1
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Zhou Y, Zhang C, Zhao W, Wang S, Zhu P. Suppression of hollow droplet rebound on super-repellent surfaces. Nat Commun 2023; 14:5386. [PMID: 37666839 PMCID: PMC10477213 DOI: 10.1038/s41467-023-40941-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2023] [Accepted: 08/15/2023] [Indexed: 09/06/2023] Open
Abstract
Droplet rebound is ubiquitous on super-repellent surfaces. Conversion between kinetic and surface energies suggests that rebound suppression is unachievable due to negligible energy dissipation. Here, we present an effective approach to suppressing rebounds by incorporating bubbles into droplets, even in super-repellent states. This suppression arises from the counteractive capillary effects within bubble-encapsulated hollow droplets. The capillary flows induced by the deformed inner-bubble surface counterbalance those driven by the outer-droplet surface, resulting in a reduction of the effective take-off momentum. We propose a double-spring system with reduced effective elasticity for hollow droplets, wherein the competing springs offer distinct behavior from the classical single-spring model employed for single-phase droplets. Through experimental, analytical, and numerical validations, we establish a comprehensive and unified understanding of droplet rebound, by which the behavior of single-phase droplets represents the exceptional case of zero bubble volume and can be encompassed within this overarching framework.
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Affiliation(s)
- Ying Zhou
- Department of Mechanical Engineering, City University of Hong Kong, 999077, Hong Kong, China
| | | | - Wenchang Zhao
- Department of Mechanical Engineering, City University of Hong Kong, 999077, Hong Kong, China
| | - Shiyu Wang
- Department of Mechanical Engineering, City University of Hong Kong, 999077, Hong Kong, China
| | - Pingan Zhu
- Department of Mechanical Engineering, City University of Hong Kong, 999077, Hong Kong, China.
- Shenzhen Research Institute, City University of Hong Kong, 518057, Shenzhen, China.
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2
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Wang X, Xu B, Guo S, Zhao Y, Chen Z. Droplet impacting dynamics: Recent progress and future aspects. Adv Colloid Interface Sci 2023; 317:102919. [PMID: 37216871 DOI: 10.1016/j.cis.2023.102919] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 05/02/2023] [Accepted: 05/11/2023] [Indexed: 05/24/2023]
Abstract
Droplet impact behaviours are widely applied in a variety of domains including self-cleaning, painting and coating, corrosion of turbine blades and aircraft, separation and oil repellency, anti-icing, heat transfer and droplet electricity generation, etc. The wetting behaviours and impact dynamics of droplets on solid and liquid surfaces involve complex solid-liquid and liquid-liquid interfacial interactions. The modulation of droplet dynamics by means of specific surface morphology and hydrophobic/hydrophilic patterns, which in turn can be derived to related applications, is one of the current promising interests in the interfacial effect modulating droplet dynamics. This review provides a detailed overview of several scientific aspects of droplet impact behaviours and heat transfer processes influenced by multiple factors. Firstly, the essential wetting theory and the fundamental parameters of impinging droplets are introduced. Secondly, the effects of different parameters on the dynamic behaviours and heat transfer of impinging droplet are discussed. Finally, the potential applications are listed. Existing concerns and challenges are summarized and future perspectives are provided to address poorly understood and conflicting issues.
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Affiliation(s)
- Xin Wang
- School of Energy and Environment, Southeast University, Nanjing, PR China; Department of Mechanical Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong, PR China
| | - Bo Xu
- School of Energy and Environment, Southeast University, Nanjing, PR China
| | - Shuai Guo
- School of Energy and Environment, Southeast University, Nanjing, PR China
| | - Yu Zhao
- School of Energy and Environment, Southeast University, Nanjing, PR China
| | - Zhenqian Chen
- School of Energy and Environment, Southeast University, Nanjing, PR China; Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, PR China; Jiangsu Provincial Key Laboratory of Solar Energy Science and Technology, School of Energy and Environment, Southeast University, Nanjing, PR China.
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3
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Adverse impact of macro-textured superhydrophobicity on contact time reduction at high Weber numbers. Colloids Surf A Physicochem Eng Asp 2022. [DOI: 10.1016/j.colsurfa.2022.129948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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4
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Shome A, Das A, Borbora A, Dhar M, Manna U. Role of chemistry in bio-inspired liquid wettability. Chem Soc Rev 2022; 51:5452-5497. [PMID: 35726911 DOI: 10.1039/d2cs00255h] [Citation(s) in RCA: 22] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Chemistry and topography are the two distinct available tools for customizing different bio-inspired liquid wettability including superhydrophobicity, superamphiphobicity, underwater superoleophobicity, underwater superoleophilicity, and liquid infused slippery property. In nature, various living species possessing super and special liquid wettability inherently comprises of distinctly patterned surface topography decorated with low/high surface energy. Inspired from the topographically diverse natural species, the variation in surface topography has been the dominant approach for constructing bio-inspired antiwetting interfaces. However, recently, the modulation of chemistry has emerged as a facile route for the controlled tailoring of a wide range of bio-inspired liquid wettability. This review article aims to summarize the various reports published over the years that has elaborated the distinctive importance of both chemistry and topography in imparting and modulating various bio-inspired wettability. Moreover, this article outlines some obvious advantages of chemical modulation approach over topographical variation. For example, the strategic use of the chemical approach has allowed the facile, simultaneous, and independent tailoring of both liquid wettability and other relevant physical properties. We have also discussed the design of different antiwetting patterned and stimuli-responsive interfaces following the strategic and precise alteration of chemistry for various prospective applications.
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Affiliation(s)
- Arpita Shome
- Bio-Inspired Polymeric Materials Lab, Department of Chemistry, Indian Institute of Technology Guwahati, Kamrup, Assam-781039, India.
| | - Avijit Das
- Bio-Inspired Polymeric Materials Lab, Department of Chemistry, Indian Institute of Technology Guwahati, Kamrup, Assam-781039, India.
| | - Angana Borbora
- Bio-Inspired Polymeric Materials Lab, Department of Chemistry, Indian Institute of Technology Guwahati, Kamrup, Assam-781039, India.
| | - Manideepa Dhar
- Bio-Inspired Polymeric Materials Lab, Department of Chemistry, Indian Institute of Technology Guwahati, Kamrup, Assam-781039, India.
| | - Uttam Manna
- Bio-Inspired Polymeric Materials Lab, Department of Chemistry, Indian Institute of Technology Guwahati, Kamrup, Assam-781039, India. .,Centre for Nanotechnology, Indian Institute of Technology Guwahati, Kamrup, Assam-781039, India.,Jyoti and Bhupat Mehta School of Health Science and Technology, Indian Institute of Technology Guwahati, Kamrup, Assam-781039, India
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5
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Han X, Li J, Tang X, Li W, Zhao H, Yang L, Wang L. Droplet Bouncing: Fundamentals, Regulations, and Applications. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2200277. [PMID: 35306734 DOI: 10.1002/smll.202200277] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 02/13/2022] [Indexed: 06/14/2023]
Abstract
Droplet impact is a ubiquitous phenomenon in nature, daily life, and industrial processes. It is thus crucial to tune the impact outcomes for various applications. As a special outcome of droplet impact, the bouncing of droplets keeps the form of the droplets after the impact and minimizes the energy loss during the impact, being beneficial in many applications. A unified understanding of droplet bouncing is in high demand for effective development of new techniques to serve applications. This review shows the fundamentals, regulations, and applications of millimeter-sized droplet bouncing on solid surfaces and same/miscible liquids (liquid pool and another droplet). Regulation methods and current applications are summarized, and potential directions are proposed.
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Affiliation(s)
- Xing Han
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, 999077, Hong Kong
| | - Jiaqian Li
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, 999077, Hong Kong
| | - Xin Tang
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, 999077, Hong Kong
| | - Wei Li
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, 999077, Hong Kong
| | - Haibo Zhao
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, 999077, Hong Kong
- Department of Mechanics and Aerospace Engineering, Southern University of Science and Technology, Shenzhen, Guangdong, 518055, China
| | - Ling Yang
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, 999077, Hong Kong
| | - Liqiu Wang
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong, 999077, Hong Kong
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6
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Baumgartner DA, Shiri S, Sinha S, Karpitschka S, Cira NJ. Marangoni spreading and contracting three-component droplets on completely wetting surfaces. Proc Natl Acad Sci U S A 2022; 119:e2120432119. [PMID: 35507868 PMCID: PMC9171644 DOI: 10.1073/pnas.2120432119] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Accepted: 03/22/2022] [Indexed: 11/24/2022] Open
Abstract
SignificanceThe shape and dynamics of small sessile droplets are dictated by capillary forces. For liquid mixtures, evaporation adds spatio-temporal modulation to these forces that can either enhance or inhibit droplet spreading, depending on the direction of the resulting Marangoni flow. This work experimentally and numerically demonstrates the coexistence of two antagonistic Marangoni flows in a ternary mixture. Played against each other, they can choreograph a boomerang-like wetting motion: Droplets initially rapidly spread, then contract into a compact cap shape. While such a behavior has been impossible in wetting scenarios of simple liquids, it enables spread-retract-remove surface processing with the addition of a single small liquid volume, demonstrated here in a surface-cleaning experiment.
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Affiliation(s)
- Dieter A. Baumgartner
- Rowland Institute, Harvard University, Cambridge, MA 02142
- Environmental Microfluidics Group, Institute of Environmental Engineering, Department of Civil, Environmental, and Geomatic Engineering, ETH Zürich, 8093 Zürich, Switzerland
| | - Samira Shiri
- Rowland Institute, Harvard University, Cambridge, MA 02142
- Department of Biomedical Engineering, Cornell University, Ithaca, NY 14850
| | | | - Stefan Karpitschka
- Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Germany
| | - Nate J. Cira
- Rowland Institute, Harvard University, Cambridge, MA 02142
- Department of Biomedical Engineering, Cornell University, Ithaca, NY 14850
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7
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Tang X, Li W, Wang L. Furcated droplet motility on crystalline surfaces. NATURE NANOTECHNOLOGY 2021; 16:1106-1112. [PMID: 34282311 DOI: 10.1038/s41565-021-00945-w] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Accepted: 06/14/2021] [Indexed: 06/13/2023]
Abstract
Directed liquid motion has been conventionally mediated by functionalizing chemical inhomogeneity or texturing topological anisotropy on target surfaces. Here we show the self-propulsion of droplets that furcated in well-defined directions on piezoelectric single crystals in the absence of any apparent asymmetry or external force. By selecting the crystal plane to interface with the droplets, the thermoelastic-piezoelectric interplay yields intricate electric potential profiles, enabling various forms of self-propulsion including unidirectional, bifurcated and trifurcated. This effect originates from an anisotropic crystalline structure that generates contrasting macroscopic liquid behaviours and is observed with cold/hot and volatile droplets. Intrinsically oriented liquid motions have broad applicability in processes ranging from soft matter engineering, autonomous material delivery and thermal management to biochemical analysis.
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Affiliation(s)
- Xin Tang
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong SAR, China
- HKU-Zhejiang Institute of Research and Innovation (HKU-ZIRI), Hangzhou, Zhejiang, China
| | - Wei Li
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong SAR, China
- HKU-Zhejiang Institute of Research and Innovation (HKU-ZIRI), Hangzhou, Zhejiang, China
| | - Liqiu Wang
- Department of Mechanical Engineering, The University of Hong Kong, Hong Kong SAR, China.
- HKU-Zhejiang Institute of Research and Innovation (HKU-ZIRI), Hangzhou, Zhejiang, China.
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8
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Abstract
Repellent materials are known for their ability to make impacting water recoil and takeoff, which keeps them dry after rain. Here we show that the ability of drops to bounce can be extended by two orders of magnitude, in terms of the liquid viscosity. We measure and model two main characteristics of these viscous rebounds, namely the contact time of the drops and the elasticity of the collision, which allows us to understand how and why viscous liquids can be repelled by hydrophobic solids.
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Affiliation(s)
- Aditya Jha
- PMMH, UMR 7636 du CNRS, ESPCI-Paris, PSL Research University, 75005 Paris, France and LadHyX, UMR 7646 du CNRS, École Polytechnique, 91128 Palaiseau, France
| | - Pierre Chantelot
- PMMH, UMR 7636 du CNRS, ESPCI-Paris, PSL Research University, 75005 Paris, France and LadHyX, UMR 7646 du CNRS, École Polytechnique, 91128 Palaiseau, France
| | - Christophe Clanet
- PMMH, UMR 7636 du CNRS, ESPCI-Paris, PSL Research University, 75005 Paris, France and LadHyX, UMR 7646 du CNRS, École Polytechnique, 91128 Palaiseau, France
| | - David Quéré
- PMMH, UMR 7636 du CNRS, ESPCI-Paris, PSL Research University, 75005 Paris, France and LadHyX, UMR 7646 du CNRS, École Polytechnique, 91128 Palaiseau, France
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9
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Shi S, Lv C, Zheng Q. Temperature-regulated adhesion of impacting drops on nano/microtextured monostable superrepellent surfaces. SOFT MATTER 2020; 16:5388-5397. [PMID: 32490478 DOI: 10.1039/d0sm00469c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The monostable Cassie state is a favorable wetting state for superhydrophobic materials, in which water drops can automatically transfer from the Wenzel wetting state to the Cassie wetting state, such that as a consequence the water repellency can be maintained. Drop impact phenomena are ubiquitous in nature and of critical importance in industry, and previous works show that the efficiency of self-cleaning and dropwise condensation could benefit from drop impact on monostable surfaces. However, whether such a feature is sufficiently robust remains unclear when the temperature of the surface is taken into consideration. Here, we report that there exists a lower bound of the temperature of the surface, under which a transition from the Cassie wetting state to the Wenzel wetting state arises. By varying the temperature of the surface, it is found that the solid-liquid wetting region could be regulated. Based on thermodynamics, we propose a model to predict the controllable wetting region, and we show that the gradual transition of the wetting state is a result of the accumulation of droplets on the nanoscale. Connections between the dynamics occurring at the solid-liquid interfaces on the microscale and the condensation occurring in the nanotextures are constructed. These results deepen our understanding of the breakdown of superhydrophobicity under dynamic impinging in high humidity. Moreover, this study will shed new light on the applications for controllable liquid deposition and surface decoration, such as catalysts on the superhydrophobic surfaces.
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Affiliation(s)
- Songlin Shi
- Department of Engineering Mechanics, Tsinghua University, 100084 Beijing, China.
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10
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Abstract
Rainfall on biological superhydrophobic surfaces is ubiquitous in nature. Previous studies in a laboratory setting have focused only on low-speed impacts, which can be quite different from rain conditions in nature. In this study, we reported unexpected and interesting shock-like patterns when a drop impacts biological surfaces at high speeds. These shock-like waves trigger sudden drop fragmentation into smaller satellite droplets and lead to a more than twofold decrease in contact time. Our findings may elucidate biological advantages (hypothermia risk reduction for birds, flight stability for insects, spore dispersal on plants) of superhydrophobic surfaces triggered by microstructures. Many biological surfaces of animals and plants (e.g., bird feathers, insect wings, plant leaves, etc.) are superhydrophobic with rough surfaces at different length scales. Previous studies have focused on a simple drop-bouncing behavior on biological surfaces with low-speed impacts. However, we observed that an impacting drop at high speeds exhibits more complicated dynamics with unexpected shock-like patterns: Hundreds of shock-like waves are formed on the spreading drop, and the drop is then abruptly fragmented along with multiple nucleating holes. Such drop dynamics result in the rapid retraction of the spreading drop and thereby a more than twofold decrease in contact time. Our results may shed light on potential biological advantages of hypothermia risk reduction for endothermic animals and spore spreading enhancement for fungi via wave-induced drop fragmentation.
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11
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Bhar K, Chang B, Virot E, Straker L, Kang H, Paris R, Clanet C, Jung S. How localized force spreads on elastic contour feathers. J R Soc Interface 2019; 16:20190267. [PMID: 31744417 DOI: 10.1098/rsif.2019.0267] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Birds can experience localized forces against their bodies due to impact against solid objects (like a branch or another bird) or water (during plunge-dives or landings). In this study, we hypothesize that densely packed contour feathers around the bird body would spread localized impact force while diving and maintaining plumage integrity. To test the hypothesis, we performed experiments with individual feathers and elastic beams, and developed a theoretical model to determine the response of feathers during the dive. First, we used a micro computed tomography scanner to characterize the internal structure of the contour feather from a northern gannet and calculate Young's modulus of feathers sampled from different parts of the body. This value was found to be of the order of 109 Pa for feathers from chest and belly. Second, we model the feathers as elastic beams taking into account their pre-curvature and non-uniform cross-section. Results from our experiments with polycarbonate beams suggest that the interaction of feathers on the skin patch redistributes the force, thereby reducing the impact on any particular area of the skin. Finally, a theoretical model of multiple overlaying feathers is proposed to quantify the spreading of impact force on the skin of the bird body which shows that the pressure on the skin at the impact point can be reduced by as much as three times the pressure if feathers had been absent.
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Affiliation(s)
- Kinjal Bhar
- Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY 14853, USA
| | - Brian Chang
- Virginia Tech, Department of Biomedical Engineering and Mechanics, Blacksburg, VA 24061, USA.,Department of Biology, Temple University, Philadelphia, PA 19122, USA
| | - Emmanuel Virot
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
| | - Lorian Straker
- Centro de Biologia Estrutural e Bioimagem - CENABIO, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-902, Brazil
| | - Hosung Kang
- Virginia Tech, Department of Biomedical Engineering and Mechanics, Blacksburg, VA 24061, USA
| | - Romain Paris
- École polytechnique, LadHyX, CNRS UMR 7646, 91128 Palaiseau, France
| | | | - Sunghwan Jung
- Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY 14853, USA
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12
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Shi S, Lv C, Zheng Q. Drop Impact on Two-Tier Monostable Superrepellent Surfaces. ACS APPLIED MATERIALS & INTERFACES 2019; 11:43698-43707. [PMID: 31644872 DOI: 10.1021/acsami.9b14880] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Superrepellency is a favorable nonwetting scenario featuring a dramatic reduction of the solid/liquid contact area. The robustness of superhydrophobicity plays a central role in self-cleaning and anti-icing. Drop impacts happen ubiquitously in natural environments and often cause a notable extension of the solid/liquid contact area. This is associated with an enhanced affinity between water and the microtextures and therefore leads to irreversible breakdowns in the superhydrophobicity. This problem remains a major challenge and limits the practical applications of superrepellent materials. In order to find a solution, in this paper, a repeated Cassie-Wenzel-Cassie wetting state transition is studied at the microscale when a drop impacts a two-tier superhydrophobic surface. In this case, the surface is completely dry without any liquid residue after the drop rebounds. The present results exhibit a striking contrast to the conventional perspective. The influence of geometrical parameters of the textured surface on the spreading and retracting behaviors of the impact drops is quantified, as well as the time-dependence scaling laws. From a practical point of view, it is demonstrated that the self-cleaning and dropwise condensation may significantly benefit from this repeated wetting transition. Dirt particles or small droplets in deep textures are able to be taken away so that the functionality and the robustness of the superhydrophobicity may be significantly strengthened. The results reported in this study facilitate the design of functional superrepellent materials.
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Affiliation(s)
- Songlin Shi
- Department of Engineering Mechanics , Tsinghua University , 100084 Beijing , People's Republic of China
- Center for Nano and Micro Mechanics , Tsinghua University , 100084 Beijing , People's Republic of China
| | - Cunjing Lv
- Department of Engineering Mechanics , Tsinghua University , 100084 Beijing , People's Republic of China
- Center for Nano and Micro Mechanics , Tsinghua University , 100084 Beijing , People's Republic of China
| | - Quanshui Zheng
- Department of Engineering Mechanics , Tsinghua University , 100084 Beijing , People's Republic of China
- Center for Nano and Micro Mechanics , Tsinghua University , 100084 Beijing , People's Republic of China
- State Key Laboratory of Tribology , Tsinghua University , 100084 Beijing , People's Republic of China
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13
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Zhu P, Chen R, Wang L. Topography-Directed Hot-Water Super-Repellent Surfaces. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2019; 6:1900798. [PMID: 31559129 PMCID: PMC6755536 DOI: 10.1002/advs.201900798] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/07/2019] [Revised: 07/04/2019] [Indexed: 05/08/2023]
Abstract
Natural and artificial super-repellent surfaces are frequently textured with pillar-based discrete structures rather than hole-based continuous ones because the former exhibits lower adhesion from the reduced length of the three-phase contact line. Counterintuitively, here, the unusual topographic effects are discovered on hot-water super-repellency where the continuous microcavity surface outperforms the discrete microneedle/micropillar surface. This anomaly arises from the different dependencies of liquid-repellency stability on the surface structure and water temperature in the two topographies. The unexpected wetting dynamics are interpreted by determining timescales for droplet evaporation, vapor condensation, and droplet bouncing. The associated heat transfer process is unique to the wetting states and remarkably distinct from each other in the two topographies. It is envisioned that hot-water super-repellent microcavity surfaces will be advantageous for a variety of applications, especially when both self-cleaning and thermal insulation are imperative, such as clothing for scald protection and digital microfluidics for exothermic reactions.
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Affiliation(s)
- Pingan Zhu
- Department of Mechanical EngineeringThe University of Hong KongHong KongChina
- HKU‐Zhejiang Institute of Research and Innovation (HKU‐ZIRI)Hangzhou311300ZhejiangChina
| | - Rifei Chen
- Department of Mechanical EngineeringThe University of Hong KongHong KongChina
- Department of Materials Science and EngineeringSouthern University of Science and TechnologyShenzhen518055China
| | - Liqiu Wang
- Department of Mechanical EngineeringThe University of Hong KongHong KongChina
- HKU‐Zhejiang Institute of Research and Innovation (HKU‐ZIRI)Hangzhou311300ZhejiangChina
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14
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Girard HL, Soto D, Varanasi KK. Waterbowls: Reducing Impacting Droplet Interactions by Momentum Redirection. ACS NANO 2019; 13:7729-7735. [PMID: 31243952 DOI: 10.1021/acsnano.9b01301] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Superhydrophobic surfaces can dramatically reduce the transport of mass or energy from impacting droplets by making them bounce off. Such transport processes are dependent on both the contact time and the contact area between the drop and the surface. To reduce transport, recent studies have focused on reducing the contact time. However, the contact area, which is dictated by the conformal spreading of the droplet, remains large, thereby limiting the reduction in the overall transport. Here, we show how surfaces can be designed to redirect the momentum of the spreading lamella causing it to lift off into 3-dimensional shapes, thereby dramatically reducing the contact area. We design superhydrophobic surfaces with an in-plane discontinuity leading to the accumulation of vertical momentum resulting in the out-of-plane ejection of the lamella into water bowls. We demonstrate a 2-fold reduction in the heat transfer between a cold rain and a warm surface. These insights can be broadly applied to other transport phenomena involving mass and energy exchange to limit heat loss under precipitation, icing of surfaces, reduce salt deposition on a surface exposed to ocean spray, or inhibit the formation of a water film on wings or wind turbine blades.
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Affiliation(s)
- Henri-Louis Girard
- Department of Mechanical Engineering , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
| | - Dan Soto
- Department of Mechanical Engineering , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
| | - Kripa K Varanasi
- Department of Mechanical Engineering , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States
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15
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Abstract
Although a hydrophobic microtexture at a solid surface most often reflects rain owing to the presence of entrapped air within the texture, it is much more challenging to repel hot water. As it contacts a colder material, hot water generates condensation within the cavities at the solid surface, which eventually builds bridges between the substrate and the water, and thus destroys repellency. Here we show that both “small” (~100 nm) and “large” (~10 µm) model features do reflect hot drops at any drop temperature and in the whole range of explored impact velocities. Hence, we can define two structural recipes for repelling hot water: drops on nanometric features hardly stick owing to the miniaturization of water bridges, whereas kinetics of condensation in large features is too slow to connect the liquid to the solid at impact. It has previously been reported that hot drops impacting on a colder surface can lead to loss of surface hydrophobicity unless the surface features are very small. Here the authors find that both small and large features but not intermediate ones are able to preserve hydrophobicity.
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16
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17
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Trapping a Hot Drop on a Superhydrophobic Surface with Rapid Condensation or Microtexture Melting. MICROMACHINES 2018; 9:mi9110566. [PMID: 30715065 PMCID: PMC6266579 DOI: 10.3390/mi9110566] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/09/2018] [Revised: 10/24/2018] [Accepted: 10/30/2018] [Indexed: 11/17/2022]
Abstract
A water drop can bounce upon impacting a superhydrophobic surface. However, on certain superhydrophobic surfaces, a water drop will stick rather than bounce if it is sufficiently hot. Here, we aim to better understand the mechanisms that can lead to this bouncing-sticking transition. Specifically, we model two potential mechanisms in which a superhydrophobic surface could trap a sufficiently hot drop within milliseconds: melting of microtextured wax and condensation of the vapor within the superhydrophobic texture. We then test these mechanisms through systematic drop impact experiments in which we independently vary the substrate and drop temperatures on a waxy superhydrophobic Nasturtium leaf. We find that, whenever the surface or the drop is above a microtexture-melting temperature, the drop sticks. Below this temperature, a critical temperature threshold for bouncing can be predicted and controlled by considering the relative timescales between condensation growth and drop residence time. We envision that these results can provide insight into the design of a new class of superhydrophobic surfaces to act as a rapid thermal fuse to prevent drops that exceed a critical temperature from bouncing onto a thermally sensitive target.
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18
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Xiao J, Pan F, Xia H, Zou S, Zhang H, George OA, Zhou F, Huang Y. Computational Study of Single Droplet Deposition on Randomly Rough Surfaces: Surface Morphological Effect on Droplet Impact Dynamics. Ind Eng Chem Res 2018. [DOI: 10.1021/acs.iecr.8b00418] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jie Xiao
- Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
| | - Fei Pan
- Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
| | - Hongtao Xia
- Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
| | - Siyu Zou
- Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
| | - Hui Zhang
- Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
| | - Oluwafemi Ayodele George
- Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
| | - Fei Zhou
- Suzhou Key Laboratory of Green Chemical Engineering, School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, China
| | - Yinlun Huang
- Department of Chemical Engineering and Materials Science, Wayne State University, Detroit, Michigan 48202, United States
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