Mechanically durable liquid-impregnated honeycomb surfaces.

Liquid repellent surfaces typically work by keeping the fouling liquid in a metastable state, with trapped pockets of air between the substrate and the liquid. An alternative method with greater long-term stability utilizes liquid-impregnated surfaces, where the liquid being repelled slides over an immiscible liquid immobilized on a porous surface. Here, we report a method for creating honeycomb surfaces amenable to liquid-impregnation. Polystyrene dissolved in a water-immiscible, volatile solvent was deposited in a humid environment on a variety of substrates to achieve the necessary porosity. Evaporative cooling results in condensation of water in a breath figure array of droplets, forming a sacrificial template for the drying polymer film. These honeycomb surfaces were further functionalized with fluorosilane and dipped in the lubricating liquid to result in a durable, liquid-repellent surface. These surfaces were found to exhibit repellency towards water and oils with extremely low tilt angles due to the smooth liquid-liquid contact between the lubricating liquid and the liquid being repelled.

Fabrication techniques for bioinspired, mechanically-durable, superliquiphobic surfaces for water, oil, and surfactant repellency.

Nature provides inspiration for liquid-repellant and low-adhesive surfaces, such as the lotus leaf and pitcher plant. While water-repellency is frequently found in nature, oil-repellency and surfactant-repellency are uncommon to nonexistent. To obtain oil- and surfactant-repellency, hierarchical, re-entrant, bioinspired surface structures along with low surface energy materials are needed. This overview presents wetting literature, common liquids and their composition, and fabrication techniques for superliquiphobic surfaces with repellency toward water, oil, and surfactant-containing liquids. Four techniques for creating such surfaces are explained in detail: nanoparticle/binder, layer-by-layer, nanoparticle-encapsulation, and liquid-impregnation. Static contact and tilt angles with water and hexadecane liquids, morphology, wear, transparency, self-cleaning, anti-smudge, and oil-water separation data are examined to compare the techniques. Data for these techniques are presented showing evidence of re-entrant geometry and the ability for these surfaces to repel surfactant-containing liquids such as shampoo and laundry detergent. The data will provide guidance in implementing superliquiphobic surfaces for self-cleaning, anti-smudge, antifouling, and low-adhesion properties for various applications including plastic packaging and biomedical devices.

Liquid-impregnated porous polypropylene surfaces for liquid repellency.

Polypropylene is a popular plastic material used in consumer packaging. It would be desirable if such plastic containers were liquid repellent and not so easily fouled by their contents. Superomniphobic surfaces typically work by keeping the fouling liquid in a metastable state, with trapped pockets of air between the substrate and the liquid. An alternative method with greater long-term stability utilizes liquid-impregnated surfaces, where the liquid being repelled slides over an immiscible liquid immobilized on a porous surface. Here, we report a method for creating porous polypropylene surfaces amenable to liquid-impregnation. A solvent-nonsolvent polypropylene solution was deposited at high temperature to achieve the necessary porosity. Such surfaces were further functionalized with fluorosilane and dipped in the lubricating liquid to result in a durable, liquid-repellent surface. It is believed these liquid-impregnated surfaces will be more industrially viable than previous examples due to the ease of fabrication and their durability. These surfaces were found to exhibit repellency towards water, oils, shampoo, and laundry detergent with extremely low tilt angles due to the smooth liquid-liquid contact between the lubricating liquid and the liquid being repelled.

Durable superoleophobic polypropylene surfaces.

Polypropylene (PP) is a popular plastic material used in consumer packaging. It would be desirable if such plastic containers were liquid repellent and not so easily fouled by their contents. Existing examples of superoleophobic surfaces typically rely on poorly adhered coatings or delicate surface structures, resulting in poor mechanical durability. Here, we report a facile method for creating superoleophobic PP surfaces via incorporation of nanoparticles (NPs) into the polymer surface. A solvent-NP-PP mixture was spin coated at high temperature to achieve the necessary roughness. Such surfaces were further functionalized with fluorosilane to result in a durable, super-repellent surface. They were also found to exhibit some repellency towards shampoos. This method of incorporating NPs into polymer surfaces could also prove useful in improving the anti-bacterial, mechanical and liquid-repellent properties of plastic devices.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'.

Bioinspired materials for water supply and management: water collection, water purification and separation of water from oil.

Access to a safe supply of water is a human right. However, with growing populations, global warming and contamination due to human activity, it is one that is increasingly under threat. It is hoped that nature can inspire the creation of materials to aid in the supply and management of water, from water collection and purification to water source clean-up and rehabilitation from oil contamination. Many species thrive in even the driest places, with some surviving on water harvested from fog. By studying these species, new materials can be developed to provide a source of fresh water from fog for communities across the globe. The vast majority of water on the Earth is in the oceans. However, current desalination processes are energy-intensive. Systems in our own bodies have evolved to transport water efficiently while blocking other molecules and ions. Inspiration can be taken from such to improve the efficiency of desalination and help purify water containing other contaminants. Finally, oil contamination of water from spills or the fracking technique can be a devastating environmental disaster. By studying how natural surfaces interact with liquids, new techniques can be developed to clean up oil spills and further protect our most precious resource.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'.

Durable, superoleophobic polymer-nanoparticle composite surfaces with re-entrant geometry via solvent-induced phase transformation.

Superoleophobic plastic surfaces are useful in a wide variety of applications including anti-fouling, self-cleaning, anti-smudge, and low-drag. Existing examples of superoleophobic surfaces typically rely on poorly adhered coatings or delicate surface structures, resulting in poor mechanical durability. Here, we report a facile method for creating re-entrant geometries desirable for superoleophobicity via entrapment of nanoparticles in polycarbonate surfaces. Nanoparticle incorporation occurs during solvent-induced swelling and subsequent crystallization of the polymer surface. The resulting surface was found to comprise of re-entrant structures, a result of the nanoparticle agglomerates acting as nucleation points for polymer crystallization. Examples of such surfaces were further functionalized with fluorosilane to result in a durable, super-repellent surface. This method of impregnating nanoparticles into polymer surfaces could prove useful in improving the anti-bacterial, mechanical, and liquid-repellent properties of plastic devices.

Bioinspired, roughness-induced, water and oil super-philic and super-phobic coatings prepared by adaptable layer-by-layer technique.

Coatings with specific surface wetting properties are of interest for anti-fouling, anti-fogging, anti-icing, self-cleaning, anti-smudge, and oil-water separation applications. Many previous bioinspired surfaces are of limited use due to a lack of mechanical durability. Here, a layer-by-layer technique is utilized to create coatings with four combinations of water and oil repellency and affinity. An adapted layer-by-layer approach is tailored to yield specific surface properties, resulting in a durable, functional coating. This technique provides necessary flexibility to improve substrate adhesion combined with desirable surface chemistry. Polyelectrolyte binder, SiO2 nanoparticles, and silane or fluorosurfactant layers are deposited, combining surface roughness and necessary chemistry to result in four different coatings: superhydrophilic/superoleophilic, superhydrophobic/superoleophilic, superhydrophobic/superoleophobic, and superhydrophilic/superoleophobic. The superoleophobic coatings display hexadecane contact angles >150° with tilt angles <5°, whilst the superhydrophobic coatings display water contact angles >160° with tilt angles <2°. One coating combines both oleophobic and hydrophobic properties, whilst others mix and match oil and water repellency and affinity. Coating durability was examined through the use of micro/macrowear experiments. These coatings display transparency acceptable for some applications. Fabrication via this novel combination of techniques results in durable, functional coatings displaying improved performance compared to existing work where either durability or functionality is compromised.

Mechanically durable, superomniphobic coatings prepared by layer-by-layer technique for self-cleaning and anti-smudge.

Superomniphobic surfaces are of interest for anti-fouling, self-cleaning, anti-smudge and low-drag applications. Many bioinspired surfaces developed previously are of limited use due to a lack of mechanical durability. From a previously developed technique, an adapted layer-by-layer approach involving charged species with electrostatic interactions between layers is combined with an uncharged fluorosilane layer to result in a durable, superomniphobic coating. This technique can provide the flexibility needed to improve adhesion to the substrate with the addition of a low surface tension coating at the air interface. In this work, polyelectrolyte binder, SiO2 nanoparticles, and fluorosilane layers are deposited, providing the combination of surface roughness and low surface tension to result in a superomniphobic coating with droplets of liquids with surface tensions from 72 to 21 mN m(-1) displaying contact angles exceeding 155° with low tilt angles. The durability of these coatings was examined through the use of micro- and macrowear experiments. These coatings currently display levels of transparency acceptable for automotive applications. Fabrication via this novel combination of techniques results in durable, superomniphobic coatings displaying improved performance compared to existing work where either the durability or the repellency is compromised.

Mechanically durable, superoleophobic coatings prepared by layer-by-layer technique for anti-smudge and oil-water separation.

Superoleophobic surfaces are of interest for anti-fouling, self-cleaning, anti-smudge, low-drag, anti-fog, and oil-water separation applications. Current bioinspired surfaces are of limited use due to a lack of mechanical durability. A so-called layer-by-layer approach, involving charged species with electrostatic interactions between layers, can provide the flexibility needed to improve adhesion to the substrate while providing a low surface tension coating at the air interface. In this work, a polyelectrolyte binder, SiO2 nanoparticles, and a fluorosurfactant are spray deposited separately to create a durable, superoleophobic coating. Polydiallyldimethylammonium chloride (PDDA) polyelectrolyte was complexed with a fluorosurfactant layer (FL), which provides oil repellency while being hydrophilic. This oleophobic/superhydrophilic behavior was enhanced through the use of roughening with SiO2 particles resulting in a superoleophobic coating with hexadecane contact angles exceeding 155° and tilt angles of less than 4°. The coating is also superhydrophilic, which is desirable for oil-water separation applications. The durability of these coatings was examined through the use of micro- and macrowear experiments. These coatings currently display characteristics of transparency. Fabrication of these coatings via the layer-by-layer technique results in superoleophobic surfaces displaying improved durability compared to existing work where either the durability or the oil-repellency is compromised.

Oxidative atomized spray deposition of electrically conductive poly(3,4-ethylenedioxythiophene).

Atomized spray deposition of 3,4-ethylenedioxythiophene monomer in the presence of triflic anhydride vapour yields electrically conducting poly(3,4-ethylenedioxythiophene) layers.