Shan Peng

Chemically stable and mechanically durable superamphiphobic aluminum surface with a micro/nanoscale binary structure.

We developed a simple fabrication method to prepare a superamphiphobic aluminum surface. On the basis of a low-energy surface and the combination of micro- and nanoscale roughness, the resultant surface became super-repellent toward a wide range of liquids with surface tensions of 25.3-72.1 mN m(-1). The applied approach involved (1) the formation of an irregular microplateau structure on an aluminum surface, (2) the fabrication of a nanoplatelet structure, and (3) fluorination treatment. The chemical stability and mechanical durability of the superamphiphobic surface were evaluated in detail. The results demonstrated that the surface presented an excellent chemical stability toward cool corrosive liquids (HCl/NaOH solutions, 25 °C) and 98% concentrated sulfuric acid, hot liquids (water, HCl/NaOH solutions, 30-100 °C), solvent immersion, high temperature, and a long-term period. More importantly, the surface also exhibited robust mechanical durability and could withstand multiple-fold, finger-touch, intensive scratching by a sharp blade, ultrasonication treatment, boiling treatment in water and coffee, repeated peeling by adhesive tape, and even multiple abrasion tests under 500 g of force without losing superamphiphobicity. The as-prepared superamphiphobic surface was also demonstrated to have excellent corrosion resistance. This work provides a simple, cost-effective, and highly efficient method to fabricate a chemically stable and mechanically robust superamphiphobic aluminum surface, which can find important outdoor applications.

Highly Efficient and Large-Scale Fabrication of Superhydrophobic Alumina Surface with Strong Stability Based on Self-Congregated Alumina Nanowires

In this study, a large-area superhydrophobic alumina surface with a series of superior properties was fabricated via an economical, simple, and highly effective one-step anodization process, and subsequently modified with low-surface-energy film. The effects of the anodization parameters including electrochemical anodization time, current density, and electrolyte temperature on surface morphology and surface wettability were investigated in detail. The hierarchical alumina pyramids-on-pores (HAPOP) rough structure which was produced quickly through the one-step anodization process together with a low-surface-energy film deposition [1H,1H,2H,2H-perfluorodecyltriethoxysilane (PDES) and stearic acid (STA)] confer excellent superhydrophobicity and an extremely low sliding angle. Both the PDES-modified superhydrophobic (PDES-MS) and the STA-modified superhydrophobic (STA-MS) surfaces present fascinating nonwetting and extremely slippery behaviors. The chemical stability and mechanical durability of the PDES-MS and STA-MS surfaces were evaluated and discussed. Compared with the STA-MS surface, the as-prepared PDES-MS surface possesses an amazing chemical stability which not only can repel cool liquids (water, HCl/NaOH solutions, around 25 °C), but also can show excellent resistance to a series of hot liquids (water, HCl/NaOH solutions, 30-100 °C) and hot beverages (coffee, milk, tea, 80 °C). Moreover, the PDES-MS surface also presents excellent stability toward immersion in various organic solvents, high temperature, and long time period. In particular, the PDES-MS surface achieves good mechanical durability which can withstand ultrasonication treatment, finger-touch, multiple fold, peeling by adhesive tape, and even abrasion test treatments without losing superhydrophobicity. The corrosion resistance and durability of the diverse-modified superhydrophobic surfaces were also examined. These fascinating performances makes the present method suitable for large-scale industrial fabrication of chemically stable and mechanically robust superhydrophobic surfaces.

Designing robust alumina nanowires-on-nanopores structures: Superhydrophobic surfaces with slippery or sticky water adhesion

Hierarchical alumina surfaces with different morphologies were fabricated by a simple one-step anodization method. These alumina films were fabricated by a new raw material: silica gel plate (aluminum foil with a low purity of 97.17%). The modulation of anodizing time enabled the formation of nanowires-on-nanopores hybrid nanostructures having controllable nanowires topographies through a self-assembly process. The resultant structures were demonstrated to be able to achieve superhydrophobicity without any hydrophobic coating layer. More interestingly, it is found that the as-prepared superhydrophobic alumina surfaces exhibited high contrast water adhesion. Hierarchical alumina film with nanowire bunches-on-nanopores (WBOP) morphology presents extremely slippery property which can obtain a sliding angle (SA) as low as 1°, nanowire pyramids-on-nanopores (WPOP) structure shows strongly sticky water adhesion with the adhesive ability to support 15 μL inverted water droplet at most. The obtained superhydrophobic alumina surfaces show remarkable mechanical durability even treated by crimping or pressing without impact on the water-repellent performance. Moreover, the created surfaces also show excellent resistivity to ice water, boiling water, high temperature, organic solvent and oil contamination, which could expand their usefulness and efficacy in harsh conditions.

Structural transition control between dipole–dipole and hydrogen bonds induced chirality and achirality

Nano-fabrication is an issue which has gained extensive attention in molecular engineering. Thus, we have probed intensively surface-based 2D self-assembly of 2-hydroxyanthraquinone (2-HA) derivatives by scanning tunneling microscopy (STM). During the STM process, two interesting nanostructures resembling closely Chinese knots and wheat were identified, thus they were denoted as Knot-like and Wheat-like patterns for legibility. Moreover, careful observation suggests that the Knot-like structure is chiral while the Wheat-like structure is achiral. Systematic analysis indicates that these two arrangements are mainly dominated by synergistic forces of dipole–dipole and hydrogen bonding interactions. To the best of our knowledge, the dipole induced chirality and achirality have been rarely reported, and the synergistic forces of dipole–dipole and hydrogen bonding interactions on dominating 2D assembly have never been proposed. In addition, structural transition between the Knot-like and Wheat-like configurations can be regulated by concentration and solvent as the alkyl chain length changes. Note that the phase transformation is in most cases incomplete. A summary of surface coverage for 2-HA-OCn (n = 12, 14, 16, 18, 20) molecules shows the general trend that a Knot-like structure is preferred in polar solvents and under low concentration, while a Wheat-like structure takes priority in nonpolar solvents and under high concentration. Besides, 2-HA-OCn (n = 11, 13, 15, 17) molecules adopted a Wheat-like pattern which differs from the Wheat-like pattern in the relative orientation of adjacent ribbons, attributed to a minimum of steric repulsion between the interdigitated alkyl chains. This study presents efficient strategies for the manipulation of chiral and achiral nanostructures, and the results are believed to be of significance to the fields of 2D self-assembly and interface science.

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.

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.