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Poles M, Meggiolaro A, Cremaschini S, Marinello F, Filippi D, Pierno M, Mistura G, Ferraro D. Shaking Device for Homogeneous Dispersion of Magnetic Beads in Droplet Microfluidics. SENSORS (BASEL, SWITZERLAND) 2023; 23:5399. [PMID: 37420565 DOI: 10.3390/s23125399] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Revised: 05/26/2023] [Accepted: 06/05/2023] [Indexed: 07/09/2023]
Abstract
Magnetic beads (or particles) having a size between 1 and 5 µm are largely used in many biochemical assays devoted to both purification and quantification of cells, nucleic acids, or proteins. Unfortunately, the use of these beads within microfluidic devices suffers from natural precipitation because of their size and density. The strategies applied thus far to cells or polymeric particles cannot be extended to magnetic beads, mainly due to their magnetization and their higher densities. We report an effective shaking device capable of preventing the sedimentation of beads that are stored in a custom PCR tube. After the characterization of the operating principle, the device is validated for magnetic beads in droplets, leading to an equal distribution between the droplets, barely affecting their generation.
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Affiliation(s)
- Maria Poles
- Department of Physics and Astronomy, University of Padua, Via Marzolo 8, 35131 Padua, Italy
| | - Alessio Meggiolaro
- Department of Physics and Astronomy, University of Padua, Via Marzolo 8, 35131 Padua, Italy
| | - Sebastian Cremaschini
- Department of Physics and Astronomy, University of Padua, Via Marzolo 8, 35131 Padua, Italy
| | - Filippo Marinello
- Department of Physics and Astronomy, University of Padua, Via Marzolo 8, 35131 Padua, Italy
| | - Daniele Filippi
- Department of Physics and Astronomy, University of Padua, Via Marzolo 8, 35131 Padua, Italy
| | - Matteo Pierno
- Department of Physics and Astronomy, University of Padua, Via Marzolo 8, 35131 Padua, Italy
| | - Giampaolo Mistura
- Department of Physics and Astronomy, University of Padua, Via Marzolo 8, 35131 Padua, Italy
| | - Davide Ferraro
- Department of Physics and Astronomy, University of Padua, Via Marzolo 8, 35131 Padua, Italy
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2
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Dimitriadis T, Stendardo L, Tagliaro I, Coclite AM, Antonini C, Maitra T. Capillary-Driven Water Transport by Contrast Wettability-Based Durable Surfaces. ACS APPLIED MATERIALS & INTERFACES 2023. [PMID: 37235501 DOI: 10.1021/acsami.3c03840] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Controlling water transport and management is crucial for continuous and reliable system operation in harsh weather conditions. Passive strategies based on nonwetting surfaces are desirable, but so far, the implementation of superhydrophobic coatings into real-world applications has been limited by durability issues and, in some cases, lack of compliance with environmental regulations. Inspired by surface patterning observed on living organisms, in this study we have developed durable surfaces based on contrast wettability for capillary-driven water transport and management. The surface fabrication process combines a hydrophobic coating with hard-anodized aluminum patterning, using a scalable femtosecond laser microtexturing technique. The concept targets heavy-duty engineering applications; particularly in aggressive weather conditions where corrosion is prevalent and typically the anodic aluminum oxide-based coating is used to protect the surface from corrosion, the concept has been validated on anodic aluminum oxide coated aluminum alloy substrates. Such substrates with contrast wettable characteristics show long-term durability in both natural and lab-based artificial UV and corrosion tests where superhydrophobic coatings tend to degrade.
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Affiliation(s)
- Theodoros Dimitriadis
- Institute of Solid-State Physics, Graz University of Technology, Graz 8010, Austria
- Department of Engineering, FT Technologies (UK) Ltd., Sunbury-on-Thames TW16 7DX, United Kingdom
| | - Luca Stendardo
- Department of Materials Science, University of Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy
| | - Irene Tagliaro
- Department of Materials Science, University of Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy
| | - Anna Maria Coclite
- Institute of Solid-State Physics, Graz University of Technology, Graz 8010, Austria
| | - Carlo Antonini
- Department of Materials Science, University of Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy
| | - Tanmoy Maitra
- Department of Engineering, FT Technologies (UK) Ltd., Sunbury-on-Thames TW16 7DX, United Kingdom
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3
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Carneri M, Ferraro D, Azarpour A, Meggiolaro A, Cremaschini S, Filippi D, Pierno M, Zanchetta G, Mistura G. Sliding and rolling of yield stress fluid droplets on highly slippery lubricated surfaces. J Colloid Interface Sci 2023; 644:487-495. [PMID: 37146485 DOI: 10.1016/j.jcis.2023.04.075] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Revised: 04/10/2023] [Accepted: 04/18/2023] [Indexed: 05/07/2023]
Abstract
HYPOTHESIS Droplets of yield stress fluids (YSFs), i.e. fluids that can flow only if they are subjected to a stress above a critical value and otherwise deform like solids, hardly move on solid surfaces due to their high viscosity. The use of highly slippery lubricated surfaces can shed light on the mobility of YSF droplets, which include everyday soft materials, such as toothpaste or mayonnaise, and biological fluids, such as mucus. EXPERIMENTS The spreading and mobility of droplets of aqueous solutions of swollen Carbopol microgels were studied on lubricant infused surfaces. These solutions represent a model system of YSFs. Dynamical phase diagrams were established by varying the concentration of the solutions and the inclination angle of the surfaces. FINDINGS Carbopol droplets deposited on lubricated surfaces could move even at low inclination angles. The droplets were found to slide because of the slip of the flowing oil that covered the solid substrate. However, as the descending speed increased, the droplets rolled down. Rolling was favored at high inclinations and low concentrations. A simple criterion based on the ratio between the yield stress of the Carbopol suspensions and the gravitational stress acting on the Carbopol droplets was found to nicely identify the transition between the two regimes.
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Affiliation(s)
- Mattia Carneri
- Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, via Marzolo 8, 35131 Padova, Italy
| | - Davide Ferraro
- Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, via Marzolo 8, 35131 Padova, Italy
| | - Afshin Azarpour
- Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, Università di Milano, via F.lli Cervi 93, 20054 Segrate, Italy
| | - Alessio Meggiolaro
- Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, via Marzolo 8, 35131 Padova, Italy
| | - Sebastian Cremaschini
- Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, via Marzolo 8, 35131 Padova, Italy
| | - Daniele Filippi
- Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, via Marzolo 8, 35131 Padova, Italy
| | - Matteo Pierno
- Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, via Marzolo 8, 35131 Padova, Italy
| | - Giuliano Zanchetta
- Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, Università di Milano, via F.lli Cervi 93, 20054 Segrate, Italy.
| | - Giampaolo Mistura
- Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, via Marzolo 8, 35131 Padova, Italy.
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4
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Liu M, Li J, Zhou X, Li J, Feng S, Cheng Y, Wang S, Wang Z. Inhibiting Random Droplet Motion on Hot Surfaces by Engineering Symmetry-Breaking Janus-Mushroom Structure. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2020; 32:e1907999. [PMID: 32078203 DOI: 10.1002/adma.201907999] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Revised: 02/08/2020] [Indexed: 06/10/2023]
Abstract
Concentrating impacting droplets onto a localized hotspot and inducing them to remain in a preferential heat transfer mode is essential for efficient thermal management such as spray cooling. Conventionally, droplets impacting on hot surfaces can randomly bounce off without becoming fully evaporated, resulting in low heat transfer efficiency. Although the directional and guided transport of impacting droplets to a preferential location can be achieved through the introduction of a structural gradient, the manifestation of such a motion requires the meticulous control of the spatial location where the droplet is released. Here, a novel surface consisting of regularly patterned posts with Janus-mushroom structure (JMS) is designed, in which the sidewalls of the individual posts are decorated with straight and curved morphologies. It is revealed that such structural symmetry-breaking in the individual posts leads to directional liquid penetration and vapor flow toward the straight sidewall, and also reduces the work of adhesion, altogether triggering collective and preferential droplet transport at a high temperature. By surrounding a conventional surface with JMS endowed with favorable directionality, it is possible to concentrate small impacting droplets preferentially onto a localized hotspot to achieve enhanced cooling efficiency.
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Affiliation(s)
- Minjie Liu
- Department of Mechanical Engineering, City University of Hong Kong, Hong Kong, 999077, China
| | - Jing Li
- Department of Mechanical Engineering, City University of Hong Kong, Hong Kong, 999077, China
| | - Xiaofeng Zhou
- Shanghai Key Laboratory of Multidimensional Information Processing, School of Communication and Electronic Engineering, East China Normal University, Shanghai, 200241, China
| | - Jiaqian Li
- Department of Mechanical Engineering, City University of Hong Kong, Hong Kong, 999077, China
| | - Shile Feng
- Department of Mechanical Engineering, City University of Hong Kong, Hong Kong, 999077, China
| | - Yaqi Cheng
- Department of Mechanical Engineering, City University of Hong Kong, Hong Kong, 999077, China
| | - Steven Wang
- Department of Mechanical Engineering, City University of Hong Kong, Hong Kong, 999077, China
| | - Zuankai Wang
- Department of Mechanical Engineering, City University of Hong Kong, Hong Kong, 999077, China
- Shenzhen Research Institute of City University of Hong Kong, Shenzhen, 518057, China
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5
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Ma B, Shan L, Dogruoz B, Agonafer D. Evolution of Microdroplet Morphology Confined on Asymmetric Micropillar Structures. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:12264-12275. [PMID: 31424229 DOI: 10.1021/acs.langmuir.9b01410] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The design of topological features to control the spreading of liquid has been widely investigated. Micropillar structures, for example, can retain stable droplets on the tip by inhibiting the contact line from advancing over a sharp solid edge. The pinning behavior of droplets on noncircular pillars, however, has received little attention. In this study, we analyze the retention of microdroplets with high and low surface tensions on axisymmetric and asymmetric porous micropillar structures. Circular, square, and triangular structures fabricated on silicon substrates are used to characterize the dynamic behavior of droplets before and after bursting. The critical pinning conditions are based on the visualization and pressure measurements of droplets. A theoretical model is developed based on a free energy analysis for predicting the change in pressure as the working fluid advances on the micropillar. For high surface tension liquids (e.g., water), the maximum pressure occurs when the contact line is pinned along the edge of the inner pore. For low surface tension liquids (e.g., Isopropanol and Novec 7500), the maximum pressure occurs when the contact line is pinned along the outer edge of the structure. The theoretical and experimental results demonstrate how a droplet pinned atop a triangular micropillar exhibits the smallest critical volume at the bursting moment. When using IPA solution (γ = 23 mN/m) and Novec 7500 (γ = 16 mN/m) as the working fluids, a change in the micropillar shape from circle to triangle, respectively, yields a 83% and 76% reduction in the critical burst volume. Meanwhile, the bursting pressure increases from 172 to 300 Pa and from 127 to 216 Pa for IPA and Novec 7500, respectively. These findings provide new insights to the rational design of surface micro/nanoengineered structures for tuning the surface wetting characteristics in scientific and engineering applications.
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Affiliation(s)
- Binjian Ma
- Mechanical Engineering and Materials Science , Washington University in St. Louis , St. Louis , Missouri 63130 , United States
| | - Li Shan
- Mechanical Engineering and Materials Science , Washington University in St. Louis , St. Louis , Missouri 63130 , United States
| | - Baris Dogruoz
- Cisco Systems Inc. , 425 E Tasman Dr. , San Jose , California 95134 , United States
| | - Damena Agonafer
- Mechanical Engineering and Materials Science , Washington University in St. Louis , St. Louis , Missouri 63130 , United States
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6
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Semprebon C, Herrmann C, Liu BY, Seemann R, Brinkmann M. Shape Evolution of Droplets Growing on Linear Microgrooves. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:10498-10511. [PMID: 30088772 DOI: 10.1021/acs.langmuir.8b01712] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Anisotropic spreading of liquids and elongated droplet shapes are often encountered on surfaces decorated with a periodic micropattern of linear surface topographies. Numerical calculations and wetting experiments show that the shape evolution of droplets that are slowly growing on a surface with parallel grooves can be grouped into two distinct morphological regimes. In the first regime, the liquid of the growing droplet spreads only into the direction parallel to the grooves. In the second regime, the three-phase contact line advances also perpendicular to the grooves, whereas the growing droplets approach a scale-invariant shape. Here, we demonstrate that shapes of droplets in contact with a large number of linear grooves are identical to the shapes of droplets confined to a plane chemical stripe, where this mapping of shapes is solely based on the knowledge of the cross section of the linear grooves and the material contact angle. The spectrum of interfacial shapes on the chemical stripe can be exploited to predict the particular growth mode and the asymptotic value of the base eccentricity in the limit of droplets covering a large number of grooves. The proposed model shows an excellent agreement with experimentally observed base eccentricities for droplets on grooves of various cross sections. The universality of the model is underlined by the accurate match with available literature data for droplet eccentricities on parallel chemical stripes.
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Affiliation(s)
- Ciro Semprebon
- Max-Planck Institute for Dynamics and Self-Organization , 37077 Göttingen , Germany
- Smart Materials & Surfaces Laboratory, Department of Mathematics, Physics and Electrical Engineering , Northumbria University , Newcastle NE7 7XA , U.K
| | - Carsten Herrmann
- Experimental Physics , Saarland University , 66123 Saarbrücken , Germany
| | - Bang-Yan Liu
- Experimental Physics , Saarland University , 66123 Saarbrücken , Germany
| | - Ralf Seemann
- Max-Planck Institute for Dynamics and Self-Organization , 37077 Göttingen , Germany
- Experimental Physics , Saarland University , 66123 Saarbrücken , Germany
| | - Martin Brinkmann
- Max-Planck Institute for Dynamics and Self-Organization , 37077 Göttingen , Germany
- Experimental Physics , Saarland University , 66123 Saarbrücken , Germany
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7
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Varagnolo S, Filippi D, Mistura G, Pierno M, Sbragaglia M. Stretching of viscoelastic drops in steady sliding. SOFT MATTER 2017; 13:3116-3124. [PMID: 28393163 DOI: 10.1039/c7sm00352h] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The sliding of non-Newtonian drops down planar surfaces results in a complex, entangled balance between interfacial forces and non-linear viscous dissipation, which has been scarcely inspected. In particular, a detailed understanding of the role played by the polymer flexibility and the resulting elasticity of the polymer solution is still lacking. To this aim, we have considered polyacrylamide (PAA) solutions of different molecular weights, suspended either in water or in glycerol/water mixtures. In contrast to drops of stiff polymers, drops of flexible polymers exhibit a remarkable elongation in steady sliding. This difference is most likely attributed to variation of viscous bending as a consequence of variation of shear thinning. Moreover, an "optimal elasticity" of the polymer seems to be required for this drop elongation to be visible. We have complemented experimental results with numerical simulations of a viscoelastic FENE-P drop. This has been a decisive step to unraveling how a change of the elastic parameters (e.g. polymer relaxation time, maximum extensibility) affects the dimensionless sliding velocity.
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Affiliation(s)
- Silvia Varagnolo
- Dipartimento di Fisica e Astronomia "Galileo Galilei"- DFA, Università di Padova, via Marzolo, 8-35131 Padova PD, Italy.
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Varagnolo S, Raccanello F, Pierno M, Mistura G, Moffa M, Persano L, Pisignano D. Highly sticky surfaces made by electrospun polymer nanofibers. RSC Adv 2017; 7:5836-5842. [PMID: 29755734 PMCID: PMC5946826 DOI: 10.1039/c6ra24922a] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2016] [Accepted: 10/31/2016] [Indexed: 01/07/2023] Open
Abstract
We report on a comprehensive study of the unique adhesive properties of mats of polymethylmethacrylate (PMMA) nanofibers produced by electrospinning. Fibers are deposited on glass, with varying of the diameter and the relative orientation of the polymer filaments (random vs. aligned configuration). While no significant variation is observed in the static contact angle (∼130°) of deposited water drops upon changing the average fiber diameter up to the micrometer scale, fibers are found to exhibit unequalled water adhesion. Placed vertically, they can hold up water drops as large as 60 μL, more than twice the values typically obtained with hairy surfaces prepared by different methods. For aligned fibers with anisotropic wetting behavior, the maximum volume measured in the direction perpendicular to the fibers goes up to 90 μL. This work suggests new routes to tailor the wetting behavior on extended areas by nanofiber coatings, with possible applications in adsorbing and catalytic surfaces, microfluidic devices, and filtration technologies.
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Affiliation(s)
- S Varagnolo
- Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, via Marzolo 8, I-35131, Padova, Italy.
| | - F Raccanello
- Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, via Marzolo 8, I-35131, Padova, Italy.
| | - M Pierno
- Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, via Marzolo 8, I-35131, Padova, Italy.
| | - G Mistura
- Dipartimento di Fisica e Astronomia "G. Galilei", Università di Padova, via Marzolo 8, I-35131, Padova, Italy.
| | - M Moffa
- NEST, Istituto Nanoscienze-CNR, Piazza S. Silvestro 12, I-56127 Pisa, Italy.
| | - L Persano
- NEST, Istituto Nanoscienze-CNR, Piazza S. Silvestro 12, I-56127 Pisa, Italy.
| | - D Pisignano
- NEST, Istituto Nanoscienze-CNR, Piazza S. Silvestro 12, I-56127 Pisa, Italy.
- Dipartimento di Matematica e Fisica "Ennio De Giorgi", Università del Salento, via Arnesano, I-73100, Lecce, Italy
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9
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Semprebon C, Varagnolo S, Filippi D, Perlini L, Pierno M, Brinkmann M, Mistura G. Deviation of sliding drops at a chemical step. SOFT MATTER 2016; 12:8268-8273. [PMID: 27510324 DOI: 10.1039/c6sm01077f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The motion of partially wetting liquid drops in contact with a solid surface is strongly affected by contact angle hysteresis and interfacial pinning. However, the majority of models proposed for drops sliding over chemical surface patterns consistently neglect the difference between advancing and receding contact angles. In this article, we present a joint experimental and numerical study of the interaction of gravity-driven drops with a chemical step formed at the junction between a hydrophilic and a hydrophobic region. It demonstrates the strong impact of a contact angle hysteresis contrast on the motion of drops at a linear chemical step. Surprisingly, the smallest driving force required to drag the drop across the step onto the lower hydrophobic surface is not observed at a right angle of incidence. Our model reveals that the non-monotonous response of this passive drop 'filter' is solely due to the higher advancing contact angle on the lower surface, and creates an instance where drop motion is affected by dissipation at the contact line rather than by surface energy.
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Affiliation(s)
- Ciro Semprebon
- Department of Mechanical Engineering, University of Edinburgh, Edinburgh EH9 3FB, UK.
| | - Silvia Varagnolo
- Dipartimento di Fisica e Astronomia 'G.Galilei' - DFA, Università di Padova, via Marzolo 8, 35131 Padova, Italy.
| | - Daniele Filippi
- Dipartimento di Fisica e Astronomia 'G.Galilei' - DFA, Università di Padova, via Marzolo 8, 35131 Padova, Italy.
| | - Luca Perlini
- Dipartimento di Fisica e Astronomia 'G.Galilei' - DFA, Università di Padova, via Marzolo 8, 35131 Padova, Italy.
| | - Matteo Pierno
- Dipartimento di Fisica e Astronomia 'G.Galilei' - DFA, Università di Padova, via Marzolo 8, 35131 Padova, Italy.
| | - Martin Brinkmann
- Experimental Physics, Saarland University, 66123 Saarbrücken, Germany
| | - Giampaolo Mistura
- Dipartimento di Fisica e Astronomia 'G.Galilei' - DFA, Università di Padova, via Marzolo 8, 35131 Padova, Italy.
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10
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Nanostructure Formation by controlled dewetting on patterned substrates: A combined theoretical, modeling and experimental study. Sci Rep 2016; 6:32398. [PMID: 27580943 PMCID: PMC5007673 DOI: 10.1038/srep32398] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 08/04/2016] [Indexed: 11/18/2022] Open
Abstract
We perform systematic two-dimensional energetic analysis to study the stability of various nanostructures formed by dewetting solid films deposited on patterned substrates. Our analytical results show that by controlling system parameters such as the substrate surface pattern, film thickness and wetting angle, a variety of equilibrium nanostructures can be obtained. Phase diagrams are presented to show the complex relations between these system parameters and various nanostructure morphologies. We further carry out both phase field simulations and dewetting experiments to validate the analytically derived phase diagrams. Good agreements between the results from our energetic analyses and those from our phase field simulations and experiments verify our analysis. Hence, the phase diagrams presented here provide guidelines for using solid-state dewetting as a tool to achieve various nanostructures.
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11
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Ekgasit S, Kaewmanee N, Jangtawee P, Thammacharoen C, Donphoongpri M. Elastomeric PDMS Planoconvex Lenses Fabricated by a Confined Sessile Drop Technique. ACS APPLIED MATERIALS & INTERFACES 2016; 8:20474-82. [PMID: 27419266 DOI: 10.1021/acsami.6b06305] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The ubiquity of high quality smartphones at affordable prices not only accelerated the social penetration in the global population but also promoted nontraditional usage of smartphones as point-of-care medical diagnostic devices, sensors, and portable digital microscopes. This paper reveals a simple, rapid, cost-effective, and template-free technique for mass-scale production of an elastomeric PDMS (ePDMS) planoconvex lens capable of converting a smartphone into a portable digital microscope. By taking advantage of the resistance to spreading of liquid by a sharp edge, highly stable spherical cap of viscous liquid PDMS (lPDMS) on a smooth PMMA circular disk was fabricated. The axisymmetric spreading of lPDMS under the gravitational force and interfacial tension force enable the formation of spherical cap with a certain radius of curvature. A thermal treatment at 80 °C for 30 min cured the spherical cap lPDMS into a bubble-free ePDMS planoconvex lens. Lenses with focal lengths of 55.2-3.4 mm could be reproducibly fabricated by adjusting the volume of dispensed lPDMSs and diameter of PMMA disks. High-resolution panoramic microscope images without a distortion of small cylindrical object could be constructed on-the-fly using the imbedded smartphone app. Applications of the smartphone digital microscope equipped with an ePDMS planoconvex lens for imaging of micro printings, gun shot residues, cylindrical objects, and bullet toolmarks were explored.
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Affiliation(s)
- S Ekgasit
- Sensor Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University , 254 Phyathai Road, Patumwan, Bangkok 10330, Thailand
| | - N Kaewmanee
- Sensor Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University , 254 Phyathai Road, Patumwan, Bangkok 10330, Thailand
| | - P Jangtawee
- Sensor Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University , 254 Phyathai Road, Patumwan, Bangkok 10330, Thailand
| | - C Thammacharoen
- Sensor Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University , 254 Phyathai Road, Patumwan, Bangkok 10330, Thailand
| | - M Donphoongpri
- Central Institute of Forensic Science (CIFS) , 8th Floor, B Building, The Government Complex, Chaengwatthana Road, Laksi, Bangkok 10210 Thailand
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12
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Dokowicz M, Nowicki W. Morphological Transitions of Droplets Wetting a Series of Triangular Grooves. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:7259-7264. [PMID: 27347695 DOI: 10.1021/acs.langmuir.6b01275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Morphology and thermodynamics of a microdroplet deposited on a grooved inhomogeneous surface with triangular cross section of the grooves were studied by computer simulations with the use of Surface Evolver program. With increasing volume of the droplet, it initially spreads along the series of grooves assuming the filament-like morphology. After reaching a certain volume, the surface wetted by the droplet is reduced and the droplet assumes the bulge morphology or spreads over the surface bordering on the groove initially occupied (it can be either a neighboring groove or a flat surface). The character of the process is determined by the geometry of the edge of the inhomogeneity studied. The effect described also depends on the number of grooves G and the Young contact angle θY. The change in the shape of the droplet becomes more pronounced with decreasing θY and G. Above a certain number of grooves, in the range of contact angles studied (e.g., G > 6 if θY = 70° and G > 4 if θY = 75°), no morphological transition of the droplet was observed.
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Affiliation(s)
- Marcin Dokowicz
- Faculty of Chemistry, Adam Mickiewicz University in Poznań , Umultowska 89b, 61-614 Poznań, Poland
| | - Waldemar Nowicki
- Faculty of Chemistry, Adam Mickiewicz University in Poznań , Umultowska 89b, 61-614 Poznań, Poland
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Orejon D, Shardt O, Waghmare PR, Kumar Gunda NS, Takata Y, Mitra SK. Droplet migration during condensation on chemically patterned micropillars. RSC Adv 2016. [DOI: 10.1039/c6ra03862j] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Droplet migration from a micropillar's side to its top due to the wettability gradient imposed by our novel fabrication process.
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Affiliation(s)
- Daniel Orejon
- International Institute for Carbon-Neutral Energy Research (WPI-I2CNER)
- Kyushu University
- Fukuoka 819-0395
- Japan
- Department of Mechanical Engineering
| | - Orest Shardt
- Department of Mechanical Engineering
- University of Alberta
- Edmonton
- Canada
- Department of Mechanical and Aerospace Engineering
| | | | - Naga Siva Kumar Gunda
- Micro & Nano-scale Transport Laboratory
- Department of Mechanical Engineering
- Lassonde School of Engineering
- York University
- Toronto M3J 1P3
| | - Yasuyuki Takata
- International Institute for Carbon-Neutral Energy Research (WPI-I2CNER)
- Kyushu University
- Fukuoka 819-0395
- Japan
- Department of Mechanical Engineering
| | - Sushanta K. Mitra
- Micro & Nano-scale Transport Laboratory
- Department of Mechanical Engineering
- Lassonde School of Engineering
- York University
- Toronto M3J 1P3
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14
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Varagnolo S, Mistura G, Pierno M, Sbragaglia M. Sliding droplets of Xanthan solutions: A joint experimental and numerical study. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2015; 38:126. [PMID: 26614497 DOI: 10.1140/epje/i2015-15126-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 11/04/2015] [Indexed: 06/05/2023]
Abstract
We have investigated the sliding of droplets made of solutions of Xanthan, a stiff rodlike polysaccharide exhibiting a non-Newtonian behavior, notably characterized by a shear thinning viscosity accompanied by the emergence of normal stress difference as the polymer concentration is increased. These experimental results are quantitatively compared with those of Newtonian fluids (water). The impact of the non-Newtonian behavior on the sliding process was shown through the relation between the average dimensionless velocity (i.e. the capillary number) and the dimensionless volume forces (i.e. the Bond number). To this aim, it is needed to define operative strategies to compute the capillary number for the shear thinning fluids and compare with the corresponding Newtonian case. The resulting capillary number for the Xanthan solutions scales linearly with the Bond number at small inclinations, as well known for Newtonian fluids, while it shows a plateau as the Bond number is increased. Experimental data were complemented with lattice Boltzmann numerical simulations of sliding droplets, aimed to disentangle the specific contribution of shear thinning and elastic effects on the sliding behavior. In particular the deviation from the linear (Newtonian) trend is more likely attributed to the emergence of normal stresses inside the non-Newtonian droplet.
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Affiliation(s)
- Silvia Varagnolo
- Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Università di Padova, Via Marzolo, 8, 35131, Padova, Italy.
| | - Giampaolo Mistura
- Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Università di Padova, Via Marzolo, 8, 35131, Padova, Italy
| | - Matteo Pierno
- Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Università di Padova, Via Marzolo, 8, 35131, Padova, Italy
| | - Mauro Sbragaglia
- Department of Physics and INFN, University of "Tor Vergata", Via della Ricerca Scientifica 1, 00133, Rome, Italy
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15
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Baldelli A, Boraey MA, Nobes DS, Vehring R. Analysis of the Particle Formation Process of Structured Microparticles. Mol Pharm 2015; 12:2562-73. [DOI: 10.1021/mp500758s] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Alberto Baldelli
- Department
of Mechanical
Engineering, University of Alberta, 4-9 Mechanical Engineering Building, Edmonton, AB, T6G 2G8, Canada
| | - Mohammed A. Boraey
- Department
of Mechanical
Engineering, University of Alberta, 4-9 Mechanical Engineering Building, Edmonton, AB, T6G 2G8, Canada
| | - David S. Nobes
- Department
of Mechanical
Engineering, University of Alberta, 4-9 Mechanical Engineering Building, Edmonton, AB, T6G 2G8, Canada
| | - Reinhard Vehring
- Department
of Mechanical
Engineering, University of Alberta, 4-9 Mechanical Engineering Building, Edmonton, AB, T6G 2G8, Canada
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16
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Tsoumpas Y, Dehaeck S, Galvagno M, Rednikov A, Ottevaere H, Thiele U, Colinet P. Nonequilibrium Gibbs' criterion for completely wetting volatile liquids. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:11847-11852. [PMID: 25222133 DOI: 10.1021/la502708f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
During the spreading of a liquid over a solid substrate, the contact line can stay pinned at sharp edges until the contact angle exceeds a critical value. At (or sufficiently near) equilibrium, this is known as Gibbs' criterion. Here, we show both experimentally and theoretically that, for completely wetting volatile liquids, there also exists a dynamically-produced contribution to the critical angle for depinning, which increases with the evaporation rate. This suggests that one may introduce a simple modification of the Gibbs' criterion for (de)pinning that accounts for the nonequilibrium effect of evaporation.
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Affiliation(s)
- Yannis Tsoumpas
- TIPs (Transfers, Interfaces and Processes), Université Libre de Bruxelles , CP 165/67, Av. F.D. Roosevelt 50, 1050 Brussels, Belgium
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17
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Varagnolo S, Schiocchet V, Ferraro D, Pierno M, Mistura G, Sbragaglia M, Gupta A, Amati G. Tuning drop motion by chemical patterning of surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:2401-9. [PMID: 24533817 DOI: 10.1021/la404502g] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
We report the results of extensive experimental studies of the sliding of water drops on chemically heterogeneous surfaces formed by square and triangular hydrophobic domains printed on glass surfaces and arranged in various symmetric patterns. Overall, the critical Bond number, that is, the critical dimensionless force needed to depin the drop, is found to be strongly affected by the shape and the spatial arrangement of the domains. Soon after the droplet begins to move, stick-slip motion is observed on all surfaces, although it is less pronounced than that on striped surfaces. On the triangular patterns, anisotropic behavior is found with drops sliding down faster when the tips of the glass hydrophilic triangles are pointing in the down-plane direction. Away from the critical Bond number, the dynamic regime depends mainly on the static contact angle and weakly on the actual surface pattern. Lattice Boltzmann numerical simulations are performed to validate the experimental results and test the importance of the viscous ratio between the droplet phase and the outer phase.
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Affiliation(s)
- S Varagnolo
- CNISM and Dipartimento di Fisica e Astronomia G. Galilei, Università di Padova , via Marzolo 8, 35131 Padova, Italy
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18
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Sbragaglia M, Biferale L, Amati G, Varagnolo S, Ferraro D, Mistura G, Pierno M. Sliding drops across alternating hydrophobic and hydrophilic stripes. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:012406. [PMID: 24580236 DOI: 10.1103/physreve.89.012406] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Indexed: 05/14/2023]
Abstract
We perform a joint numerical and experimental study to systematically characterize the motion of 30 μl drops of pure water and of ethanol in water solutions, sliding over a periodic array of alternating hydrophobic and hydrophilic stripes with a large wettability contrast and a typical width of hundreds of microns. The fraction of the hydrophobic areas has been varied from about 20% to 80%. The effects of the heterogeneous patterning can be described by a renormalized value of the critical Bond number, i.e., the critical dimensionless force needed to depin the drop before it starts to move. Close to the critical Bond number we observe a jerky motion characterized by an evident stick-slip dynamics. As a result, dissipation is strongly localized in time, and the mean velocity of the drops can easily decrease by an order of magnitude compared to the sliding on the homogeneous surface. Lattice Boltzmann numerical simulations are crucial for disclosing to what extent the sliding dynamics can be deduced from the computed balance of capillary, viscous, and body forces by varying the Bond number, the surface composition, and the liquid viscosity. Beyond the critical Bond number, we characterize both experimentally and numerically the dissipation inside the droplet by studying the relation between the average velocity and the applied volume forces.
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Affiliation(s)
- M Sbragaglia
- Department of Physics and INFN, University of "Tor Vergata," Via della Ricerca Scientifica 1, I-00133 Rome, Italy
| | - L Biferale
- Department of Physics and INFN, University of "Tor Vergata," Via della Ricerca Scientifica 1, I-00133 Rome, Italy
| | - G Amati
- SCAI, SuperComputing Applications and Innovation, Department CINECA, Via dei Tizii, I-00185 Roma, Italy
| | - S Varagnolo
- Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Universitá di Padova, Via Marzolo 8, I-35131 Padova, Italy
| | - D Ferraro
- Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Universitá di Padova, Via Marzolo 8, I-35131 Padova, Italy
| | - G Mistura
- Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Universitá di Padova, Via Marzolo 8, I-35131 Padova, Italy
| | - M Pierno
- Dipartimento di Fisica e Astronomia "G. Galilei" and CNISM, Universitá di Padova, Via Marzolo 8, I-35131 Padova, Italy
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19
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Wang Z, Yen HY, Chang CC, Sheng YJ, Tsao HK. Trapped liquid drop at the end of capillary. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:12154-12161. [PMID: 24004041 DOI: 10.1021/la4026602] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The liquid drop captured at the capillary end, which is observed in capillary valve and pendant drop technique, is investigated theoretically and experimentally. Because of contact line pinning of the lower meniscus, the lower contact angle is able to rise from the intrinsic contact angle (θ*) so that the external force acting on the drop can be balanced by the capillary force. In the absence of contact angle hysteresis (CAH), the upper contact angle remains at θ*. However, in the presence of CAH, the upper contact angle can descend to provide more capillary force. The coupling between the lower and upper contact angles determines the equilibrium shape of the captured drop. In a capillary valve, the pinned contact line can move across the edge as the pressure difference exceeds the valving pressure, which depends on the geometrical characteristic and wetting property of the valve opening. When CAH is considered, the valving pressure is elevated because the capillary force is enhanced by the receding contact angle. For a pendant drop under gravity, the maximal capillary force is achieved as the lower contact angle reaches 180° in the absence of CAH. However, in the presence of CAH, four regimes can be identified by three critical drop volumes. The lower contact angle can exceed 180°, and therefore the drop takes on the shape of a light bulb, which does not exist in the absence of CAH. The comparisons between Surface Evolver simulations and experiments are quite well.
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Affiliation(s)
- Zhengjia Wang
- Department of Chemical and Materials Engineering, National Central University , Jhongli, Taiwan 320, R.O.C
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20
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Shahraz A, Borhan A, Fichthorn KA. Wetting on physically patterned solid surfaces: the relevance of molecular dynamics simulations to macroscopic systems. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:11632-11639. [PMID: 23952673 DOI: 10.1021/la4023618] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We used molecular dynamics (MD) simulations to study the wetting of Lennard-Jones cylindrical droplets on surfaces patterned with grooves. By scaling the surface topography parameters with the droplet size, we find that the preferred wetting modes and contact angles become independent of the droplet size. This result is in agreement with a mathematical model for the droplet free energy at small Bond numbers for which the effects of gravity are negligible. The MD contact angles for various wetting modes are in good agreement with those predicted by the mathematical model. We construct phase diagrams of the dependence of the wetting modes observed in the MD simulations on the topography of the surface. Depending on the topographical parameters characterizing the surface, multiple wetting modes can be observed, as is also seen experimentally. Thus, our studies indicate that MD simulations can yield insight into the large-length-scale behavior of droplets on patterned surfaces.
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Affiliation(s)
- Azar Shahraz
- Department of Chemical Engineering and ‡Department of Physics, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
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21
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Varagnolo S, Ferraro D, Fantinel P, Pierno M, Mistura G, Amati G, Biferale L, Sbragaglia M. Stick-slip sliding of water drops on chemically heterogeneous surfaces. PHYSICAL REVIEW LETTERS 2013; 111:066101. [PMID: 23971591 DOI: 10.1103/physrevlett.111.066101] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Indexed: 05/14/2023]
Abstract
We present a comprehensive study of water drops sliding down chemically heterogeneous surfaces formed by a periodic pattern of alternating hydrophobic and hydrophilic stripes. Drops are found to undergo a stick-slip motion whose average speed is an order of magnitude smaller than that measured on a homogeneous surface having the same static contact angle. This motion is the result of the periodic deformations of the drop interface when crossing the stripes. Numerical simulations confirm this view and are used to elucidate the principles underlying the experimental observations.
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Affiliation(s)
- S Varagnolo
- CNISM and Department of Physics and Astronomy G. Galilei, University of Padova, Via Marzolo 8, 35131 Padova, Italy
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22
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Silvestrini S, Ferraro D, Tóth T, Pierno M, Carofiglio T, Mistura G, Maggini M. Tailoring the wetting properties of thiolene microfluidic materials. LAB ON A CHIP 2012; 12:4041-4043. [PMID: 22907593 DOI: 10.1039/c2lc40651a] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
A post functionalization method for the control of the wettability of thiolene resins of the NOA family is presented. Treatment of open model surfaces or closed microchannels with chlorosilane derivatives resulted in dramatic changes in the behaviour of droplets and streams contacting the surfaces. The experimental findings are confirmed by the fabrication of a Y-junction device that works as a passive valve for water streams.
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Affiliation(s)
- Simone Silvestrini
- Department of Chemical Sciences and ITM-CNR, University of Padova, Via Marzolo 1, 35131 Padova, Italy
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23
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Shahraz A, Borhan A, Fichthorn KA. A theory for the morphological dependence of wetting on a physically patterned solid surface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:14227-14237. [PMID: 22998115 DOI: 10.1021/la3026304] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We present a theoretical model for predicting equilibrium wetting configurations of two-dimensional droplets on periodically grooved hydrophobic surfaces. The main advantage of our model is that it accounts for pinning/depinning of the contact line at step edges, a feature that is not captured by the Cassie and Wenzel models. We also account for the effects of gravity (via the Bond number) on various wetting configurations that can occur. Using free-energy minimization, we construct phase diagrams depicting the dependence of the wetting modes (including the number of surface grooves involved in the wetting configuration) and their corresponding contact angles on the geometrical parameters characterizing the patterned surface. In the limit of vanishing Bond number, the predicted wetting modes and contact angles become independent of drop size if the geometrical parameters are scaled with drop radius. Contact angles predicted by our continuum-level theoretical model are in good agreement with corresponding results from nanometer-scale molecular dynamics simulations. Our theoretical predictions are also in good agreement with experimentally measured contact angles of small drops, for which gravitational effects on interface deformation are negligible. We show that contact-line pinning is important for superhydrophobicity and that the contact angle is maximized when the droplet size is comparable to the length scale of the surface pattern.
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Affiliation(s)
- Azar Shahraz
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
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24
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Morris G, Neethling SJ, Cilliers JJ. Identifying the Transition Capillary Pressure of a Superhydrophobic Surface Containing Cylindrical Rods. CHEM LETT 2012. [DOI: 10.1246/cl.2012.1303] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Gareth Morris
- Department of Earth Science and Engineering, Imperial College London
| | | | - Jan J. Cilliers
- Department of Earth Science and Engineering, Imperial College London
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25
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Ferraro D, Semprebon C, Tóth T, Locatelli E, Pierno M, Mistura G, Brinkmann M. Morphological transitions of droplets wetting rectangular domains. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:13919-23. [PMID: 22946759 DOI: 10.1021/la302854t] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
We report the results of comprehensive experiments and numerical calculations of interfacial morphologies of water confined to the hydrophilic top face of rectangular posts of width W = 500 μm and lengths between L = 5W and 30W. A continuous evolution of the interfacial shape from a homogeneous liquid filament to a bulged filament and back is observed during changes in the liquid volume. Above a certain threshold length of L* = 16.0W, the transition between the two morphologies is discontinuous and a bistability of interfacial shapes is observed in a certain interval of the reduced liquid volume V/W(3).
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Affiliation(s)
- Davide Ferraro
- CNISM and Dipartimento di Fisica G. Galilei, Università di Padova, Padova, Italy
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26
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Fang G, Amirfazli A. Understanding the edge effect in wetting: a thermodynamic approach. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:9421-30. [PMID: 22612311 DOI: 10.1021/la301623h] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
Edge effect is known to hinder spreading of a sessile drop. However, the underlying thermodynamic mechanisms responsible for the edge effect still is not well-understood. In this study, a free energy model has been developed to investigate the energetic state of drops on a single pillar (from upright frustum to inverted frustum geometries). An analysis of drop free energy levels before and after crossing the edge allows us to understand the thermodynamic origin of the edge effect. In particular, four wetting cases for a drop on a single pillar with different edge angles have been determined by understanding the characteristics of FE plots. A wetting map describing the four wetting cases is given in terms of edge angle and intrinsic contact angle. The results show that the free energy barrier observed near the edge plays an important role in determining the drop states, i.e., (1) stable or metastable drop states at the pillar's edge, and (2) drop collapse by liquid spilling over the edge completely or staying at an intermediate sidewall position of the pillar. This thermodynamic model presents an energetic framework to describe the functioning of the so-called "re-entrant" structures. Results show good consistency with the literature and expand the current understanding of Gibbs' inequality condition.
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Affiliation(s)
- Guoping Fang
- Department of Mechanical Engineering, University of Alberta, Edmonton, Alberta T6G 2G8, Canada
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27
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Dutka F, Napiórkowski M, Dietrich S. Mesoscopic analysis of Gibbs’ criterion for sessile nanodroplets on trapezoidal substrates. J Chem Phys 2012; 136:064702. [DOI: 10.1063/1.3682775] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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28
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Neuhaus S, Spencer ND, Padeste C. Anisotropic wetting of microstructured surfaces as a function of surface chemistry. ACS APPLIED MATERIALS & INTERFACES 2012; 4:123-130. [PMID: 22148671 DOI: 10.1021/am201104q] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
In order to study the influence of surface chemistry on the wetting of structured surfaces, microstructures consisting of grooves or squares were produced via hot embossing of poly(ethylene-alt-tetrafluoroethylene) ETFE substrates. The structured substrates were modified with polymer brushes, thereby changing their surface functionality and wettability. Water droplets were most strongly pinned to the structure when the surface was moderately hydrophilic, as in the case of poly(4-vinylpyridine) (P4VP) or poly(vinyl(N-methyl-2-pyridone) (PVMP) brush-modified substrates. As a result, the droplet shape was determined by the features of the microstructure. The water contact angles (CA) were considerably higher than on flat surfaces and differed, in the most extreme case, by 37° when measured on grooved substrates, parallel and perpendicular to the grooves. On hydrophobic substrates (pristine ETFE), the same effects were observed but were much less pronounced. On very hydrophilic sampes (those modified with poly(N-methyl-vinylpyridinium) (QP4VP)), the microstructure had no influence on the drop shape. These findings are explained by significant differences in apparent and real contact angles at the relatively smooth edges of the embossed structures. Finally, the highly anisotropic grooved microstructure was combined with a gradient in polymer brush composition and wettability. In the case of a parallel alignment of the gradient direction to the grooves, the directed spreading of water droplets could be observed.
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Affiliation(s)
- Sonja Neuhaus
- Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
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