS) and polystyrene. These results support the special character of EHA in eliminating confinement effects originating at free surfaces. [ABSTRACT FROM AUTHOR]

The slow Arrhenius process (SAP) is a dielectric mode connected to thermally activated equilibration mechanisms, allowing for a fast reduction in free energy in liquids and glasses. The SAP, however, is still poorly understood, and so far, this process has mainly been investigated at temperatures above the glass transition. By employing a combination of methods to analyze dielectric measurements under both isochronal and isothermal conditions, we were able to quantitatively reproduce the dielectric response of the SAP of different polymers and to expand the experimental regime over which this process can be observed down to lower temperatures, up to 70 K below the glass transition. Employing thin films of thicknesses varying between 10 and 800 nm, we further verified that the peak shape and activation energy of the SAP of poly(4-bromostyrene) are not sensitive to temperature, nor do they vary upon confinement at the nanoscale level. These observations confirm the preliminary trends reported for other polymers. We find that one single set of parameters—meaning the activation barrier and the pre-exponential factor, respectively, linked to the enthalpic and entropic components of the process—can describe the dynamics of the SAP in both the supercooled liquid and glassy states, in bulk and thin films. These results are discussed in terms of possible molecular origins of the slow Arrhenius process in polymers. [ABSTRACT FROM AUTHOR]

To elucidate the atomistic origin of volume relaxation in soda-lime silicate glass annealed below the glass transition temperature (Tg), the experimental and calculated Raman spectra were compared. By decomposing the calculated Raman spectra into specific groups of atoms, the Raman peaks at 800, 950, 1050, 1100, and 1150 cm−1 were attributed to oxygen and silicon in Si–O–Si, non-bridging oxygen in the Q2 unit, bridging oxygen in low-angle Si–O–Si, non-bridging oxygen in the Q4 unit, and bridging oxygen in high-angle Si–O–Si, respectively. Based on these attributions, we found that by decreasing the fictive temperature by annealing below Tg − 70 K, a homogenization reaction Q2 + Q4 → 2Q3 and an increase in average Si–O–Si angle occurred simultaneously. By molecular dynamics simulation, we clarified how the experimentally demonstrated increase in average Si–O–Si angle contributes to volume shrinkage; increasing Si–O–Si angles can expand the space inside the rings, and Na can be inserted into the ring center. [ABSTRACT FROM AUTHOR]

Polyrotaxanes, which consist of mechanically interlocked bonds with rings threaded onto soft polymer chains, exhibit unique mechanical properties and find applications in diverse fields. In this study, we investigate the anomalous segmental dynamics of supercooled polyrotaxane melts using coarse-grained molecular dynamics simulations. Our simulations reveal that the presence of rings effectively reduces the packing efficiency, resulting in well-contained local motion even below the glass transition temperature. We also observe variations in dynamical free volume, characterized by the Debye–Waller factor, which shows a minimum at a ring coverage of 0.1 on threading chains. Such a non-monotonic dependence on coverage shows great consistency in structural relaxation time and dynamic heterogeneity. Specifically, the high segmental mobility of threading linear chains at large coverage can be attributed to the increased dynamical free volume due to supported rigid rings. However, such anomalous segmental dynamics is limited to length scales smaller than one ring size. Beyond this characteristic length scale, the diffusion is dominated by topological constraints, which significantly reduce the mobility of polyrotaxanes and enhance the dynamic heterogeneity. These findings offer microscopic insights into the unique packing structures and anomalous segmental dynamics of supercooled polyrotaxane melts, facilitating the design of advanced materials based on mechanical interlocking polymers for various applications. [ABSTRACT FROM AUTHOR]

The fragility of glass describes how rapidly its molecules slow down as it is cooled near its glass transition temperature. In nanoscale films, polymer glasses with higher fragility experience larger reductions in their Tg compared to those with lower fragility. We investigated whether this is due to the free surface of the polymers, which can cause the surface Tg (Tgsurf) to decrease relative to the bulk Tg. By measuring Tgsurf of various polymers, we found that the shift in Tgsurf relative to the bulk Tg increased with fragility. This suggests that more fragile polymers are more susceptible to the free surface effect. We explain this using the concept of energy landscape, as it is used to explain the different slowdown rates between strong and fragile glass formers at Tg. [ABSTRACT FROM AUTHOR]

Using phase-field simulations, we investigate the bulk coarsening dynamics of ternary polymer solutions undergoing a glass transition for two models of phase separation: diffusion only and with hydrodynamics. The glass transition is incorporated in both models by imposing mobility and viscosity contrasts between the polymer-rich and polymer-poor phases of the evolving microstructure. For microstructures composed of polymer-poor clusters in a polymer-rich matrix, the mobility and viscosity contrasts significantly hinder coarsening, effectively leading to structural arrest. For microstructures composed of polymer-rich clusters in a polymer-poor matrix, the mobility and viscosity contrasts do not impede domain growth; rather, they change the transient concentration of the polymer-rich phase, altering the shape of the discrete domains. This effect introduces several complexities to the coarsening process, including percolation inversion of the polymer-rich and polymer-poor phases—a phenomenon normally attributed to viscoelastic phase separation. [ABSTRACT FROM AUTHOR]

Physical vapor deposition (PVD) provides a route to prepare highly stable and anisotropic organic glasses that are utilized in multi-layer structures such as organic light-emitting devices. While previous work has demonstrated that anisotropic glasses with uniaxial symmetry can be prepared by PVD, here, we prepare biaxially aligned glasses in which molecular orientation has a preferred in-plane direction. With the collective effect of the surface equilibration mechanism and template growth on an aligned substrate, macroscopic biaxial alignment is achieved in depositions as much as 180 K below the clearing point TLC−iso (and 50 K below the glass transition temperature Tg) with single-component disk-like (phenanthroperylene ester) and rod-like (itraconazole) mesogens. The preparation of biaxially aligned organic semiconductors adds a new dimension of structural control for vapor-deposited glasses and may enable polarized emission and in-plane control of charge mobility. [ABSTRACT FROM AUTHOR]

In the field of electronic packaging, epoxy resins with good thermal and dielectric performances have attracted extensive attention. In this work, a novel epoxy resin was synthesized from resveratrol, and its structure was characterized by NMR and FTIR. The resveratrol‐based epoxy resin was cured with an active ester, and the properties of the cured system were further studied. The results showed that the resveratrol‐based epoxy cured with active ester had excellent comprehensive properties, its dielectric constant (Dk) was 2.63, dissipation factor (Df) was 4.91‰ at high frequency of 10 GHz; moreover, its glass transition temperature (Tg) was 188°C, coefficient of thermal expansion (CTE) was 70.7 ppm/°C, 5% mass loss temperature (Td5%) was 390°C. These results suggested that a biomass epoxy resin with excellent thermal and dielectric performances had been successfully synthesized, which had potential application in the field of high‐frequency communication. [ABSTRACT FROM AUTHOR]

Silicone rubber is widely used in reinforced insulation of cable accessories due to its good electrical insulation and weather resistance. With the continuous improvement of high voltage transmission grade, higher requirements are put forward for the electrical insulation performance. The effect and mechanism of phenyl content on the electrical insulation properties of silicone rubber are investigated by the method of combination of experiments and molecular simulations. The experimental results show that the properties of silicone rubber are improved with the increase of phenyl content. Among them, the silicone rubber composite with phenyl content of 20 wt% has the best comprehensive performance. Compared with vinyl silicone rubber, the dielectric constant at 50 Hz decreases from 3.50 to 2.95, and the breakdown strength increases by 38.03%, from 56.59 to 78.11 kV/mm. In addition, the tensile strength and elongation at break are 5.44 MPa and 456%, respectively. The molecular simulation results show that with the increase of phenyl content, the glass transition temperature increases, the mean square displacement decreases, and the free volume decreases, which macroscopically leads to the change of electrical properties of the silicone rubber material. This work has a certain guiding significance for improving the electrical properties of silicone rubber for cable accessories. [ABSTRACT FROM AUTHOR]

Single pack epoxy adhesives, known for their simple operation process, combined with good reactivity at moderate temperatures and excellent storage stability, have gained extensive attention. An appropriate accelerator is crucial for enhancing their performance. This study demonstrates that the zinc zeolitic imidazolate framework ZIF‐8 (Zn(2‐methylimidazole)2) can effectively serve as an effective accelerator for the epoxy‐anhydride system, as evidenced by the complete exothermic curing curve obtained via differential scanning calorimetry (DSC) tests of the epoxy (A‐128) and anhydride (THPA) adhesive sample with ZIF‐8. The optimal addition amount of ZIF‐8 (0.9%) was determined by assessing the glass transition temperature (Tg) of the cured resin with varying ZIF‐8 weight fractions. Furthermore, the ideal curing conditions—gel temperature of 388.4 K, curing temperature of 416.7 K, and post‐treatment temperature of 441.9 K—were established by analyzing heating curves at different circumstances. The epoxy (A‐128) and anhydride (THPA) system with accelerator ZIF‐8 exhibited superior stability compared to the commercial accelerators like PN‐23 or DMP‐30. This is attributed to the steric hindrance and coordination bonds of ZIF‐8, indicated by a large pre‐exponential factor (A1 = 5.58 × 108) and low‐value reaction rate constant (k1 = 0.3461 × 10−3 s−1). In addition, the kinetic parameters, and an autocatalytic equation model for the epoxy (A‐128) and anhydride (THPA) system with accelerator ZIF‐8 have been derived through isothermal curing kinetics analysis. [ABSTRACT FROM AUTHOR]

For hydrogenated nitrile‐butadiene rubber (HNBR) modified polyvinyl chloride (PVC), magnesium hydroxide and antimony trioxide are frequently employed as flame retardants. Fume silica is thought to be useful reinforced agent for rubber as well as efficient flame retardant for polymer‐based composites. The plasticized PVC and HNBR blend in this work were combined with three fillers mentioned above to create rubber‐plastic composites that performed well overall, with a notable improvement in combustion. The limiting oxygen index of the composites increased from 23.7% to 33.8% with no droplets falling during combustion, the smoke density rating decreased from 23.8% to 7.9%, and the maximum smoke density dropped from 95.5% to 15.5%. The cone calorimetry test findings revealed that the three fillers simultaneously prevented the emission of smoke and heat from combustion. High thermal conductivity is typically linked to excellent flame retardancy. The thermal conductivity of composites rose from 0.193 to 0.583 W m−1 K−1 with the addition of fillers. Furthermore, the low glass transition temperature and permanent set of improved composites reflect its softness and rubber elasticity. Thermogravimetric analysis was used to examine the thermal stability of the composites in nitrogen and air, and the results indicated the addition of fillers improved the thermal stability. [ABSTRACT FROM AUTHOR]

This article aims to assess the suitability of natural neem gum in various composite material applications in place of epoxy resin. The assessment was done by thermal characterisation, experimental study and comparative analysis of thermal behaviour, Fourier transform IR spectroscopy (FTIR) characterisation and comparison of functional groups and mechanical properties of neat epoxy and neat neem resins. To study and compare thermal behaviour differential scanning calorimetry (DSC), thermogravimetric (TG) and relative derivative TG (DTG) analysis were conducted. The glass transition temperatures, exothermic and endothermic peaks, curing of thermosetting epoxy and crystallisation of polymeric neem, value of % cure and mass change or mass loss concerning temperature of both the resins were experimentally determined and comparative analysis was conducted to find the suitability of neem resin in composite material applications in place of epoxy resin. Functional groups of neem gum were identified and mechanical properties such as bond strength, toughness, rigidity and ductility were characterised and compared with that of epoxy resin by conducting FTIR. [ABSTRACT FROM AUTHOR]

This research focuses on the mechanical characterization of FG material graded with Graphene nano-platelets (GPLs) in the transverse direction. Different weight percentages of GPL (0–2 wt. %) were incorporated into epoxy resin for manufacturing the FGM using a simple casting method and the effects were analyzed. This paper aims to enhance the material's performance, especially focusing on its potential use in biomedical tools. Mechanical tests including assessment on tensile, flexural, impact strength, and microhardness demonstrated substantial improvement in strength and stiffness as compared to other nanocomposite structures. Microstructural analysis using scanning electron microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD) analysis which hint at the strong chemical interaction and physical association of GPL nanofiller with the epoxy resin. Thermal analysis was conducted using the Dynamic Mechanical Analysis (DMA) test, which revealed enhanced thermal stability of the FG specimen with a higher glass transition temperature than other carbon nanofillers mixed in epoxy resin. This is advantageous for the FG material to maintain its glassy state, maintaining safety and reliability during high-temperature medical applications. All these findings indicate that the proposed FG-GPL material possesses the necessary mechanical properties, suggesting that customized nanofiller integration could lead to significant advancements in medical procedures, such as in vivo stomach biopsy treatments, drug delivery systems, etc. The material also meets specific anatomical requirements and reduces the risk of malfunction, thereby ensuring patient safety as justified by current experimental investigations. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the interlaminar shear properties and failure mechanisms of plain woven carbon fabric/polyetheretherketone (CF/PEEK) thermoplastic composites under high strain rate impact loads at different temperatures (25°C, 120°C, 295°C). A reliable hot air flow heating method with SHPB is creatively employed for short beam shear experiments. A multi-scale model was developed to predict the impact behavior of plain CF/PEEK composites. Both results show that the thermoplastic composites have strong strain rate and temperature dependence, and which are more sensitive to temperature effect. As the temperature increases, the thermoplastic composites are mainly affected by the softening effect of the matrix due to the glass transition temperature. The shear modulus and peak stress appear to decline at high temperatures, while the failure strain tends to increase. The damage mode changes from interlayer delamination cracking at the glassy state to shear fracture and fiber pullout at a highly elastic state. As the strain rate increases, the failure strain decreases, while the shear modulus and peak stress show the opposite trend. Fiber bundle breakage, debonding, matrix cracking, and significant interlayer delamination occur at high strain rates. [ABSTRACT FROM AUTHOR]

This study focuses on advancing epoxy-polyamide composites through the incorporation of chitosan, derived from crab shells, a sustainable polymeric bio filler known for its ability to enhance mechanical and thermal properties. Utilizing a solution casting technique, composites were fabricated by blending various concentrations of chitosan into the epoxy-polyamide matrix. Several analytical methods, including FT-IR, XRD, SEM, DSC, and mechanical testing, were used to evaluate the modifications and properties of the composites. FT-IR confirmed successful chitosan incorporation into the ER-PA composites, supported by SEM analysis showing improved structural integrity. XRD revealed prominent diffraction peaks, reflecting increased crystallinity and efficient chitosan integration. SEM indicated uniform chitosan dispersion on smooth surfaces, enhancing fracture toughness. Mechanical study of the 1% chitosan blend demonstrated superior results, with an elasticity of 6.79 GPa and fracture elongation of 2.2%, surpassing the 5% blend. DSC data showed improved thermal stability, with the uncured composite exhibiting endothermic behavior at 100 °C and exothermic behavior at 400 °C. TGA confirmed enhanced thermal properties up to 780 °C, particularly for the 1% Cs blend, which also displayed outstanding amorphous characteristics. Overall, the mechanical study confirmed Young's best modulus, toughness, and tensile strength in the 1% blend. A noticeable shift toward higher temperatures during accelerated heating indicated enhanced material durability. These findings highlight the significant potential of chitosan to improve the mechanical strength and thermal stability of epoxy-polyamide composites, making them suitable for demanding engineering applications where endurance and performance are critical. [ABSTRACT FROM AUTHOR]

In this work, two kinds of dimaine monomers with spirocyclic structures, including 3,3,3′,3′-tetramethyl-6,6′-bis[3-amino-4-hydroxyphenoxy]-1,1′-spirobisindane (TBAHS) and 3,3,3′,3′-tetramethyl-bis(5-amino-6-hydroxyphenyl)-1,1′-spirobisindane (TBHAS) are firstly synthesized. Then, the two diamines TBAHS and TBHAS are copolymerized in different molar ratios with equimolar 4,4′-(hexafluoroisopropenyl)diphthalic anhydride (6FDA) to synthesize poly(amic acid) (PAA) solution, followed by thermal imidization to obtain a series of copolyimide (coPI) membranes. Next, these coPI(TBAHS-TBHAS) specimens are subjected to thermal rearrangement (TR) treatment at 450°C to obtain the corresponding coTR(TBAHS-TBHAS) copolymer membranes. The influences of the molar ratio of TBAHS to TBHAS, thermal treatment temperature and time on the microstructures and properties of the PI and TR copolymers are investigated. With the increase of rigid TBHAS molar ratio, the glass transition temperature (T g) and d- spacing value of the coPI(TBAHS-TBHAS) samples are significantly enhanced. Furthermore, as the thermal treatment temperature increases, the mechanical properties of the copolymer membranes display a sharply decline trend, but the d -spacing values are obviously increased. When the molar ratio of TBAHS to TBHAS is 7:3, the gas permeabilities of the coTR membrane reach 1140.5, 1180.6, 306.6, and 44.9 Barrer for H2, CO2, O2, and N 2, respectively. Meanwhile, the ideal selectivity of O2/ N 2 is 6.82, suggesting a superior separation performance close to the 2015 upper limit. Furthermore, with the increase of thermal treatment temperature and time, the gas permeabilities are also improved. [ABSTRACT FROM AUTHOR]

The main focus of the work is on developing a new class of hybrid composite with polyester as the continuous phase and micro-sized hexagonal boron nitride (hBN) and short sisal fibre as the discontinuous phases. The effect of loading of discontinuous phases on the different properties of the composites is analysed experimentally. The incorporation of either of the discontinuous phases unwillingly increases the void content and water absorption rate. With hBN content, the density increases, whereas, with sisal fibre content density decreases. The hybrid combination of fillers successfully improves the glass transition temperature (Tg) and coefficient of thermal expansion (CTE) of the polymeric resin. The maximum Tg reported is 106.2°C and the minimum CTE reported is 51.7 × 10−6/oC for the polyester reinforced with 40 wt. % hBN and 5 wt. % sisal fibre. The incorporation of hBN upsurges the thermal conductivity but also increases the dielectric properties. The dielectric properties gainfully reduce with the addition of sisal fibre. Dielectric properties also decrease with an increase in the working frequency. The incorporation of sisal fibre slightly reduces the thermal conductivity of the composites. The mechanical properties like tensile strength and flexural strength of the hybrid composite increase when the combination of hybrid fillers is judicially selected, whereas, the compressive strength and hardness of the composite increase with filler/fibre loading with maximum 131.4 MPa and 80.0 Shore D number, respectively. Due to the improved overall properties, the composite material under investigation can find its potential application in various microelectronic applications. [ABSTRACT FROM AUTHOR]

A novel lyophilization (freeze-drying) technique has been developed to produce the petroleum hydrocarbon (PH)–degrading bacterial strain powders for the enhancement of bioremediation of PH-polluted soils. Four different PH-degrading strains (Paenarthrobacter ureafaciens, Klebsiella oxytoca, Pseudomonas citronellolis, and Enterobacter cloacae) isolated from a PH-polluted site were used for bacterial strain powder production. The modified lyophilization buffer contained skimmed milk powder, trehalose, sucrose, and glycerin. The water content, bacterial activity, bacterial survival factor, glass transition temperature, and surface characteristics were analyzed to determine the properties of the produced bacterial strain powders. Addition of 20% skimmed milk powder as an excipient and 15% trehalose as a cryoprotectant could significantly enhance the stability and survival factor of the bacterial strains. The incorporation of 0.75% sucrose and 0.05% glycerol into the basic formula of skimmed milk powder and trehalose, respectively, could allow the bacterial strain powder to be stored at ambient temperature due to the effective environmental isolation and continuous nutrient supplement capabilities of the two agents. Up to 95% of the bacterial survival could be obtained when 24 h of prefreezing at −80°C was applied as the first stage of the modified lyophilization process followed by the second stage of freeze-drying for 24 h. With this process, the depreciation rate was less than 1% after storing the powder for 6-month at 25°C. The glass transition temperature of the strain powder fell within the range of 10°C to 25°C, indicating that the optimized formulation for bacterial strain powder production could facilitate the strain storage at room temperature and produce diverse powder variants. Through the application of novel lyophilization process, more stable bacterial strain powder could be produced with a higher survival factor and a longer storage period. Up to 83% of total PH removal could be obtained in microcosms with the application of strain bacterial powders. [ABSTRACT FROM AUTHOR]

This study aimed first to promote the alkylation of polyethyleneimine (PEI), developing its alkylated (quaternary) form (QA-PEI) by inserting alkyl groups into amine groups. Subsequently, polymer blends with poly(methyl methacrylate) (PMMA) were prepared via solvent casting, and finally, the physicochemical, optical, and mechanical behavior of the resulting PMMA/QA-PEI were assessed. Elemental analyses, Fourier-transform infrared spectroscopy (FT-IR), and hydrogen nuclear magnetic resonance spectroscopy (1H-NMR) confirmed that the PEI alkylation successfully converted the amine groups into quaternary ammonium groups. When added to PMMA, QA-PEI altered its coloration, making it yellow. In addition, higher contents of QA-PEI hindered PMMA transmittance and increased its opacity due to the larger QA-PEI domains. Scanning electron microscopy (SEM) images showed that PMMA and QA-PEI formed a phase-separated system, establishing a droplet-matrix morphology. The thermal and mechanical behavior showed some compatibility between PMMA and QA-PEI as thermal resistance slightly improved and PMMA glass transition temperature (Tg) decreased. The tensile strength was also improved in the PMMA/QA-PEI blends without significant change in strain at break and tensile modulus. [ABSTRACT FROM AUTHOR]

The bonding interface serves as a vulnerable point in steel structures strengthened with carbon fiber–reinforced polymer (CFRP), significantly influenced by the mechanical properties of adhesives and temperature. To understand the mechanisms through which temperature changes affect the properties of adhesive materials and the CFRP–steel interface, 70 adhesive tensile specimens and 28 CFRP–steel double-lap joint specimens were prepared based on the self-developed high-performance adhesive G3 and the typical commercial adhesive Sika30. Tests were conducted at seven different temperatures (−20°C , −5°C , 10°C, 25°C, 40°C, 55°C, and 70°C). The results indicate that compared with 25°C, an increase in temperature leads to a decrease in adhesive strength, whereas the ultimate bearing capacity of CFRP–steel double-lap joints increases when the temperature is below a certain value but still lower than the glass transition temperature (Tg) of the adhesive. However, a rapid decline in both adhesive and CFRP–steel joint performance occurs when the temperature approaches or exceeds the Tg of the adhesive. Decreasing the temperature results in a reduction in the ultimate bearing capacity of CFRP–steel double-lap joints. Therefore, when reinforcing with adhesive-bonded CFRP, it is essential to consider the adverse effects not only of adhesive softening at high temperatures but also of embrittlement in low-temperature strengthening systems. [ABSTRACT FROM AUTHOR]

In this work, a novel family of α,ω-diene carbonate monomers was synthesized via the alkoxy carbonylation reaction of bis(hydroxymethyl)furan (BHMF) with dialkyl carbonates (DACs) of varying chain lengths, containing terminal olefins, in the presence of 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). These monomers were then subjected to acyclic diene metathesis (ADMET) polymerization with seven different ruthenium catalysts. The second-generation Hoveyda–Grubbs catalyst proved to be the most effective, yielding furan-based polycarbonates with molecular weights (Mn) up to 19 kDa. The resulting bio-based polymers exhibited thermal degradation temperatures (Td5%) ranging from 156 °C to 244 °C and glass transition temperatures (Tg) from −8 °C to −36 °C. NMR studies confirmed their polymeric structures and provided insights into the polymers organization, which influenced their properties. These novel polycarbonates were then compared to previously reported polyesters and polyethers derived from similar furan-based α,ω-diene monomers. Additionally, for the first time, co-polymerization studies were conducted on three families of furan-based α,ω-diene monomers—ester, ether, and carbonate—revealing the effect of incorporating different functional groups on the properties of the resulting materials. This unprecedented comparison and co-polymerization reactions highlight the versatility of furan-based monomers, but also underscores the possibility to expand their application in creating tailored bio-based materials for diverse applications. [ABSTRACT FROM AUTHOR]

Development of the high-power devices based on the third-generation semiconductor puts forward a high requirement for the thermal performance of electronic packaging materials. In this study, we employed oligomeric bismaleimide (BMI), multifunctional epoxy resin (EP), and 4.4'-daminodiphenylmethane (DDM) as the resin matrix to prepare a new BMI/EP/DDM (BED) ternary resin molding compound aiming for high-temperature electronic packaging. With 2-ethyl-4-methylimidazole as the curing accelerator, the reactions including the addition of BMI with DDM, addition of EP with DDM, self-polymerization of EP, and self-polymerization of BMI facilely occurred during the curing process of BED system, making the molding process of BED be compatible with that of commercial epoxy molding compounds (EMC). With increasing the BMI content, the thermal stability of the cured BED resins was improved, showing the initial thermal decomposition temperature and char yield at 800 °C up to 388 °C and 55.7%, respectively. Compared with EMC, the BED molding compounds exhibited a glass transition temperature over 360 °C and a remarkable dimensional stability in the glassy state after curing, due to the enhancement of network chain rigidity by the introduction of BMI component. Although the cured BED was less ductile than the cured EMC at room temperature, showing lower flexural strength and higher flexural modulus, it had much superior flexural performance to the cured EMC at 250 °C. Therefore, BED was demonstrated to be a promising candidate for high-temperature electronic packaging applications. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms underlying living anionic polymerization is essential for advancing efficient and sustainable elastomer production technologies. This study investigates the introduction of a functional styrene derivative at the initiation of a styrene‐butadiene polymer chain with high efficiency. Butyllithium is the most widely used initiator in anionic polymerization due to its high reactivity, availability, and ability to provide precise control over polymer molecular weight and structure. Modified initiators, formed from N‐(dimethyl(vinylbenzyl)silyl)‐N,N‐bis(trimethylsilyl)amine and isomers of butyllithium (n‐, sec‐, and tert‐), increase initiation efficiency and reduce oligomer formation. The developed procedure demonstrates the effective use of a functional styrene derivative as an alpha chain‐end modifier. The formation of a unimeric structure improves from 15.6% to 88.3%, significantly increasing the yield of alpha functionalization. Direct transfer of the functional styrene derivative to the alpha position expands the potential for functionalization in anionic polymerization. The activity of the preinitiators is evaluated in styrene‐butadiene anionic copolymerization. The functional initiators are terminated and characterized by high‐performance liquid chromatography coupled with gel permeation chromatography to assess the degree of polymerization. This method enables quantitative analysis of oligomer formation. The synthesized copolymers are further characterized by their molar masses, microstructure, Mooney viscosity, and glass transition temperature. [ABSTRACT FROM AUTHOR]

This study investigated the impact of glycerin plasticization, polyvinyl alcohol (PVA) and nano-montmorillonite (MMT) compounding, and organic acid cross-linking agent on the mechanical, microstructural, crystallinity, water absorption, and thermal characteristics of carboxymethyl cellulose (CMC)-based films. The developed manufacturing technique resulted in substantial improvements in the film's tensile strength and Young's modulus, which increased by 240% and 840%, respectively. However, there was a 27% reduction in elongation at break. Scanning electron microscopy revealed that the optimal MMT concentration, which prevented agglomeration within the polymer matrix, was 4 wt.%. Evaluations of hydrophilicity/hydrophobicity demonstrated a 24% reduction in moisture absorption and a 41% decrease in water vapor permeability for the CMC-based films. This reduction significantly lowered the solubility and swelling degree of the films by 63% and 93%, respectively. Notably, beyond a cross-linker concentration of 15 wt.%, this contribution diminished slightly. Thermal analysis indicated that glycerin reduced the film's glass transition temperature from 76.2 °C to 68.9 °C, while the addition of PVA and MMT increased this temperature by 22% and 53%, respectively. The optimal formulation for an effective food packaging film was identified as CMC/PVA/glycerin at a 1/1/2 ratio, with 4 wt.% MMT and 15 wt.% cross-linker. The resulting film demonstrated an improved shelf life for food products compared to polyethylene alternatives. [ABSTRACT FROM AUTHOR]

The hygrothermal aging model, based on Fick's second law of diffusion, characterizes the degradation of engineering constants in T700 carbon fiber/epoxy resin composites. It focuses on changes in the tensile modulus, shear modulus, and transverse Poisson's ratio due to moisture absorption and temperature variations. The model validates through mass change observations before and after seawater immersion, along with surface morphology assessments and tensile experiments. The results reveal that the saturated moisture absorption rate for single-layer laminates in seawater immersion is 0.35%. Short-term seawater immersion at room temperature (≤60 days) does not induce cracks or defects (≥10 μm) on the composite's surface. The composite's modulus decreases as moisture absorption increases, with the longitudinal tensile modulus dropping by an order of 10−5%, while the other engineering constants decrease by an order of 10−3%. The modulus also decreases with rising temperature; the closer the temperature is to the matrix's glass transition, the faster the modulus declines, with the longitudinal tensile modulus decreasing by 0.84%, and the other engineering constants decreasing by 100%. This research provides valuable insights for the engineering applications of composite materials in marine environments. [ABSTRACT FROM AUTHOR]

The moisture sorption, rheological, and glass transition properties of puffed cereals, such as brown rice, barley, adlay, and amaranth, were assessed. The puffed cereals were stored in desiccators until their moisture content reached equilibrium. Moisture sorption isotherms were measured, and monomolecular adsorption moisture content was calculated through Brunauer−Emmett−Teller (BET) analysis. The glass transition temperature (Tg) was determined, and the internal structure was observed using a scanning electron microscope. The rupture force and apparent elastic modulus of puffed cereals decreased with increasing relative humidity (RH). The puffed cereals exhibited ductile fracture ,when the moisture content was >8%. The Tg of puffed cereals with 8% moisture content was approximately 40 °C. It was inferred that puffed cereals demonstrated a crispy texture in the glassy state when stored at <40 °C, but transitioned to a rubbery state at >40 °C, resulting in the loss of crispy texture. [ABSTRACT FROM AUTHOR]

Poly(lactic acid) (PLA) exhibits excellent shape memory properties but suffers from brittleness and a high glass transition temperature (Tg), limiting its utility in flexible and durable applications. This study explored the modification of PLA properties through the incorporation of poly(ethylene glycol) (PEG), varying in both content (5–20 wt%) and molecular weight (4000–12,000 g/mol), to enhance its suitability for specific applications, such as medical splints. The PLA/PEG blend, containing 15 wt% PEG and with a molecular weight of 12,000 g/mol, exhibited superior shape fixity (99.27%) and recovery (95.77%) in shape memory tests conducted at a programming temperature (Tp) of 45 °C and a recovery temperature (Tr) of 60 °C. Differential scanning calorimetry (DSC) analysis provided insights into the thermal mechanisms driving shape memory behavior of the PLA/PEG blend. The addition of PEG to the PLA blend resulted in a reduction in Tg and an increase in crystallinity, thereby facilitating enhanced chain mobility and structural reorganization. These thermal changes enhanced the shape fixity and recovery of the PLA/PEG blend. Synchrotron wide-angle X-ray scattering (WAXS) was further employed to elucidate the microstructural evolution of PLA/PEG blends during the shape memory process. Upon stretching, the PLA/PEG chains aligned predominantly along the tensile direction, reflecting strain-induced orientation. During recovery, the PLA/PEG chains underwent isotropic relaxation, reorganizing into their original configurations. This structural reorganization highlighted the critical role of chain mobility and alignment in driving the shape memory behavior of PLA/PEG blends, enabling them to effectively return to their initial shape. Mechanical testing confirmed that increasing PEG content and molecular weight enhanced elongation at break and impact strength, balancing flexibility and strength. These findings demonstrated that PLA/PEG blends, especially with 15 wt% PEG at 12,000 g/mol, offer an optimal combination of shape memory performance and mechanical properties, positioning them as promising candidates for customizable and biodegradable medical applications. [ABSTRACT FROM AUTHOR]

This research examines the possibility of palm oil and oil palm trunk biochar (OPTB) from pyrolysis effectively serving as alternative processing oils and fillers, substituting petroleum-based counterparts in natural rubber (NR) composites. Chemical, elemental, surface and morphological analyses were used to characterize both carbon black (CB) and OPTB, by using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) gas porosimetry, and scanning electron microscopy (SEM). The influences of OPTB contents from 0 to 100 parts per hundred rubber (phr) on thermal, dielectric, dynamic mechanical, and cure characteristics, and the key mechanical properties of particulate NR-composites were investigated. OPTB enhanced the characteristics of the composites, as demonstrated by a rise in dielectric constant, thermal stability, storage modulus, glass transition temperature (Tg), hardness and modulus at 300% elongation, along with a decrease in the loss tangent (tan δ). Tear strength exhibited an increase with OPTB content up to a specific threshold, whereas tensile strength and elongation at break declined. This implies a compromise between the various mechanical properties when incorporating OPTB as a filler. This work supports the potential application of OPTB as a renewable substitute for CB in the rubber industry, particularly in tire production and other industrial rubber applications, which would also bring environmental, sustainability, and economic benefits for the palm oil-related industry. [ABSTRACT FROM AUTHOR]