Recent Development of Durable and Self-Healing Surfaces with Special Wettability.

Artificial special wetting surfaces have drawn much interest due to their important applications in many fields. Nevertheless, tremendous challenges still remain for the fabrication of wetting surfaces with durable and self-healing properties. Here, recent progress of durable, self-healing wetting surfaces is highlighted by discussing the fabrications of several typical wetting surfaces including superhydrophobic surfaces, superamphiphobic surfaces, underwater superoleophobic surfaces, and high hydrophilic antifouling surfaces based on expertise and related research experience. To conclude, some perspectives on the future research and development of these special wetting surfaces are presented.

Facile fabrication of carbon spheres with tunable morphologies from novel polymeric carbon precursors.

This study presents a facile and general method for fabrication of carbon spheres with tunable morphologies based on the sol-gel reaction of a novel polymeric carbon precursor. The carbon precursor was fabricated by the synthesis of resole, a low-molecular weight polymer of phenol and formaldehyde, and then the modification with poly(ethylene glycol) monomethyl ether (PEG). By turning the modification degree of resole with different amounts of PEG and the hydrolysis and condensation reactions of this precursor, carbon spheres with various morphologies, including regular spheres, hollow spheres of different pore sizes, and raspberry- and peanut-like spheres, were produced easily. This should be attributed to the condensation, self-assembly, and phase separation of the new polymeric carbon precursors during the sol-gel process.

Synergistic antibacterial effect and mechanism between Cu2O nanoparticles and quaternary ammonium salt in moisture-curable acrylic coatings.

Combining with various antibacterial mechanisms is the preferred strategy to fabricate coatings with effective antibacterial performance. Herein, Cu2O nanoparticles and dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride, a kind of quaternary ammonium salt (QAS), were simultaneously incorporated into a moisture-curable acrylic resin in order to achieve both contact-killing and release-killing abilities for antibacterial coatings. The surface morphology, surface composition and basic properties of the coatings were thoroughly characterized. The antibacterial performance of the coatings was determined by in-vitro bacteriostatic test. Under the constant total mass fraction of antibacterial agents, both Cu2O and QAS content possessed the highest value on the coating surface at Cu2O/QAS mass ratio of 1:1, and correspondingly, the coatings reached sterilizing rate above 99 % against both E. coli and S. loihica, indicating the existence of synergistic effect between Cu2O and QAS. The synergistic antibacterial mechanism of the coatings involved two aspects. Firstly, the combination of contact-killing and release-killing biocides resulted in high bactericidal and antibiofilm activity against different bacteria. Further, the grafting of QAS molecules on the surface of Cu2O particles brought about the spontaneous migration of nanoparticles to the coating surface. The interaction between Cu2O and QAS also inhibited the phase separation of QAS and prolonged the release of Cu2+ at the same time. The coatings, therefore, exhibited stable antibacterial performance at varied service conditions.

Facile synthesis, self-assembly, and photoelectrical performance of SrTiO3 hollow spheres with open holes.

This paper presents a facile method to synthesize monodisperse SrTiO3 hollow spheres with one or two openings through a template-assisted approach. These hollow spheres were further self-assembled into densely packed nanofilms at a "hexane-water" interface. TEM, SEM, HRTEM, XRD, etc., were employed to characterize the morphology and structure of the SrTiO3 hollow spheres as well as the corresponding nanofilms. The nanofilm-based photodevice displayed considerably higher sensitivity to UV than visible light and dark.

Fabrication, properties and applications of Janus particles.

Although the concept of Janus particles was raised in the early 1990s, the related research has not attracted considerable interest until recently due to the special properties and applications of these colloidal particles as well as the advances in new fabrications. Janus particles can be divided into three categories: polymeric, inorganic, and polymeric-inorganic, and each kind of Janus particles can be spherical, dumbbell-like, half raspberry-like, cylindrical, disk-like, or any of a variety of other shapes. Different Janus particles may share common preparation principles or require specific fabrication processes, and may have different assembly behaviours and properties. This critical review discusses the main fabrication methods of the three kinds of Janus particles, and then highlights the important properties and applications of these Janus particles developed in recent years, and finally proposes some perspectives on the future of Janus particle research and development.

Sol-gel-derived hard coatings from tetraethoxysilane and organoalkoxysilanes bearing zwitterionic and isothiazolinone groups and their antifouling behaviors.

Current environmentally friendly marine antifouling (AF) coatings are mainly polymeric with a relatively low hardness. Hard sol-gel-derived AF coatings for underwater robot-cleaning are seldom used. In this work, two new organoalkoxysilanes, i.e., (N-methoxyacylethyl)-3-aminopropyltriethoxysilane and 2-(2-hydroxy-3-(3-(trimethoxysilyl)propoxy)propyl)benzo[d]isothiazol-3(2H)-one, were synthesized by a facile method. These two precursors were used with tetraethoxysilane (TEOS) to produce three series of hybrid AF coatings with zwitterionic group (Z-χ), antibacterial group (1,2-benzisothiazolin-3-one) (A-χ) and zwitterionic and antibacterial groups (S-χ) by a sol-gel process. The hardness of the coatings was measured using a pencil hardness tester and the AF behaviors of the coatings were examined by laboratory and field assays. A pencil hardness up to 5 H was achieved and slight deterioration was observed after 9 months of immersion in artificial seawater for the A-χ and S-χ coatings at a sufficiently high TEOS content. A synergistic effect between the zwitterion and antimicrobial agents existed but was not obvious. A higher TEOS content led to a higher hardness and better AF performance regardless of the type of AF group. Even with the same biofilm formation after field assay, coatings with a higher TEOS content exhibited a better resistance to mussel settlement.

Pickering emulsion approach for fabrication of waterborne cross-linkable polydimethylsiloxane coatings with high mechanical performance.

HYPOTHESIS: The Pickering emulsion approach has been frequently employed to fabricate various emulsions. However, the direct formation of cross-linked polymer films from Pickering emulsions and double functions (emulsified and mechanical reinforcement) of Pickering agents have not been sufficiently reported. EXPERIMENTS: Fumed silica was co-modified with vinyltrimethoxysilane (VTMS) and hexamethyl disilylamine (HMDS) and was further adopted to emulsify vinyl or hydrogen dimethicone. The as-obtained Pickering emulsions were mixed with Karstedt catalyst capsules to produce one-component waterborne cross-linkable polydimethylsiloxane (PDMS) coatings that were subsequently transformed into elastic films after drying at ambient temperature. FINDINGS: The co-modification of fumed silica with VTMS/HMDS is shown to balance the Pickering emulsion effect and film-forming ability of the coatings. Greater amounts of grafted VTMS/HMDS or higher modified silica dosages demonstrated better Pickering emulsion effects. Nevertheless, because Pickering agents hinder the coalescence of silicone oil droplets, the appropriate modified silica concentration is crucial for achieving the highest cross-link density and thus the highest mechanical strength. The grafted CC groups can endow the modified silica with hydrosilylation reactivity and can thus additionally contribute to the mechanical performance of PDMS film. In addition, the Pickering emulsion approach is shown to be superior to the traditional emulsion approach for acquiring waterborne coatings with high mechanical performance.

Capillary force induced formation of monodisperse polystyrene/silica organic-inorganic hybrid hollow spheres.

This paper presents a "one-spot" procedure to fabricate polystyrene/silica (PS/SiO(2)) hybrid hollow spheres. In this approach, when poly(vinylpyrrolidone)-stabilized PS colloids were deposited by sol-gel derived silica layer under acidic medium, it was interesting to find that the PS/SiO(2) core-shell colloids gradually changed to hollow structure spontaneously in the same medium as reaction went on. The formation of this hollow structure should be attributed to the diffusion of PS macromolecular chains from core particles into the voids between silica nanoparticles driven by the strong capillary force.

Formation of sulfonated aromatic ketone chromophores within styrene-acrylic acid copolymers and their pH-responsive color change.

Styrene-acrylic acid copolymer was synthesized via solution polymerization and then sulfonated by concentrated sulfuric acid. This sulfonated copolymer displays an obvious pH-responsive color change in aqueous solutions (1 g/L) from yellow (pH <6) to khaki (pH 6 to 7)/red (pH 7 to 8) to purple (pH >8). This response is as quick as for small-molecule pH indicators such as methyl orange and phenolphthalein within 1 s and can be reversible. The lowest critical concentration of this pH-responsive copolymer solution is around 0.1 g/L, which is about 50-500 times the necessary amount used for conventional small-molecule pH indicators. An intramolecular cyclization mechanism between a neighboring carboxyl group and a benzene ring to form a sulfonated aromatic ketone is proposed to explain this pH-responsive color change behavior. The molar ratio of 1:1 for styrene to acrylic acid is the most favorable for forming neighboring benzene and carboxyl group pairs in the copolymer chains and subsequently yields sulfonated aromatic ketone chromophores at full capacity.

Preparation and synergistic antifouling effect of self-renewable coatings containing quaternary ammonium-functionalized SiO2 nanoparticles.

Confronting the complexity of marine biofouling, no single ecofriendly technology has been reported for efficient anti-biofouling. Combination of multiple antifouling factors should be one of the strategies for strengthening the anti-biofouling performance. Here we synthesized quaternary ammonium modified SiO2 nanoparticles (QAS-SiO2) and incorporated them into self-polishing polymer (SP) to get the coatings combining self-renewal ability, micro-nano structured topography, and bactericidal function. The coatings acquired underwater superoleophobic surface after immersion in artificial seawater due to their micro-nano structured surface together with the hydrolyzed SP. In comparison with unmodified SiO2, QAS-SiO2 had better compatibility with SP and caused less increment of self-polishing rate. Synergistic antifouling effect was interestingly observed between self-renewal ability and bactericidal function in both the laboratory assay based on the adhesion of Shewanella loihicas and natural field trial. The micro-nano structured topography contributed to underwater superoleophobicity but did not exhibit its impact on antifouling performance. QAS-SiO2 can also slightly inhibit the adhesion of diatoms and reduce the settlement of plantigrades of the mussel. In addition, we also demonstrated the coatings with lower quantity of biofilm exhibited less settlement of plantigrades of mussel.

One-component waterborne in vivo cross-linkable polysiloxane coatings for artificial skin.

Polysiloxane-based artificial skins are able to emulate the mechanical and barrier performance of human skin. However, they are usually fabricated in vitro, restricting their diverse applications on human body. Herein, we presented one-component waterborne cross-linkable polysiloxane coatings prepared from emulsified vinyl dimethicone, emulsified hydrogen dimethicone, and Karstedt catalyst capsules that were first synthesized by solvent evaporation method. The coating had good storage stability and meanwhile could form an elastic film quickly through merging of silicone oil droplets and subsequent hydrosilylation reaction. It was found that the mass ratio of vinyl dimethicone emulsion/hydrogen dimethicone emulsion (V/H), and the dosage of Karstedt catalyst capsules (K/(V + H)) were critical to the curing time, morphology, and mechanical properties of the coatings. With appropriate values of V/H and K/(V + H), the polysiloxane film had the mechanical performance comparable to that from solvent-based one. The coating could be topically applied to human skin in vivo and in situ turned into an elastic, invisible thin film with good water resistance. In contrast to those reported polysiloxane materials, the one-component waterborne polysiloxane coating was nontoxic and convenient for in vivo application on human body, making it be a promising candidate as artificial skin in the fields of cosmetics, medical treatment, and E-skin.

Facile synthesis of superparamagnetic fluorescent Fe3O4/ZnS hollow nanospheres.

A very simple strategy for the synthesis of superparamagnetic and fluorescent Fe(3)O(4)/ZnS hollow nanospheres is presented. These hollow nanospheres are not only nontoxic with a highly porous shell and have diameters of <100 nm but also exhibit very good magnetic resonance and fluorescence.

Seawater-Induced Healable Underwater Superoleophobic Antifouling Coatings.

Creating an artificial surface, mimicking a live fish scale that repels oil underwater and with self-healing properties, would be significant for the development of nontoxic marine antifouling coatings. Here, we report a seawater-induced strategy to create in situ an underwater superoleophobic surface, starting from the coatings of a self-polishing polymer and seawater-responsive polymer-grafted SiO2 nanoparticles. The coatings' surfaces were able to renew in artificial seawater through the hydrolysis of the superficial self-polishing polymer and its subsequent dissolution. Particularly, the grafted poly(triisopropylsilyl acrylate- co-3-methacryloxypropyltrimethoxysilane) chains could transform into hydrophilic ones via seawater-induced hydrolysis, which additionally strengthened the oil-repellency (zero oil adhesive force) and endowed the surface with excellent antiprotein adsorption characteristics. Because the hydrolysis was limited to the superficial layer of the coatings, it could avoid the water-swelling that instead occurs with conventional underwater superoleophobic coatings, with significant benefits to its durability. We believe that the seawater-induced renewal of underwater superoleophobic surfaces will be useful in extreme marine environments.

Polyurethane, epoxy resin and polydimethylsiloxane altered biofilm formation and mussel settlement.

In many environments, biofilms are a major mode and an emergent form of microbial life. Biofilms play crucial roles in biogeochemical cycling and invertebrate recruitment in marine environments. However, relatively little is known about how marine biofilms form on different substrata and about how these biofilms impact invertebrate recruitment. Here, we performed a comparative analysis of a 28-day-old biofilm community on non-coated (a control glass) and coated substrata (polyurethane (PU), epoxy resin (EP) and polydimethylsiloxane (PDMS)) and examined the settlement of Mytilus coruscus plantigrades on these biofilms. PU, EP and PDMS deterred the development of marine biofilms by reducing the biofilm biomass including the biofilm dry weight, cell density of the bacteria and diatoms and chlorophyll a concentrations. Further analysis of bacterial community revealed that EP altered the bacterial community composition compared with that on the glass substrata by reducing the relative abundance of Ruegeria (Alphaproteobacteria) and by increasing the relative abundance of Methylotenera (Betaproteobacteria) and Cyanobacteria in the biofilms. However, bacterial communities developed on PU and PDMS, as well as glass and PU, EP and PDMS did not exhibit differences from each other. The M. coruscus settlement rates on biofilms on PU, EP and PDMS were reduced by 20-41% compared with those on the glass after 28 days. Thus, the tested coatings impacted the development of marine biofilms by altering the biofilm biomass and/or the bacterial community composition. The mussel settlements decreased in the biofilms that formed on the coatings compared with those on non-coated glass.

Facile method for fabrication of nanocomposite films with an ordered porous surface.

This paper presents a novel and facile method for the fabrication of nanocomposite films with ordered porous surface structures. In this approach, a water-borne poly(styrene-co-butyl acrylate-co-acrylic acid)/silica nanocomposite dispersion was synthesized in situ by surfactant-free emulsion polymerization by using 3-allyloxy-2-hydroxy-1-propanesulfonate as a polymerizable surfactant. When this dispersion was dried to form a film at a certain temperature, an ordered porous structure could be directly obtained on the surface of the nanocomposite film. SEM, TEM, and AFM were employed to observe the morphology, and XPS and particle analyzer were used to analyze the surface composition of the ordered porous nanocomposite film and the particle size, respectively.

Shape-controllable synthesis of crystalline Ni complex particles via AOT-based microemulsions.

This article presents a simple method for the fabrication of shape-controllable Ni complex particles via an AOT-based single microemulsion. In this approach, Ni(2+)/N2H4/EG solution is used as the dispersed phase, and cyclohexane is used as the continuous phase to obtain a microemulsion by the aid of the anionic surfactant AOT. The primary Ni complex particles with diameters of 20-30 nm were first formed in the reverse micelles and then self-organized into spindle-like, ellipse-like, cuboid, and cubic morphologies, depending on the reaction conditions. When aged at 100 degrees C for 24 h, these Ni complex particles changed into crystalline Ni. A possible evolution mechanism of the Ni complex particles with different morphologies is also discussed.

Fabrication of hollow silica spheres using droplet templates derived from a miniemulsion technique.

Hollow silica spheres have been successfully fabricated by means of a miniemulsion technique, in which miniemulsion droplets of tetraethoxysilane (TEOS) and octane were prepared with cetyltrimethylammonium bromide as a surfactant and hexadecane as a costabilizer and used as templates. As the TEOS diffused out from the droplets, it was hydrolyzed and condensed to form a silica shell at the oil/water interface. In this way, hollow silica spheres could be obtained directly since the miniemulsion droplets of octane could be evaporated very easily during the reaction process or the drying process; neither an additional dissolution nor a calcination process or additional surface modification of the templates were needed.

Dual-Porosity Hollow Carbon Spheres with Tunable Through-Holes for Multi-Guest Delivery.

Dual-porosity hollow carbon spheres (DPHCs) with small mesopores (2-4 nm) and large through-holes (20-30 nm) in shells were successfully synthesized using colloidal silica as the template, small silica nanoparticles as nanomasks, and nontoxic dopamine as the carbon precursor followed by post-carbonization and etching. The synthesized DPHCs were further oxidized to be hydrophilic and then used to simultaneously deliver the protein bovine serum albumin (21 × 4 × 14 nm3) and the small molecule doxorubicin (<1 nm), which exhibited a high loading capacity of 689.4 and 1421.2 mg/g, respectively. The release of these two guest molecules can be controlled independently under the stimuli of heat and acidity. In vitro and in vivo experiments also proved that the DPHCs are promising for the co-delivery of multiple cargoes of different sizes.

Rheological behavior of aqueous organosilicone resin emulsion stabilized by colloidal nanosilica particles.

Inorganic colloidal particles were usually used to stabilize the emulsions of small molecular compounds. In this paper, the stable aqueous emulsions of organosilicone resin were prepared by emulsification technique using colloidal nanosilica particles combined with very small amount of emulsifiers. The effects of the silica size and concentration on the rheological behavior of the emulsion were investigated by steady-state and transient rheological measurements and dynamic modulus measurement. It was found that all emulsions containing colloidal silica particles exhibited shear-thinning behavior. The smaller the colloidal silica size was or the more the silica content was, the greater the storage modulus was at low strain amplitude, indicating a stronger interparticle interaction and a solidlike viscoelastic behavior of the emulsion. This rheological behavior can be explained by the formation of the reversible particulate network in the emulsion.

Bioinspired Design of Three-Dimensional Ordered Tribrachia-Post Arrays with Re-entrant Geometry for Omniphobic and Slippery Surfaces.

Hydro- and oleophobic (namely, omniphobic) coatings or surfaces have many important applications, but tremendous challenges in fabrication aspects still remain. Herein, we report a bioinspired design and nanofabrication of three-dimensional (3D) tribrachia-post arrays with re-entrant geometry (3D TPARG) for superhydrophobic and oleophobic polymer films or surfaces. By simply controlling the temperatures and time to treat silica colloidal templates, we can readily fabricate 3D ordered polymer arrays of tribrachia-posts or hexagonal tribrachia-posts with re-entrant geometries that resemble the skin of a springtail insect after the template is removed. These polymer surfaces exhibit excellent and self-healing superhydrophobicity and oleophobicity even against temperature, acids, alkalis, and mechanical damage. Moreover, their liquid-infused nanostructured surfaces still display very good liquid-sliding ability for water and oils. Our 3D TPARG design strategy may help the development of omniphobic polymer coatings or surfaces for practical applications in self-cleaning surfaces, liquid transport, antifouling materials, and many other important fields.