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

It is well established that the water wettability of materials is governed by both the chemical composition and the geometrical microstructure of the surface.1 Traditional textile wet processing treatments do indeed rely fundamentally upon complete wetting out of a textile structure to achieve satisfactory performance.2 However, the complexities introduced through the heterogeneous nature of the fiber surfaces, the nature of the fiber composition and the actual construction of the textile material create difficulties in attempting to predict the exact wettability of a particular textile material. For many applications the ability of a finished fabric to exhibit water repellency (in other words low wettability) is essential2 and potential applications of highly water repellent textile materials include rainwear, upholstery, protective clothing, sportswear, and automobile interior fabrics. Recent research indicates that such applications may benefit from a new generation of water repellent materials that make use of the “lotus effect” to provide ultrahydrophobic textile materials.3,4 Ultrahydrophobic surfaces are typically termed as the surfaces that show a water contact angle greater than 150°C with very low contact angle hysteresis.4 In the case of textile materials, the level of hydrophobicity is often determined by measuring the static water contact angle only, since it is difficult to measure the contact angle hysteresis on a textile fabric because of the high levels of roughness inherent in textile structures.

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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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Oscillating Magnetic Drop: How to Grade Water-Repellent Surfaces

Coatings ◽

10.3390/coatings9040270 ◽

2019 ◽

Vol 9 (4) ◽

pp. 270 ◽

Cited By ~ 1

Author(s):

Angelica Goncalves Dos Santos ◽

Francisco Javier Montes-Ruiz Cabello ◽

Fernando Vereda ◽

Miguel A. Cabrerizo-Vilchez ◽

Miguel A. Rodriguez-Valverde

Keyword(s):

Contact Angle ◽

Ad Hoc ◽

Contact Angle Hysteresis ◽

Aqueous Suspension ◽

High Mobility ◽

Surface Friction ◽

Water Repellent ◽

Glass Substrates ◽

Drop Adhesion ◽

Solid Liquid

Evaluation of superhydrophobic (SH) surfaces based on contact angle measurements is challenging due to the high mobility of drops and the resolution limits of optical goniometry. For this reason, some alternatives to drop-shape methods have been proposed such as the damped-oscillatory motion of ferrofluid sessile drops produced by an external magnetic field. This approach provides information on surface friction (lateral/shear adhesion) from the kinetic energy dissipation of the drop. In this work, we used this method to compare the low adhesion of four commercial SH coatings (Neverwet, WX2100, Ultraever dry, Hydrobead) formed on glass substrates. As ferrofluid, we used a maghemite aqueous suspension (2% v/v) synthesized ad hoc. The rolling magnetic drop is used as a probe to explore shear solid–liquid adhesion. Additionally, drop energy dissipates due to velocity-dependent viscous stresses developed close to the solid–liquid interface. By fitting the damped harmonic oscillations, we estimated the decay time on each coating. The SH coatings were statistically different by using the mean damping time. The differences found between SH coatings could be ascribed to surface–drop adhesion (contact angle hysteresis and apparent contact area). By using this methodology, we were able to grade meaningfully the liquid-repelling properties of superhydrophobic surfaces.

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Lotus Effect and Friction: Does Nonsticky Mean Slippery?

Biomimetics ◽

10.3390/biomimetics5020028 ◽

2020 ◽

Vol 5 (2) ◽

pp. 28 ◽

Cited By ~ 1

Author(s):

Md Syam Hasan ◽

Michael Nosonovsky

Keyword(s):

Contact Angle ◽

Materials Science ◽

Contact Angle Hysteresis ◽

Water Repellent ◽

Low Friction ◽

Lotus Effect ◽

Low Surface Energy ◽

Surface Patterns ◽

Specific Fracture ◽

Common Perception

Lotus-effect-based superhydrophobicity is one of the most celebrated applications of biomimetics in materials science. Due to a combination of controlled surface roughness (surface patterns) and low-surface energy coatings, superhydrophobic surfaces repel water and, to some extent, other liquids. However, many applications require surfaces which are water-repellent but provide high friction. An example would be highway or runway pavements, which should support high wheel–pavement traction. Despite a common perception that making a surface non-wet also makes it slippery, the correlation between non-wetting and low friction is not always direct. This is because friction and wetting involve many mechanisms and because adhesion cannot be characterized by a single factor. We review relevant adhesion mechanisms and parameters (the interfacial energy, contact angle, contact angle hysteresis, and specific fracture energy) and discuss the complex interrelation between friction and wetting, which is crucial for the design of biomimetic functional surfaces.

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

Surface Review and Letters ◽

10.1142/s0218625x09013281 ◽

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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Hydrophobic and Anti-Icing Behavior of UV-Laser-Treated Polyester Resin-Based Gelcoats

Processes ◽

10.3390/pr8121642 ◽

2020 ◽

Vol 8 (12) ◽

pp. 1642

Author(s):

Rafał Kozera ◽

Bartłomiej Przybyszewski ◽

Zuzanna D. Krawczyk ◽

Anna Boczkowska ◽

Bogna Sztorch ◽

...

Keyword(s):

Contact Angle ◽

Polyester Resin ◽

Unsaturated Polyester ◽

Contact Angle Hysteresis ◽

Unsaturated Polyester Resin ◽

Water Repellent ◽

Chemical Modifiers ◽

Static Contact ◽

The Impact ◽

Hybrid Modification

Ice accumulation on wind turbine blades due to the impact of supercooled water droplets can be reduced by the application of surfaces with anti-icing properties. Hydrophobic surfaces are considered as a promising solution because of their water repellent behavior. In recent years, short-pulsed laser technologies have been developed as an efficient technique to modify the surface properties of materials. However, the anti-icing properties of such surfaces have not yet been validated. In this work, a hybrid modification of polyester resin-based gelcoats was adopted. Laser patterning (LP) was used to produce periodic surface structures on modified unsaturated polyester resin (UPR) substrates. One of the innovations of this research is the utilization of novel purpose-made chemical modifiers for gelcoats. The implementation of linear polymethylhydrosiloxane (PMHS) as a building block is a key improvement in terms of durability and functionality of the coating, since there is an option of introducing not only groups bonding in the polyester into one molecule, but also groups that increase hydrophobicity. The other novelty is a successfully conducted experiment combining such chemical modification with laser texturization of the surface. The influence of the laser energy, pattern shape, and spatial periods on the topographical characteristics and hydrophobicity as well as the anti-icing properties of the produced surfaces were investigated. To characterize the surface topography of the produced structures, scanning electron microscopy (SEM) and profilometer were utilized. Measurements of the wettability parameters (static contact angle and contact angle hysteresis) on the treated surfaces allowed the identification of the influence of wetting behavior and laser parameters on the investigated materials. Anti-icing properties were characterized by ice adhesion (IA) and freezing delay time (FDT) tests. It was found that hybrid modification of unsaturated polyester resin by chemical modifiers and laser treatment increased the hydrophobic and anti-icing properties of polyester gelcoats.

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