Methods of theoretical study of vibrational phenomena in liquids--comparative analysis

In this review, existing theoretical models of vibrational phenomena in liquids are analyzed and compared. Most attention is paid to sonoluminescence, sonolysis and related phenomena. The criteria of selection of the optimal theoretical model involve analyzing experimental results, its usefulness for evaluation of thermodynamic and other parameters of the liquid under vibration, simplicity of the mathematical solution and the time needed for computing. It is concluded that, according to these criteria, the optimal (between existing models) is the chemical model of vibration in liquid, while the best perspectives are for its combinations with other models.     

Pressure/electric-field-assisted micro/nanocasting method for replicating a lotus leaf

An electric field-aided process was introduced for a curable casting process. As a micro/nanosized pattern mask, a lotus leaf, which has a hierarchical structure, was used. The process consists of two steps: (1) applying an electric field to a liquid polymer and solidifying the polymer for use as a negative mold, and (2) using the negative polymer mold to fabricate a replicated poly(ethylene oxide) (PEO) surface in the original shape of the lotus leaf. In this process, the applied electric field induces unstable vibration of the liquid polymer, due to electrokinetic phenomena. The electrokinetic fluid motion resulted in well-replicated PEO surfaces. The quality of the fabricated surface was highly dependent on the applied field and pressure. We believe that this technique improves the quality of the standard nanocasting method and will be useful for fabricating micro/nanosized structures.     

高温熔体表面张力测量方法的进展

高温熔体表面现象在冶金、化工、熔盐和材料科学等领域十分普遍。测量高温熔体表面张力有着重要的意义。本文评述了高温熔体表面张力的测量原理和方法。并简述了当前关于高温熔体表面现象以及相关的微重力科学的研究进展。     

Optical diffraction in twisted liquid-crystalline media-phase grating mode

We have calculated the diffraction of light perpendicular to the twist axis in a chiral smectic C liquid crystal. In contrast to a cholesteric liquid crystal, in a chiral smectic C liquid crystal we find extra orders which form the odd orders in the diffraction pattern. For an incident linearly polarized light, at a general azimuth, these odd orders are linearly polarized and the even orders are elliptically polarized. The intensities of the odd orders are always independent of the azimuth of the incident light, while this is possible for even orders only at a particular tilt angle of the chiral smectic C liquid crystal. Also, for the incident vibration parallel or perpendicular to the twist axis the odd orders are polarized in the orthogonal linear state with respect to incident vibration, while the even orders are in the same linear state.     

The anharmonic character of Tg and Tm transition

The idea of anharmonic oscillations has been extended to explain the glass transition or melting point. All ideas of free volume, vacancy transport, etc., have been respected but are treated as minor phenomena relative to harmonic-anharmonic vibration transition. A simple model of coupled oscillators is studied. It is shown that coupled anharmonic oscillators can produce vibrations on entirely different levels of amplitudes, which explains the highly different coefficients of thermal expansion and c_p values for solid and liquid states. At higher temperatures, for polymers in the rubber-like zone, the theory of anharmonic coupled oscillators brings certain justification for the theories of De Gennes, Doi and Edwards or Rouse. The solid-liquid transition seems to be connected on microlevel mainly with the enlargement of vibrational amplitudes of monomer or dimer units in polymer chain as the temperature increases.     

Über schwebungseffekte in überlagerten normalschwingungen

The Superposition of the 3N-6 normal modes of vibration of a molecule to its equilibrium conformation produces interesting vibrational beating phenomena, i.e. transitory excessive deformations of internal coordinates beyond their mean vibrational distortions. For a few examples these phenomena are analysed using classical procedures. The investigations suggest that the molecular distortions caused by these phenomena can be larger in complex than in free molecules, since a larger number of 3N-6 normal modes is superimposed to the molecular framework in a complexed molecule. This indicates the possibility that, in the classical model, a molecule can be activated by kinematic effects when it becomes part of a complex. The phenomenon is of interest for catalytic processes and can be expected to be of importance especially for the efficiency of catalysts which have a high molecular weight.     

Teaching liquid crystals – observation inspired curiosity

Soft matter has become involved in all aspects of everyday life over the past few decades, from diapers and the water-absorbing colloidal crystals hidden in them to the omnipresent liquid crystal displays. This article discusses an introduction to one example of soft matter – liquid crystals – at various educational levels. It stresses the importance of experimental work and presents a few simplified versions of elaborate techniques graduate students later meet in laboratories. A set of simple experiments, which illustrate typical phenomena for liquid crystals, but use different approaches or different materials than liquid crystals, are also presented. Drawing upon analogies is an essential part of an active researcher’s thought processes. By providing analogous experiences and showing clear analogies between various phenomena, a lecturer can train students in the use of analogies as a standard approach when encountering new problems.     

The history of electrokinetic phenomena

Electrokinetic phenomena comprise the phenomena where a liquid moves tangentially to a charged surface. Well-known phenomena of this kind are electrophoresis, electro-osmosis, streaming potential and sedimentation potential. A historical review is given here, starting with their discovery by F.F. Reuss in 1808 and continuing with the early investigators including G. Wiedemann, G.Quincke, E. Dorn and U. Saxén. It is also discussed how electrokinetic phenomena gave rise to the concept electrical double layer in colloid science. The development of the theory starting with H. Helmholtz, continuing with M. Smoluchowski is described. Extension of the theory including relaxation and surface conduction is included. Finally the history of other kinds of electrokinetic phenomena such as electroacoustics and diffusiophoresis is treated.     

Transportation of a microdroplet on an oriented liquid crystal surface

Wetting phenomena play important roles in several technological applications and in many physical and biological thin‐film phenomena, such as wetting, adhesion and friction. One of key issues of these studies is to control the surface energy (or wettability) dynamically for liquid transportation. We have developed a liquid crystal (LC) surface for use as a transport substrate since we expected that the surface energy of an LC surface can be controlled rapidly using an electric field. The rapid control of the polarisability (or wettability) of a liquid crystalline surface by an electric field has been demonstrated, together with the transportation of a liquid microdroplet.     

Effect of liquid slip in electrokinetic parallel-plate microchannel flow

Liquid slip at hydrophobic surfaces in microchannels has frequently been observed. We present here an analytical solution for oscillating flow in parallel-plate microchannels by combining the electrokinetic transport phenomena with Navier's slip condition. Our parametric results suggest that electrokinetic transport phenomena and liquid slip at channel walls are both important and should be considered simultaneously. Their significance depends on channel wall material, electrolyte concentration, and pH. For pressure-driven-flow, liquid slip counteracts the effect by the electrical double layer and induces a larger flow rate. A higher apparent viscosity would be predicted if slip is neglected. For electroosmotic flow, liquid slip alters the flow rate by about 20% for a thick electrical double layer. Our results provide design guidelines to precisely control time-dependent microflow in hydrophobic microfluidic microelectromechanical system devices.     

Infrared study of molecular rotation in liquids

The study of molecular rotation in liquids by infrared spectroscopy performed in our laboratory is reviewed. A number of examples are presented, showing the variety of phenomena encountered in the study of rotational motion of molecules in the liquid state. Many of these phenomena are well understood in simple cases and the nature of the rotation involved may be correctly identified. Problems which remain to be clarified are discussed.     

Applications of electrokinetic phenomena in materials science

The discovery of electrokinetic phenomena by Reuss in 1808 and further investigations that gave rise to the concept of the electrical double layer have played an important role in the understanding of colloidal stability. Electrokinetic phenomena are a family of effects in which a liquid moves tangentially to a charged surface. Well-known phenomena of this kind are electrophoresis, electro-osmosis, streaming potential, and sedimentation potential. A review of parameters involved in the electrochemistry of suspensions is made. The practical applications of these phenomena have become widespread in a broad range of research fields such as biomaterials, biofilms, electrokinetic waste remediation, membranes, nuclear and fossil-fired power plants, adhesive and sealant science, and concrete science. The purpose of this paper is to provide an overview of electrokinetic phenomena and their application to surface modification and characterization in a large number of research fields such as corrosion and protection processes, environmental remediation (soil and sediments, transport processes, inorganic pollutants, solid particle surfaces, filter membranes, and biosorption phenomena), cement-based systems, and biological systems.     

介晶现象与液晶高分子

在物质的介晶态中着重讨论了液晶态的高分子,讨论了高分子液晶的类型和特点及高分子的结构、结构单元对液晶形成和转化条件等的影响,指出了通过结构设计加以控制的原则和途径。     

Electrochemical pressure impedance spectroscopy for investigation of mass transfer in polymer electrolyte membrane fuel cells

Mass transfer phenomena in membrane fuel cells are complex and diversified because of the presence of complex transport pathways including porous media of very different pore sizes and possible formation of liquid water. Electrochemical impedance spectroscopy, although allowing valuable information on ohmic phenomena, charge transfer and mass transfer phenomena, may nevertheless appear insufficient below 1 Hz. Use of another variable, that is, back pressure, as an excitation variable for electrochemical pressure impedance spectroscopy is shown here a promising tool for investigations and diagnosis of fuel cells.     

Effect of surface wettability on liquid density, structure, and diffusion near a solid surface

Molecular dynamics and Langevin dynamics simulations are used to elucidate the behavior of liquid atoms near a solid boundary. Correlations between the surface wettability and spatial variations in liquid density and structure are identified. The self-diffusion coefficient tensor is predicted, revealing highly anisotropic and spatially varying mass transfer phenomena near the solid boundary. This behavior affects self-diffusion at a range of time scales. Near a more-wetting surface, self-diffusion is impeded by strong solid-liquid interactions that induce sharp liquid density gradients and enhanced liquid structure. Conversely, near a less-wetting surface, where solid-liquid interactions are weaker, the liquid density is low, the atoms are disordered, and diffusion is enhanced. These findings suggest that altering the wettability of a micro- or nanochannel may provide a passive means for controlling the diffusion of select targets towards a functionalized surface and controlling the reaction rate in diffusion-limited reactions.     

Droplet on a liquid substrate: Wetting,dewetting, dynamics,instabilities

Droplets on a liquid substrate (‘liquid lenses’) play an important role in various branches of engineering, including microfluidics, chemical engineering, environment protection, etc. In the present paper, we discuss basic phenomena characteristic for liquid lenses. We recall classical results on the shape of an equilibrium droplet and the kinds of droplet wetting. We overview briefly the main theoretical approaches used for the analysis of droplet dynamics, discuss the phenomena accompanying a droplet impact, physical effects used for droplet manipulations, and the factors that determine the interaction between droplets. We describe the main types of droplet instabilities leading to oscillations, self-propulsion, and disintegration of droplets. Some promising directions of further research are listed.     

Integrated and topological liquid crystal photonics

This contribution is a personal view of the rapidly developing subfield of nematic colloids, with an emphasis on possible applications of these materials in future photonic microdevices. A brief overview of the most important phenomena, observed in the past decade in nematic colloids is given. It is explained why integrated photonics based on microstructured liquid crystals is feasible and future challenges towards the realisation of integrated liquid crystal microphotonics are discussed.     

Surface tension of liquid metals and alloys — Recent developments

Surface tension measurements are a central task in the study of surfaces and interfaces. For liquid metals, they are complicated by the high temperatures and the consequently high reactivity characterising these melts. In particular, oxidation of the liquid surface in combination with evaporation phenomena requires a stringent control of the experimental conditions, and an appropriate theoretical treatment. Recently, much progress has been made on both sides. In addition to improving the conventional sessile drop technique, new containerless methods have been developed for surface tension measurements. This paper reviews the experimental progress made in the last few years, and the theoretical framework required for modelling and understanding the relevant physico-chemical surface phenomena.     

薄膜/基片系统红外透射光谱振荡现象的研究

在研究用射频磁控共溅射法制备的不同体积含量的Au-MgF2纳米金属陶瓷复合薄膜/Si基片系统的红外光谱特性时发现:薄膜的红外光谱存在振荡现象,同时在振荡的红外光谱中出现明显的包络线,这些现象对薄膜的光学特性分析带来一定困难。定性和定量分析表明这两种现象均由光透过基片产生的多光束干涉引起,并给出了消除此现象的方法。