非晶合金及合金液体的局域五次对称性

简要回顾了从20世纪30年代至今,有关非晶合金及合金液体的局域结构五次对称性的实验、理论和模拟研究.在简单液体的早期研究中,人们已经意识到五次对称性在简单液体的无序结构、过冷和晶化等起着重要作用,二十面体短程序作为五次对称性的典型代表受到了广泛关注.自从Frank提出简单液体中二十面体短程序的结构单元,大量的理论和实验研究已经明确在简单液体、合金液体和金属玻璃中存在局域五次对称性,并且建立了局域五次对称性与合金液体复杂动力学行为、玻璃转变、液体-液体相变以及非晶合金的形变等统一的定量描述和物理图像,表明了局域五次对称性作为结构参量的简单、普遍和有效性.     

Light absorption coefficients of ionic liquids under electric field

Ionic liquids have attracted a lot of research attention for their applications in novel optoelectronic structures and devices as an optical means of regulating electricity. Although the electro-optic effect of ionic liquids is mentioned in some literature, quantitative testing and analysis are hardly found in light absorption coefficients of ionic liquids under an electric field. In the present study, an experimental apparatus is designed to measure the absorption coefficients of ionic liquids under different electric fields. Five groups of imidazole ionic liquids are experimentally investigated and an inversion is performed to determine the spectral absorption coefficients of the imidazole ionic liquids under the electric fields. Different intensities with multiple interface refractions and reflections are also considered, and the various measurement errors are analyzed through uncertainties propagation analysis. Spectral absorptions of ionic liquids from 300 nm to 2500 nm are obtained and the absorption coefficients are retrieved. It is found that the absorption behavior of ionic liquids changes in some frequency bands under an applied electric field. The experimental results show that the absorption coefficient of the ionic liquid increases with the voltage increasing at 1520 nm and 1920 nm. The change rate is affected by the types of anions and cations in the ionic liquid and the diffusion rate of the ions therein. This study provides illustrations for the ionic liquid-based electro-optical regulation in terms of physical property parameters and the testing technique.     

Hurst's empirical law in the probability of atomic distribution in liquids

The rescaled range analysis was used to examine the pair distribution function of liquids. The global statistical dependence existed in the distribution of atoms in liquids. The probability of finding a particle at a distance r from a reference particle was subject to fractional Brownian motion. More importantly, the tendency of the Hurst exponent was away from the high rate when the change of liquid structure took place. This phenomenon showed that the liquid structural change was attributed to the variation of atomic distribution and the jump of the Hurst exponent was the indicator of the change from one phase to another in liquids.     

First x-ray scattering studies on electrostatically levitated metallic liquids: demonstrated influence of local icosahedral order on the nucleation barrier

To explain the unusual stability of undercooled liquids against crystallization, Frank hypothesized that the local structures of undercooled liquids contain a significant degree of icosahedral short-range order, which is incompatible with long-range periodicity. We present here the first direct experimental demonstration of Frank's complete hypothesis, showing a correlation between the nucleation barrier and a growing icosahedral short-range order with decreasing temperature in a Ti39.5Zr39.5Ni21 liquid. A new experimental facility, BESL (Beamline Electrostatic Levitation), was developed to enable the synchrotron x-ray structural studies on deeply undercooled, reactive liquids.     

Electrowetting-Based Variable-Focus Lens for Miniature Systems

The meniscus between two immiscible liquids of different refractive indices can be used as a lens. A change in curvature of this meniscus by electrostatic control of the solid/liquid interfacial tension leads to a change in focal distance. It is demonstrated that two liquids in a tube form a self-centred variable-focus lens. The optical properties of this lens were investigated experimentally. We designed and constructed a miniature camera module based on this variable lens suitable for mobile applications. Furthermore, the liquid lens was applied in a Blu-ray Disc optical recording system to enable dual layer disc reading/writing.     

BrФnsted酸离子液体的合成和表征

制备了5类含有不同含氮官能团及不同阴离子的功能Brnsted酸离子液体,分别用核磁共振(NMR)、红外光谱(IR)、电喷雾质谱(ESI-MS)和热重分析(TG/DTA)等表征方法对制备的离子液体进行表征。结果表明:合成的10种离子液体与预期设计结构相同,纯度大于95%;热重分析表明,制备的离子液体的分解温度较高,除了[MPy]NO3为199℃以外,其他离子液体均高于300℃,具有高的热稳定性和较宽的液态范围。     

Probing the adsorption of methylimidazole at ionic liquids/Cu electrode interface by surface‐enhanced Raman scattering spectroscopy

Two kinds of room‐temperature ionic liquids, 1‐butyl‐3‐methylimidazolium bromide ([BMIM]Br) and 1‐butyl‐3‐methylimidazolium tetrafluoroboride ([BMIM]BF₄), were used as solvent, and the adsorption of the ionic liquids themselves and of N‐methylimidazole (NMIM) were investigated by electrochemical surface‐enhanced Raman scattering (SERS) over a wide potential window. The results revealed that the cation of ionic liquid adsorbed onto Cu surface with different configurations in different potential ranges. When the potential was changed from the negative to the positive range, the orientation underwent a change from flat to vertical, and the onset potential for the orientation change was dependent on the types of anion of the ionic liquid. The ionic liquid in bulk solution exhibited a remarkable effect on the adsorption of NMIM. The electrode surface structure changed from adsorbing the ionic liquid at the negative potential to coadsorbing the ionic liquid and NMIM at relative positive potential for the [BMIM]BF₄ liquids, and formed films of NMIM at extremely positive potential. Due to the strong specific adsorption of Br⁻, the coadsorption of ionic liquid and NMIM was not observed in the system [BMIM]Br. By simulating the electrode surroundings, two surface complexes [Cu(NMIM)₄Br]Br·H₂O and [Cu(NMIM)₄](BF₄)₂ were synthesized by the electrochemical method in the corresponding ionic liquids for modeling the surface coordination chemistry of NMIM. The surface coordination configuration of NMIM and ionic liquids is proposed. Copyright © 2009 John Wiley & Sons, Ltd.     

非晶态物质原子局域连接度与弛豫动力学

非晶态物质的本质及形成过程是凝聚态物理领域最困难也是最有趣的问题之一.非晶形成过程在原子结构上不会衍生出人们在传统晶体结构里所熟悉的长程有序性,因此对于此类在自然界中广泛存在的物质形态,至今还没有有效的实验表征手段和理论研究方法.非晶态物质的原子结构及其构效关系的研究是凝聚态物理和材料科学等众多研究领域所关注的热点问题之一.随着对非晶态物质物性研究的深入,人们逐渐意识到非晶态物质中原子中程序对系统性质的重要影响,建立以中程序为基础的结构-动力学关系对于理解玻璃及玻璃转变的本质起着重要的作用.本文简要综述了基于图论提出的原子局域连接度这一新的结构序参量在液体和玻璃的结构及构效关系研究中的应用.新的结构序参量从过去侧重于关注局域原子团簇的种类和分布,转移到更加关注某一类具有特殊对称性的原子的空间连接情况,即更多地尝试从原子中程序的角度来建立非晶态物质中的构效关系.新的研究结果表明,局域连接度可与非晶态物质中原子的短时或长时动力学行为、输运方式、以及振动模态等一系列物理性质建立联系.     

新型BrФnsted酸性离子液体的合成与表征

制备了五种对水稳定性好、带-SO3H官能团的磺酸类BrФnsted酸离子液体,用核磁共振(NMR)、红外光谱(IR)、电喷雾质谱(ESI-MS)、热重分析(TG)等表征手段对制备的离子液体进行了表征。结果表明,制备的离子液体与预期设计的结构一致,离子液体纯度大于95%;热重分析发现离子液体具有高的热稳定性和较宽的液态范围,其分解温度均高于300℃;五种离子液体均存在四种离子存在形式,H 可以单独以离子形式存在,并不是通常所认为的仅有两种离子存在形式。另外,研究了离子液体在常用溶剂中的溶解性,发现制备的离子液体易溶于水、甲醇,不溶于乙醚、甲苯和乙酸乙酯。     

Collective diffusion in a two-dimensional liquid composed of Janus particles

The collective diffusion of anisotropic particles in liquids plays a crucial role in many processes, such as self-assembly. The patchy particle, which is usually nearly spherical in shape, is an important anisotropic particle with different properties from other anisotropic particles like the ellipsoid liquid crystal particles. In the present study, molecular dynamics simulations are performed to study the collective diffusion of a two-dimensional anisotropic liquid system composed of Janus particles. The static structures and diffusion behaviours of anisotropic and isotropic Lennard-Jones liquids are compared. The long-time diffusion behaviour of an anisotropic liquid of nearly spherical Janus particles is found to be similar to that of an isotropic liquid because the orientation of the particles disappears over long-term averaging. The anisotropic properties of the Janus particles are mainly reflected in the spatial correlation of particle orientations and mid-time diffusion behaviour. The difference between nearly spherical anisotropic particles and rod-like particles is also discussed in this paper.     

Correlation between liquid structure and glass forming ability in glassy Ag-based binary alloys

The atomic structures of liquid Ag-based binary alloys have been investigated in the solidification process by means of X-ray diffraction. The results of liquid structure show that there is a break point in the mean nearest neighbor distance r1 and the coordination number Nmin for glass-forming liquid, while the correlation radius rc and the coordination number Nmin display a monotone variational trend above the break point. It means glass-forming liquids have a steady changing in structure above liquidus a...     

Influence of an electric field on the dynamic viscosity of liquid dielectrics

Experimental dependences of the dynamic viscosity of dielectric liquids on the applied voltage are considered. The experiment is remarkable because of the elimination of the electric current through the liquid in a series of measurements by insulating one of the electrodes from the liquid. The change in the viscosity of the liquid media can be a consequence of alteration of the structure of the liquid and the formation of ion-molecule groups differing from the previously existing ones. The variation of the mechanical properties of the medium with variation of the applied field strength points out the influence of charge formation on them. The dependences for polar and nonpolar liquids are considered. Zh. Tekh. Fiz. 68, 40–43 (January 1998)     

Brownian motion in potential wells: i) Fine structure in the far infra-red absorption of dipolar liquids

The theory of Brownian motion in cosine potential wells is used to produce fine structures in the far infra-red power absorption coefficient of dipolar liquids in the low friction limit for finite barrier heights. The broad far infra-red absorption profile evolves into many sharp, resonance peaks as the friction coefficient, β→o. The theory lends qualitative support to the recent experimental observation of fine structure in the far infra-red power absorption of acetonitrile - a highly structured liquid whose viscosity is, nonetheless, low in comparison with other molecular liquids at room temperature.     

Temperature effects on the structure of liquid D-methanol through neutron diffraction

The study of changes in the structure (H-bonded) of liquid alcohols at elevated temperatures is rare probably due to low flash points of these liquids. An indigenously devised special quartz cell is now used to carry out the structural studies of these liquids at elevated temperatures through neutron diffraction. Here, the liquid consists of deuterated methanol and neutron data was collected on the high-Q diffractometer at Dhruva, BARC. The corrected data at elevated temperatures (BP (boiling point) and double the BP) show that there is a large change in the H-bonded structure of this liquid. The pre-peak or hump, known to be signature of H-bonded clusters appears to be present at all the three temperatures studied. In the low-Q (scattering vector) data Ornstein-Zernike (OZ) behaviour is also observed. It is, however, seen that the intramolecular structure does not change very much at higher temperatures. A detailed model analysis is in progress and would be reported later.     

Temperature effects on the structure of liquid D-methanol through neutron diffraction

The study of changes in the structure (H-bonded) of liquid alcohols at elevated temperatures is rare probably due to low flash points of these liquids. An indigenously devised special quartz cell is now used to carry out the structural studies of these liquids at elevated temperatures through neutron diffraction. Here, the liquid consists of deuterated methanol and neutron data was collected on the high-Q diffractometer at Dhruva, BARC. The corrected data at elevated temperatures (BP (boiling point) and double the BP) show that there is a large change in the H-bonded structure of this liquid. The pre-peak or hump, known to be signature of H-bonded clusters appears to be present at all the three temperatures studied. In the low-Q (scattering vector) data Ornstein Zernike (OZ) behaviour is also observed. It is, however, seen that the intramolecular structure does not change very much at higher temperatures. A detailed model analysis is in progress and would be reported later.     

热驱动微光学

通过实例研究和近期报道的文献,论述了热驱动微光学的研究进展。驱动器主要通过应用在液体和液气界面的压力来调控光学微流体,包括微镜片和薄膜微透镜,热驱动器利用芯片上的温度变化产生所需要的压力差,从而对微透镜进行调控。同时还讨论了用于微光学结构的各种设备、结构、液体和膜材料,并提供了典型操作特性。     

Bernal’s road to random packing and the structure of liquids

Until the 1960s, liquids were generally regarded as either dense gases or disordered solids, and theoretical attempts at understanding their structures and properties were largely based on those concepts. Bernal, himself a crystallographer, was unhappy with either approach, preferring to regard simple liquids as ‘homogeneous, coherent and essentially irregular assemblages of molecules containing no crystalline regions’. He set about realizing this conceptual model through a detailed examination of the structures and properties of random packings of spheres. In order to test the relevance of the model to real liquids, ways had to be found to realize and characterize random packings. This was at a time when computing was slow and in its infancy, so he and his collaborators set about building models in the laboratory, and examining aspects of their structures in order to characterize them in ways which would enable comparison with the properties of real liquids. Some of the imaginative – often time consuming and frustrating – routes followed are described, as well the comparisons made with the properties of simple liquids. With the increase of the power of computers in the 1960s, computational approaches became increasingly exploited in random packing studies. This enabled the use of packing concepts, and the tools developed to characterize them, in understanding systems as diverse as metallic glasses, crystal–liquid interfaces, protein structures, enzyme–substrate interactions and the distribution of galaxies, as well as their exploitation in, for example, oil extraction, understanding chromatographic separation columns, and packed beds in industrial processes.     

Generic morphologies of viscoelastic dewetting fronts

A simple model is put forward which accounts for the occurrence of certain generic dewetting morphologies in thin liquid coatings. It demonstrates that, by taking into account the elastic properties of the coating, a morphological phase diagram may be derived which describes the observed structures of dewetting fronts. It is demonstrated that dewetting morphologies may also serve to determine nanoscale rheological properties of liquids.     

Slip, immiscibility, and boundary conditions at the liquid-liquid interface

The conventional boundary conditions at the interface between two flowing liquids include continuity of the tangential velocity. We have tested this assumption with molecular dynamics simulations of Couette and Poiseuille flows of two-layered liquid systems, with various molecular structures and interactions. When the total liquid density near the interface drops significantly compared to the bulk values, the tangential velocity varies very rapidly there, and would appear discontinuous at continuum resolution. The value of this apparent slip is given by a Navier boundary condition.