The life and death of "Bare" viscous bubbles

Air bubbles collect and explode at the surface of many viscous liquids, as observed with polymer foams, in glass furnaces, and during volcanic eruptions. The liquid film separating the bubble from bulk air can have a long lifetime (if it is viscous) even if it is not protected by a surfactant. These "bare" films display unusual dynamic behaviors in drainage and rupture. Two different model systems were studied: a polymer melt (silicone oil) and a molten (borosilicate) glass of comparable viscosity. Although the two systems differ greatly in their relaxation time, they are described by the same set of laws, which can be understood from a relatively simple hydrodynamic model.     

Aligned multiwalled carbon nanotube membranes

An array of aligned carbon nanotubes (CNTs) was incorporated across a polymer film to form a well-ordered nanoporous membrane structure. This membrane structure was confirmed by electron microscopy, anisotropic electrical conductivity, gas flow, and ionic transport studies. The measured nitrogen permeance was consistent with the flux calculated by Knudsen diffusion through nanometer-scale tubes of the observed microstructure. Data on Ru(NH3)6(3+) transport across the membrane in aqueous solution also indicated transport through aligned CNT cores of the observed microstructure. The lengths of the nanotubes within the polymer film were reduced by selective electrochemical oxidation, allowing for tunable pore lengths. Oxidative trimming processes resulted in carboxylate end groups that were readily functionalized at the entrance to each CNT inner core. Membranes with CNT tips that were functionalized with biotin showed a reduction in Ru(NH3)6(3+) flux by a factor of 15 when bound with streptavidin, thereby demonstrating the ability to gate molecular transport through CNT cores for potential applications in chemical separations and sensing.     

Ordered metal nanohole arrays made by a two-step replication of honeycomb structures of anodic alumina

A highly ordered metal nanohole array (platinum and gold) was fabricated by a two-step replication of the honeycomb structure of anodic porous alumina. Preparation of the negative porous structure of porous alumina followed by the formation of the positive structure with metal resulted in a honeycomb metallic structure. The metal hole array of the film has a uniform, closely packed honeycomb structure approximately 70 nanometers in diameter and from 1 to 3 micrometers thick. Because of its textured surface, the metal hole array of gold showed a notable color change compared with bulk gold.     

多孔介质的润湿性对聚驱稠油微宏观效率的影响

岩石表面的润湿性影响聚合物微观和宏观驱油效率。采用可视化微观模型和微观照相技术研究了强水湿和油湿多孔介质下聚合物微观驱油效率和驱替机理。分析了束缚水与稠油分别在两种润湿介质下的微观形态和分布对聚合物的吸附、滞留,连续性和非连续性流动,驱替前缘以及洗油效率的影响。微观模型实验结果表明,在水湿环境,地层水趋向分布于岩石骨架表面并在孔壁附近形成较厚的水膜,聚合物趋于附着在孔壁处,在这些区域聚合物的洗油效率较高;在油湿环境,束缚水主要以非连续相分布在孔隙介质中,聚合物溶液发生咬断效应,原油吸附在孔喉处,聚合物只能部分扫除原油,乳液的形成能辅助聚合物溶液驱替油相。聚合物在水湿介质的微观驱油效率明显高于油湿介质。岩心流动实验结果与微观模型分析一致,相同浓度的聚合物溶液在强水湿岩心前缘突破所需的时间长于油湿岩心,突破前缘更规整,水湿岩心和油湿岩心的水驱采出程度分别为21.5%OOIP和15%OOIP。聚合物在油湿岩心的“门槛”黏度较大。聚合物黏度为500 mPa·s时,水驱后水湿岩心和油湿岩心的原油采收率增幅分别为23%OOIP和17%OOIP。     

Reticulated nanoporous polymers by controlled polymerization-induced microphase separation

Materials with percolating mesopores are attractive for applications such as catalysis, nanotemplating, and separations. Polymeric frameworks are particularly appealing because the chemical composition and the surface chemistry are readily tunable. We report on the preparation of robust nanoporous polymers with percolating pores in the 4- to 8-nanometer range from a microphase-separated bicontinuous precursor. We combined polymerization-induced phase separation with in situ block polymer formation from a mixture of multifunctional monomers and a chemically etchable polymer containing a terminal chain transfer agent. This marriage results in microphase separation of the mixture into continuous domains of the etchable polymer and the emergent cross-linked polymer. Precise control over pore size distribution and mechanical integrity renders these materials particularly suited for various advanced applications.     

Large-area three-dimensional molecular ordering of a polymer brush by one-step processing

Rational molecular design and processing, enabling large-area molecular ordering, are important for creating high-performance organic materials and devices. We show that, upon one-step hot-pressing with uniaxially stretched Teflon sheets, a polymer brush carrying azobenzene-containing mesogenic side chains self-assembles into a freestanding film, where the polymer backbone aligns homeotropically to the film plane and the side chains align horizontally. Such an ordered structure forms through translation of a one-dimensional molecular order of the Teflon sheet and propagates from the interface macroscopically on both sides of the film. The resultant wide-area bimorph configuration allows the polymer film to bend rapidly and reversibly when the azobenzene units are photoisomerized. The combination of polymer brushes with hot-pressing and Teflon sheets provides many possibilities in designing functional soft materials.     

木本植物木质部栓塞修复机制的探讨

该文用几种木本植物茎做切片实验,探讨木本植物木质部栓塞的修复机制.研究发现:当脱水样品被复水后,在表面张力的作用下,其管状细胞中的空气立即回缩,形成长形或球形气泡;此后,在比较小的管状细胞中的气泡逐渐缩小直到消失;大的管状细胞中的气泡最初会伸长,然后缩短,直到消失;胞外球形泡也会一个接一个地出现; 除了来自细胞的切破处,这些胞外球形泡还来自木射线的横断面,其中小些的会缩小,大个的会长大. 这些现象说明,样品中的气体并没有如以往所云,溶解到水中之后进入大气.作者认为,空气也许从短半径气泡移动到了长半径气泡中.有两种可能的机制可以解释这一现象,一是根据表面张力附加压强公式,气体会由半径小、压强大的小气泡移动到大气泡;二是根据物理学的统计理论,从小气泡溶解到水分中的空气能够扩散,进入临近的、压强较小的大气泡. 两种机制导致样品中小管状细胞栓塞的修复. 因此,作者认为,对活体植物, 空穴化事件之后,空气难以从木质部移动到大气中,而是从小的管状细胞中运动到了大的管状细胞中或其他低气压区域,从而导致木质部栓塞的修复.      

Self-assembly of ordered, robust, three-dimensional gold nanocrystal/silica arrays

We report the synthesis of a new nanocrystal (NC) mesophase through self-assembly of water-soluble NC micelles with soluble silica. The mesophase comprises gold nanocrystals arranged within a silica matrix in a face-centered cubic lattice with cell dimensions that are adjustable through control of the nanocrystal diameter and/or the alkane chain lengths of the primary alkanethiol stabilizing ligands or the surrounding secondary surfactants. Under kinetically controlled silica polymerization conditions, evaporation drives self-assembly of NC micelles into ordered NC/silica thin-film mesophases during spin coating. The intermediate NC micelles are water soluble and of interest for biolabeling. Initial experiments on a metal-insulator-metal capacitor fabricated with an ordered three-dimensional gold nanocrystal/silica array as the "insulator" demonstrated collective Coulomb blockade behavior below 100 kelvin and established the current-voltage scaling relationship for a well-defined three-dimensional array of Coulomb islands.     

Density fluctuations under confinement: when is a fluid not a fluid?

Knowing the behavior of a fluid in small volumes is essential for the understanding of a vast array of common problems in science, such as biological interactions, fracture propagation, and molecular tribology and adhesion, as well as pressure solvation and other geophysical processes. When a fluid is confined, its phase behavior is altered and excluded-volume effects become apparent. Pioneering measurements performed with the surface forces apparatus have revealed so-called structural or oscillatory solvation forces as well as the occurrence of a finite shear stress, which was interpreted as a solidification transition. Here, we report measurements obtained with an extended surface forces apparatus, which makes use of fast spectral correlation to gain insight into the behavior of a thin film of cyclohexane confined within attoliter volumes, with simultaneous measurement of film thickness and refractive index. With decreasing pore width, cyclohexane is found to undergo a drastic transition from a three-dimensional bulk fluid to a two-dimensional adsorbate with strikingly different properties. Long-range density fluctuations of unexpected magnitude are observed.     

Interfacial polygonal nanopatterning of stable microbubbles

Micrometer-sized bubbles are unstable and therefore difficult to make and store for substantial lengths of time. Short-term stabilization is achieved by the addition of amphiphilic molecules, which reduce the driving force for dissolution. When these molecules crystallize on the air/liquid interface, the lifetime of individual bubbles may extend over a few months. We demonstrated low gas-fraction dispersions with mean bubble radii of less than 1 micrometer and stability lasting more than a year. An insoluble, self-assembled surfactant layer covers the surface of the microbubbles, which can result in nanometer-scale hexagonal patterning that we explain with thermodynamic and molecular models. The elastic response of the interface arrests the shrinkage of the bubbles. Our study identifies a route to fabricate highly stable dispersions of microbubbles.     

Investigation of 3D geometry of bulk wheat and pea pores using X-ray computed tomography images

Quantitative characterization of pore topology inside grain bulks is necessary to predict the air traverse time and the cooling or fumigation pattern for the design of storage management strategies. Quantification of 3D microarchitecture of the inter-granular airspace in the grain bulks can also contribute to the development of predictive models of insect movement and for designing acoustic systems for insect infestation detection. In this study, inter-connected 3D array of void spaces was characterized by geometrical quantities such as specific surface area, pore throat size and nodal pore volume. These features were obtained from a 13.1 cm × 13.1 cm × 5 cm volume of wheat and pea bulks. The grain bulks were imaged using a high resolution X-ray computed tomography system at 200 μm resolution. The spatial distributions were computed based on 3D medial axis analysis of the void space in the images using 3DMA-Rock software and a high performance Polaris computer. The other features calculated were medial axis tortuosity, throat surface area and porosity from the 3D images. Characterization of pore throat network provides reliable observation for facilitating realistic prediction of permeability and the nature of air and gas distribution inside grain bulks.     

龙胆草斑枯病组织病理学研究初报

通过在开花期龙胆草植株上接种龙胆草斑枯病菌,然后置于温室内保温保湿培养,每隔一定时间取样、固定、制片,来镜检观察病原菌形态结构变化及组织病变过程.结果表明:病菌分生孢子萌发后产生芽管从气孔侵入,完成侵入需要12～48h,大约在接种10天后显示症状,16天形成分生孢子器并成熟;病菌侵染寄主引起症状后,菌丝多从叶片背面跨过叶肉组织,在叶片正面的薄壁细胞间集结,最后形成分生孢子器,分生孢子器产生于表皮下薄壁细胞之间,具有一定随机性.     

Laser ablation and the production of polymer films

The formation of high-quality thin films of polytetrafluoroethylene (PTFE) is important in many applications ranging from material reinforcement to molecular electronics. Laser ablation, a technique widely used to deposit a variety of inorganic materials, can also be used as a simple and highly versatile method for forming thin polymer films. The data presented show that PTFE films can be produced on various supports by the evaporation of a solid PTFE target with a pulsed ultraviolet laser. The composition of the ablation plume suggests that PTFE ablation and subsequent film formation occur by way of a laser-induced pyrolitic decomposition with subsequent repolymerization. The polymer films produced by this method are composed of amorphous and highly crystalline regions, the latter being predominantly in a chain-folded configuration with the molecular axis aligned parallel to the substrate surface.     

聚合物分子尺寸大小及其与岩石孔喉尺寸配伍关系的试验研究

为了探索和验证聚合物分子尺寸与岩石孔喉尺寸的配伍关系,以河南油田东部老油区稀油油田为例,应用数学方法、微孔滤膜过滤方法和动态光散射方法,对开展聚合物驱条件下拟使用的聚合物的分子尺寸进行试验测定,得到了双河油田不同渗透率岩石能够匹配的聚合物分子量。     

聚合物分子尺寸大小及其与岩石孔喉尺寸配伍关系的试验研究

为了探索和验证聚合物分子尺寸与岩石孔喉尺寸的配伍关系,以河南油田东部老油区稀油油田为例,应用数学方法、微孔滤膜过滤方法和动态光散射方法,对开展聚合物驱条件下拟使用的聚合物的分子尺寸进行试验测定,得到了双河油田不同渗透率岩石能够匹配的聚合物分子量。     

Polymerization-induced epitaxy: scanning tunneling microscopy of a hydrogen-bonded sheet of polyamide on graphite

A molecularly thin film of a two-dimensional polymer network formed by hydrogen bonding was synthesized and investigated with scanning tunneling microscopy. Poly(in-caprolactam) (nylon 6) was epitaxially grown on the basal plane of graphite and an ultrathin film of the polymer was obtained after the bulk materials had been washed away with solvents. The polymer chain has a planar, all-trans conformation and adjacent chains run in the antiparallel direction. This produces complete pairing of hydrogen bonding groups, with each amide group lying on a straight line perpendicular to the polymer backbone. This hydrogen-bonded sheet is oriented so that each polymer backbone lies in the (1010) direction on the graphite hexagonal lattice, as opposed to the (1120) direction taken by other paraffinic molecules studied so far. This experiment shows that hydrogen bonding can be used to control the orientation of macromolecules in two dimensions.     

胶清胶生产曝气吹脱法除氨初探

利用池底曝气吹脱除氨对胶清橡胶生产进行初步探索,试验结果表明,增大曝气装置的气液自由接触表面积,增加曝气供气量及时间,可提高传质总系数及去除率,能使胶清中的氨含降低1/3左右,达到节能减排的目的,增加了社会效益和企业经济效益。     

Venting of carbon dioxide-rich fluid and hydrate formation in mid-okinawa trough backarc basin

Carbon dioxide-rich fluid bubbles, containing approximately 86 percent CO(2), 3 percent H(2)S, and 11 percent residual gas (CH(4) + H(2)), were observed to emerge from the sea floor at 1335- to 1550-m depth in the JADE hydrothermal field, mid-Okinawa Trough. Upon contact with seawater at 3.8 degrees C, gas hydrate immediately formed on the surface of the bubbles and these hydrates coalesced to form pipes standing on the sediments. Chemical composition and carbon, sulfur, and helium isotopic ratios indicate that the CO(2)-rich fluid was derived from the same magmatic source as dissolved gases in 320 degrees C hydrothermal solution emitted from a nearby black smoker chimney. The CO(2)-rich fluid phase may be separated by subsurface boiling of hydrothermal solutions or by leaching of CO(2)-rich fluid inclusion during posteruption interaction between pore water and volcanogenic sediments.     

Kinetics of conversion of air bubbles to air hydrate crystals in antarctic ice

The depth dependence of bubble concentration at pressures above the transition to the air hydrate phase and the optical scattering length due to bubbles in deep ice at the South Pole are modeled with diffusion-growth data from the laboratory, taking into account the dependence of age and temperature on depth in the ice. The model fits the available data on bubbles in cores from Vostok and Byrd and on scattering length in deep ice at the South Pole. It explains why bubbles and air hydrate crystals coexist in deep ice over a range of depths as great as 800 meters and predicts that at depths below approximately 1400 meters the AMANDA neutrino observatory at the South Pole will operate unimpaired by light scattering from bubbles.     

ELECTRON SHADOW MICROGRAPHY OF THE TOBACCO MOSAIC VIRUS PROTEIN

Two improvements are described in the use of shadow electron micrography for the observation of particles of macromolecular dimensions. One involves the substitution of gold for chromium as shadowing metal. The thinner gold film that can be employed gives a truer representation of the shape of particles so small that shape and size are significantly altered by the thickness of the shadowing metal deposited on them. The other consists in metal-shadowing small particles deposited on a very smooth surface such as that of polished glass and the handling of this metal film as a replica of the glass surface and the particles resting on it. This technique permits the photography of particles whose direct observation is disturbed by the fine structure that is brought out by shadowing a collodion substrate. Application of these methods to the electron micrography of the tobacco mosaic virus protein shows that its fibrils are rods about 125A both in height and breadth. Though the rods appear segmented, these segments have not been found to have a length that is constant or a small integral multiple of an underlying unit.