Decoupling between Enthalpy Relaxation and Viscous Flow and Its Structural Origin in Fragile Oxide Glass-Forming Liquids

The structural relaxation kinetics at the glass transition in tellurium oxide (TeO₂)-based glasses has been examined from viscosity and heat-capacity measurements to clarify the features of the structural relaxation in fragile oxide glass-forming liquids. A large decoupling between enthalpy relaxation and viscous flow, i.e., a large discrepancy between the activation energies for the enthalpy relaxation (recovery), Δ H , and viscous flow, E _η, has been demonstrated in TeO₂-based glasses. The values in x K₂O· x MgO·(100 − 2 x )TeO₂ glasses, for example, are ∼919–1051 kJ/mol for Δ H and ∼ 577–701 kJ/mol for E _η, given the ratio of Δ H/E _η≈ 1.44–1.59. Some viscosity and heat-capacity data (all data have been reported previously) obtained from similar experiments in Sb₂O₃–B₂O₃ glasses belonging to the category of strong glass-forming liquids have been reanalyzed in this paper for comparison; a strong coupling was found to exist between Δ H and E _η, i.e., Δ H/E _η≈ 0.98–1.18. An origin of decoupling between Δ H and E _η in fragile glass-forming systems such as TeO₂-based glasses has been discussed by considering the glass structure model for fragile glasses; strongly bonded correlated (highly constrained) regions are surrounded or connected by weakly bonded noncorrelated (unconstrained) parts.     

Anisotropic structure of alkali metaphosphate glasses

Orientation anisotropy, which is well known in organic polymers with appropriate network structures, is less common in oxide glasses. We present the intermediate-range order in anisotropic alkali metaphosphate glass which consists of oriented PO₄ tetrahedral chains and intervening alkali cations along the elongation direction. The X-ray total structure factor S(Q) indicates that the inter-chain spacing depends on the size of alkali cations and varies from 5.03 to 6.28 Å. The mixed alkali effect is primarily related to an increase of the separation. The total correlation function T(r) provides the first definite evidence that the anisotropic structure is composed of phosphorus-bridging oxygen bonds (P–O_B) lying along the elongation direction and phosphorus-non-bridging oxygen bonds (P–O_T) oriented perpendicular to the elongation direction. The present result unveils fundamental aspects of the anisotropic structure of an oxide glass and provides essential information for the development of oxide glasses to control structural anisotropy.     

Simulation of mechanical properties of epoxy-based chemically amplified resist by coarse-grained molecular dynamics

The mechanical properties of an epoxy-based chemically amplified resists with various cross-linking ratios were simulated using a newly developed coarse-grained molecular dynamics simulation that employs a bead–spring model. Models with the different cross-linking ratios were created in the molecular dynamics calculation step and uniaxial elongation simulations were performed. The results reveal that the simulated elastic modulus of the resist modeled by the Kremer–Grest model with an extended angle bending potential depends on the cross-linking ratio, its dependency exhibits good agreement with that determined by nanoindentation tests.     

Liposome‐Based in Vitro Evolution of Aminoacyl‐tRNA Synthetase for Enhanced Pyrrolysine Derivative Incorporation

Methanosarcina species pyrrolysyl‐tRNA synthetase (PylRS) attaches Pyl to its cognate amber suppressor tRNA. The introduction of two mutations (Y384F and Y306A) into PylRS was previously shown to generate a mutant, designated LysZ‐RS, that was able to attach N‐benzyloxycarbonyl‐L ‐lysine (LysZ) to its cognate tRNA. Despite the potential of LysZ derivatives, further LysZ‐RS engineering has not been performed; consequently, we aimed to generate LysZ‐RS mutants with improved LysZ incorporation activity through in vitro directed evolution. Using a liposome‐based in vitro compartmentalization (IVC) approach, we screened a randomly mutagenized gene library of LysZ‐RS and obtained a mutant that showed increased LysZ incorporation activity both in vitro and in vivo. The ease and high flexibility of liposome‐based IVC should enable the evolution of not only LysZ‐RS that can attach various LysZ derivatives but also of other enzymes involved in protein translation.     

Insights from ab initio molecular dynamics simulations for a multicomponent oxide glass

It remains a challenge to establish structural models of multicomponent oxide glass systems. In this study, we have investigated 68.3SiO₂–16.1B₂O₃–4.2Al₂O₃–11.4Na₂O glass and melt structures by ab initio molecular dynamics (AIMD) simulations. The atomic configurations obtained from AIMD simulations were validated against ¹⁷O solid‐state NMR spectrum under 24.0 T and neutron diffraction data, and excellent agreement was achieved. The bond lengths, angles, and coordination geometries were statistically analyzed for each atomic species. Here we particularly address the role of minor atomic species such as five‐coordinate Si (Si^V) and Al (Al^V). The Si^V–O bond lengths and O–Si^V–O angle distribution in the glass indicated 1.718 Å and three peaks at 90°, 120°, and 175°, which are assigned to a coordination geometry of the trigonal bipyramidal structure. Ring statistic analysis revealed that Si^V and Al^V were found to preferentially contribute to the formation of small ring sizes.     

Numerical simulations of annular extrudate swell of polymer melts

Numerical viscoelastic simulations were carried out using a K-BKZ type of separable integral constitutive equation. Both reversible and irreversible models were tried for several types of damping functions to calculate the annular extrudate behavior of high-density polyethylene (HDPE). There are two aims in this study; first, to clarify the properties of these dumping functions, and second, to investigate the influence of rheological characteristics on annular extrudate swell. In these numerical simulations, relaxation spectrum and shear viscosity were fixed, and the other characteristics were varied. The reversional response of the damping function mainly has an effect on the magnitude of the area swell even if the die is straight. The irreversible model expresses the experimental results of annular extrudate swell better than the reversible model. The accurate fitting of N1 by the damping model is important for predicting it. The magnitude of N1 predicted from the Wagner exponential model is lower than that of the PSM model, and the area swell shows the same tendency as N1. A modified PSM model that allows the N1 curve to shift can fit the magnitude of area swell. The relationship between the diameter and thickness of the extrudate depends on N2/N1, and it was estimated by simple linear elasticity of solids. The time dependent viscosity varies with the type of damping function, and it influences the time-dependent swell.     

Kinetics of Enthalpy Relaxation at the Glass Transition in Ternary Tellurite Glasses

The kinetics of enthalpy relaxation (recovery) at the glass transition in x K₂O·(20− x )MgO·80TeO₂ glasses has been examined from heat capacity measurements using differential scanning calorimetry to clarify the features of the structural relaxation in ternary TeO₂-based glasses. Ternary glasses such as 10K₂O·10MgO·80TeO₂ show high thermal resistance against crystallization compared with binary glasses. The degree of fragility m estimated from the activation energy for viscous flow E _η and the glass transition temperature T _g is m = 55–62, indicating a fragile character in TeO₂-based glasses. Large heat capacity changes of 43.1–48.2 J·mol⁻¹·K⁻¹ are also observed at the glass transition. The activation energy for enthalpy relaxation Δ H is evaluated from the cooling rate dependence of the limiting fictive temperature, and values of Δ H = 897–1268 kJ·mol⁻¹ are obtained. Negative deviation from additivity in Δ H is also observed. Values of the Kovacs–Aklonis–Huchinson–Ramos (KAHR) parameter θ estimated from Δ H and T _g are 0.33–0.42 K⁻¹. It has been proposed that ternary glasses have more homogeneous and constrained glass structure compared with binary glasses.     

Ruthenium(IV) dioxide-catalyzed reductive gasification of intractable biomass including cellulose, heterocyclic compounds, and sludge in supercritical water

Catalytic reduction gasification in the presence of ruthenium(IV) dioxide (RuO₂) in supercritical water was used to decompose intractable biomass. The gasification of model biomass samples (glucose, cellulose, and heterocyclic compounds), and low-purity biomass samples obtained from a paper-recycling facility (paper sludge) and from a sewage treatment plant (sewage sludge) were studied. In clear contrast to another catalysts, the RuO₂ catalyst completely gasified cellulose to produce mainly hydrogen, methane, and carbon dioxide under various conditions (e.g., 673 K at 30 MPa and 773 K at 50 MPa). As for heterocyclic compounds, nitrogen compounds did not deactivate the RuO₂ catalyst; the gasification of carbazole proceeded completely. Furthermore, paper sludge was almost completely decomposed in supercritical water with RuO₂ at 723 K.     

Syntheses,characterizations, and redox behaviors of new self-assembled metal complexes with bridging ligands incorporating chalcogen sites

Three new complexes, [Zn(dbsf)₂(dmf)₂] · 5.5dmf (dbsf = 4,4′-sulfonyldibenzoate) (1β), [Cu(tdsa)(phen)₂] · 1.5EtOH (tdsa = 5,5′-thiodisalicylate, phen = 1,10-phenanthroline) (2), and [Cu(sdp)(phen) · Cu(Hsdp)(phen)(CH₃COO)] · 3EtOH (sdp = 4,4′-sulfonyldiphenolate) (3) were prepared and structurally characterized. Complex 1β shows a one-dimensional coordination framework constructed from bridges between Zn(II) centers with two ligands. Complex 2 is a monomeric complex, which assembles by π–π interactions. Complex 3 shows a unique two-dimensional coordination framework that is constructed from two Cu(II) centers, sdp, and Hsdp. The redox properties of these three complexes were characterized by solid-state cyclic voltammetry. Complexes 1β and 3 show irreversible reduction waves because of the reduction of their sulfone sites. Complex 2 shows an irreversible oxidation wave because of oxidation of the sulfide site.