scholarly journals Oscillating Magnetic Drop: How to Grade Water-Repellent Surfaces

Coatings ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 270 ◽  
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.

Evaporative Particle Deposition on Superhydrophobic Surfaces

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.

scholarly journals Amphiphobic Nanostructured Coatings for Industrial Applications

Materials ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 787 ◽  
Author(s):  
Federico Veronesi ◽  
Giulio Boveri ◽  
Mariarosa Raimondo
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Photoelectron Spectroscopy ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Friction Reduction ◽  
Hybrid Coatings ◽  
Wetting Behavior ◽  
Wide Range ◽  
Solid Liquid

The search for surfaces with non-wetting behavior towards water and low-surface tension liquids affects a wide range of industries. Surface wetting is regulated by morphological and chemical features interacting with liquid phases under different ambient conditions. Most of the approaches to the fabrication of liquid-repellent surfaces are inspired by living organisms and require the fabrication of hierarchically organized structures, coupled with low surface energy chemical composition. This paper deals with the design of amphiphobic metals (AM) and alloys by deposition of nano-oxides suspensions in alcoholic or aqueous media, coupled with perfluorinated compounds and optional infused lubricant liquids resulting in, respectively, solid–liquid–air and solid–liquid–liquid working interfaces. Nanostructured organic/inorganic hybrid coatings with contact angles against water above 170°, contact angle with n-hexadecane (surface tension γ = 27 mN/m at 20 °C) in the 140–150° range and contact angle hysteresis lower than 5° have been produced. A full characterization of surface chemistry has been undertaken by X-ray photoelectron spectroscopy (XPS) analyses, while field-emission scanning electron microscope (FE-SEM) observations allowed the estimation of coatings thicknesses (300–400 nm) and their morphological features. The durability of fabricated amphiphobic surfaces was also assessed with a wide range of tests that showed their remarkable resistance to chemically aggressive environments, mechanical stresses and ultraviolet (UV) radiation. Moreover, this work analyzes the behavior of amphiphobic surfaces in terms of anti-soiling, snow-repellent and friction-reduction properties—all originated from their non-wetting behavior. The achieved results make AM materials viable solutions to be applied in different sectors answering several and pressing technical needs.

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

2014 ◽  
Vol 1 (3) ◽  
pp. 1300138 ◽  
Author(s):  
Alexander Eifert ◽  
Dorothea Paulssen ◽  
Subramanyan Namboodiri Varanakkottu ◽  
Tobias Baier ◽  
Steffen Hardt
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
Water Repellent

scholarly journals Ultrahydrophobic Textiles Using Nanoparticles: Lotus Approach

2008 ◽  
Vol 3 (4) ◽  
pp. 155892500800300 ◽  
Author(s):  
Karthik Ramaratnam ◽  
Swaminatha K. Iyer ◽  
Mark K. Kinnan ◽  
George Chumanov ◽  
Phillip J. Brown ◽  
...  
Keyword(s):  
Contact Angle ◽  
Water Contact Angle ◽  
Contact Angle Hysteresis ◽  
Water Repellency ◽  
Textile Material ◽  
Water Repellent ◽  
Complete Wetting ◽  
Water Contact ◽  
Lotus Effect ◽  
Textile Materials

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.

scholarly journals Performance of Sprayed PVDF-Al2O3 Composite Coating for Industrial and Civil Applications

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6358
Author(s):  
Adel M. A. Mohamed ◽  
Hosam Hasan ◽  
Mohamed M. El-Sayed Seleman ◽  
Essam Ahmed ◽  
Sayed M. Saleh ◽  
...  
Keyword(s):  
Contact Angle ◽  
Polyvinylidene Fluoride ◽  
Coating Layer ◽  
Composite Coatings ◽  
Contact Angle Hysteresis ◽  
Nanoindentation Test ◽  
Al2o3 Nanoparticles ◽  
Glass Substrates ◽  
Coated Materials ◽  
Al2o3 Composite

Because of their great water repellency, Superhydrophobic coatings have a major impact on a variety of industrial applications. The current study’s key originality is the development of low-cost, stable, superhydrophobic, and corrosion-resistant composite coatings. In the present work, polyvinylidene fluoride (PVDF)/Al2O3 composite coatings were produced using the spray technique to investigate the wettability and corrosion behavior of the coated materials for industrial and civil applications. PVDF was mixed with various concentrations of Al2O3 nanoparticles, and the mixture was sprayed onto steel, aluminum, and glass substrates. The wettability and morphology of the coated surfaces were investigated using the sessile droplet method and scanning electron microscopy, respectively. The corrosion resistance of bare substrates was compared to that of those coated with PVDF alone and those coated with PVDF/Al2O3 nanoparticles using Tafel polarization techniques. The force of adhesion between the coat and the substrates was measured in pounds per square inch. A nanoindentation test was also used to measure the hardness of the coating layer. The PVDF/Al2O3 coated steel showed a significantly higher water contact angle and lower contact angle hysteresis, reaching 157 ± 2° and 7 ± 1°, respectively, compared to the coated aluminum and glass substrates. Corrosion test results showed that the superhydrophobic PVDF/Al2O3 coatings had a much higher corrosion protection efficiency for steel and aluminum than that of the PVDF ones. The PVDF/Al2O3 coated substrates showed moderate but still acceptable adhesion between the coating layer and the substrates. Moreover, the PVDF/Al2O3 coatings had much better mechanical properties than the PVDF only coatings. Such type of coating could be a promising candidate for possible industrial and civil applications.

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.

Metastable Nanobubbles at the Solid–Liquid Interface Due to Contact Angle Hysteresis

Langmuir ◽  
2015 ◽  
Vol 31 (3) ◽  
pp. 982-986 ◽  
Author(s):  
Takashi Nishiyama ◽  
Yutaka Yamada ◽  
Tatsuya Ikuta ◽  
Koji Takahashi ◽  
Yasuyuki Takata
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
Liquid Interface ◽  
Solid Liquid Interface ◽  
Solid Liquid

scholarly journals Towards optimization of patterned superhydrophobic surfaces

2007 ◽  
Vol 4 (15) ◽  
pp. 643-648 ◽  
Author(s):  
Bharat Bhushan ◽  
Michael Nosonovsky ◽  
Yong Chae Jung
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
Hydrophobic Surface ◽  
Dimensional Parameter ◽  
Wetting Properties ◽  
Spacing Factor ◽  
Composite Interface ◽  
Experimental Values ◽  
Solid Liquid Interface ◽  
Solid Liquid

Experimental and theoretical study of wetting properties of patterned Si surfaces with cylindrical flat-top pillars of various sizes and pitch distances is presented. The values of the contact angle (CA), contact angle hysteresis (CAH) and tilt angle (TA) are measured and compared with the theoretical values. Transition from the composite solid–liquid–air to the homogeneous solid–liquid interface is investigated. It is found that the wetting behaviour of a patterned hydrophobic surface depends upon a simple non-dimensional parameter, the spacing factor, equal to the pillar diameter divided by the pitch. The spacing factor controls the CA, CAH and TA in the composite interface regime, as well as destabilization and transition to the homogeneous interface. We show that the assumption that the CAH is a consequence of the adhesion hysteresis and surface roughness leads to the theoretical values of the CAH that are in a reasonably good agreement with the experimental values. By decreasing the spacing factor, the values of CA=170°, CAH=5° and TA=3° are achieved. However, with further decreasing of the spacing factor, the composite interface destabilizes.

scholarly journals Superhydrophobicity and Contact-Line Issues

MRS Bulletin ◽  
2008 ◽  
Vol 33 (8) ◽  
pp. 747-751 ◽  
Author(s):  
Lichao Gao ◽  
Alexander Y. Fadeev ◽  
Thomas J. McCarthy
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Contact Angle Hysteresis ◽  
Water Repellency ◽  
Contact Angles ◽  
Single Step ◽  
Contact Lines ◽  
Lotus Effect ◽  
Three Phase ◽  
Solid Liquid

AbstractThe wettability of several superhydrophobic surfaces that were prepared recently by simple, mostly single-step methods is described and compared with the wettability of surfaces that are less hydrophobic. We explain why two length scales of topography can be important for controlling the hydrophobicity of some surfaces (the lotus effect). Contact-angle hysteresis (difference between the advancing, θA, and receding, θR, contact angles) is discussed and explained, particularly with regard to its contribution to water repellency. Perfect hydrophobicity (θA/θR = 180°/180°) and a method for distinguishing perfectly hydrophobic surfaces from those that are almost perfectly hydrophobic are described and discussed. The Wenzel and Cassie theories, both of which involve analysis of interfacial (solid/liquid) areas and not contact lines, are criticized. Each of these related topics is addressed from the perspective of the three-phase (solid/liquid/vapor) contact line and its dynamics. The energy barriers for movement of the three-phase contact line from one metastable state to another control contact-angle hysteresis and, thus, water repellency.

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

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