superhydrophobic carbon-based materials: a review of ...089-104]-02.pdf · 89 superhydrophobic...

89

Superhydrophobic carbon-based materials: a review of synthesis, structure, and applications Long-Yue Meng1,2 and Soo-Jin Park1,♠

1Department of Chemistry, Inha University, Incheon 402-751, Korea2Department of Chemical Engineering, Yanbian University, Yanji 133002, China

Received 6 February 2014Accepted 25 March 2014

*Corresponding AuthorE-mail: [email protected] Tel: +82-32-860-8438

Open Access

pISSN: 1976-4251 eISSN: 2233-4998

Carbon Letters Vol. 15, No. 2, 89-104 (2014)Review Articles

Article Info

Copyright © Korean Carbon Society

http://carbonlett.org

AbstractMaterials with appropriate surface roughness and low surface energy can form superhy-drophobic surfaces, displaying water contact angles greater than 150°. Superhydrophobic carbon-based materials are particularly interesting due to their exceptional physicochemical properties. This review discusses the various techniques used to produce superhydrophobic carbon-based materials such as carbon fibers, carbon nanotubes, graphene, amorphous car-bons, etc. Recent advances in emerging fields such as energy, environmental remediation, and thermal management in relation to these materials are also discussed.

Key words: superhydrophobicity, carbon-based materials, surface energy, surface roughness

1. Introduction

Wettability of a solid surface describes the ability of a liquid to maintain contact with the surface, which is important in the bonding or adherence of two materials [1]. Dependent on both roughness and chemical heterogeneitym, wettability is a very important characteristic in nature as well as in our daily life. Hydrophobicity and hydrophilicity are two principal wettablility conditions. The surfaces of materials are hydrophilic if the water contact angle (WCA, θ) is in the range of 0° ≤ θ < 90° and they are hydrophobic if the WCA is 90° < θ ≤ 180°. Hydrophobicity is observed in nonpolar substances, which tend to aggregate in aqueous solutions and exclude water molecules.

Superhydrophobic materials have recently attracted attention from both academic and in-dustrial circles because of their importance in fundamental research and potential industrial applications such as bio-surfaces, anti-biofouling, transparent and antireflective superhydro-phobic coatings, structural color, fluidic drag reduction, enhancing water supporting force, controlled transportation of fluids, superhydrophobic valves, battery and fuel cell applica-tions, prevention of water corrosion and oil-water separation corrosion protective coatings, preventing adhesion of water and snow to windows or antennas, self-cleaning, enhancing buoyancy, and coating films for electronic devices [2-8].

The phenomenon of superhydrophobicity was first studied by Johnson and Dettre [7] in 1964 using rough hydrophobic surfaces. They developed a theoretical model based on experiments with glass beads coated with paraffin and polytetrafluoroethylene telomere, re-spectively. Barthlott and Ehler [9] studied the self-cleaning property of superhydrophobic micro-nanostructured surfaces in 1977, and they described such self-cleaning and superhy-drophobic properties for the first time as the “lotus effect”. The superhydrophobic state of a surface is defined by the contact angle between a water droplet and the surface of a material that has a WCA above 150°. Superhydrophobic surfaces display a self-cleaning effect (water repellent) widely known as the “lotus effect.” Superhydrophobicity can be achieved either by selecting low surface energy materials or by introducing roughness [9-14].

DOI: http://dx.doi.org/DOI:10.5714/CL.2014.15.2.089

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Double-walled carbon nanotubes: synthesis, structural characterization, and applicationYoong Ahm Kim, Kap-Seung Yang, Hiroyuki Muramatsu, Takuya Hayashi, Morinobu Endo, Mauricio Terrones and Mildred S. Dresselhaus

Superhydrophobic carbon-based materials: a review of synthesis, structure, and applications Long-Yue Meng and Soo-Jin Park

KCS Korean Carbon Society

carbonlett.org

pISSN: 1976-4251 eISSN: 2233-4998

REVIEWS

VOL. 14 NO. 2 April 30 2014

Carbon Letters Vol. 15, No. 2, 89-104 (2014)

DOI: http://dx.doi.org/10.5714/CL.2014.15.2.089 90

phobic carbon-based materials such as new energy technology, green engineering, underwater applications such as antifouling, and optical applications.

2. Theoretical Background

2.1. Surface roughness

Superhydrophobicity, as shown by lotus leaves, is an area that has received much interest in the past few years in rela-tion to self-cleaning surfaces and other processes as well as in the design and production of artificial biomimetic surfaces [64-71]. Fig. 1 shows a structural diagram of the lotus effect [64]. The structures of a lotus leaf, i.e., branch-like nanostructures on top of micropapillae, have been carefully observed by scien-tists. These microscale-structures can induce superhydrophobic surfaces with large contact angles and low sliding angles. It is believed that this unique self-cleaning property is based on the surface lotus effect illustrated in Fig. 1. The roughness is caused by the microscale papillae and nanoscale tomenta (Figs. 1b-d). To construct superhydrophobic carbon-based material surfaces, it is essential to understand the wetting behavior of water on the surface of the carbons.

Superhydrophobic surfaces are generally expressed by the contact angle between a water droplet and the solid surface. Wenzel’s early works and later Cassie-Baxter’s work defined the importance of surface roughness and heterogeneity, which are now recognized as key parameters in the wettability of hy-drophobic surfaces [65,66]. Wang et al. [71] and Yu et al. [72] showed that superhydrophobic lotus leaves have a specuticular wax with two scales of roughness (a: papillose epidermal cells around 10 μm; b: tubular wax crystals around 10 nm on the pap-illose epidermal cells).

Contact angle measurements, as described by Young in 1805,

Activated carbons, graphite, carbon fibers (CFs), fullerenes, carbon nanofibers (CNFs) (carbon nanotubes [CNTs], graphite nanofibers [GNFs]), micro-/meso-porous carbon, and, more recently, graphene carbon-based materials have emerged as ex-tremely promising materials for various types of applications owing to their outstanding electronic and optical properties [15-28]. Recently, carbon-based superhydrophobic surfaces have been fabricated because of their promising applications such as conductive-transparent films, oil-water separation, and electro-magnetic-interference-shielding [29-49]. In general, small water droplets on CF fabrics will be up to 120°, but not much greater for a flat surface.

To enhance the hydrophobicity of carbon-based materials, two approaches have been established recently [30-33]. First, research on superhydrophobic carbon-based materials has fo-cused on increasing surface roughness by introducing geometric surface area.

Dip-coatings methods are also often employed to obtain superhydrophobic surfaces. As demonstrated by Nguyen et al. [31], iterative dip coating of a foam in a graphene solution allows desired amounts of graphene sheets to be deposited on the pore-wall surface of melamine foams, rendering the foams superhydrophobic and superoleophilic, with a WCA of 162° and a chloroform absorption capacity of 165 times their own weight (1.86 ton m-3) [31,50-52]. Second, various functional groups or additional organic/inorganic materials can be intro-duced to remarkably vary surface wettability [53-55]. For ex-ample, Zeng et al. [32] and Charinpanitkul et al. [52] reported a simple method to produce CNT-based films with exceptional su-perhydrophobicity and impact icephobicity based on deposition of acetone-treated single-walled CNTs (SWCNTs) onto glass substrates. The acetone-functionalized films showed a strong ability to mitigate ice accretion from supercooled water droplets (-8°C), and the droplets were found to bounce off the films tilted at 30°. The untreated nanotubes films did not display similar be-havior, and the supercooled water droplets remained attached to the films’ surfaces. Such studies could serve as the foundation of highly versatile technologies for both water and ice mitigation.

Most current research on carbon-based materials has focused on their electrical, physiochemical, and mechanical properties [56-58]. In particular, surface properties such as robustness against environmental contamination are critical design consid-erations if intrinsic properties are to be maintained. Herein, we start by discussing the properties of carbon-based materials with superhydrophobic surfaces provided by emerging methods to create superhydrophobic surfaces with enhanced bulk proper-ties. The recent advances in this field are summarized, including the wetting behavior of water on carbon materials such as CFs, CNTs, graphene, and amorphous carbons, and the formation of hierarchical structures and low surface energy chemical compo-sition, with emphasis on fundamental understanding of related processes. Potential applications in energy, environmental remediation, and thermal management are also discussed [59-63].

In this paper we discuss the recent theoretical advances in superhydrophobicity, the relation of superhydrophobicity to the more general type of “superphobic” surfaces, manufacturing methods to obtain superhydrophobicity with different kinds of carbon surfaces, and new potential applications of superhydro-

Fig. 1. Lotus effect: (a) lotus leaf and beads; (b) scanning electron mi-croscopy image of micropapillae present on the surface of a lotus leaf; (c) image of a water droplet on a lotus leaf (a); (d) structural diagram of micro- and nanostructure of a single micropapilla [43].

Superhydrophobic Carbon-Based Materials

91 http://carbonlett.org

In Eq. (3), r is equal to the ratio between the actual surface area of the rough surface and the projected (apparent) area, where the non-dimensional surface roughness factor r > 1. r em-phasizes the effect of the surface chemistry determined by the term cos q, the non-dimensional surface roughness . When q is less than 90°, an increase in the roughness factor r reduces qw but if q is higher than 90°, an increase in roughness leads to an increase in qw .

If the droplet is suspended on the surface asperities and the liquid does not penetrate the protrusions of the surface features, then this case belongs to Cassie-Baxter’s model. In this mod-el, the apparent contact angle is the result of all contributions of different phases [82]. In Eq. (4), f1 and f2 are the fraction of the projecting solid and vapor on the surface, respectively, and f1 + f2 = 1. Eq. (4) only applies to cases where the liquid only contacts the top of the surface. However, a more complex version of Eq. (4) is required when partial penetration of the grooves occurs because the pores are filled with air. The hydro-phobicity is enhanced by the increases of the vapor fraction. Because the pores are filled with air, which is hydrophobic, the contact angle always increases, relative to the behavior seen on a flat substrate having an identical chemical composition [82].

(4)

From these two theories, it can be found that surface topogra-phy can enhance surface wettability on solid surfaces, whether they are hydrophobic or hydrophilic. This finding guides us to tune the surface wettability by controlling surface geometrical structures independently of the chemical composition [82-87]. On the other hand, the surface morphology was found to be an important parameter and more precisely “reentrant” structures are required to obtain such a superhydrophobic surface (Fig. 2d). These morphologies induce a negative Laplace pressure dif-ference because they introduce a transition in the liquid-vapor interface from concave to convex, inducing a higher energy bar-rier between Wenzel’s states and Cassie-Baxter’ states [86,87].

2.2. Modification of roughness of low surface energy materials

Based on the general contact angle theory of Wenzel, two main approaches have been developed to generate superhydro-phobic surfaces. One is increasing the surface area on a micro-scopic scale of low surface energy materials, as described above in Section 2.1; the other is to fabricate a suitable surface rough-ness with certain materials and subsequently modify the as-pre-pared surface with low surface energy materials [88]. The latter method is no longer limited to low surface energy materials, and it can be extended to the fabrication of hydrophobic surfaces for many systems. Various low surface energy materials have been developed to modify microscopic scale surfaces to form superhydrophobic surfaces. Fluorinated compounds, silane, and long alkyl chain fatty acids are typical low surface energy com-pounds, and have the ability to endow various substrates (SiO2, TiO2, Al2O3, metals, polymers etc.) with high hydrophobicity. Fig. 3 shows various surface reactive molecules for low-surface-energy modifications [88-90].

The surface energy is generally defined as the work required

remain the most accurate method for determining the interaction energy between a liquid and solid in a condensed state at the minimum equilibrium distance of solid and liquid. When a drop-let of water rests on a surface, the contact angle can be measured at the edge of the droplet (Fig. 1). Fig. 2 shows the liquid droplet wetting behavior of the corresponding theory: (a) Young’s state, (b) Wenzel’s state, (c) Cassie-Baxter’s state, and (d) an example of re-entrant morphology [5,11,14]. More than 200 years ago, Young, identified in a recent biography as ‘‘the last man who knew everything’’ [73], described the forces acting on a liquid droplet spreading on a flat surface (Fig. 1a).

On flat surfaces, Young’s equation defines the contact angle (θ) depending on the solid-vapor, solid-liquid, and liquid-vapor surface tensions, as given in Eq. (1), where gSV is the interfacial tension between solid and vapor, gSL is the interfacial tension between solid and liquid, and gLV relates to the interfacial tension between liquid and vapor. Depending on the value of θ as mea-sured by water, if θ is less than 90°, the surface is conventionally described as hydrophilic; if θ varies between 90° and 150°, the surface is hydrophobic; and if θ is greater than 150°, the surface is conventionally described as superhydrophobic [74-81].

(1)

Depending on the level of surface roughness, two different models can be distinguished. The first, shown in Fig. 2b, is Wen-zel’s state. The droplet maintains contact with the surface and fills the asperities, and the surface area associated with the con-tact angle is increased by the roughness factor r.

r = roughness factor = actual surface area / planar area (2)

Wenzel’s state is described by Eq. (3).

(3)

Fig. 2. Liquid droplet spreading on (a) flat surface (b) and rough surface (b-d). Depending on the roughness of the surface, the droplet is either in the so-called (a) Young, (b) Wenzel, or (c) Cassie-Baxter state; (d) example of re-entrant morphology (color figure available online).



In addition, the total surface energy of solids and liquids depends on the different types of molecular interactions, such as the London dispersive and the polar or acid/base interactions, and is considered to be the sum of these independent components [92].

In the early 1960s, Fowkes [93,94] introduced the concept of the surface free energy of a solid. The total surface free energy can be divided into the London dispersive and specific (or polar) components [93-95].

(5)

where gS is the total surface free energy, the subscript S represents a solid state, and gS

L and gSSP are the London dispersive and specific

(Debye, Keesom of van der Waals, H-bonding, π-bonding, and other small polar effects) components of the surface free energy of the constitutive elements. The London dispersive and specific components are determined by measuring the contact angles of two testing liquids with known London dispersive and specific components. The surface free energy of a solid can be deter-mined on the basis of contact angle measurements using the geo-metric mean, according to Fowkes’ proposition based on a solid (subscript S)–liquid (L) droplet–air system, as described by the following equation [93]:

(6)

where θ is the contact angle of a liquid droplet in the solid state. As reported in our previous work, the specific component gS

SP is highly dependent on the surface functional groups, and the dis-persive component gS

L is largely dependent on the total electron density in the carbon [94].

3. Superhydrophobicity on CFs

CFs have attracted considerable interest due to their electri-cal properties, thermal conductivity, and high strength, lend-ing outstanding behavior in practical applications [96-101]. In many cases, the CF surface properties are a crucial factor in their performance. Their specific surface area, however, is not suffi-ciently large for them to serve as ideal electrochemical materials compared to other carbon nanomaterials. Superhydrophobicity is an effect where roughness and hydrophobicity combine to generate unusually hydrophobic surfaces [81,100-105]. Because CFs are intrinsically hydrophobic, surface treatment is usually required to induce a hydrophilic state prior to their practical use [106-108]. The pristine hydrophobicity of CFs hinders their widespread utilization, and research on potential applications of this material generally has been limited.

Bliznakov et al. [100] used a simple and inexpensive route for the fabrication of a superhydrophobic metal surface. First, carbon/carbon composite paper (Toray TGP-H) is electroplated with copper. The copper layer is rendered hydrophobic by self-assembling a monolayer of dodecanethiol. The surface topogra-phy required to induce superhydrophobic behavior is achieved by varying the plating bath composition (Cl-, polyethylene gly-col, and bis (3-sulfopropyl) disulfide additives) and the time of deposition (this varies the effective thickness of the Cu layer). The surface morphology created by the original arrangement of

to build a unit of area of a given surface, using the sessile drop technique [91,92]. Numerous such theories have been developed by various researchers. These methods differ in several ways, in terms of derivation and convention for example. Most importantly, they differ in the number of components or parameters. Simpler methods containing fewer components simplify the system by converging the surface energy values into one number, whereas strict methods using more components are derived to distinguish various components of the surface energy.

Fig. 3. Surface reactive molecules for low-surface-energy modifications. (a) Perfluorodecyltrichlorosilane; (b) polyethylene; (c) polytetrafluoroeth-ylene; (d) polyvinyl chloride; (e) polyvinylidene fluoride; (f ) polysiloxane; (g) long alkyl chain thiols; (h) long alkyl chain thiols bearing benzoic acid (MUABA); (i) alkyl or fluorinated organic silanes; (j) long alkyl chain fatty acids; (k) alkyl chain modified aromatic azides; (l) perfluoroalkyl ethyl methacrylate; (m) poly(TMSMA-r-fluoroMA) (3-(trimethoxysilyl)propyl methacrylate (TMSMA) and fluoromonomer(®) bearing methacrylate moi-ety (fluoroMA)).



with an average size of 20-40 nm. The contact angle of water significantly increases from 148.2 ± 2.1° to 169.7 ± 2.2° through the introduction of CNTs. This finding sheds light on how the two-tier roughness surface induces superhydrophobicity, and how the presence of CNTs reduces the area fraction of a water droplet in contact with a carbon surface with two-tier roughness. They also used a hydrophobic coating of silica nanoparticles onto microscaled CFs and investigated the superhydrophobic behavior of composite nano/microstructures (Fig. 4c) [41]. The two-tier composite surfaces are based on regularly ordered CFs (8-10 μm in diameter) that are coated with SiO2 nanoparticles with an average size of 300-500 nm. The microscale fiber is used here to provide primary surface roughness, while the silica nanoparticles lend secondary roughness, mimicking the lotus leaf in nature. Increasing the density of silica on CFs had sig-nificant effects on the enhancement of the static contact angle, decrease of the contact angle hysteresis, and superhydrophobic stability. Without any subsequent low-surface-energy treatment, the unique composites with two-tier roughness exhibited super-hydrophobicity with a high contact angle of 162.5 ± 2.2° with water. The results can be attributed to the higher density of silica coating resulting in more tortuous three-phase contact lines, thus facilitating the self-cleaning effect.

The aforementioned method for the growth of CNTs on CF surfaces has some drawbacks. For example, at the high synthesis temperature, the metal catalysts easily aggregate into large particles and form different kinds of carbon nanomaterials. In addition, these processes require purity to attain adequate superhydrophobic and electrochemical properties [104]. Park et al. [102] reported that high-density carbon nanomaterials can be prepared by the decomposition of C2H2 on CF surfaces coated with Ni-doped mesoporous silica films at high temperature to en-hance the electrical conductivity of CFs [102-105]. This method is more effective than the traditional methods that involve such tasks as controlling the diameter of the carbon nanomaterials, enhancing the contact between the carbon nanomaterials and the CF surface, and eliminating the purification requirement of catalysts. In addition, the Park group fabricated superhydrophobic electrochemical CFs with double-scale roughness by the growth of GNFs on CF surfaces (Fig. 5). High-density GNFs were synthesized by chemical decomposition of C2H2 on CF surfaces coated with a Ni-doped mesoporous TiO2 film at lower temperature. Scanning electron microscopy (SEM) images indicated that GNFs with an average diameter of 40 nm grew uniformly and densely on CF surfaces (Figs. 5a-d). The contact angle of the CF surfaces increased from 27.2 to 153.5° after growth of GNFs and coating of a fluoropolymer (FP) (Figs. 5e-h). Deionized water, diiodomethane, ethylene glycol, and glycerol were selected for measurement of the contact angle of CFs. Table 1 shows the dispersive (gS

L), polar (gSSP), and surface

free energy (gS) components of wetting liquids used in Park’s work: pristine CFs, oxidized CF-H, Ni-doped mesoporous TiO2 film coated CFs, FP coated CFs, GNF coated CFs, and FP coated CF-GNFs. It is shown that the surface treatments significantly affect the surface energy of the CFs. The total surface free en-ergy, gS

L + gSSP, for CFs before the chemical treatment was de-

termined to be 50.1 mJ/m2 (gSL = 44.5 mJ/m2, gS

SP = 5.6 mJ/m2). The total surface energy of CF-H increased after oxidation treat-ment; this is due to an increase of hydrophilic functional groups

the CFs in the Toray paper (diameter 8 μm, spacing 30 μm) does not produce superhydrophobic behavior. This is true for both continuous and incomplete copper coatings. Actual superhydro-phobic behavior (large contact angles, 160-165°, and very small contact angle hysteresis, 2 to 3°) is achieved when a continuous copper layer is deposited on the CFs and secondary microme-ter-range roughness is developed as a result of the formation of small copper crystallites (size ~1 μm).

Previous studies have mostly focused on post-treatment of the CF surface to render a chemical composition that promotes surface hydrophobicity. The Hsieh group has carried out research on developing superhydrophobic CFs. They demon-strated the influence of the fluorine/carbon (F/C) ratio on super-hydrophobicity of CNFs prepared by a template-assisted syn-thesis (Fig. 4a) [109]. To functionalize the CNFs, the thermal chemical vapor deposition (CVD) method was used to deposit a fluorocarbon (using perfluorohexane as the precursor) coat-ing on the surface of the CNFs at 100, 300, and 500°C. The resulting CNFs exhibited good water-repellent behavior owing to hydrophobic surface groups including −CF2 and −CF3 groups. The fluorocarbon coating improves the superhydrophobicity of the CNF array and an upward increase of contact angle of wa-ter with F/C ratio was observed, i.e., from 110° to 161°. The superhydrophobic behavior in this study can be explained by 1) the lower surface energies of fluorocarbon coated surfaces and 2) the highly rough CNF arrays. They also investigated a continuous forest of CNTs grown catalytically on microscaled polyacrylonitrile (PAN)-based CF through a catalytic chemi-cal vapor deposition (CCVD) technique, using Ni nanoparticles and acetylene as a catalyst and a carbon source, respectively (Fig. 4b) [40]. The nanotubes were successfully branched and decorated onto the CFs at different axes, forming a micro/nano carbon structure. The superhydrophobic surfaces are based on regularly ordered CFs (8-10 μm in diameter) decorated by CNTs

Fig. 4. Illustration of the fabrication process for superhydrophobic carbon fiber (CF) surfaces (a) fluorinated carbon nanofibers (CNFs); (b) fluorinated CNFs/CF fabric with two-tier roughness; (c) SiO2 nanoparticle coated CF composite with two-tier roughness. CCVD: catalytic chemical vapor deposition



FP onto their surface. This provides evidence that the combined effect of double-scaled roughness and low-surface-energy treat-ment minimizes surface energy.

Lu et al. [110] synthesized CFs and SiCO/carbon composite fibers with average diameters of 120 and 163 nm, respectively, by electrospinning 7 wt% PAN and 5/7 wt% polyureasilazane (PUS)/PAN in dimethylformamide (DMF), respectively, followed by cross-linking, stabilization, and carbonization at temperatures up to 1000°C. The SiCO/CFs exhibited dual superhydrophilicity (absorbing 873% water) and superoleophilicity (608% decane absorption). The electrochemical properties determined by cyclic voltammetry show that the SiCO/CFs possess better capacitance behaviors than CFs.

Seo et al. [111] fabricated nm-scale carbon structures on CFs with micrometer-scale thickness using the CVD method, where Ni nanoparticles were used as catalysts of nanostructure growth. Polydimethylsiloxane (PDMS) thin films were used to provide hydrophobic surface properties. To adjust the pH value of the aqueous solutions, HCl and NaOH were used for acidic and basic solutions, respectively. For both cases, the initial contact angle measured immediately after dropping 3 μL of liquid droplet was higher than 170°. With increasing contact time to 30 min, the contact angles were almost constant. This implies that the superhydrophobicity of PDMS-coated surfaces can be sustained in a corrosive environment.

Qiu et al. [112] fabricated a superhydrophobic CF layer. CFs with enhanced corrosion inhibition ability were catalytically grown on a Zn surface. Cu was produced by a galvanic replacement reaction, and acted as a catalyst for CF growth. CFs endow the Zn surface with superhydrophobic wettability (~150.5°), enabling it to withstand corrosion by the external environment. The Zn-CF material shows enhanced corrosion

(–OH, C=O, and O=C–O) during the acid oxidation process. On the contrary, the fluorinated CF-FP shows lower surface energy. The decrease of both gS

L and gSSP is ascribed to the substitution of

the lower energy –C-F- groups of FP. The total surface free after the growth of GNFs decreased to 11.85 mJ/m2 (gS

L = 6.45 mJ/m2, gSSP

= 5.4 mJ/m2). This decreased surface free energy is due to the hydrophobic surface of the GNFs. In the case of CF-GNF-FP, the surface free energy decreases significantly after grafting the

Table 1. Dispersive (g SL), polar (g S

SP), and surface free energy (g S) components of wetting liquids used in Park’s work: pristine CFs, oxidized CF-H, Ni-doped mesoporous TiO2 film coated CF, fluo-ropolymer coated CFs, GNF coated CFs, and fluoropolymer coated CF-GNF (unit: mJ m-2)

g LL(mJ m-2) g L

SP(mJ m-2) g L (mJ m-2)

Water 21.8 51.0 72.8

Diiodomethane 50.42 0.38 50.8

Ethylene glycol 31.0 16.7 47.7

Glycerol 33.9 29.8 63.7

CFs 44.5 5.6 50.1

CF-H 44.1 27.3 71.4

CF-FP 29.5 3.8 33.3

CF-GNF 6.45 5.4 11.85

CF-GNF-FP 4.4 3.3 7.7

CF: carbon fiber, GNF: graphite nanofiber, FP: fluoropolymer.

Fig. 5. Scanning electron microscopy (a-h) and transmission electron microsocpy (i and j) images of carbon fibers (CFs) (a-c) pristine CFs; (d) Ni-doped mesoporous TiO2 film coated CFs; (e-j) graphite nanofibers coated CFs.



a schematic representation of CNT arrays grown on silicon wa-fers, which are denoted as model surface II (WCA: 154~165°); Fig. 6c represents model surface III (WCA: 155~166°), where nanoscale roughness exists in the CNT array grooves. The only difference between surfaces II and III is the nanoscale roughness that exists in the CNT array grooves on surface III. These surfac-es are coated with 20 nm fluorocarbon layers that have low sur-face energy and stabilize the CNT arrays. The CNT array size, pitch, and height have been varied to explore geometric effects on surface hydrophobicity. Compared to patterned Si surfaces with similar geometrical sizes, the nanoscale roughness does not significantly increase the apparent WCA; the microscale rough-ness thus determines the apparent WCA provided that the mi-croscale roughness dominates the nanoscale roughness. Wong et al. [117] found that the introduction of nanoscale roughness can decrease the contact angle hysteresis to less than 1° and im-prove the stability of superhydrophobic surfaces. Furthermore, nanoscale roughness can also reduce the strict requirements of microscale roughness design for superhydrophobic surfaces. In-troduction of nanoscale roughness on the groove bottom can de-crease the microscale array height required for superhydropho-bicity. These results improve the understanding of the effects of two-tier roughness on superhydrophobicity and offer additional design approaches for stable and robust superhydrophobic sur-faces with self-cleaning properties.

Hong and Uhm [118] prepared superhydrophobic CNTs by low-pressure CF4 glow plasma to provide roughness and fluo-rination to CNTs. The total surface free energy of CNT powder treated by CF4 plasma for 20 min was calculated to be drastically decreased from 27.04 to 4.06 × 10-7 mJ/m2. Superhydrophobic CNT powders were prepared by employing CF4 glow discharge plasma to provide roughness and fluorination to CNT powders and water droplets bouncing on CNT powders were observed.

Luo et al. [43] fabricated a new flexible multifunctional CNT/Nafion composite film with superhydrophobicity and high con-ductivity via a vacuum filtering method. The surface wettability of the nanocomposite film could be conveniently controlled by varying the filtering rate and the content ratio of Nafion to CNT in the composite solution. The films fabricated by filtering a 9.8 wt% Nafion composite solution with filtering rate of 0.5 mL/min exhibited the highest WCA of 165.3 ± 1.9° and the smallest water sliding angle (SA) of 3.3 ± 0.7°. A fatigue test showed that the films retained the superhydrophobicity and the electric conductivity after 1000 bending cycles. The dramatic reduction of the anodic peak potential by the flexible CNT/Nafion nano-composite films (CNNFs) electrode in cyclic voltammograms of β-nicotinamide adenine dinucleotide (NADH) demonstrates the strong potential of CNNFs in dehydrogenase-based biosen-sor applications.

It was recently reported that vertically aligned multi-walled CNT (VACNT) films produced by different techniques can present a hydrophobic character [120]. In particular, CO2 laser irradiance was used to modify the CNT surface by decreasing the polar component of the surface energy. Ramos et al. [120] demonstrated the formation of stable superhydrophobic VACNT surfaces prepared through CO2 laser irradiance, where the con-tact angle value reached 161°. VACNT arrays were synthesized by microwave plasma CVD using N2/H2/CH4. A CO2 laser tech-nique was applied on the VACNT surfaces with irradiance at

inhibition properties compared with bare Zn because of the air barrier originating from the superhydrophobic nature of the treated surface. The failure process of the superhydrophobic surface was monitored in situ using the open circuit potential technique. The perforations caused by capillary condensation decreased the superhydrophobicity of the surface and diminished its corrosion inhibition efficacy.

4. Superhydrophobicity on CNTs

CNTs, especially those with a cylindrical nanostructure, are of immense research interest for their outstanding behavior in practical applications such as nanotechnology, electronics, optics and other fields of materials science and technology [43,63,90,113-119]. However, in many cases, CNTs wettability and dispensability are crucial factors in their performance; ex-ample applications include reinforced polymer composites, templates, sensors, catalysts, electrode, etc. To date, many in-vestigators have endeavored to fabricate CNTs having a super-hydrophobic surface.

Previous studies have mostly focused on aligned CNTs films [43,90,117-119]. Zhu et al. [117] fabricated two model surfaces with two-tier scale roughness in a well-controlled manner and compared the superhydrophobicity and contact angle hysteresis of these surfaces with those of microscale rough surfaces by controlled growth of CNT arrays followed by coating with fluo-rocarbon layers formed by plasma polymerization. A schematic illustration describing surface roughness obtained by the meth-ods investigated in this study is shown in Fig. 6. Fig. 6a is a con-trol (silicon I) surface fabricated by photolithography; Fig. 6b is

Fig. 6. Schematic representations of (a) (I) microscale roughness cre-ated by photolithography, (II) aligned carbon nanotube (CNT) arrays that establish two-tier roughness, and (III) aligned CNT films on patterned sili-con surfaces; (b) the process used to obtain switchable wettability on the CNT film.



mode for more than 80% of the total evaporation time, which is characteristic of superhydrophobic surfaces. Furthermore, the acetone-functionalized films showed a strong ability to mitigate ice accretion from supercooled water droplets (-8°C); the drop-lets were found to bounce off the films tilted at 30°.

Recently, superhydrophobic transparent conductive films have attracted considerable interest due to their importance in fundamental research and potential industrial applications [48,125-127]. Meng and Park [125] prepared multi-walled CNT (MWCNT) thin films on glass substrates. The prepared films showed transparent, conductive, and superhydrophobic proper-ties. MWCNTs were dispersed in FP solutions for modification of their surface by grafting a FP (Fig. 7). A dip-coating process was used to prepare the films at a continuous speed and differ-ent numbers of coatings were applied. Fig. 7 shows schematic diagrams illustrating the changes of the contact angle and the surface properties of the film. As shown in this figure, the water droplet retains an ellipsoidal shape on the MWCNTs with a con-tact angle of 130°, suggesting the raw MWCNT materials have a hydrophobic character (Fig. 7a). The sharp decrease of the CA from 130° to 41.9° for MWCNT-OH (Fig. 7b) originates from the hydrophilic properties of the fully H2O2 treated surface. This is due to an increase of hydrophilic functional groups (–OH, C=O, and O=C–OH) during the H2O2 oxidation process [21]. The CA of glass increases to 117.5° after being coated with FP, and this is ascribed to the surface of the glass being coated with densely packed –CF3 groups (Fig. 7c). The CA of MWCNTs-OH after treatment with the FP increased to 160.2°, and the surface showed superhydrophobicity (Fig. 7d). The CA was 160.2° even at a transmittance of 83.5% (at 550 nm) and a sheet resistance of 1.38 × 104 Ω sq-1. This clearly indicates that the networks comprised of MWCNTs increase the conductivity while those containing the FP did not affect the conductivity of the films.

Tang et al. [128] functionalized covalently MWCNTs with polyhedral oligomeric silsequioxane (POSS). A stable and

different laser powers to promote the stability of the superhydro-phobic surfaces. Contact angle measurement revealed that the irradiated VACNT surface is superhydrophobic at all irradiances tested. Unlike as-grown VACNTs, the samples treated with a CO2 laser showed no sign of water seepage even after a prolonged period of time (~24 h). They also obtained superhydrophobic VACNT films by a microwave plasma CVD method. The values of the WCA changed to 35.7 ± 4.2º and to 142.2 ± 6.5º after CO2 laser irradiance of 15 KW cm-2 and 50 KW cm-2, respectively.

Stimuli-responsive smart surfaces with dynamically tunable wettability have recently received special attention because of their potential applications [121-123]. Yang et al. [121] fabri-cated various CNTs films with tunable wettability by a one-step spray-coating method without any chemical modification, where the wettability can be reversibly switched between superhydro-phobic and superhydrophilic by alternation of UV irradiation and dark storage. The most distinctive characteristic of the film is its tunable wettability in response to UV light. When the CNT film was exposed to UV light for 40 min, the water CA was found to be about 0°; that is, it was switched from superhydro-phobic to superhydrophilic. A water droplet can immediately spread out on the surface. After the UV-irradiated film had been in the dark for 24 h, its wettability recovered to the pristine su-perhydrophobic state (Fig. 6b).

Most of the current strategies for fabricating durable hydro-phobic surfaces can provide contact angles close to 170° cou-pled with icephobicity [32,124]. Zheng et al. [32] presented a simple method to produce CNT-based films with exceptional superhydrophobicity and impact icephobicity by depositing acetone-treated SWCNTs onto glass substrates. This method is scalable and can be adopted for any substrate, both flexible and rigid. These films displayed a high contact angle, in the vicinity of 170°, verified by both static and dynamic analysis processes. Dynamic evaporation studies indicated that a droplet deposited on the treated films evaporated in the constant contact angle

Fig. 7. Preparation procedure of FP modified MWCNTs and Illustrating the changes of water contact angle of the films. (a) pristine MWCNTs coated films; (b) oxidized MWCNTs-OH coated films; (c) FP coated films; (d) MWCNTs-FP coated films (at the volume ratio of MWCNTs/FP =10:3 and 7 coating times).



Rafiee et al. [131] demonstrated that a surface roughness effect in conjunction with the surface chemistry of graphene sheets can be used to dramatically alter the wettability of a substrate. In order to disperse graphene sheets on a substrate, they performed high-power ultrasonication of graphene sheets in water or acetone. By controlling the relative proportion of acetone and water in the solvent, the contact angle of the resulting graphene film can be tailored over a wide range (from superhydrophobic to superhydrophilic). Such graphene-based coatings with controllable wetting properties provide a facile and effective means to modify the wettability of a variety of surfaces.

Lin et al. [133] prepared a novel superhydrophobic graphene aerogel (GA) with extremely low bulk density and a high WCA. GA offers lower density and simpler processing than other superhydrophobic surfaces developed using vertically aligned CNTs or silica aerogels. They demonstrated that the GA is naturally hydrophobic because of its high surface roughness; following the application of a fluorinated silane, it becomes superhydrophobic with the WCA reaching 160°.

As shown in Fig. 3, fluorinated polymers are commonly used as low surface energy materials; for example, polyvinylidene fluoride (PVDF) is used to produce superhydrophobic materials [134-136]. Zha et al. [135] demonstrated a combined method of solvent exchanging and freeze-drying to fabricate PVDF porous materials that can effectively avoid the skin-layer formation of dried materials. It was observed that the addition of graphene (1 wt%) exerted clear influences on the crystallization, morphol-

superhydrophobic surface characteristic was observed for the film made of MWCNTs grafted with POSS (MWCNT-g-POSS) even after exposure to a high-humidity environment for three weeks. The WCA of the sample was measured to be 160.5 ± 1.1°. In addition, MWCNT-g-POSS buckypaper exhibited better efficiency in fire retardancy compared to the MWCNT buckypaper. This was due to the smaller median pore size of the MWCNT-g-POSS hybrid buckypaper and char formation during combustion, which could effectively limit the heat and mass transfer and the diffusion of flammable gases and therefore slow down the combustion and degradation of the resin.

5. Superhydrophobicity on Graphene

Graphene is a single-atom-thick sheet composed of sp2-hybridized carbon atoms and it exhibits many intriguing properties [48,127-130]. A perfect graphene nanosheet is hydrophobic, but surface treatment or introduction of various functional groups or additional components will remarkably vary its surface properties. Graphene has aroused strong interest in the context of exploring novel functional superhydrophobic surfaces [30]. Several experimental and modeling studies have focused on exploiting micro-scale surface roughness to engineer superhydrophobic graphene. Several research groups have fab-ricated superhydrophobic graphene surfaces using an irregular stack of graphene oxides (GO) prepared by chemical oxidation of graphite, and pertinent results are shown in Table 2 [131-144].

Table 2. List of graphene-based superhydrophobic surfaces

Method WCA Ref.

Superhydrophobic films Thermal expansion ~160º 131

Conductive, superhydrophobic coatings Graphene/POSS/CNT 155º 132

Aerogels Fluorinated silane 160 133

Porous graphene PVDF >150 135

PVDF-HFP/graphene microspheres PVDF 151.6±1.4º 136

Graphene/Nafion films Nafion ~161º 137

Biomimetic surfaces-superhydrophobicity, and iridescence Two-beam laser interference 156.7º 138

Mesoporous graphene for separation and absorption CaCO3 microspheres-hard templates, surface modification-PDMS, CVD >150º 139

White graphenes- nano-rough films A mixture of boron (B) and boron trioxide (B2O3) powder-precursor ~152º 140

Amine functionalized GO films Alkylamine of varying chain lengths 162º 141

Superhydrophobic electroconductive graphene-coated cot-ton cellulose Dip-pad-dry method 163± 3.4º 142

3D superhydrophobic foams CVD method >150º 143

Superhydrophobic film as corrosion barrier to copper Reduced graphene sheets 150.4°. 144

WCA: water contact angle, POSS: polyhedral oligomeric silsequioxane, PVDF: polyvinylidene fluoride, HFP: hexafluoropropylene, PDMS: polydimethylsi-loxane, CVD: chemical vapor deposition, GO: graphene oxide.



blocks to create a superhydrophobic structure with an ordered pore structure of ~200 μm in dimension. The advancing WCA on the foam surface exceeded 163°. The graphene foam inher-its the pore structure of the Ni foam template used in the CVD growth process. This method can be used to uniformly tune the pore size and structure of the graphene foam by selecting the ap-propriate Ni foam template. The graphene foam can store elastic strain energy as it is deformed by the impacting drop and then deliver it back to the drop, which could assist the rebound pro-cess.

6. Superhydrophobicity on Other Carbons

There has been a continuous growth of interest throughout the world in synthesizing porous carbons to fabricate superhy-drophobic films, in addition to CFs, CNFs, CNTs, and graphene. A typical method to control the wettability of a solid is surface modification with low surface energy materials. Superhydro-phobic surfaces can then be fabricated successfully with mi-cro- or nanostructured surfaces. As an environmentally benign and economically viable optoelectronic device material, super-hydrophobic amorphous carbon films are of interest in various applications [35,145-147].

Zhou et al. [35] prepared amorphous carbon films with a nanostructured surface and deposited the films on silicon and glass substrates at different substrate temperatures through a magnetron sputtering technique. The pure carbon films exhib-ited different wettability, ranging from hydrophilicity with WCA less than 40° to superhydrophobicity with a WCA of 152°. This reveals that the surface wettability of WCA films amorphous carbon films can be controlled well by using nanostructures with various geometrical and carbon state features. The graphite-like carbon film deposited at 400°C without any modification exhib-ited super-hydrophobic properties, due to the combination of microstructures of spheres with nanostructures of protuberances and interstitials.

Li et al. [145] demonstrated that the wettability of a Pt/car-bon/Nafion catalyst layer in proton exchange membrane fuel cells is critical to their performance and durability, especially with respect to the cathode, as water is needed to transport protons to the active sites and is also involved in deleterious Pt nanoparticle dissolution and carbon corrosion. They used the water droplet impacting method to determine the wettability of 100% Nafion films as a benchmark, and then prepared Vulcan carbon (VC)/Nafion composite films. Spin-coating in a Pt-free state was used for both cases. The wettability of the VC/Nafion composite films depends significantly on the VC/Nafion mass ra-tios, even though Nafion is believed to be preferentially oriented (sulfonate groups toward VC) in all cases. At low VC contents, a significant water droplet contact angle hysteresis is seen, similar to pure Nafion films, while at higher VC contents (>30%), the films become hydrophobic, also exhibiting superhydrophobic-ity, with surface roughness playing a significant role. At VC con-tents higher than 80% VC, the surfaces become wettable again as there is insufficient Nafion loading to fully cover the carbon surface. It is thus possible to calculate the Nafion:carbon ratio required for full coverage of carbon by Nafion.

Banerjee et al. [146] synthesized highly porous activated

ogy, surface area, and wettability of PVDF. PVDF/graphene (1 wt%) porous materials are a superhydrophobic material with a large contact angle (>150°). These properties are due to it be-ing a hybrid porous material composed of strings of roughened nanospheres (250-300 nm) with hierarchical micro-/nano-scaled roughness. On the basis of the Cassie-Baxter model, such multi-level surface roughness is responsible for its superhydrophobic-ity. Zhang et al. [136] demonstrated the fabrication of hybrid PVDF-hexafluoropropylene (HFP)/graphene composite micro-spheres through a spontaneous formation process. The addition of graphene to a PVDF-HFP/DMF solution has a strong influ-ence on its gel structure in both the wet and dry states. Morpho-logical characterization by SEM indicates that the dried gel is composed of PVDF-HFP/graphene (0.25 wt% to PVDF-HFP) microspheres with a size distribution of 8~10 μm. The contact angles of pure PVDF-HFP and PVDF-HFP/graphene are 132.7 ± 2.7° and 151.6 ± 1.4°, respectively. This superhydrophobicity is due to the PVDF-HFP/graphene gel being composed of mi-crospheres with nanoscaled surface roughness.

Usually, the micro-/macro-scale surface structures of func-tional films strongly affect the critical properties, such as wet-tability, and they should exhibit super water repellency with a WCA larger than 150° for self-cleaning and antimicrobial sur-faces. Choi and Park [137] demonstrated superhydrophobic thin films of graphene-based materials induced by a hierarchically petal-like structure. The superhydrophobic graphene/Nafion nano hybrid films were prepared by controlling the structures with respect to the chemical composition from an interpenetrat-ing networked and compactly interlocked structure (specific surface area of 9.56 m2/g) to a hierarchical petal-like, porous structure (specific surface area of ~ 413 m2/g). The hybrid films revealed a petal-like, porous structure with hierarchical rough-ness, where microscale roughness was produced in the lateral direction of the hybrid sheets while nanoscopic roughness was created on the edges of the hybrid sheets. The surface morpholo-gies of the hybrids were changed with respect to the amount of Nafion and their CAs increased from ~97° to ~161° with in-creasing Nafion content.

Shanmugharaj et al. [141] demonstrated a facile method for the synthesis of amine functionalized GO films using alkyl-amines of varying chain lengths. Alkylamines consisting of hydrophobic long chain alkyl groups and hydrophilic amine groups were chemically reacted to the GO surface via two types of reactions viz. 1) An amidation reaction between amine groups and carboxylic acid sites of GO, and 2) a nucleophilic substi-tution reactions between amine and epoxy groups on the GO surface. Alkylamine-modified GO surfaces showed enhanced roughness, and this effect was more pronounced with increas-ing amine chain length. WCA measurements revealed that the hydrophobic nature of graphene depended on the chain length of the grafted alkylamines, and this may be corroborated to a decrease in the surface energy values. Grafting of long chain alkylamines such as hexadecylamine or octadecylamine on the GO surface followed by thermal reduction resulted in the for-mation of superhydrophobic surfaces with WCA values of 152° and 162°, corroborating the role of alkylamine chain length in superhydrophobic wetting control of a thermally annealed GO surface.

Singh et al. [143] used Teflon coated graphene building



[4] Fei T, Chen H, Lin J. Transparent superhydrophobic films pos-sessing high thermal stability and improved moisture resis-tance from the deposition of MTMS-based aerogels. Colloids Surf Physicochem Eng Aspects, 443, 255 (2014). http://dx.doi.org/10.1016/j.colsurfa.2013.11.027.

[5] Wolfs M, Darmanin T, Guittard F. Superhydrophobic fibrous polymers. Polym Rev, 53, 460 (2013). http://dx.doi.org/10.1080/15583724.2013.808666.

[6] Fowkes FM, Zisman WA. Contact Angle, Wettability, and Adhe-sion (Advances in Chemistry Series Vol. 43), American Chemical Society, Washington, DC (1964).

[7] Johnson RE, Dettre RH. Contact angle hysteresis. In: Fowkes FM, Zisman WA, eds. Contact Angle, Wettability, and Adhesion (Advances in Chemistry Series Vol. 43), American Chemical So-ciety, Washington, DC, 112 (1964). http://dx.doi.org/10.1021/ba-1964-0043.ch007.

[8] Ahn CH, Baek Y, Lee C, Kim SO, Kim S, Lee S, Kim SH, Bae SS, Park J, Yoon J. Carbon nanotube-based membranes: fabrica-tion and application to desalination. J Ind Eng Chem, 18, 1551 (2012). http://dx.doi.org/10.1016/j.jiec.2012.04.005.

[9] Barthlott W, Ehler N. Raster-Elektronenmikroskopie der Epidermis-Oberflachen von Spermatophyten (Tropische und subtropische Pflanzenwelt Vol. 19), Akademie der Wiss. u.d. Lit-eratur, Mainz (1977).

[10] Quéré D. Rough ideas on wetting. Physica A, 313, 32 (2002). http://dx.doi.org/10.1016/S0378-4371(02)01033-6.

[11] Celia E, Darmanin T, Taffin de Givenchy E, Amigoni S, Guit-tard F. Recent advances in designing superhydrophobic surfaces. J Colloid Interface Sci, 402, 1 (2013). http://dx.doi.org/10.1016/j.jcis.2013.03.041.

[12] Yong J, Yang Q, Chen F, Zhang D, Du G, Bian H, Si J, Yun F, Hou X. Superhydrophobic PDMS surfaces with three-dimension-al (3D) pattern-dependent controllable adhesion. Appl Surf Sci, 288, 579 (2014). http://dx.doi.org/10.1016/j.apsusc.2013.10.076.

[13] Taylor P. The wetting of leaf surfaces. Curr Opin Colloid Inter-face Sci, 16, 326 (2011). http://dx.doi.org/10.1016/j.cocis.2010. 12.003.

[14] Shirtcliffe NJ, McHale G, I. Newton M. The superhydrophobic-ity of polymer surfaces: Recent developments. J Polym Sci B, 49, 1203 (2011). http://dx.doi.org/10.1002/polb.22286.

[15] Hassan AF, Youssef AM, Priecel P. Removal of deltamethrin insecticide over highly porous activated carbon prepared from pistachio nutshells. Carbon Lett, 14, 234 (2013). http://dx.doi.org/10.5714/CL.2013.14.4.234.

[16] Song YI, Lee JW, Kim TY, Jung HJ, Jung YC, Suh SJ, Yang CM. Performance-determining factors in flexible transparent con-ducting single-wall carbon nanotube film. Carbon Lett, 14, 255 (2013). http://dx.doi.org/10.5714/CL.2013.14.4.255.

[17] Kim SG, Park OK, Lee JH, Ku BC. Layer-by-layer assembled graphene oxide films and barrier properties of thermally reduced graphene oxide membranes. Carbon Lett, 14, 247 (2013). http://dx.doi.org/10.5714/CL.2013.14.4.247.

[18] Choi WK, Kim BJ, Park SJ. Fiber surface and electrical conduc-tivity of electroless Ni-plated PET ultra-fine fibers. Carbon Lett, 14, 243 (2013). http://dx.doi.org/10.5714/CL.2013.14.4.243.

[19] Li B, Zhao Z, Gao F, Wang X, Qiu J. Mesoporous microspheres composed of carbon-coated TiO2 nanocrystals with exposed {0 0 1} facets for improved visible light photocatalytic activity. Appl Catal B, 147, 958 (2014). http://dx.doi.org/10.1016/j.ap-

carbon with a large surface area and pore volume by KOH activation using commercially available activated carbon as a precursor. By modification with PDMS, highly porous activated carbon showed superhydrophobicity with a WCA of 163.6°. The changes in wettability of PDMS- treated highly porous activated carbon were attributed to the deposition of a low-surface-energy silicon coating onto activated carbon, which had microporous characteristics. Using a facile dip-coating method, superhydro-phobic activated carbon-coated sponges were also fabricated. The sponges exhibited excellent absorption selectivity for the removal of a wide range of organics and oils from water, as well as recyclability, thus showing potential as efficient absorbents for the large-scale removal of organic contaminants or oil spills from water.

7. Summary

Carbon is a versatile material due to its porosity, conductiv-ity, thermal conductivity, wide operating potential range, high chemical stability, and reasonable cost. In this review, we have presented different techniques for the preparation of superhy-drophobic carbon-based materials such as CFs, CNFs/CNTs, graphene, amorphous carbons, and porous carbons. These su-perhydrophobic carbon-based materials hold great promise for the development of various industrial products. Overall, there are two traditional methods to control superhydrophobic sur-faces: 1) surface micro-scale roughness; and 2) low surface energy materials treatment. Several technologies that can im-prove surface roughness and decrease surface energy have been developed, including thermal treatment, chemical modification with –(CH2)n–CH3 or (CF2)n –CF3 groups containing materials, CVD method, plasma treatment, an electro-spinning. From a commercial point of view, carbon-based superhydrophobic ma-terials can be applied to smart surfaces with tunable wetting be-havior in different stimuli-responsive environments. They have attracted considerable attention for applications in self-cleaning surfaces, anti-adhesive coatings, biosensors, microfluidics, and many other areas.

Acknowledgements

We acknowledge support by the Ministry of Environment un-der the Eco-Innovation Project and the Carbon Valley Project of the Ministry of Trade, Industry and Energy, Korea.

References

[1] Qiao R, Zhang R, Zhu W, Gong P. Lab simulation of profile mod-ification and enhanced oil recovery with a quaternary ammonium cationic polymer. J Ind Eng Chem, 18, 111 (2012). http://dx.doi.org/10.1016/j.jiec.2011.11.092.

[2] Lafuma A, Quere D. Superhydrophobic states. Nat Mater, 2, 457 (2003). http://dx.doi.org/10.1038/nmat924.

[3] Feng XJ, Jiang L. Design and creation of superwetting/anti-wetting surfaces. Adv Mater, 18, 3063 (2006). http://dx.doi.org/10.1002/adma.200501961.



composites from emulsions. Chem Eng J, 221, 522 (2013). http://dx.doi.org/10.1016/j.cej.2013.01.023.

[34] Yao L, He J. Recent progress in antireflection and self-cleaning technology: from surface engineering to functional surfaces. Prog Mater Sci, 61, 94 (2014). http://dx.doi.org/10.1016/j.pmatsci.2013.12.003.

[35] Zhou Y, Wang B, Song X, Li E, Li G, Zhao S, Yan H. Control over the wettability of amorphous carbon films in a large range from hydrophilicity to super-hydrophobicity. Appl Surf Sci, 253, 2690 (2006). http://dx.doi.org/10.1016/j.apsusc.2006.05.118.

[36] Chen CH, Cai Q, Tsai C, Chen CL, Xiong G, Yu Y, Ren Z. Dropwise condensation on superhydrophobic surfaces with two-tier roughness. Appl Phys Lett, 90, 173108 (2007). http://dx.doi.org/10.1063/1.2731434.

[37] Li Y, Huang XJ, Heo SH, Li CC, Choi YK, Cai WP, Cho SO. Su-perhydrophobic bionic surfaces with hierarchical microsphere/SWCNT composite arrays. Langmuir, 23, 2169 (2006). http://dx.doi.org/10.1021/la0620758.

[38] Wang Z, Lopez C, Hirsa A, Koratkar N. Impact dynamics and rebound of water droplets on superhydrophobic carbon nano-tube arrays. Appl Phys Lett, 91, 023105 (2007). http://dx.doi.org/10.1063/1.2756296.

[39] Zhou XH, Cui GL, Zhi LJ, Zhang SS. Large-area helical carbon microcoils with superhydropho-bicity over a wide range of pH values. New Carbon Mater, 22, 1 (2007).

[40] Hsieh CT, Chen WY, Wu FL. Fabrication and superhydrophobic-ity of fluorinated carbon fabrics with micro/nanoscaled two-tier roughness. Carbon, 46, 1218 (2008). http://dx.doi.org/10.1016/j.carbon.2008.04.026.

[41] Hsieh CT, Wu FL, Yang SY. Superhydrophobicity from com-posite nano/microstructures: carbon fabrics coated with silica nanoparticles. Surf Coat Technol, 202, 6103 (2008). http://dx.doi.org/10.1016/j.surfcoat.2008.07.006.

[42] Li J, Sambandam S, Lu W, Lukehart CM. Carbon nanofi-bers “spot-welded” to carbon felt: a mechanically stable, bulk mimic of lotus leaves. Adv Mater, 20, 420 (2008). http://dx.doi.org/10.1002/adma.200700444.

[43] Luo C, Zuo X, Wang L, Wang E, Song S, Wang J, Wang J, Fan C, Cao Y. Flexible carbon nanotube: polymer composite films with high conductivity and superhydrophobicity made by solution process. Nano Lett, 8, 4454 (2008). http://dx.doi.org/10.1021/nl802411d.

[44] Ma M, Hill RM, Rutledge GC. A review of recent results on superhydrophobic materials based on micro- and nano-fibers. J Adhes Sci Technol, 22, 1799 (2008). http://dx.doi.org/10.1163/156856108X319980.

[45] Srinivasan S, Praveen VK, Philip R, Ajayaghosh A. Bioinspired superhydrophobic coatings of carbon nanotubes and linear π sys-tems based on the “bottom-up” self-assembly approach. An-gew Chem Int Ed, 47, 5750 (2008). http://dx.doi.org/10.1002/anie.200802097.

[46] Wang N, Xi J, Wang S, Liu H, Feng L, Jiang L. Long-term and thermally stable superhydrophobic surfaces of carbon nano-fibers. J Colloid Interface Sci, 320, 365 (2008). http://dx.doi.org/10.1016/j.jcis.2008.01.005.

[47] Xiao X, Cheng YT, Sheldon BW, Rankin J. Condensed water on superhydrophobic carbon films. J Mater Res, 23, 2174 (2008). http://dx.doi.org/10.1557/JMR.2008.0260.

[48] Zou J, Chen H, Chunder A, Yu Y, Huo Q, Zhai L. Preparation

catb.2013.10.027. [20] Jain A, Jayaraman S, Balasubramanian R, Srinivasan MP. Hy-

drothermal pre-treatment for mesoporous carbon synthesis: enhancement of chemical activation. J Mater Chem A, 2, 520 (2014). http://dx.doi.org/10.1039/C3TA12648J.

[21] Wu D, Li Y, Zhang Y, Wang P, Wei Q, Du B. Sensitive electro-chemical sensor for simultaneous determination of dopamine, ascorbic acid, and uric acid enhanced by amino-group functional-ized mesoporous Fe3O4@graphene sheets. Electrochim Acta, 116, 244 (2014). http://dx.doi.org/10.1016/j.electacta.2013.11.033.

[22] Zhu Z, Hu Y, Jiang H, Li C. A three-dimensional ordered meso-porous carbon/carbon nanotubes nanocomposites for super-capacitors. J Power Sources, 246, 402 (2014). http://dx.doi.org/10.1016/j.jpowsour.2013.07.086.

[23] Tao G, Zhang L, Hua Z, Chen Y, Guo L, Zhang J, Shu Z, Gao J, Chen H, Wu W, Liu Z, Shi J. Highly efficient adsorbents based on hierarchically macro/mesoporous carbon monoliths with strong hydrophobicity. Carbon, 66, 547 (2014). http://dx.doi.org/10.1016/j.carbon.2013.09.037.

[24] Liu J, Yang T, Wang DW, Lu GQ, Zhao D, Qiao SZ. A facile soft-template synthesis of mesoporous polymeric and carbona-ceous nanospheres. Nat Commun, 4, 2798 (2013). http://dx.doi.org/10.1038/ncomms3798.

[25] Kim JM, Song IS, Cho D, Hong I. Effect of carbonization tem-perature and chemical pre-treatment on the thermal change and fiber morphology of kenafbased carbon fibers. Carbon Lett, 12, 131 (2011). http://dx.doi.org/10.5714/CL.2011.12.3.131.

[26] Lee S, Kim J, Ku BC, Kim J, Chung Y. Effect of process con-dition on tensile properties of carbon fiber. Carbon Lett, 12, 26 (2011).

[27] Asghar HMA, Hussain SN, Roberts EPL, Campen AK, Brown NW. Pre-treatment of adsorbents for waste water treatment us-ing adsorption coupled-with electrochemical regeneration. J Ind Eng Chem, 19, 1689 (2013). http://dx.doi.org/10.1016/j.jiec.2013.02.007.

[28] Han M, Yun J, Kim HI, Lee YS. Effect of surface modification of graphene oxide on photochemical stability of poly(vinyl al-cohol)/graphene oxide composites. J Ind Eng Chem, 18, 752 (2012). http://dx.doi.org/10.1016/j.jiec.2011.11.122.

[29] Cho D, Yoon SB, Cho CW, Park JK. Effect of additional heat-treatment temperature on chemical, microstructural, mechani-cal, and electrical properties of commercial PAN-based carbon fibers. Carbon Lett, 12, 223 (2011). http://dx.doi.org/10.5714/CL.2011.12.4.223.

[30] Chen Z, Dong L, Yang D, Lu H. Superhydrophobic graphene-based materials: surface construction and functional applica-tions. Adv Mater, 25, 5352 (2013). http://dx.doi.org/10.1002/adma.201302804.

[31] Nguyen DD, Tai NH, Lee SB, Kuo WS. Superhydrophobic and superoleophilic properties of graphene-based sponges fabricated using a facile dip coating method. Energy Environ Sci, 5, 7908 (2012). http://dx.doi.org/10.1039/C2EE21848H.

[32] Zheng L, Li Z, Bourdo S, Khedir KR, Asar MP, Ryerson CC, Biris AS. Exceptional superhydrophobicity and low velocity impact icephobicity of acetone-functionalized carbon nanotube films. Langmuir, 27, 9936 (2011). http://dx.doi.org/10.1021/la201548k.

[33] Bayer IS, Steele A, Loth E. Superhydrophobic and electrocon-ductive carbon nanotube-fluorinated acrylic copolymer nano-



[62] Lee SY, Park SJ. TiO2 photocatalyst for water treatment ap-plications. J Ind Eng Chem, 19, 1761 (2013). http://dx.doi.org/10.1016/j.jiec.2013.07.012.

[63] Lee SY, Yop Rhee K, Nahm SH, Park SJ. Effect of p-type multi-walled carbon nanotubes for improving hydrogen storage be-haviors. J Solid State Chem, 210, 256 (2014). http://dx.doi.org/10.1016/j.jssc.2013.11.026.

[64] Mao C, Liang C, Luo W, Bao J, Shen J, Hou X, Zhao W. Prepara-tion of lotus-leaf-like polystyrene micro- and nanostructure films and its blood compatibility. J Mater Chem, 19, 9025 (2009). http://dx.doi.org/10.1039/B912314H.

[65] Barthlott W, Neinhuis C. Purity of the sacred lotus, or escape from contamination in biological surfaces. Planta, 202, 1 (1997). http://dx.doi.org/10.1007/s004250050096.

[66] Neinhuis C, Barthlott W. Characterization and distribution of water-repellent, self-cleaning plant surfaces. Ann Bot, 79, 667 (1997). http://dx.doi.org/10.1006/anbo.1997.0400.

[67] Feng L, Li S, Li Y, Li H, Zhang L, Zhai J, Song Y, Liu B, Ji-ang L, Zhu D. Super-hydrophobic surfaces: from natural to ar-tificial. Adv Mater, 14, 1857 (2002). http://dx.doi.org/10.1002/adma.200290020.

[68] Jin M, Feng X, Feng L, Sun T, Zhai J, Li T, Jiang L. Superhy-drophobic aligned polystyrene nanotube films with high adhesive force. Adv Mater, 17, 1977 (2005). http://dx.doi.org/10.1002/adma.200401726.

[69] Wenzel RN. Resistance of solid surfaces to wetting by wa-ter. Ind Eng Chem, 28, 988 (1936). http://dx.doi.org/10.1021/ie50320a024.

[70] Cassie ABD, Baxter S. Wettability of porous surfaces. Trans Faraday Soc, 40, 546 (1944). http://dx.doi.org/10.1039/TF9444000546.

[71] Wang J, Chen H, Sui T, Li A, Chen D. Investigation on hydro-phobicity of lotus leaf: experiment and theory. Plant Sci, 176, 687 (2009). http://dx.doi.org/10.1016/j.plantsci.2009.02.013.

[72] Yu Y, Zhao ZH, Zheng QS. Mechanical and superhydrophobic stabilities of two-scale surfacial structure of lotus leaves. Lang-muir, 23, 8212 (2007). http://dx.doi.org/10.1021/la7003485.

[73] Robinson A. The Last Man Who Knew Everything: Thomas Young, the Anonymous Polymath Who Proved Newton Wrong, Explained How We See, Cured the Sick, and Deciphered the Ro-setta Stone, Among Other Feats of Genius, Pi Press, New York, NY (2006).

[74] Lee MW, An S, Latthe SS, Lee C, Hong S, Yoon SS. Electros-pun polystyrene nanofiber membrane with superhydrophobicity and superoleophilicity for selective separation of water and low viscous oil. ACS Appl Mater Interfaces, 5, 10597 (2013). http://dx.doi.org/10.1021/am404156k.

[75] Chang CH, Hsu MH, Weng CJ, Hung WI, Chuang TL, Chang KC, Peng CW, Yen YC, Yeh JM. 3D-bioprinting approach to fab-ricate superhydrophobic epoxy/organophilic clay as an advanced anticorrosive coating with the synergistic effect of superhydro-phobicity and gas barrier properties. J Mater Chem A, 1, 13869 (2013). http://dx.doi.org/10.1039/C3TA12754K.

[76] Gupta N, Kavya MV, Singh YRG, Jyothi J, Barshilia HC. Su-perhydrophobicity on transparent fluorinated ethylene propylene films with nano-protrusion morphology by Ar + O2 plasma etch-ing: study of the degradation in hydrophobicity after exposure to the environment. J Appl Phys, 114, 164307 (2013). http://dx.doi.org/10.1063/1.4826897.

[77] Yu E, Lee HJ, Ko TJ, Kim SJ, Lee KR, Oh KH, Moon MW. Hi-

of a superhydrophobic and conductive nanocomposite coating from a carbon-nanotube-conjugated block copolymer disper-sion. Adv Mater, 20, 3337 (2008). http://dx.doi.org/10.1002/adma.200703094.

[49] Bai BC, Cho S, Yu HR, Yi KB, Kim KD, Lee YS. Effects of ami-nated carbon molecular sieves on breakthrough curve behavior in CO2/CH4 separation. J Ind Eng Chem, 19, 776 (2013). http://dx.doi.org/10.1016/j.jiec.2012.10.016.

[50] Ghaedi M, Montazerozohori M, Sajedi M, Roosta M, Nickoosiar Jahromi M, Asghari A. Comparison of novel sorbents for precon-centration of metal ions prior to their flame atomic absorption spectrometry determination. J Ind Eng Chem, 19, 1781 (2013). http://dx.doi.org/10.1016/j.jiec.2013.02.020.

[51] Ghaedi M, Montazerozohori M, Rahimi N, Biysreh MN. Chemi-cally modified carbon nanotubes as efficient and selective sor-bent for enrichment of trace amount of some metal ions. J Ind Eng Chem, 19, 1477 (2013). http://dx.doi.org/10.1016/j.jiec.2013.01.011.

[52] Charinpanitkul T, Suthabanditpong W, Watanabe H, Shirai T, Faungnawakij K, Viriya-empikul N, Fuji M. Improved hydrophi-licity of zinc oxide-incorporated layer-by-layer polyelectrolyte film fabricated by dip coating method. J Ind Eng Chem, 18, 1441 (2012). http://dx.doi.org/10.1016/j.jiec.2012.02.003.

[53] Bai BC, Kim JG, Im JS, Jung SC, Lee YS. Influence of oxy-fluorination on activated carbon nanofibers for CO2 stor-age. Carbon Lett, 12, 236 (2011). http://dx.doi.org/10.5714/CL.2011.12.4.236.

[54] Park SJ, Lee HY. Effect of atmospheric-pressure plasma on ad-hesion characteristics of polyimide film. J Colloid Interface Sci, 285, 267 (2005). http://dx.doi.org/10.1016/j.jcis.2004.11.062.

[55] Chauhan NPS. Structural and thermal characterization of macro-branched functional terpolymer containing 8-hydroxyquinoline moieties with enhancing biocidal properties. J Ind Eng Chem, 19, 1014 (2013). http://dx.doi.org/10.1016/j.jiec.2012.11.025.

[56] Heo GY, Yoo YJ, Park SJ. Effect of carbonization temperature on electrical conductivity of carbon papers prepared from petro-leum pitch-coated glass fibers. J Ind Eng Chem, 19, 1040 (2013). http://dx.doi.org/10.1016/j.jiec.2012.11.028.

[57] Lee JH, Kim IJ, Park SJ. Preparation and electrochemical be-haviors of styrene–acrylonitrile-based porous carbon electrodes. Electrochim Acta, 113, 23 (2013). http://dx.doi.org/10.1016/j.electacta.2013.09.006.

[58] Jin FL, Ma CJ, Park SJ. Thermal and mechanical interfacial properties of epoxy composites based on functionalized carbon nanotubes. Mater Sci Eng A, 528, 8517 (2011). http://dx.doi.org/10.1016/j.msea.2011.08.054.

[59] Bikshapathi M, Verma N, Singh RK, Joshi HC, Srivastava A. Preparation of activated carbon fibers from cost effective com-mercial textile grade acrylic fibers. Carbon Lett, 12, 44 (2011). http://dx.doi.org/10.5714/CL.2011.12.1.044.

[60] Abdullah ID, Girgis BS, Tmerek YM, Badawy EH. Potential of activated carbon derived from local common reed in the refining of raw cane sugar. Carbon Lett, 11, 192 (2011).

[61] Kaneko K, Arai M, Yamamoto M, Ohba T, Miyamoto JI, Kim DY, Tao Y, Yang CM, Urita K, Fujimori T, Tanaka H, Ohkubo T, Utsumi S, Hattori Y, Konishi T, Fujikawa T, Kanoh H, Yudasaka M, Hata K, Yumura M, Iijima S, Muramatsu H, Hayashi T, Kim YA, Endo M. Fundamental understanding of nanoporous carbons for energy application potentials. Carbon Lett, 10, 177 (2009).



Determination of the contribution to surface and interfacial ten-sions of dispersion forces in various liquids. J Phys Chem, 67, 2538 (1963). http://dx.doi.org/10.1021/j100806a008.

[95] Park SJ, Cho MS, Lee JR. Studies on the surface free energy of carbon-carbon composites: effect of filler addition on the ILSS of composites. J Colloid Interface Sci, 226, 60 (2000). http://dx.doi.org/10.1006/jcis.2000.6787.

[96] Mironov VS, Kim SY, Park M. Electrical properties of polyeth-ylene composite films filled with nickel powder and short car-bon fiber hybrid filler. Carbon Lett, 14, 105 (2013). http://dx.doi.org/10.5714/CL.2013.14.2.105.

[97] Zhu J, Park SW, Joh HI, Kim HC, Lee S. Preparation and charac-terization of isotropic pitch-based carbon fiber. Carbon Lett, 14, 94 (2013). http://dx.doi.org/10.5714/CL.2013.14.2.094.

[98] Jin FL, Lee SY, Park SJ. Polymer matrices for carbon fiber-rein-forced polymer composites. Carbon Lett, 14, 76 (2013). http://dx.doi.org/10.5714/CL.2013.14.2.076.

[99] Choi KE, Seo MK. A study on the preparation of the eco-friendly carbon fibers-reinforced composites. Carbon Lett, 14, 58 (2013). http://dx.doi.org/10.5714/CL.2013.14.1.058.

[100] Bliznakov S, Liu Y, Dimitrov N, Garnica J, Sedev R. Double-scale roughness and superhydrophobicity on metalized toray carbon fiber paper. Langmuir, 25, 4760 (2009). http://dx.doi.org/10.1021/la803932k.

[101] Park KM, Lee BS, Youk JH, Lee J, Yu WR. Moisture condensa-tion behavior of hierarchically carbon nanotube-grafted carbon nanofibers. ACS Appl Mater Interfaces, 5, 11115 (2013). http://dx.doi.org/10.1021/am403348q.

[102] Meng LY, Park SJ. Effect of growth of graphite nanofibers on su-perhydrophobic and electrochemical properties of carbon fibers. Mater Chem Phys, 132, 324 (2012). http://dx.doi.org/10.1016/j.matchemphys.2011.11.024.

[103] Meng LY, Moon CW, Im SS, Lee KH, Byun JH, Park SJ. Effect of Ni catalyst dispersion on the growth of carbon nanofibers onto carbon fibers. Microporous Mesoporous Mater, 142, 26 (2011). http://dx.doi.org/10.1016/j.micromeso.2010.10.008.

[104] Meng LY, Park SJ. Effect of growth of carbon nanofibers on the electrical conductivity of carbon fibers. Macromol Res, 19, 209 (2011). http://dx.doi.org/10.1007/s13233-011-0209-1.

[105] Meng LY, Park SJ. Influence of carbon nanofibers on electro-chemical properties of carbon nanofibers/glass fibers compos-ites. Curr Appl Phys, 13, 640 (2013). http://dx.doi.org/10.1016/j.cap.2012.10.008.

[106] Wang P, Zhang D, Qiu R, Wu J, Wan Y. Super-hydrophobic film prepared on zinc and its effect on corrosion in simulated marine atmosphere. Corros Sci, 69, 23 (2013). http://dx.doi.org/10.1016/j.corsci.2012.10.025.

[107] Jung MJ, Kim JW, Im JS, Park SJ, Lee YS. Nitrogen and hydro-gen adsorption of activated carbon fibers modified by fluorina-tion. J Ind Eng Chem, 15, 410 (2009). http://dx.doi.org/10.1016/j.jiec.2008.11.001.

[108] Kim S, Kuk Y-S, Chung YS, Jin FL, Park SJ. Preparation and characterization of polyacrylonitrile-based carbon fiber papers. J Ind Eng Chem, 2014 in press. http://dx.doi.org/10.1016/j.jiec.2013.12.032.

[109] Hsieh CT, Chen JM, Huang YH, Kuo RR, Li CT, Shih HC, Lin TS, Wu CF. Influence of fluorine/carbon atomic ratio on superhy-drophobic behavior of carbon nanofiber arrays. J Vac Sci Technol B, 24, 113 (2006). http://dx.doi.org/10.1116/1.2150224.

erarchical structures of AlOOH nanoflakes nested on Si nanopil-lars with anti-reflectance and superhydrophobicity. Nanoscale, 5, 10014 (2013). http://dx.doi.org/10.1039/C3NR02395H.

[78] Wu J, Li J, Deng B, Jiang H, Wang Z, Yu M, Li L, Xing C, Li Y. Self-healing of the superhydrophobicity by ironing for the abra-sion durable superhydrophobic cotton fabrics. Sci Rep, 3, 2951 (2013). http://dx.doi.org/10.1038/srep02951.

[79] Cao L, Liu J, Xu S, Xia Y, Huang W, Li Z. Inherent superhydro-phobicity of Sn/SnOx films prepared by surface self-passivation of electrodeposited porous dendritic Sn. Mater Res Bull, 48, 4804 (2013). http://dx.doi.org/10.1016/j.materresbull.2013.08.044.

[80] Timonen JV, Latikka M, Ikkala O, Ras RH. Free-decay and resonant methods for investigating the fundamental limit of su-perhydrophobicity. Nat Commun, 4, 2398 (2013). http://dx.doi.org/10.1038/ncomms3398.

[81] Meng LY, Rhee KY, Park SJ. Enhancement of superhydropho-bicity and conductivity of carbon nanofibers-coated glass fab-rics. J Ind Eng Chem, 2014 in press. http://dx.doi.org/10.1016/j.jiec.2013.08.015.

[82] Wang S, Song Y, Jiang L. Photoresponsive surfaces with control-lable wettability. J Photochem Photobiol C, 8, 18 (2007). http://dx.doi.org/10.1016/j.jphotochemrev.2007.03.001.

[83] Barthlott W, Schimmel T, Wiersch S, Koch K, Brede M, Barc-zewski M, Walheim S, Weis A, Kaltenmaier A, Leder A, Bohn HF. The Salvinia paradox: superhydrophobic surfaces with hy-drophilic pins for air retention under water. Adv Mater, 22, 2325 (2010). http://dx.doi.org/10.1002/adma.200904411.

[84] Cui XS, Li W. On the possibility of superhydrophobic behav-ior for hydrophilic materials. J Colloid Interface Sci, 347, 156 (2010). http://dx.doi.org/10.1016/j.jcis.2010.03.065.

[85] Marmur A. From hygrophilic to superhygrophobic: theoretical conditions for making high-contact-angle surfaces from low-con-tact-angle materials. Langmuir, 24, 7573 (2008). http://dx.doi.org/10.1021/la800304r.

[86] Liu JL, Feng XQ, Wang G, Yu SW. Mechanisms of superhydro-phobicity on hydrophilic substrates. J Phys: Condens Matter, 19, 356002 (2007). http://dx.doi.org/10.1088/0953-8984/19/35/356002.

[87] Herminghaus S. Roughness-induced non-wetting. Europhys Lett, 52, 165 (2000). http://dx.doi.org/10.1209/epl/i2000-00418-8.

[88] Zhang X, Shi F, Niu J, Jiang Y, Wang Z. Superhydrophobic sur-faces: from structural control to functional application. J Mater Chem, 18, 621 (2008). http://dx.doi.org/10.1039/B711226B.

[89] Wang FJ, Li CQ, Tan ZS, Li W, Ou JF, Xue MS. PVDF sur-faces with stable superhydrophobicity. Surf Coat Technol, 222, 55 (2013). http://dx.doi.org/10.1016/j.surfcoat.2013.02.004.

[90] Liu H, Zhai J, Jiang L. Wetting and anti-wetting on aligned car-bon nanotube films. Soft Matter, 2, 811 (2006). http://dx.doi.org/10.1039/B606654B.

[91] Park SJ, Brendle M. London dispersive component of the surface free energy and surface enthalpy. J Colloid Interface Sci, 188, 336 (1997). http://dx.doi.org/10.1006/jcis.1997.4763.

[92] Park SJ, Seo MK. Solid-liquid interface. Interface Sci Technol, 18, 147 (2011). http://dx.doi.org/10.1016/B978-0-12-375049-5.00003-7.

[93] Fowkes FM. Determination of interfacial tensions, contact an-gles, and dispersion forces in surfaces by assuming additivity of intermolecular interactions in surfaces. J Phys Chem, 66, 382 (1962). http://dx.doi.org/10.1021/j100808a524.

[94] Fowkes FM. Additivity of intermolecular forces at interfaces. I.



loid Interface Sci, 342, 559 (2010). http://dx.doi.org/10.1016/j.jcis.2009.10.022.

[126] Han JT, Kim SY, Woo JS, Lee GW. Transparent, conductive, and superhydrophobic films from stabilized carbon nanotube/silane sol mixture solution. Adv Mater, 20, 3724 (2008). http://dx.doi.org/10.1002/adma.200800239.

[127] Meng LY, Park SJ. Improvement of superhydrophobicity of multi-walled CNTs produced by fluorination. Carbon Lett, 13, 178 (2012). http://dx.doi.org/10.5714/CL.2012.13.3.178.

[128] Tang Y, Gou J, Hu Y. Covalent functionalization of carbon nano-tubes with polyhedral oligomeric silsequioxane for superhydro-phobicity and flame retardancy. Polym Eng Sci, 53, 1021 (2013). http://dx.doi.org/10.1002/pen.23338.

[129] Lee GH, Cooper RC, An SJ, Lee S, van der Zande A, Petrone N, Hammerberg AG, Lee C, Crawford B, Oliver W, Kysar JW, Hone J. High-strength chemical-vapor-deposited graphene and grain boundaries. Science, 340, 1073 (2013). http://dx.doi.org/10.1126/science.1235126.

[130] Ramos SC, Vasconcelos G, Antunes EF, Lobo AO, Trava-Airoldi VJ, Corat EJ. Total re-establishment of superhydrophobicity of vertically-aligned carbon nanotubes by Co2 laser treatment. Surf Coat Technol, 204, 3073 (2010). http://dx.doi.org/10.1016/j.surf-coat.2010.02.065.

[131] Rafiee J, Rafiee MA, Yu ZZ, Koratkar N. Superhydrophobic to superhydrophilic wetting control in graphene films. Adv Mater, 22, 2151 (2010). http://dx.doi.org/10.1002/adma.200903696.

[132] Jin J, Wang X, Song M. Graphene-based nanostructured hybrid materials for conductive and superhydrophobic functional coat-ings. J Nanosci Nanotechnol, 11, 7715 (2011). http://dx.doi.org/10.1166/jnn.2011.4730.

[133] Lin Y, Ehlert GJ, Bukowsky C, Sodano HA. Superhydrophobic functionalized graphene aerogels. ACS Appl Mater Interfaces, 3, 2200 (2011). http://dx.doi.org/10.1021/am200527j.

[134] Wang S, Yang Y, Zhang Y, Fei X, Zhou C, Zhang Y, Li Y, Yang Q, Song Y. Fabrication of large-scale superhydrophobic composite films with enhanced tensile properties by multinozzle conveyor belt electrospinning. J Appl Polym Sci, 131, 39735 (2014). http://dx.doi.org/10.1002/app.39735.

[135] Zha DA, Mei S, Wang Z, Li H, Shi Z, Jin Z. Superhydrophobic polyvinylidene fluoride/graphene porous materials. Carbon, 49, 5166 (2011). http://dx.doi.org/10.1016/j.carbon.2011.07.032.

[136] Zhang L, Zha DA, Du T, Mei S, Shi Z, Jin Z. Formation of super-hydrophobic microspheres of poly(vinylidene fluoride-hexaflu-oropropylene)/graphene composite via gelation. Langmuir, 27, 8943 (2011). http://dx.doi.org/10.1021/la200982n.

[137] Choi BG, Park HS. Superhydrophobic graphene/nafion nanohy-brid films with hierarchical roughness. J Phys Chem C, 116, 3207 (2012). http://dx.doi.org/10.1021/jp207818b.

[138] Wang JN, Shao RQ, Zhang YL, Guo L, Jiang HB, Lu DX, Sun HB. Biomimetic graphene surfaces with superhydrophobic-ity and iridescence. Chemistry, 7, 301 (2012). http://dx.doi.org/10.1002/asia.201100882.

[139] Fan ZL, Qin XJ, Sun HX, Zhu ZQ, Pei CJ, Liang WD, Bao XM, An J, La PQ, Li A, Deng WQ. Superhydrophobic mesoporous graphene for separation and absorption. ChemPlusChem, 78, 1282 (2013). http://dx.doi.org/10.1002/cplu.201300119.

[140] Li X, Li L, Wang Y, Li H, Bian X. Wetting and interfacial prop-erties of water on the defective graphene. J Phys Chem C, 117, 14106 (2013). http://dx.doi.org/10.1021/jp4045258.

[110] Lu P, Huang Q, Mukherjee A, Hsieh YL. SiCO-doped carbon fi-bers with unique dual superhydrophilicity/superoleophilicity and ductile and capacitance properties. ACS Appl Mater Interfaces, 2, 3738 (2010). http://dx.doi.org/10.1021/am100918x.

[111] Seo H, Kim KD, Jeong MG, Kim Y, Choi K, Hong E, Lee K, Lim D. Superhydrophobic carbon fiber surfaces prepared by growth of carbon nanostructures and polydimethylsiloxane coat-ing. Macromol Res, 20, 216 (2012). http://dx.doi.org/10.1007/s13233-012-0029-y.

[112] Qiu R, Zhang D, Wang P. Superhydrophobic-carbon fibre growth on a zinc surface for corrosion inhibition. Corros Sci, 66, 350 (2013). http://dx.doi.org/10.1016/j.corsci.2012.09.041.

[113] Kim KS, Park SJ. Influence of carbon shell structure on elec-trochemical performance of multi-walled carbon nanotube electrodes. Anal Chim Acta, 788, 17 (2013). http://dx.doi.org/ 10.1016/j.aca.2013.05.047.

[114] Kim KS, Park SJ. Influence of amine-grafted multi-walled car-bon nanotubes on physical and rheological properties of PMMA-based nanocomposites. J Solid State Chem, 184, 3021 (2011). http://dx.doi.org/10.1016/j.jssc.2011.09.012.

[115] Choi YC. Micro-Raman characterization of isolated single wall carbon nanotubes synthesized using Xylene. Carbon Lett, 14, 175 (2013). http://dx.doi.org/10.5714/CL.2013.14.3.175.

[116] Ibrahim KS. Carbon nanotubes: properties and applications: a review. Carbon Lett, 14, 131 (2013). http://dx.doi.org/10.5714/CL.2013.14.3.131.

[117] Zhu L, Xiu Y, Xu J, Tamirisa PA, Hess DW, Wong CP. Superhy-drophobicity on two-tier rough surfaces fabricated by controlled growth of aligned carbon nanotube arrays coated with fluoro-carbon. Langmuir, 21, 11208 (2005). http://dx.doi.org/10.1021/la051410+.

[118] Hong YC, Uhm HS. Superhydrophobicity of a material made from multiwalled carbon nanotubes. Appl Phys Lett, 88, 244101 (2006). http://dx.doi.org/10.1063/1.2210449.

[119] Jung YC, Bhushan B. Mechanically durable carbon nanotube: composite hierarchical structures with superhydrophobicity, self-cleaning, and low-drag. ACS Nano, 3, 4155 (2009). http://dx.doi.org/10.1021/nn901509r.

[120] Ramos SC, Vasconcelos G, Antunes EF, Lobo AO, Trava-Airoldi VJ, Corat EJ. CO2 laser treatment for stabilization of the superhy-drophobicity of carbon nanotube surfaces. J Vac Sci Technol B, 28, 1153 (2010). http://dx.doi.org/10.1116/1.3502024.

[121] Yang J, Zhang Z, Men X, Xu X, Zhu X. Reversible superhydro-phobicity to superhydrophilicity switching of a carbon nanotube film via alternation of UV irradiation and dark storage. Langmuir, 26, 10198 (2010). http://dx.doi.org/10.1021/la100355n.

[122] Sun W, Zhou S, You B, Wu L. Polymer brush-functionalized surfaces with unique reversible double-stimulus responsive wettability. J Mater Chem A, 1, 10646 (2013). http://dx.doi.org/10.1039/C3TA12367G.

[123] Cabane E, Zhang X, Langowska K, Palivan C, Meier W. Stim-uli-responsive polymers and their applications in nanomedicine. Biointerphases, 7, 1 (2012). http://dx.doi.org/10.1007/s13758-011-0009-3.

[124] Kulinich SA, Farzaneh M. How wetting hysteresis influences ice adhesion strength on superhydrophobic surfaces. Langmuir, 25, 8854 (2009). http://dx.doi.org/10.1021/la901439c.

[125] Meng LY, Park SJ. Effect of fluorination of carbon nanotubes on superhydrophobic properties of fluoro-based films. J Col-



copper. Appl Mech Mater, 365-366, 1100 (2013). http://dx.doi.org/10.4028/www.scientific.net/AMM.365-366.1100.

[145] Li X, Feng F, Zhang K, Ye S, Kwok DY, Birss V. Wettability of Nafion and Nafion/Vulcan carbon composite films. Langmuir, 28, 6698 (2012). http://dx.doi.org/10.1021/la300388x.

[146] Banerjee D, Das NS, Chattopadhyay KK. Enhancement of field emission and hydrophobic properties of silicon nanow-ires by chemical vapor deposited carbon nanoflakes coating. Appl Surf Sci, 261, 223 (2012). http://dx.doi.org/10.1016/j.ap-susc.2012.07.148.

[147] Sun H, Li A, Zhu Z, Liang W, Zhao X, La P, Deng W. Super-hydrophobic activated carbon-coated sponges for separation and absorption. ChemSusChem, 6, 1057 (2013). http://dx.doi.org/10.1002/cssc.201200979.

[141] Shanmugharaj AM, Yoon JH, Yang WJ, Ryu SH. Synthesis, characterization, and surface wettability properties of amine functionalized graphene oxide films with varying amine chain lengths. J Colloid Interface Sci, 401, 148 (2013). http://dx.doi.org/10.1016/j.jcis.2013.02.054.

[142] Shateri-Khalilabad M, Yazdanshenas M. Preparation of superhy-drophobic electroconductive graphene-coated cotton cellulose. Cellulose, 20, 963 (2013). http://dx.doi.org/10.1007/s10570-013-9873-y.

[143] Singh E, Chen Z, Houshmand F, Ren W, Peles Y, Cheng HM, Koratkar N. Superhydrophobic graphene foams. Small, 9, 75 (2013). http://dx.doi.org/10.1002/smll.201201176.

[144] Wang P, Zhang D. Super-hydrophobic film prepared with re-duced graphene sheets and its application as corrosion barrier to

superhydrophobic carbon-based materials: a review of ...089-104]-02.pdf · 89 superhydrophobic...

Documents