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Transparent Superhydrophobic Film Created through Biomimetics of Lotus Leaf and Moth Eye Structures
Published in Akihiro Miyauchi, Masatsugu Shimomura, Industrial Biomimetics, 2019
where f1 and f2 are fractions of materials 1 and 2 (f1 + f2 = 1) and θ1 and θ2 are the contact angles of intrinsic materials 1 and 2, respectively. Equation 11.2 was derived from Cassie’s approach when the contact angle of water to air is 180°. The contact angle of water to air can result from a water droplet becoming round in a spacecraft when there is zero gravity. For a hydrophilic surface, that is, when the intrinsic contact angle θ0 < 90°, the surface structure is expected to increase the hydrophilicity of the surface according to the Wenzel model. For a hydrophobic surface, that is, when the intrinsic contact angle θ0 > 90°, the surface structure is expected to increase the hydrophobicity of the surface according to the Cassie– Baxter model. Superhydrophilicity is defined as the state at which the water contact angle is less than 10°, and superhydrophobicity is typically defined as the state at which the water contact angle is more than 150°.
Toxicology Studies of Semiconductor Nanomaterials: Environmental Applications
Published in Suresh C. Pillai, Yvonne Lang, Toxicity of Nanomaterials, 2019
T. P. Nisha, Meera Sathyan, M. K. Kavitha, Honey John
Superhydrophilic self-cleaning surfaces can be fabricated using semiconductor photocatalysts and thus bio-mimicking the variegated forms of nature like lotus leaf, wings of butterfly, and legs of water strider. Photocatalysts like TiO2 and ZnO have an additional property that they show extreme wettability on photoirradiation. The mechanism of superhydrophilicity begins when photoinduced electrons reduce the metal centres (for example, Ti4+ gets reduced to Ti3+) and the photogenerated holes formed in the VB oxidize O2− anions of the semiconductor, causing the oxygen atoms to be ejected from the semiconductor surface and leaving vacancies. The hydroxyl anions formed during the photocatalytic mechanism or the water molecule itself get adsorbed to these oxygen vacancies leading to reconstruction of Ti-OH bonds (Banerjee et al., 2015), thereby increasing the affinity of the surface to water. The photogenerated holes are more vital than electrons for the superhydrophilic behaviour of the surface and hence their diffusion to the surface of the photocatalyst is crucial (Emeline et al., 2013). Concurrently, the photogenerated electrons will decompose the organic matter adsorbed on the photocatalyst surface. Both the photodecomposition and photoinduced superhydrophilicity (where the water sheets over the surface and water contact angle approaches zero) render the surface clean.
Hybrid materials and surfaces
Published in Chang-Sik Ha, Saravanan Nagappan, Hydrophobic and Superhydrophobic Organic-Inorganic Nanohybrids, 2018
Chang-Sik Ha, Saravanan Nagappan
Superhydrophilicity can also be achieved by treating hydrophilic or hydrophobic surfaces chemically or physically. Hydrophobic surfaces, on the other hand, show CAs over 90°-150° due to the presence of nonpolar functional groups on the surface. The nonpolar nature can show a lower affinity and resist the water droplet on the surface due to the low surface tension and lack of active functional groups at the surface for hydrogen bonding. Some examples of hydrophobic molecules include oils, greasy substance, fats, and alkanes. Hydrophobic surfaces can exhibit a smooth or rough surface morphology as well as composite surface morphology based on the surface nature and surface energy and can have many applications. Wenzel and Cassie-Baxter proposed the basic principles of surface wettability on rough and composite surfaces [49,52]. Wenzel explained that the hydrophobicity or hydrophilicity depend mainly on a homogeneous surface. The apparent CA and ideal CA are related to each on a rough surface according to Wenzel’s Eq. 1.3 [49]: cosθw=rcosθY, $$ {\text{cos}}\,\theta _{w} = {\text{ }}r\,{\text{cos}}\,\theta _{Y} , $$
Dynamic behaviours and drying processes of water droplets impacting on superhydrophilic surfaces
Published in Surface Engineering, 2021
Yan Zhu, Jialiu Liu, Yongmao Hu, De-Quan Yang, Edward Sacher
Superhydrophilicity refers to the outstanding ‘water-loving’ behaviour of specifically designed surfaces. Such surfaces have been described, in many articles, as having static water contact angles of less than 5–10°, [1–5] a range considered to represent the complete spread of water on a surface [2–10]. There is no clear definition or consensus of superhydrophilicity [3,6,10], and the exact determination of a water contact angle near zero degrees is challenging [10]. Such surfaces have attracted attention, due to their many applications, including anti-fogging [11], bio-fouling prevention [12], biomedicine [13–17] and self-cleaning [18–21] capabilities. Additional applications, in practical environments that involve dynamic water impact on such surfaces, have persuaded us to give attention to the dynamic behaviours of water droplets on these surfaces, which, although not necessarily suited to heat transport [22–24], may be important in applications such as spraying, ink-jet printing [25], pharmaceuticals [26], aircraft deicing [27,28], microfluidic devices, droplet manipulation, cell screening and water harvesting through superhydrophilic–superhydrophobic patterned surfaces [29] or switching [30].
A review on control of droplet motion based on wettability modulation: principles, design strategies, recent progress, and applications
Published in Science and Technology of Advanced Materials, 2022
Mizuki Tenjimbayashi, Kengo Manabe
Antifogging is performed by treating surfaces to superhydrophilicity with a water film in which water droplets are wetted and spread. Here, we present an example where antifogging is achieved by controlling the movement of water droplets. There are two strategies: the first method is the promotion of the coalescence of droplets on a hydrophobic surface. The energy generated during the coalescence removes the droplets from the surface (coalescence-induced jumping). The second method is the construction of hydrophilic and hydrophobic Janus surfaces and the transportation of water adhering to the surface by wettability gradients.
Novel method of obtaining textile fabrics with self-cleaning and antimicrobial properties
Published in The Journal of The Textile Institute, 2022
Iwona Masłowska-Lipowicz, Anna Słubik
The self-cleaning effect is related to the following concepts developed by scientists: TiO2-based superhydrophilic self-cleaning, lotus effect self-cleaning, gecko setae–inspired self-cleaning, and underwater organisms–inspired antifouling self-cleaning. The self-cleaning mechanism depends on the superhydrophilicity or superhydrophobicity of the surface. In the case of the superhydrophilic surface, water droplets can spread and form a thin layer on the surface that washes away contaminants as it flows off. The self-cleaning mechanism caused by superhydrophobicity, on the example of the so-called the lotus effect, is associated with the presence of numerous microtubes on the modified surface. The presence of microtubes results in a smaller contact area between the surface and the water droplets, allowing the water droplets to roll over the surface, collecting the contaminants from the surface (Chan-Juan et al., 2018; Hasan & Nosonovsky, 2020; Liu & Jiang, 2012; Shao et al., 2020). The self-cleaning properties of the surface are of great interest due to the wide range of applications in various industries (textiles, construction, sanitary appliances, car parts—car body, mirrors, photovoltaic panels, cameras, mobile phones, cosmonautics, etc.) (Han & Min, 2020). In the textile industry, self-cleaning fabrics are mainly based on surface modification with TiO2 or SiO2 nanoparticles. One of the methods of applying nanoparticles (nano-TiO2 or nano-SiO2) to fabrics is the sol-gel method. Nanoparticles are produced by acidic or alkaline hydrolysis in the presence of the so-called precursors. Precursors are most often organic salts of the appropriate metals (e.g. titanium isopropoxide, tetraethyl orthosilicate). The produced nanoparticles have a high surface area to volume ratio and high surface energy, thanks to which they show a high affinity for fabrics (Krifa & Prichard, 2020). Additionally, the use of photocatalytic nano-TiO2 gives textiles the function of photocatalytic cleaning. In this type of fabric, contaminations are broken down by UV radiation (Altangerel et al., 2020; Diaa & Hassabo, 2022; Wan et al., 2021; Wu et al., 2021).