Experimental evidence of liquid drop break-up in complete wetting experiments

We report experiments concerning the deposition of a droplet on a solid surface and the related spontaneous spreading, during which a secondary droplet is ejected. Experimental investigations and theoretical considerations have been performed in order to understand the reasons of the formation of this droplet and of its ejection and to estimate the conditions that induce these phenomena. High-speed imaging and specific deposition conditions have been necessary to visualize such phenomena. It has been shown that the ejection is possible in the complete wetting regime when low impact inertia and high position of the center of mass of the drop before spreading are achieved simultaneously. A model taking into account non-stationarity, inertia, wetting capillarity and viscous effects has been developed. It resulted in two dimensionless numbers Π₁ and Π₂ that characterize the occurrence of the ejection phenomenon.     

Static wetting of a liquid drop on a solid

A variational treatment of sessile drop shape is provided. The surface energy and the driving force for drop spreading are also analysed. This analysis demonstrates that the Young equation does indeed give the equilibrium contact angle in a gravity-free environment.     

Reactive wetting of rutile by liquid aluminium

Sessile drop wetting experiments of liquid Al on polycrystalline rutile (TiO2) were conducted in the 973.1273 K temperature range under a low total pressure (9.3 10.3 Pa, Ar) and a low oxygen partial pressure ( 1.33 10.7 Pa), as a function of temperature and time. A non-wetting (150., 973 K, t >120 min.) to partial wetting (85., 1273 K, 50.60 min.) transition reflects reactive wetting characteristics. Microstructural investigations of the metal-ceramic interface shows that TiO2 is reduced by liquid Al, resulting in the formation of Al2O3. The steady-state contact angle at 1273 K of Al on -Al2O3 and Al on rutile are very similar, and the role of Ti segregation is minimal. It appears that spreading of the Al drop on TiO2 is governed by the reduction reaction at the solid-liquid interface. The measured activation energy corresponds well to the activation energy for volume diffusion of Al, Ti and O in rutile and the volume diffusion of Al in polycrystalline -Al2O3.     

Fundamental issues of reactive wetting by liquid metals

After a brief presentation of thermodynamics and kinetics of non-reactive wetting, the recent results and theoretical developments concerning the reactive wetting of solids by liquid metals are reviewed. A section is devoted to illustrate and discuss the effect of interfacial reactions in removing the wetting barriers existing on many ceramic and metallic solids.     

Active beating modes of two clamped filaments driven by molecular motors

Biological cilia pump the surrounding fluid by asymmetric beating that is driven by dynein motors between sliding microtubule doublets. The complexity of biological cilia raises the question about minimal systems that can re-create similar patterns of motion. One such system consists of a pair of microtubules that are clamped at the proximal end. They interact through dynein motors that cover one of the filaments and pull against the other one. Here, we study theoretically the static shapes and the active dynamics of such a system. Using the theory of elastica, we analyse the shapes of two filaments of different lengths with clamped ends. Starting from equal lengths, we observe a transition similar to Euler buckling leading to a planar shape. When further increasing the length ratio, the system assumes a non-planar shape with spontaneously broken chiral symmetry after a secondary bifurcation and then transitions to planar again. The predicted curves agree with experimentally observed shapes of microtubule pairs. The dynamical system can have a stable fixed point, with either bent or straight filaments, or limit cycle oscillations. The latter match many properties of ciliary motility, demonstrating that a two-filament system can serve as a minimal actively beating model.     

Liquid drop ejection from a membrane driven by gas detonation products

The process of jet formation from a liquid drop placed on a membrane and driven by detonation of hydrogen-air mixture in a thin tube behind the membrane has been studied. It is shown that a gas mixture capable of detonating can be used instead of a solid explosive in devices for ejecting solid particles and liquid drops-in particular, for needle-free injection of drug solutions.     

Investigation of the effect of oxygen impurities on the wetting properties of alkali metal surfaces by liquid helium

The weak binding properties of heavy alkali metal surfaces for helium have been related to their metallic nature and their particularly small work function. A natural consequence would be that oxidized surfaces should loose their non wetting properties for liquid helium. It is pointed out that the special oxidization process of these metals could unexpectedly lead to an opposite result at some intermediate stage. First experimental results on rubidium shows evidences for such an effect.     

Controlled enhancement of spin-current emission by three-magnon splitting

Spin currents--the flow of angular momentum without the simultaneous transfer of electrical charge--play an enabling role in the field of spintronics. Unlike the charge current, the spin current is not a conservative quantity within the conduction carrier system. This is due to the presence of the spin-orbit interaction that couples the spin of the carriers to angular momentum in the lattice. This spin-lattice coupling acts also as the source of damping in magnetic materials, where the precessing magnetic moment experiences a torque towards its equilibrium orientation; the excess angular momentum in the magnetic subsystem flows into the lattice. Here we show that this flow can be reversed by the three-magnon splitting process and experimentally achieve the enhancement of the spin current emitted by the interacting spin waves. This mechanism triggers angular momentum transfer from the lattice to the magnetic subsystem and modifies the spin-current emission. The finding illustrates the importance of magnon-magnon interactions for developing spin-current based electronics.     

Spontaneous emission and radiation properties of a driven four-level atom embedded in an anisotropic PBG

The spontaneous emission from a driven four-level tripod atom embedded in an anisotropic photonic crystal is investigated in this paper. We find that time-evolution properties and components of the emitted fields are dependent on the relative position of the upper level of the atom from the band edge and the space between two lower levels. The radiation field emitted by the atom is calculated more accurately. The energy is translated from one form to another with the increase of distance from the atom and the upper level's relative position. The evolution properties and the spontaneous spectrum are also studied. The results analyzed here are consistent with the distribution of emitted fields.     

Controlled growth of well-aligned GaS nanohornlike structures and their field emission properties

Here, we report the synthesis of vertically aligned gallium sulfide (GaS) nanohorn arrays using simple vapor-liquid-solid (VLS) method. The morphologies of GaS nano and microstructures are tuned by controlling the temperature and position of the substrate with respect to the source material. A plausible mechanism for the controlled growth has been proposed. It is important to note that the turn-on field value of GaS nanohorns array is found to be the low turn-on field 4.2 V/μm having current density of 0.1 μA/cm(2). The striking feature of the field emission behavior of the GaS nanohorn arrays is that the average emission current remains nearly constant over long time without any degradation.     

Controlled synthesis and field emission properties of ZnO nanostructures with different morphologies

By simply controlling atmosphere, rods, tetraleg-rods, and arrays of ZnO nanostructures have been fabricated respectively through pure zinc powder evaporation without catalyst at temperature of 650 - 700 degrees C. Investigations through HRTEM and XRD showed that the growth of the synthesized ZnO nanostructures was controlled by vapor-solid mechanism. Field emission measurements revealed that all of the structures, owing to their very low turn-on voltage, sufficient emission current and proper linearity of 1/V - Ln(l/V2), are likely to be potential candidates as a field emitter. The results also indicated that field emission properties are relative to morphology and size of the tips of ZnO nanostructures, and the nanorods with sharp tips possess the first-class FE property.     

Deposition of diamond-like carbon films by using liquid phase electrodeposition technique and its electron emission properties

We have deposited diamond-like carbon (DLC) films by electrodeposition technique in methanol liquid. XPS showed the films mainly contain carbon. IR spectrum indicated that as-deposited films are hydrogenated carbon films, with the hydrogen mainly bonded to sp³ carbon. Raman measurement suggested that the films consisted of sp³ and sp² carbon. The field emission (FE) property of DLC coated on Si has been measured. The field emission of DLC films started at an applied voltage of 160 V, compared with silicon tip arrays at 600 V, and an emission current of DLC films up to 55 A at 360 V was achieved.     

悬浮单滴微萃取-液相色谱法测定苹果酒中三种杀菌剂

采用悬浮单滴微萃取-液相色谱法测定苹果酒中三唑醇、2,4,6–三氯酚和咪酰胺3种杀菌剂。8μL正十二醇作萃取剂,反相C18色谱柱,甲醇-乙腈-水(70:2:30,v/v,甲酸调pH=3.8)流动相,检测波长225 nm。采用基质校准工作曲线,3种杀菌剂线性关系良好,相关系数大于0.9992,相对标准偏差小于3.8%。     

Thermo-hydrodynamic transport phenomena in partially wetting liquid plugs moving inside micro-channels

Single-phase as well as two-phase fluid flows inside mini/micro-channels and capillary tubes are of practical importance in many miniaturized engineering systems. While several issues related to single-phase transport are fairly well understood, two-phase systems still pose challenges for engineering design. The presence of gas–liquid interfaces, dominance of surface forces, moving contact lines, wettability, dynamic contact angle hysteresis and flow in confined geometries are some of the unique features of two-phase systems, which manifest into complex transport phenomena. While Taylor plug/bubble flow is a fairly common flow pattern in several micro-fluidic devices operating at low Bond number, the ensuing transport characteristics are complex and still not fully discerned. This review paper aims at highlighting the nuances and features of a unit cell of a Taylor plug flow, especially focusing on partially wetting systems, which are more common in engineering applications. Emphasis is given to a ‘unit cell’ flow system consisting of an isolated liquid Taylor plug with adjacent gas phase, confined in a capillary tube. Such a seemingly simple flow condition poses considerable challenges for discerning and modelling local thermo-hydrodynamic transport coefficients. Relevant background information and fundamentals are carefully scrutinized while summarizing the state-of-the-art. The role of wettability and dissipation near the contact line is highlighted via available experimental and simulation results. Local momentum and heat transfer exchange processes during the motion of an isolated plug of partially wetting liquid moving inside a capillary tube are delineated.     

Motion and dissolution of a drop in a current-carrying liquid

Flow of a liquid carrying an electric current around a nonconducting drop is considered. The results are used for determining the rate of mass exchange between the drop and the surrounding liquid.     

泵内压降和水力损失耦合诱导泵内液氮空化研究

为了研究泵内压降和水力损失耦合诱导泵内液氮空化,采用Zwart空化模型和RNG k-ε湍流模型,并使用CEL语言将饱和蒸气压随温度变化函数关系式导入CFX软件中进行求解,对不同流量下低温泵的空化特性曲线进行分析。研究结果表明,低温泵内压力、温度和空泡体积分数分布与空化的发展程度有关,由于水力损失的作用,小流量工况下,泵内会出现涡状流,从而对叶轮内空化产生影响。     

Optically driven resonance of nanoscale flexural oscillators in liquid

We demonstrate the operation of radio frequency nanoscale flexural resonators in air and liquid. Doubly clamped string, as well as singly clamped cantilever resonators, with nanoscale cross-sectional dimensions and resonant frequencies as high as 145 MHz are driven in air as well as liquid with an amplitude modulated laser. We show that this laser drive technique can impart sufficient energy to a nanoscale resonator to overcome the strong viscous damping present in these media, resulting in a mechanical resonance that can be measured by optical interference techniques. Resonance in air, isopropyl alcohol, acetone, water, and phosphate-buffered saline is demonstrated for devices having cross-sectional dimensions close to 100 nm. For operation in air, quality factors as high as 400 at 145 MHz are demonstrated. In liquid, quality factors ranging from 3 to 10 and frequencies ranging from 20 to 100 MHz are observed. These devices, and an all-optical actuation and detection system, may provide insight into the physics of the interaction of nanoscale mechanical structures with their environments, greatly extending the viscosity range over which such small flexural resonant devices can be operated.