Dynamics of wicking in silicon nanopillars fabricated with interference lithography and metal-assisted chemical etching

The capillary rise of liquid on a surface, or "wicking", has potential applications in biological and industrial processes such as drug delivery, oil recovery, and integrated circuit chip cooling. This paper presents a theoretical study on the dynamics of wicking on silicon nanopillars based on a balance between the driving capillary forces and viscous dissipation forces. Our model predicts that the invasion of the liquid front follows a diffusion process and strongly depends on the structural geometry. The model is validated against experimental observations of wicking in silicon nanopillars with different heights synthesized by interference lithography and metal-assisted chemical etching techniques. Excellent agreement between theoretical and experimental results, from both our samples and data published in the literature, was achieved.     

毛细管气液色谱保留过程的研究

以ＰＥＧ２０Ｍ为代表研究了石英毛细管柱气液色谱保留过程,提出了利用毛细管柱测定分配和吸附常数的公式,并测定了９个温度下的分配和吸附常数。计算了８０℃和１２０℃下４支不同液膜厚度柱上吸附对保留的贡献。结果表明,在薄液膜的柱子上界面吸附对保留具有重要贡献;温度升高可以降低弱极性化合物（如正构烷烃和饱和醚）吸附对保留的贡献,但对其它化合物影响不明显。验证了正构烷烃、２－酮系列和正构伯醇的吸附常数的碳数规律。     

油酸/三乙醇胺/液体石蜡水体系层状润滑性能

采用^2HNMRT和IR,表征了油酸／三乙醇胺／液体石蜡／水体系层状液晶的结构,并以该体系为润滑剂,测定了其在铝合金表面的磨痕宽度和摩擦系数,同时与液体石蜡和商用润滑剂12－羟基硬脂酸锂进行了比较。结果表明,OLA／TEA／LP／H2O体系丑状液晶具有较好的极压性能,对于铝合金材料是一种较好的润滑剂。     

Shapes and dynamics of miscible liquid/liquid interfaces in horizontal capillary tubes

We report optical observations of the dissolution behaviour of glycerol/water, soybean oil/hexane, and isobutyric acid (IBA)/water binary mixtures within horizontal capillary tubes. Tubes with diameters as small as 0.2mm were initially filled with one component of the binary mixture (solute) and then immersed into a solvent-filled thermostatic bath. Both ends of the tubes were open, and no pressure difference was applied between the ends. In the case of glycerol/water and soybean oil/hexane mixtures, we managed to isolate the dissolution (the interfacial mass transfer) from the hydrodynamic motion. Two phase boundaries moving from the ends into the middle section of the tube with the speeds v～D(1/3)t(-2/3)d(2) (D,t and d are the coefficient of diffusion, time and the diameter of the tube, respectively) were observed. The boundaries slowly smeared but their smearing occurred considerably slower than their motion. The motion of the phase boundaries cannot be explained by the dependency of the diffusion coefficient on concentration, and should be explained by the effect of barodiffusion. The shapes of the solute/solvent boundaries are defined by the balance between gravity and surface tension effects. The contact line moved together with the bulk interface: no visible solute remained on the walls after the interface passage. Changes in temperature and in the ratio between gravity and capillary forces altered the apparent contact angles. The IBA/water system had different behaviour. Below the critical (consolute) point, no dissolution was observed: IBA and water behaved like two immiscible liquids, with the IBA phase being displaced from the tube by capillary pressure (the spontaneous imbibition process). Above the critical point, two IBA/water interfaces could be identified, however the interfaces did not penetrate much into the tube.     

Magnetic Actuation of Drops and Liquid Marbles Using a Deformable Paramagnetic Liquid Substrate

The magnetic actuation of deposited drops has mainly relied on volume forces exerted on the liquid to be transported, which is poorly efficient with conventional diamagnetic liquids such as water and oil, unless magnetosensitive particles are added. Herein, we describe a new and additive‐free way to magnetically control the motion of discrete liquid entities. Our strategy consists of using a paramagnetic liquid as a deformable substrate to direct, using a magnet, the motion of various floating liquid entities, ranging from naked drops to liquid marbles. A broad variety of liquids, including diamagnetic (water, oil) and nonmagnetic ones, can be efficiently transported using the moderate magnetic field (ca. 50 mT) produced by a small permanent magnet. Complex trajectories can be achieved in a reliable manner and multiplexing potential is demonstrated through on‐demand drop fusion. Our paramagnetofluidic method advantageously works without any complex equipment or electric power, in phase with the necessary development of robust and low‐cost analytical and diagnostic fluidic devices.     

Forces between a hard surface and an air–aqueous interface with and without films

The adsorption of particles to air–aqueous interfaces is vital in many applications, such as mineral flotation and the stabilization of food foams. The forces in the system determine whether a particle will attach to an air–aqueous interface. The forces between a particle and an air–aqueous interface are influenced by Derjaguin–Landau–Verwey–Overbeek forces (i.e. van der Waals and electrostatic forces), non–Derjaguin–Landau–Verwey–Overbeek forces (e.g. hydrophobic, hydrodynamic, structural, and capillary forces), liquid drainage, and liquid flow. As an air–aqueous interface can be deformed by a particle, the forces measured between an air–aqueous interface and a particle can differ from those measured between two hard surfaces separated by liquid. The presence of a film at an air–aqueous interface can also change the forces.     

Colloidal interactions between asphaltene surfaces in aqueous solutions

Asphaltene at oil/water interfaces plays a dominant role in the recovery of crude oil. In this study, asphaltene monolayer films were deposited on hydrophobic silicon wafers and silica spheres from oil-water interfaces using a Langmuir interfacial trough. The morphology of the deposited asphaltene films was characterized with an atomic force microscope (AFM). The colloidal forces between the prepared asphaltene films in aqueous solutions were measured with AFM to shed light on the stabilization of water or oil droplets coated with asphaltene films. Factors such as solution pH, KCl concentration, calcium addition, and temperature all showed a strong impact on colloidal forces between the prepared asphaltene films. The findings provided a better understanding of asphaltene interfacial films at an oil/water interface in stabilizing bitumen-in-water and water-in-bitumen emulsions.     

An experimental investigation of retention of liquids in corners of a square capillary

The retention of liquids in the corners of a 0.03-cm square capillary after the passage of a gas slug was studied experimentally as a function of capillary number in the range from 10(-3) to 10(-6). In gas-wetting liquid systems, for capillary number greater than 5 x 10(-4), the retention of a wetting liquid in the corners showed a strong dependence on the capillary number; i.e., the retention of the liquid decreased with decreasing capillary number. For capillary number less than 10(-4), the retention of a wetting liquid was found to be determined by the capillary forces and the rate (or viscous) effect was negligible. In gas-oil-water systems involving double displacements--gas was displacing oil which was in turn displacing water--the total retention of water and oil vs capillary number curve showed the same trend as the retention of a wetting phase in a gas-wetting liquid system. However, because of the viscous effect, the water retention showed a continuous decrease with decreasing capillary number and could be lower than the capillary equilibrium value at very low capillary numbers. As a result of this, the oil retention vs capillary number curve in the double displacement process showed a minimum; i.e., oil retention increased with decreasing capillary number in the range of very low capillary numbers.     

快速气相色谱法分析石油饱和烃

提出了一种快速分析原油和岩石抽提物中饱和烃组分的毛细管气相色谱(GC)方法。由于在该方法中采用了细内径毛细管柱,故饱和烃的GC分析周期由原来的80~90 min缩短至15 min,分析速度加快约5倍,大大提高了工作效率和仪器通量,使石油饱和烃得到了很好的分离分析。该方法符合中华人民共和国石油天然气行业标准SY/T5120-1997的要求。20万理论塔板数的细径柱的应用,可供石油中异构烷烃,尤其是甾烷、萜烷类的气相色谱/质谱(GC/MS)快速分析方法及芳烃的GC快速分析方法借鉴。     

Liquid Bridge between Two Moving Spheres: An Experimental Study of Viscosity Effects

The effects of viscosity on the mechanical response of a liquid bridge are investigated in the case of small amounts of liquid axially strained between two moving spheres. An experimental setup allows the measurement of capillary and viscous forces exerted on the spheres as a function of the spheres separation distance and the spheres velocity. The experimental results are found to be accurately described over a large range in spheres velocity and liquid viscosity by a simple closed-form expression. In addition, the bridge rupture distance is found to increase like the square root of the separation velocity. Copyright 2000 Academic Press.     

Interfacial tension and wetting behavior of air/oil/ionic liquid systems

We measured the interfacial tension and the density of air/n-hexane, n-decane, 1-perfluorohexane/1-hexyl-3-methyl-imidazolium hexafluorophosphate systems as a function of temperature. From the air/ionic liquid surface tension values, it was suggested that Coulombic interaction between imidazolium cations and counter anions are not so much different between the surface and bulk. The density values indicated that the decrease of surface tension by saturating organics was closely correlated to the mutual solubility between ionic liquid and organics. Interfacial tension at the oil/ionic liquid interfaces suggested that ionic liquid molecules were more ordered at the oil/ionic liquid interfaces compared to the air/ionic liquid interfaces, but the decrease of the entropy due to the interfacial orientation of ionic liquid was compensated by the increase of the entropy due to the contact of different chemical species. The initial spreading coefficients and the Hamaker constants indicated that all the oil phases spread at the air/ionic liquid interfaces spontaneously, and form the complete wetting films.     

空气/水界面水分子的取向和运动

Here we report a quantitative study of the orientational structure and motion of water molecule at the air/water interface. Analysis of Sum Frequency Generation (SFG) vibrational peak of the free O-H stretching band at 3700 cm-1 in four experimental configurations showed that orientational motion of water molecule at air/water interface is libratory within a limited angular range. The free OH bond of the interfacial water molecule is tilted around 33° from the interface normal and the orientational distribution or motion width is less than 15°. This picture is significantly different from the previous conclusion that the interfacial water molecule orientation varies over a broad range within the ultrafast vibrational relaxation time, the only direct experimental study concluded for ultrafast and broad orientational motion of a liquid interface by Wei et al.(Phys. Rev. Lett. 86, 4799, (2001)) using single SFG experimental configuration.     

Effect of liquid paraffin on the stability of aqueous foam in the presence and absence of electrolytes

The foam stability of dodecyl diphenyl ether disulfonate solution with liquid paraffin droplets in the presence and absence of electrolytes was evaluated, and the stabilization mechanisms were deduced. The foam film is stabilized when the monovalent and divalent counterion concentration is lower than a critical value. However, the foam stability declined with the addition of trivalent counterions. There are two mechanisms we have speculated. Firstly, the counterions reduce the repulsive interaction between the polar groups of surfactants adsorbed at the air/water and oil/water interfaces in the pseudo-emulsion film. Secondly, comparing with the monovalent counterions, the multivalent counterions are not only able to interconnect head groups of adjacent ionic surfactant molecules which are adsorbed at the air/water or oil/water interface, but also to attract the couples of neighboring surfactant head groups adsorbed at the air/water and oil/water interfaces. The attractive interaction between both the interfaces promotes the emulsified droplets piercing the air/water interface.     

Interfacial shear rheology of protein-surfactant layers

The shear rheology of adsorbed or spread layers at air/liquid and liquid/liquid phase boundaries is relevant in a wide range of technical applications such as mass transfer, monolayers, foaming, emulsification, oil recovery, or high speed coating. Interfacial shear rheological properties can provide important information about interactions and molecular structure in the interfacial layer. A variety of measuring techniques have been proposed in the literature to measure interfacial shear rheological properties and have been applied to pure protein or mixed protein adsorption layers at air/water or oil/water interfaces. Such systems play for example an important role as stabilizers in foams and emulsions. The aim of this contribution is to give a literature overview of interfacial shear rheological studies of pure protein and protein/surfactant mixtures at liquid interfaces measured with different techniques. Techniques which utilize the damping of waves, spectroscopic or AFM techniques and all micro-rheological techniques will not discuss here.     

Adhesion hysteresis from interdependent capillary and electrostatic forces

Adhesion hysteresis commonly occurs at the nanoscale in humid atmospheres, yet mechanisms are not entirely understood. Here, the adhesion forces between silicon (111) oxide surfaces and tungsten oxide probes have been examined using interfacial force microscopy. The results show that the adhesion forces during surface approach and separation differ not only in magnitude but also in mechanism, arising mainly from capillary and electrostatic forces, respectively. Surface contact leads to a transient intersurface potential on dewetting. This mechanism of adhesion hysteresis differs in not relying singly on hysteretic wetting. Furthermore, by biasing the surfaces, nonadditivity is demonstrated between the capillary and electrostatic forces at the onset of condensation. These results hold important implications on the interpretation of force in nanoprobe geometries in humid atmospheres.     

Experimental study of the immiscible displacement of shear-thinning fluids in pore networks

The pore scale mechanisms and network scale transient pattern of the immiscible displacement of a shear-thinning nonwetting oil phase (NWP) by a Newtonian wetting aqueous phase (WP) are investigated. Visualization imbibition experiments are performed on transparent glass-etched pore networks at a constant unfavorable viscosity ratio and varying values of the capillary number (Ca), and equilibrium contact angle (theta(e)). Dispersions of ozokerite in paraffin oil are used as the shear-thinning NWP, and aqueous solutions of PEG colored with methylene blue are used as the Newtonian WP. At high Ca values, the tip splitting and lateral spreading of WP viscous fingers are suppressed; at intermediate Ca values, the primary viscous fingers expand laterally with the growth of smaller capillary fingers; at low Ca values, network spanning clusters of capillary fingers separated by hydraulically conductive noninvaded zones of NWP arise. The spatial distribution of the mobility of shear-thinning NWP over the pore network is very broad. Pore network regions of low NWP mobility are invaded through a precursor advancement/swelling mechanism even at relatively high Ca and theta(e) values; this mechanism leads to irregular interfacial configurations and retention of a substantial amount of NWP along pore walls; it becomes the dominant mechanism in displacements performed at low Ca and theta(e) values. The residual NWP saturation increases and the end WP relative permeability decreases as Ca increases and both become more sensitive to this parameter as the shear-thinning behavior strengthens. The shear-thinning NWP is primarily entrapped in individual pores of the network rather than in clusters of pores bypassed by the WP. At relatively high flow rates, the amplitude of the variations of pressure drop, caused by fluid redistribution in the pore network, increase with shear-thinning strengthening, whereas at low flow rates, the motion of stable and unstable menisci in pores is reflected in strong pressure drop fluctuations.     

Soft Polymer Janus Nanoparticles at Liquid–Liquid Interfaces

Soft polymeric Janus nanoparticles (JNPs), made from polystyrene-b-poly(butadiene)-b-poly(methylmethacrylate), PS-PB-PMMA, triblock terpolymers, assemble into a monolayer at the water–oil interface to reduce interfacial tension. The extent to which the polymer chains can deform influences the packing density of the JNPs at the interface. The longer the polymer chains are relative to the core, the softer are the JNPs, resulting in a JNPs assembly with a lower initial lateral packing density. The interfacial activity of JNPs can be further tuned by complexation of the PMMA chains with lithium ions that are introduced into the water phase. This work provides a fundamental understanding of soft JNPs packing at the water–oil interface and provides a strategy to tailor the areal density of soft JNPs at liquid–liquid interface, enabling the design of smart responsive structured-liquid systems.     

液膜预富集水相痕量镍的分析研究

研究了液膜体系对水相中痕量镍离子的富集方法,镍离子从外相水溶液被膜相载体通过液膜运进含有反萃取剂的内相,从而达到富集效果,液膜富集一次回收率达98％,二闪富集倍数250倍,试验了载体,表面活性剂,液体石蜡,膜与内相水的水／油比,乳化液与外相水的乳／水比,内相酸度,外相PH值,富集时间的破乳剂用量等因素的影响,利用正交分析试验选出了最佳试验条件,并比较在相同条件下液膜法与萃取法提取镍的效果,通过液膜富集,使原子吸收法测定痕量镍达到了10^-9级。