scholarly journals Numerical Simulation of Droplet Impacting and Sliding on Hydrophobic Granular Surfaces

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Qing Bao ◽  
Hengyi Kang
Keyword(s):  
Water Repellency ◽  
Terminal Velocity ◽  
Practical Significance ◽  
Water Repellent ◽  
Stick Slip ◽  
Translational Movement ◽  
Particle Level ◽  
Inclined Slope ◽  
Sliding Dynamics ◽  
Granular Surface

Droplet sliding naturally happens with practical significance in developing artificial self-cleaning surfaces or impermeable barriers. On water-repellent soil surfaces, such processes evolve at very small scales, typically at the particle level. To address this, this paper presents a two-dimensional Lattice Boltzmann (LB) study on the droplet sliding dynamics on a layer of regularly arranged particles with varying size and contact angle (CA) aimed at mimicking conditions comparable to those of real soils. The numerical droplet is initialized above the inclined granular surface with different lifting distances and deposited by gravity. The droplet hits the surface with different impacting velocities and subsequently slides down the slope. Four droplet-sliding behaviors were observed: a droplet sticks to the granular surface, a droplet moves by pinning and depinning of its interface (“stick-slip”), a droplet undergoes periodic elongation and shortening during sliding, and a droplet lifts off the granular surface and may be ruptured. For a droplet that displays the “stick-slip” behavior, the sliding velocity reaches a converged terminal velocity, which increases with a higher CA, a more inclined slope, and a smaller particle size. However, nonunique terminal velocities were identified to be affected by the impacting velocities, but their correlation is not continuous and may not be positive. Finally, we propose to quantify the rotational or translational movement by effective kinematic ratio (EKR), which is defined as the translational kinematic energy divided by the total kinematic energy. The unique relation between the EKR and the terminal velocity is suggested to be one practical indicator to intrinsically characterize the water repellency at the particle level.

Non-adhesive lotus and other hydrophobic materials

2008 ◽  
Vol 366 (1870) ◽  
pp. 1539-1556 ◽  
Author(s):  
David Quéré ◽  
Mathilde Reyssat
Keyword(s):  
Solid Surface ◽  
Room Temperature ◽  
Water Repellency ◽  
Short Review ◽  
Water Repellent ◽  
Practical Applications ◽  
Hydrophobic Materials ◽  
Volatile Liquid ◽  
Air Cushion ◽  
The Stability

Superhydrophobic materials recently attracted a lot of attention, owing to the potential practical applications of such surfaces—they literally repel water, which hardly sticks to them, bounces off after an impact and slips on them. In this short review, we describe how water repellency arises from the presence of hydrophobic microstructures at the solid surface. A drop deposited on such a substrate can float above the textures, mimicking at room temperature what happens on very hot plates; then, a vapour layer comes between the solid and the volatile liquid, as described long ago by Leidenfrost. We present several examples of superhydrophobic materials (either natural or synthetic), and stress more particularly the stability of the air cushion—the liquid could also penetrate the textures, inducing a very different wetting state, much more sticky, due to the possibility of pinning on the numerous defects. This description allows us to discuss (in quite a preliminary way) the optimal design to be given to a solid surface to make it robustly water repellent.

Performance Study of Nano-TiO2 Modified Fabric

2012 ◽  
Vol 549 ◽  
pp. 733-736
Author(s):  
Xiao Mian Chen ◽  
Jing Jing Shi ◽  
Hong Sha Su ◽  
Chun Ting Lin ◽  
En Long Yang
Keyword(s):  
Titanium Dioxide ◽  
Catalytic Activity ◽  
Catalytic Properties ◽  
Antibacterial Property ◽  
Wear Behavior ◽  
Water Repellency ◽  
Innovative Technology ◽  
Water Repellent ◽  
High Catalytic Activity ◽  
Performance Study

The catalytic properties of nano-TiO2 modified fabric suits the demand for self-cleaning in recent years. In this paper, advanced and innovative technology were used to synthesize water sol of titanium dioxide photocatalyst with high catalytic activity for fabric finishing. The wear behavior, antibacterial property and water repellency of treated and untreated fabric were tested. Results indicate that finishing and washing of the titanium dioxide had no effect on wear behavior; finished and washed fabric has a certain antibacterial and water repellent properties.

scholarly journals Water repellency of clay, sand and organic soils in Finland

2008 ◽  
Vol 16 (3) ◽  
pp. 267 ◽  
Author(s):  
K. RASA ◽  
R. HORN ◽  
M. RÄTY
Keyword(s):  
Preferential Flow ◽  
Management Practice ◽  
Soil Surface ◽  
Water Repellency ◽  
Organic Soil ◽  
Water Infiltration ◽  
Organic Soils ◽  
Water Repellent ◽  
Moisture Regime ◽  
Wetting Process

Water repellency (WR) delays soil wetting process, increases preferential flow and may give rise to surface runoff and consequent erosion. WR is commonly recognized in the soils of warm and temperate climates. To explore the occurrence of WR in soils in Finland, soil R index was studied on 12 sites of different soil types. The effects of soil management practice, vegetation age, soil moisture and drying temperature on WR were studied by a mini-infiltrometer with samples from depths of 0-5 and 5-10 cm. All studied sites exhibited WR (R index >1.95) at the time of sampling. WR increased as follows: sand (R = 1.8-5.0) < clay (R = 2.4-10.3) < organic (R = 7.9-undefined). At clay and sand, WR was generally higher at the soil surface and at the older sites (14 yr.), where organic matter is accumulated. Below 41 vol. % water content these mineral soils were water repellent whereas organic soil exhibited WR even at saturation. These results show that soil WR also reduces water infiltration at the prevalent field moisture regime in the soils of boreal climate. The ageing of vegetation increases WR and on the other hand, cultivation reduces or hinders the development of WR.;

scholarly journals Spatially variable soil water repellency enhances soil respiration rates (CO<sub>2</sub> efflux)

2017 ◽  
Author(s):  
Emilia Urbanek ◽  
Stefan H. Doerr
Keyword(s):  
Soil Moisture ◽  
Soil Respiration ◽  
Soil Water ◽  
Water Distribution ◽  
Preferential Flow ◽  
Water Repellency ◽  
Water Repellent ◽  
Co2 Efflux ◽  
Soil Co2 ◽  
Soil Water Repellency

Abstract. Soil CO2 emissions are strongly dependent on water distribution in soil pores, which in turn can be affected by soil water repellency (SWR; hydrophobicity). SWR restricts infiltration and movement of water, affecting soil hydrology as well as biological and chemical processes. Effects of SWR on soil carbon dynamics and specifically on soil respiration (CO2 efflux) have been studied in a few laboratory experiments but they remain poorly understood. Existing studies suggest that soil respiration is reduced in water repellent soils, but the responses of soil CO2 efflux to varying water distribution created by SWR are not yet known. Here we report on the first field-based study that tests whether soil water repellency indeed reduces soil respiration, based on in situ field measurements carried out over three consecutive years at a grassland and pine forest site under the humid temperate climate of the UK. CO2 efflux was reduced on occasions when soil exhibited consistently high SWR and low soil moisture following long dry spells. However, the highest respiration rates occurred not when SWR was absent, but when SWR, and thus soil moisture, was spatially patchy, a pattern observed for the majority of the measurement period. This somewhat surprising phenomenon can be explained by SWR-induced preferential flow, directing water and nutrients to microorganisms decomposing organic matter concentrated in hot spots near preferential flow paths. Water repellent zones provide air-filled pathways through the soil, which facilitate soil-atmosphere O2 and CO2 exchanges. This study demonstrates that SWR have contrasting effects on CO2 fluxes and, when spatially-variable, can enhance CO2 efflux. Spatial variability in SWR and associated soil moisture distribution needs to be considered when evaluating the effects of SWR on soil carbon dynamics under current and predicted future climatic conditions.

Vacuum drying water-repellent sandy soil: Anoxic conditions retain original soil water repellency under variable soil drying temperature and air pressure

Geoderma ◽  
2020 ◽  
Vol 372 ◽  
pp. 114385
Author(s):  
Enoch V.S. Wong ◽  
Philip R. Ward ◽  
Daniel V. Murphy ◽  
Matthias Leopold ◽  
Louise Barton
Keyword(s):  
Soil Water ◽  
Sandy Soil ◽  
Water Repellency ◽  
Air Pressure ◽  
Vacuum Drying ◽  
Water Repellent ◽  
Soil Drying ◽  
Soil Water Repellency ◽  
Drying Temperature ◽  
Anoxic Conditions

Investigation of sewing and water repellent performance of outdoor clothing

2019 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Yaşar Erayman Yüksel ◽  
Yasemin Korkmaz
Keyword(s):  
Design Methodology ◽  
Water Resistance ◽  
Water Repellency ◽  
Woven Fabrics ◽  
Water Repellent ◽  
Content Type ◽  
Textile Materials ◽  
Sewing Threads ◽  
Reduced Water ◽  
Seam Pucker

Purpose Durability of textile materials under wet conditions has become very important in recent years. The water repellency performance of fabrics should be maintained in the seam areas. The purpose of this paper is to analyze the effect of water repellent agents and sewing threads on the seam and water repellency performance properties of woven fabrics. Design/methodology/approach 100 percent polyester woven fabrics were treated with three different water repellent finishing agents (silicone, fluorocarbons with 6 and 8 carbons) and then sewn with different sewing threads (unfinished/water repellent finished polyester/cotton corespun and polyamide filament). Afterwards, mechanical properties, seam performance and water repellency properties of these materials were measured. Findings The effect of finishing which was statistically significant on seam strength only in warp direction was significant on seam elongation and efficiency in both warp and weft directions. Seam strength, seam efficiency, seam slippage and seam pucker of fabrics sewn with polyamide threads were higher than others. The fluorocarbons applied to the fabrics gave higher water repellency values than silicones. In addition, as the chain length increased in fluorocarbons, water repellency performance increased. Sewing process reduced water resistance of fabrics; however, water repellent finish applied to the threads increased water resistance of fabrics. Originality/value As a result of the literature review, it was seen that water repellency property of a wear were studied in only seamless areas of fabrics. Originality of this study is that the water repellency properties are also analyzed in the seam areas of the fabrics and evaluated together with the seam performance characteristics.

Thermal Instability of Sliding and Oscillations Due to Frictional Heating Effect

1988 ◽  
Vol 110 (1) ◽  
pp. 69-72 ◽  
Author(s):  
I. L. Maksimov
Keyword(s):  
Thermal Instability ◽  
Initial Conditions ◽  
Frictional Heating ◽  
Interface Temperature ◽  
Heating Effect ◽  
Stick Slip ◽  
Instability Development ◽  
The Stability ◽  
Sliding Dynamics ◽  
Sliding Instability

The stability of sliding has been studied, taking into account frictional heating effect and friction coefficient dependence upon the interface temperature and sliding velocity. The collective—thermal and mechanical—sliding instability has been found to exist; instability emergence conditions and dynamics (both in linear and nonlinear stages) have been determined. It is shown that both the threshold and the dynamics of thermofrictional instability differ qualitatively from the analogous characteristics of “stick-slip” phenomenon. Namely, the oscillational instability behavior due to the energy exchange between thermal and mechanical modes has been found to occur under certain initial conditions; the velocities range has been determined for which collective sliding instability may occur whereas the stick-slips would be not possible. The nonlinear analysis of instability evolution has been carried out for pairs with the negative thermal-frictional sliding characteristics, the final stage of sliding dynamics has been described. It is found that stable thermofrictional oscillations can occur on the nonlinear stage of sliding instability development; the oscillations frequency and amplitude have been determined. The possibility has been discussed of the experimental observation of new dynamical sliding phenomena at low temperatures.

scholarly journals Superhydrophobic surfaces

2012 ◽  
Vol 21 (1-2) ◽  
pp. 21-32 ◽  
Author(s):  
Ioannis Karapanagiotis ◽  
Panagiotis Manoudis
Keyword(s):  
Water Repellency ◽  
Superhydrophobic Surfaces ◽  
Water Repellent ◽  
Baxter Equation ◽  
Feature Article ◽  
Surface Protection ◽  
Recent Developments ◽  
Potential Applications ◽  
Nanoparticle Composites ◽  
Potential Use

AbstractSuperhydrophobicity – also known as water repellency – has recently attracted considerable attention because of its numerous potential applications. However, the fundamental concepts and equations describing the wettability of superhydrophobic surfaces have been known since the 1940s. These concepts are reviewed and discussed in the present feature article in light of the recent developments. Furthermore, the potential use of water-repellent siloxane-nanoparticle composites for surface protection and consolidation of stones and mortars used in outdoor objects of cultural heritage is investigated. Finally, it is shown that the wettability of the composite surfaces can be predicted by the Cassie-Baxter equation.

scholarly journals Water-Repellent Fluoropolymer-Based Coatings

Coatings ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 293 ◽  
Author(s):  
Paz-Gómez ◽  
Caño-Ochoa ◽  
Rodríguez-Alabanda ◽  
Romero ◽  
Cabrerizo-Vílchez ◽  
...  
Keyword(s):  
Laser Ablation ◽  
Surface Texturing ◽  
Environmental Scanning Electron Microscopy ◽  
Water Repellency ◽  
Environmental Scanning ◽  
Water Repellent ◽  
Current Development ◽  
Laser Patterning ◽  
Water Drops ◽  
Scanning Electron

Fluoropolymer-based coatings are widely used for release applications. However, these hydrophobic surfaces do not reveal a significantly low adhesion. Water repellency incorporated to fluoropolymer coatings might enhance their release performance. In this work, we focused on the surface texturing of a well-known polytetrafluoroethylene (PTFE)-based coating. We explored as texturing routes: sanding, sandblasting and laser ablation. We examined the surface roughness with white light confocal microscopy and the surface morphology with environmental scanning electron microscopy (ESEM). Water-repellent fluoropolymer coatings were reproduced in all cases, although with different degree, parametrized with bounces of water drops (4–5 μL). Laser ablation enabled the lowest adhesion of coatings with 24 ± 2 bounces. This result and the current development of laser patterning for industry assure the incipient use of laser ablation for release coatings.

Development of multifunctional cotton fabric via chemical foam application method

2019 ◽  
Vol 90 (9-10) ◽  
pp. 991-1001 ◽  
Author(s):  
Zeynep Omerogullari Basyigit ◽  
Dilek Kut ◽  
Peter Hauser
Keyword(s):  
Cotton Fabric ◽  
Textile Industry ◽  
Performance Test ◽  
Water Repellency ◽  
Contact Angles ◽  
Water Repellent ◽  
Test Results ◽  
Important Place ◽  
Application Method ◽  
Color Spectrum

Nowadays, the methods and techniques used in the textile industry are required to be environmentally friendly, and water and energy saving. In addition to these, they should transfer more than one functionality, in other words give multifunctionality to the textile material with reliable and sufficient results in terms of efficiency and permanence. With the increase in and diversification of today's industrial requirements, one functionality on the fabric may be insufficient to meet the requirements, and therefore the subject of multifunctionality holds an important place in the textile industry. Therefore, in this study flame retardant, antibacterial and water-repellent, single-layered multifunctional 100% cotton fabrics with different functionalities on different sides (back and face surfaces) of the fabric were obtained via a chemical foam application method, which has many advantages compared with conventional methods. In some of the experimental parts, impregnation and foam application methods were combined in the process in order to optimize the multifunctionality properties of the fabrics. In order to indicate the performance test of cotton fabric, vertical burning test, contact angle test, antibacterial test against Gram positive and Gram negative bacteria, color spectrum analysis and tearing strength test were carried out while, in terms of characterization tests, Fourier transform infrared (attenuated total reflectance) and scanning electron microscope analyses were performed. According to the test results, the flame retardancy effect of the samples was improved significantly while antibacterial results showed a 99% reduction of bacteria and the finished fabrics demonstrated improved water repellency with contact angles up to 125°. In addition, the functionalities were durable up to 50 washing and 50 drying cycles.

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