Alcohol-triggered silk fibroin hydrogels having random coil and β-turn structures enhanced for cytocompatible cell response

Alcohol additive is one of the stimulants that induces the fast gelation of silk fibroin solution. Based on our previous report, different alcohol types influence the gelation kinetic and the properties of resulting silk fibroin hydrogels. Here, the effects of alcohol concentrations on the silk fibroin gelation and cell response were reported. All fibroin hydrogels prepared with various alcohol additives showed cell biocompatibility, especially the fibroin hydrogel prepared with 10 wt % n-butanol. Results on the mechanical properties of hydrogels, n-butanol additive enhanced a higher compressive modulus up to ~ 22 times in comparison to non-alcoholic fibroin hydrogel. Fourier transform infrared analysis and peak deconvolution showed a possible formation of more β-turn linkage and random coil structure of fibroin segments in alcoholic fibroin hydrogel. So, the micro-segmental structure of fibroin hydrogel caused the higher compressive modulus, prolonged deformation of the hydrogels, and efficient cell growth on the fibroin hydrogel. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48731.     

Ferroelectric phase transition and electrical conduction mechanisms in high Curie-temperature PMN-PHT piezoelectric ceramics

Ferroelectric phase transition characteristic and electrical conduction mechanism of the high Curie-point (T_C) 0.15Pb(Mg_1/3Nb_2/3)O₃−0.4PbHfO₃−0.45PbTiO₃ (PMN-PHT) piezoelectric ceramics were studied by the temperature dependent Raman spectra and electrical properties. Sole first-order ferroelectric phase transition is demonstrated by the thermal hysteresis behavior of the temperature dependent dielectric constant and the dramatic drop of the derivative of inverse dielectric constant ξ= d(1/ε_r)/dT around T_C in the PMN-PHT ceramics. The temperature dependent Raman spectroscopy not only provides further evidence for the ferroelectric to paraelectric phase transition appearing around T_C in the PMN-PHT ceramics, but also reveals the successive phase symmetry changes of the polar nanoregions (PNRs), in which apparent anomalies appear in the Raman peaks' wavenumber, wavenumber distance, intensity, intensity ratio, and line width of some selected Raman modes upon heating. Typical sole cole-cole circle is obtained for the PMN-PHT ceramics in the temperature range of 440–560 °C, based on which the activation energy (E_a) of the electrical conduction is calculated being ~1.2 eV. Such low value of E_a indicates that the oxygen vacancies formed in the PHT-PMN ceramics induced by the evaporation of Pb during the sintering process dominate the high-temperature extrinsic electrical conduction.     

Effect of glassy bonding materials on the properties of LAS/SiC porous ceramics with near zero thermal expansion

Near zero thermal expansion porous ceramics were fabricated by using SiC and LiAlSiO₄ as positive and negative thermal expansion materials, respectively, bonded by glassy material. The coefficient of thermal expansion value of a desired porous composite can be easily controlled by choosing the appropriate ratios of the different phases. It was shown that some of LiAlSiO₄ was decomposed to LiAlSi₂O₆ and LiAlO₂, some of LiAlSiO₄ reacted with SiO₂ to form LiAlSi₂O₆ during sintering. With increasing the content of glassy materials, the reaction between LiAlSiO₄ and SiO₂ was accelerated. The Young's modulus increased due to the neck growth between the SiC grains. The 52.5 vol% LiAlSiO₄ (LAS)/SiC ceramics with ∼36% porosity had a combination of near zero coefficient of thermal expansion ∼0.39 × 10⁻⁶ K⁻¹ at room temperature and relatively high Young's modulus ∼59 GPa.     

Investigation the effect of B4C addition on properties of TZM alloy prepared by spark plasma sintering

TZM alloy is one of the most important molybdenum (Mo) based alloy which has a nominal composition containing 0.5–0.8 wt.% titanium (Ti), 0.08–0.1 wt.% zirconium (Zr) and 0.016–0.02 wt.% carbon (C). It is a possible candidate for high temperature applications in a variety of industries. However, the rapid oxidation of TZM alloys at high temperature in air is considered to be one of the drawback. In this study, TZM alloys with additions of 0–5 wt.% B₄C were prepared by spark plasma sintering (SPS) at 1420 °C utilizing 40 MPa pressure for 5 min under vacuum. The effects of B₄C addition on oxidation, densification behavior, microstructure, and mechanical properties were investigated. The TZM alloy with 5 wt.% B₄C have exhibited an approximately 66% reduction in mass loss under normal atmospheric conditions in oxidation tests made at 1000 °C for 60 min. And an increase from 1.9 GPa to 7.8 GPa has been determined in hardness of the alloy.     

Selective hydrogenation of 4-isobutylacetophenone over a sodium-promoted Pd/C catalyst

The effect of sodium promotion on the selective hydrogenation of 4-isobutylacetophenone, 4-IBAP, was investigated over a Pd/C catalyst. A precipitation and deposition method was used to prepare the catalyst, and sodium was promoted on the Pd/C catalyst via post-impregnation while varying the sodium content. The sodium-promoted Pd/C catalyst resulted in a significantly improved yield greater than 96% of the desired product, 1-(4-isobutylphenyl) ethanol (4-IBPE), compared with the non-patented literature results under a mild hydrogenation condition. A detailed hydrogenation network over the Pd/C catalyst was suggested. The reaction mechanism for the yield and selectivity enhancement of 4-IBPE induced-by the promoted Pd/C was elucidated in relation to the geometric and electronic effects of reactant molecules in the microporous support depending on the reaction steps.     

Fast microwave syntheses of fly ash based porous geopolymers in the presence of high alkali concentration

Microwave synthesis of porous fly ash geopolymers was achieved using a household microwave oven. Fly ash paste containing SiO₂ and Al₂O₃ component was mixed with sodium silicate (Na₂SiO₃) solutions at different concentrations of sodium hydroxide (NaOH) of 2, 5, 10, and 15 M, which were used as NaOH activators of geopolymerization. The mass ratio of Na₂SiO₃/NaOH was fixed at 2.5 with SiO₂/Al₂O₃ at 2.69. After the fly ash and alkali activators were mixed for 1 min until homogeneous, the geopolymer paste was cured for 1 min using household microwave oven at different output powers of 200, 500, 700, and 850 W. Porous geopolymers were formed immediately. Micro X-ray CT and SEM results showed that the porous structure of the geopolymers was developed at higher NaOH concentrations when using 850 W power of the microwave oven. These results derive from the immediate increase of the temperature in the geopolymer paste at higher NaOH concentrations, meaning that aluminosilicate bonds formed easily in the geopolymers within 1 min.     

Organic–inorganic nanomatrix structure and properties of related naturally occurring rubbery macromolecules

The outstanding mechanical properties of soft materials i.e. natural rubber are partly due to the organic–inorganic nanomatrix structure because numerous organic microparticles are dispersed in a small amount of an inorganic nanomatrix composed of inorganic nanoparticles and organic macromolecules. Here we form an organic–inorganic nanomatrix using graft-copolymerization of a vinyl monomer with an inorganic oxide precursor onto natural rubber particles with an average diameter of 1 μm dispersed in water. The inorganic oxide precursor is converted into inorganic oxide nanoparticles through hydrolysis and condensation, forming chemical linkages between natural rubber microparticles and inorganic oxide nanoparticles. Transmission electron microscopy indicates that the organic–inorganic nanomatrix is densely filled with inorganic oxide nanoparticles and the natural rubber microparticles are dispersed in the nanomatrix. This nanomatrix composite realizes both energetic elasticity and entropic elasticity of a soft material, opening a novel field of building block chemistry with respect to a pair of organic microparticles and inorganic nanoparticles.     

Analysis of composition homogeneity and polarization orientation of PZT submicron fibers by micro-Raman spectroscopy

Micro-Raman spectroscopy is a convenient tool to probe individual objects with a feature size on the submicron scale. The phase, composition, and orientation of Pb(Zr,Ti)O₃ fibers fabricated via hydrothermal processing have been characterized by this technique, with the working principles given in the paper. It is shown that the prepared PZT submicron fibers are of a tetragonal pervoskite phase, with Zr/(Zr + Ti) varying from 0.05 to 0.25. The spontaneous polarization has been confirmed to be along the length direction and one of its {1 0 0} planes parallel to the substrate plane.     

Cathodic reduction of the anodically formed zinc species as a contribution to the study of the potentiodynamic passivation of zinc in alkaline media

The cathodic part of the potentiodynamic curves obtained for upward-facing horizontal 99.9% zinc electrodes in KOH solutions 0.4, 1.0, 2.0 and 3.0 M and sweep rates in the range 1–100 mV s⁻¹ have been systematically analyzed in order to assign the possible species formed and contribute to the study of the potentiodynamic passivation of Zn in alkaline media. The anodic limit of the potentiodynamic cycles was changed and set for significant points of the total curve (between hydrogen and oxygen evolution). Also, the anodic sweep was interrupted at the potentials corresponding to the anodic limit and the cathodic sweep applied immediately from a potential near that of zero current of the cathodic half-cycle. Only two cathodic peaks have been found for the non-interrupted cycles. The assignation of peaks according to the equilibrium potentials of the reduction of the possible species implied, ie Zn(OH)²⁻₄, Zn(OH)₂ and ZnO, is not possible because local pH changes are expected and the zincate concentration near the electrode is unknown. The peak placed at more positive potentials for KOH concentrations 0.4 and 1.0 M is assigned to zincate and that at more negative potentials, to the reduction of the film. Just the opposite assignation has been found for 2.0 and 3.0 M KOH solutions. The experimental results can be interpreted assuming that the product formed at the passivation potential consists of the same chemical species as those corresponding to the first anodic peak, probably Zn(OH)₂ or hydrated ZnO. From calculating the maximum film thickness according to the charge passed and taking into account the recent theoretical analysis made by Chang and Prentice, it is concluded that the direct formation of ZnO on the electrode at the passivation potential as a consequence of local pH changes is not probable.