Bio-inspired antifogging PDMS coupled micro-pillared superhydrophobic arrays and SiO2 coatings

Advances in Bioinspired Superhydrophobic Surfaces Made from Silicones: Fabrication and Application

As research on superhydrophobic materials inspired by the self-cleaning and water-repellent properties of plants and animals in nature continues, the superhydrophobic preparation methods and the applications of superhydrophobic surfaces are widely reported. Silicones are preferred for the preparation of superhydrophobic materials because of their inherent hydrophobicity and strong processing ability. In the preparation of superhydrophobic materials, silicones can both form micro-/nano-structures with dehydration condensation and reduce the surface energy of the material surface because of their intrinsic hydrophobicity. The superhydrophobic layers of silicone substrates are characterized by simple and fast reactions, high-temperature resistance, UV resistance, and anti-aging. Although silicone superhydrophobic materials have the disadvantages of relatively low mechanical stability, this can be improved by the rational design of the material structure. Herein, we summarize the superhydrophobic surfaces made from silicone substrates, including the cross-linking processes of silicones through dehydration condensation and hydrosilation, and the surface hydrophobic modification by grafting hydrophobic silicones. The applications of silicone-based superhydrophobic surfaces have been introduced such as self-cleaning, corrosion resistance, oil-water separation, etc. This review article should provide an overview to the bioinspired superhydrophobic surfaces of silicone-based materials, and serve as inspiration for the development of polymer interfaces and colloid science.

Durable 3D Porous Superhydrophobic Composites for Versatile Emulsion Separation in Multiple Environments

Polydopamine as a multifunctional biomimetic polymer with nonselective strong adhesion properties has become a hot research topic in recent years. However, there are a few reports on the durable and effective emulsion separation of polydopamine composites from other materials. Therefore, it is necessary to construct durable polydopamine composites to achieve selective adsorption of materials. In this work, polypyrrole (PPy)-PDA was obtained on sponges by an in situ polymerization reaction, followed by the attachment of SiO₂ nanoparticles to the surface by polydimethylsiloxane to achieve superhydrophobicity. As a result, previously unreported selective superhydrophobic adsorbents for PPy-PDA coatings were obtained. The prepared sponges have an excellent adsorption capacity for oils and organic solvents. Not only can the sponges absorb 19-39 g of organic solvents per gram but they can also absorb oil from oil-in-water emulsions. The chemical oxygen demand value of the emulsion can be reduced to 219 mg/L after separation. More importantly, the performance remains good in the cycle test, and due to the construction of a durable superhydrophobic sponge, it can still maintain its relatively good performance in artificial seawater, acid-base environments, and can achieve relatively stable emulsion separation. At the same time, the potential of the polymer material composited with PDA in lasting and stable emulsion separation was also verified.

Reduced Crystalline Biofilm Formation on Superhydrophobic Silicone Urinary Catheter Materials

Crystalline biofilm formation in indwelling urinary catheters is a serious health problem as it creates a barrier for antibacterial coatings. This emphasizes the failure of antibacterial coatings that do not have a mechanism to reduce crystal deposition on catheter surfaces. In this study, trifluoropropyl spray-coated polydimethylsiloxane (TFP-PDMS) has been employed as an antibiofilm forming surface without any antibacterial agent. Here, TFP was coated on half-cured PDMS using the spray coating technique to obtain a durable superhydrophobic coating for a minimum five cycles of different sterilization methods. The crystalline biofilm-forming ability of Proteus mirabilis in artificial urine, under static and flow conditions, was assessed on a TFP-PDMS surface. In comparison to the commercially available silver-coated latex and silicone catheter surfaces, TFP-PDMS displayed reduced bacterial attachment over 14 days. Moreover, the elemental analysis determined by atomic absorption spectroscopy and energy-dispersive X-ray analysis revealed that the enhanced antibiofilm forming ability of TFP-PDMS was due to the self-cleaning activity of the surface. We believe that this modified surface will significantly reduce biofilm formation in indwelling urinary catheters and further warrant future clinical studies.

Energy conversion based on superhydrophobic surfaces

Covering about 70% of the earth's surface, water contains considerable energy that remains unexploited. Superhydrophobic surfaces (SHSs) possess excellent water repellency, and energy conversion based on SHSs has opened up a new avenue for efficient collection and utilization of water energy. Therefore, it is of great significance to efficiently prepare SHSs and apply them for energy conversion in different fields. In this review, we first summarize the fabrication methods of SHSs, and then provide an overview of the energy conversion forms based on SHSs. Finally, the related applications corresponding to the energy conversion forms are introduced, including renewable energy collection and utilization, wearable device design, use of liquid sensors, surface cooling and heat dissipation, self-propelled devices, droplet manipulation and lab-on-a-chip devices; and their challenges and future perspectives are highlighted.

Underwater writable and heat-insulated paper with robust fluorine-free superhydrophobic coatings

Since its invention invented in China, paper has been widely used in the world for quite a long time. However, some intrinsic defects servely hinder its application in some extreme conditions, such as underwater or in fire. Herein, a bio-inspired durable paper with robust fluorine-free coatings was fabricated via a two-step spray-deposition technique. It not only consisted of modified SiO₂ microspheres and nanoparticles, but also contained an epoxy resin, endowing the paper with multifunctional properties. First, this bio-inspired functional paper showed excellent superhydrophobic and self-cleaning properties with a high static water contact angle (WCA) of 162.7 ± 0.5° and a low sliding angle (SA) of 5.7 ± 0.6°. Moreover, it possessed unusual repellent properties toward multiple aqueous-based liquids and heat-insulated properties. Second, this paper could be used for writing underwater and maintained satisfactory superhydrophobic performance for a long time with a WCA of 153.3 ± 1.8°. Besides, its high mechanical robustness was also experimentally confirmed in harsh working conditions, such as strong acid/alkali, boiling water, abrasion, bending, and folding. Compared with conventional paper, it is anticipated that this bio-inspired functional paper would be really competitive and demonstrate great potential in the field of underwater and fire-proof applications.

Fabrication of mechanically resistant superhydrophobic synthetic suede materials

Functionalization of synthetic suede materials with excellent superhydrophobicity can expand their application ranges. Superhydrophobic synthetic suede was obtained by coating with polydimethylsiloxane (PDMS) and octadecyltrichlorosilane (OTS). Utilizing the synthetic suede effect of the fibrous rough structures in combination with the low surface energy micro-nano rough structure on fibers resulting from PDMS and OTS, the surface was easily turned superhydrophobic with self-cleaning properties. Abrasion tests showed that the superhydrophobic synthetic suede has excellent superhydrophobic performance after more than 2000 severe abrasion tests. This research provides a facile strategy for the preparation of practical superhydrophobic synthetic suede materials.