有机硅改性丙烯酸环氧树脂的透光性及其耐候性研究

采用自由基溶液共聚合和溶胶-凝胶法制备了有机硅改性丙烯酸酯环氧树脂有机/无机杂化材料。结果表明,随着TEOS含量的增大,杂化材料在可见光区域的透光率有所降低,耐光老化性相应提高。     

On the possibility of existence of η5-π-complexes of C60 fullerene: π-complexes with silicon

Qualitative estimates of possibility of the formation of fullerene ⁵--complexes have been carried out by the MNDO/PM3 method. It was shown, as exemplified by the C₆₀ cluster, that the introduction of five univalent functional groups R (R = H, Cl, Br) to -positions of a separate pentagon of C₆₀ with the formation of [R₅C₆₀]^– anions results in a pronounced increase in the -electron density on the atoms of this five-membered cycle and more favorable conditions for the formation of -bonds with the ⁵-ligand. The nature of the interaction between the atoms of the separate cycle in [R₅C₆₀]^– anion and ⁵-ligand was analyzed by the example of hypothetical sandwich systems R₅C₆₀SiCp. Half-sandwich complexes R₅C₆₀SiX (X = H, Cl) were also investigated. The local energy minima were found on the potential energy surfaces (PES) of systems R₅C₆₀SiCp and R₅C₆₀SiX with C_5p symmetry. These systems transform barrirlessly into q5-7E-complexes with the angular structure if the symmetry restrictions are removed. The most favorable conditions for ⁵--complexes of R₅C₆₀ to form are realized for R = H. The results obtained were compared to those of semiempirical and nonempirical calculations of bis (cyclopentadienyl) silicon.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2422–2429, October, 1996.     

Fatigue crack propagation and related failure in modified,andhydride-cured epoxy resins

The fatigue crack propagation (FCP) of neat and modified, anhydridecured epoxy resin (EP) was studied in tensile-tensile mode at ambient temperature. As modifiers, liquid carboxyl-terminated acrylonitrile-butadiene (CTBN) and silicon rubber (SI) dispersions were used. The latter modifier in a defined particle size distribution was produced by a special latex technology, whereas the former developed in situ in the EP by phase separation during curing. The dispersion-type morphologies of the EPs were characterized by using polished sections and viewing them in a scanning electron microscope (SEM). The resulting frequency distribution curves were compared with those analyzed from fatigue fracture surfaces. Probable failure mechanisms were also studied by SEM-fractography.Both modifiers improved the resistance to FCP by shifting the curves to higher stress intensity factor ranges (K) in relation to the reference curve determined for the neat EP-matrix. The failure mechanisms, summarized also schematically, differed basically for the various modifiers. According to this, rubber-induced cavitation and shear yielding of the matrix seemed to be dominant for CTBN, which did not affect the principal crack plane. In contrast to this, crack bifurcation, branching and, hence, a forced deviation in the fatigue crack path induced by debonded SI-particles in the EP-matrix were concluded for the SI modifier. The common use of both modifiers yielded a positive synergistic effect due to the superposition of the above failure mechanisms.Dedicated to the 60th birthday of Prof. H. H. Kausch     

促进分类思想形成的“硅”教学设计

以含硅材料的主要成分为分类依据,对“无机非金属材料的主角--硅”第1课时进行了教学设计。旨在以含硅材料为载体,在落实“硅及其化合物”知识与技能目标过程中,促进学生分类方法和分类思想的形成,从而促进学生对“硅为什么是无机非金属材料的主角”的理解。     

Solar Water Splitting with a Hydrogenase Integrated in Photoelectrochemical Tandem Cells

Hydrogenases (H₂ases) are benchmark electrocatalysts for H₂ production, both in biology and (photo)catalysis in vitro. We report the tailoring of a p‐type Si photocathode for optimal loading and wiring of H₂ase through the introduction of a hierarchical inverse opal (IO) TiO₂ interlayer. This proton‐reducing Si|IO‐TiO₂|H₂ase photocathode is capable of driving overall water splitting in combination with a photoanode. We demonstrate unassisted (bias‐free) water splitting by wiring Si|IO‐TiO₂|H₂ase to a modified BiVO₄ photoanode in a photoelectrochemical (PEC) cell during several hours of irradiation. Connecting the Si|IO‐TiO₂|H₂ase to a photosystem II (PSII) photoanode provides proof of concept for an engineered Z‐scheme that replaces the non‐complementary, natural light absorber photosystem I with a complementary abiotic silicon photocathode.     

A Fluorooxosilicophosphate with an Unprecedented SiO2F4 Species

The large number and structural beauty of silicates are largely due to the variety of connection mode of SiO₄ tetrahedra. SiO₆ and SiF₆ octahedra are also known and give rise for structural versatility of inorganic silicates. However, to date, the crystal structure of inorganic fluorooxosilicates with oxofluoride SiO_xF_4?x or SiO_xF_6?x species are unknown. Now, fluorine was successfully introduced into the silicophosphates, and the first fluorooxosilicophosphate K₄Si₃P₂O₇F₁₂ with an unprecedented SiO₂F₄ species was synthesized. The existence of Si?F bonds was verified by comprehensively experimental and theoretical work. Using ab initio and bond valence calculations, the oxofluoride SiO_xF_6?x species is shown to be stable when oxygen atoms connect to other atoms with strong covalent interactions. This work will contribute to the structural diversity of silicate chemistry by the exploration of the new fluorooxosilicates.     

Bench‐Stable Stock Solutions of Silicon Grignard Reagents: Application to Iron‐ and Cobalt‐Catalyzed Radical C(sp3)–Si Cross‐Coupling Reactions

A robust method for the preparation of silicon‐based magnesium reagents is reported. The MgBr₂ used in the lithium‐to‐magnesium transmetalation step is generated in situ from 1,2‐dibromoethane and elemental magnesium in hot THF. No precipitation of MgBr₂ occurs in the heat, and transmetalation at elevated temperature leads to homogeneous stock solutions of the silicon Grignard reagents that are stable and storable in the fridge. This method avoids the preparation of silicon pronucleophiles such as Si?Si and Si?B reagents. The new Grignard reagents were applied to unprecedented iron‐ and cobalt‐catalyzed cross‐coupling reactions of unactivated alkyl bromides. The functional‐group tolerance of these magnesium reagents is excellent.     

Incorporating Si3N4 into PEEK to Produce Antibacterial,Osteocondutive, and Radiolucent Spinal Implants

Polyetheretherketone (PEEK) is a popular polymeric biomaterial which is primarily used as an intervertebral spacer in spinal fusion surgery; but it is developed for trauma, prosthodontics, maxillofacial, and cranial implants. It has the purported advantages of an elastic modulus which is similar to native bone and it can be easily formed into custom 3D shapes. Nevertheless, PEEK's disadvantages include its poor antibacterial resistance, lack of bioactivity, and radiographic transparency. This study presents a simple approach to correcting these three shortcomings while preserving the base polymer's biocompatibility, chemical stability, and elastic modulus. The proposed strategy consists of preparing a PEEK composite by dispersing a minor fraction (i.e., 15 vol%) of a silicon nitride (Si₃N₄) powder within its matrix. In vitro tests of PEEK composites with three Si₃N₄ variants—β‐Si₃N₄, α‐Si₃N₄, and β‐SiYAlON—demonstrate significant improvements in the polymer's osteoconductive versus SaOS‐2 cells and bacteriostatic properties versus gram‐positive Staphylococcus epidermidis bacteria. These properties are clearly a consequence of adding the bioceramic dispersoids, according to chemistry similar to that previously demonstrated for bulk Si₃N₄ ceramics in terms of osteogenic behavior (vs both osteosarcoma and mesenchymal progenitor cells) and antibacterial properties (vs both gram‐positive and gram‐negative bacteria).     

Electrochemical Detection of Acetaminophen with Silicon Nanowires

Acetaminophen (APAP) is an antipyretic, analgesic agent, the overdose of which during medical treatment poses a risk for liver failure. Hence, it is important to develop methods to monitor physiological APAP levels to avoid poisoning. Here, we report an efficient, selective electrochemical APAP sensor made from depositing silicon nanowires (SiNWs) onto glassy carbon electrodes (GCEs). Electrocatalytic activity of the SiNW/GCE sensors was monitored under varying pH and concentrations of APAP using cyclic voltammetry (CV) and chronoamperometry (CA). CV of the SiNWs at 0.5 to 13 mmol dm⁻³ APAP concentrations was used to determine the oxidation and reduction potentials of APAP. The selective detection of APAP was then demonstrated using CA at +0.568 V vs Ag/AgCl, where APAP is fully oxidized, in the 0.01 to 3 mmol dm⁻³ concentration range with potentially‐interfering analytes. The SiNW sensor has the ability to detect APAP well within the detection limits for APAP toxicity, showing promise as a practical biosensor.     

Reversible CO2 Addition to a Si=O Bond and Synthesis of a Persistent SiO2–CO2 Cycloadduct Stabilized by a Lewis Donor–Acceptor Ligand

The donor‐stabilized sila‐β‐lactone 1 reacts with CO₂ via a remarkable reversible [2+2]‐cycloaddition reaction to form the spiro‐cyclic silicon carbonate derivative 2 . Furthermore, photolysis of 2 under pressure of CO₂ affords the first persistent SiO₂–CO₂ cycloadduct 3 , presenting a Si₂O₄‐like structure, which is stabilized by a Lewis donor–acceptor type ligand. As predicted by theoretical calculations, in marked contrast to the thermodynamically stable SiO₂ dimer, the SiO₂–CO₂ mixed cycloadduct 3 is labile and readily releases CO₂.