Superhydrophobic surfaces developed by mimicking hierarchical surface morphology of lotus leaf.

The lotus plant is recognized as a 'King plant' among all the natural water repellent plants due to its excellent non-wettability. The superhydrophobic surfaces exhibiting the famous 'Lotus Effect', along with extremely high water contact angle (>150°) and low sliding angle (<10°), have been broadly investigated and extensively applied on variety of substrates for potential self-cleaning and anti-corrosive applications. Since 1997, especially after the exploration of the surface micro/nanostructure and chemical composition of the lotus leaves by the two German botanists Barthlott and Neinhuis, many kinds of superhydrophobic surfaces mimicking the lotus leaf-like structure have been widely reported in the literature. This review article briefly describes the different wetting properties of the natural superhydrophobic lotus leaves and also provides a comprehensive state-of-the-art discussion on the extensive research carried out in the field of artificial superhydrophobic surfaces which are developed by mimicking the lotus leaf-like dual scale micro/nanostructure. This review article could be beneficial for both novice researchers in this area as well as the scientists who are currently working on non-wettable, superhydrophobic surfaces.

A facile approach for oil-water separation using superhydrophobic polystyrene-silica coated stainless steel mesh bucket.

Inspired by traditional shaduf technology in the irrigation field, we fabricated a superhydrophobic stainless steel mesh bucket by layering polystyrene and SiO2 nanoparticles through a facile dip coating technique for effective oil-water separation. The superhydrophobic steel mesh bucket could effectively lift oil as well as microplastic pollutants from the water surface. The water contact angle of a two-layered polystyrene-silica coating was 158.5° ± 2°, while the oil contact angle was nearly 0°. The oil-water separation performance of superhydrophobic mesh was tested using several kinds of oil. The separation efficiency achieved for low viscous oil was 99.33 %, while 86.66 % efficiency was recorded for high viscous oil. The superhydrophobic mesh showed high durability against mechanical tests including bending, folding, twisting, adhesive tape tearing (25 cycles), and sandpaper abrasion (20 cycles). The mesh presented admirable thermal and chemical durability. The present superhydrophobic steel mesh bucket is a suitable candidate for large-scale application.

Highly efficient wettability control via three-dimensional (3D) suspension of titania nanoparticles in polystyrene nanofibers.

Electrospinning is a simple and highly versatile method for the large-scale fabrication of polymeric nanofibers. Additives or fillers can also be used to functionalize the nanofibers for use in specific applications. Herein, we demonstrate a novel and efficient way to fabricate superhydrophobic to hydrophilic tunable mats with the combined use of electrospinning and electrospraying that may be suitable for mass production on the merits of rapid deposition. The tunable nanocomposite mats were comprised of hydrophobic polystyrene nanofibers and hydrophilic titania nanoparticles. When the electrical conductivity of the electrospinning solution was increased, the surface morphology of the mats changed noticeably from a bead-on-string structure to an almost bead-free structure. Polystyrene (PS)-titania nanocomposite mats initially yielded a static water contact angle as high as 140° ± 3°. Subsequently exposing these mats with relatively weak ultraviolet irradiation (λ = 365 nm, I = 0.6 mW/cm²) for 2 h, the unique 3D suspension of the photoactive titania nanoparticles maximized the hydrophilic performance of the mats, reducing the static water contact angle to as low as 26° ± 2°. The tunable mats were characterized by scanning electron microscopy (SEM), static water contact angle (WCA) measurements, and energy-dispersive X-ray spectroscopy (EDX). Our findings confirmed that the tunable mats fabricated by the simultaneous implementation of electrospraying and electrospinning had the most efficient ultraviolet (UV)-driven wettability control in terms of cost-effectiveness. Well-controlled tunable hydrophobic and hydrophilic mats find potential applications in functional textiles, environmental membranes, biological sensors, scaffolds, and transport media.

Water repellent porous silica films by sol-gel dip coating method.

The wetting of solid surfaces by water droplets is ubiquitous in our daily lives as well as in industrial processes. In the present research work, water repellent porous silica films are prepared on glass substrate at room temperature by sol-gel process. The coating sol was prepared by keeping the molar ratio of methyltriethoxysilane (MTES), methanol (MeOH), water (H(2)O) constant at 1:12.90:4.74, respectively, with 2M NH(4)OH throughout the experiments and the molar ratio (M) of MTES/Ph-TMS was varied from 0 to 0.22. A simple dip coating technique is adopted to coat silica films on the glass substrates. The static water contact angle as high as 164° and water sliding angle as low as 4° was obtained for silica film prepared from M=0.22. The surface morphological studies of the prepared silica film showed the porous structure with pore sizes typically ranging from 200nm to 1.3µm. The superhydrophobic silica films prepared from M=0.22 retained their superhydrophobicity up to a temperature of 285°C and above this temperature the films became superhydrophilic. The porous and water repellent silica films are prepared by proper alteration of the Ph-TMS in the coating solution. The prepared silica films were characterized by surface profilometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform Infrared (FT-IR) spectroscopy, humidity tests, chemical aging tests, static and dynamic water contact angle measurements.