| 1. |
- Cohen, Céline, et al.
(författare)
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Parallelised production of fine and calibrated emulsions by coupling flow-focusing technique and partial wetting phenomenon
- 2014
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Ingår i: Microfluidics and Nanofluidics. - : Springer. - 1613-4982 .- 1613-4990. ; 17:5, s. 959-966
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Tidskriftsartikel (refereegranskat)abstract
- The capacity of microfluidic technology to fabricate monodisperse emulsion droplets is well established. Parallelisation of droplet production is a prerequisite for using such an approach for making high-quality materials for either fundamental or industrial applications where product quantity matters. Here, we investigate the emulsification efficiency of parallelised drop generators based on a flow-focusing geometry when incorporating the role of partial wetting in order to make emulsion droplets with a diameter below 10 μm. Confinement intrinsically encountered in microsystems intensifies the role played by interfaces between liquids and solids. We thus take advantage of partial wetting to enhance the maximum confinement accessible due to liquid flow focusing. We compare the performances brought by partial wetting to more established routes such as step emulsification. We show that the step configuration and the partial wetting regime are both well suited for being parallelised and thus open the way to the production of fine and calibrated emulsions for further applications. Finally, this new route of emulsification that exploits partial wetting between the fluids and the channel walls opens possibilities to the formation of substantially smaller droplets, as required in many fields of application.
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| 2. |
- Do-Quang, Minh, et al.
(författare)
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Fluid dynamic behavior of dispensing small droplets through a thin liquid film
- 2010
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Ingår i: Microfluidics and Nanofluidics. - : Springer Science and Business Media LLC. - 1613-4982 .- 1613-4990. ; 9:2-3, s. 303-311
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a technology for dispensing droplets through thin liquid layers. The system consists of a free liquid film, which is suspended in a frame and positioned in front of a piezoelectric printhead. A droplet, generated by the printhead, merges with the film, but due to its momentum, passes through and forms a droplet that separates on the other side and continues its flight. The technology allows the dispensing, mixing and ejecting of picolitre liquid samples in a single step. This paper overviews the concept, potential applications, experiments, results and a numerical model. The experimental work includes studying the flight of ink droplets, which ejected from an inkjet print head, fly through a free ink film, suspended in a frame and positioned in front of the printhead. We experimentally observed that the minimum velocity required for the 80 pl droplets to fly through the 75 ± 24 lm thick ink film was of 6.6 m s-1. We also present a numerical simulation of the passage of liquid droplets through a liquid film. The numerical results for different initial speeds of droplets and their shapes are taken into account. We observed that during the droplet-film interaction, the surface energy is partially converted to kinetic energy, and this, together with the impact time, helps the droplets penetrate the film. The model includes the Navier- Stokes equations with continuum-surface-tension force derived from the phase-field/Cahn-Hilliard equation. This system allows us to simulate the motion of a free surface in the presence of surface tension during merging, mixing and ejection of droplets. The influence of dispensing conditions was studied and it was found that the residual velocity of droplets after their passage through the thin liquid film well matches the measured velocity from the experiment.
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| 3. |
- Gong, Shengjie, et al.
(författare)
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Diagnostic techniques for the dynamics of a thin liquid film under forced flow and evaporating conditions
- 2010
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Ingår i: MICROFLUID NANOFLUID. - : Springer Science and Business Media LLC. - 1613-4982. ; 9:6, s. 1077-1089
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by quantification of micro-hydrodynamics of a thin liquid film which is present in industrial processes, such as spray cooling, heating (e.g., boiling with the macrolayer and the microlayer), coating, cleaning, and lubrication, we use micro-conductive probes and confocal optical sensors to measure the thickness and dynamic characteristics of a liquid film on a silicon wafer surface with or without heating. The simultaneous measurement on the same liquid film shows that the two techniques are in a good agreement with respect to accuracy, but the optical sensors have a much higher acquisition rate up to 30 kHz which is more suitable for rapid process. The optical sensors are therefore used to measure the instantaneous film thickness in an isothermal flow over a silicon wafer, obtaining the film thickness profile and the interfacial wave. The dynamic thickness of an evaporating film on a horizontal silicon wafer surface is also recorded by the optical sensor for the first time. The results indicate that the critical thickness initiating film instability on the silicon wafer is around 84 mu m at heat flux of similar to 56 kW/m(2). In general, the tests performed show that the confocal optical sensor is capable of measuring liquid film dynamics at various conditions, while the micro-conductive probe can be used to calibrate the optical sensor by simultaneous measurement of a film under quasi-steady state. The micro-experimental methods provide the solid platform for further investigation of the liquid film dynamics affected by physicochemical properties of the liquid and surfaces as well as thermal-hydraulic conditions.
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| 4. |
- Ogden, Sam, 1979-, et al.
(författare)
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Fluid behavior of supercritical carbon dioxide with water in a double-Y-channel microfluidic chip
- 2014
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Ingår i: Microfluidics and Nanofluidics. - : Springer Science and Business Media LLC. - 1613-4982 .- 1613-4990. ; 17:6, s. 1105-1112
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Tidskriftsartikel (refereegranskat)abstract
- The use of supercritical carbon dioxide (scCO(2)) as an apolar solvent has been known for decades. It offers a greener approach than, e.g., hexane or chloroform, when such solvents are needed. The use of scCO(2) in microsystems, however, has only recently started to attract attention. In microfluidics, the flow characteristics need to be known to be able to successfully design such components and systems. As supercritical fluids exhibit the exciting combination of low viscosity, high density, and high diffusion rates, the fluidic behavior is not directly transferrable from aqueous systems. In this paper, three flow regimes in the scCO(2)-liquid water two-phase microfluidic system have been mapped. The effect of both total flow rate and relative flow rate on the flow regime is evaluated. Furthermore, the droplet dynamics at the bifurcating exit channel are analyzed at different flow rates. Due to the low viscosity of scCO(2), segmented flows were observed even at fairly high flow rates. Furthermore, the carbon dioxide droplet behavior exhibited a clear dependence on both flow rate and droplet length.
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| 5. |
- Ogden, Sam, 1979-, et al.
(författare)
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Review on miniaturized paraffin phase change actuators, valves, and pumps
- 2014
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Ingår i: Microfluidics and Nanofluidics. - : Springer Science and Business Media LLC. - 1613-4982 .- 1613-4990. ; 17:1, s. 53-71
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Forskningsöversikt (refereegranskat)abstract
- During the last fifteen years, miniaturised paraffin actuation has evolved through the need of a simple actuation principle, still able to deliver large strokes and high actuation forces at small scales. This is achieved by the large and rather incompressible volume expansion associated with the solid-to-liquid phase transition of paraffin. The common approach has been to encapsulate the paraffin by a stiff surrounding that directs the volume expansion towards a flexible membrane, which deflects in a directed stroke. However, a number of alternative methods have also been used in the literature. The most common applications to this date have been switches, positioning actuators, and microfluidic valves and pumps. This review will treat the historical background, as well as the fundamentals in paraffin actuation, including material properties of paraffin. Besides reviewing the three major groups of paraffin actuator applications; actuators, valves, and pumps, the modelling done on paraffin actuation will be explored. Furthermore, a section focusing on fabrication of paraffin microactuators is also included. The review ends with conclusions and outlook of the field, identifying unexplored potential of paraffin actuation.
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| 6. |
- Ohlsson, Gabriel, 1982, et al.
(författare)
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A miniaturized flow reaction chamber for use in combination with QCM-D sensing
- 2010
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Ingår i: Microfluidics and Nanofluidics. - : Springer Science and Business Media LLC. - 1613-4990 .- 1613-4982. ; 9:4-5, s. 705-716
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Tidskriftsartikel (refereegranskat)abstract
- A miniaturized flow chamber for quartz crystal microbalance with dissipation monitoring (QCM-D) has been developed. The main purpose was to reduce the total liquid sample consumption during an experiment, but also to gain advantages with respect to kinetics and mass transport by reducing the boundary diffusion layer. The bottom of the flow chamber is a QCM-D sensor surface, on which a polydimethylsiloxane spacer ring, fabricated onto a poly(methyl methacrylate) lid, is placed symmetrically around the QCM-D electrode (diameter similar to 10 mm). The spacer ring defines the inner chamber height (typically 40-50 mu m) and provides sealing. Through the lid, there are inlet and outlet channels. The typical chamber volume is in the range of 2.5-3.5 mu l (with a 10 mu l dead volume). In flow mode, we have operated the cell at flow rates of 6-50 mu l/min, i.e., volume turnovers of 2-17 per min. As a model system, to test the microcell, the formation of supported phospholipid bilayers on a SiO2 surface was studied. For comparison, the same process was studied in a commercially available QCM-D equipment with significantly larger total volume (by a factor of 20). The decrease in effective sample consumption to produce a bilayer on the sensor surface in the chamber was approximately proportional to the decrease in chamber volume. Smaller volume also reduced the liquid exchange time. Potential improvements of the chamber include further optimization of the flow profile and, in addition, further miniaturization by decreasing the chamber height and the sensor radius.
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| 7. |
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| 8. |
- Oko, Asaf, et al.
(författare)
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Infiltration and dimensional scaling of inkjet droplets on thick isotropic porous materials
- 2014
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Ingår i: Microfluidics and Nanofluidics. - : Springer Science and Business Media LLC. - 1613-4982 .- 1613-4990. ; 17:2, s. 413-422
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Tidskriftsartikel (refereegranskat)abstract
- We study the imbibition of picoliter (pL)-sized inkjet droplets on controlled pore glass membranes (CPG), as a suitable model for isotropic three-dimensional porous materials. We do so using a variety of liquids, i.e., water, formamide and diiodomethane, and measure the evolution of the imbibition process using high-speed digital imaging. Here, experiments were conducted on 2-280 nm CPG membranes with drops with initial volumes ranging from 100 to 600 pL. We derive scaling laws for imbibition through dimensional analysis and advance the argument that the rate of absorption is related to two-dimensionless groups where v(t) is the imbibed volume, as determined from experiments, t is the time, v (tot) the total liquid volume, the porosity, mu the liquid viscosity, k the permeability, and p (c) the Laplace capillary pressure. We show this scaling to well describe the system at intermediate T values and report that V alpha T-0.8.
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| 9. |
- Pardon, Gaspard, 1983-, et al.
(författare)
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Rapid mold-free manufacturing of microfluidic devices with robust and spatially directed surface modifications
- 2014
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Ingår i: Microfluidics and Nanofluidics. - : Springer Berlin/Heidelberg. - 1613-4982 .- 1613-4990. ; 17:4, s. 773-779
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Tidskriftsartikel (refereegranskat)abstract
- A new method that allows for mold-free, rapid and easy-to-use proto- typing of micro uidic devices comprising channels, access holes and surface modied patterns, is presented. The innovative method is based on direct photolithographic patterning of an o-stoichiometry thiol-ene (OSTE) polymer formulation, tailor-made for photolithography, which oers unprecedented spatial resolution and allow for ecient, robust and reliable, room temperature surface modication and glue-free, covalent room temperature bonding. This mold-free process does not require cleanroom equipment and therefore allows for rapid, i.e. less than one hour, design-fabricate-test cycles, using a material suited for larger scale production. The excellent photolithographic properties of this new OSTE formulation allow for high-resolution patterning in hundreds of micrometers thick layers, 200 m thick in this work. Moreover, we demonstrate robust (covalent) and spatially controlled modication of the microchannel surfaces with a contact angle of 76 degrees to hydrophobic/hydrophilic areas with contact angles of 102 and 43 degrees, respectively.
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| 10. |
- Pihl, Maria, 1978, et al.
(författare)
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Effect of patchwise slip on fluid flow
- 2014
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Ingår i: Microfluidics and Nanofluidics. - : Springer Science and Business Media LLC. - 1613-4982 .- 1613-4990. ; 17:2, s. 341-347
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we show that large connected slip patches (hydrophobic patches) are a necessity to induce macroscopic slip effects of water flow in microchannels. For this purpose, the 2D fluid flow between a planar stationary surface with alternating stick and slip patches and a parallel planar surface moving with a constant relative velocity has been studied by computer simulations based on Navier-Stokes equations. A slip patch is defined as the slipping length in a 2D system or a slip area of the surface in a 3D system. The simulations reveal that the ratio (size of each slip patch)/(distance between the two parallel interfaces) has profound effect on the viscous stress on the moving surface when this ratio is around and above one. However, when the ratio is much below one, the effect of the slip patches are minor, even if the area fraction of slip patches are higher than 50 %. Obviously, the stick patches adjacent to the slip patches act as effective barriers, preventing the fluid velocity to increase near the surface with alternating stick and slip patches. The obtained results are scalable and applicable on all length scales, with an exception for narrow channels in the subnano regime, i.e. < 1 nm where specific effects as the atomistic composition and the nanostructure of the wall as well as the interactions between the wall and the water molecules have an effect.
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| 11. |
- van der Wijngaart, Wouter
(författare)
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Capillary pumps with constant flow rate
- 2014
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Ingår i: Microfluidics and Nanofluidics. - Springer : Springer Science and Business Media LLC. - 1613-4982 .- 1613-4990. ; 16:5, s. 829-837
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Tidskriftsartikel (refereegranskat)abstract
- This paper unambiguously derives, ab initio starting from the Navier–Stokes and Laplace equations, the geometric parameters defining capillary pumps (CPs) with rectangular cross section with constant volumetric flow rate and steady velocity profile. The parametric formulation of the channel shape is derived using Taylor series approximations of the capillary pressure and the hydrodynamic flow resistance with negligible error. First, the design parameters are derived for a CP consisting of a single channel and illustrated with an example. Thereafter, the design parameters for multichannel and for micropillar array CPs are derived. Finally, the design of CPs for multistep constant flow rates derived and those for arbitrarily varying flow rates are discussed.
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