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

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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Postulated role of intrinsic contact-angle hysteresis in mercury porosimetry

Powder Technology ◽

10.1016/0032-5910(86)80047-x ◽

1986 ◽

Vol 48 (3) ◽

pp. 233-238 ◽

Cited By ~ 3

Author(s):

R.W. Smithwick

Keyword(s):

Contact Angle ◽

Contact Angle Hysteresis ◽

Mercury Porosimetry ◽

Intrinsic Contact Angle

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

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2009.0014 ◽

2009 ◽

Vol 367 (1894) ◽

pp. 1631-1672 ◽

Cited By ~ 503

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.

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Eco-friendly and facile fabrication of superhydrophobic aluminum alloy

Proceedings of the Institution of Mechanical Engineers Part J Journal of Engineering Tribology ◽

10.1177/13506501211028397 ◽

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.

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Relationship between Work of Adhesion and Contact Angle Hysteresis on Superhydrophobic Surfaces

The Journal of Physical Chemistry C ◽

10.1021/jp711571k ◽

2008 ◽

Vol 112 (30) ◽

pp. 11403-11407 ◽

Cited By ~ 85

Author(s):

Yonghao Xiu ◽

Lingbo Zhu ◽

Dennis W. Hess ◽

C. P. Wong

Keyword(s):

Contact Angle ◽

Contact Angle Hysteresis ◽

Superhydrophobic Surfaces ◽

Work Of Adhesion

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A Simple Method to Create Superhydrophobic Aluminium Surfaces

Materials Science Forum ◽

10.4028/www.scientific.net/msf.706-709.2874 ◽

2012 ◽

Vol 706-709 ◽

pp. 2874-2879 ◽

Cited By ~ 10

Author(s):

R. Jafari ◽

Masoud Farzaneh

Keyword(s):

Contact Angle ◽

Stearic Acid ◽

Synergistic Effects ◽

Low Cost ◽

Contact Angle Hysteresis ◽

Spray Coating ◽

Superhydrophobic Surfaces ◽

Water Contact ◽

Simple Method ◽

Static Contact

Superhydrophobic surfaces were prepared using a very simple and low-cost method by spray coating. A high static water contact angle of about 154° was obtained by deposition of stearic acid on an aluminium alloy. However, this coating demonstrated a high contact angle hysteresis (~ 30º). On the other hand, superhydrophobic surfaces with a static contact angle of about 162º and 158º, and a low contact angle hysteresis of about 3º and 5º were respectively obtained by incorporating nanoparticles of SiO2and CaCO3in stearic acid. The excellent resulting hydrophobicity is attributed to the synergistic effects of micro/nanoroughness and low surface energy. A study of the wettability of these surfaces at temperatures ranging from 20 to-10 °C showed that the superhydrophobic surface becomes rather hydrophobic at supercooled temperatures.

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Evaporative Particle Deposition on Superhydrophobic Surfaces

Volume 10: Micro- and Nano-Systems Engineering and Packaging ◽

10.1115/imece2013-63928 ◽

2013 ◽

Author(s):

Mercy Dicuangco ◽

Susmita Dash ◽

Justin A. Weibel ◽

Suresh V. Garimella

Keyword(s):

Contact Angle ◽

Particle Deposition ◽

Contact Angle Hysteresis ◽

Droplet Evaporation ◽

Superhydrophobic Surfaces ◽

Contact Radius ◽

Droplet Shape ◽

Substrate Heating ◽

Solid Liquid ◽

Constant Contact Angle

The ability to control the size, shape, and location of particulate deposits is important in patterning, nanowire growth, sorting biological samples, and many other industrial and scientific applications. It is therefore of interest to understand the fundamentals of particle deposition via droplet evaporation. In the present study, we experimentally probe the assembly of particles on superhydrophobic surfaces by the evaporation of sessile water droplets containing suspended latex particles. Superhydrophobic surfaces are known to result in a significant decrease in the solid-liquid contact area of a droplet placed on such a substrate, thereby increasing the droplet contact angle and reducing the contact angle hysteresis. We conduct experiments on superhydrophobic surfaces of different geometric parameters that are maintained at different surface temperatures. The transient droplet shape and wetting behavior during evaporation are analyzed as a function of substrate temperature as well as surface morphology. During the evaporation process, the droplet exhibits a constant contact radius mode, a constant contact angle mode, or a mixed mode in which the contact angle and contact radius change simultaneously. The evaporation time of a droplet can be significantly reduced with substrate heating as compared to room-temperature evaporation. To describe the spatial distribution of the particle residues left on the surfaces, qualitative and quantitative evaluations of the deposits are presented. The results show that droplet evaporation on superhydrophobic surfaces, driven by mass diffusion under isothermal conditions or by substrate heating, suppresses particle deposition at the contact line. This preempts the so-called coffee-ring and allows active control of the location of particle deposition.

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Simple Fabrication of Robust Water-Repellent Surfaces with Low Contact-Angle Hysteresis Based on Impregnation

Advanced Materials Interfaces ◽

10.1002/admi.201300138 ◽

2014 ◽

Vol 1 (3) ◽

pp. 1300138 ◽

Cited By ~ 62

Author(s):

Alexander Eifert ◽

Dorothea Paulssen ◽

Subramanyan Namboodiri Varanakkottu ◽

Tobias Baier ◽

Steffen Hardt

Keyword(s):

Contact Angle ◽

Contact Angle Hysteresis ◽

Water Repellent

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Biomimetics inspired surfaces for drag reduction and oleophobicity/philicity

Beilstein Journal of Nanotechnology ◽

10.3762/bjnano.2.9 ◽

2011 ◽

Vol 2 ◽

pp. 66-84 ◽

Cited By ~ 121

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.

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