Hole-burning spectroscopy and relaxation dynamics of amorphous solids at low temperatures

The magnitude and temperature dependence of most of the properties of amorphous solids are anomalous at very low temperatures ( less, similar1 Kelvin). Phonon-assisted tunneling of a distribution of glassy bistable configurations, or two-level systems, can account for these anomalies. A unified understanding of the low-temperature properties is required for an understanding of the glassy state. Persistent nonphotochemical hole burning of impurity optical transitions allows a glass state to be produced that is thermally inaccessible to the preburn state, and that allows the probing of tunneling dynamics on time scales that range between picoseconds and days. These data combined with recently obtained distribution functions for the two-level systems offer new insights into the tunneling dynamics.     

水分含量对玉米淀粉颗粒结晶度的影响

 应用X-射线衍射方法对不同水分含量的玉米淀粉颗粒的结晶度进行了研究。只有在玻璃态情况下,淀粉的无定型区域才产生X-射线衍射图样,衍射峰的强度、面积在某种程度上依赖于淀粉的含水量。玉米淀粉颗粒的X-射线衍射图形是由两部分组成的:微晶区域和无定型区域。随着水分含量的增加,样品的结晶度从小到大,并达到一个平衡值(约45%)。室温下,当水分含量处于低水平时(小于11.25%),玉米淀粉颗粒中的无定型区域处于玻璃态,衍射图形显示的是微晶区域和无定型区域两部分的衍射图形的综合。当水分含量处于较高水平时(大于18.55%),淀粉颗粒中的无定型区域处于橡胶态,其X-射线衍射图形仅由微晶区域形成。在较低水分含量时(小于18.55%),由于塑化作用的影响,增大含水量会导致更多的微晶的形成。当水分含量超过18.55%之后,再增大水分,就会导致微晶片层和剩余的无定型片层的同时分解。     

Is the fragility of a liquid embedded in the properties of its glass?

When a liquid is cooled below its melting temperature, it usually crystallizes. However, if the quenching rate is fast enough, the system may remain in a disordered state, progressively losing its fluidity upon further cooling. When the time needed for the rearrangement of the local atomic structure reaches approximately 100 seconds, the system becomes "solid" for any practical purpose, and this defines the glass transition temperature Tg. Approaching this transition from the liquid side, different systems show qualitatively different temperature dependencies of the viscosity, and accordingly they have been classified by introducing the concept of "fragility." We report experimental observations that relate the microscopic properties of the glassy phase to the fragility. We find that the vibrational properties of the glass well below Tg are correlated with the fragility value. Consequently, we extend the fragility concept to the glassy state and indicate how to determine the fragility uniquely from glass properties well below Tg.     

Single crystals of linear polyethylene crystallized from the glass

Isolated single crystals of polyethylene have been crystallized from the glassy state by annealing uniformly thick films of amorphous linear polyethylene just above their glass transition temperature. In agreement with previous results for polycarbonate, substantial molecular mobility at the glass transition temperature is.     

Short-and Intermediate-Range Structural Ordering in Glassy Boron Oxide

Ordering at short-length scales is a universal feature of the glassy state. Experiments on boron oxide and other materials indicate that ordering on mesoscopic-length scales may also be universal. The high-resolution nuclear magnetic resonance (NMR) measurements of oxygen in boron oxide glass presented here provide evidence for structural units responsible for ordering on short- and intermediate-length scales. At the molecular level, planar BO(3/2) units accounted for the local ordering. Oxygen-17 NMR spectra resolved detailed features of the inclusion of these units in boroxol rings, oxygen bridging two rings, and oxygen shared between two nonring BO(3/2) units. On the basis of these and corroborative boron-11 NMR and scattering results, boron oxide glass consists of domains that are rich or poor in boroxol rings; these domains are proposed to be the structural basis of intermediate-range order in glassy boron oxide.     

Disordered materials: a survey of amorphous solids

A brief historical perspective and a review of the current research on amorphous or glassy materials are presented. Glass formation by natural processes and by laboratory synthesis techniques is described. Recent efforts to characterize and model the atomic scale structure of amorphous phases are surveyed. The relation between amorphous and liquid states is emphasized in a discussion of thermodynamics and kinetics. The topic of crystal-to-glass transformation in the solid state and the related issue of crystal stability and melting are discussed.     

解冻方法对冷藏部分玻璃态西兰花品质的影响

为获得高品质的速冻蔬菜,采用微波解冻、高静水压解冻、真空解冻和空气解冻4种方法,分析不同解冻方法对冷藏部分玻璃态西兰花解冻品质的影响,结果表明:微波解冻法、高静水压解冻法解冻时间短,分别为1.8 min和1.1 min,而且解冻复水性好,汁液流失少、VC损失少;同时明确了微波解冻时采用功率420 W和高静水压解冻时采用压强 50～150 MP解冻的西兰花品质的最佳.     

不同含水率速生杨木DMA图谱分析及应用

采用动态热机械分析仪对绝干、6％、12％、18％、30％、50％、100％和水饱和8种含水率速生杨木试件进行了动态黏弹性分析.动态力学分析参数为:温度扫描范围35～ 350℃,升温速度5℃·min-1,测量频率10Hz.储能模量的变化表明:各含水率试件在整个扫描温度范围内均出现2个明显的弹性转变过程,完成次级弹性转变的...     

Colloidal jamming at interfaces: a route to fluid-bicontinuous gels

Colloidal particles or nanoparticles, with equal affinity for two fluids, are known to adsorb irreversibly to the fluid-fluid interface. We present large-scale computer simulations of the demixing of a binary solvent containing such particles. The newly formed interface sequesters the colloidal particles; as the interface coarsens, the particles are forced into close contact by interfacial tension. Coarsening is markedly curtailed, and the jammed colloidal layer seemingly enters a glassy state, creating a multiply connected, solidlike film in three dimensions. The resulting gel contains percolating domains of both fluids, with possible uses as, for example, a microreaction medium.     

Controlled deposition, soft landing, and glass formation in nanocluster-surface collisions

Molecular dynamics simulations have been used to investigate the dynamics and redistribution of energy during the impact of a nanocrystal with adsorbed liquid films. Although impact of a 32-molecule NaCl cluster on a solid surface at 3 kilometers per second leads to melting, disordering, fragmentation, and rebounding, the same size cluster colliding with a liquid neon film transfers its energy efficiently to the liquid for a controlled soft landing. Impact on a higher density film (argon) leads to rapid attenuation of the cluster velocity, accompanied by fast heating. Subsequent disordering, melting, and fast cooling by evaporation of argon quench the cluster to a glassy state. These results suggest a method for the controlled growth of nanophase materials.     

The elusive Bose metal

The conventional theory of metals is in crisis. In the past 15 years, there has been an unexpected sprouting of metallic states in low-dimensional systems, directly contradicting conventional wisdom. For example, bosons are thought to exist in one of two ground states: condensed in a superconductor or localized in an insulator. However, several experiments on thin metal-alloy films have observed that a metallic phase disrupts the direct transition between the superconductor and the insulator. We analyze the experiments on the insulator-superconductor transition and argue that the intervening metallic phase is bosonic. All relevant theoretical proposals for the Bose metal are discussed, particularly the recent idea that the metallic phase is glassy. The implications for the putative vortex-glass state in the copper oxide superconductors are examined.     

lnterferometric Examination of Small (Glassy Spherules and Related Objects in a 5-Graml Lunar Dust Sample

Over two hundred spherules and cylinders were extracted from the lunar dust sample. Sizes ranged from 0.7 to 0.03 millimeters, and most were shiny glassy objects, which were studied by interferometry. This study reveals very high spcular feflection, frequentperfect sphericity, and clear evidence n some objects of micracking and microchipping. Many spheres were once projectiles. Some have inpacted in free flight with much smaller pices of rocky material, which embedded in the surface. It is conjectured that the glassy spherules originated as a gas-blown shower from a pool of molten glass.     

Organic glasses with exceptional thermodynamic and kinetic stability

Vapor deposition has been used to create glassy materials with extraordinary thermodynamic and kinetic stability and high density. For glasses prepared from indomethacin or 1,3-bis-(1-naphthyl)-5-(2-naphthyl)benzene, stability is optimized when deposition occurs on substrates at a temperature of 50 K below the conventional glass transition temperature. We attribute the substantial improvement in thermodynamic and kinetic properties to enhanced mobility within a few nanometers of the glass surface during deposition. This technique provides an efficient means of producing glassy materials that are low on the energy landscape and could affect technologies such as amorphous pharmaceuticals.     

Ultrapermeable, reverse-selective nanocomposite membranes

Polymer nanocomposites continue to receive tremendous attention for application in areas such as microelectronics, organic batteries, optics, and catalysis. We have discovered that physical dispersion of nonporous, nanoscale, fumed silica particles in glassy amorphous poly(4-methyl-2-pentyne) simultaneously and surprisingly enhances both membrane permeability and selectivity for large organic molecules over small permanent gases. These highly unusual property enhancements, in contrast to results obtained in conventional filled polymer systems, reflect fumed silica-induced disruption of polymer chain packing and an accompanying subtle increase in the size of free volume elements through which molecular transport occurs, as discerned by positron annihilation lifetime spectroscopy. Such nanoscale hybridization represents an innovative means to tune the separation properties of glassy polymeric media through systematic manipulation of molecular packing.     

用CONE法研究ULDM的阻燃特性

采用硼、氮-磷、硅和卤素系4种组分复合的无机阻燃剂制备难燃超轻质木纤维发泡材料(ULDM),通过锥形量热仪(CONE)法对超轻质木纤维发泡材料独特的燃烧热解特点、燃烧过程的热释放及阻燃剂各组分协效作用进行研究。结果表明,超轻质木纤维发泡材料的燃烧热解有不同于其他木质材料的爆燃现象,放热集中且迅速,瞬间放热量高。经无机复合阻燃处理后的超轻质木纤维发泡材料有焰燃烧时间低于30 s,在火场高温中能够维持阴燃状态,燃烧热解进程缓和,放热平稳。证明了复合阻燃剂各组分可充分产生协效阻燃作用,硼系能迅速形成玻璃态隔离层,氮-磷系能促进脱水成炭,硅系能有效增强纤维和炭层热稳定性,卤素系能极大降低有效燃烧热。     

Chondrules: suggestion concerning the origin

The millimeter-sized, sometimes glassy spheroids called chondrules that occur abundantly in stony meteorites may have been produced by lightning in the primitive Laplaciantype nebula while earthy materials were condensing and collecting to form the asteroids and the terrestrial planets.     

Amorphous ice: density and reflectivity

Amorphous ice prepared under a wide range of conditions has a density, determined from its buoyancy in liquid oxygen, of 0.94+/-0.02 gram per cubic centimeter, the same as that of ordinary hexagonal ice, with no indication of the glassy superdense ice (2.32 grams per cubic centimeter) reported recently. The diffuse reflectivity shows a small increase as the ice crystallizes at 153 degrees K. This increase is followed by a much larger increase (probably associated with crystal growth) as the sample warms, and the reflectivity reaches a maximum well below the melting temperature. Although the ice deposits appear translucent, the specular reflectivity is low, thus indicating a dull rather than a glassy surface.     

Molecular cell biology. A powerhouse rises in reborn Dresden

Two years in the making, a new Max Planck Institute is about to open its doors to scores of talented scientists--many from rival Heidelberg. Next month, the Max Planck Society's Institute of Molecular Cell Biology and Genetics will open its glassy new headquarters in Dresden.     

DDDMAC合成中胺值的测定

在季铵盐的合成中，用非水电位滴定法来测定胺值，采用铂电极代替玻璃电极为指示电极获得满意的结果。     

3种常绿阔叶植物越冬期间叶片水分及可溶性糖的动态变化

该文研究了卫矛科3种常绿阔叶植物在保定越冬期间叶组织水分及可溶性糖、淀粉的动态变化。结果表明,随着越冬进程,叶组织含水量呈下降趋势,而水分饱和亏缺,束缚水/自由水逐渐增大,温度达最低后这些指标开始恢复。越冬期间3种植物细胞中可溶性糖含量均呈现先上升后下降的趋势;而可溶性淀粉变化趋势与其相反。水分含量及可溶性糖,淀粉季节性动态变化与植物的抗寒性发育及越冬适应性具有高度一致性。文中对所测指标在植物越冬期间的生理意义给予了探讨。