scholarly journals Unexpected Frictional Behavior of Laser-Textured Hydrophobic Surfaces

Lubricants ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 31
Author(s):  
Hiba Jendoubi ◽  
Olga Smerdova ◽  
Noël Brunetière
Keyword(s):  
High Pressure ◽  
Regime Theory ◽  
Textured Surfaces ◽  
Hydrophobic Surfaces ◽  
Frictional Behavior ◽  
Low Surface Energy ◽  
Energy Material ◽  
Circular Holes ◽  
Lubricated Contact ◽  
Generation Of Vortices

Hydrophobic surfaces can allow a liquid to slip over the surface and can thus reduce friction in lubricated contact working in a full film regime. Theory supports that the amount of slip can be increased if super-hydrophobic surfaces that are composed of a textured low surface energy material are used. In this work, polytetrafluoroethylene (PTFE) polymer samples were textured with a femto second laser to create super-hydrophobic surfaces by machining a hexagonal network of small circular holes with 10 and 20 μm lattice sides. The frictional behavior of these surfaces was compared to the smooth PTFE samples. Surprisingly, the textured surfaces revealed higher friction coefficients than the smooth surfaces. This higher friction can be explained by a change of wetting regime due to high pressure in fluid and a possible generation of vortices in the cavities.

scholarly journals Wettability on Different Surfaces

2020 ◽  
Author(s):  
Yeeli Kelvii Kwok
Keyword(s):  
Contact Angle ◽  
Textured Surface ◽  
Original Material ◽  
Textured Surfaces ◽  
Hydrophobic Surfaces ◽  
Hydrophilic Surfaces ◽  
Young's Equation

Wettability has been explored for 100 years since it is described by Young’s equation in 1805. It is all known that hydrophilicity means contact angle (θ), θ < 90°; hydrophobicity means contact angle (θ), θ > 90°. The utilization of both hydrophilic surfaces and hydrophobic surfaces has also been achieved in both academic and practical perspectives. In order to understand the wettability of a droplet distributed on the textured surfaces, the relevant models are reviewed along with understanding the formation of contact angle and how it is affected by the roughness of the textured surface aiming to obtain the required surface without considering whether the original material is hydrophilic or hydrophobic.

scholarly journals SUPERHYDROPHOBIC SURFACES FOR DRAG REDUCTION

2014 ◽  
Author(s):  
Alessandro Bottaro
Keyword(s):  
Drag Reduction ◽  
Slip Length ◽  
Superhydrophobic Surfaces ◽  
Transition To Turbulence ◽  
Effective Coupling ◽  
Instability Waves ◽  
Low Surface Energy ◽  
Apparent Slip ◽  
Energy Material ◽  
Relevant Length Scale

Properties of superhydrophobic materials are examined in light of their possible use for drag reduction in naval applications. To achieve superhydrophobicity a low-surface-energy material must be structured so as to minimize the liquid-solid interactions. The crucial aspect is that of maintaining a layer of gas in between the (rough) wall and the liquid, and this can be achieved by hierarchical micro- and nano-structuring of the solid surface, to ensure a sufficiently large apparent slip of the fluid at the wall, thus reducing skin friction. The behavior of the liquid is quantified by a slip length; recent results have shown that this length can be as large as 400 μm. As far as transition to turbulence is concerned, we show that superhydrophobic surfaces are effective (i.e. they delay the onset of travelling instability waves) only in channels with characteristic dimensions of a few millimeters. Conversely, when the fluid flow has already attained a turbulent state, the gain in term of drag reduction can be very significant also in macroscopic configurations. This occurs because the relevant length scale of the boundary layer is now the thickness of the viscous sub-layer, which can be of magnitude comparable to the slip length, so that an effective coupling emerges. Finally, some procedures to produce superhydrophobic surfaces are examined, in light of the possible application of such innovative coatings on the hull of ships.

scholarly journals Bioinspired super-hydrophobic fractal array via a facile electrochemical route: preparation and corrosion inhibition for Cu

RSC Advances ◽  
2022 ◽  
Vol 12 (1) ◽  
pp. 265-276
Author(s):  
Robert H. B. Miller ◽  
Yinsha Wei ◽  
Cong Ma ◽  
Longyun Li ◽  
Jihan Shao ◽  
...  
Keyword(s):  
Surface Energy ◽  
Corrosion Protection ◽  
Corrosion Inhibition ◽  
Energy Materials ◽  
Hydrophobic Surfaces ◽  
Low Surface Energy

Super-hydrophobic surfaces (SHS) usually are formed from a combination of low surface energy materials and micro/nanostructures via two-step approaches, and they have promising applications in material corrosion protection.

PFPE Modified Silicon Nano-Textured Surfaces for Adhesion and Friction Reduction

2008 ◽  
Author(s):  
Ying Song ◽  
Hengyu Wang ◽  
Min Zou
Keyword(s):  
Amorphous Silicon ◽  
Silicon Surface ◽  
Surface Hydrophobicity ◽  
Friction Reduction ◽  
New Technique ◽  
Textured Surface ◽  
Textured Surfaces ◽  
Hydrophobic Surfaces ◽  
A New Technique ◽  
Induced Crystallization

This paper reports a new technique of producing hydrophobic surfaces with WCA as high as 147°. This technique consists of first generating nano-textures on a silicon surface via aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) and then applying perfluoropolyether (PFPE) on the nano-textured surface (NTS). The resulting PFPE-modified NTS showed significant improvement on both surface hydrophobicity and tribological performances compared to a PFPE-modified smooth silicon surface.

scholarly journals Greigite (Fe3S4) is thermodynamically stable: Implications for its terrestrial and planetary occurrence

2020 ◽  
Vol 117 (46) ◽  
pp. 28645-28648
Author(s):  
Tamilarasan Subramani ◽  
Kristina Lilova ◽  
Mykola Abramchuk ◽  
Kurt D. Leinenweber ◽  
Alexandra Navrotsky
Keyword(s):  
High Pressure ◽  
Monoclinic Phase ◽  
Iron Sulfide ◽  
Enthalpies Of Formation ◽  
Stable Phase ◽  
Fine Grained ◽  
Low Surface Energy ◽  
Iron Sulfide Minerals ◽  
The Common ◽  
The Stability

Iron sulfide minerals are widespread on Earth and likely in planetary bodies in and beyond our solar system. Using measured enthalpies of formation for three magnetic iron sulfide phases: bulk and nanophase Fe3S4spinel (greigite), and its high-pressure monoclinic phase, we show that greigite is a stable phase in the Fe–S phase diagram at ambient temperature. The thermodynamic stability and low surface energy of greigite supports the common occurrence of fine-grained Fe3S4in many anoxic terrestrial settings. The high-pressure monoclinic phase, thermodynamically metastable below about 3 GPa, shows a calculated negative P-T slope for its formation from the spinel. The stability of these three phases suggests their potential existence on Mercury and their magnetism may contribute to its present magnetic field.

FRICTIONAL BEHAVIOR OF MICRO/NANOTEXTURED SURFACES INVESTIGATED BY ATOMIC FORCE MICROSCOPE: A REVIEW

2015 ◽  
Vol 22 (06) ◽  
pp. 1530001 ◽  
Author(s):  
XIAOLIANG ZHANG ◽  
JUNHONG JIA
Keyword(s):  
Atomic Force Microscope ◽  
Friction Pair ◽  
Volume Ratio ◽  
Contact Pair ◽  
Nanoelectromechanical Systems ◽  
Textured Surfaces ◽  
Effective Technique ◽  
Frictional Behavior ◽  
Atomic Force ◽  
Atmosphere Environment

Tribological issues between friction pair are fundamental problems for minimized devices because of their higher surface-to-volume ratio. Micro/nanotexturing is an effective technique to reduce actual contact area between contact pair at the nanoscale. Micro/nanotexture made a great impact on the frictional behavior of textured surfaces. This paper summarizes the recent advancements in the field of frictional behavior of micro/nanotextured surfaces, which are based on solid surface contact in atmosphere environment, especially focusing on the factors influencing the frictional behavior: Surface property, texturing density, texturing height, texturing structure and size of contact pair (atomic force microscope (AFM) tip) and texturing structures. Summarizing the effects of these factors on the frictional behavior is helpful for the understanding and designing of the surfaces in sliding micro/nanoelectromechanical systems (MEMS/NEMS). Controlling and reducing the friction force in moving mechanical systems is very important for the performance and reliability of nanosystems, which contribute to a sustainable future.

The Effect of Thermal Resistance for Dropwise Condensation on Hydrophobic Micro-Pillared Structures

2012 ◽  
Author(s):  
Sara S. Beaini ◽  
Hector Mendoza ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Surface Energy ◽  
Thermal Resistance ◽  
Droplet Growth ◽  
Dropwise Condensation ◽  
Textured Surfaces ◽  
Critical Question ◽  
Low Surface Energy ◽  
The Continuum

Superhydrophobic/hydrophobic surfaces, developed to promote dropwise condensation, can be produced by modifying the surface chemically with low surface energy films, and/or structurally by fabricating micro-textured surfaces. Some research has reported the increased thermal resistance from the added chemical layer and its effect on condensation heat transfer. A critical question of interest is the thermal resistance due to micro-pillared structures and their influence on droplet growth during condensation as compared to smooth or non-textured surfaces. Though idealized, this paper presents a theoretical and computational model for evaluating and quantifying the effects of the pillared structures thermal resistance, as well as the continuum versus non-continuum mechanisms affecting droplet growth during dropwise condensation. The model is used to compare different micro-pillared surfaces, cited in the literature, and to predict which micro-pillar dimensions contribute to slower condensate growth despite the higher contact angle advantage during dropwise condensation.

scholarly journals A Review of Fabrication Methods, Properties and Applications of Superhydrophobic Metals

Processes ◽  
2021 ◽  
Vol 9 (4) ◽  
pp. 666
Author(s):  
Kosmas Ellinas ◽  
Panagiotis Dimitrakellis ◽  
Panagiotis Sarkiris ◽  
Evangelos Gogolides
Keyword(s):  
Surface Energy ◽  
Real Life ◽  
Nanometer Scale ◽  
Metallic Surfaces ◽  
Wetting Properties ◽  
Low Surface Energy ◽  
Sacred Lotus ◽  
Energy Material ◽  
Surface Topographies ◽  
Self Cleaning

Hydrophobicity and superhydrophobicity with self-cleaning properties are well-known characteristics of several natural surfaces, such as the leaves of the sacred lotus plant (Nelumbo nucifera). To achieve a superhydrophobic state, micro- and nanometer scale topography should be realized on a low surface energy material, or a low surface energy coating should be deposited on top of the micro-nano topography if the material is inherently hydrophilic. Tailoring the surface chemistry and topography to control the wetting properties between extreme wetting states enables a palette of functionalities, such as self-cleaning, antifogging, anti-biofouling etc. A variety of surface topographies have been realized in polymers, ceramics, and metals. Metallic surfaces are particularly important in several engineering applications (e.g., naval, aircrafts, buildings, automobile) and their transformation to superhydrophobic can provide additional functionalities, such as corrosion protection, drag reduction, and anti-icing properties. This review paper focuses on the recent advances on superhydrophobic metals and alloys which can be applicable in real life applications and aims to provide an overview of the most promising methods to achieve sustainable superhydrophobicity.

Three-level hierarchical superhydrophobic Cu–Zn coating on a steel substrate without chemical modification for self-cleaning property

2017 ◽  
Vol 41 (13) ◽  
pp. 5436-5444 ◽  
Author(s):  
Hao Li ◽  
Sirong Yu
Keyword(s):  
Surface Energy ◽  
Chemical Modification ◽  
Steel Surface ◽  
Steel Substrate ◽  
Chemically Modified ◽  
Low Surface Energy ◽  
Energy Material ◽  
One Step ◽  
Self Cleaning

A superhydrophobic Cu–Zn coating was fabricated on a steel surface by facile one-step electrodeposition, without being chemically modified by a low surface energy material.

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