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Bandyopadhyay S, Shristi A, Kumawat V, Gope A, Mukhopadhyay A, Chakraborty S, Mukherjee R. Droplet Impact Dynamics on Biomimetic Replica of Yellow Rose Petals: Rebound to Micropinning Transition. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:6051-6060. [PMID: 37067511 DOI: 10.1021/acs.langmuir.3c00063] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Rose petals exhibit a phenomenal wetting property of being sticky and superhydrophobic simultaneously. A recent study has shown that for short timescales, associated with drop impact phenomenon, lotus leaf and rose petal replicas exhibit similar wettability, thereby highlighting the difference between long and short time wettability. Also, short time wetting on rose petals of different colors remains completely unaddressed, as almost all existing study on wetting of rose petals have been performed with the classical red rose (Rosa chinensis). In this paper, we compare the drop impact studies on replicas of a yellow rose petal, with those on extensively studied red rose petal replicas and the lotus leaf over a wide range of Weber number (We), by varying the height of fall (h) from 10 to 375 mm. Our results reveal that over the replica of a yellow rose petal, the initial impact outcome varies from complete rebound to micro pinning and eventually complete pinning depending on the kinetic energy of the impacting drop, in contrast to that on red rose petal replica on which the droplet always pinned. Based on experimental finding, we present a comprehensive regime phase map of the post impact behavior of the drop on different surfaces as a function of impact height. We also present a simple scaling analysis to understand the combined effect of pattern height and periodicity on the critical h corresponding to wetting regime transition. Additionally, variation of maximum spreading diameter and spreading time with the h for the different surfaces is also discussed. The results highlight that the initial impact dynamics of a water drop over a topographically patterned substrate is a strong function of the topographical parameters and can be very different from the equilibrium wetting state.
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Affiliation(s)
- Saumyadwip Bandyopadhyay
- Advanced Technology Development Centre, Indian Institute of Technology Kharagpur, Kharagpur, 721302 West Bengal, India
| | - Anshika Shristi
- Instability & Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, 721302 West Bengal, India
| | - Vinit Kumawat
- Instability & Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, 721302 West Bengal, India
| | - Ayan Gope
- Advanced Technology Development Centre, Indian Institute of Technology Kharagpur, Kharagpur, 721302 West Bengal, India
| | - Anurup Mukhopadhyay
- School of Medical Science and Technology, Indian Institute of Technology Kharagpur, Kharagpur, 721302 West Bengal, India
| | - Suman Chakraborty
- Advanced Technology Development Centre, Indian Institute of Technology Kharagpur, Kharagpur, 721302 West Bengal, India
- Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, 721302 West Bengal, India
| | - Rabibrata Mukherjee
- Advanced Technology Development Centre, Indian Institute of Technology Kharagpur, Kharagpur, 721302 West Bengal, India
- Instability & Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, 721302 West Bengal, India
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2
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Lin M, Vo Q, Mitra S, Tran T. Viscous droplet impingement on soft substrates. SOFT MATTER 2022; 18:5474-5482. [PMID: 35833825 DOI: 10.1039/d2sm00709f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Viscous droplets impinging on soft substrates may exhibit several distinct behaviours including repeated bouncing, wetting, and hovering, i.e., spreading and retracting after impact without bouncing back or wetting. We experimentally study the conditions enabling these characteristic behaviours by systematically varying substrate elasticity, impact velocity and liquid viscosity. For each substrate elasticity, the transition to wetting is determined as the dependence of the Weber number We, which measures the droplet's kinetic energy against its surface energy, on the Ohnesorge number Oh, which compares viscosity to inertia and capillarity. We find that while We at the wetting transition monotonically decreases with Oh for relatively rigid substrates, it exhibits a counter-intuitive behaviour in which it first increases and then gradually decreases for softer substrates. We experimentally determine the dependence of the maximum Weber number allowing non-wetting impacts on substrate elasticity and show that it provides an excellent quantitative measure of liquid repellency for a wide range of surfaces, from liquid to soft surfaces and non-deformable surfaces.
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Affiliation(s)
- Marcus Lin
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
| | - Quoc Vo
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
| | - Surjyasish Mitra
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore
| | - Tuan Tran
- School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore
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3
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Damak M, de Ruiter J, Panat S, Varanasi KK. Dynamics of an impacting emulsion droplet. SCIENCE ADVANCES 2022; 8:eabl7160. [PMID: 35302841 PMCID: PMC8932654 DOI: 10.1126/sciadv.abl7160] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2021] [Accepted: 01/27/2022] [Indexed: 06/01/2023]
Abstract
Emulsions are widely used in agriculture where oil-based pesticides are sprayed as an emulsion. However, emulsion droplets can bounce off hydrophobic plant surfaces, leading to major health and environmental issues as pesticides pollute water sources and soils. Here, we report an unexpected transition from bouncing to sticking to bouncing as the droplet impact speed increases. We show that the physics are governed by an in situ, self-generated lubrication of the surface leading to a suction force from the nascent oil layer around the droplet. We demonstrate that this phenomenon can be controlled by a careful balance of three time scales: the contact time of the droplet, the impregnation time scale of the oil, and the oil ridge formation time scale. We lastly build a design map to precisely control the bouncing of droplets and the oil coverage of the target surface. These insights have broad applicability in agriculture, cooling sprays, combustion, and additive manufacturing.
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Affiliation(s)
- Maher Damak
- Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
- Infinite Cooling Inc., 121 Madison st, Malden, MA 02148, USA
| | - Jolet de Ruiter
- Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
- Thermo Fisher Scientific, Achtseweg Noord 5, 5651 GG Eindhoven, The Netherlands
| | - Sreedath Panat
- Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
| | - Kripa K. Varanasi
- Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
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4
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Singla T, Roy T, Parmananda P, Rivera M. An alternate approach to simulate the dynamics of perturbed liquid drops. CHAOS (WOODBURY, N.Y.) 2022; 32:023106. [PMID: 35232026 DOI: 10.1063/5.0071930] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Accepted: 01/10/2022] [Indexed: 06/14/2023]
Abstract
Liquid drops when subjected to external periodic perturbations can execute polygonal oscillations. In this work, a simple model is presented that demonstrates these oscillations and their characteristic properties. The model consists of a spring-mass network such that masses are analogous to liquid molecules and the springs correspond to intermolecular links. Neo-Hookean springs are considered to represent these intermolecular links. The restoring force of a neo-Hookean spring depends nonlinearly on its length such that the force of a compressed spring is much higher than the force of the spring elongated by the same amount. This is analogous to the incompressibility of liquids, making these springs suitable to simulate the polygonal oscillations. It is shown that this spring-mass network can imitate most of the characteristic features of experimentally reported polygonal oscillations. Additionally, it is shown that the network can execute certain dynamics, which so far have not been observed in a perturbed liquid drop. The characteristics of dynamics that are observed in the perturbed network are polygonal oscillations, rotation of network, numerical relations (rational and irrational) between the frequencies of polygonal oscillations and the forcing signal, and that the shape of the polygons depends on the parameters of perturbation.
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Affiliation(s)
- Tanu Singla
- Tecnologico de Monterrey, Calle del Puente 222, Colonia Ejidos de Huipulco, Tlalpan, CP 14380 Ciudad de México, Mexico
| | - Tanushree Roy
- Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
| | - P Parmananda
- Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
| | - M Rivera
- Centro de Investigación en Ciencias-(IICBA), UAEM, Avenida Universidad 1001, Colonia Chamilpa, CP 62209 Cuernavaca, Morelos, Mexico
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5
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Li T, Wu Y. Impact Dynamics of Nanodroplets on V-Shaped Substrates: Asymmetrical Behavior and Fast-Rebound Dynamics. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:13170-13178. [PMID: 34699717 DOI: 10.1021/acs.langmuir.1c02488] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Controlling the drop impact behaviors plays an important role in both designing surface functional materials and improving industrial techniques. Here, the impact dynamics of nanodroplets on "V-shaped" substrates is studied, which is manifested as asymmetrical spreading and retraction behaviors that could be weakened by increasing the angles of the "V" shape, accompanied by the evolution of the shape from leaf-like, stripe-like, to dumbbell-like at v = 20 Å/ps. When v increases to 40 Å/ps, the previously deposited nanodroplets could be transformed to a rebound one at α = 60 and 90°, which is ascribed to the combined effect of the confinement conditions and the extrusion force. Furthermore, an impact behavior map as a function of impact velocity and angle is depicted, which suggests that a decrease in angles or an increase in the impact velocity is likely to cause the nanodroplets to rebound. More importantly, the results give visible evidence that compared to the flat substrates, the V-shaped structure is advantageous for achieving a fast-rebound behavior even at a low speed of impact, which should be good news for practical applications in many multidisciplinary fields, such as self-cleaning, anti-icing/fogging, pollution prevention, energy storage, and so forth.
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Affiliation(s)
- Tao Li
- Department of Physics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong 999077, China
- Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials, Ministry of Education, Shandong University, Jinan 250061, China
| | - Yan Wu
- Department of Chemistry, Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong 999077, China
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Vo Q, Tran T. Mediation of lubricated air films using spatially periodic dielectrophoretic effect. Nat Commun 2021; 12:4289. [PMID: 34257292 PMCID: PMC8277893 DOI: 10.1038/s41467-021-24534-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 06/18/2021] [Indexed: 12/05/2022] Open
Abstract
A stone thrown in a lake captures air as it collides with water and sinks; likewise a rain drop falling on a flat surface traps air bubbles underneath and creates a spectacular splash. These natural occurrences, from bubble entrapment to liquid ejection, happen as air fails to escape from the closing gap between liquid and solid surfaces. Trapping of air is devastating for casting, coating, painting, and printing industries, or those intolerant of water entry noise. Attempts to eliminate the interfering air rely on either reducing the ambient pressure or modifying the solid surfaces. The former approach is inflexible in its implementation, while the latter one is inherently limited by the wetting speed of liquid or the draining capacity of air passages created on the solid. Here, we present a “divide and conquer” approach to split the thin air gap into tunnels and subsequently squeeze air out from the tunnels against its viscous resistance using spatially periodic dielectrophoretic force. We confirm the working principles by demonstrating suppression of both bubble entrapment and splash upon impacts of droplets on solid surfaces. The violent splash of a droplet caused by residual air pockets trapped during impact on a solid surface appears inevitable. Vo and Tran show how to vent the drop on short notice for a smooth touchdown, harnessing dielectrophoretic forces to create dynamic drainage channels.
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Affiliation(s)
- Quoc Vo
- School of Mechanical & Aerospace Engineering, HP-NTU Digital Manufacturing Corporate Lab, Nanyang Technological University, Singapore, Singapore
| | - Tuan Tran
- School of Mechanical & Aerospace Engineering, HP-NTU Digital Manufacturing Corporate Lab, Nanyang Technological University, Singapore, Singapore. .,Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore.
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7
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Mitra S, Vo Q, Tran T. Bouncing-to-wetting transition of water droplets impacting soft solids. SOFT MATTER 2021; 17:5969-5977. [PMID: 34047748 DOI: 10.1039/d1sm00339a] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Soft surfaces impacted by liquid droplets trap more air underneath than their rigid counterparts. The extended lifetime of the air film not only facilitates bouncing behaviours of the impacting droplets but also increases the possibility of interactions between the air film itself and the air cavity formed inside the droplets by capillary waves. Such interactions may cause rupture of the trapped air film by a so-called dimple inversion phenomenon and suppress bouncing. In this work, we systematically investigate the relationship between air cavity collapse and air film rupture for water droplets impacting soft, hydrophobic surfaces. By constructing a bouncing-to-wetting phase diagram based on the rupturing dynamics of the trapped air film, we observe that the regime in which air film rupture is induced by dimple inversion consistently separates the bouncing regime and the one in which wetting is caused by random rupture. We also found that air film rupture by dimple inversion in-turn affects both the collapsing dynamics of the air cavity and the resulting high-speed jet. We then provide a detailed characterisation of the collapsing dynamics of the air cavity and subsequent jetting.
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Affiliation(s)
- Surjyasish Mitra
- School of Physical & Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798
| | - Quoc Vo
- School of Mechanical & Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798.
| | - Tuan Tran
- School of Mechanical & Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798.
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8
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The Role of Electric Pressure/Stress Suppressing Pinhole Defect on Coalescence Dynamics of Electrified Droplet. COATINGS 2021. [DOI: 10.3390/coatings11050503] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The dimple occurs by sudden pressure inversion at the droplet’s bottom interface when a droplet collides with the same liquid-phase or different solid-phase. The air film entrapped inside the dimple is a critical factor affecting the sequential dynamics after coalescence and causing defects like the pinhole. Meanwhile, in the coalescence dynamics of an electrified droplet, the droplet’s bottom interfaces change to a conical shape, and droplet contact the substrate directly without dimple formation. In this work, the mechanism for the dimple’s suppression (interfacial change to conical shape) was studied investigating the effect of electric pressure. The electric stress acting on a droplet interface shows the nonlinear electric pressure adding to the uniform droplet pressure. This electric stress locally deforms the droplet’s bottom interface to a conical shape and consequentially enables it to overcome the air pressure beneath the droplet. The electric pressure, calculated from numerical tracking for interface and electrostatic simulation, was at least 108 times bigger than the air pressure at the center of the coalescence. This work helps toward understanding the effect of electric stress on droplet coalescence and in the optimization of conditions in solution-based techniques like printing and coating.
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9
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Shin S, Li M, Wu X, Saha A, Bae J. Role of soft-gel substrates on bouncing-merging transition in drop impact on a liquid film. SOFT MATTER 2021; 17:571-579. [PMID: 33185222 DOI: 10.1039/d0sm01675f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Liquid droplets impacting on liquid films is common in many industrial and natural processes. It is crucial to understand the impact of droplets on a liquid film resting on soft deformable substrates in some of the applications including 3D printing of engineering structures, prosthetic implants and tissue engineering. By recognizing the practical relevance of soft-substrates, we present an experimental investigation to assess the role of deformable substrates on bouncing-to-merging transition in droplet impact on the liquid film. First, we prepared polyacrylamide (PAAm) soft-gel substrates with various "softness" (i.e., Young's modulus) by modulating the concentration of a crosslinker, N,N-methylene-bis-acrylamide (BIS). We found that the Young's modulus of PAAm initially increases with the concentration of crosslinker, and subsequently becomes almost constant due to inhomogeneity of crosslinking. Next, through the experiments of droplet impact on the liquid film resting on soft substrates with different Young's moduli, we observe that the early merging and corresponding bouncing-to-merging transitional boundaries remain unaffected by the "softness" since such merging occurs further away from the substrate. However, the late merging, which appears during the retraction process of the deformed droplet, occurs relatively close to the substrate, and hence is found to be significantly affected by its "softness". A scaling analysis is presented to quantify the role of change in Young's modulus of the substrate on late merging, which is supported by the experimental data.
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Affiliation(s)
- Soyoung Shin
- Department of NanoEngineering, University of California San Diego, La Jolla, CA 92093, USA. and Chemical Engineering Program, University of California San Diego, La Jolla, CA 92093, USA
| | - Minghao Li
- Material Science and Engineering Program, University of California San Diego, La Jolla, CA 92093, USA
| | - Xian Wu
- Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, CA 92093, USA.
| | - Abhishek Saha
- Department of Mechanical and Aerospace Engineering, University of California San Diego, La Jolla, CA 92093, USA.
| | - Jinhye Bae
- Department of NanoEngineering, University of California San Diego, La Jolla, CA 92093, USA. and Chemical Engineering Program, University of California San Diego, La Jolla, CA 92093, USA and Material Science and Engineering Program, University of California San Diego, La Jolla, CA 92093, USA and Sustainable Power and Energy Center (SPEC), University of California San Diego, La Jolla, CA 92093, USA
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10
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Wu H, Mendel N, van den Ende D, Zhou G, Mugele F. Energy Harvesting from Drops Impacting onto Charged Surfaces. PHYSICAL REVIEW LETTERS 2020; 125:078301. [PMID: 32857530 DOI: 10.1103/physrevlett.125.078301] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Revised: 05/15/2020] [Accepted: 06/25/2020] [Indexed: 05/12/2023]
Abstract
We use a combination of high-speed video imaging and electrical measurements to study the direct conversion of the impact energy of water drops falling onto an electrically precharged solid surface into electrical energy. Systematic experiments at variable impact conditions (initial height; impact location relative to electrodes) and electrical parameters (surface charge density; external circuit resistance; fluid conductivity) allow us to describe the electrical response quantitatively without any fit parameters based on the evolution of the drop-substrate interfacial area. We derive a scaling law for the energy harvested by such "nanogenerators" and find that optimum efficiency is achieved by matching the timescales of the external electrical energy harvesting circuit and the hydrodynamic spreading process.
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Affiliation(s)
- Hao Wu
- Physics of Complex Fluids, Faculty of Science and Technology, MESA+ Institute for Nanotechnology, University of Twente, Enschede 7500AE, The Netherlands
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, People's Republic of China
| | - Niels Mendel
- Physics of Complex Fluids, Faculty of Science and Technology, MESA+ Institute for Nanotechnology, University of Twente, Enschede 7500AE, The Netherlands
| | - Dirk van den Ende
- Physics of Complex Fluids, Faculty of Science and Technology, MESA+ Institute for Nanotechnology, University of Twente, Enschede 7500AE, The Netherlands
| | - Guofu Zhou
- Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, People's Republic of China
| | - Frieder Mugele
- Physics of Complex Fluids, Faculty of Science and Technology, MESA+ Institute for Nanotechnology, University of Twente, Enschede 7500AE, The Netherlands
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11
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Nguyen TV, Ichiki M. Bubble entrapment during the recoil of an impacting droplet. MICROSYSTEMS & NANOENGINEERING 2020; 6:36. [PMID: 34567650 PMCID: PMC8433192 DOI: 10.1038/s41378-020-0158-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/25/2019] [Revised: 03/09/2020] [Accepted: 03/30/2020] [Indexed: 06/13/2023]
Abstract
When a droplet impacts a (super-)hydrophobic surface, there is a range of Weber numbers within which bubble entrapment will occur during droplet recoil due to closure of the air cavity developed when the droplet spreads out during the impact. In this study, we studied bubble entrapment using a microelectromechanical system (MEMS)-based acoustic sensor fabricated on a substrate. We found that bubble entrapment is followed by an acoustic vibration that can be detected by the sensor. Moreover, the frequency of the vibration is inversely proportional to the radius of the droplet, which indicates that this vibration is the resonant oscillation of the bubble. Therefore, the MEMS-based acoustic sensor can be used not only to detect but also to measure the size of the entrapped bubble. Finally, we demonstrated that it is possible to prevent bubble formation by allowing the air to escape to the underside of the droplet contact area. This can be done by creating through-holes on the substrate or decorating the substrate with sufficiently large textures.
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Affiliation(s)
- Thanh-Vinh Nguyen
- Sensing System Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Japan, 1-2-1 Namiki, Tsukuba-shi, Ibaraki 305-8564 Japan
| | - Masaaki Ichiki
- Sensing System Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Japan, 1-2-1 Namiki, Tsukuba-shi, Ibaraki 305-8564 Japan
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12
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Qi H, Wang T, Che Z. Air layer during the impact of droplets on heated substrates. Phys Rev E 2020; 101:043114. [PMID: 32422751 DOI: 10.1103/physreve.101.043114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2019] [Accepted: 03/30/2020] [Indexed: 06/11/2023]
Abstract
When a droplet impacts on a substrate, the air underneath the droplet is compressed to form an air layer of a dimple shape before the droplet wets the substrate. This air layer is important to the impact dynamics, and many studies have been performed to investigate the air layer during the impact process on unheated substrates. In this experimental study of the air layer, our results reveal that the air layer is profoundly affected by the substrate temperature, even if the substrate temperature is below the boiling point of the droplet fluid. We use high-speed imaging and color interferometry to measure the air layer with nanometer accuracy. The results show that the thickness of the air layer increases with increasing the substrate temperature. Compared with the impact of the droplet on the unheated substrate, the average thickness of the air layer on the heated substrate at 70 °C is about 12% thicker. This will affect the subsequent bubble entrapment, which is an important feature of the impact dynamics. A simplified model is proposed to consider the heat transfer in the air layer. Additionally, the effects of the Weber number, the fluid viscosity, and the size of the droplet on the air layer are also analyzed. This study sheds light on controlling the impact dynamics of droplets by adjusting the substrate temperature.
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Affiliation(s)
- Haicheng Qi
- State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China
| | - Tianyou Wang
- State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China
| | - Zhizhao Che
- State Key Laboratory of Engines, Tianjin University, Tianjin 300072, China
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13
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Blanken N, Saleem MS, Antonini C, Thoraval MJ. Rebound of self-lubricating compound drops. SCIENCE ADVANCES 2020; 6:eaay3499. [PMID: 32201721 PMCID: PMC7069704 DOI: 10.1126/sciadv.aay3499] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Accepted: 12/13/2019] [Indexed: 06/02/2023]
Abstract
Drop impact on solid surfaces is encountered in numerous natural and technological processes. Although the impact of single-phase drops has been widely explored, the impact of compound drops has received little attention. Here, we demonstrate a self-lubrication mechanism for water-in-oil compound drops impacting on a solid surface. Unexpectedly, the core water drop rebounds from the surface below a threshold impact velocity, irrespective of the substrate wettability. This is interpreted as the result of lubrication from the oil shell that prevents contact between the water core and the solid surface. We combine side and bottom view high-speed imaging to demonstrate the correlation between the water core rebound and the oil layer stability. A theoretical model is developed to explain the observed effect of compound drop geometry. This work sets the ground for precise complex drop deposition, with a strong impact on two- and three-dimensional printing technologies and liquid separation.
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Affiliation(s)
- Nathan Blanken
- State Key Laboratory for Strength and Vibration of Mechanical Structures, Shaanxi Key Laboratory of Environment and Control for Flight Vehicle, International Center for Applied Mechanics, School of Aerospace, Xi’an Jiaotong University, Xi’an 710049, P. R. China
| | - Muhammad Saeed Saleem
- State Key Laboratory for Strength and Vibration of Mechanical Structures, Shaanxi Key Laboratory of Environment and Control for Flight Vehicle, International Center for Applied Mechanics, School of Aerospace, Xi’an Jiaotong University, Xi’an 710049, P. R. China
| | - Carlo Antonini
- Department of Materials Science, University of Milano-Bicocca, Milan, Italy
- Cellulose and Wood Materials, Swiss Federal Laboratories for Materials Science and Technology (Empa), Dübendorf, Switzerland
| | - Marie-Jean Thoraval
- State Key Laboratory for Strength and Vibration of Mechanical Structures, Shaanxi Key Laboratory of Environment and Control for Flight Vehicle, International Center for Applied Mechanics, School of Aerospace, Xi’an Jiaotong University, Xi’an 710049, P. R. China
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14
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Sharma M, Gopu M, George JE, Gupta S, Mampallil D. Drop impact on thin powder layers: pattern formation by air entrapment. SOFT MATTER 2020; 16:1342-1348. [PMID: 31934709 DOI: 10.1039/c9sm01887e] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Impact of drops on thin powder layers displaces the powder particles radially outward producing shallow craters with thick rims, for example, as observed on dust layers on the floor. Here, we report that the patterns formed on thin powder layers by drop impact are not limited to such crater-like ones. Instead, depending upon the layer properties, disc or disc-plus-ring shaped patterns are formed at the impact point. We show that air entrapment and micro-bubble formation during the drop impact result in the formation of such patterns. Based on high-speed imaging, scaling analyses, and measurements with various liquids and powder layers, we propose a mechanism for the formation of such patterns. The phenomenon that we report can open further investigations on drop impact on the granular matter.
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Affiliation(s)
- Meenakshi Sharma
- Indian Institute of Science Education & Research Tirupati, Mangalam P. O. PIN 517507, Tirupati, AP, India.
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15
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Universality in the viscous-to-inertial coalescence of liquid droplets. Proc Natl Acad Sci U S A 2019; 116:23467-23472. [PMID: 31690659 DOI: 10.1073/pnas.1910711116] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We present a theory on the coalescence of 2 spherical liquid droplets that are initially stationary. The evolution of the radius of a liquid neck formed upon coalescence was formulated as an initial value problem and then solved to yield an exact solution without free parameters, with its 2 asymptotic approximations reproducing the well-known scaling relations in the inertially limited viscous and inertial regimes. The viscous-to-inertial crossover observed in previous research is also recovered by the theory, rendering the collapse of data of different viscosities onto a single curve.
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16
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Xu H, Chang C, Yi N, Tao P, Song C, Wu J, Deng T, Shang W. Coalescence, Spreading, and Rebound of Two Water Droplets with Different Temperatures on a Superhydrophobic Surface. ACS OMEGA 2019; 4:17615-17622. [PMID: 31681868 PMCID: PMC6822121 DOI: 10.1021/acsomega.9b01181] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/24/2019] [Accepted: 07/25/2019] [Indexed: 06/10/2023]
Abstract
This paper studied the coalescence, spreading, and rebound of two droplets with different temperatures on a superhydrophobic surface. When the temperature of the impacting droplet was the same as that of the stationary droplet, there was a large deformation of both droplets before the coalescence and the energy dissipation was also large. The coalescence happened at the time close to the maximum spreading. When the temperature of the impacting droplet increased, the deformation of both droplets became smaller before the coalescence and the coalescence happened at or even before the droplets started to spread. The energy dissipation and loss in the later situation is less than those in the previous case. The rebounding characteristics of the merged droplets were also found to be dependent on the temperature. There is an optimum temperature at which the merged droplets can rebound for more times due to the balance of energy loss and also the interaction of the merged droplets with the underlying superhydrophobic substrate. These findings may help further the fundamental understanding of droplet collision on a superhydrophobic surfaces and also offer an alternative strategy to remove droplets from the underlying surfaces for different industrial applications, including condensation heat transfer in steam power plants and phase-change-based thermal management systems.
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Affiliation(s)
- Hao Xu
- State
Key Laboratory of Metal Matrix Composites, Advanced Energy Materials
and Technology Center, School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, P. R. China
| | - Chao Chang
- State
Key Laboratory of Metal Matrix Composites, Advanced Energy Materials
and Technology Center, School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, P. R. China
- Institute
of Marine Engineering and Thermal Science, Marine Engineering College, Dalian Maritime University, Dalian 116026, P. R. China
| | - Nan Yi
- State
Key Laboratory of Metal Matrix Composites, Advanced Energy Materials
and Technology Center, School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, P. R. China
| | - Peng Tao
- State
Key Laboratory of Metal Matrix Composites, Advanced Energy Materials
and Technology Center, School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, P. R. China
| | - Chengyi Song
- State
Key Laboratory of Metal Matrix Composites, Advanced Energy Materials
and Technology Center, School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, P. R. China
| | - Jianbo Wu
- State
Key Laboratory of Metal Matrix Composites, Advanced Energy Materials
and Technology Center, School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, P. R. China
| | - Tao Deng
- State
Key Laboratory of Metal Matrix Composites, Advanced Energy Materials
and Technology Center, School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, P. R. China
| | - Wen Shang
- State
Key Laboratory of Metal Matrix Composites, Advanced Energy Materials
and Technology Center, School of Materials Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, P. R. China
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17
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Gao F, Yi H, Qi L, Qiao R, Deng W. Weakly charged droplets fundamentally change impact dynamics on flat surfaces. SOFT MATTER 2019; 15:5548-5553. [PMID: 31194205 DOI: 10.1039/c9sm00895k] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Electric charges are often found in naturally or artificially formed droplets, such as raindrops and those generated by Kelvin's water dropper. In contrast to the impact of neutral droplets on a flat solid surface upon which a thin convex lens shape layer of the gas film is typically formed, we show that the delicate gas thin film can be fundamentally altered for even weakly charged droplets. As the charge level is raised above a critical level of ∼1% of the Rayleigh limit for representative impact conditions, the Maxwell stress overcomes the gas pressure buildup to deform the droplet bottom surface. A conical liquid tip forms and pierces through the gas film, leading to a circular contact line moving outwards that does not trap any gas. The critical charge level only depends on the capillary number based on the gas viscosity. This finding applies to common liquids and molten alloy droplets, providing new insights into a range of applications such as mitigating pinhole defects in additive manufacturing.
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Affiliation(s)
- Fan Gao
- Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen 518055, China. and Mechanical Engineering Department, Virginia Tech, Blacksburg, VA 24061, USA
| | - Hao Yi
- School of Mechanical Engineering, Northwestern Polytechnical University, Xi'an 710072, China and College of Mechanical Engineering, Chongqing University, Chongqing 400030, China
| | - Lehua Qi
- School of Mechanical Engineering, Northwestern Polytechnical University, Xi'an 710072, China
| | - Rui Qiao
- Mechanical Engineering Department, Virginia Tech, Blacksburg, VA 24061, USA
| | - Weiwei Deng
- Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen 518055, China.
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18
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Pack M, Kaneelil P, Kim H, Sun Y. Contact Line Instability Caused by Air Rim Formation under Nonsplashing Droplets. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:4962-4969. [PMID: 29620373 DOI: 10.1021/acs.langmuir.8b01082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Drop impact is fundamental to various natural and industrial processes such as rain-induced soil erosion and spray-coating technologies. The recent discovery of the role of air entrainment between the droplet and the impacting surface has produced numerous works, uncovering the unique physics that correlates the air film dynamics with the drop impact outcomes. In this study, we focus on the post-failure air entrainment dynamics for We numbers well below the splash threshold under different ambient pressures and elucidate the interfacial instabilities formed by air entrainment at the wetting front of impacting droplets on perfectly smooth, viscous films of constant thickness. A high-speed total internal reflection microscopy technique accounting for the Fresnel reflection at the drop-air interface allows for in situ measurements of an entrained air rim at the wetting front. The presence of an air rim is found to be a prerequisite to the interfacial instability which is formed when the capillary pressure in the vicinity of the contact line can no longer balance the increasing gas pressure near the wetting front. A critical capillary number for the air rim formation is experimentally identified above which the wetting front becomes unstable where this critical capillary number inversely scales with the ambient pressure. The contact line instabilities at relatively low We numbers ( We ∼ O(10)) observed in this study provide insight into the conventional understanding of hydrodynamic instabilities under drop impact which usually require We ≫ 10.
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Affiliation(s)
- Min Pack
- Department of Mechanical Engineering and Mechanics , Drexel University , Philadelphia , Pennsylvania 19104 , United States
| | - Paul Kaneelil
- Department of Mechanical Engineering and Mechanics , Drexel University , Philadelphia , Pennsylvania 19104 , United States
| | - Hyoungsoo Kim
- Department of Mechanical and Aerospace Engineering , Princeton University , Princeton , New Jersey 08544 , United States
- Department of Mechanical Engineering , KAIST , Daejeon 34141 , South Korea
| | - Ying Sun
- Department of Mechanical Engineering and Mechanics , Drexel University , Philadelphia , Pennsylvania 19104 , United States
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19
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Che Z, Matar OK. Impact of Droplets on Liquid Films in the Presence of Surfactant. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:12140-12148. [PMID: 28771014 DOI: 10.1021/acs.langmuir.7b01901] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The impact of droplets on liquid films is ubiquitous in natural and industrial processes, and surfactants can significantly alter the impact process by changing the local surface tension. Here we study the impact of droplets on liquid films in the presence of surfactant using high-speed photography, and reveal the flow pattern by dye-tracing. The effects of the droplet size and speed, and the initial film thickness on the impact process are elucidated. The results show that the flow is significantly affected by adding surfactant to the droplet, the liquid film, or to both phases. In particular, the film dye patterns form concentric circles and flower-shaped structures at low and high droplet Weber numbers, respectively. We also show how surfactant-induced Marangoni stresses modify these flow patterns, and alter the characteristics of the phenomena associated with the impact process, such as the propagation of capillary waves, the evolution of the crown, and the formation of secondary droplets. During the impact of surfactant droplets on thin water films, the Marangoni stresses can be sufficiently strong so as to drive film dewetting.
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Affiliation(s)
- Zhizhao Che
- State Key Laboratory of Engines, Tianjin University , Tianjin, 300072, China
- Department of Chemical Engineering, Imperial College London , London, SW7 2AZ, United Kingdom
| | - Omar K Matar
- Department of Chemical Engineering, Imperial College London , London, SW7 2AZ, United Kingdom
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20
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Pack M, Hu H, Kim D, Zheng Z, Stone HA, Sun Y. Failure mechanisms of air entrainment in drop impact on lubricated surfaces. SOFT MATTER 2017; 13:2402-2409. [PMID: 28287231 DOI: 10.1039/c7sm00117g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Lubricated surfaces have recently been introduced and studied due to their potential benefit in various configurations and applications. Combining the techniques of total internal reflection microscopy and reflection interference microscopy, we examine the dynamics of an underlying air film upon drop impact on a lubricated substrate where the thin liquid film is immiscible to the drop. In contrast to drop impact on solid surfaces where even the smallest asperities cause random breakup of the entraining air film, we report two air film failure mechanisms on lubricated surfaces. In particular, using ≈5 μm thick liquid films of high viscosity, which should make the substrate nearly atomically smooth, we show that air film rupture shifts from asperity-driven to a controlled event. At low Weber numbers (We < 2, We = ρlU02R/σ, U0 the impact velocity, R the drop radius, and ρl the density and σ the surface tension of the droplet) the droplet bounces. At intermediate We (2 < We < 10), the air film fails at the center as the top surface of the drop crashes downward owing to impact-induced capillary waves; the resulting liquid-liquid contact time is found to be independent of We. In contrast, at high We (We > 10), the air film failure occurs much earlier in time at the first inflection point of the air film shape away from the drop center, where the liquid-liquid van der Waals interactions become important. The predictable failure modes of the air film upon drop impact sheds light on droplet deposition in applications such as lubricant-infused self-cleaning surfaces.
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Affiliation(s)
- M Pack
- Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA, USA.
| | - H Hu
- Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA, USA.
| | - D Kim
- Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA, USA.
| | - Z Zheng
- Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, USA
| | - H A Stone
- Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ, USA
| | - Y Sun
- Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA, USA.
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21
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Zhao SC, de Jong R, van der Meer D. Liquid-Grain Mixing Suppresses Droplet Spreading and Splashing during Impact. PHYSICAL REVIEW LETTERS 2017; 118:054502. [PMID: 28211715 DOI: 10.1103/physrevlett.118.054502] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2016] [Indexed: 06/06/2023]
Abstract
Would a raindrop impacting on a coarse beach behave differently from that impacting on a desert of fine sand? We study this question by a series of model experiments, where the packing density of the granular target, the wettability of individual grains, the grain size, the impacting liquid, and the impact speed are varied. We find that by increasing the grain size and/or the wettability of individual grains the maximum droplet spreading undergoes a transition from a capillary regime towards a viscous regime, and splashing is suppressed. The liquid-grain mixing is discovered to be the underlying mechanism. An effective viscosity is defined accordingly to quantitatively explain the observations.
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Affiliation(s)
- Song-Chuan Zhao
- Physics of Fluids Group, MESA+ Institute for Nanotechnology, and Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Rianne de Jong
- Physics of Fluids Group, MESA+ Institute for Nanotechnology, and Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Devaraj van der Meer
- Physics of Fluids Group, MESA+ Institute for Nanotechnology, and Faculty of Science and Technology, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
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22
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Observations of internal flow inside an evaporating nanofluid sessile droplet in the presence of an entrapped air bubble. Sci Rep 2016; 6:32767. [PMID: 27615999 PMCID: PMC5018722 DOI: 10.1038/srep32767] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Accepted: 08/15/2016] [Indexed: 11/18/2022] Open
Abstract
Using a unique, near-field microscopy technique, fringe patterns and nanoparticle motions are visualized immediately following a nanofluid droplet deposition on a glass substrate in which an air bubble is entrapped. The nanofluid consists of DI-water, 0.10% Aluminum Oxide nanoparticles with an average diameter of 50 nm, and 0.0005% yellow-green polystyrene fluorescent particles of 1 μm diameter. High-speed, fluorescent-mode confocal imaging enables investigation of depth-wise sectioned particle movements in the nanofluid droplet inside which a bubble is entrapped. The static contact angle is increased when a bubble is applied. In the presence of the bubble in the droplet, the observed flow toward the center of the droplet is opposite to the flow observed in a droplet without the bubble. When the bubble is present, the evaporation process is retarded. Also, random motion is observed in the contact line region instead of the typical evaporation-driven flow toward the droplet edge. Once the bubble bursts, however, the total evaporation time decreases due to the change in the contact line characteristics. Moreover, the area of fringe patterns beneath the bubble increases with time. Discussed herein is a unique internal flow that has not been observed in nanofluid droplet evaporation.
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23
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Enhancing droplet deposition through in-situ precipitation. Nat Commun 2016; 7:12560. [PMID: 27572948 PMCID: PMC5013560 DOI: 10.1038/ncomms12560] [Citation(s) in RCA: 114] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2016] [Accepted: 07/14/2016] [Indexed: 12/22/2022] Open
Abstract
Retention of agricultural sprays on plant surfaces is an important challenge. Bouncing of sprayed pesticide droplets from leaves is a major source of soil and groundwater pollution and pesticide overuse. Here we report a method to increase droplet deposition through in-situ formation of hydrophilic surface defects that can arrest droplets during impact. Defects are created by simultaneously spraying oppositely charged polyelectrolytes that induce surface precipitation when two droplets come into contact. Using high-speed imaging, we study the coupled dynamics of drop impact and surface precipitate formation. We develop a physical model to estimate the energy dissipation by the defects and predict the transition from bouncing to sticking. We demonstrate macroscopic enhancements in spray retention and surface coverage for natural and synthetic non-wetting surfaces and provide insights into designing effective agricultural sprays. The extensive use of pesticides in agriculture calls for efficient spraying techniques to reduce pollution of soils and groundwater by toxic chemicals. Damak et al. simultaneously spray liquids containing oppositely charged polyelectrolytes that form defects, pinning droplets on targeted surfaces.
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24
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Hao C, Liu Y, Chen X, Li J, Zhang M, Zhao Y, Wang Z. Bioinspired Interfacial Materials with Enhanced Drop Mobility: From Fundamentals to Multifunctional Applications. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2016; 12:1825-1839. [PMID: 26865317 DOI: 10.1002/smll.201503060] [Citation(s) in RCA: 98] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2015] [Revised: 11/19/2015] [Indexed: 06/05/2023]
Abstract
The development of bioinspired interfacial materials with enhanced drop mobility that mimic the innate functionalities of nature will have a significant impact on the energy, environment and global healthcare. Despite extensive progress, state of the art interfacial materials have not reached the level of maturity sufficient for industrial applications in terms of scalability, stability, and reliability. These are complicated by their operating environments and lack of facile approaches to control the local structural texture and chemical composition at multiple length scales. The recent advances in the fundamental understanding are reviewed, as well as practical applications of bioinspired interfacial materials, with an emphasis on the drop bouncing and coalescence-induced jumping behaviors. Perspectives on how to catalyze new discoveries and to foster technological adoption to move this exciting area forward are also suggested.
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Affiliation(s)
- Chonglei Hao
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, 999077, Hong Kong
| | - Yahua Liu
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, 999077, Hong Kong
| | - Xuemei Chen
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, 999077, Hong Kong
| | - Jing Li
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, 999077, Hong Kong
| | - Mei Zhang
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, 999077, Hong Kong
| | - Yanhua Zhao
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, 999077, Hong Kong
| | - Zuankai Wang
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, 999077, Hong Kong
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25
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Symmetry breaking in drop bouncing on curved surfaces. Nat Commun 2015; 6:10034. [PMID: 26602170 PMCID: PMC4674688 DOI: 10.1038/ncomms10034] [Citation(s) in RCA: 146] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2015] [Accepted: 10/28/2015] [Indexed: 12/24/2022] Open
Abstract
The impact of liquid drops on solid surfaces is ubiquitous in nature, and of practical importance in many industrial processes. A drop hitting a flat surface retains a circular symmetry throughout the impact process. Here we show that a drop impinging on Echevaria leaves exhibits asymmetric bouncing dynamics with distinct spreading and retraction along two perpendicular directions. This is a direct consequence of the cylindrical leaves that have a convex/concave architecture of size comparable to the drop. Systematic experimental investigations on mimetic surfaces and lattice Boltzmann simulations reveal that this novel phenomenon results from an asymmetric momentum and mass distribution that allows for preferential fluid pumping around the drop rim. The asymmetry of the bouncing leads to ∼40% reduction in contact time. Designing superhydrophobic surfaces that water does not wet is crucial for many applications ranging from water harvesting to self-cleaning. Here, Liu et al. show how to minimize the contact of liquid drops impacting on solid surfaces with convex and concave macrotextures comparable to the size of drops.
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26
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Edwards C, Arbabi A, Bhaduri B, Wang X, Ganti R, Yunker PJ, Yodh AG, Popescu G, Goddard LL. Measuring the Nonuniform Evaporation Dynamics of Sprayed Sessile Microdroplets with Quantitative Phase Imaging. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:11020-11032. [PMID: 26389788 DOI: 10.1021/acs.langmuir.5b02148] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We demonstrate real-time quantitative phase imaging as a new optical approach for measuring the evaporation dynamics of sessile microdroplets. Quantitative phase images of various droplets were captured during evaporation. The images enabled us to generate time-resolved three-dimensional topographic profiles of droplet shape with nanometer accuracy and, without any assumptions about droplet geometry, to directly measure important physical parameters that characterize surface wetting processes. Specifically, the time-dependent variation of the droplet height, volume, contact radius, contact angle distribution along the droplet's perimeter, and mass flux density for two different surface preparations are reported. The studies clearly demonstrate three phases of evaporation reported previously: pinned, depinned, and drying modes; the studies also reveal instances of partial pinning. Finally, the apparatus is employed to investigate the cooperative evaporation of the sprayed droplets. We observe and explain the neighbor-induced reduction in evaporation rate, that is, as compared to predictions for isolated droplets. In the future, the new experimental methods should stimulate the exploration of colloidal particle dynamics on the gas-liquid-solid interface.
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Affiliation(s)
- Chris Edwards
- Photonic Systems Laboratory, Micro and Nanotechnology Laboratory, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
- Quantitative Light Imaging Laboratory, Beckman Institute for Advanced Science and Technology, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Amir Arbabi
- Photonic Systems Laboratory, Micro and Nanotechnology Laboratory, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Basanta Bhaduri
- Quantitative Light Imaging Laboratory, Beckman Institute for Advanced Science and Technology, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Xiaozhen Wang
- Photonic Systems Laboratory, Micro and Nanotechnology Laboratory, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Raman Ganti
- Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
| | - Peter J Yunker
- Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
| | - Arjun G Yodh
- Department of Physics and Astronomy, University of Pennsylvania , Philadelphia, Pennsylvania 19104, United States
| | - Gabriel Popescu
- Quantitative Light Imaging Laboratory, Beckman Institute for Advanced Science and Technology, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
| | - Lynford L Goddard
- Photonic Systems Laboratory, Micro and Nanotechnology Laboratory, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
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27
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Hao C, Li J, Liu Y, Zhou X, Liu Y, Liu R, Che L, Zhou W, Sun D, Li L, Xu L, Wang Z. Superhydrophobic-like tunable droplet bouncing on slippery liquid interfaces. Nat Commun 2015; 6:7986. [PMID: 26250403 PMCID: PMC4918357 DOI: 10.1038/ncomms8986] [Citation(s) in RCA: 113] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Accepted: 07/03/2015] [Indexed: 12/28/2022] Open
Abstract
Droplet impacting on solid or liquid interfaces is a ubiquitous phenomenon in nature. Although complete rebound of droplets is widely observed on superhydrophobic surfaces, the bouncing of droplets on liquid is usually vulnerable due to easy collapse of entrapped air pocket underneath the impinging droplet. Here, we report a superhydrophobic-like bouncing regime on thin liquid film, characterized by the contact time, the spreading dynamics, and the restitution coefficient independent of underlying liquid film. Through experimental exploration and theoretical analysis, we demonstrate that the manifestation of such a superhydrophobic-like bouncing necessitates an intricate interplay between the Weber number, the thickness and viscosity of liquid film. Such insights allow us to tune the droplet behaviours in a well-controlled fashion. We anticipate that the combination of superhydrophobic-like bouncing with inherent advantages of emerging slippery liquid interfaces will find a wide range of applications. The impact of drops on surfaces is highly relevant to our daily life and many industrial applications, such as self-cleaning and ink printing. Here, Hao et al. show the transition from superhydrophobic-like drop bouncing, due to a trapped air layer, to substrate-dependent bouncing on a liquid thin film.
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Affiliation(s)
- Chonglei Hao
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong 999077, China
| | - Jing Li
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong 999077, China
| | - Yuan Liu
- Department of Physics, Chinese University of Hong Kong, Hong Kong 999077, China
| | - Xiaofeng Zhou
- Science and Technology on Microsystem Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050, China
| | - Yahua Liu
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong 999077, China
| | - Rong Liu
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong 999077, China
| | - Lufeng Che
- Science and Technology on Microsystem Laboratory, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050, China
| | - Wenzhong Zhou
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong 999077, China
| | - Dong Sun
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong 999077, China
| | - Lawrence Li
- Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong 999077, China
| | - Lei Xu
- Department of Physics, Chinese University of Hong Kong, Hong Kong 999077, China
| | - Zuankai Wang
- 1] Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong 999077, China [2] Shenzhen Research Institute, City University of Hong Kong, Shenzhen 518057, China
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28
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Che Z, Deygas A, Matar OK. Impact of droplets on inclined flowing liquid films. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 92:023032. [PMID: 26382528 DOI: 10.1103/physreve.92.023032] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2015] [Indexed: 06/05/2023]
Abstract
The impact of droplets on an inclined falling liquid film is studied experimentally using high-speed imaging. The falling film is created on a flat substrate with controllable thicknesses and flow rates. Droplets with different sizes and speeds are used to study the impact process under various Ohnesorge and Weber numbers, and film Reynolds numbers. A number of phenomena associated with droplet impact are identified and analyzed, such as bouncing, partial coalescence, total coalescence, and splashing. The effects of droplet size, speed, as well the film flow rate are studied culminating in the generation of an impact regime map. The analysis of the lubrication force acted on the droplet via the gas layer shows that a higher flow rate in the liquid film produces a larger lubrication force, slows down the drainage process, and increases the probability of droplet bouncing. Our results demonstrate that the flowing film has a profound effect on the droplet impact process and associated phenomena, which are markedly more complex than those accompanying impact on initially quiescent films.
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Affiliation(s)
- Zhizhao Che
- Department of Chemical Engineering, Imperial College London, London SW7 2AZ, United Kingdom
| | - Amandine Deygas
- Department of Chemical Engineering, Imperial College London, London SW7 2AZ, United Kingdom
| | - Omar K Matar
- Department of Chemical Engineering, Imperial College London, London SW7 2AZ, United Kingdom
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29
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Dölle S, Stannarius R. Microdroplets Impinging on Freely Suspended Smectic Films: Three Impact Regimes. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:6479-6486. [PMID: 26010557 DOI: 10.1021/acs.langmuir.5b00756] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We employ high-speed video imaging to study microdroplets of a few picoliters volume impacting freely suspended smectic liquid-crystal films. Depending on the impact parameters, in particular, droplet velocity and mass, three different regimes are observed such as trapping, rebounding, and tunneling. Fast droplets penetrate the films completely. After they have passed the film, they are coated with a layer of film material while the original smectic film remains intact. Droplets in a certain intermediate velocity range bounce back from the film. After impact, the film deforms and hurls the droplet back, depleting a substantial share of the initial kinetic energy. Slow droplets are caught and embedded in the film. During impact and tunneling, an appreciable amount of kinetic energy is lost. The energy is partially dissipated during droplet impact and during subsequent mechanical vibrations and oscillations of the film and the droplet. The tunneling process of high-speed droplets can be exploited to prepare smectic shells of well-defined sizes that enclose picoliters of an immiscible liquid.
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Affiliation(s)
- Sarah Dölle
- Otto von Guericke University Magdeburg, Department of Nonlinear Phenomena, PB 4120, 39016 Magdeburg, Germany
| | - Ralf Stannarius
- Otto von Guericke University Magdeburg, Department of Nonlinear Phenomena, PB 4120, 39016 Magdeburg, Germany
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Dehaeck S, Tsoumpas Y, Colinet P. Analyzing closed-fringe images using two-dimensional Fan wavelets. APPLIED OPTICS 2015; 54:2939-2952. [PMID: 25967210 DOI: 10.1364/ao.54.002939] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Accepted: 02/24/2015] [Indexed: 06/04/2023]
Abstract
In this paper, it will be shown how the use of two 2D Fan wavelets to analyze closed-fringe images can lead to a relatively fast and exceptionally noise-resistant algorithm capable of extracting not only local phase but also local frequency information. Our algorithm is up to 10 times faster than the current state-of-the-art in wavelet processing techniques and even up to 30 times faster than "windowed Fourier" transform programs, which achieve similar noise-resiliency figures. This improvement is mainly achieved by the use of Fan wavelets instead of Morlet wavelets, but a more efficient scale-space discretization strategy is also described, and three different alternatives are suggested capable of solving the phase sign-ambiguity problem in a quick and efficient manner. Finally, the application of the algorithm to real and numerically generated images shows that a precision of 1/30th of a fringe is achievable for noise levels going up to 1/5th of the input contrast.
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31
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Emelyanenko KA, Emelyanenko AM, Boinovich L. Image-charge forces in thin interlayers due to surface charges in electrolyte. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 91:032402. [PMID: 25871118 DOI: 10.1103/physreve.91.032402] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2014] [Indexed: 06/04/2023]
Abstract
The surface forces arising in wetting films of nonpolar liquids or in thin air interlayers between an electrolyte and a nonpolar medium in the case of discrete charging of the dielectric-electrolyte interface are considered. The contributions of polarization effects to the distribution of the electrostatic potential in the three contacting media were calculated. Within the Debye-Hückel approximation, the analytical solutions were derived for the disjoining pressure in thin films, for the case of either dilute or relatively concentrated electrolyte solutions in the aforementioned systems. Analysis of the analytical and numerical results demonstrated that for dilute solutions the contribution of image forces to the disjoining pressure may significantly exceed the van der Waals forces for films from a few to tens of nanometers thick.
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Affiliation(s)
- Kirill A Emelyanenko
- A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Prospect 31 Building 4, 119071 Moscow, Russia
| | - Alexandre M Emelyanenko
- A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Prospect 31 Building 4, 119071 Moscow, Russia
| | - Ludmila Boinovich
- A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky Prospect 31 Building 4, 119071 Moscow, Russia
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32
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Kelvin-Helmholtz instability in an ultrathin air film causes drop splashing on smooth surfaces. Proc Natl Acad Sci U S A 2015; 112:3280-4. [PMID: 25713350 DOI: 10.1073/pnas.1417718112] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
When a fast-moving drop impacts onto a smooth substrate, splashing will be produced at the edge of the expanding liquid sheet. This ubiquitous phenomenon lacks a fundamental understanding. Combining experiment with model, we illustrate that the ultrathin air film trapped under the expanding liquid front triggers splashing. Because this film is thinner than the mean free path of air molecules, the interior airflow transfers momentum with an unusually high velocity comparable to the speed of sound and generates a stress 10 times stronger than the airflow in common situations. Such a large stress initiates Kelvin-Helmholtz instabilities at small length scales and effectively produces splashing. Our model agrees quantitatively with experimental verifications and brings a fundamental understanding to the ubiquitous phenomenon of drop splashing on smooth surfaces.
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33
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Klaseboer E, Manica R, Chan DYC. Universal behavior of the initial stage of drop impact. PHYSICAL REVIEW LETTERS 2014; 113:194501. [PMID: 25415908 DOI: 10.1103/physrevlett.113.194501] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2014] [Indexed: 06/04/2023]
Abstract
During the early stages of the impact of a drop on a solid surface, pressure builds up in the intervening thin lubricating air layer and deforms the drop. The extent of the characteristic deformation is determined by the competition between capillary, gravitational, and inertial forces that has been encapsulated in a simple analytic scaling law. For millimetric drops, variations of the observed deformation with impact velocity V exhibit a maximum defined by the Weber and Eötvös numbers: We=1+Eo. The deformation scales as V(1/2) at the low-velocity capillary regime and as V(-1/2) at the high-velocity inertia regime, in excellent agreement with a variety of experimental systems.
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Affiliation(s)
- Evert Klaseboer
- Institute of High Performance Computing, 1 Fusionopolis Way, 138632 Singapore, Singapore
| | - Rogerio Manica
- Institute of High Performance Computing, 1 Fusionopolis Way, 138632 Singapore, Singapore
| | - Derek Y C Chan
- Institute of High Performance Computing, 1 Fusionopolis Way, 138632 Singapore, Singapore and Department of Mathematics and Statistics, University of Melbourne, Parkville 3010, Australia and Department of Chemistry and Biotechnology, Swinburne University of Technology, Hawthorn 3122, Australia
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34
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Dölle S, Harth K, John T, Stannarius R. Impact and embedding of picoliter droplets into freely suspended smectic films. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:12712-12720. [PMID: 25268303 DOI: 10.1021/la503082c] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We study the impact of liquid microdroplets on thin freely suspended smectic films. Such films are very thin but robust objects that can serve as model systems for quasi-two-dimensional liquids. Droplet velocities and sizes determine the character of the collisions. The dynamics of the integration of droplets into the film can be divided into three phases, starting with the impact and a dissipation of the kinetic energy, followed by a balancing of capillary forces within fractions of a second. The analysis of the droplet shape evolution with high-speed imaging allows us to study the dynamics of this process. The final phase, formation of a meniscus of smectic material, takes several seconds up to minutes.
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Affiliation(s)
- Sarah Dölle
- Department of Nonlinear Phenomena, Otto von Guericke University Magdeburg , PB 4120, 39016 Magdeburg, Germany
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35
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Maitra T, Antonini C, Tiwari MK, Mularczyk A, Imeri Z, Schoch P, Poulikakos D. Supercooled water drops impacting superhydrophobic textures. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:10855-10861. [PMID: 25157476 DOI: 10.1021/la502675a] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Understanding the interaction of supercooled metastable water with superhydrophobic surface textures is of fundamental significance for unraveling the mechanisms of icing as well as of practical importance for the rational development of surface treatment strategies to prevent icing. We investigate the problem of supercooled water drops impacting superhydrophobic textures for drop supercooling down to -17 °C and find that increased viscous effects significantly influence all stages of impact dynamics, in particular, the impact and meniscus impalement behavior, with severe implications to water retention by the textures (sticky versus rebounding drop) and possible icing. Viscous effects in water supercooling conditions cause a reduction of drop maximum spreading (∼25% at an impact speed of 3 m/s for a millimetric drop) and can significantly decrease the drop recoil speed when the meniscus partially penetrates into the texture, leading to an increase of the contact time up to a factor of 2 in supercooling conditions compared to room temperature. We also show that meniscus penetration upon drop impact occurs with full penetration at the center, instead of ring shape, common to room temperature drop impact. To this end, we describe an unobserved mechanism for superhydrophobicity breakdown: unlike for room temperature drops, where transition from bouncing to sticky (impaled) behavior occurs sharply at the condition of full texture penetration, with a bubble captured at the point of impact, under supercooled conditions, the full penetration velocity threshold is increased markedly (increasing by ∼25%, from 2.8 to 3.5 m/s) and no bubble is entrapped. However, even though only partial texture penetration takes place, failure to completely dewet because of viscous effects can still prohibit complete supercooled drop rebound.
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Affiliation(s)
- Tanmoy Maitra
- Laboratory of Thermodynamics in Emerging Technologies, Mechanical and Process Engineering Department, ETH Zurich , 8092 Zurich, Switzerland
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36
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Stevens CS, Latka A, Nagel SR. Comparison of splashing in high- and low-viscosity liquids. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:063006. [PMID: 25019878 DOI: 10.1103/physreve.89.063006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Indexed: 05/26/2023]
Abstract
We explore the evolution of a splash when a liquid drop impacts a smooth dry surface. There are two splashing regimes that occur when the liquid viscosity is varied as is evidenced by its dependence on ambient gas pressure. A high-viscosity drop splashes by emitting a thin sheet of liquid from a spreading liquid lamella long after the drop has first contacted the solid. Likewise, we find that there is also a delay in the ejection of a thin sheet when a low-viscosity drop splashes. We show how the ejection time of the thin sheet depends on liquid viscosity and ambient gas pressure.
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Affiliation(s)
- Cacey S Stevens
- Department of Physics, The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA
| | - Andrzej Latka
- Department of Physics, The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA
| | - Sidney R Nagel
- Department of Physics, The James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA
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37
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A nanometre-scale resolution interference-based probe of interfacial phenomena between microscopic objects and surfaces. Nat Commun 2013; 4:1919. [PMID: 23715278 PMCID: PMC3675327 DOI: 10.1038/ncomms2865] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Accepted: 04/11/2013] [Indexed: 12/03/2022] Open
Abstract
Interferometric techniques have proven useful to infer proximity and local surface profiles of microscopic objects near surfaces. But a critical trade-off emerges between accuracy and mathematical complexity when these methods are applied outside the vicinity of closest approach. Here we introduce a significant advancement that enables reflection interference contrast microscopy to provide nearly instantaneous reconstruction of an arbitrary convex object’s contour next to a bounding surface with nanometre resolution, making it possible to interrogate microparticle/surface interaction phenomena at radii of curvature 1,000 times smaller than those accessible by the conventional surface force apparatus. The unique view-from-below perspective of reflection interference contrast microscopy also reveals previously unseen deformations and allows the first direct observation of femtolitre-scale capillary condensation dynamics underneath micron-sized particles. Our implementation of reflection interference contrast microscopy provides a generally applicable nanometre-scale resolution tool that can be potentially exploited to dynamically probe ensembles of objects near surfaces so that statistical/probabilistic behaviour can be realistically captured. Interferometric techniques can provide valuable contact and profile information of microscopic objects on surfaces. This work uses reflection interference contrast microscopy to directly observe contact phenomena and presents novel analytical methods offering high-accuracy nanoscale resolution.
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38
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Thoraval MJ, Thoroddsen ST. Contraction of an air disk caught between two different liquids. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:061001. [PMID: 24483378 DOI: 10.1103/physreve.88.061001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2013] [Indexed: 06/03/2023]
Abstract
When a drop impacts a pool of liquid it entraps a thin disk of air under its center. This disk contracts rapidly into a bubble to minimize surface energy. Herein we use ultra-high-speed imaging to measure the contraction speed of this disk when the drop and pool are of different liquids. For miscible liquids the contraction rate is governed by the weaker of the two surface tensions. Some undulations are observed on the edge of the disk for a water drop impacting a pool of water, but not on a pool of lower surface tension. Similar results are observed for a pair of immiscible liquids.
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Affiliation(s)
- M-J Thoraval
- Division of Physical Sciences and Engineering and Clean Combustion Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
| | - S T Thoroddsen
- Division of Physical Sciences and Engineering and Clean Combustion Research Center, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
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39
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Singh E, Thomas AV, Mukherjee R, Mi X, Houshmand F, Peles Y, Shi Y, Koratkar N. Graphene drape minimizes the pinning and hysteresis of water drops on nanotextured rough surfaces. ACS NANO 2013; 7:3512-3521. [PMID: 23484526 DOI: 10.1021/nn400466t] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Previous studies of the interaction of water with graphene-coated surfaces have been limited to flat (smooth) surfaces. Here we created a rough surface by nanopatterning and then draped the surface with a single-layer graphene sheet. We found that the ultrasheer graphene drape prevents the penetration of water into the textured surface thereby drastically reducing the contact angle hysteresis (which is a measure of frictional energy dissipation) and preventing the liquid contact line from getting pinned to the substrate. This has important technological implications since the main obstacle to the motion of liquid drops on rough surfaces is contact angle hysteresis and contact line pinning. Graphene drapes could therefore enable enhanced droplet mobility which is required in a wide range of applications in micro and nanofluidics. Compared to polymer coatings that could fill the cavities between the nano/micropores or significantly alter the roughness profile of the substrate, graphene provides the thinnest (i.e., most sheer) and most conformal drape that is imaginable. Despite its extreme thinness, the graphene drape is mechanically robust, chemically stable, and offers high flexibility and resilience which can enable it to reliably drape arbitrarily complex surface topologies. Graphene drapes may therefore provide a hitherto unavailable ability to tailor the dynamic wettability of surfaces for a variety of applications.
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Affiliation(s)
- Eklavya Singh
- Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
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40
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Lee JS, Weon BM, Je JH, Fezzaa K. How does an air film evolve into a bubble during drop impact? PHYSICAL REVIEW LETTERS 2012; 109:204501. [PMID: 23215492 DOI: 10.1103/physrevlett.109.204501] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2012] [Revised: 09/14/2012] [Indexed: 06/01/2023]
Abstract
When a liquid drop impacts a solid surface, air is generally entrapped underneath. Using ultrafast x-ray phase-contrast imaging, we directly visualized the profile of an entrapped air film and its evolution into a bubble during drop impact. We identified a complicated evolution process that consists of three stages: inertial retraction of the air film, contraction of the top air surface into a bubble, and pinch-off of a daughter droplet inside the bubble. Energy transfer during retraction drives the contraction and pinch-off of a daughter droplet. The wettability of the solid surface affects the detachment of the bubble, suggesting a method for bubble elimination in many drop-impact applications.
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Affiliation(s)
- Ji San Lee
- X-ray Imaging Center, Department of Materials Science and Engineering, Pohang University of Science and Technology, San 31, Hyoja-dong, Pohang 790-784, Korea
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41
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Rykaczewski K, Landin T, Walker ML, Scott JHJ, Varanasi KK. Direct imaging of complex nano- to microscale interfaces involving solid, liquid, and gas phases. ACS NANO 2012; 6:9326-9334. [PMID: 23020195 DOI: 10.1021/nn304250e] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Surfaces with special wetting properties not only can efficiently repel or attract liquids such as water and oils but also can prevent formation of biofilms, ice, and clathrate hydrates. Predicting the wetting properties of these special surfaces requires detailed knowledge of the composition and geometry of the interfacial region between the droplet and the underlying substrate. In this work we introduce a 3D quantitative method for direct nanoscale visualization of such interfaces. Specifically, we demonstrate direct nano- to microscale imaging of complex fluidic interfaces using cryostabilization in combination with cryogenic focused ion beam milling and SEM imaging. We show that application of this method yields quantitative information about the interfacial geometry of water condensate on superhydrophilic, superhydrophobic, and lubricant-impregnated surfaces with previously unattainable nanoscale resolution. This type of information is crucial to a fundamental understanding as well as the design of surfaces with special wetting properties.
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Affiliation(s)
- Konrad Rykaczewski
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
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42
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Latka A, Strandburg-Peshkin A, Driscoll MM, Stevens CS, Nagel SR. Creation of prompt and thin-sheet splashing by varying surface roughness or increasing air pressure. PHYSICAL REVIEW LETTERS 2012; 109:054501. [PMID: 23006177 DOI: 10.1103/physrevlett.109.054501] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Revised: 05/29/2012] [Indexed: 05/26/2023]
Abstract
A liquid drop impacting a solid surface may splash either by emitting a thin liquid sheet that subsequently breaks apart or by promptly ejecting droplets from the advancing liquid-solid contact line. Using high-speed imaging, we show that surface roughness and air pressure influence both mechanisms. Roughness inhibits thin-sheet formation even though it also increases prompt splashing at the advancing contact line. If the air pressure is lowered, droplet ejection is suppressed not only during thin-sheet formation but also for prompt splashing.
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Affiliation(s)
- Andrzej Latka
- The James Franck Institute, The University of Chicago, Illinois 60637, USA.
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43
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Hendrix MHW, Manica R, Klaseboer E, Chan DYC, Ohl CD. Spatiotemporal evolution of thin liquid films during impact of water bubbles on glass on a micrometer to nanometer scale. PHYSICAL REVIEW LETTERS 2012; 108:247803. [PMID: 23004333 DOI: 10.1103/physrevlett.108.247803] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2012] [Indexed: 06/01/2023]
Abstract
Collisions between millimeter-size bubbles in water against a glass plate are studied using high-speed video. Bubble trajectory and shape are tracked simultaneously with laser interferometry between the glass and bubble surfaces that monitors spatial-temporal evolution of the trapped water film. Initial bubble bounces and the final attachment of the bubble to the surface have been quantified. While the global Reynolds number is large (∼10(2)), the film Reynolds number remains small and permits analysis with lubrication theory with tangentially immobile boundary condition at the air-water interface. Accurate predictions of dimple formation and subsequent film drainage are obtained.
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Affiliation(s)
- Maurice H W Hendrix
- Physics of Fluids, University of Twente, P. O. Box 217, 7500 AE Enschede, The Netherlands
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