Stable Superhydrophobic Surface via Carbon Nanotubes Coated with a ZnO Thin Film

Conformal chemical vapor deposition of B4C thin films onto carbon nanotubes

The unique attributes of carbon nanotubes (CNTs) establish them as the preferred material for fabricating sophisticated membrane architectures. However, CNT membranes are also susceptible to degradation under harsh environmental conditions, necessitating protective measures to maintain their functionalities. This study presents deposition of boron carbide (B4C) thin films as protective coatings on CNT membranes using chemical vapor deposition. Electron microscopy shows that B4C films were uniformly deposited on the CNTs. Raman spectroscopy shows the preservation of the G and D bands, with a notable stability in the RBM bands, while XPS measurements show sp2 hybridized C-C bonds and an additional shoulder characteristic of the deposited B4C film. This suggests that the CVD process does not degrade the CNTs, but merely adds a layer of B4C to their outer surface. This deposition process also allows for precise control over the membrane's pore size, offering the potential to fine-tune the properties of CNT membranes.

Research Progress of Superhydrophobic Materials in the Field of Anti-/De-Icing and Their Preparation: A Review

Accumulated ice has brought much damage to engineering and people's lives. The accumulation of ice can affect the flight safety of aircraft and lead to the failure of cables and power generation blades; it can even cause damage to human life. Traditional anti-icing and de-icing strategies have many disadvantages such as high energy consumption, low efficiency, or pollution of the environment. Therefore, inspired by animal communities, researchers have developed new passive anti-icing materials such as superhydrophobic material. In this paper, the solid surface wetting phenomenon and superhydrophobic anti-icing and de-icing mechanism were introduced. The methods of fabrication of superhydrophobic surfaces were summarized. The research progress of wear-resistant superhydrophobic coatings, self-healing/self-repairing superhydrophobic coatings, photothermal superhydrophobic coatings, and electrothermal superhydrophobic coatings in the field of anti-icing and de-icing was reviewed. The current problems and challenges were analyzed, and the development trend of superhydrophobic materials was also prospected in the field of anti-icing and de-icing. The practicality of current superhydrophobic materials should continue to be explored in depth.

Treatment to surfactant containing wastewater with membrane distillation membrane with novel sandwich structure

Surfactant containing wastewater widely exists in textile industry, which hardly to be treated by membrane technology due to its high in salinity and wetting potential. In this study, PVDF membrane was modified by constructing a PDMS-SiO₂-PDMS "sandwich" structure on top of its surface via coating to achieve resistance to surfactant induced wetting. The "sandwich" layer was optimized based on the membrane performance during membrane distillation. Compared to the pristine PVDF membrane with contact angle of 92°, the water contact angle of the membrane with a "sandwich" layer of 0.44 μm increased to 153°. For the feed contained 0.5 wt% NaCl and 0.25 wt% surfactant, there was no membrane wetting occurred during the experiment period using the membrane with a "sandwich" structure, in comparison to the pristine PVDF membrane being wetted from beginning. For a challenge experiment to the developed membrane lasting for 100 h using a surfactant containing feed, there is no wetting sign observed and the stable flux is 20 kg·m^-2·h^-1.

Superhydrophobic and Corrosion Behaviour of PVDF-CeO2 Composite Coatings

Composite coatings of polyvinylidene fluoride (PVDF)/CeO₂ were developed by using the spray approach to explore the wetting and corrosion behaviour of coated materials for applications related to industry. PVDF was combined with different quantities of CeO₂ nanoparticles followed by spraying onto glass, aluminium, and steel substrates. The sessile droplet method and microscopy studies were used to assess the wetting behaviour and morphology of the coated surfaces, respectively. The corrosion resistance of uncoated substrates coated with PVDF only was compared with those coated with PVDF/CeO₂ nanoparticles through Tafel polarization techniques. In psi, the force of adhesion was measured between the coating layer and the substrates. The PVDF/CeO₂-coated steel had a significantly greater water contact angle and lower contact angle hysteresis than coated aluminium and glass substrates, reaching 157 ± 2° and 8 ± 1°, respectively. The corrosion protection efficiency of the superhydrophobic PVDF/CeO₂ coatings was considerably higher for steel and aluminium when compared with PVDF coatings. The PVDF/CeO₂ coated substrates had modest adhesion between the coating layer and the substrates, but it was still acceptable. Furthermore, the PVDF/CeO₂ coatings outperformed PVDF alone in terms of mechanical properties.

Blown film extrusion of PBAT/TPS/ZnO nanocomposites for shelf-life extension of meat packaging

Biodegradable polymers typically have inferior barrier properties compared to petroleum-based nonbiodegradable plastic. The addition of zinc oxide nanoparticles may enhance the functional properties of biodegradable packaging and extends the shelf life of packaged foods. Polybutylene adipate-co-terephthalate (PBAT) and thermoplastic starch (TPS) blended ZnO (1-5%) nanocomposite films were developed via blown extrusion for functional active meat packaging. The nanocomposite film morphology showed agglomeration of the nanoparticles, causing poor mechanical properties. Nanovoids formed at the interface between the polymer and nanoparticles, increasing permeability. Dispersion of ZnO nanofillers modified CO and C-O ester bonding in PBAT and increased hydrogen bonding with TPS. The interaction between ZnO and polymers increased the dispersion and reduced the agglomeration of nanoparticles. The highest ZnO content at 5% resulted in a stronger interaction between ZnO and TPS due to increased amorphous starch content, which improved homogeneous dispersion within the matrices, reducing nanoparticle size. The ZnO nanocomposite films reduced lipid oxidation and delayed microbial growth, resulting in a lower total viable count, lactic acid bacteria and yeast and mold in packaged pork meat. Higher ZnO concentrations from 3% showed microbial inhibitory effects. The growth of microorganisms was controlled by residual oxygen, morphology of the films and nanoparticle characteristics. The nanocomposite films effectively extended the shelf life by more than 3 days under refrigerated conditions.

Advances in the development of superhydrophobic and icephobic surfaces

Superhydrophobicity and icephobicity are governed by surface chemistry and surface structure. These two features signify a potential advance in surface engineering and have recently garnered significant attention from the research community. This review aims to simulate further research in the development of superhydrophobic and icephobic surfaces in order to achieve their wide-spread adoption in practical applications. The review begins by establishing the fundamentals of the wetting phenomenon and wettability parameters. This is followed by the recent advances in modeling and simulations of the response of superhydrophobic surfaces to static and dynamic droplets contact and impingement, respectively. In view of their versatility and multifunctionality, a special attention is given to the development of these surfaces using nanocomposites. Furthermore, the review considers advances in icephobicity, its comprehensive characterization and its relation to superhydrophobicity. The review also includes the importance of the use of superhydrophobic surface to combat viral and bacterial contamination that exist in fomites.

Enhanced Phase-Change Heat Transfer by Surface Wettability Control

The phase-change heat-transfer coefficient can be improved by several orders of magnitude through the design of micro-nanostructures on typical surfaces. However, with the rapid development of intelligent and integrated devices, there is an increasing desire to regulate the heat exchange form of the surface to adapt to various environmental requirements. This study concerns the design of a carbon nanotube array-based phase-change heat-transfer surface, which can switch its wettability between superhydrophobicity and superhydrophilicity. By installing this surface on a device that integrates boiling heat transfer and condensation heat transfer, the device can independently adjust the surface wettability for different heat-transfer requirements. As a result, this surface can enhance condensation heat-transfer coefficient over 90 % in the superhydrophobic state and enhance the boiling heat-transfer coefficient over 41 % in the superhydrophilic state. Surfaces with controllable wettability can aid development of a new generation of smart control technologies to actively regulate system and device temperatures.

Surface and Interface Investigations of Matrix-Fillers in Heterogeneous Amorphous Semiconductors

Phosphate glass-based composites are prone to be as effective as amorphous semiconductors, enhancing the glass properties by the addition of a small amount of metallic fillers (Cr, Co, Ni, and Zn) and leading to the creation of composite materials where the conductive particles can be distributed in the glass matrix PbO-P₂O₅ (PbP) at the micrometer level. This paper deals with scanning electron microscopy (SEM) examination and the wetting behavior of the phosphate glass-metal powder composites. We focused on the filler effect on wetting characteristics, such as interfacial free energy. The change in the contact angle of water on the glass surface was also measured. Scanning electron microscopy images of the composites showed a good dispersion in the fillers within the glass matrix. The contact angles of the composites with water and three polar and apolar solvents were calculated. The total solid surface free energy was analyzed. The interaction parameter between the composites and the liquid has been calculated using Owens-Wendt equation.

Performance of Sprayed PVDF-Al2O3 Composite Coating for Industrial and Civil Applications

Because of their great water repellency, Superhydrophobic coatings have a major impact on a variety of industrial applications. The current study's key originality is the development of low-cost, stable, superhydrophobic, and corrosion-resistant composite coatings. In the present work, polyvinylidene fluoride (PVDF)/Al₂O₃ composite coatings were produced using the spray technique to investigate the wettability and corrosion behavior of the coated materials for industrial and civil applications. PVDF was mixed with various concentrations of Al₂O₃ nanoparticles, and the mixture was sprayed onto steel, aluminum, and glass substrates. The wettability and morphology of the coated surfaces were investigated using the sessile droplet method and scanning electron microscopy, respectively. The corrosion resistance of bare substrates was compared to that of those coated with PVDF alone and those coated with PVDF/Al₂O₃ nanoparticles using Tafel polarization techniques. The force of adhesion between the coat and the substrates was measured in pounds per square inch. A nanoindentation test was also used to measure the hardness of the coating layer. The PVDF/Al₂O₃ coated steel showed a significantly higher water contact angle and lower contact angle hysteresis, reaching 157 ± 2° and 7 ± 1°, respectively, compared to the coated aluminum and glass substrates. Corrosion test results showed that the superhydrophobic PVDF/Al₂O₃ coatings had a much higher corrosion protection efficiency for steel and aluminum than that of the PVDF ones. The PVDF/Al₂O₃ coated substrates showed moderate but still acceptable adhesion between the coating layer and the substrates. Moreover, the PVDF/Al₂O₃ coatings had much better mechanical properties than the PVDF only coatings. Such type of coating could be a promising candidate for possible industrial and civil applications.

The Role of the Fiber/Bead Hierarchical Microstructure on the Properties of PVDF Coatings Deposited by Electrospinning

Among the various polymeric options employed for the deposition of electrospun coatings, poly(vinylidene fluoride) (PVDF) has been widely investigated thanks to its excellent mechanical properties, high chemical resistance, and good thermal stability. In this work, the electrospinning technique is used for the fabrication of functional PVDF fibers in order to identify and evaluate the influence of the experimental conditions on the nanofiber properties in terms of optical transmittance, wettability, corrosion resistance, and surface morphology. Some of these properties can play a relevant role in the prevention of ice formation in aircrafts. According to this, a matrix of 4 × 4 samples of aluminum alloy AA 6061T6 was successfully coated by controlling two operational input parameters such as the resultant applied voltage (from 10 up to 17.5 KV) and the flow rate (from 800 up to 1400 µL/h) for a fixed polymeric precursor concentration (15 wt.%). The experimental results have shown a multilevel fiber-bead structure where the formation of a fiber mesh directly depends on the selected operational parameters. Several microscopy and surface analysis techniques such as confocal microscopy (CM), field emission scanning electron microscopy (FE-SEM), UV/vis spectroscopy, and water contact angle (WCA) were carried out in order to corroborate the morphology, transmittance, and hydrophobicity of the electrospun fiber composite. Finally, the corrosion behavior was also evaluated by electrochemical tests (Tafel curves measurement), showing that the presence of electrospun PVDF fibers produces a relevant improvement in the resultant corrosion resistance of the coated aluminum alloys.

Self-Cleaning Polyester Fabric Prepared with TiOF2 and Hexadecyltrimethoxysilane

In this study, self-cleaning polyester (PET) fabrics were prepared using TiOF2 and hexadecyltrimethoxysilane(HDS) treatment. TiOF2 was synthesized via direct fluorination of a precursor TiO2 at various reaction temperatures. The prepared PET fabrics had superior photocatalytic self-cleaning properties compared with anatase TiO2/HDS-treated PET fabrics under UV and sunlight with 98% decomposition of methylene blue. TiOF2/HDS-treated PET fabrics also had superior superhydrophobic self-cleaning properties compared with anatase TiO2/HDS-treated PET fabrics with a 161° water contact angle and 6° roll-off angle. After the self-cleaning tests of the non-dyed TiOF2/HDS-treated PET fabrics, we prepared dyed TiOF2/HDS-treated PET fabrics to test practical aspects of the treatment method. These PET fabrics were barely stained by tomato ketchup; even when stained, they could be self-cleaned within 4 h. These results suggest that practical self-cleaning PET fabrics with superhydrophobicity and photocatalytic degradation could be prepared using TiOF2/HDS-treatment.

Wetting Properties of Graphene Aerogels

Graphene hydrophobic coatings paved the way towards a new generation of optoelectronic and fluidic devices. Nevertheless, such hydrophobic thin films rely only on graphene non-polar surface, rather than taking advantage of its surface roughness. Furthermore, graphene is typically not self-standing. Differently, carbon aerogels have high porosity, large effective surface area due to their surface roughness, and very low mass density, which make them a promising candidate as a super-hydrophobic material for novel technological applications. However, despite a few works reporting the general super-hydrophobic and lipophilic behavior of the carbon aerogels, a detailed characterization of their wetting properties is still missing, to date. Here, the wetting properties of graphene aerogels are demonstrated in detail. Without any chemical functionalization or patterning of their surface, the samples exhibit a super-lipophilic state and a stationary super-hydrophobic state with a contact angle up to 150 ± 15° and low contact angle hysteresis  ≈ 15°, owing to the fakir effect. In addition, the adhesion force of the graphene aerogels in contact with the water droplets and their surface tension are evaluated. For instance, the unique wettability and enhanced liquid absorption of the graphene aerogels can be exploited for reducing contamination from oil spills and chemical leakage accidents.

Fabrication of a Pt nanoparticle surface on an aluminum substrate to achieve excellent superhydrophobicity and catalytic activity

A superhydrophobic Pt–Al₂O₃/Al surface with excellent application characteristics has been fabricated on an aluminium substrate by a chemical method and annealing process.

Graphene tailored by Fe3O4 nanoparticles: low-adhesive and durable superhydrophobic coatings

This study reports stable superhydrophobic Fe₃O₄/graphene hybrid coatings prepared by spin coating of the Fe₃O₄/graphene/PDMS mixed solution on titanium substrates. By tailoring graphene sheets with Fe₃O₄ nanoparticles, the superhydrophobicity of graphene platelets was largely enhanced with a water contact angle of 164° and sliding angle <2°. Fe₃O₄ nanoparticles interact with FLG sheets via Fe–O–C covalent link, to form a graphene micro-sheet pinned strongly by nano-sized Fe₃O₄. The newly-formed micro/nano-structured sheets interact with each other via strong dipole–dipole attractions among Fe₃O₄ nanoparticles, confirmed by the blue shifts of G band observed in Raman spectra. The strongly interactive micro/nano-structured sheets are responsible for the improvement of both the surface hydrophobicity and the durability towards water impacting. The obtained hybrid coatings possess excellent durability in various environments, such as acidic and basic aqueous solutions, simulating ocean water. And also the coatings can retain their stable superhydrophobicity in Cassie–Baxter state even after annealing at 250 °C or refrigerating at −39 °C for 10 h. We employed an AFM to probe nanoscale adhesion forces to examine further the ability of the as-prepared coatings to resist the initial formation of water layers which reflects the ability to prevent the water spreading. The most superhydrophobic and durable hybrid coating with 1.8 g Fe₃O₄, shows the smallest adhesion force, as expected, indicating this surface possesses the weakest initial water adhesive strength. The resulting low-adhesive superhydrophobic coating shows a good self-cleaning ability. This fabrication of low-adhesive and durable superhydrophobic Fe₃O₄/FLG hybrid coatings advances a better understanding of the physics of wetting and yield a prospective candidate for various practical applications, such as self-cleaning, microfluidic devices, etc.

Strongly interactive graphene micro-sheets tailored by Fe₃O₄ nanoparticles exhibit low-adhesive and durable superhydrophobicity.

Heterogeneous ZIF-L membranes with improved hydrophilicity and anti-bacterial adhesion for potential application in water treatment

Although different metal–organic framework (MOF) membranes have been widely studied for gas separation, their application for water treatment is still in its infancy. MOF membranes with improved hydrophilicity and stability are particularly essential for water/wastewater treatment. Herein, we have successfully developed heterogeneous membranes (Zn/Co-ZIF-L) composed of vertically standing leaf-like crystals of Zn-ZIF-L grown in situ onto porous ceramic supports, followed by the subsequent heterogeneous growth of Co-ZIF-L. The heterogeneous membranes show improved hydrophilicity (WCA = 13.6 ± 1.6°) and enhanced anti-bacterial adhesion. Significantly, they simultaneously deliver a relative high water flux and much improved anti-bacterial adhesion when compared with the homogeneous membranes (Co-ZIF-L and Zn-ZIF-L). The improvements are attributed to the intrinsic hydrophilic nature of Co-ZIF-L, their epitaxial growth onto Zn-ZIF-L as well as the increased surface roughness. The success of constructing a heterogeneous MOF structure shows an effective strategy to achieve the hydrophilic MOF membranes with considerably enhanced stability for water treatment.

Heterogeneous Zn/Co-ZIF-L membranes were prepared through the successive growth of Zn-ZIF-L and Co-ZIF-L on the macroporous ceramic supports, and the obtained heterogeneous membranes showed improved hydrophilicity and anti-bacterial adhesion.

Robust Superhydrophobic Carbon Nanotube Film with Lotus Leaf Mimetic Multiscale Hierarchical Structures

Superhydrophobic carbon nanotube (CNT) films have demonstrated many fascinating performances in versatile applications, especially for those involving solid/liquid interfacial processes, because of their ability to affect the material/energy transfer at interfaces. Thus, developing superhydrophobic CNTs has attracted extensive research interests in the past decades, and it could be achieved either by surface coating of low-free energy materials or by constructing micro/nanohierarchical structures via various complicated processes. So far, developing a simple approach to fabricate stable superhydrophobic CNTs remains a challenge because the capillary force induced coalescence frequently happens when interacting with liquid. Herein, drawing inspirations from the lotus leaf, we proposed a simple one-step chemical vapor deposition approach with programmable controlled gas flow to directly fabricate a CNT film with rather stable superhydrophobicity, which can effectively prevent even small water droplets from permeating into the film. The robust superhydrophobicity was attributable to typical lotus-leaf-like micro/nanoscale hierarchical surface structures of the CNT film, where many microscale clusters composed of entangled nanotubes randomly protrude out of the under-layer aligned nanotubes. Consequently, dual-scale air pockets were trapped within each microscale CNT cluster and between, which could largely reduce the liquid/solid interface, leading to a Cassie state. Moreover, the superhydrophobicity of the CNT film showed excellent durability after long time exposure to air and even to corrosive liquids with a wide range of pH values. We envision that the approach developed is advantageous for versatile physicochemical interfacial processes, such as drag reduction, electrochemical catalysis, anti-icing, and biosensors.

Surface modification of poly(vinylidene fluoride) hollow fibre membranes for biogas purification in a gas-liquid membrane contactor system

The wetting of hollow fibre membranes decreases the performance of the liquid-gas membrane contactor for CO₂ capture in biogas upgrading. To solve this problem, in this work, a poly(vinylidene fluoride) (PVDF) hollow fibre membrane for a liquid-gas membrane contactor was coated with a superhydrophobic layer composed of a combination of hydrophobic SiO₂ nanoparticles and polydimethylsiloxane (PDMS) by the method of spray deposition. A rough layer of SiO₂ deposited on the PVDF membrane resulted in an enhanced surface hydrophobicity. The surface structure of the pristine PVDF significantly affected the homogeneity of the generated SiO₂ layer. A uniform surface coating on the PVDF upper layer resulted from the presence of micrometre and nanometre-sized roughness on the surface of the PVDF membrane, which was achieved with a SiO₂ concentration of 4.44 mg ml^-1 (0.2 g/45 ml) in the coating solution. As a result, the water contact angle of the modified surface was recorded as 155 ± 3°, which is higher than that of the pristine surface. The high contact angle is advantageous for reducing the wetting of the membrane. Additional mass transfer resistance was introduced by the superhydrophobic layer. In addition, continuous CO₂ absorption tests were carried out in original and modified PVDF hollow fibre membrane contactors, using monoethanolamine (MEA) solution as the absorbent. A long-term stability test revealed that the modified PVDF hollow fibre membrane contactor was able to outperform the original membrane contactor and demonstrated outstanding long-term stability, suggesting that spray deposition is a promising approach to obtain superhydrophobic PVDF membranes for liquid-gas membrane absorption.

Non-metal photocatalyst nitrogen-doped carbon nanotubes modified mpg-C(3)N(4):facile synthesis and the enhanced visible-light photocatalytic activity

Nitrogen-doped carbon nanotubes (N-CNT) is a promising metal-free candidate and electronic acceptor. It has been employed to modify mesoporous carbon nitride (mpg-C₃N₄) for photocatalytic degradation of organic dye and antibiotics under visible-light irradiation. Herein, we report a facile synthesis strategy involving polymerization of cyanamide as the precursor in the presence of N-CNT via thermal polycondensation. The morphology and structure of as-prepared N-CNT/mpg-C₃N₄ were analyzed by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The N-CNT/mpg-C₃N₄-15 exhibited increased photocatalytic activity for rhodamine B (RhB), methyl orange (MO) and tetracycline hydrochloride (TC) degradation compared with the pure one under visible-light irradiation, which is mainly due to the efficiently separation of photogenerated electron-hole pairs for the introduction of N-CNT as electronic acceptor. The photocatalytic reaction can fit the first order kinetics. Additionally, superoxide radical (O₂^-) was regarded as main reactive species participating in the photodegradation reaction process. Furthermore, the reason for enhancing photocatalytic activity of N-CNT/mpg-C₃N₄ is mainly attributed to synergistic effects between mpg-C₃N₄ as main ingredient and N-CNT as electron acceptor.

Three-level hierarchical superhydrophobic Cu–Zn coating on a steel substrate without chemical modification for self-cleaning property

A superhydrophobic Cu–Zn coating was fabricated on a steel surface by facile one-step electrodeposition, without being chemically modified by a low surface energy material.

Vibration of Piezoelectric ZnO-SWCNT Nanowires

A hybrid nanowire (HNW) was constructed by coating a single-wall carbon nanotube (SWCNT) with piezoelectric zinc oxide (ZnO). The two components of the HNW interact with each other via the van der Waals (vdW) force. This paper aims to study the effect of the piezoelectricity in the ZnO layer and the inter-phase vdW interaction on the fundamental vibration of the HNWs. In doing this, a new model was developed where the two components of the HNWs were modeled as Euler beams coupled via the interphase vdW interaction. Based on the model, the dependence of the frequency on an applied electrical voltage was calculated for HNWs of different geometric sizes to reveal the voltage effect. The results were then compared with those calculated without considering the inter-phase vdW interaction. It was found that the interphase vdW interaction can substantially decrease the structural stiffness, leading to a greatly enhanced piezoelectric effect but a lower frequency for the vibration of the HNWs.

Superhydrophobic hierarchically structured surfaces in biology: evolution, structural principles and biomimetic applications

A comprehensive survey of the construction principles and occurrences of superhydrophobic surfaces in plants, animals and other organisms is provided and is based on our own scanning electron microscopic examinations of almost 20 000 different species and the existing literature. Properties such as self-cleaning (lotus effect), fluid drag reduction (Salvinia effect) and the introduction of new functions (air layers as sensory systems) are described and biomimetic applications are discussed: self-cleaning is established, drag reduction becomes increasingly important, and novel air-retaining grid technology is introduced. Surprisingly, no evidence for lasting superhydrophobicity in non-biological surfaces exists (except technical materials). Phylogenetic trees indicate that superhydrophobicity evolved as a consequence of the conquest of land about 450 million years ago and may be a key innovation in the evolution of terrestrial life. The approximate 10 million extant species exhibit a stunning diversity of materials and structures, many of which are formed by self-assembly, and are solely based on a limited number of molecules. A short historical survey shows that bionics (today often called biomimetics) dates back more than 100 years. Statistical data illustrate that the interest in biomimetic surfaces is much younger still. Superhydrophobicity caught the attention of scientists only after the extreme superhydrophobicity of lotus leaves was published in 1997. Regrettably, parabionic products play an increasing role in marketing.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'.

Atomic layer deposition coating of carbon nanotubes with zinc oxide causes acute phase immune responses in human monocytes in vitro and in mice after pulmonary exposure

Background

Atomic layer deposition (ALD) is a method for applying conformal nanoscale coatings on three-dimensional structures. We hypothesized that surface functionalization of multi-walled carbon nanotubes (MWCNTs) with polycrystalline ZnO by ALD would alter pro-inflammatory cytokine expression by human monocytes in vitro and modulate the lung and systemic immune response following oropharyngeal aspiration in mice.

Methods

Pristine (U-MWCNTs) were coated with alternating doses of diethyl zinc and water over increasing ALD cycles (10 to 100 ALD cycles) to yield conformal ZnO-coated MWCNTs (Z-MWCNTs). Human THP-1 monocytic cells were exposed to U-MWCNTs or Z-MWCNTs in vitro and cytokine mRNAs measured by Taqman real-time RT-PCR. Male C57BL6 mice were exposed to U- or Z-MWCNTs by oropharyngeal aspiration (OPA) and lung inflammation evaluated at one day post-exposure by histopathology, cytokine expression and differential counting of cells in bronchoalveolar lavage fluid (BALF) cells. Lung fibrosis was evaluated at 28 days. Cytokine mRNAs (IL-6, IL-1β, CXCL10, TNF-α) in lung, heart, spleen, and liver were quantified at one and 28 days. DNA synthesis in lung tissue was measured by bromodeoxyuridine (BrdU) uptake.

Results

ALD resulted in a conformal coating of MWCNTs with ZnO that increased proportionally to the number of coating cycles. Z-MWCNTs released Zn⁺² ions in media and increased IL-6, IL-1β, CXCL10, and TNF-α mRNAs in THP-1 cells in vitro. Mice exposed to Z-MWCNTs by OPA had exaggerated lung inflammation and a 3-fold increase in monocytes and neutrophils in BALF compared to U-MWCNTs. Z-MWCNTs, but not U-MWCNTs, induced IL-6 and CXCL10 mRNA and protein in the lungs of mice and increased IL-6 mRNA in heart and liver. U-MWCNTs but not Z-MWCNTs stimulated airway epithelial DNA synthesis in vivo. Lung fibrosis at 28 days was not significantly different between mice treated with U-MWCNT or Z-MWCNT.

Conclusions

Pulmonary exposure to ZnO-coated MWCNTs produces a systemic acute phase response that involves the release of Zn⁺², lung epithelial growth arrest, and increased IL-6. ALD functionalization with ZnO generates MWCNTs that possess increased risk for human exposure.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-016-0141-9) contains supplementary material, which is available to authorized users.

Development of Hybrid Surfaces with Tunable Wettability by Selective Surface Modifications

Recent advances in micro/nano technology have driven artificial modifications of surface wettability by mimicking biological surfaces, such as superhydrophobic and water-harvesting surfaces. In this study, surface wettability of polycarbonate (PC) films was modified using various surface treatments: micropatterning using ultrasonic imprint lithography, fluorinate silane coating, and electron beam irradiation. To modify surface wettability selectively in a specified region, these three treatments were performed using profiled masks with the corresponding shapes. Various combinations of these treatments were investigated in terms of wettability changes, by measuring contact angle (CA). The semi-hydrophobic PC film (CA: 89.2°) was modified to create a super- hydrophobic state (CA: 155.9°) by virtue of the selective micropatterning and coating. The electron beam irradiation had an opposite effect, reducing the CA (48.2°), so that the irradiated region was modified to create a hydrophilic state. Two combinations of the proposed surface modifications made it possible to have a great difference in CA on a single surface (107.7°), and to have four different wetting states on a single surface. Various water-drop experiments proved that the developed hybrid surfaces were selectively wettable and showed water-collecting capability.

Achieving Antifingerprinting and Antibacterial Effects in Smart-Phone Panel Applications Using ZnO Thin Films without a Protective Layer

When crystalline ZnO films with a thickness of 30 nm and hydrophilic properties were deposited at room temperature onto a glass substrate via radio frequency sputtering, they exhibited antifingerprinting qualities following annealing treatment that was simple and accomplished at low temperature (100 °C). Hydrophobic properties were achieved using as-deposited ZnO films with hydrophilic properties via annealing treatment without the deposition of a protective layer with hydrophobic properties. The annealed 30 nm ZnO films showed a high transmittance (∼91.3%) comparable to that of a glass substrate at a wavelength of 550 nm. The annealed films showed strong antibacterial activity against E. coli and S. aureus bacteria. The ZnO films with a thickness of 30 nm showed predominant mechanical durability with strong antibacterial activity for smart-phone panel applications.

Controlled three-dimensional interconnected capillary structures for liquid repellency engineering

The wetting properties of solvents on highly periodic, porous substrates with various layer thicknesses of three-dimensional nanoshell structures of TiO₂ with interconnected capillary spaces were demonstrated.

A facile synthesis of a highly stable superhydrophobic nanofibrous film for effective oil/water separation

An oil/water separation film with excellent durability and stable recyclability is highly desired for the treatment of oil containing effluents, like industrial oily wastewater.

Enhanced performance of nanocrystalline ZnO DNA biosensor via introducing electrochemical covalent biolinkers

Zinc oxide (ZnO) is considered to be one of the most promising candidates for the third-generation DNA biosensor because of its good chemical stability, wonderful biocompatibility, easy surface modification, and numerous kinds of nanostructures. In this work, we report a new and simple method to modify ZnO surface for the immobilization of oligonucleotides by electrochemical covalent grafting of diazonium salts. The atomic force microscope, X-ray photoelectron spectroscopy, surface contact angle system, and electrochemical workstation were employed to characterize the functionalization process. Fluorescence results show that this kind of DNA biosensor from covalently linking strategy has an enhanced performance compared to that based on an electrostatic adsorption route. The functionalized ZnO biosensor has the capability to distinguish four-base mismatched, one-base mismatched, and complementary DNA sequences. Moreover, a linear relationship has been observed between the fluorescence intensity and the concentration of the complementary DNA in the solution within the range from 10(-6) to 10(-9) M, offering us a possibility in the qualitative determination of the level of target DNA.

Super-hydrophobic multi-walled carbon nanotube coatings for stainless steel

We have taken advantage of the native surface roughness and the iron content of AISI 316 stainless steel to directly grow multi-walled carbon nanotube (MWCNT) random networks by chemical vapor deposition (CVD) at low-temperature (1000°C) without the addition of any external catalysts or time-consuming pre-treatments. In this way, super-hydrophobic MWCNT films on stainless steel sheets were obtained, exhibiting high contact angle values (154°C) and high adhesion force (high contact angle hysteresis). Furthermore, the investigation of MWCNT films with scanning electron microscopy (SEM) reveals a two-fold hierarchical morphology of the MWCNT random networks made of hydrophilic carbonaceous nanostructures on the tip of hydrophobic MWCNTs. Owing to the Salvinia effect, the hydrophobic and hydrophilic composite surface of the MWCNT films supplies a stationary super-hydrophobic coating for conductive stainless steel. This biomimetical inspired surface not only may prevent corrosion and fouling, but also could provide low friction and drag reduction.

Multi-fractal hierarchy of single-walled carbon nanotube hydrophobic coatings

A hierarchical structure is an assembly with a multi-scale morphology and with a large and accessible surface area. Recent advances in nanomaterial science have made increasingly possible the design of hierarchical surfaces with specific and tunable properties. Here, we report the fractal analysis of hierarchical single-walled carbon nanotube (SWCNT) films realized by a simple, rapid, reproducible, and inexpensive filtration process from an aqueous dispersion, then deposited by drytransfer printing method on several substrates, at room temperature. Furthermore, by varying the thickness of carbon nanotube random networks, it is possible tailoring their wettability due to capillary phenomena in the porous films. Moreover, in order to describe the wetting properties of such surfaces, we introduce a two-dimensional extension of the Wenzel-Cassie-Baxter theory. The hierarchical surface roughness of SWCNT coatings coupled with their exceptional and tunable optical and electrical properties provide an ideal hydrophobic composite surface for a new class of optoelectronic and nanofluidic devices.

Exploiting the hierarchical morphology of single-walled and multi-walled carbon nanotube films for highly hydrophobic coatings

Self-assembled hierarchical solid surfaces are very interesting for wetting phenomena, as observed in a variety of natural and artificial surfaces. Here, we report single-walled (SWCNT) and multi-walled carbon nanotube (MWCNT) thin films realized by a simple, rapid, reproducible, and inexpensive filtration process from an aqueous dispersion, that was deposited at room temperature by a dry-transfer printing method on glass. Furthermore, the investigation of carbon nanotube films through scanning electron microscopy (SEM) reveals the multi-scale hierarchical morphology of the self-assembled carbon nanotube random networks. Moreover, contact angle measurements show that hierarchical SWCNT/MWCNT composite surfaces exhibit a higher hydrophobicity (contact angles of up to 137°) than bare SWCNT (110°) and MWCNT (97°) coatings, thereby confirming the enhancement produced by the surface hierarchical morphology.

Micro-/nano-structured superhydrophobic surfaces in the biomedical field: part I: basic concepts and biomimetic approaches

Inspired by natural structures, great attention has been devoted to the study and development of surfaces with extreme wettable properties. The meticulous study of natural systems revealed that the micro/nano-topography of the surface is critical to obtaining unique wettability features, including superhydrophobicity. However, the surface chemistry also has an important role in such surface characteristics. As the interaction of biomaterials with the biological milieu occurs at the surface of the materials, it is expected that synthetic substrates with extreme and controllable wettability ranging from superhydrophilic to superhydrophobic regimes could bring about the possibility of new investigations of cell–material interactions on nonconventional surfaces and the development of alternative devices with biomedical utility. This first part of the review will describe in detail how proteins and cells interact with micro/nano-structured surfaces exhibiting extreme wettabilities.

Controllable fabrication of stable superhydrophobic surfaces on iron substrates

A stable superhydrophobic surface with excellent corrosion resistance has been fabricated via electrochemical machining and anneal without organic modification.

Non-fluorinated superhydrophobic and micro/nano hierarchical Al doped ZnO film: the effect of Al doping on morphological and hydrophobic properties

The azo micro/nano hierarchical fluffy clew-like films and their superhydrophobic properties have been experimentally investigated and computationally simulated.

Controllable wettability of micro- and nano-dendritic structures formed on aluminum substrates

A stable superhydrophobic surface with excellent anti-corrosion, anti-icing and deicing properties has been fabricated via annealing treatment from a superhydrophilic surface.