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Mo M, Bai X, Liu Z, Huang Z, Xu M, Ma L, Lai W, Mo Q, Xie S, Li Y, Huang Y, Xiao N, Zheng Y. Defect by design: Harnessing the "petal effect" for advanced hydrophobic surface applications. J Colloid Interface Sci 2024; 673:37-48. [PMID: 38875796 DOI: 10.1016/j.jcis.2024.05.192] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2024] [Revised: 05/15/2024] [Accepted: 05/24/2024] [Indexed: 06/16/2024]
Abstract
HYPOTHESIS In the interfacial wetting boundary, the superhydrophobic surface is often damaged, and the anisotropic wettability of its surface has attracted many researchers' attention. The "petal effect" surface has typical anisotropic wettability. We predict that under the dual conditions of structural defects and high impact velocity, the "petal effect" becomes more adhesive on the surface. EXPERIMENTS This study refers to the droplet state on rose petals, structural defects were constructed on the superhydrophobic surface. This paper studies the influence of macro-structural defects on the wettability change from natural to bionic "lotus effect" to "petal effect" in both static and dynamic angles. FINDINGS Macro defects significantly change the static contact angle of the superhydrophobic surface. The higher the impact velocity of the droplet, the higher the energy dissipation of the "petal effect" surface (DSHS), which improves the adhesion of the surface to the droplet and prolongs the contact time. It is found that the defect structure and high impact velocity will directly affect the deposition and desorption of droplets on the superhydrophobic surface, and they are both essential. This wetting dynamic law is very likely to be helpful in the quantitative design of defect structure scale for dynamic desorption of droplets on superhydrophobic surfaces.
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Affiliation(s)
- Min Mo
- College of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China
| | - Xingjia Bai
- College of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China
| | - Zhonglin Liu
- Guangxi Key Laboratory of Advanced Microwave Manufacturing Technology, Advanced Materials Industry Institute of Guangxi Academy of Science, Guangxi Academy of Sciences, Nanning 530007, China
| | - Zhimin Huang
- Guangxi Key Laboratory of Advanced Microwave Manufacturing Technology, Advanced Materials Industry Institute of Guangxi Academy of Science, Guangxi Academy of Sciences, Nanning 530007, China
| | - Mengxue Xu
- Guangxi Key Laboratory of Advanced Microwave Manufacturing Technology, Advanced Materials Industry Institute of Guangxi Academy of Science, Guangxi Academy of Sciences, Nanning 530007, China
| | - Lanyu Ma
- Guangxi Key Laboratory of Advanced Microwave Manufacturing Technology, Advanced Materials Industry Institute of Guangxi Academy of Science, Guangxi Academy of Sciences, Nanning 530007, China
| | - Wenqin Lai
- Guangxi Key Laboratory of Advanced Microwave Manufacturing Technology, Advanced Materials Industry Institute of Guangxi Academy of Science, Guangxi Academy of Sciences, Nanning 530007, China
| | - Qiufeng Mo
- Guangxi Key Laboratory of Advanced Microwave Manufacturing Technology, Advanced Materials Industry Institute of Guangxi Academy of Science, Guangxi Academy of Sciences, Nanning 530007, China
| | - Songbo Xie
- Guangxi Key Laboratory of Advanced Microwave Manufacturing Technology, Advanced Materials Industry Institute of Guangxi Academy of Science, Guangxi Academy of Sciences, Nanning 530007, China
| | - Yanming Li
- Guangxi Key Laboratory of Advanced Microwave Manufacturing Technology, Advanced Materials Industry Institute of Guangxi Academy of Science, Guangxi Academy of Sciences, Nanning 530007, China
| | - Yifeng Huang
- Guangxi Key Laboratory of Advanced Microwave Manufacturing Technology, Advanced Materials Industry Institute of Guangxi Academy of Science, Guangxi Academy of Sciences, Nanning 530007, China
| | - Ning Xiao
- National Key Laboratory of Non-Food Biomass Energy Technology, Guangxi Academy of Sciences, Nanning 530007, China
| | - Yihua Zheng
- Guangxi Key Laboratory of Advanced Microwave Manufacturing Technology, Advanced Materials Industry Institute of Guangxi Academy of Science, Guangxi Academy of Sciences, Nanning 530007, China.
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Bai J, Wang X, Zhang M, Yang Z, Zhang J. Turning Non-Sticking Surface into Sticky Surface: Correlation between Surface Topography and Contact Angle Hysteresis. MATERIALS (BASEL, SWITZERLAND) 2024; 17:2006. [PMID: 38730813 PMCID: PMC11084899 DOI: 10.3390/ma17092006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2024] [Revised: 04/20/2024] [Accepted: 04/24/2024] [Indexed: 05/13/2024]
Abstract
We present a surface modification technique that turns CuNi foam films with a high contact angle and non-sticking property into a sticky surface. By decorating with mesh-like biaxially oriented polypropylene (BOPP) and adjusting the surface parameters, the surface exhibits water-retaining capability even when being held upside down. The wetting transition process of droplets falling on its surface were systematically studied using the finite element simulation method. It is found that the liquid filled the surface microstructure and curvy three-phase contact line. Moreover, we experimentally demonstrated that this surface can be further applied to capture underwater air bubbles.
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Affiliation(s)
- Jingyuan Bai
- School of Intelligent Manufacturing, Lishui Vocational and Technical College, Lishui 323000, China;
| | - Xuejiao Wang
- School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China; (X.W.); (M.Z.)
| | - Meilin Zhang
- School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China; (X.W.); (M.Z.)
| | - Zhou Yang
- Engineering Research Center of Continuous Extrusion, Ministry of Education, Dalian Jiaotong University, Dalian 116028, China;
- Key Laboratory of Near-Net Forming of Light Metals of Liaoning Province, Dalian Jiaotong University, Dalian 116028, China
| | - Jin Zhang
- Engineering Research Center of Continuous Extrusion, Ministry of Education, Dalian Jiaotong University, Dalian 116028, China;
- Key Laboratory of Near-Net Forming of Light Metals of Liaoning Province, Dalian Jiaotong University, Dalian 116028, China
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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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Ge-Zhang S, Cai T, Yang H, Ding Y, Song M. Biology and nature: Bionic superhydrophobic surface and principle. Front Bioeng Biotechnol 2022; 10:1033514. [PMID: 36324886 PMCID: PMC9618887 DOI: 10.3389/fbioe.2022.1033514] [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: 08/31/2022] [Accepted: 09/27/2022] [Indexed: 11/18/2022] Open
Abstract
Nature is the source of human design inspiration. In order to adapt to the environment better, creatures in nature have formed various morphological structures during billions of years of evolution, among which the superhydrophobic characteristics of some animal and plant surface structures have attracted wide attention. At present, the preparation methods of bionic superhydrophobic surface based on the microstructure of animal and plant body surface include vapor deposition, etching modification, sol-gel method, template method, electrostatic spinning method and electrostatic spraying method, etc., which have been used in medical care, military industry, shipping, textile and other fields. Based on nature, this paper expounds the development history of superhydrophobic principle, summarizes the structure and wettability of superhydrophobic surfaces in nature, and introduces the characteristics differences and applications of different superhydrophobic surfaces in detail. Finally, the challenge of bionic superhydrophobic surface is discussed, and the future development direction of this field is prospected.
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Ge-Zhang S, Yang H, Ni H, Mu H, Zhang M. Biomimetic superhydrophobic metal/nonmetal surface manufactured by etching methods: A mini review. Front Bioeng Biotechnol 2022; 10:958095. [PMID: 35992341 PMCID: PMC9388738 DOI: 10.3389/fbioe.2022.958095] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Accepted: 07/04/2022] [Indexed: 11/24/2022] Open
Abstract
As an emerging fringe science, bionics integrates the understanding of nature, imitation of nature, and surpassing nature in one aspect, and it organically combines the synergistic complementarity of function and structure–function integrated materials which is of great scientific interest. By imitating the microstructure of a natural biological surface, the bionic superhydrophobic surface prepared by human beings has the properties of self-cleaning, anti-icing, water collection, anti-corrosion and oil–water separation, and the preparation research methods are increasing. The preparation methods of superhydrophobic surface include vapor deposition, etching modification, sol–gel, template, electrostatic spinning, and electrostatic spraying, which can be applied to fields such as medical care, military industry, ship industry, and textile. The etching modification method can directly modify the substrate, so there is no need to worry about the adhesion between the coating and the substrate. The most obvious advantage of this method is that the obtained superhydrophobic surface is integrated with the substrate and has good stability and corrosion resistance. In this article, the different preparation methods of bionic superhydrophobic materials were summarized, especially the etching modification methods, we discussed the detailed classification, advantages, and disadvantages of these methods, and the future development direction of the field was prospected.
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Affiliation(s)
| | - Hong Yang
- College of Science, Northeast Forestry University, Harbin, China
| | - Haiming Ni
- College of Science, Northeast Forestry University, Harbin, China
| | - Hongbo Mu
- College of Science, Northeast Forestry University, Harbin, China
- *Correspondence: Hongbo Mu, ; Mingming Zhang,
| | - Mingming Zhang
- College of Bioinformatics Science and Technology, Harbin Medical University, Harbin, China
- *Correspondence: Hongbo Mu, ; Mingming Zhang,
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Hydrophobic Antiwetting of Aquatic UAVs: Static and Dynamic Experiment and Simulation. APPLIED SCIENCES-BASEL 2022. [DOI: 10.3390/app12157626] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The adhesion of water to the surfaces of unmanned aerial vehicles (UAVs) adversely affects the function. The proposed UAVs will have underwater as well as flight capability, and these aquatic UAVs must shed water to resume flight. The efficient separation of the adhering water from aquatic-UAV surfaces is a challenging problem; we investigated the application of hydrophobic surfaces as a potential solution. Using aquatic-UAV models, one with hydrophilic surfaces and the other with superhydrophobic anisotropic textured surfaces, the antiwetting mechanism of the hydrophobic surfaces was investigated using a simulated-precipitation system and instrumentation to measure the load of the water adhering to the aquatic UAV, and to measure the impact energies. When the model was stationary (passive antiwetting), no adhesion occurred on the superhydrophobic surfaces, while continuous asymmetric thick liquid films were observed on the hydrophilic surfaces. The superhydrophobic surfaces reduced the rain loading by 87.5%. The vibration and movement of the model (dynamic antiwetting, simulating flight motions) accelerated the separation process and reduced the contact time. The observed results were augmented by the use of computational fluid dynamics with lattice Boltzmann methods (LBM) to analyze the particle traces inside the droplets, the liquid phase velocity-field and pressure-field strengths, and the backward bouncing behavior of the derived droplet group induced by the moving surface. The synergy between the superhydrophobic surfaces and the kinetic energy of the droplets promotes the breakup of drops, which avoids the significant lateral unbalance observed with hydrophilic surfaces during simulated flight.
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Shao J, Huang Y, Zhao M, Yang Y, Zheng Y, Zhu R. Molecular Dynamics Simulation on the Wettability of Nanoscale Wrinkles: High Water Adhesion of Rose Petals. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:8854-8861. [PMID: 35834741 DOI: 10.1021/acs.langmuir.2c00974] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Understanding the high water adhesion of rose petals is of great significance in artificial surface design. With all-atom molecular dynamics simulation, the wettability of nanoscale wrinkles was explored and compared to that of nanoscale strips with favorable hydrophobicity. The dewetting and wetting of gaps between nanoscale structures represent the Cassie-Baxter (CB) and Wenzel (WZ) states of the macroscopic droplet deposited on the textured surface, respectively. We uncovered the intermediate state, which is different from the CB and WZ states for wrinkles. Structures and free-energy profiles of metastable and transition states under various pressures were also investigated. Moreover, free-energy barriers for the (de)wetting transitions were quantified. On this basis, the roles of pressure and the unique structures of nanoscale wrinkles in the high water adhesion of rose petals were identified.
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Affiliation(s)
- Jinwei Shao
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, People's Republic of China
| | - Yinguo Huang
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, People's Republic of China
| | - Meirong Zhao
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, People's Republic of China
| | - Yong Yang
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, People's Republic of China
| | - Yelong Zheng
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, People's Republic of China
| | - Rui Zhu
- Shanghai YangZhi Rehabilitation Hospital (Shanghai Sunshine Rehabilitation Center), School of Medicine, Tongji University, Shanghai 200092, China
- Shanghai University of Medicine and Health Sciences, 279 Zhouzhu Road, Shanghai 201318, China
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8
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Zhang X, Chen J, Chen Y, Lin X, Wang B, Liu Y, Jiang Y, Zhang H. Studies on Hydrophobic Silica/Silicone Rubber Composite Microspheres with Dual-Size Microstructures. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:14668-14678. [PMID: 34877859 DOI: 10.1021/acs.langmuir.1c02398] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
In this study, a series of microsphere composites were prepared by the hydrosilylation of nanospherical SiO2 and silicon rubber microspheres. The influence of different host-guest size ratios on the wettability of the SiO2/silicone rubber composite microspheres was explored. The structures and performance of the composite microspheres were investigated using scanning electron microscopy and contact angle testing. The results showed that the prepared SiO2/silicone rubber composite microspheres had a raspberry-like structure and exhibited a rose petal effect. When the SiO2 content was 30%, the water contact angle of the SiO2/silicone rubber composite microspheres reached a maximum, and 30% was used as the optimal ratio for compounding SiO2 having different particle diameters with silicone rubber microspheres. Wettability calculations and analyses were performed for the surface with the composite microspheres. The results indicated that the structure with dual-size roughness could significantly improve surface hydrophobicity. As the ratio of the host-guest size increased, the contact angle of the water phase also increased. However, the surface structures of the composite microspheres were not uniform because of the surface chemical composition and the uncontrollable distribution of the small spheres on the surface of the large spheres during compounding. As a result, water droplets appeared in the Cassie-impregnated state on the composite microsphere particle coating, resulting in the phenomenon of high hydrophobicity and high adhesion.
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Affiliation(s)
- Xiaomei Zhang
- National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Changzhou 213164, People's Republic of China
| | - Juan Chen
- National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Changzhou 213164, People's Republic of China
| | - Yuying Chen
- National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Changzhou 213164, People's Republic of China
| | - Xing Lin
- National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Changzhou 213164, People's Republic of China
| | - Bodong Wang
- National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Changzhou 213164, People's Republic of China
| | - Yifan Liu
- National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Changzhou 213164, People's Republic of China
| | - Yan Jiang
- National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Changzhou 213164, People's Republic of China
| | - Hongwen Zhang
- National Experimental Demonstration Center for Materials Science and Engineering, Changzhou University, Changzhou 213164, People's Republic of China
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Kim SH, Kang HS, Sohn EH, Chang BJ, Park IJ, Lee SG. A strategy for preparing controllable, superhydrophobic, strongly sticky surfaces using SiO 2@PVDF raspberry core-shell particles. RSC Adv 2021; 11:23631-23636. [PMID: 35479804 PMCID: PMC9036573 DOI: 10.1039/d1ra03928h] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Accepted: 06/30/2021] [Indexed: 01/14/2023] Open
Abstract
In nature, wetting by water droplets on superhydrophobic materials is governed by the Cassie-Baxter or Wenzel models. Moreover, sticky properties, derived from these types of wettings, are required for a wide range of applications involving superhydrophobic materials. As a facile new strategy, a method employing a gaseous fluorine precursor to fabricate core-shell particles, comprising perfectly shaped fluorine shells with adjustable adhesive strength, is described in this paper. Silica was used as the hydrophilic core, while polyvinylidene fluoride (PVDF) was used for the hydrophobic shell coating, forming a raspberry-like shape. In addition, controlling the amount of PVDF coated on the silica surface enabled the water droplets to come into contact with both the PVDF of the shell and the silica of the core, thereby controlling both the superhydrophobicity and the adhesive strength. Thus, the synthesized particles formed a structured coating with controllable stickiness and contact angles of 131-165°. Furthermore, on surfaces with high adhesivity, the water droplets remained stable at tilt angles of 90° and 180° even under a strong centrifugal force, whereas on surfaces with low adhesivity, the water droplets slid off when the substrate was tilted at 4°.
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Affiliation(s)
- Seung-Hyun Kim
- Interface Materials and Chemical Engineering Research Center, Korea Research Institute of Chemical Technology Daejeon 34114 Republic of Korea
| | - Hong Suk Kang
- Interface Materials and Chemical Engineering Research Center, Korea Research Institute of Chemical Technology Daejeon 34114 Republic of Korea
| | - Eun-Ho Sohn
- Interface Materials and Chemical Engineering Research Center, Korea Research Institute of Chemical Technology Daejeon 34114 Republic of Korea
| | - Bong-Jun Chang
- Interface Materials and Chemical Engineering Research Center, Korea Research Institute of Chemical Technology Daejeon 34114 Republic of Korea
| | - In Jun Park
- Interface Materials and Chemical Engineering Research Center, Korea Research Institute of Chemical Technology Daejeon 34114 Republic of Korea
| | - Sang Goo Lee
- Interface Materials and Chemical Engineering Research Center, Korea Research Institute of Chemical Technology Daejeon 34114 Republic of Korea
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Lin HP, Chen LJ. Direct observation of wetting behavior of water drops on single micro-scale roughness surfaces of rose petal effect. J Colloid Interface Sci 2021; 603:539-549. [PMID: 34216950 DOI: 10.1016/j.jcis.2021.06.132] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Revised: 06/21/2021] [Accepted: 06/22/2021] [Indexed: 01/28/2023]
Abstract
HYPOTHESIS It has been verified that a surface of single micro-scale structures with certain roughness could exhibit petal effect. That is, water drops with a contact angle larger than 150° would pin on the petal effect surface. It is conjectured that the water drop could pin on the single micro-scale roughness petal effect surface by totally infiltrating into spaces (or grooves) between micro-pillars. EXPERIMENTS An inverted optical microscopy system is synchronically applied in the process of advancing/receding contact angle (ACA/RCA) measurements to directly observe the wetting behavior of water droplets on hydrophobic patterned surfaces with regular arrays of square micro-pillars. FINDINGS A sequence of wetting behavior evolution, Wenzel → petal → pseudo-lotus → lotus, is observed on the hydrophobic patterned surfaces along with increasing surface roughness. It is interesting to observe a Cassie-Wenzel transition for water drops on a petal substrate during the ACA measurement (embedded needle method), leading to two ACAs, one before (in Cassie state) and one after the transition (in Wenzel state). Thus, the petal substrates have large contact angle hysteresis (CAH) (with both ACA and RCA in Wenzel state) to pin the water drop in Wenzel state. A Cassie-Wenzel transition is consistently observed during the evaporation process of water drops on pseudo-lotus substrates, leading to two RCAs: one in Cassie state and one in Wenzel state. The pseudo-lotus substrates have CAH (with both ACA and RCA in Cassie state) small enough to make water drops easily slide off.
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Affiliation(s)
- Hui-Ping Lin
- Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
| | - Li-Jen Chen
- Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan.
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Zheng Y, Zhang C, Wang J, Yang L, Shen C, Han Z, Liu Y. Nonwet Kingfisher Flying in the Rain: The Tumble of Droplets on Moving Oriented Anisotropic Superhydrophobic Substrates. ACS APPLIED MATERIALS & INTERFACES 2020; 12:35707-35715. [PMID: 32640153 DOI: 10.1021/acsami.0c08889] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Extensive studies of antiwetting have been restricted to stationary substrates, while dewetting mechanisms on moving interfaces are still poorly understood. Due to the hydrophobic and anisotropic surface characteristics of kingfishers, they are able to easily change flight direction even under high-intensity precipitation. The present study aims to mechanistically analyze how the synergy of interfacial movement, anisotropy, and superhydrophobicity affects rapid dehydration. We have designed a droplet-conveyor system to simulate the bouncing of droplets on moving anisotropic superhydrophobic targets and performed simulations via the lattice Boltzmann algorithm. The moving interface can induce a directional tumbling behavior of the droplet and effectively avoid continuous wetting in the same region. We found that droplet tumbling is essentially caused by transformed depinning velocity vectors at the interface downstream. Also, the hang time of a tumbling droplet is positively related to the angle between the motion vector and the texture. The oriented anisotropic motion facilitates the tumbling of droplets and decreases their hang time by up to 23% as compared to that on a stationary inclined superhydrophobic surface. Similar interfacial process dehydration also occurs on a nonwet kingfisher flying in the rain, and we believe that these findings provide valuable new insights for high-efficiency water repellency of surfaces.
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Affiliation(s)
- Yihua Zheng
- Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun 130022, China
- Advanced Materials Industry Institute, Guangxi Academy of Sciences, Guangxi 530007, China
| | - Chengchun Zhang
- Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun 130022, China
- State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun 130022, China
| | - Jing Wang
- College of Physics, Jilin University, Changchun 130012, China
| | - Liang Yang
- Centre for Renewable Energy Systems, Cranfield University, Cranfield MK43 0AL, United Kingdom
| | - Chun Shen
- Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun 130022, China
| | - Zhiwu Han
- Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun 130022, China
| | - Yan Liu
- Key Laboratory of Bionic Engineering (Ministry of Education), Jilin University, Changchun 130022, China
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Zhang C, Wu Z, Shen C, Zheng Y, Yang L, Liu Y, Ren L. Effects of eigen and actual frequencies of soft elastic surfaces on droplet rebound from stationary flexible feather vanes. SOFT MATTER 2020; 16:5020-5031. [PMID: 32452492 DOI: 10.1039/d0sm00315h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The aim of this paper is to investigate the effect of eigenfrequency and the actual frequency of the elastic surface for droplet rebound. The elastic surface used in this study is the stationary flexible feather vanes. A fluid-structure interaction (FSI) numerical model is proposed to predict the phenomenon, and later it is validated by an experiment where droplets impact the stationary flexible feather vanes. The effect of mass and stiffness of the surface is analysed. First, a suitable combination of mass and stiffness of the surface will enhance the drop rebound. Second, a small mass system with a higher eigenfrequency will decrease the minimum contact time. Finally, the actual frequencies of the elastic surface, approximately 75 Hz, can accelerate the drop rebound for all cases.
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Affiliation(s)
- Chengchun Zhang
- Key Laboratory of Engineering Bionics (Ministry of Education), Jilin University, Changchun 130022, China.
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