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  • 1. Balestra, G.
    et al.
    Zhu, Lailai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Gallaire, F.
    Viscous Taylor droplets in axisymmetric and planar tubes: from Bretherton’s theory to empirical models2018Inngår i: Microfluidics and Nanofluidics, ISSN 1613-4982, E-ISSN 1613-4990, Vol. 22, nr 6, artikkel-id 67Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study is to derive accurate models for quantities characterizing the dynamics of droplets of non-vanishing viscosity in capillaries. In particular, we propose models for the uniform-film thickness separating the droplet from the tube walls, for the droplet front and rear curvatures and pressure jumps, and for the droplet velocity in a range of capillary numbers, Ca, from 10 - 4 to 1 and inner-to-outer viscosity ratios, λ, from 0, i.e. a bubble, to high-viscosity droplets. Theoretical asymptotic results obtained in the limit of small capillary number are combined with accurate numerical simulations at larger Ca. With these models at hand, we can compute the pressure drop induced by the droplet. The film thickness at low capillary numbers (Ca< 10 - 3) agrees well with Bretherton’s scaling for bubbles as long as λ< 1. For larger viscosity ratios, the film thickness increases monotonically, before saturating for λ> 10 3 to a value 2 2 / 3 times larger than the film thickness of a bubble. At larger capillary numbers, the film thickness follows the rational function proposed by Aussillous and Quéré (Phys Fluids 12(10):2367–2371, 2000) for bubbles, with a fitting coefficient which is viscosity-ratio dependent. This coefficient modifies the value to which the film thickness saturates at large capillary numbers. The velocity of the droplet is found to be strongly dependent on the capillary number and viscosity ratio. We also show that the normal viscous stresses at the front and rear caps of the droplets cannot be neglected when calculating the pressure drop for Ca> 10 - 3.

  • 2. Cohen, Céline
    et al.
    Giles, Rory
    Sergeyeva, Victoria
    Mittal, Nitesh
    Ecole Polytech, F-91128 Palaiseau, France.
    Tabeling, Patrick
    Zerrouki, Djamal
    Baudry, Jean
    Bibette, Jérôme
    Bremond, Nicolas
    Parallelised production of fine and calibrated emulsions by coupling flow-focusing technique and partial wetting phenomenon2014Inngår i: Microfluidics and Nanofluidics, ISSN 1613-4982, E-ISSN 1613-4990, Vol. 17, nr 5, s. 959-966Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 3. Ogden, S.
    et al.
    Boden, R.
    Do-Quang, Minh
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
    Wu, Z. G.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
    Hjort, K.
    Fluid behavior of supercritical carbon dioxide with water in a double-Y-channel microfluidic chip2014Inngår i: Microfluidics and Nanofluidics, ISSN 1613-4982, E-ISSN 1613-4990, Vol. 17, nr 6, s. 1105-1112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 4.
    Oko, Asaf
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. SP Technical Research Institute of Sweden, Sweden.
    Martinez, D.Mark
    Swerin, Agne
    KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap. SP Technical Research Institute of Sweden, Sweden.
    Infiltration and dimensional scaling of inkjet droplets on thick isotropic porous materials2014Inngår i: Microfluidics and Nanofluidics, ISSN 1613-4982, E-ISSN 1613-4990, Vol. 17, nr 2, s. 413-422Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

  • 5.
    Pardon, Gaspard
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Saharil, Farizah
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Karlsson, J. Mikael
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Supekar, Omkar
    Indian Institute of Technology Bombay.
    Carlborg, Carl Fredrik
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    van der Wijngaart, Wouter
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Haraldsson, Tommy
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Rapid mold-free manufacturing of microfluidic devices with robust and spatially directed surface modifications2014Inngår i: Microfluidics and Nanofluidics, ISSN 1613-4982, E-ISSN 1613-4990, Vol. 17, nr 4, s. 773-779Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

    Fulltekst (pdf)
    fulltext
  • 6.
    van der Wijngaart, Wouter
    KTH, Skolan för elektro- och systemteknik (EES), Mikro- och nanosystemteknik.
    Capillary pumps with constant flow rate2014Inngår i: Microfluidics and Nanofluidics, ISSN 1613-4982, E-ISSN 1613-4990, Vol. 16, nr 5, s. 829-837Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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.

    Fulltekst (pdf)
    CPs with constant flow
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