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Kern VR, Carlson A. Twisted fibers enable drop flow control and enhance fog capture. Proc Natl Acad Sci U S A 2024; 121:e2402252121. [PMID: 39074268 PMCID: PMC11317607 DOI: 10.1073/pnas.2402252121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2024] [Accepted: 06/16/2024] [Indexed: 07/31/2024] Open
Abstract
Drop-fiber interactions are fundamental to the operation of technologies such as atmospheric fog capture, oil filtration, refrigeration, and dehumidification. We demonstrate that by twisting together two fibers, a sliding drop's flow path can be controlled by tuning the ratio between its size and the twist wavelength. We find both experimentally and numerically that twisted fiber systems are able to asymmetrically stabilize drops, both enhancing drop transport speeds and creating a rich array of new flow patterns. We show that the passive flow control generated by twisting fibers allows for woven nets that can be "programmed" with junctions that predetermine drop interactions and can be anticlogging. Furthermore, it is shown that twisted fiber structures are significantly more effective at capturing atmospheric fog compared to straight fibers.
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Affiliation(s)
- Vanessa R. Kern
- Niels Henrik Abels Hus, Department of Mathematics, Mechanics Section, University of Oslo, Oslo0851, Norway
| | - Andreas Carlson
- Niels Henrik Abels Hus, Department of Mathematics, Mechanics Section, University of Oslo, Oslo0851, Norway
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2
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Singh S, Abdur R, Sheikh MAK, Swain BS, Song J, Kim JH, Nam HS, Kim SH, Lee H, Lee J. Selective Spin Dewetting for Perovskite Solar Modules Fabricated on Engineered Au/ITO Substrates. NANOMATERIALS (BASEL, SWITZERLAND) 2024; 14:424. [PMID: 38470755 DOI: 10.3390/nano14050424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2024] [Revised: 02/21/2024] [Accepted: 02/24/2024] [Indexed: 03/14/2024]
Abstract
We introduce a novel method for fabricating perovskite solar modules using selective spin-coating on various Au/ITO patterned substrates. These patterns were engineered for two purposes: (1) to enhance selectivity of monolayers primarily self-assembling on the Au electrode, and (2) to enable seamless interconnection between cells through direct contact of the top electrode and the hydrophobic Au connection electrode. Utilizing SAMs-treated Au/ITO, we achieved sequential selective deposition of the electron transport layer (ETL) and the perovskite layer on the hydrophilic amino-terminated ITO, while the hole transport layer (HTL) was deposited on the hydrophobic CH3-terminated Au connection electrodes. Importantly, our approach had a negligible impact on the series resistance of the solar cells, as evidenced by the measured specific contact resistivity of the multilayers. A significant outcome was the production of a six-cell series-connected solar module with a notable average PCE of 8.32%, providing a viable alternative to the conventional laser scribing technique.
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Affiliation(s)
- Son Singh
- School of Advanced Materials Engineering, Kookmin University, Seoul 02707, Republic of Korea
| | - Rahim Abdur
- School of Advanced Materials Engineering, Kookmin University, Seoul 02707, Republic of Korea
| | - Md Abdul Kuddus Sheikh
- School of Advanced Materials Engineering, Kookmin University, Seoul 02707, Republic of Korea
| | - Bhabani Sankar Swain
- School of Advanced Materials Engineering, Kookmin University, Seoul 02707, Republic of Korea
| | - Jindong Song
- Center for Opto-Electronic Materials and Devices, Korea Institute of Science and Technology (KIST), Seoul 02792, Republic of Korea
| | - Jae-Hun Kim
- School of Advanced Materials Engineering, Kookmin University, Seoul 02707, Republic of Korea
| | - Ho-Seok Nam
- School of Advanced Materials Engineering, Kookmin University, Seoul 02707, Republic of Korea
| | - Sung-Hyon Kim
- Department of Fashion Design, Kookmin University, Seoul 02707, Republic of Korea
| | - Hyunseung Lee
- Department of Fashion Industry, Incheon National University, Incheon 22012, Republic of Korea
| | - Jaegab Lee
- School of Advanced Materials Engineering, Kookmin University, Seoul 02707, Republic of Korea
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3
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Satarifard V, Grafmüller A, Lipowsky R. Nanodroplets at Membranes Create Tight-Lipped Membrane Necks via Negative Line Tension. ACS NANO 2018; 12:12424-12435. [PMID: 30525450 DOI: 10.1021/acsnano.8b06634] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The response of biomembranes to aqueous-phase separation and to the resulting water-in-water droplets has been recently studied on the micrometer scale using optical microscopy and elasticity theory. When such a droplet adheres to the membrane, it forms a contact area that is bounded by a contact line. For a micrometer-sized droplet, the line tension associated with this contact line can usually be ignored compared with the surface tensions. However, for a small nanoscopic droplet, this line tension is expected to affect the membrane-droplet morphology. Here, we use molecular simulations to study nanodroplets at membranes and to gain insight into these line tension effects. The latter effects are shown to depend strongly on another key parameter, the mechanical tension experienced by the membrane. For a large membrane tension, a droplet adhering to the membrane is only partially engulfed by the membrane, and the membrane-droplet system exhibits an axisymmetric morphology. A reduction of the membrane tension leads to an increase in the contact area and a decrease in the interfacial area of the droplet, initially retaining its axisymmetric shape, which implies a circular contact line and a circular membrane neck. However, when the tension falls below a certain threshold value, the system undergoes a morphological transition toward a non-axisymmetric morphology with a non-circular membrane neck. This morphology persists until the nanodroplet is completely engulfed by the membrane and the membrane neck has closed into a tight-lipped shape. The latter morphology is caused by a negative line tension, which is shown to be a robust feature of membrane-droplet systems. A closed membrane neck with a tight-lipped shape suppresses both thermally activated and protein-induced scission of the neck, implying a reduction in the cellular uptake of nanodroplets by pinocytosis and fluid-phase endocytosis. Furthermore, based on our results, we can also draw important conclusions about the time-dependent processes corresponding to the surface nucleation and growth of nanodroplets at membranes.
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Affiliation(s)
- Vahid Satarifard
- Theory & Biosystems , Max Planck Institute of Colloids and Interfaces , 14424 Potsdam , Germany
| | - Andrea Grafmüller
- Theory & Biosystems , Max Planck Institute of Colloids and Interfaces , 14424 Potsdam , Germany
| | - Reinhard Lipowsky
- Theory & Biosystems , Max Planck Institute of Colloids and Interfaces , 14424 Potsdam , Germany
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4
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Trobo ML, Albano EV, Binder K. Heterogeneous nucleation of a droplet pinned at a chemically inhomogeneous substrate: A simulation study of the two-dimensional Ising case. J Chem Phys 2018; 148:114701. [PMID: 29566529 DOI: 10.1063/1.5016612] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Heterogeneous nucleation is studied by Monte Carlo simulations and phenomenological theory, using the two-dimensional lattice gas model with suitable boundary fields. A chemical inhomogeneity of length b at one boundary favors the liquid phase, while elsewhere the vapor is favored. Switching on the bulk field Hb favoring the liquid, nucleation and growth of the liquid phase starting from the region of the chemical inhomogeneity are analyzed. Three regimes occur: for small fields, Hb<Hbcrit, the critical droplet radius is so large that a critical droplet having the contact angle θc required by Young's equation in the region of the chemical inhomogeneity does not yet "fit" there since the baseline length of the circle-cut sphere droplet would exceed b. For Hbcrit<Hb<Hb*, such droplets fit inside the inhomogeneity and are indeed found in simulations with large enough observation times, but these droplets remain pinned to the chemical inhomogeneity when their baseline has grown to the length b. Assuming that these pinned droplets have a circle cut shape and effective contact angles θeff in the regime θc < θeff < π/2, the density excess due to these droplets can be predicted and is found to be in reasonable agreement with the simulation results. On general grounds, one can predict that the effective contact angle θeff and the excess density of the droplets, scaled by b, are functions of the product bHb but do not depend on both variables separately. Since the free energy barrier for the "depinning" of the droplet (i.e., growth of θeff to π - θc) vanishes when θeff approaches π/2, in practice only angles θeff up to about θeffmax≃70° were observed. For larger fields (Hb>Hb*), the droplets nucleated at the chemical inhomogeneity grow to the full system size. While the relaxation time for the growth scales as τG∝Hb-1, the nucleation time τN scales as lnτN∝Hb-1. However, the prefactor in the latter relation, as evaluated for our simulations results, is not in accord with an extension of the Volmer-Turnbull theory to two-dimensions, when the theoretical contact angle θc is used.
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Affiliation(s)
- Marta L Trobo
- Instituto de Física de Líquidos y Sistemas Biológicos (IFLYSIB), CCT-CONICET La Plata, UNLP, Calle 59 Nro. 789, 1900 La Plata, Argentina
| | - Ezequiel V Albano
- Instituto de Física de Líquidos y Sistemas Biológicos (IFLYSIB), CCT-CONICET La Plata, UNLP, Calle 59 Nro. 789, 1900 La Plata, Argentina
| | - Kurt Binder
- Institut für Physik, Johannes Gutenberg-Universität Mainz Staudinger Weg 7, D-55099 Mainz, Germany
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Luginsland T, Sauer RA. A computational study of wetting on chemically contaminated substrates. Colloids Surf A Physicochem Eng Asp 2017. [DOI: 10.1016/j.colsurfa.2017.06.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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6
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Eckstein R, Alt M, Rödlmeier T, Scharfer P, Lemmer U, Hernandez-Sosa G. Digitally Printed Dewetting Patterns for Self-Organized Microelectronics. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2016; 28:7708-7715. [PMID: 27346645 DOI: 10.1002/adma.201602082] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Revised: 05/25/2016] [Indexed: 06/06/2023]
Abstract
Self-organization of functional materials induced by low surface-energetic direct printed structures is presented. This study investigates fundamental fluid and substrate interactions and fabricates all-printed small area organic photodetectors with On-Off ratios of ≈10(5) and dark current densities of ≈10(-4) mA cm(-2) , as well as ring oscillators based on n-type organic field-effect transistors showing working frequencies up to 400 Hz.
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Affiliation(s)
- Ralph Eckstein
- Karlsruhe Institute of Technology, Light Technology Institute, Engesser Str. 13, 76131, Karlsruhe, Germany.
- InnovationLab, Speyererstr. 4, 69115, Heidelberg, Germany.
| | - Milan Alt
- Karlsruhe Institute of Technology, Light Technology Institute, Engesser Str. 13, 76131, Karlsruhe, Germany
- InnovationLab, Speyererstr. 4, 69115, Heidelberg, Germany
| | - Tobias Rödlmeier
- Karlsruhe Institute of Technology, Light Technology Institute, Engesser Str. 13, 76131, Karlsruhe, Germany
- InnovationLab, Speyererstr. 4, 69115, Heidelberg, Germany
| | - Philip Scharfer
- InnovationLab, Speyererstr. 4, 69115, Heidelberg, Germany
- Karlsruhe Institute of Technology, Institute of Thermal Process Engineering, Thin Film Technology, Kaiserstr. 12, 76131, Karlsruhe, Germany
| | - Uli Lemmer
- Karlsruhe Institute of Technology, Light Technology Institute, Engesser Str. 13, 76131, Karlsruhe, Germany
- InnovationLab, Speyererstr. 4, 69115, Heidelberg, Germany
- Institute of Microstructure Technology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
| | - Gerardo Hernandez-Sosa
- Karlsruhe Institute of Technology, Light Technology Institute, Engesser Str. 13, 76131, Karlsruhe, Germany.
- InnovationLab, Speyererstr. 4, 69115, Heidelberg, Germany.
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7
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Affiliation(s)
- Vijay Kumar
- Mechanical Engineering Department; Birla Institute of Technology and Science; Pilani 333031 Rajasthan India
| | - Niti Nipun Sharma
- Mechanical Engineering Department; Birla Institute of Technology and Science; Pilani 333031 Rajasthan India
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8
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Dörfler F, Rauscher M, Dietrich S. Stability of thin liquid films and sessile droplets under confinement. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:012402. [PMID: 23944464 DOI: 10.1103/physreve.88.012402] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Indexed: 06/02/2023]
Abstract
The stability of nonvolatile thin liquid films and of sessile droplets is strongly affected by finite size effects. We analyze their stability within the framework of density functional theory using the sharp kink approximation, i.e., on the basis of an effective interface Hamiltonian. We show that finite size effects suppress spinodal dewetting of films because it is driven by a long-wavelength instability. Therefore nonvolatile films are stable if the substrate area is too small. Similarly, nonvolatile droplets connected to a wetting film become unstable if the substrate area is too large. This instability of a nonvolatile sessile droplet turns out to be equivalent to the instability of a volatile drop which can attain chemical equilibrium with its vapor.
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Affiliation(s)
- Fabian Dörfler
- Max-Planck-Institut für Intelligente Systeme, Heisenbergstr. 3, 70569 Stuttgart, Germany
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9
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Wetting dynamics on lyophilic solid surfaces patterned by lyophobic islands. Colloids Surf A Physicochem Eng Asp 2013. [DOI: 10.1016/j.colsurfa.2013.02.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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10
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Tsekov R, Grozev NA, Delcheva IV, Ivanov IT, Balashev K, Karakashev SI. Delta-comb potential in modeling three-phase contact line (TPCL) on periodically patterned surfaces. J Phys Chem B 2012; 116:13248-53. [PMID: 23078081 DOI: 10.1021/jp307250c] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This work is a study of wetting of small water droplets on smooth glass surfaces with periodic patterns in the form of imprinted net with hydrophilic cells and hydrophobic bars. Microcover slides consisted of soda lime glass were used. The imprinted images of the net were with cell sizes in the range 40-200 μm, which corresponds to a quite narrow scope of hydrophilic surface fractions f(1)(30-36%) due to the relative increase in the size of the hydrophobic bars. The receding contact angles θ(R) of small water droplets, positioned on the patterned surfaces, were measured. The experiment showed significantly lower receding contact angles as compared to the theoretical expectations by the Cassie formula, which accounts for the contribution to the contact angle of the surface fraction of the imprinted hydrophobic/hydrophilic net. For this reason, we developed new theory accounting for the periodicity of the surface and the contribution of the three-phase contact line on the contact angle. This new theory considered delta-comb potential energy Δ(x,y) of the surface, effective line tension κ, and the lattice parameter a. The restriction of theory was discussed as well. It was pointed out that the theory is not valid for very small and very large lattice parameters.
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Affiliation(s)
- Roumen Tsekov
- Department of Physical Chemistry, University of Sofia, 1164 Sofia, Bulgaria
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11
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Seemann R, Brinkmann M, Herminghaus S, Khare K, Law BM, McBride S, Kostourou K, Gurevich E, Bommer S, Herrmann C, Michler D. Wetting morphologies and their transitions in grooved substrates. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:184108. [PMID: 21508471 DOI: 10.1088/0953-8984/23/18/184108] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
When exposed to a partially wetting liquid, many natural and artificial surfaces equipped with complex topographies display a rich variety of liquid interfacial morphologies. In the present article, we focus on a few simple paradigmatic surface topographies and elaborate on the statics and dynamics of the resulting wetting morphologies. It is demonstrated that the spectrum of wetting morphologies increases with increasing complexity of the groove structure. On elastically deformable substrates, additional structures in the liquid morphologies can be observed, which are caused by deformations of the groove geometry in the presence of capillary forces. The emergence of certain liquid morphologies in grooves can be actively controlled by changes in wettability and geometry. For electrically conducting solid substrates, the apparent contact angle can be varied by electrowetting. This allows, depending on groove geometry, a reversible or irreversible transport of liquid along surface grooves. In the case of irreversible liquid transport in triangular grooves, the dynamics of the emerging instability is sensitive to the apparent hydrodynamic slip at the substrate. On elastic substrates, the geometry can be varied in a straightforward manner by stretching or relaxing the sample. The imbibition velocity in deformable grooves is significantly reduced compared to solid grooves, which is a result of the microscopic deformation of the elastic groove material close to the three phase contact line.
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Affiliation(s)
- Ralf Seemann
- Experimental Physics, Saarland University, D-66123 Saarbrücken, Germany.
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12
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Jaiswal PK, Vashishtha M, Khanna R, Puri S. Amplification of fluctuations in unstable systems with disorder. J Phys Chem B 2011; 115:4399-403. [PMID: 21449546 DOI: 10.1021/jp112354e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We study the early stage kinetics of thermodynamically unstable systems with quenched disorder. We show analytically that the growth of initial fluctuations is amplified by the presence of disorder. This is confirmed by numerical simulations of morphological phase separation in thin liquid films and spinodal decomposition in binary mixtures. We also discuss the experimental implications of our results.
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Affiliation(s)
- Prabhat K Jaiswal
- School of Physical Sciences, Jawaharlal Nehru University, New Delhi, India
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13
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Chen F, Zhang D, Yang Q, Wang X, Dai B, Li X, Hao X, Ding Y, Si J, Hou X. Anisotropic wetting on microstrips surface fabricated by femtosecond laser. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2011; 27:359-365. [PMID: 21141976 DOI: 10.1021/la103293j] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
In this paper, we present a new method to realize anisotropy by restricting a droplet on an unstructured Si hydrophobic domain between two superhydrophobic strips fabricated by femtosecond laser. The water contact angles and corresponding water baseline length were investigated. The results showed that anisotropy would vary with the volume-induced pinning-depinning-repinning behavior of the droplet. Furthermore, through the observation of water response on small Si domain, the adhesive force of the structure is proven to be the key factor giving rise to the anisotropy wetting. This phenomenon could potentially be used as a model for fundamental research, and such structures could be utilized to control large volume in microfluidic devices, lab-on-chip system, microreactors, and self-cleaning surfaces.
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Affiliation(s)
- Feng Chen
- Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, 710049, China.
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14
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Vashishtha M, Jaiswal PK, Khanna R, Puri S, Sharma A. Spinodal phase separation in liquid films with quenched disorder. Phys Chem Chem Phys 2010; 12:12964-8. [PMID: 20838676 DOI: 10.1039/c0cp00776e] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We study spinodal phase separation in unstable thin liquid films on chemically disordered substrates via simulations of the thin-film equation. The disorder is characterized by immobile patches of varying size and Hamaker constant. The effect of disorder is pronounced in the early stages (amplification of fluctuations), remains during the intermediate stages and vanishes in the late stages (domain growth). These findings are in contrast to the well-known effects of quenched disorder in usual phase-separation processes, viz. the early stages remain undisturbed and domain growth is slowed down in the asymptotic regime. We also address the inverse problem of estimating disorder by thin-film experiments.
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Affiliation(s)
- Manish Vashishtha
- Department of Chemical Engineering, Indian Institute of Technology Delhi, New Delhi, India
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15
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Schäfle C, Brinkmann M, Bechinger C, Leiderer P, Lipowsky R. Morphological wetting transitions at ring-shaped surface domains. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:11878-11885. [PMID: 20462246 DOI: 10.1021/la1011023] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The wetting behavior of ring-shaped (or annular) surface domains is studied both experimentally and theoretically. The ring-shaped domains are lyophilic and embedded in a lyophobic substrate. Liquid droplets deposited on these domains can attain a variety of morphologies depending on the liquid volume and on the dimensions of the ringlike surface domains. In the experiments, the liquid volume is changed in a controlled manner by varying the temperature of the sample. Such a volume change leads to a characteristic sequence of droplet shapes and to morphological wetting transitions between these shapes. The experimental observations are in good agreement with analytical and numerical calculations based on the minimization of the interfacial free energy. Small droplets form ringlike liquid channels (or filaments) that are confined to the ring-shaped domains and do not spread onto the lyophobic disks enclosed by these rings. As one increases the volume of the droplets, one finds two different morphologies depending on the width of the ring-shaped domains. For narrow rings, the droplets form nonaxisymmetric liquid channels with a pronounced bulge. For broad rings, the droplets form axisymmetric caps that cover both the lyophilic rings and the lyophobic disks.
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Affiliation(s)
- Claudia Schäfle
- Fachhochschule Rosenheim, Fakultat für Angewandte Natur- und Geisteswissenschaften, Hochschulstrasse 1, 83024 Rosenheim, Germany
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17
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Blecua P, Brinkmann M, Lipowsky R, Kierfeld J. Morphological transitions of liquid droplets on circular surface domains. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:13493-13502. [PMID: 19746938 DOI: 10.1021/la901990z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We study morphological transitions of droplets on a structured substrate containing two circular lyophilic domains for arbitrary domain and substrate wettabilities. We derive the stability criterion that at least one of the droplets must be pinned at the domain boundary with a contact angle smaller than (pi)/(2). This determines seven classes of stable or metastable droplet morphologies of the system. We present a complete classification of stability and metastability of these morphologies as a function of three control parameters as provided by the total droplet volume, substrate wettability, and domain wettability. We find different types of morphological transitions at the stability boundaries: (i) depinning transitions of the contact lines, (ii) symmetry-breaking transitions, where the two droplets acquire different volumes, and (iii) dewetting transitions, where one domain dewets and one of the droplets disappears. We find that depinning transitions of two droplets become discontinuous between two universal values of substrate wettability. Furthermore, below a critical domain wettability, one domain always dewets irrespective of the total volume. We discuss experimental realizations and applications of our results for controlled switching between observed wetting morphologies.
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Affiliation(s)
- Pedro Blecua
- Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
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18
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Wong TS, Ho CM. Dependence of macroscopic wetting on nanoscopic surface textures. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:12851-4. [PMID: 19842620 PMCID: PMC2783847 DOI: 10.1021/la902430w] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The hydrophobicity of a surface can be enhanced by physical textures. However, no existing theories of surface wetting can provide guidance to pinpoint the texture size requirement to achieve super/ultrahydrophobicity. Here, we show that the three-phase contact line tension, tau, is an important link to understand the dependence of macroscopic wetting on physical texture size in an ideal Cassie regime. Specifically, we show that texture size is the dominant parameter in determining surface hydrophobicity when the size approaches a limiting physical length scale, as defined by tau and the surface tension of the liquid.
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19
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Minet I, Delhalle J, Hevesi L, Mekhalif Z. Surface-initiated ATRP of PMMA, PS and diblock PS-b-PMMA copolymers from stainless steel modified by 11-(2-bromoisobutyrate)-undecyl-1-phosphonic acid. J Colloid Interface Sci 2009; 332:317-26. [PMID: 19168187 DOI: 10.1016/j.jcis.2008.12.066] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2008] [Revised: 12/11/2008] [Accepted: 12/24/2008] [Indexed: 11/17/2022]
Affiliation(s)
- Isabelle Minet
- CES Laboratory, Department of Chemistry, Facultés Universitaires Notre-Dame de la Paix, Rue de Bruxelles, 61, B-5000 Namur, Belgium
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20
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Khare K, Herminghaus S, Baret JC, Law BM, Brinkmann M, Seemann R. Switching liquid morphologies on linear grooves. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:12997-13006. [PMID: 18001065 DOI: 10.1021/la701899u] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The morphology of liquids confined to linear micrometer-sized grooves of triangular and rectangular cross section is studied for different substrate wettabilities. Depending on the wettability and exact geometry, either droplike morphologies or elongated liquid filaments represent the generic equilibrium structures on the substrate. Upon changing the apparent contact angle of aqueous drops by electrowetting, we are able to trigger the transition between elongated filaments and droplets. In the case of rectangular grooves, this transition allows us to advance liquid reversibly into the grooves while crossing a certain threshold contact angle. In triangular grooves, however, these elongated filaments undergo a dynamic instability when the contact angle returns to a value above the filling threshold. The different filling and drainage behavior is explained by specific aspects of the triangular and rectangular groove geometry.
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Affiliation(s)
- Krishnacharya Khare
- Max Planck Institute for Dynamics and Self-Organization, D-37018 Göttingen, Germany
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21
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Schoen M. Fluid bridges confined between chemically nanopatterned solid substrates. Phys Chem Chem Phys 2007; 10:223-56. [PMID: 18213411 DOI: 10.1039/b706674k] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We discuss equilibrium properties of classical fluids confined to nanoscopic volumes by solid substrates. The substrates themselves are endowed with wettable chemical patterns of variable symmetry. We develop a thermodynamic description suitable for these highly anisotropic systems. Based upon a combination of Monte Carlo simulations in the grand canonical ensemble and lattice density functional theory at mean-field level we analyze the structure and phase behaviour of the confined fluid. Under suitable thermodynamic conditions the fluid may condense partially in regions controlled by the wettable nanopatterns. The resulting fluid bridges are established as thermodynamic phases and exhibit unique rheological features.
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Affiliation(s)
- Martin Schoen
- Stranski-Laboratorium für Physikalische und Theoretische Chemie, Institut für Chemie, Fakultät für Mathematik und Naturwissenschaften, Technische Universität Berlin, Strasse des 17. Juni 135, Berlin, Germany.
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22
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Gao L, McCarthy TJ. How Wenzel and cassie were wrong. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:3762-5. [PMID: 17315893 DOI: 10.1021/la062634a] [Citation(s) in RCA: 380] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
We argue using experimental data that contact lines and not contact areas are important in determining wettability. Three types of two-component surfaces were prepared that contain "spots" in a surrounding field: a hydrophilic spot in a hydrophobic field, a rough spot in a smooth field, and a smooth spot in a rough field. Water contact angles were measured within the spots and with the spot confined to within the contact line of the sessile drop. Spot diameter and contact line diameter were varied. All of the data indicate that contact angle behavior (advancing, receding, and hysteresis) is determined by interactions of the liquid and the solid at the three-phase contact line alone and that the interfacial area within the contact perimeter is irrelevant. The point is made that Wenzel's and Cassie's equations are valid only to the extent that the structure of the contact area reflects the ground state energies of contact lines and the transition states between them.
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Affiliation(s)
- Lichao Gao
- Polymer Science and Engineering Department, University of Massachusetts, Amherst, Massachusetts 01003, USA
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23
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Blecua P, Lipowsky R, Kierfeld J. Line tension effects for liquid droplets on circular surface domains. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2006; 22:11041-59. [PMID: 17154583 DOI: 10.1021/la0609773] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
We study the morphologies of single liquid droplets wetting a substrate in the presence of the line tension of the three-phase contact line. On a homogeneous substrate, the line tension leads to a discontinuous unbinding of the droplet if its volume is decreased below a critical value. For a droplet wetting a structured surface with a circular domain, a line tension contrast gives rise to discontinuous depinning transitions of the contact line from the domain boundary as the droplet volume is varied. We calculate the corresponding free energy bifurcation diagram analytically for axisymmetric droplet shapes. Numerical minimization of the droplet free energy shows that line tension contrasts can stabilize nonaxisymmetric droplet shapes, thus modifying the bifurcation diagram. These latter shapes should be accessible to experiments and can be used to reveal the presence of a line tension contrast.
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Affiliation(s)
- Pedro Blecua
- Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
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24
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Iwamatsu M. Contact angle hysteresis of cylindrical drops on chemically heterogeneous striped surfaces. J Colloid Interface Sci 2006; 297:772-7. [PMID: 16337219 DOI: 10.1016/j.jcis.2005.11.032] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2005] [Revised: 11/09/2005] [Accepted: 11/12/2005] [Indexed: 11/19/2022]
Abstract
Contact angle hysteresis of a macroscopic droplet on a heterogeneous but flat substrate is studied using the interface displacement model. First, the apparent contact angle of a droplet on a heterogeneous surface under the condition of constant volume is considered. By assuming a cylindrical liquid-vapor surface (meniscus) and minimizing the total free energy, we derive an equation for the apparent contact angle, which is similar but different from the well-known Cassie's law. Next, using this modified Cassie's law as a guide to predict the behavior of a droplet on a heterogeneous striped surface, we examine several scenarios of contact angle hysteresis using a periodically striped surface model. By changing the volume of the droplet, we predict a sudden jump of the droplet edge, and a continuous change of the apparent contact angle at the edge of two stripes. Our results suggest that as drop volume is increased (advancing contact lines), the predominant drop configuration observed is the one whose contact angle is large; whereas, decreasing drop volume from a large value (receding contact lines) yields drop configuration that predominantly exhibit the smaller contact angle.
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Affiliation(s)
- Masao Iwamatsu
- Department of Physics, General Education Center, Musashi Institute of Technology, Setagaya-ku, Tokyo 158-8557, Japan.
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25
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Porcheron F, Monson PA, Schoen M. Wetting of rings on a nanopatterned surface: a lattice model study. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 73:041603. [PMID: 16711817 DOI: 10.1103/physreve.73.041603] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Indexed: 05/09/2023]
Abstract
We perform mean-field density functional theory calculations on a lattice model to study the wetting of a solid substrate decorated with a ring pattern of nanoscale dimensions. We have found three different liquid morphologies on the substrate: a ring morphology where the liquid covers the pattern, a bulge morphology where a droplet is forming on one side of the ring, and a morphology where the liquid forms a cap spanning the nonwetting disk inside the pattern. We investigate the relative stability of these morphologies as a function of the ring size, wall-fluid interaction, and temperature. The results found are in very good agreement with experiments and calculations performed on similar systems at a micrometer length scale. The bulge morphology has also been observed in Monte Carlo simulations of the lattice model. Our results show that (i) morphologies of wetting patterns previously observed on a much larger (microm) scale can also form on a nm length scale, (ii) whether or not this happens depends crucially on the size of the wettable pattern, and (iii) the wettable ring may only be partially wet by the bulge morphology of the fluid. This morphology is a result of a spontaneously broken symmetry in the system.
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Affiliation(s)
- Fabien Porcheron
- Department of Chemical Engineering, University of Massachusetts, 159 Goessmann Laboratory, 686 North Pleasant Street, Amherst, MA 01003-9303, USA
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26
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Guzzardi L, Rosso R, Virga EG. Residual stability of sessile droplets with negative line tension. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 73:021602. [PMID: 16605345 DOI: 10.1103/physreve.73.021602] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2005] [Revised: 10/11/2005] [Indexed: 05/08/2023]
Abstract
We study the local stability of a sessile droplet with nonvanishing line tension along the contact line, where three phases are in equilibrium. We confirm Widom's results [J. Phys. Chem. 99, 2803 (1995)] on the local stability of a droplet with positive line tension in a larger class of perturbations. When the line tension is negative, we prove that the restricted class of perturbations employed by Widom fails to capture the instability of equilibria. A notion of residual stability is introduced, which makes quantitative the condition under which equilibrium of droplets with negative line tension are likely to be observed.
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Affiliation(s)
- Luca Guzzardi
- Dipartimento di Matematica, Università di Firenze, Viale Morgagni 67a, 50134 Firenze, Italy.
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27
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Brinkmann M, Kierfeld J, Lipowsky R. A general stability criterion for droplets on structured substrates. ACTA ACUST UNITED AC 2004. [DOI: 10.1088/0305-4470/37/48/003] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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28
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Rosso R, Virga EG. Sign of line tension in liquid bridge stability. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2004; 70:031603. [PMID: 15524530 DOI: 10.1103/physreve.70.031603] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/15/2004] [Indexed: 05/24/2023]
Abstract
We apply the stability criterion we recently proposed for a general wetting functional [Phys. Rev. E 68, 012601 (2003)] to find out whether straight liquid bridges can be stable when subject to line tension of either sign. Our main conclusion is that, even when the line tension is negative, a straight liquid bridge can be stable, and so observable, provided that the line tension is not too large in absolute value.
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Affiliation(s)
- Riccardo Rosso
- Dipartimento di Matematica, Istituto Nazionale di Fisica della Materia, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy
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29
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Brinkmann M, Blossey R. Blobs, channels and "cigars": morphologies of liquids at a step. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2004; 14:79-89. [PMID: 15221593 DOI: 10.1140/epje/i2004-10008-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/29/2004] [Indexed: 05/24/2023]
Abstract
We have studied the equilibria of liquid droplets wetting a step edge with an opening angle 0 < alpha < pi by a combination of analytical and numerical methods. Depending on the wetting properties of the substrate walls and on the liquid volume, different locally or globally stable liquid morphologies are found. Complete spreading of the liquid along the bottom edge of the step is observed at equilibrium contact angles theta satisfying theta < theta(s) = pi/2 - alpha/2. If the contact angle theta exceeds a threshold value theta(b) the liquid exists in a blob-like configuration. Surprisingly, we find an intermediate regime at a sufficiently high liquid volume and in a range of contact angles theta(s) < theta < theta(b), in which "cigar"-shaped configurations arise in addition to the blob. We close the paper by a detailed discussion of the stability of this novel liquid morphology.
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Affiliation(s)
- M Brinkmann
- Interdisciplinary Research Institute, c/o IEMN Avenue Poincaré BP 69, F-59652 Villeneuve d'Ascq, France
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30
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31
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Yaneva J, Milchev A, Binder K. Polymer nanodroplets forming liquid bridges in chemically structured slit pores: A computer simulation. J Chem Phys 2004; 121:12632-9. [PMID: 15606288 DOI: 10.1063/1.1826037] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Using a coarse-grained bead-spring model of flexible polymer chains, the structure of a polymeric nanodroplet adsorbed on a chemically decorated flat wall is investigated by means of molecular dynamics simulation. We consider sessile drops on a lyophilic (attractive for the monomers) region of circular shape with radius R(D) while the remaining part of the substrate is lyophobic. The variation of the droplet shape, including its contact angle, with R(D) is studied, and the density profiles across these droplets also are obtained. In addition, the interaction of droplets adsorbed on two walls forming a slit pore with two lyophilic circular regions just opposite of one another is investigated, paying attention to the formation of a liquid bridge between both walls. A central result of our study is the measurement of the force between the two substrate walls at varying wall separation as well as the kinetics of droplet merging. Our results are compared to various phenomenological theories developed for liquid droplets of mesoscopic rather than nanoscopic size.
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Affiliation(s)
- Jacqueline Yaneva
- Institute for Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria
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32
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Rosso R, Virga EG. General stability criterion for wetting. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2003; 68:012601. [PMID: 12935183 DOI: 10.1103/physreve.68.012601] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2002] [Indexed: 05/24/2023]
Abstract
We propose a general stability criterion for the wetting of solid substrates, both arbitrarily curved and inhomogeneous. In addition to the classical surface tension, the adhering drops can also exhibit a tension along the contact line where three phases meet, namely, the solid, the liquid, and the environment fluid. Moreover, we show how some stability issues currently debated in the specialized literature of disparate fields could profit from the application of this general criterion.
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Affiliation(s)
- Riccardo Rosso
- Dipartimento di Matematica, Istituto Nazionale di Fisica della Materia, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy
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33
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34
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Kargupta K, Sharma A. Morphological self-organization by dewetting in thin films on chemically patterned substrates. J Chem Phys 2002. [DOI: 10.1063/1.1434949] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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35
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Kargupta K, Sharma A. Templating of thin films induced by dewetting on patterned surfaces. PHYSICAL REVIEW LETTERS 2001; 86:4536-4539. [PMID: 11384277 DOI: 10.1103/physrevlett.86.4536] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2000] [Indexed: 05/23/2023]
Abstract
The instability, dynamics, and morphological transitions of patterns in thin liquid films on chemically heterogeneous striped surfaces are investigated based on 3D nonlinear simulations. The film breakup is suppressed on some potentially destabilizing nonwettable sites when their spacing is below a characteristic length scale of the instability, lambda(h). The thin film pattern replicates the substrate surface energy pattern closely only when (i) the periodicity of substrate pattern lies between lambda(h) and 2lambda(h), and (ii) the stripe width is within a range bounded by a lower critical length, below which no heterogeneous rupture occurs, and an upper transition length above which complex morphological features unlike the substrate pattern are formed.
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Affiliation(s)
- K Kargupta
- Department of Chemical Engineering, Indian Institute of Technology, Kanpur, UP 208 016, India
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36
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37
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Impact of nanometer-scale roughness on contact-angle hysteresis and globulin adsorption. ACTA ACUST UNITED AC 2001. [DOI: 10.1116/1.1392402] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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