Combination of Bioinspiration: A General Route to Superhydrophobic Particles

Versatile Core-Shell Nanoparticle@Metal-Organic Framework Nanohybrids: Exploiting Mussel-Inspired Polydopamine for Tailored Structural Integration

We report a versatile strategy based on the use of multifunctional mussel-inspired polydopamine for constructing well-defined single-nanoparticle@metal-organic framework (MOF) core-shell nanohybrids. The capability of polydopamine to form a robust conformal coating on colloidal substrates of any composition and to direct the heterogeneous nucleation and growth of MOFs makes it possible for customized structural integration of a broad range of inorganic/organic nanoparticles and functional MOFs. Furthermore, the unique redox activity of polydopamine adds additional possibilities to tailor the functionalities of the nanohybrids by sandwiching plasmonic/catalytic metal nanostructures between the core and shell via localized reduction. The core-shell nanohybrids, with the molecular sieving effect of the MOF shell complementing the intrinsic properties of nanoparticle cores, represent a unique class of nanomaterials of considerable current interest for catalysis, sensing, and nanomedicine.

Smart enrichment and facile separation of oil from emulsions and mixtures by superhydrophobic/superoleophilic particles

The separation and removal of oil or organic pollutants from water is highly imperative. The oil phases in surfactant-free oil-in-water emulsions or in free oil/water mixtures can be smartly enriched and transported by using superhydrophobic/superoleophilic iron particles (SHIPs) under a magnetic field. For water-in-oil emulsion, SHIPs-based composite membranes selectively allow the oil to pass through. Their convenient and scalable preparation, excellent separation performance, and good reusability are of great advantages for practical applications in wastewater treatment, the cleanup of oil spills, emulsion concentration, and fuel purification.

Mussel-adhesive-inspired fabrication of multifunctional silver nanoparticle assemblies

The assembly of metal nanoparticles (NPs) has attracted a great deal of attention recently because of their collective properties that could not be exhibited by individual NPs. Here a one-step approach was reported for the fabrication of spherical silver NP assemblies (AgNAs). The formation of AgNAs simply included the stirring of silver ammonia and 3,4-dihydroxy-l-phenylalanine (DOPA) in aqueous solution at room temperature, in which DOPA acted as a reductant for AgNPs first because of its reducing ability and then directed the assembly of AgNPs into AgNAs. The AgNAs exhibited hierarchical structure with controllable sizes ranging from 180 to 610 nm by adjusting the concentrations of reagents. The two individual components, AgNPs and polyDOPA, also allowed AgNAs with multiple functions as demonstrated in this study of durable catalytic activity, high SERS sensitivity, and good antioxidant properties. The thin polyDOPA layer coated on AgNAs further offered the opportunity to modify the surface of AgNAs. The results presented here may provide a green and facile approach to designing multifunctional NP assemblies.

Liquid marbles: topical context within soft matter and recent progress

The study of particle stabilized interfaces has a long history in terms of emulsions, foams and related dry powders. The same underlying interfacial energy principles also allow hydrophobic particles to encapsulate individual droplets into a stable form as individual macroscopic objects, which have recently been called "Liquid Marbles". Here we discuss conceptual similarities to superhydrophobic surfaces, capillary origami, slippery liquids-infused porous surfaces (SLIPS) and Leidenfrost droplets. We provide a review of recent progress on liquid marbles, since our earlier Emerging Area article (Soft Matter, 2011, 7, 5473-5481), and speculate on possible future directions from new liquid-infused liquid marbles to microarray applications. We highlight a range of properties of liquid marbles and describe applications including detecting changes in physical properties (e.g. pH, UV, NIR, temperature), use for gas sensing, synthesis of compounds/composites, blood typing and cell culture.

Self-polymerization of dopamine and polyethyleneimine: novel fluorescent organic nanoprobes for biological imaging applications

The development of novel fluorescent nanoprobes has attracted great current research interest over the past few decades due to their superior optical properties and multifunctional capability as compared with small organic dyes. Although great advance has been made in the utilization of fluorescent nanoprobes for biomedical applications, development of novel fluorescent nanoprobes that possess good fluorescent properties, biocompatibility, biodegradability and water dispersibility through a convenient and effective route is still highly desirable. In this work, we reported for the first time that novel fluorescent organic nanoparticles (FONs) can be conveniently fabricated via self-polymerization of dopamine and polyethyleneimine at room temperature and in an air atmosphere within 2 h. These FONs exhibited strong green fluorescence, high water stability and excellent biocompatibility, making them highly potential for biological imaging applications. More importantly, due to the high reactivity of polydopamine, these FONs might also be further functionalized with other functional components through Michael addition or Schiff base reaction. Therefore the method described in this work would open new avenues for the fabrication of fluorescent nanoprobes for various biomedical applications.

Simple synthesis of smart magnetically driven fibrous films for remote controllable oil removal

Inspired by the marine mussel adhesive protein, smart, magnetically controllable, oil adsorption nanofibrous materials were successfully fabricated in this research. Taking advantage of the properties of dopamine whose molecular structure mimics the single unit of the marine mussel adhesive protein and can be polymerized in alkaline solution forming a "glue" layer on many kinds of material surfaces, magnetic iron(II, III) oxide (Fe3O4) nanoparticles were easily and robustly anchored on to electrospun poly(vinylidene fluoride) fibrous films. After fluorination, the as-prepared hierarchical structured films exhibited superhydrophobicity, superoleophilicity and an excellent oil adsorption capacity from water. Importantly, because of the magnetically controllable property endowed by the Fe3O4 nanoparticles, such fibrous films act as a "smart magnetically controlled oil removal carrier", which effectively overcome the drawbacks of other in situ oil adsorbant materials and can also be easily recovered. This work provides a simple strategy to fabricate magnetic responsive intelligent oil removal materials, which will find broad applications in complex environment oil-water separation.

One-step modification of fabrics with bioinspired polydopamine@octadecylamine nanocapsules for robust and healable self-cleaning performance

An in-situ polymerization to coat fabrics with polydopamine-encapsulated octadecylamine endows the fabrics with self-cleaning and self-healing abilities. The treated fabric exhibits self-healing after losing its hydrophobicity. It is durable against washing and mechanical abrasion without changing the hydrophobicity. Thanks to the versatile adhesive property of polydopamine, the approach is compatibile with a variety of substrates, such as fabrics, glass, sponge, paper, and polymeric materials.

Micro/nano-structured superhydrophobic surfaces in the biomedical field: part II: applications overview

The properties of surfaces define the acceptance and integration of biomaterials in vivo, as well as the material's efficiency when used at research or manufacturing levels. The presence of micro/nano-topographical structures and low surface energies could bring several advantages when highly repellent surfaces are employed in the biomedical field. Biomimetic superhydrophobic surfaces have been explored for diverse applications: as an intrinsic characteristic of biomaterials to be implanted; as materials that exhibit special interactions with biological entities; or to be used in ex vivo applications. This article aims to focus on the main motivations and requirements in the biomedical field that pushed for the utilization of superhydrophobic surfaces as suitable alternatives, as well as the great evolution of applications that have emerged in the last few years.

A facile approach to transform stainless steel mesh into pH-responsive smart material

A facile method for the preparation of smart pH-responsive interface based on stainless steel mesh.

Ternary silicone sponge with enhanced mechanical properties for oil–water separation

Sponge-like silicone polymers were obtained from a mixture of silanes with di-, tri- and tetra-functional groups. The optimized material exhibited enhanced mechanical properties and stable adsorption capacities for various organic solvents, as well as an excellent recyclability for oil–water separations.

Facile synthesis of novel size-controlled antibacterial hybrid spheres using silver nanoparticles loaded with poly-dopamine spheres

Sub-micrometer hybrid spheres with a poly-dopamine core and loaded with silver nanoparticles (NPs) were fabricated by a facile method. The new hybrid spheres show a strong antibacterial activity due to their special structure, effectively preventing silver NP aggregation.

Synthesis of conductive magnetic nickel microspheres and their applications in anisotropic conductive film and water treatment

Synthesized conductive magnetic Ni microspheres not only can be used for anisotropic conductive films, but also can be used for rapid waste removal and detoxification extraction with a very simple and efficient procedure.

Biomimetic super-lyophobic and super-lyophilic materials applied for oil/water separation: a new strategy beyond nature

Investigations in the field of oil/water separation materials with special wettability may accelerate the settlement of industrial oily wastewater and ocean oil spill accidents.

Antibacterial and osteoinductive capability of orthopedic materials via cation-π interaction mediated positive charge

Both implant centered infection and deficient osteoinduction are pivotal issues for orthopedic implants in early and long-term osseointegration, but constructing a functional bio-interface that can overcome these two problems is highly challenging. Our study reveals that a bio-interface with promoted positive charges plays an active role in simultaneously enhancing the antibacterial and osteoinductive capability of orthopedic implants. The positively charged bio-interface is fabricated by a simple dipping method, in which the cationic polymer (polyhexamethylene biguanidine, PHMB) is immobilized in the conjugated polydopamine coating. Mediated by the cation-π interaction, the immobilized PHMB elevates the surface potential resulting in excellent antibacterial efficacy corresponding to 5 ppm of free PHMB. The materials exhibit far better cytocompatibility than free PHMB at the dose which kills over 50% of the cells. Most importantly, the cationic surface can function as a bioelectrical microenvironment to guide bone mesenchymal stem cells and consequently, enhanced cellular viability and proliferation together with upregulated osteogenesis are achieved. The cation-π interaction mediated cationic surface overcomes the disadvantages plaguing the immobilized cationic antibacterial compounds prepared by other methods and is applicable to different types of biomedical materials requiring antibacterial and osteoinductive bio-interfaces.

Fluoro-polymer functionalized graphene for flexible ferroelectric polymer-based high-k nanocomposites with suppressed dielectric loss and low percolation threshold

Flexible nanodielectric materials with high dielectric constant and low dielectric loss have huge potential applications in the modern electronic and electric industry. Graphene sheets (GS) and reduced-graphene oxide (RGO) are promising fillers for preparing flexible polymer-based nanodielectric materials because of their unique two-dimensional structure and excellent electrical and mechanical properties. However, the easy aggregation of GS/RGO significantly limits the potential of graphene in enhancing the dielectric constant of polymer composites. In addition, the poor filler/matrix nanoscale interfacial adhesion also causes difficulties in suppressing the dielectric loss of the composites. In this work, using a facile and environmentally friendly approach, polydopamine coated RGO (PDA-RGO) and fluoro-polymer functionalized RGO (PF-PDA-RGO) were prepared. Compared with the RGO prepared by the conventional methods [i.e. hydrazine reduced-graphene oxide (H-RGO)] and PDA-RGO, the resulting PF-PDA-RGO nanosheets exhibit excellent dispersion in the ferroelectric polymer matrix [i.e. poly(vinylidene fluoride-co-hexafluoro propylene), P(VDF-HFP)] and strong interfacial adhesion with the matrix, leading to a low percolation threshold (fc = 1.06 vol%) and excellent flexibility for the corresponding nanocomposites. Among the three nanocomposites, the P(VDF-HFP)/PF-PDA-RGO nanocomposites exhibited the optimum performance (i.e. simultaneously having high dielectric constant and low dielectric loss). For instance, at 1000 Hz, the P(VDF-HFP) nanocomposite sample with 1.0 vol% PF-PDA-RGO has a dielectric constant of 107.9 and a dielectric loss of 0.070, showing good potential for dielectric applications. Our strategy provides a new pathway to prepare high performance flexible nanodielectric materials.

UV-triggered dopamine polymerization: control of polymerization, surface coating, and photopatterning

UV irradiation is demonstrated to initiate dopamine polymerization and deposition on different surfaces under both acidic and basic pH. The observed acceleration of the dopamine polymerization is explained by the UV-induced formation of reactive oxygen species that trigger dopamine polymerization. The UV-induced dopamine polymerization leads to a better control over polydopamine deposition and formation of functional polydopamine micropatterns.

Investigating and biomimicking the surface wetting behaviors of ginkgo leaf

For the first time, the surface composite Cassie-Baxter wetting state is carefully investigated using ginkgo biloba as natural model. Investigations follow two directions: (a) low local solid contact areal fraction leading to high apparent contact angles; and (b) thick air plastron trapped at the contacting interface leading to stable dewetting state.

Supramolecular polymers as surface coatings: rapid fabrication of healable superhydrophobic and slippery surfaces

Supramolecular polymerization for non-wetting surface coatings is described. The self-assembly of low-molecular-weight gelators (LMWGs) with perfluorinated side chains can be utilized to rapidly construct superhydrophobic, as well as liquid-infused slippery surfaces within minutes. The lubricated slippery surface exhibits impressive repellency to biological li-quids, such as human serum and blood, and very fast self-healing.

Mussel-inspired hydrophobic coatings for water-repellent textiles and oil removal

A series of catechol derivatives with a different number of linear alkyl chain substituents, and different length, have been shown to polymerize in the presence of aqueous ammonia and air, yielding hydrophobic coatings that present the ability to provide robust and efficient water repellency on weaved textiles, including hydrophilic cotton. The polymerization strategy presented exemplifies an alternative route to established melanin- and polydopamine-like functional coatings, affording designs in which all catechol (adhesive) moieties support specific functional side chains for maximization of the desired (hydrophobic) functionality. The coatings obtained proved effective in the transformation of polyester and cotton weaves, as well as filter paper, into reusable water-repellent, oil-absorbent materials capable of retaining roughly double their weight in model compounds (n-tetradecane and olive oil), as well as of separating water/oil mixtures by simple filtration.

Mussel-inspired one-step copolymerization to engineer hierarchically structured surface with superhydrophobic properties for removing oil from water

In the present study, a superhydrophobic polyurethane (PU) sponge with hierarchically structured surface, which exhibits excellent performance in absorbing oils/organic solvents, was fabricated for the first time through mussel-inspired one-step copolymerization approach. Specifically, dopamine (a small molecular bioadhesive) and n-dodecylthiol were copolymerized in an alkaline aqueous solution to generate polydopamine (PDA) nanoaggregates with n-dodecylthiol motifs on the surface of the PU sponge skeletons. Then, the superhydrophobic sponge that comprised a hierarchical structured surface similar to the chemical/topological structures of lotus leaf was fabricated. The topological structures, surface wettability, and mechanical property of the sponge were characterized by scanning electron microscopy, contact angle experiments, and compression test. Just as a result of the highly porous structure, superhydrophobic property and strong mechanical stability, this sponge exhibited desirable absorption capability of oils/organic solvents (weight gains ranging from 2494% to 8670%), suggesting a promising sorbents for the removal of oily pollutants from water. Furthermore, thanks to the nonutilization of the complicated processes or sophisticated equipment, the fabrication of the superhydrophobic sponge seemed to be quite easy to scale up. All these merits make the sponge a competitive candidate when compared to the conventional absorbents, for example, nonwoven polypropylene fabric.

Jack of all trades: versatile catechol crosslinking mechanisms

Catechols play an important role in many natural systems. They are known to readily interact with both organic (e.g., amino acids) and inorganic (e.g., metal ions, metal oxides) compounds, thereby providing a powerful system for protein curing. Catechol crosslinked protein networks, such as sclerotized cuticle and byssal threads of the mussel, have been shown to exhibit excellent mechanical properties. A lot of effort has been devoted to mimicking the natural proteins using synthetic catechol-functionalized polymers. Despite the success in developing catechol-functionalized materials, the crosslinking chemistry of catechols is still a subject of debate. To develop materials with controlled and superior properties, a clear understanding of the crosslinking mechanism of catechols is of vital importance. This review describes the crosslinking pathways of catechol and derivatives in both natural and synthetic systems. We discuss existing pathways of catechol crosslinking and parameters that affect the catechol chemistry in detail. This overview will point towards a rational direction for further investigation of the complicated catechol chemistry.

Facile immobilization of ag nanocluster on nanofibrous membrane for oil/water separation

Superhydrophobic and superoleophilic electrospun nanofibrous membranes exhibiting excellent oil/water separation performance were green fabricated by a facile route combining the amination of electrospun polyacrylonitrile (APAN) nanofibers and immobilization of a Ag nanocluster with an electroless plating technique, followed by n-hexadecyl mercaptan (RSH) surface modification. By introducing the hierarchically rough structures and low surface energy, the pristine superhydrophilic APAN nanofibrous membranes could be endowed with a superhydrophobicity with water contact angle of 171.1 ± 2.3°, a superoleophilicity with oil contact angle of 0° and a self-cleaning surface arising from the extremely low water contact angle hysteresis (3.0 ± 0.6°) and a low water-adhesion property. Surface morphology studies have indicated that the selective wettability of the resultant membranes could be manipulated by tuning the electroless plating time as well as the hierarchical structures. More importantly, the extremely high liquid entry pressure of water (LEPw, 175 ± 3 kPa) and the robust fiber morphology of the APAN immobilized Ag nanocluster endowed the as-prepared membranes with excellent separation capability and stability for oil/water separation by a solely gravity-driven process. The resultant membranes exhibited remarkable separation efficiency in both hyper-saline environment and broad pH range conditions, as well as excellent recyclability, which would make them a promising candidate for industrial oil-contaminated water treatments and marine spilt oil cleanup, and provided a new prospect to achieve functional nanofibrous membranes for oil/water separation.

Insertion and confinement of hydrophobic metallic powder in water: the bubble-marble effect

Metallic powders such as thermite are known as efficient fuels also applicable in oxygen-free environments. However, due to their hydrophobicity, they hardly penetrate into water. This paper presents an effect that enables the insertion and confinement of hydrophobic metallic powders in water, based on encapsulating an air bubble surrounded by a hydrophobic metallic shell. This effect, regarded as an inverse of the known liquid-marble effect, is named here "bubble marble" (BM). The sole BM is demonstrated experimentally as a stable, maneuverable, and controllable soft-solid-like structure, in a slightly deformed hollow spherical shape of ∼1-cm diameter. In addition to experimental and theoretical BM aspects, this paper also demonstrates its potential for underwater applications, such as transportation of solid objects within BM and underwater combustion of thermite BM by localized microwaves. Hence, the BM phenomena may open new possibilities for heat and thrust generation, as well as material processing and mass transfer underwater.

Stimuli-responsive composite particles as solid-stabilizers for effective oil harvesting

The polymer-grafted magnetic composite particles have been synthesized and developed to harvest oil by use of their speical wettability. Different from gravity-driven oil-water separation, the prepared polymer brushes-grafted magnetic composite particles can act as solid-stabilizers that diffuse to the oil-water interfical region and effectively minimize the direct oil-water interfical area by volume exclusion, whereas the magnetic Fe3O4 core allows easy separation of Pickering emulsions from oil-water mixture under an external magnetic field. When the emulsions were heated from room temperature to 50 °C, the coil-to-globule transition of poly(N-isopropylacrylamide) (PNIPAM) acts as the driving force for the destabilization of the emulsion, thereby achieving the release of oil. The novel materials can be used in aspects of oil-water separation, inducing oil droplet transport and release of lipophilic substrates.

Selecting water-alcohol mixed solvent for synthesis of polydopamine nano-spheres using solubility parameter

The solvent plays an important role in a given chemical reaction. Since most reaction in nature occur in the mixed-solvent systems, a comprehensive principle for solvent optimization was required. By calculating the Hansen solubility parameters (HSP) distance R_a, we designed a model experiment to explore the influence of mixed solvents on the chemical synthesis. The synthesis of polydopamine (PDA) in the water-alcohol system was chosen as model. As predicted, the well-dispersed PDA spheres were obtained in selected solvents with smaller R_a values: methanol/water, ethanol/water and 2-propanol/water. In addition, the mixed solvent with smaller R_avalues gave a higher conversion of dopamine. The strategy for mixed solvent selection is might be useful to choose optimal reaction media for efficient chemical synthesis.

A facile solvent-manipulated mesh for reversible oil/water separation

A controllable oil/water separation mesh has been successfully developed and easily manipulated by immersion in a stearic acid ethanol solution and tetrahydrofuran with a very short period of time. The superhydrophilic and underwater superoleophobic mesh is first obtained via a one-step chemical oxidation and subsequently converts to superhydrophobic after it is immersed in an ethanol solution of stearic acid for 5 min. The surface wettability is regained to superhydrophilic quickly by immersion in tetrahydrofuran for 5 min. More importantly, the reversible superhydrophobic-and-superhydrophilic switching can be repeated multiple times with almost no visible morphology variation. Therefore, this approach provides potential application in controllable oil/water separation and opens up new perspectives in manipulation of various metallic oxide substrates.

Core-shell-corona-structured polyelectrolyte brushes-grafting magnetic nanoparticles for water harvesting

A novel superhydrophilic material, charged polymer brushes-grafted magnetic core-shell-corona composite nanoparticles (Fe3O4@SiO2@PSPMA), was developed to harvest water through the hydration effect. Because of both the strong hydration capability and the good swelling performance, the negatively charged polymer brushes, PSPMA brushes, endow the composite nanoparticles with superhydrophilicity and a good water-absorbing performance like a sponge, while the magnetic Fe3O4 cores allow easy separation of Fe3O4@SiO2@PSPMA nanoparticles with absorbed water from oil/water mixture under an external magnetic field. The functional particles have the capability of harvesting water droplets whether floating on an oil surface or in the oil. This water-absorbing material uses selective wettability to harvest water and achieve oil-water separation and may be useful in finding novel approaches for recycling water from sewage and removing water in the petroleum industry.

Superwetting double-layer polyester materials for effective removal of both insoluble oils and soluble dyes in water

Inspired by the mussel adhesive protein and the lotus leaf, Ag-based double-layer polyester (DL-PET) textiles were fabricated for effective removal of organic pollutants in water. The DL-PET textiles are composed of a top superamphiphilic layer and a bottom superhydrophobic/superoleophilic layer. First, the PET textiles were modified with a layer of polydopamine (PDA) and deposited with Ag nanoparticles to form the PET@PDA@Ag textiles. The top superamphiphilic layer, formed by immobilizing Ag3PO4 nanoparticles on the PET@PDA@Ag textile, shows excellent visible-light photocatalytic activity. The bottom superhydrophobic/superoleophilic layer, formed by modifying the PET@PDA@Ag textile using dodecyl mercaptan, is mechanically, environmentally, and chemically very stable. The water-insoluble oils with low surface tension can penetrate both layers of the DL-PET textiles, while the water with soluble organic dyes can only selectively wet the top layer owing to their unique wettability. Consequently, the water-soluble organic contaminants in the collected water can be decomposed by the Ag3PO4 nanoparticles of the top layer under visible-light irradiation or even sunlight in room conditions. Thus, the DL-PET textiles can remove various kinds of organic pollutants in water including both insoluble oils and soluble dyes. The DL-PET textiles feature unique wettability, high oil/water separation efficiency, and visible-light photocatalytic activity.

Facile preparation of durable and robust superhydrophobic textiles by dip coating in nanocomposite solution of organosilanes

This article presents a facile approach for the preparation of durable and robust superhydrophobic textiles by simply dip coating in a nanocomposite solution of fluoro-free organosilanes. The superhydrophobic textiles exhibit good water repellency and excellent mechanical, chemical and environmental stability.

Cocoon-in-web-like superhydrophobic aerogels from hydrophilic polyurea and use in environmental remediation

Polyurea (PUA) develops H-bonding with water and is inherently hydrophilic. The water contact angle on smooth dense PUA derived from an aliphatic triisocyanate and water was measured at θ=69.1±0.2°. Nevertheless, texture-related superhydrophobic PUA aerogels (θ'=150.2°) were prepared from the same monomer in one step with no additives, templates, or surfactants via sol-gel polymerization carried out in polar, weakly H-bonding acetonitrile. Those materials display a unique nanostructure consisting of micrometer-size spheres distributed randomly and trapped in a nanofiber web of the same polymer. Morphostructurally, as well as in terms of their hydrophobic properties, those PUA aerogels are analogous to well-studied electrospun fiber mats incorporating particle-like defects. PUA aerogels have the advantage of easily scalable synthesis and low cost of the raw materials. Despite large contact angles and small contact areas, water droplets (5 μL) stick to the aerogels surface when the substrate is turned upside-down. That so-called Petal effect is traced to H-bonding at the points of contact between the water droplet and the apexes of the roughness of the aerogel surface. Monoliths are flexible and display oleophilicity in inverse order to their hydrophobicity; oil fills all the available open porosity (94% v/v) of cocoon-in-web like aerogels with bulk density ρb=0.073 g cm(-3); that capacity for oil absorption is >10:1 w/w and translates into ∼6:1 w/v relative to state-of-the-art materials (e.g., graphene-derived aerogels). Oil soaked monoliths float on water and can be harvested off.