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Vortex of Viscoelastic Fluid Electroosmotic Flow at the Micro-nanochannel Interface. Colloids Surf A Physicochem Eng Asp 2023. [DOI: 10.1016/j.colsurfa.2023.131071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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Viscoelasticity-Induced Instability in Plane Couette Flow at Very Low Reynolds Number. FLUIDS 2022. [DOI: 10.3390/fluids7070241] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Elasto-inertial turbulence (EIT), a new turbulent state found in polymer solutions with viscoelastic properties, is associated with drag-reduced turbulence. However, the relationship between EIT and drag-reduced turbulence is not currently well-understood, and it is important to elucidate the mechanism of the transition to EIT. The instability of viscoelastic fluids has been studied in a canonical wall-bounded shear flow to investigate the transition process of EIT. In this study, we numerically deduced that an instability occurs in the linearly stable viscoelastic plane Couette flow for lower Reynolds numbers, at which a non-linear unstable solution exists. Under instability, the flow structure is elongated in the spanwise direction and regularly arranged in the streamwise direction, which is a characteristic structure of EIT. The regularity of the flow structure depends on the Weissenberg number, which represents the strength of elasticity; the structure becomes disordered under high Weissenberg numbers. In the energy spectrum of velocity fluctuations, a steep decay law of the structure’s scale towards a small scale is observed, and this can be recognized as a ubiquitous feature of EIT. The existence of instability in viscoelastic plane Couette flow supports the idea that the transitional path toward EIT may be mediated by subcritical instability.
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Ren YJ, Joo SW. The Effects of Viscoelasticity on Droplet Migration on Surfaces with Wettability Gradients. MICROMACHINES 2022; 13:mi13050729. [PMID: 35630196 PMCID: PMC9146577 DOI: 10.3390/mi13050729] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Revised: 04/26/2022] [Accepted: 04/29/2022] [Indexed: 11/22/2022]
Abstract
A finite-volume method based on the OpenFOAM is used to numerically study the factors affecting the migration of viscoelastic droplets on rigid surfaces with wettability gradients. Parameters investigated include droplet size, relaxation time, solvent viscosity, and polymer viscosity of the liquid comprising droplets. The wettability gradient is imposed numerically by assuming a linear change in the contact angle along the substrate. As reported previously for Newtonian droplets, the wettability gradient induces spontaneous migration from hydrophobic to hydrophilic region on the substrate. The migration of viscoelastic droplets reveals the increase in the migration speed and distance with the increase in the Weissenberg number. The increase in droplet size also shows the increase in both the migration speed and distance. The increase in polymer viscosity exhibits the increase in migration speed but the decrease in migration distance.
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The Effect of Surface Wettability on Viscoelastic Droplet Dynamics under Electric Fields. MICROMACHINES 2022; 13:mi13040580. [PMID: 35457884 PMCID: PMC9029302 DOI: 10.3390/mi13040580] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Revised: 04/01/2022] [Accepted: 04/05/2022] [Indexed: 02/05/2023]
Abstract
The effects of surface wettability and viscoelasticity on the dynamics of liquid droplets under an electric field are studied experimentally. A needle-plate electrode system is used as the power source to polarize a dielectric plate by the corona discharge emitted at the needle electrode, creating a new type of steerable electric field realized. The dynamics of droplets between the dielectric plate and a conductive substrate include three different phenomena: equilibrium to a stationary shape on substrates with higher wettability, deformation to form a bridge between the top acrylic plate and take-off on the substrates with lower wettability. Viscoelastic droplets differ from water in the liquid bridge and takeoff phenomena in that thin liquid filaments appear in viscoelastic droplets, not observed for Newtonian droplets. The equilibrated droplet exhibits more pronounced heights for Newtonian droplets compared to viscoelastic droplets, with a decrease in height with the increase in the concentration of the elastic constituent in the aqueous solution. In the take-off phenomenon, the time required for the droplet to contact the upper plate decreases with the concentration of the elastic constituent increases. It is also found that the critical voltage required for the take-off phenomenon to occur decreases as the elasticity increases.
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Kumar V, Mukherjee J, Sinha SK, Ghosh U. Combined electromechanically driven pulsating flow of nonlinear viscoelastic fluids in narrow confinements. J R Soc Interface 2022; 19:20210876. [PMID: 35382577 PMCID: PMC8984355 DOI: 10.1098/rsif.2021.0876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Controlled microscale transport is at the core of many scientific and technological advancements, including medical diagnostics, separation of biomolecules, etc., and often involves complex fluids. One of the challenges in this regard is to actuate flows at small scales in an energy efficient manner, given the strong viscous forces opposing fluid motion. We try to address this issue here by probing a combined time-periodic pressure and electrokinetically driven flow of a viscoelastic fluid obeying the simplified linear Phan-Thien-Tanner model, using numerical as well as asymptotic tools, in view of the fact that oscillatory fields are less energy intensive. We establish that the interplay between oscillatory electrical and mechanical forces can lead to complex temporal mass flow rate variations with short-term bursts and peaks in the flow rate. We further demonstrate that an oscillatory pressure gradient or an electric field, in tandem with another steady actuating force can indeed change the net throughput significantly-a paradigm that is not realized in Newtonian or other simpler polymeric liquids. Our results reveal that the extent of augmentation in the flow rate strongly depends on the frequency of the imposed actuating forces along with their waveforms. We also evaluate the streaming potential resulting from an oscillatory pressure-driven flow and illustrate that akin to the volume throughput, the streaming potential also shows complex temporal variations, while its time average gets augmented in the presence of a time-periodic pressure gradient in a nonlinear viscoelastic medium.
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Affiliation(s)
- Vishal Kumar
- Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar, Punjab 140 001, India
| | - Joydeb Mukherjee
- Department of Chemical Engineering, Institute of Chemical Technology, Mumbai 400019, India
| | - Sudipta Kumar Sinha
- Department of Chemistry, Indian Institute of Technology Ropar, Rupnagar, Punjab 140 001, India
| | - Uddipta Ghosh
- Discipline of Mechanical Engineering, Indian Institute of Technology Gandhinagar, Palaj, Gujarat 382355, India
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Bentor J, Raihan MK, McNeely C, Liu Z, Song Y, Xuan X. Fluid rheological effects on streaming dielectrophoresis in a post-array microchannel. Electrophoresis 2021; 43:717-723. [PMID: 34657307 DOI: 10.1002/elps.202100270] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Revised: 10/06/2021] [Accepted: 10/12/2021] [Indexed: 11/06/2022]
Abstract
Recent studies have demonstrated the strong influences of fluid rheological properties on insulator-based dielectrophoresis (iDEP) in single-constriction microchannels. However, it is yet to be understood how iDEP in non-Newtonian fluids depends on the geometry of insulating structures. We report in this work an experimental study of fluid rheological effects on streaming DEP in a post-array microchannel that presents multiple contractions and expansions. The iDEP focusing and trapping of particles in a viscoelastic polyethylene oxide solution are comparable to those in a Newtonian buffer, which is consistent with the observations in a single-constriction microchannel. Similarly, the insignificant iDEP effects in a shear-thinning xanthan gum solution also agree with those in the single-constriction channel except that gel-like structures are observed to only form in the post-array microchannel under large DC electric fields. In contrast, the iDEP effects in both viscoelastic and shear-thinning polyacrylamide solution are significantly weaker than in the single-constriction channel. Moreover, instabilities occur in the electroosmotic flow and appear to be only dependent on the DC electric field. These phenomena may be associated with the dynamics of polymers as they are electrokinetically advected around and through the posts.
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Affiliation(s)
- Joseph Bentor
- Department of Mechanical Engineering, Clemson University, Clemson, South Carolina, USA
| | - Mahmud Kamal Raihan
- Department of Mechanical Engineering, Clemson University, Clemson, South Carolina, USA
| | - Colin McNeely
- Department of Mechanical Engineering, Clemson University, Clemson, South Carolina, USA
| | - Zhijian Liu
- Department of Mechanical Engineering, Clemson University, Clemson, South Carolina, USA.,College of Marine Engineering, Dalian Maritime University, Dalian, P. R. China
| | - Yongxin Song
- College of Marine Engineering, Dalian Maritime University, Dalian, P. R. China
| | - Xiangchun Xuan
- Department of Mechanical Engineering, Clemson University, Clemson, South Carolina, USA
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Bentor J, Malekanfard A, Raihan MK, Wu S, Pan X, Song Y, Xuan X. Insulator-based dielectrophoretic focusing and trapping of particles in non-Newtonian fluids. Electrophoresis 2021; 42:2154-2161. [PMID: 33938011 DOI: 10.1002/elps.202100005] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2021] [Revised: 03/17/2021] [Accepted: 04/27/2021] [Indexed: 11/09/2022]
Abstract
Insulator-based dielectrophoretic (iDEP) microdevices have been limited to work with Newtonian fluids. We report an experimental study of the fluid rheological effects on iDEP focusing and trapping of polystyrene particles in polyethylene oxide, xanthan gum, and polyacrylamide solutions through a constricted microchannel. Particle focusing and trapping in the mildly viscoelastic polyethylene oxide solution are slightly weaker than in the Newtonian buffer. They are, however, significantly improved in the strongly viscoelastic and shear thinning polyacrylamide solution. These observed particle focusing behaviors exhibit a similar trend with respect to electric field, consistent with a revised theoretical analysis for iDEP focusing in non-Newtonian fluids. No apparent focusing of particles is achieved in the xanthan gum solution, though the iDEP trapping can take place under a much larger electric field than the other fluids. This is attributed to the strong shear thinning-induced influences on both the electroosmotic flow and electrokinetic/dielectrophoretic motions.
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Affiliation(s)
- Joseph Bentor
- Department of Mechanical Engineering, Clemson University, Clemson, SC, USA
| | | | | | - Sen Wu
- Department of Mechanical Engineering, Clemson University, Clemson, SC, USA.,College of Marine Engineering, Dalian Maritime University, Dalian, P. R. China
| | - Xinxiang Pan
- College of Marine Engineering, Dalian Maritime University, Dalian, P. R. China.,College of Electronics and Information Engineering, Guangdong Ocean University, Zhanjiang, P. R. China
| | - Yongxin Song
- College of Marine Engineering, Dalian Maritime University, Dalian, P. R. China
| | - Xiangchun Xuan
- Department of Mechanical Engineering, Clemson University, Clemson, SC, USA
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Casas L, Ortega JA, Gómez A, Escandón J, Vargas RO. Analytical Solution of Mixed Electroosmotic/ Pressure Driven Flow of Viscoelastic Fluids between a Parallel Flat Plates Micro-Channel: The Maxwell Model Using the Oldroyd and Jaumann Time Derivatives. MICROMACHINES 2020; 11:mi11110986. [PMID: 33142886 PMCID: PMC7692626 DOI: 10.3390/mi11110986] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/20/2020] [Revised: 10/22/2020] [Accepted: 10/28/2020] [Indexed: 11/16/2022]
Abstract
In the present work, an analytical approximate solution of mixed electroosmotic/pressure driven flow of viscoelastic fluids between a parallel plates microchannel is reported. Inserting the Oldroyd, Jaumann, or both time derivatives into the Maxwell model, important differences in the velocity profiles were found. The presence of the shear and normal stresses is only close to the wall. This model can be used as a tool to understand the flow behavior of low viscosity fluids, as most of them experiment on translation, deformation and rotation of the flow. For practical applications, the volumetric flow rate can be controlled with two parameters, namely the gradient pressure and the electrokinetic parameter, once the fluid has been rheologically characterized.
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Affiliation(s)
- Laura Casas
- SEPI-ESIME Zacatenco, Departamento de Diseño, Instituto Politécnico Nacional, Av. Luis Enrique Erro S/N, Unidad Profesional Adolfo López Mateos, Zacatenco, Alcaldía Gustavo A. Madero, Ciudad de México, 07738, Mexico; (L.C.); (J.A.O.)
| | - José A. Ortega
- SEPI-ESIME Zacatenco, Departamento de Diseño, Instituto Politécnico Nacional, Av. Luis Enrique Erro S/N, Unidad Profesional Adolfo López Mateos, Zacatenco, Alcaldía Gustavo A. Madero, Ciudad de México, 07738, Mexico; (L.C.); (J.A.O.)
| | - Aldo Gómez
- Departamento de Ingeniería, Universidad Nacional Autónoma de México, FES Cuautitlán, Sección Mecánica, Av. Teoloyucan Km 2.5, Col. San Sebastián Xhala, Cuautitlán Izcalli 54714, Estado de México, Mexico;
| | - Juan Escandón
- Departamento de Termofluidos, Instituto Politécnico Nacional, SEPI-ESIME Azcapotzalco, Av. de las Granjas No. 682, Col. Santa Catarina, Alcaldía Azcapotzalco, Ciudad de México 02250, Mexico;
| | - René O. Vargas
- Departamento de Termofluidos, Instituto Politécnico Nacional, SEPI-ESIME Azcapotzalco, Av. de las Granjas No. 682, Col. Santa Catarina, Alcaldía Azcapotzalco, Ciudad de México 02250, Mexico;
- Correspondence: ; Tel.: +52-55-5729-6000 (ext. 64511)
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Editorial for the Special Issue on Micro/Nano-Chip Electrokinetics, Volume III. MICROMACHINES 2020; 11:mi11050482. [PMID: 32397064 PMCID: PMC7281164 DOI: 10.3390/mi11050482] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Accepted: 05/06/2020] [Indexed: 11/23/2022]
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