二维泡沫稳定性与拓扑学性质关系的研究

研究了二维泡沫形成、进化及其拓扑学性质随时间的变化关系以及影响其稳定性的因素。探索了二维泡沫初始有序化的气泡进化和完全无序化的气泡进化的两种过程，并分析在无序化气泡的进化过程中，平均气泡面积随时间的变化呈现出α=1．5的幂指数关系，以及该指数大于Von Neuman定律的时间常数的可能原因。讨论了气泡的边数分布及其二阶矩。     

新型球形孔低孔隙率高强度泡沫铝合金

采用位移传感计算机技术, 实时测量液态泡沫铝合金孔隙率随时间变化P_l-t曲线. 研究了铝合金熔体泡沫化过程中熔体泡沫的孔隙率与泡沫孔形状从球形、类球形到多边形的变化规 律, 以及气泡孔径及壁厚变化规律. 由此获得了新型球形孔低孔隙率泡沫铝合金的控制方法. 研究了其压缩应力-应变曲线及吸能性能, 并与多边形孔高孔隙率泡沫铝合金的性能相比较.     

金属铜电沉积过程分形研究

对金属铜电沉积过程中的二维枝晶生长现象进行了研究,测定了沉积时间和电流之间的关系曲线,分析了外加电压、电解质浓度以及实验温度等实验条件对电沉积产物形貌及其分形维数的影响.分形维数随外加电压的改变呈现不规则的变动,随电解质浓度的增大而增大,随着电沉积温度的升高,沉积产物的分形维数先呈现上升趋势,当温度达到某一数值后,沉积产物的分形维数则在某一温度范围内呈现在波动现象,随着电沉积温度的进一步上升,沉积产物的分形维数呈现出下降的趋势.     

蒸馒头化学原理的探讨

馒头是人们喜爱的面食,做出美味馒头的关键是生成气泡、固住气泡。分析了和面过程中面筋指数随巯基和二硫键的变化,阐释了和面时间与馒头韧性的关系;分析了发酵阶段温度对馒头蓬松程度的影响和不同发酵剂对发酵效果的影响;通过分析蒸制过程中pH与还原糖含量随时间的变化,探讨了蒸制时间对馒头甜度的影响。生活中处处蕴含着化学原理,借此文使读者了解蒸馒头的化学原理,并激发学生对化学的兴趣。     

层状液晶凝胶对微泡沫的稳定作用

以非离子表面活性剂单硬脂酸甘油酯(GMS)制备出稳定的微泡沫. 采用偏光显微镜、冷冻断裂蚀刻透射电子显微镜(FF-TEM)、差示扫描量热仪(DSC)和流变仪对其表面活性剂溶液相态、泡沫体系的微观结构、相变行为和流变性进行研究以探索微泡沫的稳定机理. 实验结果表明, 表面活性剂分子吸附在气泡界面, 发生晶化形成有序、紧密排列的层状液晶凝胶相液膜, 该液膜具有较强的刚性, 能抵抗由Laplace附加压力驱使的气泡溶解和聚并行为. 微泡沫可稳定10个月, 无明显的相分离和气泡破裂现象. 其稳定作用机理是通过影响泡沫排液过程, 增强Gibbs-Marangoni效应, 从而提高了气泡液膜强度, 减缓了气相扩散速率.     

水溶性高分子弱凝胶体系凝胶化过程的Monte Carlo模拟

为研究弱凝胶的形成过程,并把高分子弱凝胶用于三次采油,采用三维Monte Carlo模拟了高分子溶液凝胶化过程. 模拟预测了凝胶化开始的时间,得到了凝胶化过程中分子量分布的演化规律和胶团生长的三维图像. 发现生成溶胶与凝胶团的歧化过程,初始聚合物的浓度对能否形成凝胶至关重要,低于临界浓度不能形成凝胶. 模拟了凝胶化速度和聚合物浓度以及交联剂浓度的关系,并与粘度随凝胶化时间变化的实验结果进行比较, 结果表明, 聚合物浓度较高时,浓度对交联反应的影响减弱,这一趋势与实验结果相一致.     

流化床燃烧器中气泡相和密相氧浓度的理论预测与实验验证Ⅰ．理论模型

基于流态化两相理论，建立了描述流化床燃烧器中煤焦间歇燃烧过程的数学模型。该模型只有一个可调参数（△Ｔ），能够预测煤焦的烧失时间以及气泡相和密相氧浓度随时间的变化。对模型输入参数的敏感性分析表明，煤焦加入量、探头位置以及过剩空气速度是影响气泡相和密相氧浓度的主要操作因素。     

向列型液晶与硬粒子两相体系的织态演化动力学研究

用二维XY模型和CDS元胞动力学方法研究了向列型液晶与少量硬粒子组成的两相体系的织态演化动力学. 通过模拟给出了织态演化过程的偏光图案, 其中纯液晶体系的偏光图案与实验观察到的结果一致; 并计算得到了空间相关函数和结构因子以及相区域的特征长度随时间t增长的标度关系. 同时统计了体系中缺陷点的数目, 得到了缺陷数目随时间t减少的标度关系. 发现粒子与液晶的相互作用将导致序参量有序化过程、 相区域增长速度和缺陷湮灭速度减慢.     

高分子相分离的分子动力学模拟

用粗粒化分子动力学(MD)模拟方法从分子层次研究两组分聚合物共混体系相分离过程中的动力学. 在相分离初期, 相区尺寸不随时间增加而变化; 在相分离中期, 相区尺寸与时间有很好的标度关系, 标度指数(α=1/3)符合Lifshiz-Slyozov提出的以扩散为主导的蒸发-凝聚机理的标度预测; 在相分离后期, 体系实现宏观相分离, 相区尺寸不再随时间改变而变化. 体积分数小的高分子链尺寸在相分离过程中先收缩再扩张, 在实现宏观相分离后, 高分子链尺寸又回到本体状态尺寸.     

金属锌电沉积过程的分形研究

对金属锌电沉积过程中的二维枝晶生长进行了研究,分析了外加电压、电解质浓度以及温度等实验条件对电沉积产物形貌及其分形维数的影响.结果表明,随着外加电压的增大,沉积产物形貌的变化趋势为由开放的分枝结晶向较为致密的生长形貌转变;随着硫酸锌浓度的增大,沉积产物具有分叉结构的致密纤维状枝晶簇和较为粗壮的开放型规则的分叉状枝晶,分形维数发生相应的变化;随着温度的升高,沉积产物的枝晶呈均匀化、致密化,沉积产物分形维数呈明显增大的趋势.     

Mathematical Model of Foam Flowing Characteristics by Snap-Off Mechanisms at Steady State in Porous Media

Flow characteristics and regeneration processes of foams were influenced by lamella properties and pore-throat structure in porous media. In this article, porous media was simplified as a bunch of constricted capillary tubes according to grain size, pore-throat radius, and immobile water saturation in porous media. Based on an analysis of forces upon liquid lamella, a mathematical model of foam migration and regeneration at steady state was established according to the mass conservation law and the momentum conservation law in porous media. The model could be used to calculate some important parameters in porous media, such as pressure distribution, shearing stress, lamella morphology, liquid-layer thickness, regeneration bubble size, etc. A series of flow experiments were carried out to investigate the influence of liquid properties and pore-throat structure on flow characteristics and resistance behavior of foams in porous media. The experimental results showed that pressure distribution monotonously decreased along porous media. The theoretical results were in good agreement with the experimental results. Foam structure, that is, foam quality was an important factor upon foam resistance behavior in porous media. The strongest resistance ability of foams was achieved at foam quality of 85% in porous media.      

Two‐Dimensional Noble‐Metal Chalcogenides and Phosphochalcogenides

Noble‐metal chalcogenides, dichalcogenides, and phosphochalcogenides are an emerging class of two‐dimensional materials. Quantum confinement (number of layers) and defect engineering enables their properties to be tuned over a broad range, including metal‐to‐semiconductor transitions, magnetic ordering, and topological surface states. They possess various polytypes, often of similar formation energy, which can be accessed by selective synthesis approaches. They excel in mechanical, optical, and chemical sensing applications, and feature long‐term air and moisture stability. In this Minireview, we summarize the recent progress in the field of noble‐metal chalcogenides and phosphochalcogenides and highlight the structural complexity and its impact on applications.     

Shear-induced lamellar ionic liquid-crystal foam

In a recent paper we reported an experimental study of two N-alkylimidazolium salts. These ionic compounds exhibit liquid crystalline behaviour with melting points above 50°C in bulk. However, if they are sheared, a (possibly non-equilibrium) lamellar phase forms at room temperature. Upon shearing a thin film of the material between microscope slides, textures were observed that are strikingly similar to liquid (wet) foams. The images obtained from polarising optical microscopy (POM) were found to share many of the known quantitative properties of a two-dimensional foam coarsening process. Here we report an experimental study of this foam using a shearing system coupled with POM. The structure and evolution of the foam are investigated through the image analysis of time sequences of micrographs obtained for well-controlled sets of physical parameters (sample thickness, shear rate and temperature). In particular, we find that there is a threshold shear rate below which no foam can form. Above this threshold, a steady-state foam pattern is obtained where the mean cell area generally decreases with increasing shear rate. Furthermore, the steady-state internal cell angles and distribution of the cell number of sides deviate from their equilibrium (i.e. zero-shear) values.     

The Effect of Macromolecules on Foam Stability in Sodium Dodecyl Sulfate/Cetylpyridinium Bromide Mixtures

Abstract

The effects of macromolecules, gelatin, and polyvinylpyrrolidone (PVP), on the properties of foam comprising sodium dodecyl sulfate (SDS) and cetylpyridinium bromide (CPDB) have been studied by measurements of foamability, foam stability, surface tension, and solution specific viscosity. The results indicate that foamability and foam stability are significantly improved when macromolecules are added into mixed systems. Both gelatin and PVP associate with SDS/CPDB surfactants and form aggregates. Electrostatic repulsion and steric stabilization between the two sides of the foam lamellae, due to aggregation, and prevention of drainage in the lamellae, achieved by the long chains of macromolecules are the reasons for increasing foamability and foam stability. The interactions between PVP and surfactants is weaker than those between gelatin and surfactants. The strongest association between macromolecules and surfactants occurs when the molar ratio of SDS/CPDB is 1:1. By comparing PVP with gelatin, the former is favored to increase foamability, and the latter is favored to increase foam stability.     

Electrochemical Studies of Three Dimensional Graphene Foam as an Electrode Material

Graphene foam is one kind of network of three dimensional (3D) graphene, which inherits the properties of two dimensional graphene and overcomes the aggregation/stacking of graphene sheets. In this work, graphene foam has been characterized by scanning electron microscopy and Raman spectroscopy. A graphene foam electrode was evaluated as a new electrode material by cyclic voltammetry (CV) and used for the detection of trace level of Pb²⁺ by anodic stripping voltammetry (ASV). Under the optimized condition of deposition potential (‐1.2 V) and deposition time (2 min), the detection limit is estimated to be 40 nM for Pb²⁺ based on the 3σ method.     

Correlation between transient shear experiments and structure evolution of aqueous foams

This experimental work deals with rheological properties of aqueous foams and slip phenomena. Rheological measurements are performed on a stable foam with a parallel plate rheometer. When a constant shear rate is applied to foam, two regimes can be identified in the recorded stress vs time curve: a transient regime where the structure evolves and where the recorded stress varies, followed by a steady state regime where the stress is stabilized. Measurements, modeling, and elimination of the slip velocity are performed. Experiments with grooved surfaces allow elimination of slip at the wall. From measurements at two gaps with smooth surfaces, we use two slip correction methods and check their validity by a direct comparison with actual measurements (with grooved surfaces). A foam rheological equation can be determined from the measurements. Finally, using an optical device coupled with image analysis software, foam texture is investigated on the basis of its evolution with shear rate and time. Evolution of the bubbles size and arrangement into the gap with time of shearing are shown. The transient regime is identified as a regime where the intimate structure of the foam evolves. Slip velocity is also evidenced and measured with the visualization device.     

Unforced translocation of a polymer chain through a nanopore: the solvent effect

The authors have performed the Langevin dynamics simulation to investigate the unforced polymer translocation through a narrow nanopore in an impermeable membrane. The effects of solvent quality controlled by the attraction strength lambda of the Lennard-Jones cosine potential between polymer beads and beads on two sides of the membrane on the translocation processes are extensively examined. For polymer translocation under the same solvent quality on both sides of the membrane, the two-dimensional and three-dimensional simulations confirm the scaling law of tautrans approximately N1+2upsilon for the translocation in the good solvent, where tautrans is the translocation time, N is the chain length, and upsilon is the Flory exponent. For the three-dimensional polymer translocation under different solvent qualities on two sides of the membrane, the translocation efficiency may be notably improved. The scaling law between tautrans and N varies from tautrans approximately N1+2upsilon to tautrans approximately N with the increase of the difference of solvent qualities, and the crossover occurs at the theta temperature point, where a scaling law of tautrans approximately N1.27 is found. The simulation results here also show that the translocation time changes from a wide and asymmetric distribution with a long tail to a narrow and symmetric distribution with the increase of the difference of the solvent qualities.     

HCN→HNC异构化反应过渡态附近的拓扑特性

电荷密度拓扑分析方法(topological analysis of charge distribution)已经被广泛应用于研究化合物的各种静态性质及反应特性.对IRC反应途径上过渡态附近构型的拓扑性质研究报导较少.本工作是用电荷密度分布的拓扑分析方法对HCN→HNC异构化反应IRC过渡态附近的性质进行了研究.对电荷密度分布拓扑分析和IRC途径确定选用相同的基组,得到了一些新的结论。     

Structure of liquid films of an ordered foam confined in a narrow channel

A bamboo foam is the simplest case of an ordered foam confined in a narrow channel. It is made of a regular film distribution, arranged perpendicularly to the channel. Our work consists of studying the structural properties of several films taken in a drained foam. X-ray experiments highlighted the equality of the equilibrium thickness for each film within a foam. The same thickness was found as by measurements of disjoining pressure isotherms, proving as well that films of a bamboo foam behave like isolated ones. The refinement of X-ray data by a simple model of specular reflectivity showed a significant variation of the electronic distribution of the surfactant layer for a common black film forwarding from one equilibrium state to another. A discussion on the organization of the surfactant molecules to the gas/liquid interface and film is proposed.     

A Combined Experimental and Theoretical Electron Density Study of Intra‐ and Intermolecular Interactions in Thiourea S,S‐Dioxide

The thiourea S,S‐dioxide molecule is recognized as a zwitterion with a high dipole moment and an unusually long C? S bond. The molecule has a most interesting set of intermolecular interactions in the crystalline state—a relatively strong O???H? N hydrogen bond and very weak intermolecular C???S and N???O interactions. The molecule has C_s symmetry, and each oxygen atom is hydrogen‐bonded to two hydrogen atoms with O???H? N distances of 2.837 and 2.826 Å and angles of 176.61 and 158.38°. The electron density distribution is obtained both from Xray diffraction data at 110 K and from a periodic density functional theory (DFT) calculation. Bond characterization is made in terms of the analysis of topological properties. The covalent characters of the C? N, N? H, C? S, and S? O bonds are apparent, and the agreement on the topological properties between experiment and theory is adequate. The features of the Laplacian distributions, bond paths, and atomic domains are comparable. In a systematic approach, DFT calculations are performed based on a monomer, a dimer, a heptamer, and a crystal to see the effect on the electron density distribution due to the intermolecular interactions. The dipole moment of the molecule is enhanced in the solid state. The typical values of ρ_b and H_b of the hydrogen bonds and weak intermolecular C???S and N???O interactions are given. All the interactions are verified by the location of the bond critical point and its associated topological properties. The isovalue surface of Laplacian charge density and the detailed atomic graph around each atomic site reveal the shape of the valence‐shell charge concentration and provide a reasonable interpretation of the bonding of each atom.