New strong cement materials: chemically bonded ceramics

New cements developed in recent years have strengths that are greater by an order of magnitude than those of conventional hydraulic cements. These low-temperature materials, whose strengths approach those of many traditional high-temperature ceramics, are termed chemically bonded ceramics. The different routes to generating strong cementitious materials, including warm pressing, chemical modification, high-shear mixing with polymer additions, and the making of fiber and particulate composites, are reviewed. Strength, toughness, durability, impermeability, and abrasion resistance of these new materials have been greatly improved, as have certain electrical and acoustical properties.     

桦木单板/玻璃纤维复合材料声学振动性能的研究

目的面对我国乐器音板用材资源的严重不足,寻找新材料替代传统乐器木质音板用材是非常有必要的。方法本试验以玻璃纤维为增强材料,桦木单板为基体,按照单板层积材结构设计制备桦木单板/玻璃纤维复合材料。通过对玻璃纤维复合材料声学振动性能检测分析,探究玻璃纤维布的不同铺放位置和铺放层数对复合材料声学振动性能的影响。结果用1层玻璃纤维布铺放在表层单板下的复合材料A的比动弹性模量和E/G值分别为22.20GPa和16.55,比用1层玻璃纤维布铺放在芯层单板单侧的复合材料B分别高了8.7%、17.8%。用2层玻璃纤维布分别铺放在上下表层单板内的复合材料C的比动弹性模量和E/G值分别为25.04GPa和17.04,比用玻璃纤维布铺放在芯层单板两侧的复合材料D高了7.5%和18.0%。纤维铺放位置对声辐射品质常数和声阻抗的影响较小。玻璃纤维布的层数与复合材料的声学振动性能不成线性关系,铺放2层玻璃纤维布的复合材料具有较高的比动弹性模量和E/G值。玻璃纤维布铺放3层和4层的复合材料的比动弹性模量和E/G比铺放2层的都小。随着玻璃纤维布层数的增加,声辐射品质常数呈减小的趋势。通过综合评分法分析发现:玻璃纤维布铺放在表层单板下的复合材料综合评分值都高于铺放在靠近芯层单板的复合材料,铺放2层玻璃纤维布的复合材料的综合评分值达到最大。结论玻璃纤维布铺放在表层单板下的复合材料声学振动性能优于纤维布铺放在靠近芯层单板的复合材料。铺放2层玻璃纤维布的复合材料C的声学振动性能达到最好。尽管复合材料C的E/G值约为西加云杉的80%,但比动弹性模量和西加云杉的相接近,说明桦木单板/玻璃纤维复合材料具有替代传统木质音板用材的可能性。      

Block copolymer assembly via kinetic control

Block copolymers consist of two or more chemically different polymer segments, or blocks, connected by a covalent linkage. In solution, amphiphilic blocks can self-assemble as a result of energetic repulsion effects between blocks. The degree of repulsion, the lengths of the block segments, and the selectivity of the solvent primarily control the resultant assembled morphology. In an ideal situation, one would like to be able to alter the morphology that forms without having to change the chemistry of the block copolymer. Through the kinetic manipulation of charged, amphiphilic block copolymers in solution, we are able to generate different nanoscale structures with simple block copolymer chemistry. The technique relies on divalent organic counter ions and solvent mixtures to drive the organization of the block copolymers down specific pathways into complex one-dimensional structures. Block copolymers are increasingly used as templating materials; thus, the ability to control the formation of specific patterns and structures is of growing interest and applicability.     

Method of vital staining of the central nervous system and organs of animals for determining their functional state in a toxicological assessment of polymer materials

Data are given on a toxicological investigation of polymer building materials with the use of a physicochemical method of vital staining of the central nervous system and organs in vivo of rat pups for determining denaturation changes of proteins and their physiological condition. The sanitary chemical evaluation of polymer building materials is performed by the gas chromatography method.     

Computational design of self-assembling protein nanomaterials with atomic level accuracy

We describe a general computational method for designing proteins that self-assemble to a desired symmetric architecture. Protein building blocks are docked together symmetrically to identify complementary packing arrangements, and low-energy protein-protein interfaces are then designed between the building blocks in order to drive self-assembly. We used trimeric protein building blocks to design a 24-subunit, 13-nm diameter complex with octahedral symmetry and a 12-subunit, 11-nm diameter complex with tetrahedral symmetry. The designed proteins assembled to the desired oligomeric states in solution, and the crystal structures of the complexes revealed that the resulting materials closely match the design models. The method can be used to design a wide variety of self-assembling protein nanomaterials.     

Mussel-inspired surface chemistry for multifunctional coatings

We report a method to form multifunctional polymer coatings through simple dip-coating of objects in an aqueous solution of dopamine. Inspired by the composition of adhesive proteins in mussels, we used dopamine self-polymerization to form thin, surface-adherent polydopamine films onto a wide range of inorganic and organic materials, including noble metals, oxides, polymers, semiconductors, and ceramics. Secondary reactions can be used to create a variety of ad-layers, including self-assembled monolayers through deposition of long-chain molecular building blocks, metal films by electroless metallization, and bioinert and bioactive surfaces via grafting of macromolecules.     

混凝土小型空心砌块砌体房屋墙体裂缝的防治

近年来，新型墙体材料混凝土小型空心砌块在住宅工程中得到了越来越多的应用．然而，混凝土小型空心砌块建筑墙体的裂缝问题制约着混凝土小型空心砌块建筑的发展．分析了混凝土小型空心砌块墙体裂缝的特征及产生的原因，从材料本身、设计及施工方面提出了防治裂缝的有效措施．     

Bioinspired design and assembly of platelet reinforced polymer films

Although strong and stiff human-made composites have long been developed, the microstructure of today's most advanced composites has yet to achieve the order and sophisticated hierarchy of hybrid materials built up by living organisms in nature. Clay-based nanocomposites with layered structure can reach notable stiffness and strength, but these properties are usually not accompanied by the ductility and flaw tolerance found in the structures generated by natural hybrid materials. By using principles found in natural composites, we showed that layered hybrid films combining high tensile strength and ductile behavior can be obtained through the bottom-up colloidal assembly of strong submicrometer-thick ceramic platelets within a ductile polymer matrix.     

DNA-templated carbon nanotube field-effect transistor

The combination of their electronic properties and dimensions makes carbon nanotubes ideal building blocks for molecular electronics. However, the advancement of carbon nanotube-based electronics requires assembly strategies that allow their precise localization and interconnection. Using a scheme based on recognition between molecular building blocks, we report the realization of a self-assembled carbon nanotube field-effect transistor operating at room temperature. A DNA scaffold molecule provides the address for precise localization of a semiconducting single-wall carbon nanotube as well as the template for the extended metallic wires contacting it.     

Crystallography of the hexagonal ferrites

The hexagonal ferrites form an unusual group of complex, ferrimagnetic oxides embodying some 60 known crystal structures. These include phases for which the structural unit cell is larger than that in any known inorganic materials. The various hexagonal ferrite modifications fall into two distinct structural series, each formed by the ordered interlayering (stacking) of two discrete building blocks; these blocks stack along the c crystallographic axis in varying ratios and varying permutations to form strictly coherent, reproducible crystal structures. This mixed-layering aspect of the hexagonal ferrites permits direct, visual observation of the sequence of their subunit-cell stacking elements, after etching, by means of electron microscopy. The sequence of stacked blocks in such structures constitutes the only information lacking for a complete, three-dimensional structure determination. Direct access to this information provides an immediate, unique solution of the crystal structure problem in each case and thereby avoids the dilemmas of a classical diffraction approach to such large unit cells. Ferrite structures with hexagonal c dimensions of 1455 and 1577 angstroms have been uniquely solved by direct electron microscopic readout of surface etch features. One must exercise caution, however, in generalizing these findings to other materials. The method is successful in the case of the hexagonal ferrites because these are mixed-layer structures, wherein the building blocks react at different rates to a specific etchant. Mixed-layer systems are not uncommon in crystallography, and it is likely that similar techniques can be developed for other such materials. Regardless of the validity of this prognosis, however, it is quite evident that high-resolution replica electron microscopy is a most promising tool for the direct observation of surface structure on an ultramicro scale. During the studies reported here replica resolution capability was improved to about 10 angstroms; final resolution is limited by the particle size of the platinum shadowing material. Careful control of experimental conditions during replica preparation or an alternate choice of shadowing material, or both, might reasonably improve the resolution by a factor of 2. This resolution is within the range of most unit cell dimensions and approaches interatomic distances in solid-state materials. The potential of such an experimental capability needs no elaboration.     

Materials for aesthetic, energy-efficient, and self-diagnostic buildings

It has become desirable to reduce the nonrenewable content and energy footprint of the built environment and to develop "smart buildings" that allow for inexpensive monitoring and self-diagnostic capabilities. Latest-generation embedded sensors, self-healing composites, and nanoscale and responsive materials may augur a time when buildings can substantially adjust to changing environmental and functional demands. However, faced with the legal liability resulting from unknown lifetime performance, designers and engineers have had little incentive to incorporate new material technologies into building designs. As efficiency issues become more acute, the potential for improvement in performance from new materials, together with partnerships between the materials science community and those entrusted with the design and engineering of the built environment, may offer real breakthroughs for the future.     

Freezing as a path to build complex composites

Materials that are strong, ultralightweight, and tough are in demand for a range of applications, requiring architectures and components carefully designed from the micrometer down to the nanometer scale. Nacre, a structure found in many molluscan shells, and bone are frequently used as examples for how nature achieves this through hybrid organic-inorganic composites. Unfortunately, it has proven extremely difficult to transcribe nacre-like clever designs into synthetic materials, partly because their intricate structures need to be replicated at several length scales. We demonstrate how the physics of ice formation can be used to develop sophisticated porous and layered-hybrid materials, including artificial bone, ceramic-metal composites, and porous scaffolds for osseous tissue regeneration with strengths up to four times higher than those of materials currently used for implantation.     

Detection of a deep 3-microm absorption feature in the spectrum of Amalthea (JV)

Near-infrared spectra of Jupiter's small inner satellites Amalthea and Thebe are similar to those of D-type asteroids in the 0.8- to 2.5-micrometer wavelength range. A deep absorption feature is detected at 3 micrometers in the spectra of the trailing side of Amalthea, which is similar to that of the non-ice components of Callisto and can be attributed to hydrous minerals. These surface materials cannot be explained if the satellite formed at its present orbit by accreting from a circumjovian nebula. Amalthea and Thebe may be the remnants of Jupiter's inflowing building blocks that formed in the outer part or outside of the circumjovian nebula.     

Dispersible exfoliated zeolite nanosheets and their application as a selective membrane

Thin zeolite films are attractive for a wide range of applications, including molecular sieve membranes, catalytic membrane reactors, permeation barriers, and low-dielectric-constant materials. Synthesis of thin zeolite films using high-aspect-ratio zeolite nanosheets is desirable because of the packing and processing advantages of the nanosheets over isotropic zeolite nanoparticles. Attempts to obtain a dispersed suspension of zeolite nanosheets via exfoliation of their lamellar precursors have been hampered because of their structure deterioration and morphological damage (fragmentation, curling, and aggregation). We demonstrated the synthesis and structure determination of highly crystalline nanosheets of zeolite frameworks MWW and MFI. The purity and morphological integrity of these nanosheets allow them to pack well on porous supports, facilitating the fabrication of molecular sieve membranes.     

Porous semiconductor chalcogenide aerogels

Chalcogenide aerogels based entirely on semiconducting II-VI or IV-VI frameworks have been prepared from a general strategy that involves oxidative aggregation of metal chalcogenide nanoparticle building blocks followed by supercritical solvent removal. The resultant materials are mesoporous, exhibit high surface areas, can be prepared as monoliths, and demonstrate the characteristic quantum-confined optical properties of their nanoparticle components. These materials can be synthesized from a variety of building blocks by chemical or photochemical oxidation, and the properties can be further tuned by heat treatment. Aerogel formation represents a powerful yet facile method for metal chalcogenide nanoparticle assembly and the creation of mesoporous semiconductors.     

Building programmable jigsaw puzzles with RNA

One challenge in supramolecular chemistry is the design of versatile, self-assembling building blocks to attain total control of arrangement of matter at a molecular level. We have achieved reliable prediction and design of the three-dimensional structure of artificial RNA building blocks to generate molecular jigsaw puzzle units called tectosquares. They can be programmed with control over their geometry, topology, directionality, and addressability to algorithmically self-assemble into a variety of complex nanoscopic fabrics with predefined periodic and aperiodic patterns and finite dimensions. This work emphasizes the modular and hierarchical characteristics of RNA by showing that small RNA structural motifs can code the precise topology of large molecular architectures. It demonstrates that fully addressable materials based on RNA can be synthesized and provides insights into self-assembly processes involving large populations of RNA molecules.     

三种环境材料复合对土壤水肥保持同步增效的影响

为研发基于功能互补的不同环境材料复合对土壤水分和氮磷肥保持增效的同步效应,本文选取保水剂(A)、腐植酸(B)和沸石(C),通过室内土柱模拟方法,采用正交实验设计,探究3种不同环境材料复合对土壤水分和氮磷肥保持同步增效的主次和不同目标的组合优化,最终获得提高土壤水分和土壤氮磷保持增效的最优组合,通过过程分析探讨不同环境材料对土壤水肥保持的效应机理。结果表明:3种环境材料复合对土壤水分和氮磷肥保持增效有明显效果,对水分保持和氮磷肥同步增效的最优组合为A3B3C2(即保水剂、腐植酸和沸石添加量为1.5、1.5 g·kg~(-1)和9.0 g·kg~(-1)),该组合相比CK的土壤水分淋出量减少3.5%,氮素淋出量减少12.1%,磷素淋出量增多65.5%;比较发现,沸石对土壤淋溶液p H和EC值影响最大,保水剂居中,腐植酸作用最小;3种环境材料的添加可增加土壤孔隙度,改善土壤团粒结构,具有改良土壤的效应。研究结果为新型肥料研发提供重要参考。     

Periodic mesoporous dendrisilicas

We report the synthesis of a new class of materials called periodic mesoporous dendrisilicas. They are prepared from dendrimers with trialkoxysilyl groups at the outmost shell. Dendrimers of various cores and numbers of shells are used. The dendrisilica synthesis is based on acid- or base-catalyzed hydrolysis of the trialkoxysilyl groups and subsequent template-directed condensation of the dendrimers into an ordered template-dendrisilica nanocomposite. The template can be removed with organic solvents, producing a periodic mesoporous dendrisilica whose pore walls consist of interconnected dendrimer building blocks.     

镁基复合材料储氢性能的研究

镁基储氢材料是目前该研究领域中的研究热点,镁基储氢合金研究较多,镁基储氢复合材料是研究的新点.笔者重点讨论了镁基储氢复合材料在储氢性能改善方面的问题.     

Interstellar chemistry recorded in organic matter from primitive meteorites

Organic matter in extraterrestrial materials has isotopic anomalies in hydrogen and nitrogen that suggest an origin in the presolar molecular cloud or perhaps in the protoplanetary disk. Interplanetary dust particles are generally regarded as the most primitive solar system matter available, in part because until recently they exhibited the most extreme isotope anomalies. However, we show that hydrogen and nitrogen isotopic compositions in carbonaceous chondrite organic matter reach and even exceed those found in interplanetary dust particles. Hence, both meteorites (originating from the asteroid belt) and interplanetary dust particles (possibly from comets) preserve primitive organics that were a component of the original building blocks of the solar system.