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Micromachines
Special Issues
Rheology and Complex Fluid Flows in Microfluidics
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Rheology and Complex Fluid Flows in Microfluidics

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "A：Physics".

Deadline for manuscript submissions: closed (15 March 2020) | Viewed by 16974

Special Issue Editors

Dr. Monica S. N. Oliveira

E-Mail Website1 Website2
Guest Editor
James Weir Fluids Laboratory, Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow, UK
Interests: Newtonian and non-Newtonian fluid dynamics; rheology; viscoelasticity; elastic instabilities; CFD; biofluid flows; thermal–Marangoni flows; microfluidics; microdevice optimisation
Dr. Manuel A. Alves

E-Mail Website
Guest Editor
CEFT, Department of Chemical Engineering, Faculty of Engineering, University of Porto, Porto, Portugal
Interests: non-Newtonian fluid dynamics; computational rheology; microfluidics; elastic instabilities; elastic turbulence

Special Issue Information

Dear Colleagues,

We are pleased to announce the Special Issue on the theme of “Rheology and Flows of Complex Fluids in Microfluidic Devices” to be published in Micromachines. Many artificial and natural fluids contain macromolecules, particles, or droplets that impart complex rheology and flow behaviour to the fluid. It is well known that the overall rheological properties of these fluids are determined by events occurring at the microscopic level, and that the conditions encountered in microfluidic devices can be particularly suitable to study such behaviour.

This Special Issue seeks to showcase research papers, short communications, and topical review articles that focus on recent developments in complex fluid flows at the microscale, including polymer solutions and polymer melts, suspensions, active fluids, biological fluids, surfactant solutions, gels, and liquid crystals. We invite contributions in all areas of experimental and computational complex fluid mechanics and rheology, where the non-Newtonian character of the fluid is important in determining the characteristics of the flow at the microscale.

Dr. Monica S. N. Oliveira
Dr. Manuel A. Alves
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • rheology
  • non-Newtonian fluid flows
  • elastic instabilities
  • active fluids
  • microfluidics
  • computational rheology
  • viscoelasticity

Published Papers (5 papers)

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Research

16 pages, 2719 KiB  
Article
Rheology of a Dilute Suspension of Aggregates in Shear-Thinning Fluids
by Marco Trofa and Gaetano D’Avino
Micromachines 2020, 11(4), 443; https://doi.org/10.3390/mi11040443 - 22 Apr 2020
Cited by 4 | Viewed by 2447
Abstract
The prediction of the viscosity of suspensions is of fundamental importance in several fields. Most of the available studies have been focused on particles with simple shapes, for example, spheres or spheroids. In this work, we study the viscosity of a dilute suspension [...] Read more.
The prediction of the viscosity of suspensions is of fundamental importance in several fields. Most of the available studies have been focused on particles with simple shapes, for example, spheres or spheroids. In this work, we study the viscosity of a dilute suspension of fractal-shape aggregates suspended in a shear-thinning fluid by direct numerical simulations. The suspending fluid is modeled by the power-law constitutive equation. For each morphology, a map of particle angular velocities is obtained by solving the governing equations for several particle orientations. The map is used to integrate the kinematic equation for the orientation vectors and reconstruct the aggregate orientational dynamics. The intrinsic viscosity is computed by a homogenization procedure along the particle orbits. In agreement with previous results on Newtonian suspensions, the intrinsic viscosity, averaged over different initial orientations and aggregate morphologies characterized by the same fractal parameters, decreases by increasing the fractal dimension, that is, from rod-like to spherical-like aggregates. Shear-thinning further reduces the intrinsic viscosity showing a linear dependence with the flow index in the investigated range. The intrinsic viscosity can be properly scaled with respect to the number of primary particles and the flow index to obtain a single curve as a function of the fractal dimension. Full article
(This article belongs to the Special Issue Rheology and Complex Fluid Flows in Microfluidics)
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12 pages, 3256 KiB  
Article
Microfluidic In-Situ Measurement of Poisson’s Ratio of Hydrogels
by Jean Cappello, Vincent d’Herbemont, Anke Lindner and Olivia du Roure
Micromachines 2020, 11(3), 318; https://doi.org/10.3390/mi11030318 - 19 Mar 2020
Cited by 28 | Viewed by 3848
Abstract
Being able to precisely characterize the mechanical properties of soft microparticles is essential for numerous situations, from the understanding of the flow of biological fluids to the development of soft micro-robots. Here, we present a simple measurement technique for determining Poisson’s ratio of [...] Read more.
Being able to precisely characterize the mechanical properties of soft microparticles is essential for numerous situations, from the understanding of the flow of biological fluids to the development of soft micro-robots. Here, we present a simple measurement technique for determining Poisson’s ratio of soft micron-sized hydrogels in the presence of a surrounding liquid. This method relies on the measurement of the deformation, in two orthogonal directions, of a rectangular hydrogel slab compressed uni-axially inside a microfluidic channel. Due to the in situ character of the method, the sample does not need to be dried, allowing for the measurement of the mechanical properties of swollen hydrogels. Using this method, we determined Poisson’s ratio of hydrogel particles composed of polyethylene glycol (PEG) and varying solvents fabricated using a lithography technique. The results demonstrate, with high precision, the dependence of the hydrogel compressibility on the solvent fraction and character. The method is easy to implement and can be adapted for the measurement of a variety of soft and biological materials. Full article
(This article belongs to the Special Issue Rheology and Complex Fluid Flows in Microfluidics)
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16 pages, 15158 KiB  
Article
Fluid Rheological Effects on the Flow of Polymer Solutions in a Contraction–Expansion Microchannel
by Purva P. Jagdale, Di Li, Xingchen Shao, Joshua B. Bostwick and Xiangchun Xuan
Micromachines 2020, 11(3), 278; https://doi.org/10.3390/mi11030278 - 08 Mar 2020
Cited by 24 | Viewed by 4656
Abstract
A fundamental understanding of the flow of polymer solutions through the pore spaces of porous media is relevant and significant to enhanced oil recovery and groundwater remediation. We present in this work an experimental study of the fluid rheological effects on non-Newtonian flows [...] Read more.
A fundamental understanding of the flow of polymer solutions through the pore spaces of porous media is relevant and significant to enhanced oil recovery and groundwater remediation. We present in this work an experimental study of the fluid rheological effects on non-Newtonian flows in a simple laboratory model of the real-world pores—a rectangular sudden contraction–expansion microchannel. We test four different polymer solutions with varying rheological properties, including xanthan gum (XG), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), and polyacrylamide (PAA). We compare their flows against that of pure water at the Reynolds ( R e ) and Weissenburg ( W i ) numbers that each span several orders of magnitude. We use particle streakline imaging to visualize the flow at the contraction–expansion region for a comprehensive investigation of both the sole and the combined effects of fluid shear thinning, elasticity and inertia. The observed flow regimes and vortex development in each of the tested fluids are summarized in the dimensionless W i − R e and χ L − R e parameter spaces, respectively, where χ L is the normalized vortex length. We find that fluid inertia draws symmetric vortices downstream at the expansion part of the microchannel. Fluid shear thinning causes symmetric vortices upstream at the contraction part. The effect of fluid elasticity is, however, complicated to analyze because of perhaps the strong impact of polymer chemistry such as rigidity and length. Interestingly, we find that the downstream vortices in the flow of Newtonian water, shear-thinning XG and elastic PVP solutions collapse into one curve in the χ L − R e space. Full article
(This article belongs to the Special Issue Rheology and Complex Fluid Flows in Microfluidics)
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19 pages, 1465 KiB  
Article
Numerical Study of Electro-Osmotic Fluid Flow and Vortex Formation
by Wesley De Souza Bezerra, Antonio Castelo and Alexandre M. Afonso
Micromachines 2019, 10(12), 796; https://doi.org/10.3390/mi10120796 - 20 Nov 2019
Cited by 7 | Viewed by 2688
Abstract
The phenomenon of electro-osmosis was studied by performing numerical simulations on the flow between parallel walls and at the nozzle microchannels. In this work, we propose a numerical approximation to perform simulations of vortex formation which occur after the passage of the fluid [...] Read more.
The phenomenon of electro-osmosis was studied by performing numerical simulations on the flow between parallel walls and at the nozzle microchannels. In this work, we propose a numerical approximation to perform simulations of vortex formation which occur after the passage of the fluid through an abrupt contraction at the microchannel. The motion of the charges in the solution is described by the Poisson–Nernst–Planck equations and used the generalized finite differences to solve the numerical problem. First, solutions for electro-osmotic flow were obtained for the Phan–Thien/Thanner model in a parallel walls channel. Later simulations for electro-osmotic flow were performed in a nozzle. The formation of vortices near the contraction within the nozzle was verified by taking into account a flow perturbation model. Full article
(This article belongs to the Special Issue Rheology and Complex Fluid Flows in Microfluidics)
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19 pages, 3796 KiB  
Article
Microfluidic-Based Biosensor for Sequential Measurement of Blood Pressure and RBC Aggregation Over Continuously Varying Blood Flows
by Yang Jun Kang
Micromachines 2019, 10(9), 577; https://doi.org/10.3390/mi10090577 - 30 Aug 2019
Cited by 7 | Viewed by 2814
Abstract
Aggregation of red blood cells (RBCs) varies substantially depending on changes of several factors such as hematocrit, membrane deformability, and plasma proteins. Among these factors, hematocrit has a strong influence on the aggregation of RBCs. Thus, while measuring RBCs aggregation, it is necessary [...] Read more.
Aggregation of red blood cells (RBCs) varies substantially depending on changes of several factors such as hematocrit, membrane deformability, and plasma proteins. Among these factors, hematocrit has a strong influence on the aggregation of RBCs. Thus, while measuring RBCs aggregation, it is necessary to monitor hematocrit or, additionally, the effect of hematocrit (i.e., blood viscosity or pressure). In this study, the sequential measurement method of pressure and RBC aggregation is proposed by quantifying blood flow (i.e., velocity and image intensity) through a microfluidic device, in which an air-compressed syringe (ACS) is used to control the sample injection. The microfluidic device used is composed of two channels (pressure channel (PC), and blood channel (BC)), an inlet, and an outlet. A single ACS (i.e., air suction = 0.4 mL, blood suction = 0.4 mL, and air compression = 0.3 mL) is employed to supply blood into the microfluidic channel. At an initial time (t < 10 s), the pressure index (PI) is evaluated by analyzing the intensity of microscopy images of blood samples collected inside PC. During blood delivery with ACS, shear rates of blood flows vary continuously over time. After a certain amount of time has elapsed (t > 30 s), two RBC aggregation indices (i.e., SEAI: without information on shear rate, and erythrocyte aggregation index (EAI): with information on shear rate) are quantified by analyzing the image intensity and velocity field of blood flow in BC. According to experimental results, PI depends significantly on the characteristics of the blood samples (i.e., hematocrit or base solutions) and can be used effectively as an alternative to blood viscosity. In addition, SEAI and EAI also depend significantly on the degree of RBC aggregation. In conclusion, on the basis of three indices (two RBC aggregation indices and pressure index), the proposed method is capable of measuring RBCs aggregation consistently using a microfluidic device. Full article
(This article belongs to the Special Issue Rheology and Complex Fluid Flows in Microfluidics)
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