Fabrication and characterization of the hierarchical structure for superhydrophobicity and self-cleaning

Hierarchical roughness is beneficial for the superhydrophobicity. Surfaces with microstructure, nanostructure and hierarchical structure were fabricated by replication of micropattern and self-assembly of hydrophobic alkanes. The fabrication technique used is a low-cost two-step process, which provides flexibility in fabrication of variety of hierarchical structures. Fabricated structures and surface chemistry mimic the hierarchical surfaces of superhydrophobic and self-cleaning plant surfaces. The influence of structure on the superhydrophobicity at different length scales is demonstrated by investigation of contact angle, contact angle hysteresis, droplet evaporation and propensity of the air pocket formation as well as adhesive forces.     

Single-step prepared hybrid ZnO/CuO nanopowders for water repellent and corrosion resistant coatings

In this study, ZnO/CuO hybrid hydrophobic nanopowders were synthesized using a common single-step chemical precipitation route without using modifiers. Influence of initial ZnO:CuO precursor concentrations and alkaline agent type on the wettability behavior of the prepared samples were investigated. Wettability properties of the prepared samples were assessed by measuring the water contact angle and contact angle hysteresis values. Fourier transform infrared spectra, scanning electron microscope micrographs and X-ray diffraction patterns were applied to identify the surface chemistry and morphological features. Scanning electron microscope images of the synthesized ZnO/CuO nanocomposites indicated flower-like morphologies containing plenty of nano-needles, -rods, and -sheets with thicknesses lower than 90 nm. The sample prepared under the optimum conditions was superhydrophobic having water contact angle and contact angle hysteresis of 162.6°±1 and 2°, respectively. It was applied to coat the surface of stainless steel meshes by spray deposition method. The resultant superhydrophobic surface exhibited excellent self-cleaning (water repellency) property and a suitable stabilities under the ambient and saline solution (NaCl, 3.5%) media. Additionally, electrochemical corrosion tests confirmed that the corrosion resistance of the fabricated ZnO–CuO coating was higher than the initial bare mesh.     

A one-step process to engineer superhydrophobic copper surfaces

Superhydrophobic surfaces are conventionally prepared employing two steps: roughening a surface and lowering their surface energy. In the present work, a direct voltage (DC) is applied between two copper plates immersed in a dilute ethanolic stearic acid solution. The surface of the anodic copper electrode transforms to superhydrophobic due to a reaction between copper and stearic acid solution. The fabrication process of superhydrophobic copper surfaces is simplified in just one-step. The surface of the anodic copper is found to be covered with flower-like low surface energy copper stearate films providing the water contact angle of 153 ± 2° with the roll-off properties.     

Self‐Assembled Nanoparticles Based Fabrication of Gecko Foot‐Hair‐Inspired Polymer Nanofibers

Wafer‐scale polymer nanofabrillar structures have been fabricated using the combination of colloidal nanolithography, deep‐silicon etching, and nanomolding to mimic the nanostructure of gecko foot‐hairs. The artificial surface features densely packed polymeric nanofibrils with super‐hydrophobic, water‐repellent, and “easy‐to‐clean” characteristics. The lateral dimension of the nanofibrils is as small as 250 nm and an aspect‐ratio as high as 10:1 has been achieved without lateral collapse between neighboring fibrils. The method allows both fabrication of synthetic structures over a large area and direct integration of a flexible membrane to assist the array of nanofibrils in making intimate contact with uneven surfaces. A single nanofibril exhibits a mean adhesive force ranging from (0.91 ± 0.34) nN to (1.35 ± 0.37) nN. In the macroscopic scale, the nanostructured surface can adhere firmly to a smooth glass substrate and inherits the in‐use, self‐cleaning property of the setal nanostructures found in gecko lamellae.     

Highly resistant icephobic coatings on aluminum alloys

Aluminum alloys are widely used for outdoor structures such as ground wires and phase conductors of overhead power lines, as well as aircrafts wings and fuselage. To protect these surfaces against excessive ice accumulation, icephobic coatings must be highly reliable and durable. New coatings with icephobic characteristics and excellent mechanical properties have been developed. The method consisted in depositing an extremely adherent poly(tetrafluoroethylene) (PTFE) coating on an Al₂O₃ underlayer produced by anodizing in a phosphoric acid electrolyte followed by an oxide etching step to enhance surface roughness. PTFE impregnation was carried out at low temperature (320 °C) and coating adhesion was assessed using tape and bend tests. Some of these coatings showed superhydrophobic properties; ice adhesion was around four times lower than bare aluminum. As well, they remained effective after ten ice-shedding events using an aggressive centrifugal technique. Moreover, no sign of PTFE degradation after 14 ice removals was noted and the coatings remained extremely adherent and very hydrophobic. This technique therefore shows very good potential and could be applied to new high-voltage overhead aluminum cables as protection against excessive ice or snow accumulation.     

Superhydrophobic PDMS/SiNPs/T-ZnOw coating with reduced adhesion of Streptococcus mutans for dental caries prevention

The prevention of dental caries is based mainly on killing the cariogenic bacteria Streptococcus mutans. Prevention of S. mutans adhesion through the development of physical structures is rarely utilized. In this study, a superhydrophobic PDMS/SiNPs/T-ZnOw (PST) coating was prepared for use on a bovine tooth by mixing polydimethylsiloxane (PDMS), silicon dioxide nanoparticles (SiNPs), and tetrapod-like zinc oxide whiskers (T-ZnOw) using one-pot solution and spray methods. The results showed that the superhydrophobicity and roughness of the coating, affected by the PDMS content, were positively correlated with the anti-adhesive effect on S. mutans. The PST coating with PDMS, SiNPs, and T-ZnOw at a ratio of 2.5:1:1 exhibited the highest water contact angle (161°) and the best anti-adhesion effect (97.2% at 4 h and 98.1% at 12 h). The anti-adhesion property towards S. mutans was attributed to its needle-like structure, and the biofilm live-dead staining test showed that the coating had no bactericidal effect. In addition, the coating exhibited favorable durability and biocompatibility, providing a solid foundation for application in the human oral cavity. Thus, this study provides an effective method for caries prevention.