Superhydrophobic Carbon Nanotube Research Articles

The performance of superhydrophobic and superoleophilic carbon nanotube meshes in water–oil filtration

Vertically-aligned multi-walled carbon nanotubes (CNTs) were grown on stainless steel (SS) mesh by thermal chemical vapor deposition with a diffusion barrier of Al 2O 3 film. These three-dimensional porous structures (SS-CNT meshes) were found to be superhydrophobic and superoleophilic. Water advancing contact angles of 145–150° were determined for these SS-CNT meshes in air and oil (gasoline, isooctane). Oil, on the other hand, completely wet the SS-CNT meshes. This combined superhydrophobic and superoleophilic property repelled water while allowed the permeation of oil. Filtration tests demonstrated efficiencies better than 80% of these SS-CNT meshes as the filtration membranes of the water-in-oil emulsions. We have conducted quantitative analysis on the diameters of the oil droplets in both the feed emulsion and the filtrate. Then, we have evaluated the issue of water blockage and possible way to improve the filtration efficiency. Finally, the filtration and blockage mechanisms are proposed.

Thermo-responsive surface wettability on a pristine carbon nanotube film

A superhydrophobic carbon nanotube (CNT) film is fabricated by a simple spray-coating method without any chemical modification. The superhydrophobic surface changes after heating to a state of superhydrophilic wettability, and such transition may be attributed to the change of electronic structures of CNTs since the surface structure and composition after treated remain the same as the pristine CNTs. The initial wettability state is reestablished within 24 h of storage in air, and the time can be shortened to only 1 min when the heated CNT film was stored in deionized water.

Reversible Superhydrophobicity to Superhydrophilicity Switching of a Carbon Nanotube Film via Alternation of UV Irradiation and Dark Storage

We describe a simple method of fabricating a superhydrophobic carbon nanotube (CNT) film without any chemical modification. A remarkable surface wettability transition between superhydrophobicity and superhydrophilicity can be easily observed by the alternation of UV irradiation and dark storage. The adsorption and desorption of surface water molecules on the CNT surfaces account for their tunable surface wettability, which is disclosed by X-ray photoelectron spectroscopy analysis. We also perform a series of comparison experiments to confirm the explanation of its distinctive surface wettability. This switchable wettability on the CNT film could have potential applications in areas requiring multifunctional CNT-based films.

Study on superhydrophobic hybrids fabricated from multiwalled carbon nanotubes and stearic acid

A waterproof biomaterial, stearic acid (STA), which is one of components of the wax present on the lotus leaf surface, was used as the material with low surface energy to fabricate superhydrophobic multiwalled carbon nanotube (MWCNT) hybrids through a solution method. This method involved preparation of a sodium stearate (SST)-stabilized MWCNT dispersion, followed by a precipitating process. STA was assembled on the MWCNT–SST hybrid surface by a reaction of SST with acetic acid. The rough surface with multiscale protuberances was revealed by scanning electron microscopy (SEM). The effect of SST/MWCNT weight ratio on water contact angle (CA) and the temperature dependence and alkali resistance of superhydrophobicity of MWCNT hybrids have been investigated. With increasing the SST/MWCNT weight ratio, the water CA of MWCNT hybrid increased and then decreased after a maximum value of 163° at the ratio of 1/1. It was interesting that the wetting property of MWCNT hybrids (SST/MWCNT = 0.5/1 and 1/1) was tunable between superhydrophobicity and superhydrophilicity by changing temperature. Potential applications of these superhydrophobic materials to make large-area superhydrophobic coatings have been proposed.

Mechanically Durable Carbon Nanotube−Composite Hierarchical Structures with Superhydrophobicity, Self-Cleaning, and Low-Drag

Superhydrophobic surfaces with high contact angle and low contact angle hysteresis exhibit a self-cleaning effect and low drag for fluid flow. The lotus (Nelumbo nucifera) leaf is one of the examples found in nature for superhydrophobic surfaces. For the development of superhydrophobic surfaces, which is important for various applications such as glass windows, solar panels, and microchannels, materials and fabrication methods need to be explored to provide mechanically durable surfaces. It is necessary to perform durability studies on these surfaces. Carbon nanotube (CNT), composite structures which would lead to superhydrophobicity, self-cleaning, and low-drag, were prepared using a spray method. As a benchmark, structured surfaces with lotus wax were also prepared to compare with the durability of CNT composite structures. To compare the durability of the various fabricated surfaces, waterfall/jet tests were conducted to determine the loss of superhydrophobicity by changing the flow time and pressure conditions. Wear and friction studies were also performed using an atomic force microscope (AFM) and a ball-on-flat tribometer. The changes in the morphology of the structured surfaces were examined by AFM and optical imaging. We find that superhydrophobic CNT composite structures showed good mechanical durability, superior to the structured surfaces with lotus wax, and may be suitable for real world applications.

Fabrication of stable, transparent and superhydrophobic nanocomposite films with polystyrene functionalized carbon nanotubes

Stable, transparent and superhydrophobic carbon nanotube (CNT) nanocomposite films were fabricated by one-step spray casting process using the polystyrene functionalized CNTs, which were prepared by “living” free-radical polymerization and analyzed by means of infrared spectroscopy and thermal gravimetric analysis. The CNT film has a high water contact angle of 160° and a sliding angle of less than 3°. The surface topography of the fabricated film was characterized by field emission scanning electron microscopy. The transparency of the CNT film was investigated by UV–vis spectroscopy. The result shows that the CNT film has light transmittance of about 78% in the visible light region.

Superhydrophobic Conductive Carbon Nanotube Coatings for Steel

We report the synthesis of superhydrophobic coatings for steel using carbon nanotube (CNT)-mesh structures. The CNT coating maintains its structural integrity and superhydrophobicity even after exposure to extreme thermal stresses and has excellent thermal and electrical properties. The coating can also be reinforced by optimally impregnating the CNT-mesh structure with cross-linked polymers without significantly compromising on superhydrophobicity and electrical conductivity. These superhydrophobic conductive coatings on steel, which is an important structural material, open up possibilities for many new applications in the areas of heat transfer, solar panels, transport of fluids, nonwetting and nonfouling surfaces, temperature resilient coatings, composites, water-walking robots, and naval applications.

Electric Field Induced, Superhydrophobic to Superhydrophilic Switching in Multiwalled Carbon Nanotube Papers

Superhydrophobic multiwalled carbon nanotube bucky paper, fabricated after ozonolysis, shows fascinating electrowetting behavior, which could be remarkably tuned by changing key solution variables like the ionic strength, the nature of the electrolyte, and the pH of the water droplet. More significantly, the droplet behavior can be reversibly switched between superhydrophobic, Cassie-Baxter state to hydrophilic, Wenzel state by the application of an electric field, especially below a threshold value.

Impact dynamics and rebound of water droplets on superhydrophobic carbon nanotube arrays

The authors report the impact response of water droplets impinging on superhydrophobic carbon nanotube arrays and observe that arrays with different wetting properties display significantly different responses. For an array with a static contact angle of 163°, the droplet bounces off the surface several times, while for an array with a reduced contact angle of 140°, the droplet does not rebound and remains pinned. The contact angle hysteresis and contact line pinning for the 140° array suggest that the momentum of the droplet during the initial impact enables it to penetrate and displace the air pockets that are responsible for the superhydrophobicity of the array under static conditions.

Slippage of Water Past Superhydrophobic Carbon Nanotube Forests in Microchannels

We present in this Letter an experimental characterization of liquid flow slippage over superhydrophobic surfaces made of carbon nanotube forests, incorporated in microchannels. We make use of a particle image velocimetry technique to achieve the submicrometric resolution on the flow profile necessary for accurate measurement of the surface hydrodynamic properties. We demonstrate boundary slippage on the Cassie superhydrophobic state, associated with slip lengths of a few microns, while a vanishing slip length is found in the Wenzel state when the liquid impregnates the surface. Varying the lateral roughness scale L of our carbon nanotube forest-based superhydrophobic surfaces, we demonstrate that the slip length varies linearly with L in line with theoretical predictions for slippage on patterned surfaces.

Fabrication of superhydrophobic surfaces with non-aligned alkyl-modified multi-wall carbon nanotubes

Films of superhydrophobic multi-wall carbon nanotubes (MWCNTs) have been obtained by using alkyl-modified MWCNTs (MWCNT(COOC 18H 37) n ) and a simple and effective preparation method. The films show both a high contact angle and a small sliding angle for water droplets. A particular characteristic is that on the superhydrophobic surface the alkyl-modified MWCNTs are not intentionally aligned, thus avoiding the preparation techniques using aligned carbon nanotubes to produce the same effect.

Super-hydrophobicity of multi-walled carbon nanotubes treated by a glow discharge

Super-hydrophobic carbon nanotubes (CNTs) were prepared by employing tetrafluoromethane (CF 4) glow discharge plasma at low pressure to provide roughness and fluorination in CNT powders. The water droplet falling freely on the super-hydrophobic CNT powders bounced dynamically and then a contact angle (CA) was about 165° in static state, while the droplet falling freely on the untreated CNT powders was immediately absorbed. From the experimental results of SEM, TEM and XPS, the super-hydrophobicity of the CNT powders was resulted from the combined effects of the chemical modification of the surfaces and surface roughness.

Surface transformation of carbon nanotube powder into super-hydrophobic and measurement of wettability

Super-hydrophobic carbon nanotube (CNT) powders were formed by NF 3 glow-discharge plasma at low-pressure and their surface free energies were directly determined from the contact angles with probe liquids using the Owens–Wendt plotting. The cushion made of plasma-treated CNT powders revealed super-hydrophobicity (contact angle > 153°), regardless of kinds of probe liquids and treatment-time. The surface free energy of the NF 3 plasma-treated CNT powders decreased drastically from 82.6 to 0.12 mJ/m 2. The plasma treatment using fluorinated compound gases may be useful for dispersing, separating, and cutting CNTs since CNTs have tendency to aggregate in bundles and poor solubility.

Superhydrophobicity of a material made from multiwalled carbon nanotubes

Superhydrophobic carbon nanotubes (CNTs) were prepared by low-pressure CF4 glow plasma to provide roughness and fluorination in CNTs. The water droplet falling freely on the superhydrophobic CNT powders bounced dynamically. The superhydrophobicity resulted from the combined effects of the chemical modification and surface roughness. Using the contact angles obtained from the capillary rise method based on the Washburn equation, the total surface free energy of CNT powder treated by CF4 plasma for 20min was calculated to be drastically decreased from 27.04to4.06×10−7mJ∕m2.

Superhydrophobic Carbon Nanotube Forests

The present study demonstrates the creation of a stable, superhydrophobic surface using the nanoscale roughness inherent in a vertically aligned carbon nanotube forest together with a thin, conformal hydrophobic poly(tetrafluoroethylene) (PTFE) coating on the surface of the nanotubes. Superhydrophobicity is achieved down to the microscopic level where essentially spherical, micrometer-sized water droplets can be suspended on top of the nanotube forest.