scholarly journals Biomimetics inspired surfaces for drag reduction and oleophobicity/philicity

2011 ◽  
Vol 2 ◽  
pp. 66-84 ◽  
Author(s):  
Bharat Bhushan
Keyword(s):  
Contact Angle ◽  
Fluid Flow ◽  
Drag Reduction ◽  
Organic Contaminants ◽  
Contact Angle Hysteresis ◽  
Hierarchical Structures ◽  
Aquatic Animal ◽  
Plant Leaves ◽  
Reduction Efficiency ◽  
Self Cleaning

The emerging field of biomimetics allows one to mimic biology or nature to develop nanomaterials, nanodevices, and processes which provide desirable properties. Hierarchical structures with dimensions of features ranging from the macroscale to the nanoscale are extremely common in nature and possess properties of interest. There are a large number of objects including bacteria, plants, land and aquatic animals, and seashells with properties of commercial interest. Certain plant leaves, such as lotus (Nelumbo nucifera) leaves, are known to be superhydrophobic and self-cleaning due to the hierarchical surface roughness and presence of a wax layer. In addition to a self-cleaning effect, these surfaces with a high contact angle and low contact angle hysteresis also exhibit low adhesion and drag reduction for fluid flow. An aquatic animal, such as a shark, is another model from nature for the reduction of drag in fluid flow. The artificial surfaces inspired from the shark skin and lotus leaf have been created, and in this article the influence of structure on drag reduction efficiency is reviewed. Biomimetic-inspired oleophobic surfaces can be used to prevent contamination of the underwater parts of ships by biological and organic contaminants, including oil. The article also reviews the wetting behavior of oil droplets on various superoleophobic surfaces created in the lab.

Micro-, nano- and hierarchical structures for superhydrophobicity, self-cleaning and low adhesion

2009 ◽  
Vol 367 (1894) ◽  
pp. 1631-1672 ◽  
Author(s):  
Bharat Bhushan ◽  
Yong Chae Jung ◽  
Kerstin Koch
Keyword(s):  
Contact Angle ◽  
Low Cost ◽  
Contact Angle Hysteresis ◽  
Hierarchical Structures ◽  
Adhesive Force ◽  
Water Repellent ◽  
Lotus Effect ◽  
Composite State ◽  
Static Contact ◽  
Self Cleaning

Superhydrophobic surfaces exhibit extreme water-repellent properties. These surfaces with high contact angle and low contact angle hysteresis also exhibit a self-cleaning effect and low drag for fluid flow. Certain plant leaves, such as lotus leaves, are known to be superhydrophobic and self-cleaning due to the hierarchical roughness of their leaf surfaces. The self-cleaning phenomenon is widely known as the ‘lotus effect’. Superhydrophobic and self-cleaning surfaces can be produced by using roughness combined with hydrophobic coatings. In this paper, the effect of micro- and nanopatterned polymers on hydrophobicity is reviewed. Silicon surfaces patterned with pillars and deposited with a hydrophobic coating were studied to demonstrate how the effects of pitch value, droplet size and impact velocity influence the transition from a composite state to a wetted state. In order to fabricate hierarchical structures, a low-cost and flexible technique that involves replication of microstructures and self-assembly of hydrophobic waxes is described. The influence of micro-, nano- and hierarchical structures on superhydrophobicity is discussed by the investigation of static contact angle, contact angle hysteresis, droplet evaporation and propensity for air pocket formation. In addition, their influence on adhesive force as well as efficiency of self-cleaning is discussed.

scholarly journals Constructing a Dual-Function Surface by Microcasting and Nanospraying for Efficient Drag Reduction and Potential Antifouling Capabilities

Micromachines ◽  
2019 ◽  
Vol 10 (7) ◽  
pp. 490 ◽  
Author(s):  
Liguo Qin ◽  
Mahshid Hafezi ◽  
Hao Yang ◽  
Guangneng Dong ◽  
Yali Zhang
Keyword(s):  
Contact Angle ◽  
Drag Reduction ◽  
High Speed ◽  
Contact Angle Hysteresis ◽  
Dual Function ◽  
Water Contact ◽  
Shark Skin ◽  
Biomimetic Surface ◽  
Self Cleaning ◽  
Living Organisms

To improve the drag-reducing and antifouling performance of marine equipment, it is indispensable to learn from structures and materials that are found in nature. This is due to their excellent properties, such as intelligence, microminiaturization, hierarchical assembly, and adaptability. Considerable interest has arisen in fabricating surfaces with various types of biomimetic structures, which exhibit promising and synergistic performances similar to living organisms. In this study, a dual bio-inspired shark-skin and lotus-structure (BSLS) surface was developed for fabrication on commercial polyurethane (PU) polymer. Firstly, the shark-skin pattern was transferred on the PU by microcasting. Secondly, hierarchical micro- and nanostructures were introduced by spraying mesoporous silica nanospheres (MSNs). The dual biomimetic substrates were characterized by scanning electron microscopy, water contact angle characterization, antifouling, self-cleaning, and water flow impacting experiments. The results revealed that the BSLS surface exhibited dual biomimetic features. The micro- and nano-lotus-like structures were localized on a replicated shark dermal denticle. A contact angle of 147° was observed on the dual-treated surface and the contact angle hysteresis was decreased by 20% compared with that of the nontreated surface. Fluid drag was determined with shear stress measurements and a drag reduction of 36.7% was found for the biomimetic surface. With continuous impacting of high-speed water for up to 10 h, the biomimetic surface stayed superhydrophobic. Material properties such as inhibition of protein adsorption, mechanical robustness, and self-cleaning performances were evaluated, and the data indicated these behaviors were significantly improved. The mechanisms of drag reduction and self-cleaning are discussed. Our results indicate that this method is a potential strategy for efficient drag reduction and antifouling capabilities.

Eco-friendly and facile fabrication of superhydrophobic aluminum alloy

2021 ◽  
pp. 135065012110283
Author(s):  
Jayanth Ivvala ◽  
Priya Mandal ◽  
Harpreet Singh Arora ◽  
Harpreet Singh Grewal
Keyword(s):  
Contact Angle ◽  
Aluminum Alloy ◽  
Large Scale ◽  
Prolonged Exposure ◽  
Contact Angle Hysteresis ◽  
Hierarchical Structures ◽  
Superhydrophobic Surfaces ◽  
Developed Surface ◽  
Vapor Deposition Technique ◽  
Self Cleaning

Synthetic superhydrophobic surfaces have drawn significant interest owing to their water-resistant and self-cleaning applications. However, most of the fabrication practices involve complex processes that are unsustainable to withstand large-scale fabrication to transform into standard industrial practice. The desired durability of these surfaces is another crucial challenge that makes the translation of these products difficult. In this paper, we reported the fabrication of superhydrophobic aluminum alloy with a simpler, low-cost, and eco-friendly technique using the hydrothermal treatment. Subsequently, the surface energy of the processed substrate was modulated using a chemical vapor deposition technique. The developed surface shows an extreme water repellency with a contact angle above 160° and a very low contact angle hysteresis and rolling angle (<5°). Surface morphological characterizations showed the formation of nanoscale hierarchical structures which resulted in a stable Cassie state due to the effective entrapment of air and exhibiting self-cleaning ability. The developed surface showed extreme wetting resilience during exposure to a droplet impingement with an impinging velocity of >2 m/s. Further, these superhydrophobic surfaces were exposed to atmospheric weather conditions to check their robustness. During a rain simulator testing, a developed surface showed low contact angle hysteresis (<10°) after enduring multiple cycles. The processed surface also showed significant de-wetting behavior during condensation experiments and chemical resistance under prolonged exposure. Weathering tests performed under outdoor conditions showed an insignificant influence on the de-wettability of the processed sample. The present study highlights the fabrication of superhydrophobic durable metallic surfaces through a facile and green fabrication route for multifunctional applications.

scholarly journals One-Step Preparation of Durable Super-Hydrophobic MSR/SiO2 Coatings by Suspension Air Spraying

Micromachines ◽  
2018 ◽  
Vol 9 (12) ◽  
pp. 677 ◽  
Author(s):  
Zhengyong Huang ◽  
Wenjie Xu ◽  
Yu Wang ◽  
Haohuan Wang ◽  
Ruiqi Zhang ◽  
...  
Keyword(s):  
Contact Angle ◽  
Adhesion Strength ◽  
Contact Angle Hysteresis ◽  
Surface Hardness ◽  
Hierarchical Structures ◽  
Hydrophobic Surface ◽  
Water Contact ◽  
Hydrophobic Coating ◽  
Mechanical Durability ◽  
One Step

In this study, we develop a facial one-step approach to prepare durable super-hydrophobic coatings on glass surfaces. The hydrophobic characteristics, corrosive liquid resistance, and mechanical durability of the super-hydrophobic surface are presented. The as-prepared super-hydrophobic surface exhibits a water contact angle (WCA) of 157.2° and contact angle hysteresis of 2.3°. Mico/nano hierarchical structures and elements of silicon and fluorine is observed on super-hydrophobic surfaces. The adhesion strength and hardness of the surface are determined to be 1st level and 4H, respectively. The coating is, thus, capable of maintaining super-hydrophobic state after sand grinding with a load of 200 g and wear distances of 700 mm. The rough surface retained after severe mechanical abrasion observed by atomic force microscope (AFM) microscopically proves the durable origin of the super-hydrophobic coating. Results demonstrate the feasibility of production of the durable super-hydrophobic coating via enhancing its adhesion strength and surface hardness.

Bioinspired surfaces to delay biofilm formation: different surfaces with different mechanisms

2020 ◽  
Author(s):  
Jinju Chen
Keyword(s):  
Contact Angle ◽  
Biofilm Formation ◽  
Early Stage ◽  
Contact Angle Hysteresis ◽  
Antibacterial Properties ◽  
Hierarchical Structures ◽  
Bacterial Cells ◽  
Biofilm Growth ◽  
Porous Surfaces ◽  
Rose Petal

&lt;p&gt;Biofilm associated infections are the fourth leading cause of death worldwide, within the U.S. about 2 million annual cases lead to more than $5 billion USD in added medical costs per annum. Therefore, it is important to control biofilm growth and reduce the instances of infections.&amp;#160; Physical strategies, in particular the use of rationally designed surface topographies or surface energies, have present us with an interesting approach to prevent bacterial adherence and biofilm growth without the requirement for antimicrobials.&lt;/p&gt; &lt;p&gt;A variety of natural surfaces exhibit antibacterial properties. Examples of such surfaces include rose petals with hierarchical structures and Nepenthes pitcher plants with slippery liquid-infused porous surfaces. &amp;#160;&lt;/p&gt; &lt;p&gt;In this study, we fabricated different &amp;#160;biomimetic surfaces (rose-petal surfaces and slippery liquid-infused porous surfaces). &amp;#160;&amp;#160;We have demonstrated that rose-petal surface can delay early stage P. aeruginosa and S. epidermidis biofilms formation (2 days) by about 70% and control&amp;#160; biofilm &amp;#160;formation according to surface structures.&amp;#160; The mechanisms of hierarchical structures &amp;#160;of rose-petal influence biofilm formation are two folds: 1) Papillae microstructure block &amp;#160;the bacterial clusters in between the valleys, limiting the potential for cell-cell communication via fibrous networks, thereby resulting in impaired biofilm growth. 2) The secondary structure (nano-folds) on microstructures can align bacterial cells within the constrained grooves, thereby delaying cell clusters formation during short term growth of biofilm.&lt;/p&gt; &lt;p&gt;While, the slippery liquid-infused porous surface(s) can prevent over 90% P. aeruginosa and S. epidermidis biofilms formation for a duration of 6 days.&amp;#160; These are mainly attributed to their high contact angle and extreme low contact angle hysteresis.&lt;/p&gt;

A SUPERHYDROPHOBIC COATING ON TITANIUM ALLOYS BY SIMPLE CHEMICAL ETCHING

2021 ◽  
pp. 2150027
Author(s):  
YUFENG ZHANG ◽  
GUOLIANG CHEN ◽  
YAMING WANG ◽  
YONGCHUN ZOU
Keyword(s):  
Contact Angle ◽  
Titanium Alloy ◽  
Electrochemical Impedance ◽  
Contact Angle Hysteresis ◽  
Manufacturing Strategy ◽  
Superhydrophobic Coating ◽  
Sliding Angle ◽  
The Hierarchical Structure ◽  
Silane Modification ◽  
Self Cleaning

In the present study, a scalable-manufactured and environmental-friendly method was proposed to fabricate the superhydrophobic coating on titanium alloy. The hierarchical binary surface structures were obtained by hydrothermal treatment of titanium alloy with oxalic acid and sodium hydroxide solutions successively. The hierarchical structure surfaces after fluoroalkyl-silane modification possessed a maximum contact angle of 158.7° and a sliding angle of 4.3°. The low contact angle hysteresis surface can lead to efficient self-cleaning performance, which was confirmed by the bounce and roll off of water droplet on the surface. Furthermore, the anticorrosion behaviors of the superhydrophobic coating in 3.5[Formula: see text]wt.% NaCl solution was evaluated by the electrochemical impedance spectroscopy (EIS). It was found that the superhydrophobic coating can maintain its superhydrophobic state (150°) within 48 h, thereby effectively preventing the corrosive medium from penetrating into the coating. This simple yet fast anti-corrosion/self-cleaning superhydrophobic coating manufacturing strategy will enlighten its potential application in the engineering fields.

Controlling the Wetting State With Bio-Mimetic Hierarchical Conical Microstructures

2018 ◽  
Author(s):  
Il Woong Park ◽  
Maria Fernandino ◽  
Carlos Alberto Dorao
Keyword(s):  
Contact Angle ◽  
Geometric Parameter ◽  
Contact Angle Hysteresis ◽  
Apparent Contact Angle ◽  
The Self ◽  
Self Cleaning ◽  
Conical Structures

Achieving a high apparent contact angle with a low contact angle hysteresis represent a major enabling step in applications by the self-cleaning property. In this work, bio-mimetic inspired structures complemented with silanization coating are presented for developing surfaces with a high apparent contact angle with a low contact angle hysteresis. The structures are based on hierarchical conical structures with the different geometric parameter. It was observed that the fabricated surface has high apparent contact angle and low contact angle hysteresis. For that, bio-mimetic texturing of surface and silanization coating can be applied. In this study, hierarchical conical structures were fabricated. The shape of the structures has been inspired from the surface from nature. Moreover, the effect of the silanization coating on the surfaces which has different geometric parameter has been identified.

Measurement Studies on Superhydrophobic Materials

2014 ◽  
Vol 988 ◽  
pp. 134-142
Author(s):  
Sheila Devasahayam ◽  
Prasad Yarlagadda
Keyword(s):  
Surface Roughness ◽  
Contact Angle ◽  
Reynolds Number ◽  
Drag Reduction ◽  
Contact Line ◽  
Contact Time ◽  
Contact Angle Hysteresis ◽  
Surface Friction ◽  
Solid Surfaces ◽  
Geometrical Configuration

Superhydrophobicity is directly related to the wettability of the surfaces. Cassie-Baxter state relating to geometrical configuration of solid surfaces is vital to achieving the Superhydrophobicity and to achieve Cassie-Baxter state the following two criteria need to be met: 1) Contact line forces overcome body forces of unsupported droplet weight and 2) The microstructures are tall enough to prevent the liquid that bridges microstructures from touching the base of the microstructures [1]. In this paper we discuss different measurements used to characterise/determine the superhydrophobic surfaces.Keywords: Wettability, contact angle, contact angle hysteresis, contact time, surface roughness, drag reduction measurements, morphology, surface friction, Reynolds number

SUPERHYDROPHOBIC SURFACES FOR WATER-REPELLENT OR SELF-CLEANING BEHAVIOR: CHEMICAL EFFECT

2009 ◽  
Vol 16 (05) ◽  
pp. 645-652
Author(s):  
Y. P. ZHOU ◽  
Z. W. LIN ◽  
J. BROWN
Keyword(s):  
Contact Angle ◽  
Thermodynamic Analysis ◽  
Contact Angle Hysteresis ◽  
Superhydrophobic Surfaces ◽  
Chemical Effect ◽  
Water Repellent ◽  
Cleaning Behavior ◽  
Self Cleaning ◽  
Intrinsic Contact Angle

In this study, a thermodynamic analysis is conducted to investigate the chemical effect, in terms of intrinsic contact angle (CA), on the superhydrophobic behavior. It is theoretically revealed that the essential effect of intrinsic CA is to promote the composite transition. In particular, a large intrinsic CA more than 90° is necessary for such transition. Furthermore, for a pillar system with an intrinsic CA smaller than 90°, composite states are not impossible but is thermodynamically unstable. Once composite states are achieved, the advancing or maximum CA always approaches 180° whether an intrinsic CA is larger or smaller than 90°. In addition, the role of intrinsic CA in the water-repellent or self-cleaning behavior such as contact angle hysteresis (CAH) and equilibrium CA has been discussed in detail.

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