Mengying Long

A robust superhydrophobic PDMS@ZnSn(OH)6 coating with under-oil self-cleaning and flame retardancy

Some drawbacks such as lack of durability, requirement for high-cost fluorosilane modification, and complicated fabrication processes have limited the practical applications of superhydrophobic coatings for several years. In this work, we provide a novel method to fabricate a robust superhydrophobic coating without pre-modification by pressing ZnSn(OH)6 (ZHS) particles into polydimethylsiloxane (PDMS) solution, and then curing. PDMS used in this work is not only a low surface energy material, but also an adhesive to enhance the bonding force between particles and substrates. The PDMS@ZHS coating (ZHS particles coated on PDMS) is also superhydrophobic when it is immersed into dodecane, and shows excellent self-cleaning in air and oil environments. After undergoing serious chemical corrosion and mechanical abrasion, the superhydrophobicity of the coating remained well. For different kinds of substrates, this coating can be covered and repels water as well. Owing to the excellent flame-retardancy of ZHS particles, PDMS@ZHS coated paper displays excellent flame retardancy in limiting oxygen index (LOI), vertical flame, and cone calorimeter tests. We believe that this simple, environmentally friendly, and versatile fabrication of the PDMS@ZHS coating has excellent real-life applications.

One-Step Fabrication of Non-Fluorinated Transparent Super-Repellent Surfaces with Tunable Wettability Functioning in Both Air and Oil

In this paper, we have developed a one-step thermal treatment of polydimethylsiloxane (PDMS) liquid to create transparent super-repellent surface (TSS) and super-repellent powder. They are super-repellent toward water and ethylene glycol. During the one-step thermal treatment, PDMS soot is generated and deposited onto a glass slide (GS) surface to fabricate the TSS without fluorosilane modification. The facilely obtained TSS presented superhydrophobicity and self-cleaning property when immersed into very low surface tension oils such as petroleum ether, hexadecane, peanut oil, and dodecane. Interestingly, by controlling heating time and temperature, wettability of the treated GS surface and the remained white powder can be regulated. The mechanism of tunable wettability was revealed and analyzed by investigating the variations of surface morphology and chemical composition. More importantly, TSS was able to repel highly corrosive aqua regia and saturated NaOH solutions. TSS maintained excellent superhydrophobicity even after chemical and mechanical damages. This simple thermal deposition method was also applicable for other thermally stable substrates to achieve super-repellency, which are believed to find very promising applications.

Robust and thermal-healing superhydrophobic surfaces by spin-coating of polydimethylsiloxane

HYPOTHESIS Superhydrophobic surfaces easily lose their excellent water-repellency after damages, which limit their broad applications in practice. Thus, the fabrication of superhydrophobic surfaces with excellent durability and thermal healing should be taken into consideration. EXPERIMENTS In this work, robust superhydrophobic surfaces with thermal healing were successfully fabricated by spin-coating method. To achieve superhydrophobicity, cost-less and fluoride-free polydimethylsiloxane (PDMS) was spin-coated on rough aluminum substrates. FINDINGS After being spin-coated for one cycle, the superhydrophobic PDMS coated hierarchical aluminum (PDMS-H-Al) surfaces showed excellent tolerance to various chemical and mechanical damages in lab, and outdoor damages for 90days. When the PDMS-H-Al surfaces underwent severe damages such as oil contamination (peanut oil with high boiling point) or sandpaper abrasion (500g of force for 60cm), their superhydrophobicity would lose. Interestingly, through a heating process, cyclic oligomers generating from the partially decomposed PDMS acted as low-surface-energy substance on the damaged rough surfaces, leading to the recovery of superhydrophobicity. The relationship between the spin-coating cycles and surface wettability was also investigated. This paper provides a facile, fluoride-free and efficient method to fabricate superhydrophobic surfaces with thermal healing.

Highly efficient separation of surfactant stabilized water-in-oil emulsion based on surface energy gradient and flame retardancy

HYPOTHESIS Surface energy gradient would generate an imbalance force to drive tiny water droplets in dry air from the hydrophilic bumps to superhydrophobic domains, which has found on the Stenocara beetles back. EXPERIMENTS Inspired by this phenomenon, we introduced a pristine superhydrophilic filter paper on the lower surface energy superhydrophobic filter paper. ZnSn(OH)6 particles and polydimethylsiloxane were mixed to prepare the superhydrophobic coating, and the coating was spray-coated on the poly(dialkyldimethylammonium chloride) covered filter paper to separate the span 80 stabilized water-in-isooctane emulsion. A pristine filter paper was added on the superhydrophobic filter paper to fabricate another membrane for separation. FINDINGS The results revealed that with a pristine filter paper, the membrane performed higher efficiency and more recyclability, and it could separate the emulsions with higher surfactant concentrations. The stabilized water droplets passed the superamphiphilic surface, and hindered by the superhydrophobic surface, generating a surface energy gradient for better separation. In addition, the superhydrophobic membrane could be protected from fire to some degree due to the introduced ZnSn(OH)6 particles with excellent flame retardancy. This easy and efficient approach via simply bringing in pristine superhydrophilic membrane has great potential applications for water-in-oil emulsion separation or oil purification.

One-step preparation of superhydrophobic acrylonitrile-butadiene-styrene copolymer coating for ultrafast separation of water-in-oil emulsions

HYPOTHESIS Superhydrophobic membranes with opposite wettability toward water and oil are able to separate water-in-oil emulsions. By constructing porous and hierarchal-structured superhydrophobic coating on filter paper, we hope a quick separation process could be achieved due to the acceleration of both demulsification and penetration process. EXPERIMENTS Here, superhydrophobic coatings were prepared by simply spraying environmental and cost-effective acrylonitrile-butadiene-styrene copolymer (ABS) colloid in dichloromethane onto filter paper. The morphologies and wettability of the obtained coatings were carefully studied. Moreover, the separation performances in dealing with various surfactant-stabilized water-in-oil emulsions (SSWOE) were also investigated to verify our hypothesis. FINDINGS The morphologies of the ABS coatings varied with its weight concentration in dichloromethane and they changed from porous and plain surface into porous and hierarchal-structured surface. Besides, the hydrophobicity of the above coatings varied form hydrophobic to superhydrophobic. Moreover, the resulted superhydrophobic membranes show great separation capability in separating various span 80-stabilized water-in-oil emulsions with oil filtrate purities larger than 99.90% and huge penetration fluxes whose maximum is over 13,000L/(m2h). Thus, we envision that such membrane can be a practical candidate in dealing with water-in-oil emulsions to obtain pure oils.

Superamphiphobic aluminum surfaces that maintain robust stability after undergoing severe chemical and physical damage

This work demonstrated a simple, effective and economic method to fabricate robust superamphiphobic aluminum surfaces that showed super-repellency even towards very low-surface-tension liquids, including octane with a surface tension of 21.7 mN m−1. The dual microstep/nanopore structures were firstly constructed through combining chemical etching, anodization, and a subsequent pore-widening treatment. The pore-widening time that controlled the pore size and porosity determined the surface oil-repellent ability. With an appropriate pore-widening time, these nanopores broke down and were over-etched, and ultimately turned into large-area nanowire arrays. The hierarchical microstep/nanowire array architecture, when modified with fluorosilane, finally made the surface realize superamphiphobicity towards octane. The surface wettabilities of the hierarchical-nanopore structure and hierarchical-nanowire array structure towards various oils were investigated and compared in detail. More importantly, the final superamphiphobic surfaces simultaneously presented robust stabilities and high resistances to severe chemical and physical damage. The hierarchical-nanowire surfaces were able to repel strong HCl/NaOH solutions (25 °C), hot solutions (water, HCl/NaOH solutions, 30–100 °C), and even 98% concentrated H2SO4. Furthermore, when the surfaces were submerged in NaCl solution for 48 h, exposed in a thermal atmosphere (280 °C for 4 h), immersed in solvent, and stored under air conditions for 8 months, the super-liquid-repellency of the surfaces remained unchanged. They impressively sustained their superamphiphobicity after intensive scratching with an incisive blade, contaminated finger-contact, multiple bending to 180°, repeated peeling tests by adhesive tape, and reciprocating abrasion treatment under 500 g of force. The superior stability of the superamphiphobic surfaces is attributed to their stable surface structure and composition, and is believed to broaden their outdoor applications.