Academic literature on the topic 'Liquid junction interface'

Distribution characteristics of boundary phase in BaB2O4 added BaTiO3 ceramics were investigated with a focus on the curvature difference of solid–liquid interfaces at two-grain and triple junctions. High-resolution transmission electron microscopy revealed that the triple junction of solid grains showed the positive curvature of solid–liquid interface and consisted of the mixture of liquid phase and crystallized BaB2O4 phase. On the other hand, flat amorphous thin film of 2.5-nm thickness was observed at the two-grain junction. This kind of boundary phase distribution characteristic was explained by the solubility difference between two kinds of junctions of solid grains that had different curvature of solid–liquid interfaces.

The interaction between liquid and solid metals where the liquid-solid interface contains three grain boundary lines which meet in triple junction point is considered. The assumption that the liquid grooves may be formed not only along grain boundaries but along triple junctions is presented. The variation of Gibbs energy during the formation of triangle pyramidal groove along triple junction is determined. The dependence of Gibbs energy variation from groove dimensions shows that the wetting of triple junctions occurs by lower temperatures than the wetting of grain boundaries. This result allows to take into account the existence of grain size effect on the liquid phase penetration depth into the polycrystalline sample. The proposed mechanism of wetting in polycrystalline metal contains two stages: the outstrip melt penetration along triple junctions and the liquid grooving on grain boundaries forming the triple junctions. One of the processes – triple junction diffusion or liquid diffusion – may control the wetting in the polycrystalline sample.

The solid/liquid interface is a junction between two condensed phases with completely different atomic arrangements. At the interface between the periodically ordered solid and the amorphous liquid, the atoms adopt a structure that minimizes the excess energy due to the abrupt change between the surrounding phases. Faceted and diffuse interfaces describe two extremes in morphology of a solid/liquid interface. In a faceted interface, the change from solid to liquid occurs over one atomic layer, however periodic order extends into the first few liquid layers adjacent to the crystalline solid, as predicted by numerous models.1 The faceted interface advances by nucleation and growth of ledges on the interface. A diffuse interface has a structure in which the change from solid to liquid occurs over several atomic layers. This interface contains many ledges to which liquid atoms may attach continuously as the interface advances.

AbstractIn situtransmission electron microscopy (TEM) studies allow one to determine the structure, chemistry, and kinetic behavior of solid–liquid (S–L) interfaces with subnanometer spatial resolution. This article illustrates some important contributions ofin situTEM to our understanding of S–L interfaces in Al-Si alloys and liquid In particles in Al and Fe matrices.Four main areas are discussed:ordering in the liquid at a S–L interface, compositional changes across the interface, the kinetics and mechanisms of interface migration, and the contact angles and equilibrium melting temperature of small particles.Results from these studies reveal that (1)partially ordered layers form in the liquid at a Si{111} S–L interface in an Al–Si alloy, (2)the crystalline and compositional changes occur simultaneously across an Al S–L interface, (3)the Al interface is diffuse and its growth can be followed at velocities of a fewnm/s at extremely low undercoolings, and (4)the melting temperature of In particles less than ~ 10 nm in diameter can be raised or lowered in Al or Fe, depending on the contact angle that the S–L interface makes at the three-phase junction. These results illustrate the benefits of in situ TEM for providing fundamental insight into the mechanisms that control the behavior of S–L interfaces in materials.

The component of the liquid-junction potential due to the diffusion of ions across an interface of electrolyte solutions in different solvents was formulated by taking into account the solvent dependence of the transport numbers, t, and of the chemical potentials of ions in the interphase region as determined from experimental data on their variation in the mixed-solvent compositions. The new equation was applied to NaCl/NaCl and HCl/HCl junctions between water and methanol-water solvents over the entire solvent range. Significant differences between the results obtained with the new equation and the old formulation, which treated the transport numbers as solvent-independent, were observed only for the HCl junctions involving 90-100 wt % aqueous methanol, where tH exhibits a sharp minimum as a function of the solvent composition.

The droplet formation in the presence of nanoparticles was studied in a T-shaped microfluidic device numerically. Nanoparticles in continuous phase did not influence droplet formation dynamics obviously. Contrarily, the presence of nanoparticles in dispersed phase will influence evidently droplet formation dynamics, the possible reason is that the accumulation of nanoparticles at the liquid-liquid interface would cause the variation of interfacial tension and the anisotropy of nanoparticles? movement at interface. Discussions on microscopic mechanism of droplet formation in the presence of nanoparticles were carried out.

Chemistry
Ph.D.
Understanding charge transport through molecular junctions and factors affecting the conductivity at the single molecule level is the first step in designing functional electronic devices using individual molecules. A variety of methods have been developed to fabricate metal-molecule-metal junctions in order to evaluate Single Molecule Conductance (SMC). Single molecule junctions usually are formed by wiring a molecule between two metal electrodes via anchoring groups that provide efficient electronic coupling and bind the organic molecular backbone to the metal electrodes. We demonstrated a novel strategy to fabricate single molecule junctions by employing the stabilization provided by the long range ordered structure of the molecules on the surface. The templates formed by the ordered molecular adlayer immobilize the molecule on the electrode surface and facilitate conductance measurements of single molecule junctions with controlled molecular orientation. This strategy enables the construction of orientation-controlled single molecule junctions, with molecules lacking proper anchoring groups that cannot be formed via conventional SMC methods. Utilizing Scanning Tunneling Microscopy (STM) imaging and STM break junction (STM-BJ) techniques combined, we employed the molecular assembly of mesitylene to create highly conductive molecular junctions with controlled orientation of benzene ring perpendicular to the STM tip as the electrode. The long range ordered structure of mesitylene molecules imaged using STM, supports the hypothesis that mesitylene is initially adsorbed on the Au(111) with the benzene ring lying flat on the surface and perpendicular to the Au tip. Thus, long range ordered structure of mesitylene facilitates formation of Au-π-Au junctions. Mesitylene molecules do not have standard anchoring groups providing enough contact to the gold electrode and the only assumable geometry for the molecules in the junction is via direct contact between Au and the π system of the benzene ring in mesitylene. SMC measurements for Au/mesitylene/Au junctions results in a molecular conductance value around 0.125Go, two orders of magnitude higher than the measured conductance of a benzene ring connected via anchoring groups. We attributed this conductance peak to charge transport perpendicular to the benzene ring due to direct coupling between the π system and the gold electrode that happens in planar orientation. The conductance we measured for planar orientation of benzene ring is two order of magnitude larger than conductance of junctions formed with benzene derivatives with conventional linkers. Thus, altering the orientation of a single benzene-containing molecule between the two electrodes from planar orientation to the upright attached via the linkers, results in altering the conductivity in a large order. Based on these findings, by utilizing STM imaging and STM-BJ in an electrochemical environment including potential induced self-assembly formation of terephthalic acid, we designed an electrochemical single molecule switch. Terephthalic acid forms large domains of ordered structure on negatively charged Au(111) surface under negative electrochemical surface potentials with the benzene ring lying flat on the surface due to hydrogen bonding between carboxylic acid groups of neighboring molecules. Formation of long range ordered structure facilitates direct contact between the π system of the benzene ring and the gold electrodes resulting in the conductance peak. On positively charged Au(111), deprotonation of carboxylic acid groups leads to absence of long range ordered structure of molecules with planar orientation and absence of the conductance peak. In this case alternating the surface (electrode) potential from negative to positive charge densities induces a transition in the adlayer structure on the surface and switches conductance value. Hence, electrochemical surface potential can, in principle, be employed as an external stimulus to switch single molecule arrangement on the surface and the conductance in the junction. The observation of conductance switching due to molecule’s arrangement in the junction lead to the hypothesis that for any benzene derivative, an orientation-dependent conductance in the junction due to the contact geometry (i.e. electrode-anchoring groups versus direct electrode-π contact) should be expected. Conventional techniques in fabricating single molecule junctions enable accessing charge transport along only one direction, i.e., between two anchoring groups. However, molecules such as benzene derivatives are anisotropic objects and we are able to measure an orientation-dependent conductance. In order to systematically study anisotropic conductivity at single molecule level, we need to measure the conductance in different and well-controlled orientations of single molecules in the junction. We employed the same EC-STM-BJ set up for SMC measurements and utilize electrochemical potential of the substrate (electrode) as the tuning source to variate the orientation of the single molecule in the junction. We investigated single molecule conductance of the benzene rings with carboxylic acid functional groups in two orientations: one with the benzene ring bridging between two electrodes using carboxylic acids as anchoring groups (upright); and one with the molecule lying flat on the substrate perpendicular to the STM tip (planar). Physisorption of these species on the Au (111) single crystal electrode surface at negative electrochemical potentials results in an ordered structure with the benzene ring in a planar orientation. Positive electrochemical potentials cause formation of the ordered structure with molecules standing upright due to coordination of a deprotonated carboxyl groups to the electrode surface. Thus, formation of the single molecule junction and consequently conductivity measurements is facilitated in two directions for the same molecule and anisotropic conductivity can be studied. In engineering well-ordered two-dimensional (2-D) molecular structures with controlled assembly of molecular species, pH can be employed as another tuning source for the molecular structures and adsorption in experiments conducted in aqueous solutions. Based on simple chemical principles, amine (NH2) groups are hydrogen bond acceptors and donors. Amines are soluble in water and protonation results in protonated (NH3+) and unprotonated (NH2) amine groups in acidic and moderately acidic/neutral solutions, respectively. Thus, amines are suitable molecular building blocks for fabricating 2-D supramolecular structures where pH is employed as a knob to manipulate intermolecular hydrogen bonding leading to phase transitions. We investigated pH induced structural changes in the 1,3,5–triaminobenzene (TAB) monolayer and the formation/disruption of hydrogen bonds between neighboring molecules. Our STM images indicate that in the concentrated acidic solution, the protonated amine groups of TAB are not able to form H-bonds and long range ordered structure of TAB does not form on the Au(111) surface. However, in moderately acidic solution (pH ~ 5.5) at room temperature, protonation on the ring carbon atom generates species capable of forming H-bonds leading to the formation of the long range ordered structures of TAB molecules. Utilizing EC-STM set up, we investigated the controllable fabrication of a TAB 2-D supramolecular structure based on amine-amine hydrogen bonding and effect of pH in formation of ordered/disordered TAB network.
Temple University--Theses

Tato práce je zaměřena jak na cílený tak na přehledný přístup ve studiu proteomiky. Cílená proteomika přináší informace o přítomnosti proteinu a jeho lokalizaci v buňce či tkáni pomocí luminiscenčních značek na bázi kvantových teček, zatímco přehledná proteomika se zabývá identifikací změn v proteomu dvou nebo více jedinců stejného druhu vystavených různým podmínkám. Protože proteomika vyžaduje vysoce citlivé separační a identifikační techniky, byly v této práci ověřeny různé metody zlepšení citlivosti kapilární elektroforézy s hmotnostní detekcí. Použití rozhraní s kapalinovým spojem pro spojení těchto dvou technik, které zajišťuje vyšší citlivost analýz, bylo také ověřeno analýzou metabolitů etanolu a kokainu v lidské moči. Zavedené techniky instrumentace jsou využitelné při posouzení vlivu významných faktorů životního prostředí na živé systémy jak na buněčné tak na molekulární úrovni.

L'etude electrochimique et photoelectrochimique des jonctions semiconducteur-electrolyte non aqueux (ch::(3)oh et ch::(3)cn) de gaas et si permet de mettre en evidence les proprietes de surface de ces materiaux. Realisations des cellules minces (pec), gaas(ch::(3)oh)sno::(2) montrent des rendements de conversion de l'ordre de 12 a 13%

碩士
國立臺灣大學
化學研究所
95
Trifluroacetic acid (TFA) is a commonly used ion-pair reagent in HPLC to improve peak shapes and hence the separation efficiency of peptides. However, TFA is known to cause significant signal suppression when analyzed by electrospray ionization mass spectrometry (ESI-MS). In this study, we try to use TFA as mobile phase additive for capillary electrochromatography (CEC) in the analysis of peptides. Liquid junction interface is used and by manipulating the diameter of the spray tip and the ESI voltage applied, the introduction of make-up solution and TFA within into ESI-MS can be prevented successfully. However, the above interface has limited utility when applied in CEC because the flow rate of the spray tip is much higher than CEC flow rate. In order to match the flow rate of the tip and CEC column the optimized flow rate of ESI will not be achieved. Therefore, a low flow interface is introduced and placed in front of liquid junction interface to separate the ESI voltage, and the voltage applied on the make-up solution can be easily adjusted to match the flow rate of both sides of liquid junction without compromising the ESI optimized flow rate. By using liquid junction-low flow interface, it is possible to employ TFA in CEC for peptide separation and alleviate the suppression effect by TFA at the same time.

It is shown that n-ZnO/H₂O-A/A⁻ junctions (A/A⁻ = [Co(bpy)₃]³⁺/²⁺ or [OsL₂L']³⁺/²⁺) display energetic and kinetic behavior of unprecedented ideality. The rate constant of the junction with the highest driving force increased when the driving force was lowered, which indicates that the junction operated in the inverted regime. The driving force was varied by shifting the conduction-band edge of the semiconductor with pH. The contact with the lowest driving force was found to operate in the normal regime of charge transfer. These results provide the first experimental indication that semiconductor/liquid contacts can operate in the inverted regime. Junctions having a similar driving force but different reorganization energies show the expected dependence of the rate constant on the reorganization energy.

Low surface-recombination velocities (SRVs) were observed for systems with an accumulation of holes or electrons at the Si surface. Formation of the charge-carrier accumulation layer was confirmed by a solution-gated transistor method. Digital simulations revealed that SRVs < 10 cm s⁻¹ can be produced by surfaces with trap densities as large as 10¹² cm⁻² provided that the surface is in accumulation or inversion. The degree of band bending and SRVs of Si(111) in contact with a variety of aqueous fluoride solutions were determined for the first time at open circuit. An accumulation of electrons at the surface is responsible for the low effective SRVs in NH₄F and buffered HF solutions. The protonation of basic defect sites is important for the low SRV of Si(111)/H₂SO_4(aq) and Si(111)/HF_(aq) contacts.

The J-E characteristics of electron-tunnel junctions formed by the electromigration of metal nanowires without a molecule bridging the gap were explored in detail. The low-temperature J-E curves of some junctions showed regions of zero conductivity near zero bias, while such features were absent in the data collected for other junctions. A common pattern was discerned in that the low-bias resistances of all junctions decreased by at least an order of magnitude with increasing temperature according to Abeles' model for electron tunneling in granular metal junctions. These findings were consistent with the Coulomb blockade effect and can be attributed to metal islands in the gap.

Rapid fluid mixing phenomenon in microchannels offers significant advantages in lab-on-chip testing, drug preparations, micro-assay, and micro-combustor applications. Development of new materials for microchannels and advances in micro fabrication techniques continue to aid fluid mixing research that is vital to microfludic applications. Due to the need for low cost and biocompatibility, polymers began to play important role in design of micromixers. Recently, a number of methods and devices are designed to enhance mixing at the microscale [1–3]. A novel idea of introducing bubbles into two mixing streams with three mixing chambers downstream is tested by means of experiments [3]. The interaction among the bubbles in the mixing chamber results in the stretching and folding of the laminar flow interface leading to a rapid chaotic mixing in short period of time. However, the physics of recirculation zones, bubble formation, and bubble fragmentation must be fully understood in order to design efficient micromixers using this technique. The objective of the present work is to numerically study the formation of recirculation zones, bubble formation, and bubble break-up in microchannels. Numerical calculations were performed with finite volume CFD code ANSYS Fluent. Results obtained with structured grids with about 47,000 grid points. Different gas velocities, liquids velocities and inlet angles were used to investigate the flowfield. Results show that the liquid velocity has a major effect on the circulations inside the channel which impact the formation of the gas bubble. Also, at low liquid velocities, the length of the gas slug is affected by the gas velocity.

Droplet formation in a microfluidic T-junction device which is high aspect ratio rectangular channel connected by a perpendicular channel were investigated experimentally. This geometry is quite similar to the classic T-junction device, however the perpendicular channel is a slightly narrower with respect to the dispersed phase inlet, leading to remarkably different result. The perfectly controllable droplets were found to be monodispersed with a less than 2% variation in micron size. Experimental results, including the relation between diameter and flow rates, the change of the velocity and pressure at drop break-up process, had been analyzed in detail. The single breakup process and the quasistatic character were described by evolution of the width and length of the liquid-liquid interface. Finally, in contrast to the capillary instability in an unbounded fluid, the breakup process was explained in term of absolute instabilities.

This paper aims to investigate a mechanism of microdroplet formation using “multicolor confocal micro particle image velocimetry (PIV)” technique. The present system can measure dynamical behavior of multiphase flow separately and simultaneously. It also enables to identify the interactions between two immiscible fluids. We have applied this system to measure the water droplet formation at a micro T-shaped junction. We have also succeeded in dispersing fluorescent tracer particles into both phases. The interaction between the internal flow of to-be-dispersed water phase and of continuous oil phase is measured as a liquid-liquid multiphase flow. As a result of PIV measurement and interfacial geometry scanning, the relationship between flow structure of each fluid and interfacial geometry is clarified. It indicates that the gap between the tip of discontinuous flow and capillary wall, and interface area play an important role in the flow structure and shear stress on the interface.

In this paper a novel optofluidic setup, fabricated on a single layer device for in-line droplet characterization yielding droplet-size, droplet-frequency, and optical properties with compatibility for full on-chip integration is presented. Chips were fabricated using a simple, fast, and cost effective technology. A T-junction arrangement on the device is used for droplet generation. The optical part of the setup consists of an external light source, external silicon photodetectors, integrated air micro-lenses, and an integrated waveguide. The design makes use of partial light reflection/transmission at the solid-liquid interface to count, size, and discriminate droplets based on their optical properties. When passing the interrogation point, droplets having a lower refractive index as the continuous phase result in light deflections. Both, reflected and transmitted light, are detected simultaneously. A relation of those two signals is then used for the analysis resulting in a continuously stable signal. The generated pattern is unique for different droplets and can be exploited for droplet characterization. Using this arrangement, droplets of de-ionized water (DI) were counted at frequencies of up to 320 droplets per second. In addition, information about the droplet sizes and their variations could be obtained. Finally, 5 mol/L CaCl2 and DI droplets, having different indices of refraction were examined and could clearly be discriminated based on their unique reflected and transmitted light signals. This principle can be applied for the detection of dissolved molecules in droplets as long as they influence the index of refraction. Examples could be the determination of DNA or protein content in the droplet.

In this paper the Navier-stokes equations for a single liquid slug have been solved in order to predict the circulation patterns within the slug. Surface tension effects on the air-water interface have been investigated by solving the Young–Laplace equation. The calculated interface shape has been utilized to define the liquid slug geometry at the front and tail interfaces of the slug. Then the effects of the surface tension on the hydrodynamics of the two-phase slug flow have been compared to those where no surface tension forces exist. The importance of the complex flow field features in the vicinity of the two interfaces has been investigated by defining a non-dimensional form of the wall shear stress. The latter quantity has been formulated based on non-dimensional parameters in order to define a general Moody friction factor for typical two-phase slug flows in microchannels. Moreover, the hydrodynamics of slug flow formation has been examined using computational fluid dynamics (CFD). The volume-of-fluid (VOF) method has been applied to monitor the growth of the instability at the air-water interface. The lengths of the slugs have been correlated to the pressure fluctuations in the mixing region of the air and water streams at an axisymmetric T-junction. The main frequencies of the pressure fluctuations have been investigated using the Fast Fourier Transform (FFT) method.

We present a front-tracking/finite difference method for simulation of drop solidification, where the melt is confined by its own surface tension. The problem includes temporal evolution of three interfaces, i.e. solid–liquid, solid–air, and liquid–air, that are explicitly tracked under the assumption of axisymmetry. The solid–liquid interface is propagated with a normal velocity that is calculated from the normal temperature gradient across the front and the latent heat. The liquid–air front is advected by the velocity interpolated from nearest bulk fluid flow velocities. Method validation is carried out by comparing computational results with exact solutions for two-dimensional Stefan problems, and with related experiments. We then use the method to investigate a drop solidifying on a cold plate in which there exists volume expansion due to density difference between the solid and liquid phases. Effects of the tri-junction in terms of growth angles on the solidification process are also investigated. Computational results show that a decrease in the density ratio of solid to liquid or an increase in the growth angle results in an increase in the height of the solidified drop. In addition, reducing the gravitational effect also increases the drop height after solidification.

Abstract The p-n junction of a GaAs light emitting diode is fabricated using liquid phase epitaxy (LPE). The junction is grown on a Si doped (~1018/cm3) GaAs substrate. Intermittent yield loss due to forward voltage snapback was observed. Historically, out of specification forward voltage (Vf) parameters have been correlated to abnormalities in the junction formation. Scanning electron (SEM) and optical microscopy of cleaved and stained samples revealed a continuous layer of material approximately 2.5 to 3.0 urn thick at the n-epi/substrate interface. Characterization of a defective wafer via secondary ion mass spectroscopy (SIMS) revealed an elevated concentration of O throughout the region containing the defect. X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) data taken from a wafer prior to growth of the epi layers did not reveal any unusual oxidation or contamination. Extensive review of the processing data suggested LPE furnace pressure was the obvious source of variability. Processing wafers through the LPE furnace with a slight positive H2 gas pressure has greatly reduced the occurrence of this defect.

This article examines the velocity distributions of microscopic liquid-liquid two-phase flows by means of micro particle image velocimetry (micro-PIV). Aqueous droplets are dispersed into an oil bulk at the T-junction of a micro fluidic Polydimethylsiloxane (PDMS) device. The channel geometry is rectangular (H: 100μm, W: 100μm). The flow is pressure driven. Tracer particles (D: 0.5–1.2μm) are added to either phase, enabling simultaneous measurements in both phases. However, the use of immiscible liquids causes optical disturbances due to a difference in refractive indices of the two liquids and due to a curved interface geometry. Particle images are thus imaged in a distorted field of view. The results of a PIV analysis will be inaccurate in scaling as well as in location of the velocity vectors — depending on the mismatch of the refractive index. We present a basic analysis on the effect of mismatched refractive indices on the precision of the velocity measurements. The estimation is based on Snell’s law and the simplified geometry of a spherical droplet. Furthermore, we propose a method to match not only the index of refraction accurately but also to leave one additional degree of freedom to set an additional property of the liquid-liquid system, e.g. viscosity ratio or density ratio. The latter ensures that properties of the modified liquid-liquid system are close to those of the non-modified two-phase system. The findings of this study are part of the design of a Lab-on-a-Chip device. It performs a DNA analysis in an online quality control application. The miniaturization of a two-phase flow combines the benefits of confined sample compartments (i.e. droplets) with the easy-to-control process parameters of a miniaturized device (e.g. temperature, pressure). Thus band broadening of the sample by Taylor-Aris dispersion is avoided and the processes can be set accurately.

We have investigated heat and mass transport in single-walled carbon nanotubes (SWNTs) using molecular dynamics methods. Particular attention was paid on the non-equilibrium dynamics at the interface between SWNT and other materials, which strongly manifests in nanoscale. In the first part, we have investigated the heat transport through the interface between SWNTs and surrounding argon matrices in liquid and solid phases. By analyzing the energy relaxation from SWNT to the matrices using non-stationary molecular dynamics simulations, elastic and inelastic thermal energy transports across the interface were separately quantified. The result reveals that the elastic interaction transports energy much faster than the inelastic one, but carries much smaller energy due to slow intra-SWNT phonon relaxation. In the second part, we have investigated a possibility to utilize nonequilibrium thermal interface to transport water through an SWNT. By applying the longitudinal temperature gradient to the SWNT, it is demonstrated that the water cluster is efficiently driven at average acceleration proportional to the temperature gradient. However, the transport simulations with a junction of two different SWNTs suggest that an angstrom diameter difference may result in a significant drag for small diameter SWNTs.

A novel concept of mixing based on 2-D numerical study is proposed where Taylor bubble flows past an obstacle inside a horizontal microchannel. A square shaped obstacle of size 0.02 × 0.02 mm2 is considered inside a microchannel of diameter 0.2 mm. Water and air enters at the two inlet ends of a T-junction and creates Taylor bubble flow at the junction. The obstacle is placed in the downstream at a sufficient distance from the junction where air and water meet. This ensures stability of the Taylor bubble by the time it touches the obstacle. The position of the obstacle is varied along the perpendicular to the flow direction. First, the obstacle is placed exactly at the centre, thus providing equal space of 0.09 mm each on its either side. When Taylor bubble touches this obstacle, it splits and moves through both sides of the obstacle with perfect symmetric flow. The bubbles again join to form the original bubble as it moves past the obstacle. This is inline with the prior expectation. Next, the obstacle is moved by 0.02 mm away from the centre line towards one side, thus providing gap of 0.11 mm and 0.07 mm respectively on the two sides of the obstacle. Now it is found that when the bubble touches the obstacle it do not split in to two, rather the whole bubble moves through the bigger opening of 0.11 mm and only water flows through the smaller opening of 0.07 mm. Similar phenomena is observed when the bubble is further moved away from the centre line towards one side. The liquid-gas interface is found to be continuously changing its shape due to disturbance created by the presence of an obstacle. This causes turbulence inside the liquid plug between two consecutive bubbles, which is confirmed from velocity vector fields. This raises a hope to enhance heat and mass transfer in microchannels by placing multiple obstacles.