1
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Shao J, Huang Y, Zhao M, Yang Y, Zheng Y, Zhu R. Molecular Dynamics Simulation on the Wettability of Nanoscale Wrinkles: High Water Adhesion of Rose Petals. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:8854-8861. [PMID: 35834741 DOI: 10.1021/acs.langmuir.2c00974] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Understanding the high water adhesion of rose petals is of great significance in artificial surface design. With all-atom molecular dynamics simulation, the wettability of nanoscale wrinkles was explored and compared to that of nanoscale strips with favorable hydrophobicity. The dewetting and wetting of gaps between nanoscale structures represent the Cassie-Baxter (CB) and Wenzel (WZ) states of the macroscopic droplet deposited on the textured surface, respectively. We uncovered the intermediate state, which is different from the CB and WZ states for wrinkles. Structures and free-energy profiles of metastable and transition states under various pressures were also investigated. Moreover, free-energy barriers for the (de)wetting transitions were quantified. On this basis, the roles of pressure and the unique structures of nanoscale wrinkles in the high water adhesion of rose petals were identified.
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Affiliation(s)
- Jinwei Shao
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, People's Republic of China
| | - Yinguo Huang
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, People's Republic of China
| | - Meirong Zhao
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, People's Republic of China
| | - Yong Yang
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, People's Republic of China
| | - Yelong Zheng
- State Key Laboratory of Precision Measuring Technology and Instruments, Tianjin University, Tianjin 300072, People's Republic of China
| | - Rui Zhu
- Shanghai YangZhi Rehabilitation Hospital (Shanghai Sunshine Rehabilitation Center), School of Medicine, Tongji University, Shanghai 200092, China
- Shanghai University of Medicine and Health Sciences, 279 Zhouzhu Road, Shanghai 201318, China
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2
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Zajdel P, Madden DG, Babu R, Tortora M, Mirani D, Tsyrin NN, Bartolomé L, Amayuelas E, Fairen-Jimenez D, Lowe AR, Chorążewski M, Leao JB, Brown CM, Bleuel M, Stoudenets V, Casciola CM, Echeverría M, Bonilla F, Grancini G, Meloni S, Grosu Y. Turning Molecular Springs into Nano-Shock Absorbers: The Effect of Macroscopic Morphology and Crystal Size on the Dynamic Hysteresis of Water Intrusion-Extrusion into-from Hydrophobic Nanopores. ACS APPLIED MATERIALS & INTERFACES 2022; 14:26699-26713. [PMID: 35656844 PMCID: PMC9204699 DOI: 10.1021/acsami.2c04314] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Accepted: 05/23/2022] [Indexed: 05/27/2023]
Abstract
Controlling the pressure at which liquids intrude (wet) and extrude (dry) a nanopore is of paramount importance for a broad range of applications, such as energy conversion, catalysis, chromatography, separation, ionic channels, and many more. To tune these characteristics, one typically acts on the chemical nature of the system or pore size. In this work, we propose an alternative route for controlling both intrusion and extrusion pressures via proper arrangement of the grains of the nanoporous material. To prove the concept, dynamic intrusion-extrusion cycles for powdered and monolithic ZIF-8 metal-organic framework were conducted by means of water porosimetry and in operando neutron scattering. We report a drastic increase in intrusion-extrusion dynamic hysteresis when going from a fine powder to a dense monolith configuration, transforming an intermediate performance of the ZIF-8 + water system (poor molecular spring) into a desirable shock-absorber with more than 1 order of magnitude enhancement of dissipated energy per cycle. The obtained results are supported by MD simulations and pave the way for an alternative methodology of tuning intrusion-extrusion pressure using a macroscopic arrangement of nanoporous material.
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Affiliation(s)
- Paweł Zajdel
- Institute
of Physics, University of Silesia in Katowice, 75 Pulku Piechoty 1, 41-500 Chorzow, Poland
| | - David G. Madden
- The
Adsorption & Advanced Materials Laboratory (AML),
Department of Chemical Engineering & Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, U.K.
| | - Robin Babu
- The
Adsorption & Advanced Materials Laboratory (AML),
Department of Chemical Engineering & Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, U.K.
| | - Marco Tortora
- Dipartimento
di Ingegneria Meccanica e Aerospaziale, Sapienza Università di Roma, via Eudossiana 18, 00184 Rome, Italy
| | - Diego Mirani
- Department
of Chemistry & INSTM University of Pavia, Via Taramelli 14, Pavia I-27100, Italy
| | - Nikolay Nikolaevich Tsyrin
- Laboratory
of Thermomolecular Energetics, National
Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic
Institute”, Pr.
Peremogy 37, 03056 Kyiv, Ukraine
| | - Luis Bartolomé
- Centre for
Cooperative Research on Alternative Energies (CIC energiGUNE), Basque Research and Technology Alliance (BRTA), Albert Einstein 48, 01510 Vitoria-Gasteiz, Spain
| | - Eder Amayuelas
- Centre for
Cooperative Research on Alternative Energies (CIC energiGUNE), Basque Research and Technology Alliance (BRTA), Albert Einstein 48, 01510 Vitoria-Gasteiz, Spain
| | - David Fairen-Jimenez
- The
Adsorption & Advanced Materials Laboratory (AML),
Department of Chemical Engineering & Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, U.K.
| | - Alexander Rowland Lowe
- Institute
of Chemistry, University of Silesia in Katowice, Szkolna 9, 40-006 Katowice, Poland
| | - Mirosław Chorążewski
- Institute
of Chemistry, University of Silesia in Katowice, Szkolna 9, 40-006 Katowice, Poland
| | - Juscelino B. Leao
- NIST
Center for Neutron Research, National Institute
of Standards and Technology, Gaithersburg, Maryland 20899, United States
| | - Craig M. Brown
- NIST
Center for Neutron Research, National Institute
of Standards and Technology, Gaithersburg, Maryland 20899, United States
- Chemical
and Biochemical Department, University of
Delaware, Newark, Delaware 19716, United
States
| | - Markus Bleuel
- NIST
Center for Neutron Research, National Institute
of Standards and Technology, Gaithersburg, Maryland 20899, United States
- Department
of Materials Science and Engineering, University
of Maryland, College Park, Maryland 20742-2115, United States
| | - Victor Stoudenets
- Laboratory
of Thermomolecular Energetics, National
Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic
Institute”, Pr.
Peremogy 37, 03056 Kyiv, Ukraine
| | - Carlo Massimo Casciola
- Dipartimento
di Ingegneria Meccanica e Aerospaziale, Sapienza Università di Roma, via Eudossiana 18, 00184 Rome, Italy
| | - María Echeverría
- Centre for
Cooperative Research on Alternative Energies (CIC energiGUNE), Basque Research and Technology Alliance (BRTA), Albert Einstein 48, 01510 Vitoria-Gasteiz, Spain
| | - Francisco Bonilla
- Centre for
Cooperative Research on Alternative Energies (CIC energiGUNE), Basque Research and Technology Alliance (BRTA), Albert Einstein 48, 01510 Vitoria-Gasteiz, Spain
| | - Giulia Grancini
- Department
of Chemistry & INSTM University of Pavia, Via Taramelli 14, Pavia I-27100, Italy
| | - Simone Meloni
- Dipartimento di Scienze Chimiche e Farmaceutiche
(DipSCF), Università degli Studi
di Ferrara (Unife), Via
Luigi Borsari 46, I-44121 Ferrara, Italy
| | - Yaroslav Grosu
- Centre for
Cooperative Research on Alternative Energies (CIC energiGUNE), Basque Research and Technology Alliance (BRTA), Albert Einstein 48, 01510 Vitoria-Gasteiz, Spain
- Institute
of Chemistry, University of Silesia in Katowice, Szkolna 9, 40-006 Katowice, Poland
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3
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Zhang BX, Wang SL, Wang YB, Yang YR, Wang XD, Yang RG. Harnessing Reversible Wetting Transition to Sweep Contaminated Superhydrophobic Surfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:3929-3938. [PMID: 33760619 DOI: 10.1021/acs.langmuir.1c00157] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Sweeping deposited particles is absolutely essential in order to maintain the excellent functionality of superhydrophobic surfaces. Many methods have been proposed to sweep microparticles deposited on tips of micro/nanostructures. However, how to sweep nanoparticles trapped in cavities of superhydrophobic surfaces has remained an outstanding issue. Here, we show that harnessing the reversible wetting transition provides a feasible way to sweep such nanoparticles. Using molecular dynamics simulations, we demonstrate that the electrically induced CB-W wetting transition makes liquid intrude into a groove and wet a trapped hydrophilic nanoparticle; however, once the electric field is removed, a spontaneous W-CB dewetting transition happens, and the extruded liquid transports the hydrophilic nanoparticle to the groove top, successfully picking up the trapped hydrophilic nanoparticle. We further find that the adhesion between the nanoparticle and groove bottom wall hinders the successful pickup, and picking up such a nanoparticle requires a stronger particle hydrophilicity. With the introduction of amphiphilic Janus particles into a liquid, we exhibit that the electrically induced reversible wetting transition can also successfully pick up a trapped hydrophobic nanoparticle. By means of calculations of the potential of mean force (PMF), we reveal pathways of both the CB-W wetting transition and the W-CB dewetting transition and hence answer why and how a hydrophilic or a hydrophobic nanoparticle is picked up successfully.
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Affiliation(s)
| | | | | | | | | | - Rong-Gui Yang
- School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
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4
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Wang Z, Pereira JM, Gan Y. Effect of Wetting Transition during Multiphase Displacement in Porous Media. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:2449-2458. [PMID: 32070092 DOI: 10.1021/acs.langmuir.9b03780] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The effects of wettability on multiphase displacement in porous media have been studied extensively in the past, and the contact angle is identified as an important factor influencing the displacement patterns. At the same time, it has been found that the effective contact angle can vary drastically in a time-dependent manner on rough surfaces due to the Cassie-Wenzel wetting transition. In this study, we develop a theoretical model at the pore scale describing the apparent contact angle on a rough interface as a function of time. The theory is then incorporated into the lattice Boltzmann method for simulation of multiphase displacement in disordered porous media. A dimensionless time ratio, Dy, describing the relative speed of the wetting transition and pore invasion is defined. We show that the displacement patterns can be significantly influenced by Dy, where more trapped defending ganglia are observed at large Dy values, leading to lower displacement efficiency. We investigate the mobilization of trapped ganglia through identifying different mobilization dynamics during displacement, including translation, coalescence, and fragmentation. Agreement is observed between the mobilization statistics and the total pressure gradient across a wide range of Dy values. Understanding the effect of the wetting transition during multiphase displacement in porous media is of importance for applications such as carbon geosequestration and oil recovery, especially for porous media where solid surface roughness cannot be neglected.
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Affiliation(s)
- Zhongzheng Wang
- School of Civil Engineering, The University of Sydney, Sydney, 2006, New South Wales , Australia
- Navier, Ecole des Ponts, Université Gustave Eiffel, CNRS, 77420, Marne-la-Vallée, France
| | - Jean-Michel Pereira
- Navier, Ecole des Ponts, Université Gustave Eiffel, CNRS, 77420, Marne-la-Vallée, France
| | - Yixiang Gan
- School of Civil Engineering, The University of Sydney, Sydney, 2006, New South Wales , Australia
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5
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Giacomello A, Schimmele L, Dietrich S, Tasinkevych M. Recovering superhydrophobicity in nanoscale and macroscale surface textures. SOFT MATTER 2019; 15:7462-7471. [PMID: 31512709 PMCID: PMC8751625 DOI: 10.1039/c9sm01049a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Accepted: 08/15/2019] [Indexed: 05/30/2023]
Abstract
Here, we investigate the complete drying of hydrophobic cavities in order to elucidate the dependence of drying on the size, the geometry, and the degree of hydrophobicity of the confinement. Two complementary theoretical approaches are adopted: a macroscopic one based on classical capillarity and a microscopic classical density functional theory. This combination allows us to pinpoint unique drying mechanisms at the nanoscale and to clearly differentiate them from the mechanisms operational at the macroscale. Nanoscale hydrophobic cavities allow the thermodynamic destabilization of the confined liquid phase over an unexpectedly broad range of conditions, including pressures as large as 10 MPa and contact angles close to 90°. On the other hand, for cavities on the micron scale, such destabilization occurs only for much larger contact angles and close to liquid-vapor coexistence. These scale-dependent drying mechanisms are used to propose design criteria for hierarchical superhydrophobic surfaces capable of spontaneous self-recovery over a broad range of operating conditions. In particular, we detail the requirements under which it is possible to realize perpetual superhydrophobicity at positive pressures on surfaces with micron-sized textures by exploiting drying, facilitated by nanoscale coatings. Concerning the issue of superhydrophobicity, these findings indicate a promising direction both for surface fabrication and for the experimental characterization of perpetual surperhydrophobicity. From a more basic perspective, the present results have an echo on a wealth of biological problems in which hydrophobic confinement induces drying, such as in protein folding, molecular recognition, and hydrophobic gating.
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Affiliation(s)
- Alberto Giacomello
- Sapienza Università di Roma, Dipartimento di Ingegneria Meccanica e Aerospaziale, 00184 Rome, Italy. and Max-Planck-Institut für Intelligente Systeme, 70569 Stuttgart, Germany
| | - Lothar Schimmele
- Max-Planck-Institut für Intelligente Systeme, 70569 Stuttgart, Germany
| | - Siegfried Dietrich
- Max-Planck-Institut für Intelligente Systeme, 70569 Stuttgart, Germany and IV. Institut für Theoretische Physik, Universität Stuttgart, 70569 Stuttgart, Germany
| | - Mykola Tasinkevych
- Centro de Física Teórica e Computacional, Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, P-1749-016 Lisboa, Portugal
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6
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Amabili M, Grosu Y, Giacomello A, Meloni S, Zaki A, Bonilla F, Faik A, Casciola CM. Pore Morphology Determines Spontaneous Liquid Extrusion from Nanopores. ACS NANO 2019; 13:1728-1738. [PMID: 30653291 DOI: 10.1021/acsnano.8b07818] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
In this contribution we explore by means of experiments, theory, and molecular dynamics the effect of pore morphology on the spontaneous extrusion of nonwetting liquids from nanopores. Understanding and controlling this phenomenon is central for manipulating nanoconfined liquids, e. g., in nanofluidic applications, drug delivery, and oil extraction. Qualitatively different extrusion behaviors were observed in high-pressure water intrusion-extrusion experiments on porous materials with similar nominal diameter and hydrophobicity: macroscopic capillary models and molecular dynamics simulations revealed that the very presence or absence of extrusion is connected to the internal morphology of the pores and, in particular, to the presence of small-scale roughness or pore interconnections. Additional experiments with mercury confirmed that this mechanism is generic for nonwetting liquids and is rooted in the pore topology. The present results suggest a rational way to engineer heterogeneous systems for energy and nanofluidic applications in which the extrusion behavior can be controlled via the pore morphology.
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Affiliation(s)
- Matteo Amabili
- Dipartimento di Ingegneria Meccanica e Aerospaziale , Sapienza Università di Roma , 00184 Rome , Italy
| | - Yaroslav Grosu
- CIC Energigune , Albert Einstein 48 , Miñano ( Álava ) 01510 , Spain
| | - Alberto Giacomello
- Dipartimento di Ingegneria Meccanica e Aerospaziale , Sapienza Università di Roma , 00184 Rome , Italy
| | - Simone Meloni
- Dipartimento di Ingegneria Meccanica e Aerospaziale , Sapienza Università di Roma , 00184 Rome , Italy
| | - Abdelali Zaki
- CIC Energigune , Albert Einstein 48 , Miñano ( Álava ) 01510 , Spain
| | - Francisco Bonilla
- CIC Energigune , Albert Einstein 48 , Miñano ( Álava ) 01510 , Spain
| | - Abdessamad Faik
- CIC Energigune , Albert Einstein 48 , Miñano ( Álava ) 01510 , Spain
| | - Carlo Massimo Casciola
- Dipartimento di Ingegneria Meccanica e Aerospaziale , Sapienza Università di Roma , 00184 Rome , Italy
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7
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Zhang BX, Wang SL, Wang XD. Wetting Transition from the Cassie-Baxter State to the Wenzel State on Regularly Nanostructured Surfaces Induced by an Electric Field. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:662-670. [PMID: 30601010 DOI: 10.1021/acs.langmuir.8b03808] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
When droplets are placed on hydrophobic textured surfaces, different wetting states Cassie-Baxter (CB) state or Wenzel (W) state may occur depending on materials and structures of surfaces, types and sizes of droplets, thermal fluctuations, and external stimuli. The wetting transition from the CB to the W state and the opposite process have attracted a great deal of attention because of their primary importance for designing and fabricating textured surfaces. In this work, molecular dynamics (MD) simulations are employed to understand the mechanism behind the CB-to-W transition for a nanoscale water film placed on a surface decorated with a single nanogroove when an external electric field is applied. The free energy variation during the transition process is computed on the basis of the restrained MD simulations. Water intrusion into the groove is observed by simulation snapshots, which provides direct evidence for the electric field-induced CB-to-W transition. In the previous experiments, however, only a sharp reduction in the apparent contact angle is employed to judge whether the transition takes place. The free energy curves reveal that there are two energy barriers separating the CB and W states (Δ E1) as well as separating the W and CB states (Δ E2). Owing to the presence of Δ E1, although the CB state has a higher free energy than the W state, it cannot spontaneously convert to the W state. When the external energy input exceeds Δ E1, the CB-to-W transition can be triggered, otherwise the transition will stop, and the water film will return to the CB state. Moreover, it is found that the maximum of free energy always occurs after the film touches the groove bottom. Thus, the requirement that the film should touch the groove bottom is responsible for the presence of the energy barrier Δ E1. Finally, the dependence of the two energy barriers on the electric field strength, groove aspect ratio, and intrinsic contact angle of the groove is also discussed.
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8
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Lisi E, Amabili M, Meloni S, Giacomello A, Casciola CM. Self-Recovery Superhydrophobic Surfaces: Modular Design. ACS NANO 2018; 12:359-367. [PMID: 29182848 DOI: 10.1021/acsnano.7b06438] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Superhydrophobicity, the enhanced hydrophobicity of surfaces decorated with textures of suitable size, is associated with a layer of gas trapped within surface roughness. The reduced liquid/solid contact makes superhydrophobicity attractive for many technological applications. This gas layer, however, can break down with the liquid completely wetting the surface. Experiments have shown that the recovery of the "suspended" superhydrophobic state from the wet one is difficult. Self-recovery-the spontaneous restoring of the gas layer at ambient conditions-is one of the dreams of research in superhydrophobicity as it would allow to overcome the fragility of superhydrophobicity. In this work we have performed a theoretical investigation of the wetting and recovery processes on a set of surfaces characterized by textures of different dimensions and morphology in order to elucidate the optimal parameters for avoiding wetting and achieving self-recovery. Results show that texture size in the nanometer range is a necessary but not sufficient condition for self-recovery: the geometry plays a crucial role, nanopillars prevent self-recovery, while surfaces with square pores exhibit self-recovery even at large positive pressures. However, the optimal morphology for self-recovery, the square pore, is suboptimal for the functional properties of the surface, for example, high slippage. Our calculations show that these two properties are related to regions of the texture separated in space: self-recovery is controlled by the characteristics of the bottom surface, while wetting and slip are controlled by the cavity mouth. We thus propose a modular design strategy which combines self-recovery and good functional properties: Square pores surmounted by ridges achieve self-recovery even at 2 MPa and have a very small liquid/solid contact area. The macroscopic calculations, which allowed us to efficiently devise design criteria, have been validated by atomistic simulations, with the optimal texture showing self-recovery on atomic time scales, τ ∼ 2 ns.
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Affiliation(s)
- Emanuele Lisi
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , Rome, Italy
| | - Matteo Amabili
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , Rome, Italy
| | - Simone Meloni
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , Rome, Italy
| | - Alberto Giacomello
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , Rome, Italy
| | - Carlo Massimo Casciola
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , Rome, Italy
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9
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Amabili M, Meloni S, Giacomello A, Casciola CM. Activated Wetting of Nanostructured Surfaces: Reaction Coordinates, Finite Size Effects, and Simulation Pitfalls. J Phys Chem B 2017; 122:200-212. [PMID: 29200302 DOI: 10.1021/acs.jpcb.7b07429] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A liquid in contact with a textured surface can be found in two states, Wenzel and Cassie. In the Wenzel state the liquid completely wets the corrugations while in the Cassie state the liquid is suspended over the corrugations with air or vapor trapped below. The superhydrophobic properties of the Cassie state are exploited for self-cleaning, drag reduction, drug delivery, etc., while in the Wenzel state most of these properties are lost; it is therefore of great fundamental and technological interest to investigate the kinetics and mechanism of the Cassie-Wenzel transition. Computationally, the Cassie-Wenzel transition is often investigated using enhanced sampling ("rare events") techniques based on the use of collective variables (CVs). The choice of the CVs is a crucial task because it affects the free-energy profile, the estimation of the free-energy barriers, and the evaluation of the mechanism of the process. Here we investigate possible simulation artifacts introduced by common CVs adopted for the study of the Cassie-Wenzel transition: the average particle density in the corrugation of a textured surface and the coarse-grained density field at various levels of coarse graining. We also investigate possible additional artifacts associated with finite size effects. We focus on a pillared surface, a system often used in technological applications. We show that the use of a highly coarse-grained density (a single CV) of the fluid in the interpillar region brings to severe artifacts: errors of hundreds of kBT in the difference of free energy between the Cassie and Wenzel states, of tens of kBT in the estimate of the free-energy barriers, and erroneous wetting mechanisms. A proper description of the wetting mechanism and its energetics apparently requires a fine discretization of the density field. Concerning the finite-size effects, we have found that the typical systems employed in simulations of the Cassie-Wenzel transition, containing a single pillar within periodic boundary conditions, prevent the complete break of translational symmetry of the liquid-vapor meniscus during the process. Capturing this break of symmetry is crucial for describing the transition state along the wetting process and the early stage of the opposite process, the Wenzel-Cassie transition.
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Affiliation(s)
- M Amabili
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , 00184 Rome, Italy
| | - S Meloni
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , 00184 Rome, Italy
| | - A Giacomello
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , 00184 Rome, Italy
| | - C M Casciola
- Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma "La Sapienza" , 00184 Rome, Italy
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10
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Tricinci O, Terencio T, Pugno NM, Greco F, Mazzolai B, Mattoli V. Air Trapping Mechanism in Artificial Salvinia-Like Micro-Hairs Fabricated via Direct Laser Lithography. MICROMACHINES 2017; 8:mi8120366. [PMID: 30400556 PMCID: PMC6187866 DOI: 10.3390/mi8120366] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Revised: 12/06/2017] [Accepted: 12/15/2017] [Indexed: 12/13/2022]
Abstract
Salvinia leaves represent an extraordinary example of how nature found a strategy for the long term retainment of air, and thus oxygen, on a surface, the so-called ‘Salvinia effect’, thanks to the peculiar three-dimensional and hierarchical shape of the hairs covering the leaves. Here, starting from the natural model, we have microfabricated hairs inspired by those present on the Salvinia molesta leaves, by means of direct laser lithography. Artificial hairs, like their natural counterpart, are composed of a stalk and a crown-like head, and have been reproduced in the microscale since this ensures, if using a proper design, an air-retaining behavior even if the bulk structural material is hydrophilic. We have investigated the capability of air retainment inside the heads of the hairs that can last up to 100 h, demonstrating the stability of the phenomenon. For a given dimension of the head, the greater the number of filaments, the greater the amount of air that can be trapped inside the heads since the increase in the number of solid–air interfaces able to pin the liquid phase. For this reason, such type of pattern could be used for the fabrication of surfaces for controlled gas retainment and gas release in liquid phases. The range of applications would be quite large, including industrial, medical, and biological fields.
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Affiliation(s)
- Omar Tricinci
- Center for Micro-BioRobotics @SSSA, Istituto Italiano di Tecnologia, Viale Rinaldo Piaggio 34, 56025 Pontedera, Italy.
| | - Tercio Terencio
- Center for Micro-BioRobotics @SSSA, Istituto Italiano di Tecnologia, Viale Rinaldo Piaggio 34, 56025 Pontedera, Italy.
| | - Nicola M Pugno
- Laboratory of Bio-Inspired and Graphene Nanomechanics, Department of Civil, Environmental and Mechanical Engineering, University of Trento, 38123 Trento, Italy.
- School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK.
- Ket Labs, Edoardo Amaldi Foundation, Italian Space Agency, Via del Politecnico snc, Rome 00133, Italy.
| | - Francesco Greco
- Center for Micro-BioRobotics @SSSA, Istituto Italiano di Tecnologia, Viale Rinaldo Piaggio 34, 56025 Pontedera, Italy.
- Department of Life Science and Medical Bioscience, Graduate School of Advanced Science and Engineering, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, 169-8480 Tokyo, Japan.
| | - Barbara Mazzolai
- Center for Micro-BioRobotics @SSSA, Istituto Italiano di Tecnologia, Viale Rinaldo Piaggio 34, 56025 Pontedera, Italy.
| | - Virgilio Mattoli
- Center for Micro-BioRobotics @SSSA, Istituto Italiano di Tecnologia, Viale Rinaldo Piaggio 34, 56025 Pontedera, Italy.
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11
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Abstract
Molecular springs, constituted by nanoporous materials immersed in a nonwetting liquid, are compact, economical, and efficient means of storing energy, owing to their enormous surface area. Surface energy is accumulated during liquid intrusion inside the pores and released by decreasing liquid pressure and thus triggering confined cavitation. State-of-the-art atomistic simulations shed light on the intrusion and extrusion of water in hydrophobic nanopores, revealing conspicuous deviations from macroscopic theories, which include accelerated cavitation, increased intrusion pressure, and reversible intrusion and extrusion processes. Understanding these nanoscale phenomena is the key to a better design of molecular springs as it allows relating the characteristics of the materials to the overall properties of the devices, e.g., their operational pressure and efficiency. Heterogeneous systems composed of hydrophobic nanoporous materials and water are capable, depending on their characteristics, of efficiently dissipating (dampers) or storing (“molecular springs”) energy. However, it is difficult to predict their properties based on macroscopic theories—classical capillarity for intrusion and classical nucleation theory (CNT) for extrusion—because of the peculiar behavior of water in extreme confinement. Here we use advanced molecular dynamics techniques to shed light on these nonclassical effects, which are often difficult to investigate directly via experiments, owing to the reduced dimensions of the pores. The string method in collective variables is used to simulate, without artifacts, the microscopic mechanism of water intrusion and extrusion in the pores, which are thermally activated, rare events. Simulations reveal three important nonclassical effects: the nucleation free-energy barriers are reduced eightfold compared with CNT, the intrusion pressure is increased due to nanoscale confinement, and the intrusion/extrusion hysteresis is practically suppressed for pores with diameters below 1.2 nm. The frequency and size dependence of hysteresis exposed by the present simulations explains several experimental results on nanoporous materials. Understanding physical phenomena peculiar to nanoconfined water paves the way for a better design of nanoporous materials for energy applications; for instance, by decreasing the size of the nanopores alone, it is possible to change their behavior from dampers to molecular springs.
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Liu Y, Zhang X. Molecular dynamics simulation of nanobubble nucleation on rough surfaces. J Chem Phys 2017; 146:164704. [DOI: 10.1063/1.4981788] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Affiliation(s)
- Yawei Liu
- State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China
| | - Xianren Zhang
- State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China
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