共查询到20条相似文献，搜索用时 15 毫秒
1.
在三次采油提高原油采收率的过程中,向油层注入表面活性剂,是当今提高原油采收率的重要方法。但单独使用非离子或阴离子表面活性剂都具有一定局限性。复配后的混合体系具有两种表面活性剂的优点,又可产生超低界面张力。本文分析了表面活性剂驱油机理,结合阴离子表面活性剂与非离子表面活性剂的性能特点,通过现场实验和理论分析得出了复配所产生的优良性质对驱油的作用,可以在驱油过程中产生超低界面张力。如果界面张力足够低,则滞留油就可变为流动油而开采出来,从而达到提高原油采收率的目的。 相似文献
2.
An emulsion system was simulated under simple shear rates to analyze its rheological
characteristics using a hierarchical multi-scale approach. The molecular dynamics (MD) simulation
was used to describe the interface of droplets in an emulsion. The equations derived from the MD
simulation relative to interfacial tension, temperature, and surfactant concentration were applied
as input parameters within lattice Boltzmann method (LBM) calculations. In the LBM simulation, we
calculated the relative viscosity of an emulsion under a simple shear rate along with changes in
temperature, shear rate, and surfactant concentration. The equations from the MD simulation showed
that the interfacial tension of the droplets tended to decrease with an increase in temperature and
surfactant concentration. The relative viscosity from the LBM simulation decreased with an increase
in temperature. The shear thinning phenomena explaining the inverse proportion between shear rate
and viscosity were observed. An increase in the surfactant concentration caused an increase in the
relative viscosity for a decane-in-water emulsion, because the increased deformation caused by the
decreased interfacial tension significantly influenced the wall shear stress. 相似文献
3.
The applicability of droplet-based microfluidic systems to many research fields stems from the fact that droplets are generally considered individual and self-contained reaction vessels. This study demonstrates that, more often than not, the integrity of droplets is not complete, and depends on a range of factors including surfactant type and concentration, the micro-channel surface, droplet storage conditions, and the flow rates used to form and process droplets. Herein, a model microfluidic device is used for droplet generation and storage to allow the comparative study of forty-four different oil/surfactant conditions. Assessment of droplet stability under these conditions suggests a diversity of different droplet failure modes. These failure modes have been classified into families depending on the underlying effect, with both numerical and qualitative models being used to describe the causative effect and to provide practical solutions for droplet failure amelioration in microfluidic systems. 相似文献
4.
Deformation-based circulating tumor cell (CTC) microchips are a representative diagnostic device for early cancer detection. This type of device usually involves a process of CTC trapping in a confined microgeometry. Further understanding of the CTC flow regime, as well as the threshold passing-through pressure, is a key to the design of deformation-based CTC filtration devices. In the present numerical study, we investigate the transitional deformation and pressure signature from surface tension dominated flow to viscous shear stress dominated flow using a droplet model. Regarding whether CTC fully blocks the channel inlet, we observe two flow regimes: CTC squeezing and shearing regime. By studying the relation of CTC deformation at the exact critical pressure point for increasing inlet velocity, three different types of cell deformation are observed: (1) hemispherical front, (2) parabolic front, and (3) elongated CTC co-flowing with carrier media. Focusing on the circular channel, we observe a first increasing and then decreasing critical pressure change with increasing flow rate. By pressure analysis, the concept of optimum velocity is proposed to explain the behavior of CTC filtration and design optimization of CTC filter. Similar behavior is also observed in channels with symmetrical cross sections like square and triangular but not in rectangular channels which only results in decreasing critical pressure. 相似文献
5.
Droplet based microfluidic systems provide an ideal platform for partitioning and manipulating aqueous samples for analysis. Identifying stable operating conditions under which droplets are generated is challenging yet crucial for real-world applications. A novel three-dimensional microfluidic platform that facilitates the consistent generation and gelation of alginate-calcium hydrogel microbeads for microbial encapsulation, over a broad range of input pressures, in the absence of surfactants is described. The unique three-dimensional design of the fluidic network utilizes a height difference at the junction between the aqueous sample injection and organic carrier channels to induce droplet formation via a surface tension enhanced self-shearing mechanism. Combined within a flow-focusing geometry, under constant pressure control, this arrangement facilitates predictable generation of droplets over a much broader range of operating conditions than that of conventional two-dimensional systems. The impact of operating pressures and geometry on droplet gelation, aqueous and organic material flow rates, microbead size, and bead generation frequency are described. The system presented provides a robust platform for encapsulating single microbes in complex mixtures into individual hydrogel beads, and provides the foundation for the development of a complete system for sorting and analyzing microbes at the single cell level. 相似文献
6.
This work proposes the use of charged droplets driven by the Coulombic force as solution-phase reaction chambers for biological microreactions. A droplet can be charged near an electrode under dc voltage by direct contact to the electrode. This process is called electrical charging of droplet (ECOD). This charged droplet can then be transported rapidly between electrodes following the arc of an electric field line by exploiting electrostatic force. As on-demand electrocoalescence, both alkalization of phenolphthalein and bioluminescence reaction of luciferase in the presence of adenosine triphosphate are studied to test the feasibility of the biochemical microreactors using ECOD. Two oppositely charged droplets are merged to have a color change immediately after microchemical reaction. The applicability of an ECOD-driven droplet to measurement of glucose concentration is also tested. The glucose concentration is measured using a colorimetric enzyme-kinetic method based on Trinder’s reaction [J. Clin. Pathol. 22, 158 (1969)]. The color change in the merged droplet is detected with an absorbance measurement system consisting of a photodiode and a light emitting diode. 相似文献
7.
人体就像一个弹簧,劳累、紧张就是外力;学习、生活、生存又是内力。当内外压力超过极限或持续时间过长时,身体这个弹簧就会发生永久变形,精神就会走向崩溃。 相似文献
8.
Specific binding and magnetic concentration of CD8+ T-lymphocytes on electrowetting-on-dielectric platform 总被引：1，自引：0，他引：1
In the quest to create a low-power portable lab-on-a-chip system, we demonstrate the specific binding and concentration of human CD8+ T-lymphocytes on an electrowetting-on-dielectric (EWOD)-based digital microfluidic platform using antibody-conjugated magnetic beads (MB-Abs). By using a small quantity of nonionic surfactant, we enable the human cell-based assays with selective magnetic binding on the EWOD device in an air environment. High binding efficiency (～92%)of specific cells on MB-Abs is achieved due to the intimate contact between the cells and the magnetic beads (MBs) produced by the circulating flow within the small droplet. MBs have been used and cells manipulated in the droplets actuated by EWOD before; reported here is a cell assay of a clinical protocol on the EWOD device in air environment. The present technique can be further extended to capture other types of cells by suitable surface modification on the MBs. 相似文献
9.
We present a novel method of generating and retrieving droplets stored in microfluidic grooves or cavity structures. First we designed and fabricated polydimethylsiloxane microchannels with grooves on the walls and then produced a two-phase flow of oil and aqueous phases to form aqueous phase droplets in an oil state. We propose the following three mechanisms of droplet generation: the contact line on the groove wall continues moving along the wall and descends to the bottom of the cavity, confining the aqueous phase in the cavity; once the interface between the oil and aqueous phases moves into the cavity, the interface contacts the top of the neighboring groove; and a spherical droplet forms at the corner in the cavity due to surface tension. The viscosity of the oil phase and the surface tension of the interface determine whether a droplet can be generated. Then, we could adjust the velocity of the interface and the aspect ratio of the cavity to achieve the optimal conditions for generating the single droplet. We observed that the largest droplet is stably generated without a daughter droplet at typical values of free-stream velocity (10 μl∕min) and groove pitch 110 μm for all three cases with different oil phases (20, 50, and 84 cP). This technique is expected to serve as a platform for droplet-based reaction systems, particularly with regard to monitoring cell behavior, in vitro expression, and possibly even micropolymerase chain reaction chambers. 相似文献
10.
11.
Jairus Kleinert Vijay Srinivasan Arnaud Rival Cyril Delattre Orlin D. Velev Vamsee K. Pamula 《Biomicrofluidics》2015,9(3)
The operation of digital microfluidic devices with water droplets manipulated by electrowetting is critically dependent on the static and dynamic stability and lubrication properties of the oil films that separate the droplets from the solid surfaces. The factors determining the stability of the films and preventing surface fouling in such systems are not yet thoroughly understood and were experimentally investigated in this study. The experiments were performed using a standard digital microfluidic cartridge in which water droplets enclosed in a thin, oil-filled gap were transported over an array of electrodes. Stable, continuous oil films separated the droplets from the surfaces when the droplets were stationary. During droplet transport, capillary waves formed in the films on the electrode surfaces as the oil menisci receded. The waves evolved into dome-shaped oil lenses. Droplet deformation and oil displacement caused the films at the surface opposite the electrode array to transform into dimples of oil trapped over the centers of the droplets. Lower actuation voltages were associated with slower film thinning and formation of fewer, but larger, oil lenses. Lower ac frequencies induced oscillations in the droplets that caused the films to rupture. Films were also destabilized by addition of surfactants to the oil or droplet phases. Such a comprehensive understanding of the oil film behavior will enable more robust electrowetting-actuated lab-on-a-chip devices through prevention of loss of species from droplets and contamination of surfaces at points where films may break. 相似文献
12.
辽中城市群规模结构演变分析 总被引：11，自引：0，他引：11
通过构建首位城市规模、城镇数目、城市首位度、大城市增长指数和城镇规模分布的基尼系数 5个指标 ,对经济转型期辽中城市群规模结构演变进行数量分析 .辽中城市群规模结构为极不平衡的首位分布 ,并且城乡差距逐步扩大 .辽中城市群规模结构演变的驱动因子中 ,制度变迁是深层次的驱动因素 ,经济增长是最直接的驱动因素 ,技术和产业组织的二元结构是城乡二元结构的重要影响因素 .最后从城乡一体化的角度提出建立农村土地使用权市场和大力提高农民素质等结构优化对策 . 相似文献
13.
Zhichao Guan Yuan Zou Mingxia Zhang Jiangquan Lv Huali Shen Pengyuan Yang Huimin Zhang Zhi Zhu Chaoyong James Yang 《Biomicrofluidics》2014,8(1)
Although digital detection of nucleic acids has been achieved by amplification of single templates in uniform microfluidic droplets and widely used for genetic analysis, droplet-based digital detection of proteins has rarely been reported, largely due to the lack of an efficient target amplification method for protein in droplets. Here, we report a key step towards digital detection of proteins using a highly parallel microfluidic droplet approach for single enzyme molecule detection in picoliter droplets via enzyme catalyzed signal amplification. An integrated microfluidic chip was designed for high throughput uniform droplet generation, monolayer droplet collection, incubation, detection, and release. Single β-galatosidase (β-Gal) molecules and the fluorogenic substrate fluorescein di-β-D-galactopyranoside were injected from two separated inlets to form uniform 20 μm droplets in fluorinated oil at a frequency of 6.6 kHz. About 200 000 droplets were captured as a monolayer in a capture well on-chip for subsequent imaging detection. A series of β-Gal solutions at different concentrations were analyzed at the single-molecule level. With no enzyme present, no droplets were found to fluoresce, while brightly fluorescent droplets were observed under single-enzyme molecule conditions. Droplet fluorescence intensity distribution analysis showed that the distribution of enzyme molecules under single-molecule conditions matched well with theoretical prediction, further proving the feasibility of detecting single enzyme molecules in emulsion droplets. Moreover, the population of fluorescent droplets increased as the β-Gal concentration increased. Based on a digital counting method, the measured concentrations of the enzyme were found to match well with input enzyme concentration, establishing the accuracy of the digital detection method for the quantification of β-Gal enzyme molecules. The capability of highly parallel detection of single enzyme molecules in uniform picoliter droplets paves the way to microdroplet based digital detection of proteins. 相似文献
14.
We present the conformal coating of non-spherical magnetic particles in a co-laminar flow
microfluidic system. Whereas in the previous reports spherical particles had been coated with thin
films that formed spheres around the particles; in this article, we show the coating of
non-spherical particles with coating layers that are approximately uniform in thickness. The novelty
of our work is that while liquid-liquid interfacial tension tends to minimize the surface area of
interfaces—for example, to form spherical droplets that encapsulate spherical particles—in our
experiments, the thin film that coats non-spherical particles has a non-minimal interfacial area. We
first make bullet-shaped magnetic microparticles using a stop-flow lithography method that was
previously demonstrated. We then suspend the bullet-shaped microparticles in an aqueous solution and
flow the particle suspension with a co-flow of a non-aqueous mixture. A magnetic field gradient from
a permanent magnet pulls the microparticles in the transverse direction to the fluid flow, until the
particles reach the interface between the immiscible fluids. We observe that upon crossing the
oil-water interface, the microparticles become coated by a thin film of the aqueous fluid. When we
increase the two-fluid interfacial tension by reducing surfactant concentration, we observe that the
particles become trapped at the interface, and we use this observation to extract an approximate
magnetic susceptibility of the manufactured non-spherical microparticles. Finally, using
fluorescence imaging, we confirm the uniformity of the thin film coating along the entire curved
surface of the bullet-shaped particles. To the best of our knowledge, this is the first
demonstration of conformal coating of non-spherical particles using microfluidics. 相似文献
15.
Microorganisms can effectively generate propulsive force at the microscale where viscous forces overwhelmingly dominate inertia forces; bacteria achieve this task through flagellar motion. When swarming bacteria, cultured on agar plates, are blotted onto the surface of a microfabricated structure, a monolayer of bacteria forms what is termed a “bacterial carpet,” which generates strong flows due to the combined motion of their freely rotating flagella. Furthermore, when the bacterial carpet coated microstructure is released into a low Reynolds number fluidic environment, the propulsive force of the bacterial carpet is able to give the microstructure motility. In our previous investigations, we demonstrated motion control of these bacteria powered microbiorobots (MBRs). Without any external stimuli, MBRs display natural rotational and translational movements on their own; this MBR self-actuation is due to the coordination of flagella. Here, we investigate the flow fields generated by bacterial carpets, and compare this flow to the flow fields observed in the bulk fluid at a series of locations above the bacterial carpet. Using microscale particle image velocimetry, we characterize the flow fields generated from the bacterial carpets of MBRs in an effort to understand their propulsive flow, as well as the resulting pattern of flagella driven self-actuated motion. Comparing the velocities between the bacterial carpets on fixed and untethered MBRs, it was found that flow velocities near the surface of the microstructure were strongest, and at distances far above, the surface flow velocities were much smaller. 相似文献
16.
In this study, a microfluidic process is proposed for preparing monodisperse micrometer-sized hydrogel beads. This process utilizes non-equilibrium aqueous droplets formed in a polar organic solvent. The water-in-oil droplets of the hydrogel precursor rapidly shrunk owing to the dissolution of water molecules into the continuous phase. The shrunken and condensed droplets were then gelled, resulting in the formation of hydrogel microbeads with sizes significantly smaller than the initial droplet size. This study employed methyl acetate as the polar organic solvent, which can dissolve water at 8%. Two types of monodisperse hydrogel beads—Ca-alginate and chitosan—with sizes of 6–10 μm (coefficient of variation < 6%) were successfully produced. In addition, we obtained hydrogel beads with non-spherical morphologies by controlling the degree of droplet shrinkage at the time of gelation and by adjusting the concentration of the gelation agent. Furthermore, the encapsulation and concentration of DNA molecules within the hydrogel beads were demonstrated. The process presented in this study has great potential to produce small and highly concentrated hydrogel beads that are difficult to obtain by using conventional microfluidic processes. 相似文献
17.
We report how cell rheology measurements can be performed by monitoring the deformation of a cell in a microfluidic constriction, provided that friction and fluid leaks effects between the cell and the walls of the microchannels are correctly taken into account. Indeed, the mismatch between the rounded shapes of cells and the angular cross-section of standard microfluidic channels hampers efficient obstruction of the channel by an incoming cell. Moreover, friction forces between a cell and channels walls have never been characterized. Both effects impede a quantitative determination of forces experienced by cells in a constriction. Our study is based on a new microfluidic device composed of two successive constrictions, combined with optical interference microscopy measurements to characterize the contact zone between the cell and the walls of the channel. A cell squeezed in a first constriction obstructs most of the channel cross-section, which strongly limits leaks around cells. The rheological properties of the cell are subsequently probed during its entry in a second narrower constriction. The pressure force is determined from the pressure drop across the device, the cell velocity, and the width of the gutters formed between the cell and the corners of the channel. The additional friction force, which has never been analyzed for moving and constrained cells before, is found to involve both hydrodynamic lubrication and surface forces. This friction results in the existence of a threshold for moving the cells and leads to a non-linear behavior at low velocity. The friction force can nevertheless be assessed in the linear regime. Finally, an apparent viscosity of single cells can be estimated from a numerical prediction of the viscous dissipation induced by a small step in the channel. A preliminary application of our method yields an apparent loss modulus on the order of 100 Pa s for leukocytes THP-1 cells, in agreement with the literature data. 相似文献
18.
Highly motile Phytophthora sojae (P. sojae) zoospores of an oomycete plant pathogen and antioomycete candidate chemicals were encapsulated into microdroplets. Random fast self-motion of P. sojae zoospores was overcome by choosing an appropriate flow rate for a zoospore suspension. To influence stochastic loading of zoospores into a microfluidic channel, a zoospore suspension was directly preloaded into a microtubing with a largely reduced inner diameter. A relatively high single zoospore encapsulation rate of 60.5% was achieved on a most trivial T-junction droplet generator platform, without involving any specially designed channel geometry. We speculated that spatial reduction in the diameter direction of microtubing added a degree of zoospore ordering in the longitudinal direction of microtubing and thus influenced positively to change the inherent limitation of stochastic encapsulation of zoospores. Comparative phenotypic study of a plant oomycete pathogen at a single zoospore level had not been achieved earlier. Phenotypic changes of zoospores responding to various chemical concentration conditions were measured in multiple droplets in parallel, providing a reliable data set and thus an improved statistic at a low chemical consumption. Since each droplet compartment contained a single zoospore, we were able to track the germinating history of individual zoospores without being interfered by other germinating zoospores, achieving a high spatial resolution. By adapting some existing droplet immobilization and concentration gradient generation techniques, the droplet approach could potentially lead to a medium-to-high throughput, reliable screening assay for chemicals against many other highly motile zoospores of pathogens. 相似文献
19.
20.
A novel actuation method of transporting droplets by using electrical charging of droplet in a dielectric fluid 总被引：1，自引：0，他引：1
We evaluate the feasibility of manipulating droplets in two dimensions by exploiting Coulombic forces acting on conductive droplets immersed in a dielectric fluid. When a droplet suspended in an immiscible fluid is located near an electrode under a dc voltage, the droplet can be charged by direct contact, by charge transfer along an electrically conducting path, or by both mechanisms. This process is called electrical charging of droplet (ECOD). This charged droplet may then be transported rapidly by exploiting Coulombic forces. We experimentally demonstrate electrical actuation of a charged droplet by applying voltage sequences. A charged droplet is two dimensionally actuated by following the direction of the electrical field signal. The droplet does not contact the surface of the microfluidic chip when it moves. This characteristic is very advantageous because treatments of the substrate surfaces of microfluidic chip become simpler. In order to test the feasibility of using ECOD in a droplet-based microreactor, electrocoalescence of two oppositely charged droplets is also studied. When two droplets approach each other due to Coulombic attraction, a liquid bridge is formed between them. We postulate that if the applied electric field is weaker than a certain critical level, the two droplets coalesce instantaneously when the charges are exchanged and redistributed through this liquid bridge. 相似文献