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Surface-Tension-Driven Flows for Shaping and Fragmenting Matter on the Submillimeter Scale

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Chemistry".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 16347

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Prof. Dr. José María Montanero

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Guest Editor

Departamento de Ingeniería Mecánica, Energética y de los Materiales, Universidad de Extremadura, Badajoz, Spain
Interests: microfluidics; surface-tension-driven flows; interfacial rheology; viscoelasticity; flow stability

Special Issue Information

Dear Colleagues,

A multitude of technological applications demand the shaping and fragmentation of a continuous phase (gas, liquid, or solid) down to the submillimeter scale in a controlled manner. This fragmentation can be produced by gently deforming, stretching, and splitting matter in its fluid form. The flows arising in these microfluidic processes involve an ample variety of complex phenomena in which the interfacial/surface tension always plays a major role. While microfluidics researchers typically pay attention to the development and characterization of techniques for the purposes mentioned above, fluid dynamicists focus on rather fundamental questions in the quest to reveal the physics involved. This Special Issue aims to present modern microfluidic technologies for shaping and atomizing liquids and gases. It also considers advances in the understanding and modeling of the physical mechanisms underlying those technologies.

It is my pleasure to invite you to submit a manuscript for this Special Issue. Full papers, communications, and reviews are all welcome.

Prof. Dr. José María Montanero
Guest Editor

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Keywords

Microfluidics
Atomization
Interfacial flows
Dripping
Jetting
Tip streaming
Electrohydrodynamics
Surfactants
Viscoelasticity

Published Papers (7 papers)

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Research

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29 pages, 41619 KiB

Open AccessArticle

Consistent Thermo-Capillarity and Thermal Boundary Conditions for Single-Phase Smoothed Particle Hydrodynamics

by Claas Bierwisch

Materials 2021, 14(16), 4530; https://doi.org/10.3390/ma14164530 - 12 Aug 2021

Cited by 6 | Viewed by 1928

Abstract

A model for capillary phenomena including temperature-dependency and thermal boundary conditions is presented in the numerical framework of smoothed particle hydrodynamics (SPH). The model requires only a single fluid phase and is therefore computationally more efficient than surface tension schemes which need an explicit fluid-fluid or fluid-gas interface. The model makes use of a surface identification mechanism based on the SPH renormalization tensor. All relevant properties of the continuum surface force (CSF) based approach, i.e., the delta function, normal vector and curvature, are calculated in a consistent manner. The model is parametrized by physical material properties and is successfully validated by means of a large set of analytical test cases. The applicability of the proposed model to more complex scenarios is demonstrated. Full article

(This article belongs to the Special Issue Surface-Tension-Driven Flows for Shaping and Fragmenting Matter on the Submillimeter Scale)

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11 pages, 2618 KiB

Open AccessArticle

Numerical Study of the Micro-Jet Formation in Double Flow Focusing Nozzle Geometry Using Different Water-Alcohol Solutions

by Grega Belšak, Saša Bajt and Božidar Šarler

Materials 2021, 14(13), 3614; https://doi.org/10.3390/ma14133614 - 28 Jun 2021

Cited by 3 | Viewed by 1790

Abstract

The purpose of this work is to determine, based on the computational model, whether a mixture of a binary liquid is capable of producing longer, thinner and faster gas-focused micro-jets, compared to the mono-constituent liquids of its components. Mixtures of water with two different alcohols, water + ethanol and water + 2-propanol, are considered. The numerical study of pre-mixed liquids is performed in the double flow focusing nozzle geometry used in sample delivery in serial femtosecond crystallography experiments. The study reveals that an optimal mixture for maximizing the jet length exists both in a water + ethanol and in a water + 2-propanol system. Additionally, the use of 2-propanol instead of ethanol results in a 34% jet length increase, while the jet diameters and velocities are similar for both mixtures. Pure ethanol and pure 2-propanol are the optimum liquids to achieve the smallest diameter and the fastest jets. However, the overall aim is to find a mixture with the longest, the smallest and the fastest jet. Based on our simulations, it appears that water + 2-propanol mixture might be slightly better than water + ethanol. This study reveals the dominant effect of liquid viscosity on the jet breakup process in a flow focusing nozzles operated under atmospheric conditions. Full article

(This article belongs to the Special Issue Surface-Tension-Driven Flows for Shaping and Fragmenting Matter on the Submillimeter Scale)

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12 pages, 3090 KiB

Open AccessArticle

On the Ejection of Filaments of Polymer Solutions Triggered by a Micrometer-Scale Mixing Mechanism

by Fernando Marín-Brenes, Jesús Olmedo-Pradas, Alfonso M. Gañán-Calvo and Luis Modesto-López

Materials 2021, 14(12), 3399; https://doi.org/10.3390/ma14123399 - 19 Jun 2021

Cited by 6 | Viewed by 2380

Abstract

Polymer filaments constitute precursor materials of so-called fiber mats, ubiquitous structures across cutting-edge technological fields. Thus, approaches that contribute to large-scale production of fibers are desired from an industrial perspective. Here, we use a robust liquid atomization device operated at relatively high flow rates, ~20 mL/min, as facilitating technology for production of multiple polymer filaments. The method relies on a turbulent, energetically efficient micro-mixing mechanism taking place in the interior of the device. The micro-mixing is triggered by radial implosion of a gas current into a liquid feeding tube, thus resulting in breakup of the liquid surface. We used poly(ethylene oxide) solutions of varying concentrations as test liquids to study their fragmentation and ejection dynamics employing ultra-high speed imaging equipment. Taking an energy cascade approach, a scaling law for filament diameter was proposed based on gas pressure, liquid flow rate and viscosity. We find that a filament dimensionless diameter,

D_{f}^{*}

, scales as a non-dimensional liquid flow rate

Q^{*}

to the

1 / 5

. The study aims to elucidate the underlying physics of liquid ejection for further applications in material production. Full article

(This article belongs to the Special Issue Surface-Tension-Driven Flows for Shaping and Fragmenting Matter on the Submillimeter Scale)

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17 pages, 5961 KiB

Open AccessArticle

Alternative Geometric Arrangements of the Nozzle Outlet Orifice for Liquid Micro-Jet Focusing in Gas Dynamic Virtual Nozzles

by Božidar Šarler, Rizwan Zahoor and Saša Bajt

Materials 2021, 14(6), 1572; https://doi.org/10.3390/ma14061572 - 23 Mar 2021

Cited by 12 | Viewed by 2773

Abstract

Liquid micro-jets are crucial for sample delivery of protein crystals and other macromolecular samples in serial femtosecond crystallography. When combined with MHz repetition rate sources, such as the European X-ray free-electron laser (EuXFEL) facility, it is important that the diffraction patterns are collected before the samples are damaged. This requires extremely thin and very fast jets. In this paper we first explore numerically the influence of different nozzle orifice designs on jet parameters and finally compare our simulations with the experimental data obtained for one particular design. A gas dynamic virtual nozzle (GDVN) model, based on a mixture formulation of Newtonian, compressible, two-phase flow, is numerically solved with the finite volume method and volume of fluid approach to deal with the moving boundary between the gas and liquid phases. The goal is to maximize the jet velocity and its length while minimizing the jet thickness. The design studies incorporate differently shaped nozzle orifices, including an elongated orifice with a constant diameter and an orifice with a diverging angle. These are extensions of the nozzle geometry we investigated in our previous studies. Based on these simulations it is concluded that the extension of the constant diameter channel makes a negligible contribution to the jet’s length and its velocity. A change in the angle of the nozzle outlet orifice, however, has a significant effect on jet parameters. We find these kinds of simulation extremely useful for testing and optimizing novel nozzle designs. Full article

(This article belongs to the Special Issue Surface-Tension-Driven Flows for Shaping and Fragmenting Matter on the Submillimeter Scale)

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12 pages, 2458 KiB

Open AccessArticle

Electrical Conductivity of a Stretching Viscoelastic Filament

by Manuel Rubio, Samir Sadek, Emilio José Vega, Alfonso Miguel Gañán-Calvo and José María Montanero

Materials 2021, 14(5), 1294; https://doi.org/10.3390/ma14051294 - 08 Mar 2021

Cited by 1 | Viewed by 1652

Abstract

Long polymeric chains highly stretched and aligned with the flow confer a strong mechanical anisotropy on a viscoelastic solution. The electrically-driven transport of free ions under such conditions is far from being understood. In this paper, we determine experimentally whether the above-mentioned deviation from isotropy affects the electric charge transport across the liquid. To this end, we measure the electrical conductivity in the flow (stretching) direction of the cylindrical liquid filament formed in the elasto-capillary thinning that arises during the breakup of a viscoelastic liquid bridge. First, we examine the behavior of monodisperse solutions of polyethylene oxide (PEO) in a mixture of glycerine and water. For all the concentrations and molecular weights considered, the filament conductivity remains practically the same as the isotropic conductivity measured under hydrostatic conditions. However, we observe a decrease in the electric current at the end of elasto-capillary regime which may partially be attributed to the reduction of the liquid conductivity. Then, we measure the conductivity of bidisperse solutions of PEO with very different molecular weights. In this case, a significant decrease in conductivity is observed as the filament radius decreases. This constitutes the first experimental evidence of ion mobility reduction in stretching viscoelastic filaments, a relevant effect in applications such as electrospinning. Full article

(This article belongs to the Special Issue Surface-Tension-Driven Flows for Shaping and Fragmenting Matter on the Submillimeter Scale)

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17 pages, 4552 KiB

Open AccessArticle

Capabilities and Limitations of Fire-Shaping to Produce Glass Nozzles

by Alejandro Rubio, Sergio Rodríguez and Maria G. Cabezas

Materials 2020, 13(23), 5477; https://doi.org/10.3390/ma13235477 - 01 Dec 2020

Cited by 3 | Viewed by 1548

Abstract

Microfluidic devices for drop and emulsion production are often built using fire-shaped (or fire-polished) glass nozzles. These are usually fabricated manually with inexpensive equipment. The shape limitations and poor reproducibility are pointed as the main drawbacks. Here, we evaluate the capabilities of a new fire-shaping approach which fabricates the nozzle by heating a vertical rotating capillary at the Bottom of a Lateral Flame (BLF). We analyze the effect of the heating conditions, and the capillary size and tolerances. The shape reproducibility is excellent for nozzles of the same size produced with the same conditions. However, the size reproducibility is limited and does not seem to be significantly affected by the heating conditions. Specifically, the minimum neck diameter standard deviation is 3%. Different shapes can be obtained by changing the heating position or the capillary dimensions, though, for a given diameter reduction, there is a minimum nozzle length due to the overturning of the surface. The use of thinner (wall or inner diameter) capillaries allows producing much shorter nozzles but hinders the size reproducibility. Finally, we showed an example of how the performance of a microfluidic device is affected by the nozzle shape: a Gas Dynamic Virtual Nozzle (GDVN) built with a higher convergent rate nozzle works over a wider parametric range without whipping. Full article

(This article belongs to the Special Issue Surface-Tension-Driven Flows for Shaping and Fragmenting Matter on the Submillimeter Scale)

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Review

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32 pages, 57776 KiB

Open AccessReview

Blood Particulate Analogue Fluids: A Review

by Samir Hassan Sadek, Manuel Rubio, Rui Lima and Emilio José Vega

Materials 2021, 14(9), 2451; https://doi.org/10.3390/ma14092451 - 09 May 2021

Cited by 21 | Viewed by 3561

Abstract

Microfluidics has proven to be an extraordinary working platform to mimic and study blood flow phenomena and the dynamics of components of the human microcirculatory system. However, the use of real blood increases the complexity to perform these kinds of in vitro blood experiments due to diverse problems such as coagulation, sample storage, and handling problems. For this reason, interest in the development of fluids with rheological properties similar to those of real blood has grown over the last years. The inclusion of microparticles in blood analogue fluids is essential to reproduce multiphase effects taking place in a microcirculatory system, such as the cell-free layer (CFL) and Fähraeus–Lindqvist effect. In this review, we summarize the progress made in the last twenty years. Size, shape, mechanical properties, and even biological functionalities of microparticles produced/used to mimic red blood cells (RBCs) are critically exposed and analyzed. The methods developed to fabricate these RBC templates are also shown. The dynamic flow/rheology of blood particulate analogue fluids proposed in the literature (with different particle concentrations, in most of the cases, relatively low) is shown and discussed in-depth. Although there have been many advances, the development of a reliable blood particulate analogue fluid, with around 45% by volume of microparticles, continues to be a big challenge. Full article

(This article belongs to the Special Issue Surface-Tension-Driven Flows for Shaping and Fragmenting Matter on the Submillimeter Scale)

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