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Behera N, Chakraborty S. Electrically modulated relaxation dynamics of pre-stretched droplets post switched-off uniaxial extensional flow. SOFT MATTER 2022; 18:3678-3697. [PMID: 35502790 DOI: 10.1039/d1sm01813b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Droplets are known to elongate in extensional flow and exhibit capillary instabilities following flow cessation. Under several practical scenarios, where the deformed drops are exposed to electrified environments, the interplay between capillary and electric forces can further modulate the capillary-driven instability that may lead to novel drop evolution, which has not yet been explored. In the present study, we probe the transient droplet deformation under combined electrohydrodynamic and extensional flows, with a particular focus on the relaxation dynamics in a post-elongation phase, as the external flow field is withdrawn while the electric field remains on. Based on pre-relaxed droplet morphology and electric field strength, the drops appear to relax faster or slower, leading to a steady-state or a plethora of breakup events. The slightly deformed drops relax into stable prolate or oblate shape depending on the electrophysical properties of the fluid pairs. On the other hand, under large deformation limit, our results reveal that in the post-elongation phase, the electric field may either stabilize the droplet or may enforce its breakup primarily via two modes: mid-pinching and end-pinching. We have shown that the post-relaxation events can be mapped into the relevant parametric phase space as a function of the relative strengths of the various forcing parameters as well as geometric parameters. These results present new avenues of droplet manipulation in industrial and microfluidic applications by utilizing unique connectivity between the relaxation kinematics and imposed electrical forcing, a paradigm that has hitherto remained unaddressed.
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Affiliation(s)
- Nalinikanta Behera
- Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal-721302, India.
| | - Suman Chakraborty
- Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal-721302, India.
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2
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Khobaib K, Rozynek Z, Hornowski T. Mechanical properties of particle-covered droplets probed by nonuniform electric field. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.118834] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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3
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Khobaib K, Hornowski T, Rozynek Z. Particle-covered droplet and a particle shell under compressive electric stress. Phys Rev E 2021; 103:062605. [PMID: 34271657 DOI: 10.1103/physreve.103.062605] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2020] [Accepted: 05/20/2021] [Indexed: 11/07/2022]
Abstract
Understanding of the behavior of an individual droplet suspended in a liquid and subjected to a stress is important for studying and designing more complex systems, such as emulsions. Here, we present an experimental study of the behavior of a particle-covered droplet and its particle shell under compressive stress. The stress was induced by an application of a DC electric field. We studied how the particle coverage (φ), particle size (d), and the strength of an electric field (E) influence the magnitude of the droplet deformation (D). The experimental results indicate that adding electrically insulating particles to a droplet interface drastically changes the droplet deformation by increasing its magnitude. We also found that the magnitude of the deformation is not retraceable during the electric field sweeping, i.e., the strain-stress curves form a hysteresis loop due to the energy dissipation. The field-induced droplet deformation was accompanied by structural and morphological changes in the particle shell. We found that shells made of smaller particles were more prone to jamming and formation of arrested shells after removal of an electric stress.
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Affiliation(s)
- Khobaib Khobaib
- Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland
| | - Tomasz Hornowski
- Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland
| | - Zbigniew Rozynek
- Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland.,PoreLab, The Njord Centre, Department of Physics, University of Oslo, Blindern, N-0316 Oslo, Norway
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4
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Khobaib K, Mikkelsen A, Vincent-Dospital T, Rozynek Z. Electric-field-induced deformation, yielding, and crumpling of jammed particle shells formed on non-spherical Pickering droplets. SOFT MATTER 2021; 17:5006-5017. [PMID: 33908579 DOI: 10.1039/d1sm00125f] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Droplets covered with densely packed solid particles, often called Pickering droplets, are used in a variety of fundamental studies and practical applications. For many applications, it is essential to understand the mechanics of such particle-laden droplets subjected to external stresses. Several research groups have studied theoretically and experimentally the deformation, relaxation, rotation, and stability of Pickering droplets. Most of the research concerns spherical Pickering droplets. However, little is known about non-spherical Pickering droplets with arrested particle shells subjected to compressive stress. The experimental results presented here contribute to filling this gap in research. We deform arrested non-spherical Pickering droplets by subjecting them to electric fields, and study the effect of droplet geometry and size, as well as particle size and electric field strength, on the deformation and yielding of arrested non-spherical Pickering droplets. We explain why a more aspherical droplet and/or a droplet covered with a shell made of larger particles required higher electric stress to deform and yield. We also show that an armored droplet can absorb the electric stress differently (i.e., through either in-plane or out-of-plane particle rearrangements) depending on the strength of the applied electric field. Furthermore, we demonstrate that particle shells may fail through various crumpling instabilities, including ridge formation, folding, and wrinkling, as well as inward indentation.
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Affiliation(s)
- K Khobaib
- Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland.
| | - A Mikkelsen
- Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland.
| | - T Vincent-Dospital
- PoreLab, The Njord Centre, Department of Physics, University of Oslo, Blindern, N-0316 Oslo, Norway
| | - Z Rozynek
- Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland. and PoreLab, The Njord Centre, Department of Physics, University of Oslo, Blindern, N-0316 Oslo, Norway
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5
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Oil-in-oil pickering emulsions stabilized by diblock copolymer nanoparticles. J Colloid Interface Sci 2020; 580:354-364. [DOI: 10.1016/j.jcis.2020.07.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2020] [Revised: 06/12/2020] [Accepted: 07/03/2020] [Indexed: 12/18/2022]
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6
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Abbasi MS, Song R, Cho S, Lee J. Electro-Hydrodynamics of Emulsion Droplets: Physical Insights to Applications. MICROMACHINES 2020; 11:E942. [PMID: 33080954 PMCID: PMC7603096 DOI: 10.3390/mi11100942] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/29/2020] [Revised: 10/14/2020] [Accepted: 10/14/2020] [Indexed: 12/31/2022]
Abstract
The field of droplet electrohydrodynamics (EHD) emerged with a seminal work of G.I. Taylor in 1966, who presented the so-called leaky dielectric model (LDM) to predict the droplet shapes undergoing distortions under an electric field. Since then, the droplet EHD has evolved in many ways over the next 55 years with numerous intriguing phenomena reported, such as tip and equatorial streaming, Quincke rotation, double droplet breakup modes, particle assemblies at the emulsion interface, and many more. These phenomena have a potential of vast applications in different areas of science and technology. This paper presents a review of prominent droplet EHD studies pertaining to the essential physical insight of various EHD phenomena. Here, we discuss the dynamics of a single-phase emulsion droplet under weak and strong electric fields. Moreover, the effect of the presence of particles and surfactants at the emulsion interface is covered in detail. Furthermore, the EHD of multi-phase double emulsion droplet is included. We focus on features such as deformation, instabilities, and breakups under varying electrical and physical properties. At the end of the review, we also discuss the potential applications of droplet EHD and various challenges with their future perspectives.
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Affiliation(s)
- Muhammad Salman Abbasi
- School of Mechanical Engineering, Sungkyunkwan University, Suwon 16419, Korea; (M.S.A.); (R.S.); (S.C.)
- Faculty of Mechanical Engineering, University of Engineering and Technology, Lahore 54890, Pakistan
| | - Ryungeun Song
- School of Mechanical Engineering, Sungkyunkwan University, Suwon 16419, Korea; (M.S.A.); (R.S.); (S.C.)
| | - Seongsu Cho
- School of Mechanical Engineering, Sungkyunkwan University, Suwon 16419, Korea; (M.S.A.); (R.S.); (S.C.)
| | - Jinkee Lee
- School of Mechanical Engineering, Sungkyunkwan University, Suwon 16419, Korea; (M.S.A.); (R.S.); (S.C.)
- Institute of Quantum Biophysics, Sungkyunkwan University, Suwon 16419, Korea
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7
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Bielas R, Surdeko D, Kaczmarek K, Józefczak A. The potential of magnetic heating for fabricating Pickering-emulsion-based capsules. Colloids Surf B Biointerfaces 2020; 192:111070. [PMID: 32361373 DOI: 10.1016/j.colsurfb.2020.111070] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Revised: 04/17/2020] [Accepted: 04/20/2020] [Indexed: 11/22/2022]
Abstract
Pickering emulsions (particle-stabilized emulsions) have been widely explored due to their potential applications, one of which is using them as precursors for the formation of colloidal capsules that could be utilized in, among others, the pharmacy and food industries. Here, we present a novel approach to fabricating such colloidal capsules by using heating in the alternating magnetic field. When exposed to the alternating magnetic field, magnetic particles, owing to the hysteresis and/or relaxation losses, become sources of nano- and micro-heating that can significantly increase the temperature of the colloidal system. This temperature rise was evaluated in oil-in-oil Pickering emulsions stabilized by both magnetite and polystyrene particles. When a sample reached high enough temperature, particle fusion caused by glass transition of polystyrene was observed on surfaces of colloidal droplets. Oil droplets covered with shells of fused polystyrene particles were proved to be less susceptible to external stress, which can be evidence of the successful formation of capsules from Pickering emulsion droplets as templates.
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Affiliation(s)
- Rafał Bielas
- Department of Acoustics, Faculty of Physics, Adam Mickiewicz University in Poznań, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland
| | - Dawid Surdeko
- Department of Acoustics, Faculty of Physics, Adam Mickiewicz University in Poznań, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland; Faculty of Science and Technology, University of Twente, P.O. BOX 217, 7500 AE Enschede, The Netherlands
| | - Katarzyna Kaczmarek
- Department of Acoustics, Faculty of Physics, Adam Mickiewicz University in Poznań, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland
| | - Arkadiusz Józefczak
- Department of Acoustics, Faculty of Physics, Adam Mickiewicz University in Poznań, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland.
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Kubiak T, Banaszak J, Józefczak A, Rozynek Z. Direction-Specific Release from Capsules with Homogeneous or Janus Shells Using an Ultrasound Approach. ACS APPLIED MATERIALS & INTERFACES 2020; 12:15810-15822. [PMID: 32186360 DOI: 10.1021/acsami.9b21484] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
A variety of approaches have been developed to release contents from capsules, including techniques that use electric or magnetic fields, light, or ultrasound as a stimulus. However, in the majority of the known approaches, capsules are disintegrated in violent way and the liberation of the encapsulated material is often in a random direction. Thus, the controllable and direction-specific release from microcapsules in a simple and effective way is still a great challenge. This greatly limits the use of microcapsules in applications where targeted and directional release is desirable. Here, we present a convenient ultrasonic method for controllable and unidirectional release of an encapsulated substance. The release is achieved by using MHz-frequency ultrasound that enables the inner liquid stretching, which imposes mechanical stress on the capsule's shell. This leads to the puncturing of the shell and enables smooth liberation of the liquid payload in one direction. We demonstrate that 1-4.3 MHz acoustic waves with the intensity of a few W/cm2 are capable of puncturing of particle capsules with diameters ranging from around 300 μm to 5 mm and the release of the encapsulated liquid in a controlled manner. Various aspects of our route, including the role of the capsule size, ultrasound wavelength, and intensity in the performance of the method, are studied in detail. We also show that the additional control of the release can be achieved by using capsules having patchy shells. The presented method can be used to facilitate chemical reactions in micro- and nanolitre droplets and various small-scale laboratory operations carried in bulk liquids in microenvironment. Our results may also serve as an entry point for testing other uses of the method and formulation of theoretical modeling of the presented ultrasound mechanism.
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Affiliation(s)
- Tomasz Kubiak
- Institute of Acoustics, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland
- Hipolit Cegielski State University of Applied Sciences, Stefana Wyszyńskiego 38, 62-200 Gniezno, Poland
| | - Joanna Banaszak
- Institute of Acoustics, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland
| | - Arkadiusz Józefczak
- Institute of Acoustics, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland
| | - Zbigniew Rozynek
- Institute of Acoustics, Faculty of Physics, Adam Mickiewicz University, Uniwersytetu Poznańskiego 2, 61-614 Poznań, Poland
- Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States
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9
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Mikkelsen A, Rozynek Z. Mechanical Properties of Particle Films on Curved Interfaces Probed through Electric Field-Induced Wrinkling of Particle Shells. ACS APPLIED MATERIALS & INTERFACES 2019; 11:29396-29407. [PMID: 31329414 DOI: 10.1021/acsami.9b08045] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Similar to the human skin, a monolayer of packed particles capillary bound to a liquid interface wrinkles when subjected to compressive stress. The induced wrinkles absorb the applied stress and do not disappear unless the stress is removed. Experimental and theoretical investigations of wrinkle formation typically concern flat particle monolayers subjected to uniaxial stress. In this work, we extend the results on wrinkling of particle-covered interfaces to the investigation of mechanical properties of particle films on a curved interface, that is, we study particle shells formed on droplets and subjected to hoop stress. Opposed to flat particle layers where liquid buoyancy alone acts as the effective stiffness, the mechanical properties of particle layers on small droplets are also affected by the surface curvature. We show here that this leads to formation of wrinkles with different characteristic wavelengths compared to those found at flat interfaces. Our experimental results also reveal that the wrinkle wavelength of particle shells is proportional to the square root of particle size and the size of the droplets on which the shells are formed. Wrinkling of particle layers composed of microparticles with diameters ranging from around 1-100 μm was induced using a novel approach combining electrodeformation and electrohydrodynamic flows. We demonstrate that our contactless approach for studying the mechanical properties of particle shells enables estimation of elasticity, particle film thickness, and bending stiffness of particle shells. The proposed approach is insensitive to both particle coverage and electric field strength. In addition, it enables manipulation of particle packing that is intimately linked with formation of wrinkling patterns. With a wide range of applications depending on accurate mechanical properties (e.g., drug-delivery capsules to self-healing materials), this work provides a valuable method to characterize the mechanical properties of shells and tailor their surface properties (i.e., permeability and roughness).
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Affiliation(s)
- A Mikkelsen
- Faculty of Physics , Adam Mickiewicz University , Uniwersytetu Poznańskiego 2 , Poznań 61-614 , Poland
| | - Z Rozynek
- Faculty of Physics , Adam Mickiewicz University , Uniwersytetu Poznańskiego 2 , Poznań 61-614 , Poland
- Harvard John A. Paulson School of Engineering and Applied Sciences , Harvard University , Cambridge , Massachusetts 02138 , United States
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10
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Mikkelsen A, Khobaib K, Eriksen FK, Måløy KJ, Rozynek Z. Particle-covered drops in electric fields: drop deformation and surface particle organization. SOFT MATTER 2018; 14:5442-5451. [PMID: 29901062 DOI: 10.1039/c8sm00915e] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Drops covered by adsorbed particles are a prominent research topic because they hold promise for a variety of practical applications. Unlocking the enormous potential of particle-laden drops in new material fabrication, for instance, requires understanding how surface particles affect the electrical and deformation properties of drops, as well as developing new routes for particle manipulation at the interface of drops. In this study, we utilized electric fields to experimentally investigate the mechanics of particle-covered silicone oil drops suspended in castor oil, as well as particle assembly at drop surfaces. We used particles with electrical conductivities ranging from insulating polystyrene to highly conductive silver. When subjected to electric fields, drops can change shape, rotate, or break apart. In the first part of this work, we demonstrate how the deformation magnitude and shape of drops, as well as their electrical properties, are affected by electric field strength, particle size, conductivity, and coverage. We also discuss the role of electrohydrodynamic flows on drop deformation. In the second part, we present the electric field-directed assembly and organization of particles at drop surfaces. In this regard, we studied various parameters in detail, including electric field strength, particle size, coverage, and electrical conductivity. Finally, we present a novel method for controlling the local particle coverage and packing of particles on drop surfaces by simply tuning the frequency of the applied electric field. This approach is expected to find uses in optical materials and applications.
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Affiliation(s)
- A Mikkelsen
- Institute of Acoustics, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland.
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