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Patrícia da Silva Ramos I, Gavazzoni C, Lazzari D, Brito C. Hierarchical structured surfaces enhance the contact angle of the hydrophobic (meta-stable) state. J Chem Phys 2023; 158:2882244. [PMID: 37093992 DOI: 10.1063/5.0146948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Accepted: 03/27/2023] [Indexed: 04/26/2023] Open
Abstract
The relation between wetting properties and geometric parameters of fractal surfaces are widely discussed on the literature and, however, there are still divergences on this topic. Here we propose a simple theoretical model to describe the wetting properties of a droplet of water placed on a hierarchical structured surface and test the predictions of the model and the dependence of the droplet wetting state on the initial conditions using simulation of the 3-spin Potts model. We show that increasing the auto-similarity level of the hierarchy - called n - does not affect considerably the stable wetting state of the droplet but increases its contact angle. Simulations also explicit the existence of metastable states on this type of surfaces and shows that, when n increases, the metastability becomes more pronounced. Finally we show that the fractal dimension of the surface is not a good predictor of the contact angle of the droplet.
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Affiliation(s)
- Iara Patrícia da Silva Ramos
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP, 91501-970 Porto Alegre, Rio Grande do Sul, Brazil
| | - Cristina Gavazzoni
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP, 91501-970 Porto Alegre, Rio Grande do Sul, Brazil
| | - Davi Lazzari
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP, 91501-970 Porto Alegre, Rio Grande do Sul, Brazil
| | - Carolina Brito
- Instituto de Física, Universidade Federal do Rio Grande do Sul, Caixa Postal 15051, CEP, 91501-970 Porto Alegre, Rio Grande do Sul, Brazil
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Feldmann D, Pinchasik BE. The temperature dependent dynamics and periodicity of dropwise condensation on surfaces with wetting heterogeneities. J Colloid Interface Sci 2023; 644:146-156. [PMID: 37105038 DOI: 10.1016/j.jcis.2023.04.060] [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: 04/14/2022] [Revised: 04/07/2023] [Accepted: 04/13/2023] [Indexed: 04/29/2023]
Abstract
HYPOTHESIS Biphilic surfaces, namely surfaces comprising hydrophilic areas with a (super)hydrophobic background, are used in nature and engineering for controlled dropwise condensation and liquid transport. These, however, are highly dependent on the surface temperature and subcooling. EXPERIMENTS Here, biphilic surfaces were cooled inside a rotatable environmental chamber under controlled humidity. The condensation dynamics on the surface was quantified, depending on the subcooling, and compared to uniform superhydrophobic (USH) surfaces. Rates of condensation and transport were analyzed in terms of droplet number and size, covered area and fluid volume over several length scales. Specifically, from microscale condensation to macroscale droplet roll-off. FINDINGS Four phases of condensation were identified: a) initial nucleation, b) droplets on single patches, c) droplets covering adjacent patches and d) multi-patch droplets. Only the latter become mobile and roll off the surface. Cooling the surface to temperatures between T = 2-16 °C shows that lowering the temperature shortens some of the condensation parameters linearly, while others follow a power law, as expected from the theory of condensation. The temperature dependent condensation dynamics on (super)biphilic surfaces is faster in comparison to uniform superhydrophobic surfaces. Nevertheless, within time intervals of a few hours, droplets are mostly immobile. This sets guiding lines for using biphilic surfaces in applications such as water collection, heat transfer and separation processes. Generally, biphilic surfaces are suitable for applications in which fluids should be collected, concentrated and immobilized in specific areas.
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Affiliation(s)
- David Feldmann
- Tel Aviv University School of Mechanical Engineering, Faculty of Engineering, Ramat Aviv 69978, Tel-Aviv, Israel
| | - Bat-El Pinchasik
- Tel Aviv University School of Mechanical Engineering, Faculty of Engineering, Ramat Aviv 69978, Tel-Aviv, Israel.
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Zhang R, Wang Y, Yang Z. Spatially arranging interfacial droplets at the oil-solid interface. SOFT MATTER 2020; 16:107-113. [PMID: 31651918 DOI: 10.1039/c9sm01720h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The controlling and patterning of small droplets on a solid surface is of significant interest to understand interfacial phenomena and for practical applications. Among interfacial phenomena, the formation of interfacial droplets attracts scientists' attention, as the mechanism of this phenomenon where water molecules can spontaneously accumulate at the hydrophobic oil/solid interface is still not fully understood. Further investigation is needed to find out specifically where the driving force comes from and how to spatially arrange the interfacial droplets. Herein, self-assembled monolayers are formed on a gold substrate, and it turns out that the hydrophobic surface with a monolayer formed from HS(CH2)11CH3 could inhibit the formation of interfacial droplets; by contrast, the hydrophilic surfaces with monolayers formed from HS(CH2)11COOH, HS(CH2)11NH3·Cl and HS(CH2)11OH, all promote water accumulation. It suggests that the hydrogen bonding between the surface and water proves to be critical in inducing interfacial droplet formation but this has been neglected in past studies. Taking advantage of microcontact printing, the surface chemistry can be controlled at the micron scale and allows spatial arrangement of interfacial droplets at specific regions. This work moves a further step in understanding the mechanism of interfacial droplet formation, and can be potentially exploited for the collection of water and fabrication of microtemplates.
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Affiliation(s)
- Ran Zhang
- Key Laboratory of Organic Optoelectronics and Molecular Engineering of the Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China.
| | - Yao Wang
- Key Laboratory of Organic Optoelectronics and Molecular Engineering of the Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China.
| | - Zhongqiang Yang
- Key Laboratory of Organic Optoelectronics and Molecular Engineering of the Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China.
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Qian J, Arends GF, Zhang X. Surface Nanodroplets: Formation, Dissolution, and Applications. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:12583-12596. [PMID: 31132276 DOI: 10.1021/acs.langmuir.9b01051] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Droplets at solid-liquid interfaces play essential roles in a broad range of fields, such as compartmentalized chemical reactions and conversions, high-throughput analysis and sensing, and super-resolution near-field imaging. Our recent work has focused on understanding and controlling the nanodroplet formation on solid surfaces in ternary liquid mixtures. These surface nanodroplets resemble tiny liquid lenses with a typical height of <1 μm and a volume of subfemtoliters. The solvent exchange is based on the process of displacing a droplet liquid solution by a poor solvent to create a transient oversaturation for droplet formation. A quantitative understanding of growth dynamics of surface nanodroplets in ternary liquid mixtures not only provides insight into the liquid-liquid phase separation induced by solvent addition in general but also has made it possible to control the droplet size well. This review article will summarize our findings in the last ∼5 years from the research with our collaborators. The first part will explain the fundamental aspects that are key to the formation and stability of surface nanodroplets. In the second part, we will highlight the applications of nanodroplets in chemical analysis and functional surface fabrication and finally point out future directions in droplet-based applications.
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Affiliation(s)
- Jiasheng Qian
- Department of Chemical and Materials Engineering , University of Alberta , Alberta T6G 1H9 , Canada
| | - Gilmar F Arends
- Department of Chemical and Materials Engineering , University of Alberta , Alberta T6G 1H9 , Canada
| | - Xuehua Zhang
- Department of Chemical and Materials Engineering , University of Alberta , Alberta T6G 1H9 , Canada
- Physics of Fluids Group, Max-Planck-Center Twente for Complex Fluid Dynamics, Mesa+ Institute and J. M. Burgers Centre for Fluid Dynamics, Department of Science and Technology , University of Twente , P.O. Box 217, 7500 AE Enschede , The Netherlands
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Zhong X, Ren J, Chong KSL, Ong KS, Duan F. Wetting Transition at a Threshold Surfactant Concentration of Evaporating Sessile Droplets on a Patterned Surface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:4509-4517. [PMID: 30865459 DOI: 10.1021/acs.langmuir.9b00170] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Wetting transitions induced by varying the components in a solution of a drying droplet can lead to its evolving shape on a textured surface. It can provide new insights on liquid pattern control through manipulating droplet solutions. We show the pronounced transitions of wetting for surfactant solution droplets drying on a micropyramid-patterned surface. At low initial surfactant concentrations, the droplet maintains an octagonal shape until the end of drying. At intermediate initial surfactant concentrations, the early octagon spreads to a square, which later evolves to a stretched rectangle. At high initial surfactant concentrations, the droplet mainly exhibits the "octagon-to-square" transition, and the square shape is maintained until the end. The octagon-to-square transition occurs at similar temporal volume-averaged surfactant concentrations for the various initial surfactant concentrations. It results from the dependence of the surface energy change of spread over the micropyramid structure on the temporal volume-averaged surfactant concentration. At high initial surfactant concentrations, the accumulation of the surfactant near the contact line driven by outward flows could raise the local viscosity and enhance the pinning effect, leading to the great suppression of the "square-to-rectangle" transition.
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Affiliation(s)
- Xin Zhong
- School of Mechanical and Aerospace Engineering , Nanyang Technological University , 50 Nanyang Avenue , Singapore 639798 , Singapore
- State Key Laboratory of Multiphase Flow in Power Engineering , Xi'an Jiaotong University , Xi'an 710049 , P. R. China
| | - Junheng Ren
- School of Mechanical and Aerospace Engineering , Nanyang Technological University , 50 Nanyang Avenue , Singapore 639798 , Singapore
| | - Karen Siew-Ling Chong
- Institute of Materials Research and Engineering, A*Star , 2 Fusionopolis Way, Innovis, Level 9 , Singapore 138634 , Singapore
| | - Kian-Soo Ong
- Institute of Materials Research and Engineering, A*Star , 2 Fusionopolis Way, Innovis, Level 9 , Singapore 138634 , Singapore
| | - Fei Duan
- School of Mechanical and Aerospace Engineering , Nanyang Technological University , 50 Nanyang Avenue , Singapore 639798 , Singapore
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Feng W, Ueda E, Levkin PA. Droplet Microarrays: From Surface Patterning to High-Throughput Applications. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2018; 30:e1706111. [PMID: 29572971 DOI: 10.1002/adma.201706111] [Citation(s) in RCA: 107] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2017] [Revised: 11/29/2017] [Indexed: 05/09/2023]
Abstract
High-throughput screening of live cells and chemical reactions in isolated droplets is an important and growing method in areas ranging from studies of gene functions and the search for new drug candidates, to performing combinatorial chemical reactions. Compared with microfluidics and well plates, the facile fabrication, high density, and open structure endow droplet microarrays on planar surfaces with great potential in the development of next-generation miniaturized platforms for high-throughput applications. Surfaces with special wettability have served as substrates to generate and/or address droplets microarrays. Here, the formation of droplet microarrays with designed geometry on chemically prepatterned surfaces is briefly described and some of the newer and emerging applications of these microarrays that are currently being explored are highlighted. Next, some of the available technologies used to add (bio-)chemical libraries to each droplet in parallel are introduced. Current challenges and future prospects that would benefit from using such droplet microarrays are also discussed.
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Affiliation(s)
- Wenqian Feng
- Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Hermann-von-Helmholtz Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
| | - Erica Ueda
- Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Hermann-von-Helmholtz Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
| | - Pavel A Levkin
- Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Hermann-von-Helmholtz Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
- Institute of Organic Chemistry, Karlsruhe Institute of Technology, 76131, Karlsruhe, Germany
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Zhong X, Ren J, Chong KSL, Ong KS, Duan F. Controlling Octagon-to-Square Wetting Interface Transition of Evaporating Sessile Droplet through Surfactant on Microtextured Surface. ACS APPLIED MATERIALS & INTERFACES 2018; 10:11425-11429. [PMID: 29582984 DOI: 10.1021/acsami.8b02509] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Producing and maintaining specific liquid patterns during evaporation holds great potential for techniques of printing and coating. Here we report the control over the evolution of surfactant solution droplets on the micropyramid substrates during evaporation. The polygonal droplet shape is achieved during the drying rather than solely at the beginning. As the initial surfactant concentration is 0.04 mM, the droplet maintains its initial octagonal shape throughout the lifetime. Interestingly, the initial octagonal shape transforms into a square during the evaporation as the initial surfactant concentration reaches 0.8 mM. These findings can shed light on wetting pattern control for complex solutions required in various applications.
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Affiliation(s)
- Xin Zhong
- School of Mechanical and Aerospace Engineering , Nanyang Technological University , 50 Nanyang Avenue , Singapore 639798 , Singapore
| | - Junheng Ren
- School of Mechanical and Aerospace Engineering , Nanyang Technological University , 50 Nanyang Avenue , Singapore 639798 , Singapore
| | - Karen Siew-Ling Chong
- Institute of Materials Research and Engineering , A*Star , 2 Fusionopolis Way, Innovis, Level 9 , Singapore 138634 , Singapore
| | - Kian-Soo Ong
- Institute of Materials Research and Engineering , A*Star , 2 Fusionopolis Way, Innovis, Level 9 , Singapore 138634 , Singapore
| | - Fei Duan
- School of Mechanical and Aerospace Engineering , Nanyang Technological University , 50 Nanyang Avenue , Singapore 639798 , Singapore
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Bao L, Spandan V, Yang Y, Dyett B, Verzicco R, Lohse D, Zhang X. Flow-induced dissolution of femtoliter surface droplet arrays. LAB ON A CHIP 2018; 18:1066-1074. [PMID: 29487930 DOI: 10.1039/c7lc01321c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The dissolution of liquid nanodroplets is a crucial step in many applied processes, such as separation and dispersion in the food industry, crystal formation of pharmaceutical products, concentrating and analysis in medical diagnosis, and drug delivery in aerosols. In this work, using both experiments and numerical simulations, we quantitatively study the dissolution dynamics of femtoliter surface droplets in a highly ordered array under a uniform flow. Our results show that the dissolution of femtoliter droplets strongly depends on their spatial positions relative to the flow direction, drop-to-drop spacing in the array, and the imposed flow rate. In some particular cases, the droplet at the edge of the array can dissolve about 30% faster than the ones located near the centre. The dissolution rate of the droplet increases by 60% as the inter-droplet spacing is increased from 2.5 μm to 20 μm. Moreover, the droplets close to the front of the flow commence to shrink earlier than those droplets in the center of the array. The average dissolution rate is faster for the faster flow. As a result, the dissolution time (Ti) decreases with the Reynolds number (Re) of the flow as Ti ∝ Re-3/4. The experimental results are in good agreement with the numerical simulations where the advection-diffusion equation for the concentration field is solved and the concentration gradient on the surface of the drop is computed. The findings suggest potential approaches to manipulate nanodroplet sizes in droplet arrays simply by dissolution controlled by an external flow. The obtained droplets with varying curvatures may serve as templates for generating multifocal microlenses in one array.
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Affiliation(s)
- Lei Bao
- Soft Matter & Interfaces Group, School of Engineering, RMIT University, Melbourne, VIC 3001, Australia
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Kumar A, Raj R. Droplets on Microdecorated Surfaces: Evolution of the Polygonal Contact Line. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:4854-4862. [PMID: 28447801 DOI: 10.1021/acs.langmuir.7b00559] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Interaction of liquids with surfaces is ubiquitous in our physical environment as well as many engineering applications. Recent advances on this topic have not only provided us with valuable insight into nature's design, but also enabled improved fluidic manipulation for liquid-based printing applications such as biomicroarrays for protein and DNA sequencing, multicolor polymer-based LED displays, inkjet printing, and solder droplet printing, among others. For example, droplet contact lines, which are typically circular on a smooth and homogeneous surface, when deposited on a microdecorated surface may take various common polygonal shapes such as squares, rectangles, hexagons, octagons and dodecagons. These polygonal contact line shapes are highly stable due to the local energy barriers associated with the anisotropy in depinning contact angles. In addition to the knowledge of the eventual contact line shapes, liquid-based printing applications would require accurate prediction of temporal evolution of contact line on these surfaces. In this work, we model and validate the evolution of droplets on microdecorated surfaces with microgoniometry experiments reported in the literature. We show that various metastable contact line shapes are formed in-between the well-known stable polygonal contact line shapes usually observed in experiments. We elucidate that the movement of the contact line between adjacent micropillars can primarily be categorized as primary zipping and transition zipping. Primary zipping occurs when the contact line moves radially outward to the next row of pillars, often resulting in the formation of a metastable contact line shape. Conversely, metastable droplet attains stable polygonal contact line shape via transition zipping wherein the contact line advances sideways. We believe that the current simulation approach can be effectively utilized for designing optimized textured surfaces for applications where control over liquid supply via surface design is required.
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Affiliation(s)
- Alok Kumar
- Thermal and Fluid Transport Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Patna, Bihar 801103, India
| | - Rishi Raj
- Thermal and Fluid Transport Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Patna, Bihar 801103, India
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Peng S, Zhang X. Simple Nanodroplet Templating of Functional Surfaces with Tailored Wettability and Microstructures. Chem Asian J 2017; 12:1538-1544. [DOI: 10.1002/asia.201700358] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Revised: 04/06/2017] [Indexed: 12/19/2022]
Affiliation(s)
- Shuhua Peng
- Soft Matter & Interfaces Group; School of Engineering; RMIT University; Melbourne VIC 3001 Australia
| | - Xuehua Zhang
- Soft Matter & Interfaces Group; School of Engineering; RMIT University; Melbourne VIC 3001 Australia
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