1
|
Yi C, Hu C, Shi L, Bai M, Li Y, Tang D. Simulation-based research on enhancing lubricity: investigating wettability and textured surfaces in alkane lubricants under boundary lubrication conditions. NANOTECHNOLOGY 2024; 35:475705. [PMID: 39106877 DOI: 10.1088/1361-6528/ad6b9e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Accepted: 08/06/2024] [Indexed: 08/09/2024]
Abstract
Changing the wettability and surface texturing have a significant impact on lubrication. In this study, the researchers used the molecular dynamics method to investigate how adjusting the interaction between alkanes and the wall affects oil film morphology and frictional properties under boundary lubrication. The findings revealed that the bearing capacity was influenced by both the morphology of the oil film and the strength of solid-liquid adsorption. In cases where the walls had weak wettability, the alkanes formed clusters to effectively separate the walls, while in cases where the walls had strong wettability, the oil film spread and formed a strong adsorption film. The super oleophilic textured surface could enhance the oil film adsorption capacity and replenish the oil film to the friction area in time, and the super oleophobic smooth surface could further reduce the friction coefficient. Therefore, a composite surface consisting of a super oleophilic textured surface and a super oleophobic smooth surface can be designed to enhance the bearing capacity of the oil film and reduce friction.
Collapse
Affiliation(s)
- Changli Yi
- China Gas Turbine Establishment, Aviation Industry Corporation of China, Chengdu 610500, People's Republic of China
| | - Chengzhi Hu
- Laboratory of Ocean Energy Utilization of Ministry of Education, School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, People's Republic of China
| | - Lin Shi
- Laboratory of Ocean Energy Utilization of Ministry of Education, School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, People's Republic of China
| | - Minli Bai
- Laboratory of Ocean Energy Utilization of Ministry of Education, School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, People's Republic of China
| | - Yubai Li
- Laboratory of Ocean Energy Utilization of Ministry of Education, School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, People's Republic of China
| | - Dawei Tang
- Laboratory of Ocean Energy Utilization of Ministry of Education, School of Energy and Power Engineering, Dalian University of Technology, Dalian 116024, People's Republic of China
| |
Collapse
|
2
|
Yang Y, Liu D, Wang Q, Mahmood A, Lin M. Unveiling the Interactions between Water Molecule Clusters and Conical Structures via Molecular Dynamics Simulations. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2023; 39:13028-13037. [PMID: 37671509 DOI: 10.1021/acs.langmuir.3c01228] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/07/2023]
Abstract
Water scarcity presents a pressing global challenge, necessitating innovative solutions, such as the collection of water from the air using conical structures. However, current research primarily focuses on mist collection rather than on nanoscale clusters of water molecules. Under standard atmospheric conditions, water vapor predominantly exists as imperceptible clusters. Therefore, it is crucial to investigate the interactions between these water molecule clusters and conical structures, particularly regarding whether the conical shape induces Laplace pressure difference on the adhering cluster formations. To gain deeper insights and determine optimal droplet collection structures, we conducted molecular dynamics simulations to investigate interactions between water molecule clusters and conical structures. Our investigations focused on studying the interactions between conical structures and water molecule clusters with varying densities, as well as the impact of surface energies on the collection of water by these conical structures. Notably, our simulations unveiled the significant roles played by van der Waals forces and Laplace pressure in the process of collecting water molecule clusters. Furthermore, our simulations revealed that Janus conical structures, featuring two distinct surface energy regions, played a crucial role in promoting the aggregation of water molecules, resulting in the formation of larger droplets. This aggregation was driven by surface tension gradients, which arise from the contrasting wetting properties in different regions of the Janus structure. As a consequence, under the influence of gravitational forces, these larger droplets could eventually detach from the structure. Through the combined effects of surface tension gradients and gravitational forces, Janus conical structures offer a promising avenue for enhancing the collection efficiency of water from the air. Our research sheds light on the fundamental mechanisms governing water molecule cluster-based water collection and provides valuable insights for the design of more efficient and effective water collection systems.
Collapse
Affiliation(s)
- Yingying Yang
- College of Physics and Electronic Information Engineering, Minjiang University, Fuzhou 350108, China
| | - Dong Liu
- Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
- College of Physics and Electronic Information Engineering, Minjiang University, Fuzhou 350108, China
| | - Qiuyan Wang
- College of Physics and Electronic Information Engineering, Minjiang University, Fuzhou 350108, China
- College of Mechanical and Electrical Engineering, Qingdao University, Qingdao 266071, China
| | - Awais Mahmood
- Institute for Advanced Study, Shenzhen University, Shenzhen 518060, China
- College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China
| | - Meijia Lin
- College of Physics and Electronic Information Engineering, Minjiang University, Fuzhou 350108, China
| |
Collapse
|
3
|
Mahmood A, Liu D, Sun Y, Wang Q, Chen S, Wang B, Chen L. Directional movement of gold nanoparticles on the silicon substrate due to the Laplace pressure: a molecular dynamics simulation study. J Mol Liq 2023. [DOI: 10.1016/j.molliq.2023.121767] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023]
|
4
|
Lee E, Müller-Plathe F. Contact Line Friction and Dynamic Contact Angles of a Capillary Bridge between Superhydrophobic Nanostructured Surfaces. J Chem Phys 2022; 157:024701. [DOI: 10.1063/5.0098150] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
The Cassie-Baxter state of wetting explains a large equilibrium contact angle and the slippery dynamics of a water droplet on a superhydrophobic rough surface. It also causes a contact angle hysteresis (CAH) which cannot be fully described by dynamic wetting theories including the molecular kinetic theory (MKT). We analyze the contact line dynamics on a superhydrophobic surface in the framework of the MKT. Multi-body dissipative particle dynamics simulations of a capillary bridge confined between two rough surfaces under steady shear are performed. We find that, in addition to the contact line friction force from the MKT, an additional friction force contribution is needed on rough surface, which is almost constant at all contact line velocities. Thus, it is directly related to the CAH. The CAH originates not only from contact line pinning but also from the shear flow due to the strong friction in the central region of the liquid-solid interface away from the contact line. The analysis of the particle flow inside the capillary bridge shows that liquid particles trapped in the grooves of the surface texture actually move with the same velocity as the surface, and exert strong additional friction to other liquid particles. This work extends the MKT to rough surfaces, as well as to elucidate the origin of the CAH of a capillary bridge. The finding would help to better understand also other situations of dynamic wetting on superhydrophobic surfaces.
Collapse
Affiliation(s)
- Eunsang Lee
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technical University of Darmstadt, Germany
| | | |
Collapse
|
5
|
Chu KC, Tsao HK, Sheng YJ. Spontaneous spreading of nanodroplets on partially wetting surfaces with continuous grooves: Synergy of imbibition and capillary condensation. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.117270] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
6
|
Wang Q, Dumond JJ, Teo J, Low HY. Superhydrophobic Polymer Topography Design Assisted by Machine Learning Algorithms. ACS APPLIED MATERIALS & INTERFACES 2021; 13:30155-30164. [PMID: 34128635 DOI: 10.1021/acsami.1c04473] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Superhydrophobic surfaces have been largely achieved through various surface topographies. Both empirical and numerical simulations have been reported to help understand and design superhydrophobic surfaces. Many such successful surfaces have also been achieved using bioinspired and biomimetic designs. Despite this, identifying the right surface texture to meet the requirements of specific applications is not a straightforward task. Here, we report a hybrid approach that includes experimental methods, numerical simulations, and machine learning (ML) algorithms to create design maps for superhydrophobic polymer topographies. Two design objectives to investigate superhydrophobic properties were the maximum water contact angle (WCA) and Laplace pressure. The design parameters were the geometries of an isotropic pillar structure in micrometer and sub-micrometer length scales. The finite element method (FEM) was validated by the experimental data and employed to generate a labeled dataset for ML training. Artificial neural network (ANN) models were then trained on the labeled database for the topographic parameters (width W, height H, and pitch P) with the corresponding WCA and Laplace pressure. The ANN models yielded a series of nonlinear relationships between the topographic design parameters and the WCA and Laplace pressure and substantial differences between the micrometer and sub-micrometer length scales. Design maps that span the topography design parameters provide optimal design or tradeoff parameters. This research demonstrates the potential of ANN as a rapid design tool for surface topography exploration.
Collapse
Affiliation(s)
- Qiang Wang
- Digital Manufacturing and Design Centre (DManD), Singapore University of Technology and Design (SUTD), 8 Somapah Road, Singapore 487372, Singapore
| | - Jarrett J Dumond
- NILT US Inc., 95 Brown Rd Ste 246, m/s 1024, Ithaca, New York 14850, United States
| | - Jarren Teo
- Department of Mechanical and Mechatronics Engineering, University of Waterloo, 200 University Avenue, West Waterloo, Ontario N2L 3G1, Canada
| | - Hong Yee Low
- Digital Manufacturing and Design (DManD), Engineering Product Development Pillar, Singapore University of Technology and Design, 8 Somapah Road, Singapore 487372, Singapore
| |
Collapse
|
7
|
Dey P, Saha SK, Chakraborty S. Surface Nanostructure-Wettability Coupling Leads to Unique Topological Evolution Dictating Water Transport over Nanometer Scales. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:8111-8122. [PMID: 32589848 DOI: 10.1021/acs.langmuir.0c00955] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Surface nanostructure, either designed or generated as an artifact of the fabrication procedure, is known to influence interfacial phenomena intriguingly. While surface roughness-wettability coupling over nanometer scales has been addressed to some extent, the explicit interplay of hydrodynamics and confinement toward dictating the underlying characteristics for practically relevant material interfaces remains unexplored. Here, we bring out unique roles of surface nanostructures toward altering flow of water in a copper nanochannel, by capturing an exclusive interplay of confinement, roughness, wettability and flow dynamics. Toward this, non-equilibrium molecular dynamics (NEMD) simulations are performed to examine the effect of nanoscale triangular roughness. The width and height of the triangular microgroove are varied along with different driving forces at the channel inlet, and the results are compared with those corresponding to smooth-walled nanochannels. We also unveil the nontrivial characteristics of the interfacial topology as a consequence of spontaneous phase separation at the fluid-solid interface. For a constant driving force, we show that the interface may exhibit concave or convex topology, depending on the nanogroove geometry. Our results provide new vistas on how designed nanoscale roughness structures can be harnessed toward controlling the transport of water in a practically engineered nanosystem, as demanded by the specific application on hand.
Collapse
Affiliation(s)
- Prasenjit Dey
- Department of Mechanical Engineering, National Institute of Technology Goa, Ponda 403401, India
| | - Sandip K Saha
- Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India
| | - Suman Chakraborty
- Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India
| |
Collapse
|
8
|
Mahmood A, Chen S, Chen L, Chen C, Liu D, Weng D, Wang J. Spontaneous propulsion of a water nanodroplet induced by a wettability gradient: a molecular dynamics simulation study. Phys Chem Chem Phys 2020; 22:4805-4814. [PMID: 32068225 DOI: 10.1039/c9cp06718c] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The directional propulsion of liquid droplets at the nanoscale is quite an interesting topic of research in the fields of micro/nano-fluidics, water filtration, precision medicine, and cooling of electronics. In this study, the unidirectional spontaneous transport of a water nanodroplet on a solid surface with a multi-gradient surface (MGS) inspired by natural species is modeled and analyzed using molecular dynamics (MD) simulations. There are three different MGSs considered in this study containing different wedge angles of the hydrophilic region of the solid surface. The MGSs contain two regions: a hydrophilic wedge-shaped region with a constant surface energy parameter equal to 50 meV and a hydrophobic region with a tuned surface energy parameter. The energy parameter of the hydrophobic region is set equal to 1, 5, 10, 20, 30, and 40 meV in order to alter the intensity of the wettability gradient of the two surfaces and its effect on the propulsion of the water nanodroplet is analyzed. Furthermore, three different sizes of water droplets containing 6000, 8000, and 10 000 water molecules are also used in this study and their effect on the transport behavior of the water nanodroplet is also measured. Moreover, two different designs on a solid surface with a continuous wettability gradient are modelled and the impact of solid surface geometry on the transport of the water droplet is calculated by means of mean square displacement (MSD) and average velocity data. In addition, the wedge-shaped surface is found to be more superior to the parallel-shaped surface for the spontaneous propulsion of the water droplet.
Collapse
Affiliation(s)
- Awais Mahmood
- State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084, China.
| | - Shuai Chen
- Institute of High Performance Computing, A*STAR, 138632, Singapore
| | - Lei Chen
- State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084, China.
| | - Chaolang Chen
- State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084, China.
| | - Dong Liu
- State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084, China.
| | - Ding Weng
- State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084, China.
| | - Jiadao Wang
- State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084, China.
| |
Collapse
|
9
|
Fan P, Pan R, Zhong M. Ultrafast Laser Enabling Hierarchical Structures for Versatile Superhydrophobicity with Enhanced Cassie-Baxter Stability and Durability. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:16693-16711. [PMID: 31782653 DOI: 10.1021/acs.langmuir.9b02986] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The controllable and facile fabrication of surface micro/nanostructures with the required dimensions and morphologies is the key to achieving surface superhydrophobicity. With the advantages of being a noncontact, maskless, programmable, and one-step process, ultrafast laser irradiation is a very flexible and adaptive technique for fabricating various microscale, nanoscale, and micro/nanomultiscale surface structures on diverse solids, thus realizing superhydrophobicity on their surfaces. In this feature article, a comprehensive review of our recent research advances on versatile superhydrophobic surfaces enabled by ultrafast lasers is presented from the perspectives of materials, methodologies, and functionalization. The realization of superhydrophobicity and even superamphiphobicity on varied solid surfaces through ultrafast laser treatment and the underlying mechanisms for the wettability transition of ultrafast-laser-processed surfaces from superhydrophilicity to superhydrophobicity will be discussed. For the sake of practical applications, the ultrafast-laser-based strategies for the large-scale and cost-effective fabrication of superhydrophobic surface micro/nanostructures will be introduced. A special focus will be devoted to the enhancement of structural durability and the Cassie-Baxter stability of ultrafast-laser-enabled superhydrophobic surfaces. Beyond that, the achievement of integrated surface functions including remarkable wetting functions such as the directional collection of water droplets and superhydrophobic surfaces simultaneously with unique optical properties will also be presented.
Collapse
Affiliation(s)
- Peixun Fan
- Laser Materials Processing Research Centre, School of Materials Science and Engineering , Tsinghua University , Beijing 100084 , P. R. China
| | - Rui Pan
- Laser Materials Processing Research Centre, School of Materials Science and Engineering , Tsinghua University , Beijing 100084 , P. R. China
| | - Minlin Zhong
- Laser Materials Processing Research Centre, School of Materials Science and Engineering , Tsinghua University , Beijing 100084 , P. R. China
| |
Collapse
|
10
|
Geng X, Yu X, Bao L, Priezjev NV, Lu Y. Directed transport of liquid droplets on vibrating substrates with asymmetric corrugations and patterned wettability: a dissipative particle dynamics study. MOLECULAR SIMULATION 2019. [DOI: 10.1080/08927022.2019.1667498] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Xinran Geng
- Jilin Provincial Key Laboratory for Numerical Simulation, Jilin Normal University, Siping, People’s Republic of China
| | - Xiaopeng Yu
- Jilin Provincial Key Laboratory for Numerical Simulation, Jilin Normal University, Siping, People’s Republic of China
| | - Luyao Bao
- School of Marine Science and Technology, Northwestern Polytechnical University, Xi'an, People’s Republic of China
| | - Nikolai V. Priezjev
- Department of Mechanical and Materials Engineering, Wright State University, Dayton, OH, USA
| | - Yang Lu
- Jilin Provincial Key Laboratory for Numerical Simulation, Jilin Normal University, Siping, People’s Republic of China
| |
Collapse
|
11
|
Song F, Ju D, Fan J, Chen Q, Yang Q. Deformation hysteresis of a water nano-droplet in an electric field. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2019; 42:120. [PMID: 31494769 DOI: 10.1140/epje/i2019-11885-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2019] [Accepted: 08/06/2019] [Indexed: 06/10/2023]
Abstract
Electric field is an effective method to manipulate droplets in micro/nano-scale, and various physical phenomena have been found due to the interaction of electric field and fluid flow. In this study, we developed a molecular dynamic model to investigate the deforming behavior of a nano-droplet in a uniform electric field. The nano-droplet was initially confined between two plates and then wetted on the lower plate (i.e., substrate) until an equilibrium state, after that a uniform electric field in vertical direction was imposed to the system. Due to the electrical force, the droplet started to deform until achieving a new equilibrium state and the dynamic process is recorded. By comparing the equilibrium state under different electric field strength, we found a deformation hysteresis phenomenon, i.e., different deformations were obtained when increasing and decreasing the electric field. To be specific, a large electric field (E = 0.57 V ·nm^-1) is needed to stretch the nano-droplet to touch the upper plate, while a relatively lower field (E = 0.40 V ·nm^-1) is adequate to keep it contacting with the plate. Accompanied by the deformation hysteresis, a distribution hysteresis of the average dipole orientations of water molecules in the nano-droplet is also found. Such a hysteresis phenomenon is caused by the electrohydrodynamic interactions between droplet and plates, and the findings of this study could enhance our understanding of droplet deformation in an electric field.
Collapse
Affiliation(s)
- Fenhong Song
- School of Energy and Power Engineering, Northeast Electric Power University, Jilin, 132012, Jilin, P.R. China
| | - Dapeng Ju
- School of Energy and Power Engineering, Northeast Electric Power University, Jilin, 132012, Jilin, P.R. China
| | - Jing Fan
- School of Energy and Power Engineering, Northeast Electric Power University, Jilin, 132012, Jilin, P.R. China
| | - Qicheng Chen
- School of Energy and Power Engineering, Northeast Electric Power University, Jilin, 132012, Jilin, P.R. China
| | - Qingzhen Yang
- The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, 710049, Xi'an, Shaanxi, P.R. China.
- Bioinspired Engineering and Biomechanics Center (BEBC), Xi'an Jiaotong University, 710049, Xi'an, Shaanxi, P.R. China.
| |
Collapse
|
12
|
Zhao L, Cheng J. Characterizing the bifurcating configuration of hydrogen bonding network in interfacial liquid water and its adhesion on solid surfaces. RSC Adv 2019; 9:16423-16430. [PMID: 35516358 PMCID: PMC9064418 DOI: 10.1039/c9ra02578b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Accepted: 05/21/2019] [Indexed: 12/22/2022] Open
Abstract
The interfacial structures of liquid water molecules adjacent to a solid surface contribute significantly to the interfacial properties of aqueous solutions, and are of prime importance in a wide spectrum of applications. In this work, we use molecular dynamics (MD) simulations to explore the interfacial structures, mainly in term of hydrogen bonding network, of a liquid water film interacting intimately with solid surfaces, which are composed of [100] face centered cubic (FCC) lattices. We disclose the formation of a bifurcating configuration of hydrogen bonds in interfacial liquid water and ascribe its occurrence to the collective effects of water density depletion, hydrogen bonds and local polarization. Such bifurcating configuration of interfacial water molecules consists of repetitive layer by layer water sheets with intra-layer hydrogen bonding network being formed in each layer, and inter-layer defects, i.e., hydrogen bonds formed between two neighboring layers of interfacial water. A lower bound of 2.475 for the average number of hydrogen bonds per interfacial water molecule is expected. Our MD study on the interfacial configuration of water on solid surfaces reveals a quadratic dependence of adhesion on the solid-liquid affinity, bridging the gap between the macroscopic interfacial property W adh and the microscopic parameter ε SL of the depth of the Lennard-Jones solid-liquid potential.
Collapse
Affiliation(s)
- Lei Zhao
- Department of Mechanical Engineering, Virginia Polytechnic Institute and State University Blacksburg VA 24061 USA +1 (540) 231 4161
| | - Jiangtao Cheng
- Department of Mechanical Engineering, Virginia Polytechnic Institute and State University Blacksburg VA 24061 USA +1 (540) 231 4161
| |
Collapse
|
13
|
Chen S, Du C, Feng D, Chen C, Wang J. A Monte Carlo model for self-assembly of polytetrafluoroethylene nanoparticle films via repulsive electrostatic interactions. Phys Chem Chem Phys 2019; 21:12477-12484. [DOI: 10.1039/c9cp01856e] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
This work formulates a Monte Carlo model to make predictions on the repulsive electrostatic self-assembly of close-packed monolayer and multilayer PTFE nanoparticle films.
Collapse
Affiliation(s)
- Shuai Chen
- State Key Laboratory of Tribology
- Tsinghua University
- Beijing 100084
- China
- Institute of High Performance Computing
| | - Chuan Du
- State Key Laboratory of Tribology
- Tsinghua University
- Beijing 100084
- China
| | - Dong Feng
- State Key Laboratory of Tribology
- Tsinghua University
- Beijing 100084
- China
| | - Chaolang Chen
- State Key Laboratory of Tribology
- Tsinghua University
- Beijing 100084
- China
| | - Jiadao Wang
- State Key Laboratory of Tribology
- Tsinghua University
- Beijing 100084
- China
| |
Collapse
|
14
|
Song F, Ma L, Fan J, Chen Q, Zhang L, Li BQ. Wetting Behaviors of a Nano-Droplet on a Rough Solid Substrate under Perpendicular Electric Field. NANOMATERIALS (BASEL, SWITZERLAND) 2018; 8:E340. [PMID: 29772828 PMCID: PMC5977354 DOI: 10.3390/nano8050340] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Revised: 05/14/2018] [Accepted: 05/15/2018] [Indexed: 12/27/2022]
Abstract
Molecular dynamic simulations were adopted to study the wetting properties of nanoscale droplets on rough silicon solid substrate subject to perpendicular electric fields. The effect of roughness factor and electric field strength on the static and dynamic wetting behaviors of a nano-droplet on a solid surface was investigated at the molecular level. Results show that the static contact angle tends to decrease slightly and show small difference with the increase of roughness factor, while it shows an obvious increase for the ramp-shaped surface because the appearing bottom space reduces the wettability of solid surface. Additionally, under the electric field, a nano-droplet was elongated in the field direction and the equilibrium contact angle increases with the increase of electric field strength. The nano-droplet was completely stretched to be column-shaped at a threshold value of the field. Besides, accompanied by the shape variation of water droplets, the molecular dipole orientations of water molecules experience a remarkable change from a random disordered distribution to an ordered profile because of the realignment of water molecules induced by electric fields.
Collapse
Affiliation(s)
- Fenhong Song
- School of Energy and Power Engineering, Northeast Electric Power University, Jilin 132012, China.
| | - Long Ma
- School of Energy and Power Engineering, Northeast Electric Power University, Jilin 132012, China.
| | - Jing Fan
- School of Energy and Power Engineering, Northeast Electric Power University, Jilin 132012, China.
| | - Qicheng Chen
- School of Energy and Power Engineering, Northeast Electric Power University, Jilin 132012, China.
| | - Lihui Zhang
- Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education, Zhejiang University of Technology, Hangzhou 310014, China.
| | - Ben Q Li
- Department of Mechanical Engineering, University of Michigan, Dearborn, MI 48128, USA.
| |
Collapse
|
15
|
Zhao L, Cheng J. The mechanism and universal scaling law of the contact line friction for the Cassie-state droplets on nanostructured ultrahydrophobic surfaces. NANOSCALE 2018; 10:6426-6436. [PMID: 29564459 DOI: 10.1039/c8nr00354h] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Besides the Wenzel state, liquid droplets on micro/nanostructured surfaces can stay in the Cassie state and consequently exhibit intriguing characteristics such as a large contact angle, small contact angle hysteresis and exceptional mobility. Here we report molecular dynamics (MD) simulations of the wetting dynamics of Cassie-state water droplets on nanostructured ultrahydrophobic surfaces with an emphasis on the genesis of the contact line friction (CLF). From an ab initio perspective, CLF can be ascribed to the collective effect of solid-liquid retarding and viscous damping. Solid-liquid retarding is related to the work of adhesion, whereas viscous damping arises from the viscous force exerted on the liquid molecules within the three-phase (liquid/vapor/solid) contact zone. In this work, a universal scaling law is derived to generalize the CLF on nanostructured ultrahydrophobic surfaces. With the decreasing fraction of solid-liquid contact (i.e., the solid fraction), CLF for a Cassie-state droplet gets enhanced due to the fact that viscous damping is counter-intuitively intensified while solid-liquid retarding remains unchanged. Nevertheless, the overall friction between a Cassie-state droplet and the structured surface is indeed reduced since the air cushion formed in the interstices of the surface roughness underneath the Cassie-state droplet applies negligible resistance to the contact line. Our results have revealed the genesis of CLF from an ab initio perspective, demonstrated the effects of surface structures on a moving contact line and justified the critical role of CLF in the analysis of wetting-related situations.
Collapse
Affiliation(s)
- Lei Zhao
- Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
| | - Jiangtao Cheng
- Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
| |
Collapse
|
16
|
Xiao S, Zhang Z, He J. Atomistic dewetting mechanics of Wenzel and monostable Cassie–Baxter states. Phys Chem Chem Phys 2018; 20:24759-24767. [DOI: 10.1039/c8cp03256d] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Pulling force was used to dewet water droplets in the Wenzel and the monostable Cassie–Baxter wetting states. The nanomechanics of water adhesion on nanopillars and flat surfaces in the dynamic process of dewetting was revealed. The details of effects from nanopillars and surface energy on water dewetting were clarified.
Collapse
Affiliation(s)
- Senbo Xiao
- NTNU Nanomechanical Lab, Department of Structural Engineering, Norwegian University of Science and Technology (NTNU)
- 7491 Trondheim
- Norway
| | - Zhiliang Zhang
- NTNU Nanomechanical Lab, Department of Structural Engineering, Norwegian University of Science and Technology (NTNU)
- 7491 Trondheim
- Norway
| | - Jianying He
- NTNU Nanomechanical Lab, Department of Structural Engineering, Norwegian University of Science and Technology (NTNU)
- 7491 Trondheim
- Norway
| |
Collapse
|
17
|
Song F, Ma L, Fan J, Chen Q, Lei G, Li BQ. Electro-wetting of a nanoscale water droplet on a polar solid surface in electric fields. Phys Chem Chem Phys 2018; 20:11987-11993. [DOI: 10.1039/c8cp00956b] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Water molecules interact with a polar surface in an electric field to realign their point dipoles, which determine the spreading behaviors of the droplets.
Collapse
Affiliation(s)
- Fenhong Song
- School of Energy and Power Engineering
- Northeast Electric Power University
- Jilin 132012
- China
| | - Long Ma
- School of Energy and Power Engineering
- Northeast Electric Power University
- Jilin 132012
- China
| | - Jing Fan
- School of Energy and Power Engineering
- Northeast Electric Power University
- Jilin 132012
- China
| | - Qicheng Chen
- School of Energy and Power Engineering
- Northeast Electric Power University
- Jilin 132012
- China
| | - Guangping Lei
- School of Energy and Power Engineering
- North University of China
- Taiyuan 030051
- China
| | - Ben Q. Li
- Department of Mechanical Engineering
- University of Michigan
- Dearborn
- USA
| |
Collapse
|
18
|
|
19
|
Abstract
Superrepellency is an extreme situation where liquids stay at the tops of rough surfaces, in the so-called Cassie state. Owing to the dramatic reduction of solid/liquid contact, such states lead to many applications, such as antifouling, droplet manipulation, hydrodynamic slip, and self-cleaning. However, superrepellency is often destroyed by impalement transitions triggered by environmental disturbances whereas inverse transitions are not observed without energy input. Here we show through controlled experiments the existence of a "monostable" region in the phase space of surface chemistry and roughness, where transitions from Cassie to (impaled) Wenzel states become spontaneously reversible. We establish the condition for observing monostability, which might guide further design and engineering of robust superrepellent materials.
Collapse
Affiliation(s)
- Yanshen Li
- Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
- Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China
| | - David Quéré
- Physique et Mécanique des Milieux Hétérogènes, UMR 7636 du CNRS, École Supérieure de Physique et Chimie Industrielles, 75005 Paris, France
| | - Cunjing Lv
- Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China
- Institute for Nano- and Microfluidics, Center of Smart Interfaces, Technische Universität Darmstadt, 64287 Darmstadt, Germany
| | - Quanshui Zheng
- Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China;
- Center for Nano and Micro Mechanics, Tsinghua University, Beijing 100084, China
- Applied Mechanics Lab, Tsinghua University, Beijing 100084, China
- State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
| |
Collapse
|