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Fluid Manipulation: From Fundamentals to Applications

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

Deadline for manuscript submissions: closed (31 December 2023) | Viewed by 24035

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Dr. Pingan Zhu

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Department of Mechanical Engineering, City University of Hong Kong, Hong Kong 999077, China
Interests: microfluidics; fluid mechanics; wettability; biomimetics; micro/nanorobots
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Dr. Ye Tian

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Guest Editor

College of Medicine and Biological Information Engineering, Northeastern University, Shenyang 02115-5005, China
Interests: microfluidics; soft materials; flexible electronics; sensors and probes
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Dear Colleagues,

Fluid manipulation has emerged as a versatile and powerful platform for fostering multidisciplinary applications in physics, chemistry, biology, engineering, environment, and medicine, to name a few. In recent years, the content of fluid manipulation has been continuously enriched with interdisciplinary innovations. For example, the advancement of surface engineering greatly boosts the development of fluid manipulation in an open space or under a liquid for larger ramifications; the thriving of 3D printing technology substantially benefits the fabrication of microfluidic devices, especially those with complex configurations, for small-scale fluid manipulation with high precision; the integration of machine learning and microfluidics revolutionizes fluid manipulation for various applications, such as materials synthesis and Lab-on-a-Chip; the emerging of bioinspired engineering promotes the development of fluid directional transport and collection. Having been burgeoning for decades, fluid manipulation is undergoing a “golden” development age with new concepts and technologies continuing to be witnessed. This Special Issue aims to showcase research papers, communications, and review articles that focus on recent advancements in the fundamentals and applications of fluid manipulation, including but not limited to the (1) fundamental understanding of interfacial fluid flows, (2) design and fabrication of innovative fluid manipulation systems, and (3) diverse applications related to fluid manipulation.

Dr. Pingan Zhu
Dr. Ye Tian
Guest Editors

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Keywords

fluid manipulation
interfacial fluid flows
microfluidics
droplets
bubbles
liquid films
soft interfaces
surface wettability.

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Related Special Issue

Droplet-Based Microfluidics: Design, Fabrication and Applications in Micromachines (18 articles)

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Research

Jump to: Review

16 pages, 4258 KiB

Open AccessArticle

Droplet Motion Driven by Liquid Dielectrophoresis in the Low-Frequency Range

by Sarah Günther-Müller, Raschid Azizy and Steffen Strehle

Micromachines 2024, 15(1), 151; https://doi.org/10.3390/mi15010151 - 19 Jan 2024

Viewed by 1197

Abstract

Electrohydrodynamic wetting manipulation plays a major role in modern microfluidic technologies such as lab-on-a-chip applications and digital microfluidics. Liquid dielectrophoresis (LDEP) is a common driving mechanism, which induces hydrodynamic motion in liquids by the application of nonhomogeneous electrical fields. Among strategies to analyze droplet movement, systematic research on the influence of different frequencies under AC voltage is missing. In this paper, we therefore present a first study covering the motion characteristics of LDEP-driven droplets of the dielectric liquids ethylene glycol and glycerol carbonate in the driving voltage frequency range from 50 Hz to 1600 Hz. A correlation between the switching speed of LDEP-actuated droplets in a planar electrode configuration and the frequency of the applied voltage is shown. Hereby, motion times of different-sized droplets could be reduced by up to a factor of 5.3. A possible excitation of the droplets within their range of eigenfrequencies is investigated using numerical calculations. The featured fluidic device is designed using larger-sized electrodes rather than typical finger or strip electrodes, which are commonly employed in LDEP devices. The influence of the electrode shape is considered simulatively by studying the electric field gradients. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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17 pages, 8709 KiB

Open AccessArticle

Kinetic and Parametric Analysis of the Separation of Ultra-Small, Aqueous Superparamagnetic Iron Oxide Nanoparticle Suspensions under Quadrupole Magnetic Fields

by Stefano Ciannella, Xian Wu, Cristina González-Fernández, Bahareh Rezaei, Jacob Strayer, Hyeon Choe, Kai Wu, Jeffrey Chalmers and Jenifer Gomez-Pastora

Micromachines 2023, 14(11), 2107; https://doi.org/10.3390/mi14112107 - 17 Nov 2023

Cited by 3 | Viewed by 1701

Abstract

Superparamagnetic iron oxide nanoparticles (SPIONs) have gathered tremendous scientific interest, especially in the biomedical field, for multiple applications, including bioseparation, drug delivery, etc. Nevertheless, their manipulation and separation with magnetic fields are challenging due to their small size. We recently reported the coupling of cooperative magnetophoresis and sedimentation using quadrupole magnets as a promising strategy to successfully promote SPION recovery from media. However, previous studies involved SPIONs dispersed in organic solvents (non-biocompatible) at high concentrations, which is detrimental to the process economy. In this work, we investigate, for the first time, the magnetic separation of 20 nm and 30 nm SPIONs dispersed in an aqueous medium at relatively low concentrations (as low as 0.5 g·L⁻¹) using our custom, permanent magnet-based quadrupole magnetic sorter (QMS). By monitoring the SPION concentrations along the vessel within the QMS, we estimated the influence of several variables in the separation and analyzed the kinetics of the process. The results obtained can be used to shed light on the dynamics and interplay of variables that govern the fast separation of SPIONs using inexpensive permanent magnets. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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17 pages, 3426 KiB

Open AccessArticle

Transit Time Theory for a Droplet Passing through a Slit in Pressure-Driven Low Reynolds Number Flows

by Spencer W. Borbas, Kevin Shen, Catherine Ji, Annie Viallat, Emmanuèle Helfer and Zhangli Peng

Micromachines 2023, 14(11), 2040; https://doi.org/10.3390/mi14112040 - 31 Oct 2023

Viewed by 1239

Abstract

Soft objects squeezing through small apertures are crucial for many in vivo and in vitro processes. Red blood cell transit time through splenic inter-endothelial slits (IESs) plays a crucial role in blood filtration and disease progression, while droplet velocity through constrictions in microfluidic devices is important for effective manipulation and separation processes. As these transit phenomena are not well understood, we sought to establish analytical and numerical solutions of viscous droplet transit through a rectangular slit. This study extends from our former theory of a circular pore because a rectangular slit is more realistic in many physiological and engineering applications. Here, we derived the ordinary differential equations (ODEs) of a droplet passing through a slit by combining planar Poiseuille flow, the Young–Laplace equations, and modifying them to consider the lubrication layer between the droplet and the slit wall. Compared to the pore case, we used the Roscoe solution instead of the Sampson one to account for the flow entering and exiting a rectangular slit. When the surface tension and lubrication layer were negligible, we derived the closed-form solutions of transit time. When the surface tension and lubrication layer were finite, the ODEs were solved numerically to study the impact of various parameters on the transit time. With our solutions, we identified the impact of prescribed pressure drop, slit dimensions, and droplet parameters such as surface tension, viscosity, and volume on transit time. In addition, we also considered the effect of pressure drop and surface tension near critical values. For this study, critical surface tension for a given pressure drop describes the threshold droplet surface tension that prevents transit, and critical pressure for a given surface tension describes the threshold pressure drop that prevents transit. Our solutions demonstrate that there is a linear relationship between pressure and the reciprocal of the transit time (referred to as inverse transit time), as well as a linear relationship between viscosity and transit time. Additionally, when the droplet size increases with respect to the slit dimensions, there is a corresponding increase in transit time. Most notably, we emphasize the initial antagonistic effect of surface tension which resists droplet passage but at the same time decreases the lubrication layer, thus facilitating passage. Our results provide quantitative calculations for understanding cells passing through slit-like constrictions and designing droplet microfluidic experiments. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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18 pages, 12289 KiB

Open AccessArticle

Behaviour of Acoustically Levitated Drops in Mid-Water

by Jan-Paul Ruiken, Jörn Villwock and Matthias Kraume

Micromachines 2023, 14(10), 1923; https://doi.org/10.3390/mi14101923 - 10 Oct 2023

Cited by 1 | Viewed by 1824

Abstract

A low-impact acoustic levitation system has been developed to study immobilised single drops in liquid–liquid systems. The ability to observe liquid drops several millimetres in diameter for days enables fundamental research into a wide range of mechanisms. Non-invasive optical measurements with excellent optical accessibility are possible. This experimental work provides the basis for mass transfer studies, emphasizing the precise volume determination, signal noise, reproducibility, and the impact of the acoustic field on the drop and its surrounding environment. The setup can be effectively controlled and proves beneficial for research objectives provided that all liquid phases are entirely degassed, and there are no compressible voids present within the liquids. In addition to the precise, uniform, and reliable measurement conditions, we observed no acoustic streaming in the proximity of the drop and there was no significant vibration of the drop. Qualitative observations using rainbow schlieren deflectometry indicate that the nodal or anti-nodal planes of the standing waves can act as barriers to the dispersion of inhomogeneous dissolved substances in the continuous phase. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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9 pages, 2933 KiB

Open AccessArticle

Stable Superhydrophobic and Antimicrobial ZnO/Polytetrafluoroethylene Films via Radio Frequency (RF) Magnetron Sputtering

by Aoyun Zhuang, Ke Wu, Yao Lu and Jianping Yu

Micromachines 2023, 14(7), 1292; https://doi.org/10.3390/mi14071292 - 24 Jun 2023

Cited by 2 | Viewed by 1456

Abstract

In this study, superhydrophobic ZnO/Polytetrafluoroethylene (ZnO/PTFE) films with water droplet contact angles (CA) observed as high as 165° and water droplet sliding angles of (SA) <1° have been prepared on glass substrates by RF magnetron sputtering. The PTFE was wrapped on a nano-rod made of a ZnO film with superhydrophobic properties while providing excellent UV resistance compared to hexadecyltrimethoxysilane (HDTMS) hydrophobic agents. The upper surface of the rough ZnO film was coated with PTFE, and most of the underlying coating was bare ZnO, which could well make contact with bacteria. For the Gram-negative strain, E. coli, the cell viability count of the ZnO/PTFE sample (3.5 log reduction, 99.96%) was conspicuously lower than that of the ZnO/HDTMS sample (1.2 log reduction, 93.87%) under 1 h illumination of UV light, which showed that the ZnO/PTFE sample has a better photocatalytic property than the ZnO/ HDTMS films. The ZnO/PTFE films also showed good mechanical robustness, which is an important consideration in their widespread real-world adoption. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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14 pages, 3736 KiB

Open AccessArticle

Numerical Investigation of Transonic Flow-Induced Spontaneous Condensation in Micro-Ejector Nozzles

by Yu Han, Xiaodong Wang, Wei Wang, Yuan Xien Lee and Ao Li

Micromachines 2023, 14(6), 1260; https://doi.org/10.3390/mi14061260 - 16 Jun 2023

Cited by 2 | Viewed by 1433

Abstract

Micro-cooling systems are compact refrigeration systems widely applicable in microchemical analysis, biomedicine, and microelectromechanical systems (MEMS). These systems rely on the use of micro-ejectors to achieve precise, fast, and reliable flow and temperature control. However, the efficiency of micro-cooling systems is hindered by spontaneous condensation occurring downstream of the nozzle throat and within the nozzle itself, impacting the performance of the micro-ejector. A micro-scale ejector mathematical model describing wet steam flow was simulated to investigate the steam condensation phenomenon and its influence on flow, incorporating equations for liquid phase mass fraction and droplet number density transfer. The simulation results of wet vapor flow and ideal gas flow were compared and analyzed. The findings revealed that the pressure at the micro-nozzle outlet exceeded predictions based on the ideal gas assumption, while the velocity fell below it. These discrepancies indicated that condensation of the working fluid reduces the pumping capacity and the efficiency of the micro-cooling system. Furthermore, simulations explored the impact of inlet pressure and temperature conditions on spontaneous condensation within the nozzle. The results demonstrated that the properties of the working fluid directly influence transonic flow condensation, underscoring the importance of selecting appropriate working fluid parameters for nozzle design to ensure nozzle stability and optimal micro-ejector operation. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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11 pages, 1744 KiB

Open AccessArticle

Acoustic Atomization-Induced Pumping Based on a Vibrating Sharp-Tip Capillary

by Balapuwaduge Lihini Mendis, Ziyi He, Xiaojun Li, Jing Wang, Chong Li and Peng Li

Micromachines 2023, 14(6), 1212; https://doi.org/10.3390/mi14061212 - 8 Jun 2023

Viewed by 1950

Abstract

Pumping is an essential component in many microfluidic applications. Developing simple, small-footprint, and flexible pumping methods is of great importance to achieve truly lab-on-a-chip systems. Here, we report a novel acoustic pump based on the atomization effect induced by a vibrating sharp-tip capillary. As the liquid is atomized by the vibrating capillary, negative pressure is generated to drive the movement of fluid without the need to fabricate special microstructures or use special channel materials. We studied the influence of the frequency, input power, internal diameter (ID) of the capillary tip, and liquid viscosity on the pumping flow rate. By adjusting the ID of the capillary from 30 µm to 80 µm and the power input from 1 V_pp to 5 V_pp, a flow rate range of 3 to 520 µL/min can be achieved. We also demonstrated the simultaneous operation of two pumps to generate parallel flow with a tunable flow rate ratio. Finally, the capability of performing complex pumping sequences was demonstrated by performing a bead-based ELISA in a 3D-printed microdevice. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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11 pages, 2013 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Designing Versatile Superhydrophilic Structures via an Alginate-Based Hydrophilic Plasticene

by Wenbo Shi, Haoyu Bai, Yaru Tian, Xinsheng Wang, Zhe Li, Xuanbo Zhu, Ye Tian and Moyuan Cao

Micromachines 2023, 14(5), 962; https://doi.org/10.3390/mi14050962 - 28 Apr 2023

Cited by 2 | Viewed by 1731

Abstract

The rational design of superhydrophilic materials with a controllable structure is a critical component in various applications, including solar steam generation, liquid spontaneous transport, etc. The arbitrary manipulation of the 2D, 3D, and hierarchical structures of superhydrophilic substrates is highly desirable for smart liquid manipulation in both research and application fields. To design versatile superhydrophilic interfaces with various structures, here we introduce a hydrophilic plasticene that possesses high flexibility, deformability, water absorption, and crosslinking capabilities. Through a pattern-pressing process with a specific template, 2D prior fast spreading of liquids at speeds up to 600 mm/s was achieved on the superhydrophilic surface with designed channels. Additionally, 3D superhydrophilic structures can be facilely designed by combining the hydrophilic plasticene with a 3D-printed template. The assembly of 3D superhydrophilic microstructure arrays were explored, providing a promising route to facilitate the continuous and spontaneous liquid transport. The further modification of superhydrophilic 3D structures with pyrrole can promote the applications of solar steam generation. The optimal evaporation rate of an as-prepared superhydrophilic evaporator reached ~1.60 kg·m⁻²·h⁻¹ with a conversion efficiency of approximately 92.96%. Overall, we envision that the hydrophilic plasticene should satisfy a wide range of requirements for superhydrophilic structures and update our understanding of superhydrophilic materials in both fabrication and application. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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14 pages, 2148 KiB

Open AccessArticle

First Experimental Evidence of Anti-Stokes Laser-Induced Fluorescence Emission in Microdroplets and Microfluidic Systems Driven by Low Thermal Conductivity of Fluorocarbon Carrier Oil

by Zain Hayat and Abdel El Abed

Micromachines 2023, 14(4), 765; https://doi.org/10.3390/mi14040765 - 29 Mar 2023

Cited by 1 | Viewed by 1824

Abstract

With the advent of many optofluidic and droplet microfluidic applications using laser-induced fluorescence (LIF), the need for a better understanding of the heating effect induced by pump laser excitation sources and good monitoring of temperature inside such confined microsystems started to emerge. We developed a broadband highly sensitive optofluidic detection system, which enabled us to show for the first time that Rhodamine-B dye molecules can exhibit standard photoluminescence as well as blue-shifted photoluminescence. We demonstrate that this phenomenon originates from the interaction between the pump laser beam and dye molecules when surrounded by the low thermal conductive fluorocarbon oil, generally used as a carrier medium in droplet microfluidics. We also show that when the temperature is increased, both Stokes and anti-Stokes fluorescence intensities remain practically constant until a temperature transition is reached, above which the fluorescence intensity starts to decrease linearly with a thermal sensitivity of about

- 0.4 % / °

C for Stokes emission or

- 0.2 % / °

C for anti-Stokes emission. For an excitation power of 3.5 mW, the temperature transition was found to be about 25

°

C, whereas for a smaller excitation power (0.5 mW), the transition temperature was found to be about 36

°

C. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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10 pages, 2849 KiB

Open AccessArticle

A Liquid Mirror Resonator

by Elad Haber, Mark Douvidzon, Shai Maayani and Tal Carmon

Micromachines 2023, 14(3), 624; https://doi.org/10.3390/mi14030624 - 8 Mar 2023

Viewed by 1546

Abstract

We present the first experimental demonstration of a Fabry‒Perot resonator that utilizes total internal reflection from a liquid–gas interface. Our hybrid resonator hosts both optical and capillary waves that mutually interact. Except for the almost perfect reflection by the oil–air interface at incident angles smaller than the critical angle, reflections from the liquid-phase boundary permit optically examining thermal fluctuations and capillary waves at the oil surface. Characterizing our optocapillary Fabry‒Perot reveals optical modes with transverse cross-sectional areas of various shapes and longitudinal modes that are separated by the free spectral range. The optical finesse of our hybrid optocapillary resonator is Fo = 60, the optical quality factor is Qo = 20 million, and the capillary quality factor is Qc = 6. By adjusting the wavelength of our laser near the optical resonance wavelength, we measure the liquid’s Brownian fluctuations. As expected, the low-viscosity liquid exhibits a distinct frequency of capillary oscillation, indicating operation in the underdamped regime. Conversely, going to the overdamped regime reveals no such distinct capillary frequency. Our optocapillary resonator might impact fundamental studies and applications in surface science by enabling optical interrogation, excitation, and cooling of capillary waves residing in a plane. Moreover, our optocapillary Fabry‒Perot might permit photographing thermal capillary oscillation, which the current state-of-the-art techniques do not support. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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Review

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28 pages, 17030 KiB

Open AccessReview

Biomimetic Superhydrophobic Materials through 3D Printing: Progress and Challenges

by Haishuo Liu, Zipeng Zhang, Chenyu Wu, Kang Su and Xiaonan Kan

Micromachines 2023, 14(6), 1216; https://doi.org/10.3390/mi14061216 - 8 Jun 2023

Cited by 10 | Viewed by 3484

Abstract

Superhydrophobicity, a unique natural phenomenon observed in organisms such as lotus leaves and desert beetles, has inspired extensive research on biomimetic materials. Two main superhydrophobic effects have been identified: the “lotus leaf effect” and the “rose petal effect”, both showing water contact angles larger than 150°, but with differing contact angle hysteresis values. In recent years, numerous strategies have been developed to fabricate superhydrophobic materials, among which 3D printing has garnered significant attention due to its rapid, low-cost, and precise construction of complex materials in a facile way. In this minireview, we provide a comprehensive overview of biomimetic superhydrophobic materials fabricated through 3D printing, focusing on wetting regimes, fabrication techniques, including printing of diverse micro/nanostructures, post-modification, and bulk material printing, and applications ranging from liquid manipulation and oil/water separation to drag reduction. Additionally, we discuss the challenges and future research directions in this burgeoning field. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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28 pages, 5060 KiB

Open AccessReview

Microfluidic Methods for Generation of Submicron Droplets: A Review

by Biao Huang, Huiying Xie and Zhenzhen Li

Micromachines 2023, 14(3), 638; https://doi.org/10.3390/mi14030638 - 11 Mar 2023

Cited by 6 | Viewed by 3337

Abstract

Submicron droplets are ubiquitous in nature and widely applied in fields such as biomedical diagnosis and therapy, oil recovery and energy conversion, among others. The submicron droplets are kinetically stable, their submicron size endows them with good mobility in highly constricted pathways, and the high surface-to-volume ratio allows effective loading of chemical components at the interface and good heat transfer performance. Conventional generation technology of submicron droplets in bulk involves high energy input, or relies on chemical energy released from the system. Microfluidic methods are widely used to generate highly monodispersed micron-sized or bigger droplets, while downsizing to the order of 100 nm was thought to be challenging because of sophisticated nanofabrication. In this review, we summarize the microfluidic methods that are promising for the generation of submicron droplets, with an emphasize on the device fabrication, operational condition, and resultant droplet size. Microfluidics offer a relatively energy-efficient and versatile tool for the generation of highly monodisperse submicron droplets. Full article

(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)

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