List of recent publications on various methods for creating anti-wetting surfaces
The investigations of superhydrophobicity and self-cleaning surfaces have been given a lot of attention in the last few decades. The surfaces having water contact angle larger than 90° are termed as hydrophobic surfaces and those which exhibit contact angle higher than 150° are said to be superhydrophobic. Such surfaces were first observed in nature in various plants and animals, for example, lotus leaf-like structures. Water repellence of various materials have shown great influences on various applications such as self-cleaning, anti-ageing, water-oil separation, water corrosion in electrical industry, water proof textiles, controlled transportation of fluids, etc. Generally, surface micro/nanostructuring combined with low surface energy of materials leads to extreme anti-wetting properties. The hundreds of research articles and more than 450 patents on the subject of nature mimicking self-cleaning surfaces prove the potential of this topic.
- natural mimics
- hierarchical structure
Wetting properties of various solid surfaces with various polar and non-polar solvents are getting attention in recent decades because of the increased demand for them in various fields of applications. Superhydrophilicity and superhydrophobicity are two important terms used to explain the wetting behaviour of solid surfaces. Any surface which allows the spreading of a water droplet to provide a contact angle value below 5° is called superhydrophilic surface, whereas the criteria for the surface to be superhydrophobic is to get the water contact angle to a value above 150° . On the other hand, observed values of static contact angle measurements depend on the used fitting mode . For a proper comparison, one should repeatedly use the same volume of water droplet since the volume can also affect the measurement results. In addition, contact angle hysteresis needs to be taken into consideration because hydrophobic surfaces are widely used for self-cleaning applications. Contact angle hysteresis is defined as the difference between the advancing and receding contact angles. The lower the value, the easier the drop will roll off from the surface.
The idea of hydrophobic surfaces came from nature itself —observing the self-cleaning ability of plant leaves and animal wings to roll off water droplet from the surface, termed as lotus effect. The naturally occurring hydrophobic surfaces achieve the high contact angle values because of the rough surfaces coated with the low surface energy wax, which has high repelling interactions with the polar solvents including water . Many such surfaces have a coating composed of particles with size ranging from 20-40 µm, with or without hierarchical structures to provide additional surface area . To explain the stability of the water drop on the surfaces there are two major theories put forward in which the water exists in either Wenzel or Cassie state. In Wenzel model, the water drop fit inside the grooves of the rough surface [Figure 1A] and is described by equation 1,
There are some reports which questions the co-existence of both Wenzel and Cassie states. However, these two models are well accepted to explain the existence of solvent on a solid surface .
2. Methods for generating superhydrophobic surfaces
The water repelling ability of various materials have shown great influence on various applications such as self-cleaning, anti-ageing, water-oil separation, water corrosion in electrical industry, water proof textiles, controlled transportation of fluids, etc. [2, 4, 8, 9]. Generally, surface micro/nanostructuring combined with low surface energy of materials leads to extreme anti-wetting properties. Hundreds of research articles and more than 450 patents on the subject of nature mimicking self-cleaning surfaces show the potential of this topic. For the fabrication of superhydrophobic surfaces, various physical and chemical methods have been used. Methods such as templating, plasma surface modifications, physical and chemical deposition, layer by layer deposition, electrospinning, hydrothermal process and sol-gel processing have been used for achieving desired roughness and surface chemistry on various substrates. The texturing and coating are explained in short in the following text on the basis of very recent articles in terms of application point of view to give the reader a general idea of the field.
Templating method refers to the copying of a rough surface with superhydrophobic properties. With this technique, a suitable 2D or 3D surface pattern is filled with certain soft material as the first step, then the material is hardened and the template removed by a suitable method keeping the replica intact . The main advantage of this method is that it is very easy to copy water repelling natural surfaces in a large-scale level. This method is comparatively cheap and very suitable for patterning soft materials such as polymers where, in most of the cases, the template can be recycled . Feng et al. created fine superhydrophobic nano fibre structures of poly vinyl alcohol (PVA) with aluminium oxide membrane as a template . When the PVA precursors were extruded in solution through the nano porous template membrane, the polymer molecules underwent an alignment with the hydrophobic methylene groups pointing towards the external environment. A number of factors, including intermolecular hydrogen bonding, made it possible to attain a superhydrophobic surface of an amphilic material. Superhydrophobic polymer materials, especially those that have large surface area, are interesting for large-scale applications for separating hydrocarbon solvents from water, oil from water sources, etc. . By applying a suitable soft material we can directly replicate the topography of various naturally occupying superhydrophobic surfaces. For example,
On the other hand, heat and pressure-driven nanostructuring on the polystyrene substrate with alumina template gave raise to specifically aligned nanoemboss, nanopost array with embossed base and aligned polymer nanofibres. Such nanofibres with small aspect ratio resembled the wings of
However, the template removing step — especially for delicate materials including polymers — can be really challenging since it is associated with high temperature processes or strong chemical etch [15, 16]. Exposure to non-friendly chemicals or to very high temperature can easily disorder the mesostructures or make unfavourable chemical changes to the polymer chains. To avoid these complications, use of easily removable templates is preferred. The new developments in the field focus on templates which undergo chemical changes and completely disappear or are naturally removed from the replica into the reaction medium. For instance, various metal oxide templates are utilized as a catalyst for the polymerisation process, where the metal undergoes change in oxidation state with the progress of reaction and completely converts into a water soluble form [17, 18]. These by-products are easily washed away. In some other cases, the template is formed in situ as a complex which decomposes with the ion consumption during the progress of the reaction . Template-assisted micro and nanostructuring is also used for fabrication of superhydrophobic inorganic materials [20, 21]. Introducing thermal annealing as another step into the assisted sol-gel process resulted in much higher water contact angle of the 2D hierarchical structure replica due to heat deformation of the template, prior to the process . Using inexpensive template methods, both doubly and triply scaled hydrophobic metal oxide as well as metal interfaces could be generated . In contrast, embedding of desired material into the template can be achieved also by non-wetting methods. In a recent study, Ganesh et al. used sputtering at glancing angle to directly deposit a metal into the aluminium template pores . This method has significant control over the morphology and distribution for the generation of nanorods of aluminium and tungsten through the template and the length of the wires depend solely on the deposition time.
The process of electrospinning makes the practical use of electrostatic force to generate continuous and fine filaments from melt, sol-gel or solutions of various polymeric materials. The schematic of the process is shown in Figure 3. The main advantage of electrospinning is that it allows the addition of suitable fillers, including clay or other inorganic particles, directly into the solution to get a composite filament, while the diameter can be kept at around 10 nm . Moreover, electrospinning is a low cost process and can be easily scaled up for industrial production. The surface energy and topological characteristics can be controlled by choosing the right material and suitable process parameters . The material which is released from the needle tip gets deposited directly on the collector and there is no material loss during the production. Electrospinning forms nanofibres, which provide a high degree of roughness on the surface. In addition to roughness, surface tension can also be tailored by choosing the appropriate material or adding sufficient amount of additives in to the spinning solution. Appropriate combination of both effects gives superhydrophobic surface.
Electrospinning technique has been utilized to generate natural mimic surfaces. Lei
In addition to this, various advanced techniques such as coaxial electrospinning, electrospinning with a rotating disk, needleless electrospinning, etc. are used for improving the properties of electrospun fibres . For instance, recently designed multi-nozzle electrospinning set up has an advantage to create micro sized beads from one nozzle where the other one creates fibre-like structures. The membrane maintains mechanical integrity and superhydrophobicity . For further improvement in the hydrophobic character of electrospun fibres, different surface modifications are also found effective. But with many of the low energy polymeric materials, hydrophobicity can be achieved without any secondary modifications [24, 32].
Electrospinning technology is even used for fabrication of superhydrophobic inorganic surfaces. Such inorganic nanomaterials could be used in various fields including optoelectronics and sensing devices . In most of the cases, precursor is created in the form of thin nanofibres of the desired oxide and hydrophobised with suitable post treatments . But in certain cases, metal particles that are inserted into low energy polymers are directly used for the required applications including acid corrosion resistance .
2.3. Hydrothermal synthesis
Many inorganic oxides are highly insoluble in water under room temperature. The insolubility may be overcome by use of hydrothermal process which is employed with increased temperature and even pressure in certain cases. This method is very efficient in the preparation of compounds of elements in oxidation states that are difficult to obtain otherwise, synthesis of meta-stable states and varieties of crystals in high quality and good control over size and morphology . Although it is widely used even in material synthesis, very high production cost and difficulty to monitor the crystal growth during the course of the process are some disadvantages.
Hydrothermal synthesis can provide hierarchical structures which can provide both hydrophilic and hydrophobic behaviour after suitable modifications. The control over the morphology is governed by the reaction time and temperature . Generation of highly rough flake, flower-like or rod structures of metallic substrates are sufficient to provide enough roughness for constructing superhydrophobicity . But as in the case of sol-gel synthesis, suitable surface modification is needed. Various polymeric supports, such as polyethylene glycol, are typically used for the improvement of topological properties. These supports, when adsorbed on the metal substrates, inhibit the crystal growth on certain spots and provide micro/nanoroughness to the material . Hydrothermal process with only ultra-pure water as the reaction medium is a green technique and efficient in the production of complex biomimics with rough textures directly on metal surfaces. With additional hydrophobisation with suitable methods, hydrothermal process has been proven to be a great manner to protect various metals from corrosion [40, 41]. Very recent reports showed some interesting hierarchical mixed metal oxide nanoarrays, in which the hairy-like structures out of ZnO was grown on copper oxide nanowires by hydrothermal process followed by thermal oxidation as shown in Figure 5. After silynization of the surface, the contact angle went to a value of about 170°. These kinds of materials show a shift between Wenzel and Cassie state and are self-cleanable . Similarly, hierarchical structured topology is applied even for the inner and outer surfaces of metallic cylinders for increasing the water repellence and thereby corrosion resistance and iceophobic properties [43, 44].
Sol-gel method is associated with the change of the state from colloidal suspension of solid particles into a liquid dispersed in solid. During this transformation, the repelling particle interaction has been changed into attractive interaction between the particles within the colloidal state. Sol-gel processing can transmit multifunctional characteristics to the surface because of the presence of more than single functionalities in the sol state. This is typically carried out by hydrolysis and polycondensation in the presence of a suitable solvent. The solvent must have desired polarity and gets trapped inside the solid particles and forms a gel during the procedure . Such gels can be easily applied on to the substrate, for example dip or spray coating with or without additives, depending on the nature of the material and the synthesised sol. The topological and chemical properties of so created surfaces largely depend on the physical properties and chemical composition of the reaction mixture. The main advantage of this method is that it is very easy to apply on to a large area of complicated structures. The hydrophobicity of composites has been improved by the incorporation or functionalization of the nanoparticles used for the processing or by various surface modifications, such as etching, to tailor the roughness . Silica is one of the major nanocoatings for hydrophobisation and can be easily synthesised by sol-gel method. However, silica particles can behave as hydrophilic material because of the large amount of silanol groups on the surface. Thus, in many studies silanol groups have been functionalized with non-polar chains to induce better hydrophobicity . But one disadvantage of such functionalization is that the moisture absorption can be increased with surface contamination and ageing . However, metal oxides do not behave as hydrophobic surfaces without suitable functionalization in most of the cases. In case of metal oxides, functionalization could be their treatment with suitable acids and consequential surface conversion into salt, which provides improved water repellence .
One of the important applications of the sol-gel method in the recent years is the coating of fabrics of natural fibres with hydrophobic metal oxide colloids. This provides an open way for the fabrication of water repellent textiles for mass production. Various organosilanes and mono-carboxylic acid functionalised alumina were found very efficient [50, 51]. Such organically modified nanoparticle coating gives an additional benefit of UV blocking, and thus makes this method more interesting for textile industries . Sol-gel synthesis started to utilise supramolecular assembly of long chain molecules, formed as a result of intra molecular hydrogen bonding (Figure 6) . Another advantage of this method is that it is easy to conduct template-assisted sol-gel synthesis, which makes the replication much easier.
2.5. Layer by layer method
In this technique, the generation of one layer of material over the other is performed to get a multilayer composite material surface. Techniques, typically used to achieve this, include dip coating, spray coating or spin coating. The prominent application of this method is to combine the properties of various nanomaterials with polymers, which are efficiently used in biological applications . Besides coating, supramolecular self-assembly can be used to generate hydrophobic surfaces. This is mostly applicable to polyelectrolyte macromolecules because of the ability of opposite charges to accumulate as layer. However, the other neutral type nanoparticles can be deposited as different layers . On the other hand, charged inorganic materials along with polyelectrolytes are also employed in many cases which provide a simple route for self-assembly on various substrates and avoid the requirements for using deposition techniques . Cheap scalable antifouling superhydrophobic coatings can be fabricated by introducing a lubricant into the pores of the nanostructured surface.
Layer by layer techniques are often combined with other deposition techniques for achieving higher contact angles. These deposition techniques are used for easier deposition of inorganic particles on the self-assembled macroscopic layers. Combinations of such techniques have been utilized for creating natural mimics . One of the limitations for using highly charged macromolecules is that it is highly influenced by the strength of the ions present in the solution, which may result in the disassembly of the layers . Such influences of the ionic concentrations can be excluded via covalent bonding of one layer over the other. Covalently bonded molecules with very long non-polar tails can thus provide water contact angle above 150° and in addition the extra stability. Other chemical interactions, such as hydrogen bonding, can also be utilized for self-assembly of layers but these are not as strong as covalent bonds. To stabilize such assemblies we need to provide additional stabilization methods such as incorporation of electrostatic copolymer with suitable multivalent ions, or suitable thermal or radiation curing of the films .
2.6. Deposition methods
2.6.1. Vapour depositions: PVD and CVD
Physical vapour deposition (PVD) and chemical vapour deposition (CVD) are the two major vapour deposition techniques used for making very thin layer of coating on various substrates. PVD utilizes the evaporated pure material whereas CVD utilizes a mixture of chemically reactive components, which are deposited on the surface, leaving the desired thin layer of coating. For the production of superhydrophobic surfaces, very low surface energy components’ vapours are applied on to the surface to form a thin layer of rough and water repellent surface. For depositing such materials, various techniques including plasma, thermal evaporation or even both are used [62, 63]. Typically, plasma-assisted vaporization requires much less thermal excitation, which is a special advantage . The vapour deposition coatings can be extended from inorganic metal oxides to various organic low energy materials, depending on the requirement and the substrate to be coated. Recently, surface modified silica deposition was achieved at a very low temperature of 40° C by implementing NH3 as a catalyst into the processing chamber . Developing such a low temperature processing is the best choice for coating thermally unstable surfaces. CVD has significant achievements even to control the crystallinity of the coated polymeric surfaces, tuned by controlling the deposition parameters . Such control over orientation of the polymer chain deposited can significantly affect the topology of the surfaces.
Since carbon nanotubes and other graphene-related materials have excellent surface roughness and low surface energy, they are used as intrinsic hydrophobic coating, applied for water-oil separation . Template-assisted vapour deposition of graphene is becoming popular for improving the porous structure with better control over the morphology, although it needs to be coated with non-polar polymer or other coatings for hydrophobisation . On the other hand, carbon vapour deposited nanotubes can show superoleophilicity without any further modification . Zwitter ionic deposition is another recent development for ant-fouling surfaces, where the surface energy depends on the number of exposed zwitter ions and the type of atmosphere that is exposed to the periphery, but has to be modified further to reach higher contact angle values .
2.7. Plasma surface treatment
Gaseous plasma is by definition partially or fully ionised gas, but it can contain also neutral gas which can be in excited state . Plasma discharge can be achieved by different setups, and the reader is encouraged to read more about them [72-74]. In general, plasma particles are excited (ionised, metastabled) and even more energetic than neutral gas, and thus they can physically or chemically react with treated material. The interaction can lead to etching or deposition. Etching is achieved through physical sputtering by ions or chemical reactions with the surface and desorption (i.e. oxygen neutral atoms chemically bond to a carbon on a polymer surface and CO or CO2 molecule is desorbed). Deposition can occur through chemical bonding of precursors from plasma to the surface or by plasma-activated chemical reactions of chemicals that are on the surface.
2.7.1. Plasma etching
Creating appropriate topography of the micro-rough surface for obtaining superhydrophobicity can be a challenge. Akinoglu
Despite slower etching rates, Salapare
PTFE was treated also with a mixture of oxygen/argon magnetron plasma . With plasma etching, micro-rough surface was established, and after 4h of treatment, leaf-like protrusions were created. The contact angle changed from non-treated sample at 102° to super-hydrophobic at 158° (Figure 8). The hydrophobicity was asserted to surface roughness and not surface chemistry, which was confirmed by XPS and Raman measurements.
One has to be careful when using plasma etching, because it can also damage the surface and deteriorate the hydrophobicity as demonstrated by Zylka . He prepared samples from silicone rubber with surface moulded by an acrylic paint template and left them exposed to the outside weather conditions for 45 days. The water contact angle on this surface was 149°. Then he treated the samples' surface with atmospheric air corona discharge for 100 h, and the contact angle dropped to 119°.
However, superhydrophobicity can be achieved on silicon surface too. In  complicated plasma etching procedure was used to create nanopillar and nanocone silicon surface. The surface was additionally passivated by octadecyltrichlorosilane monolayer. In both cases super-hydrophobic surface was achieved—contact angles were 150° for nanopillars and 165° for nanocones.
Another way of obtaining superhydrophobic properties of a surface is to deposit a thin layer on it and then modify this layers wettability. This challenge was addressed by Cai
2.7.2. Combination of plasma etching and deposition
To avoid many-step procedures and complicated setups, plasma etching and plasma deposition can assist in producing superhydrophobic polymer surface. Plasma etching break chemical bonds via high energy particle interaction with the surface and creates micro or nanorough surfaces by taking out the pieces of degraded polymers atom-by-atom into volatile molecules. This was nicely demonstrated for polymethyl methacrylate etched in helicon RF plasma, where etching was controlled by ion flux . The ion flux was adjusted with oxygen pressure and ion energy by biasing the samples (Figure 9). The roughness was increased with lower ion flux and with higher ion energy. When bias and pressure are set, time of plasma treatment determines the RMS roughness. Additional deposition of CFx film passivizes the surface, namely reduces the surface energy. The contact angle increases with etching time and reaches maximum value of 150° after 2 min. Similar work was performed on polystyrene, where first etching was performed with CF4 plasma and then CFx film was deposited by PECVD from C4F8 gas . In this case, CCP plasma was used. Plasma etching at 50 W was the most optimal for designing superhydrophobicity of the surface with the resulting contact angle of almost 160°. This surface property might be due to the highest fluorine-to-carbon atomic ratio on the surface after the deposition on this micro-surface structure. When the power was raised, the ion flux to the surface increased, leading to increase in the roughness and decrease in contact angle.
An interesting case is also treatment of paper (cellulose fibres) with plasma. Balu
|O2 plasma + Plasma polymer||148||152||92||133|
With a combination of plasma etching and deposition one can tailor the surface properties in the way that, in addition to superhydrophobicity, increased repellence of non-polar liquids is achieved at the same time. Coulson
Sometimes one would need hydrophobic and hydrophilic surface on same kind of sample for different use. Ruiz
Then they coated the etched surface with CF plasma, and afterwards they deposited polyacrylic acid (PAA) by capacitively coupled plasma. The etching already caused the superhydrophobicity, which was then slightly increased by the CF coating. However, the PAA drastically changed the surface energy and caused surface superhydrophilicity (Figure 9c).
2.8. Plasma deposition
Plasma deposition is an efficient process to deposit material with low surface energy and effectively improve hydrophobic properties. The deposited films can contribute to increase in the hydrophobicity with their structure. Most of the effects that lead to surface energy modification were already described before.
Typically, highly polar material gets deposited in a way that the surface is nanorough. Examples are atmospheric pressure plasma polymerization of the toluene/HMDSO , expanding plasma arc deposition of Teflon , pulsed CCP RF plasma deposition of fluoro-carbon films from C6F6 monomer precursor  and ICP plasma deposition of perfluorooctyl acrylate film  that all cause the superhydrophobicity.
In this chapter various methods were introduced on how to deal with the surface energy modifications. There are three major aspects for this, either by modifying the surface morphology in the way to mimic natural structures, which are effective for water repelling (lotus effect), by functionalization of the surface by non-polar group, or deposition of material with low surface energy. It was also shown that the most successful way is a combination of the techniques—deposition of the low surface energy material on the surface and creation of its microstructure, which can additionally increase the water contact angle.
Methods such as sol gel are very simple route to achieve the high water repellence and scaling up of the process is easily achievable. Herein, many techniques for the modification of surfaces or deposition of different low energy materials are presented, which easily lead to superhydrophobicity of surface. The future challenge has now shifted towards beneficial properties of the surfaces or the deposited thin layers like transparency, flexibility, electrical conductivity, catalytic properties, etc. without losing the superhydrophobic affiliation. Creation of anti-bacterial and anti-fungal surfaces for bio-medical applications are also very promising applications of such surfaces.
Feng. X., Jiang. L., Design and creation of superwetting/antiwetting surfaces. Advanced Materials. 2006;18:3063-3078. DOI: 10.1002/adma.200501961
Zhang. X., Shi. F., Niu. J., Jiang. Y., Wang. Z., Superhydrophobic surfaces: from structural control to functional application. Journal of Materials Chemistry. 2008;18:621-633. DOI: 10.1039/b711226b
Shirtcliffe. N. J., McHale. G., Atherton. S., Newton. M. I., An introduction to superhydrophobicity. Advances in Colloid and Interface Science. 2010;161:124-138. DOI: 10.1016/j.cis.2009.11.001
Aminayi. P., Abidi. N., Imparting super hydro/oleophobic properties to cotton fabric by means of molecular and nanoparticles vapor deposition methods. Applied Surface Science. 2013;287:223- 231. DOI: 10.1016/j.apsusc.2013.09.132
Wenzel. R. N., Resistance of solid surfaces to wetting by water. Industrial and Engineering Chemistry. 1936;28:988-994. DOI: 10.1021/ie50320a024
Cassie. A. B. D., Baxter. S.,Wettability of porous surfaces. Transactions of Faraday Society. 1944;40:546-551. DOI: 10.1039/TF9444000546
Gao. L., McCarthy. T. J., How Wenzel and Cassie were wrong. Langmuir. 2007;23:3762-3765. DOI: 10.1021/la062634a
Yao. X., Song. Y., Jiang. L., Applications of bio-inspired special wettable surfaces. Advanced Materials. 2011;23:719-734. DOI: 10.1002/adma.201002689
Nosonovsky. M., Bhushan. B. Superhydrophobic surfaces and emerging applications: non-adhesion, energy, green engineering. Current Opinion in Colloid & Interface Science. 2009;14:270-280. DOI: 10.1016/j.cocis.2009.05.004
Roach. P., Shirtcliffe. N. J., Newton. M. I.,. Progess in superhydrophobic surface development. Soft Matter. 2008;4:224-240. DOI: 10.1039/B712575P
Feng. L., Song. Y., Zhai. J., Liu. B., Xu. B., Jiang. L. Zhu. D.. Creation of a superhydrophobic surface from an amphiphilic polymer. Angewandte Chemie International Edition. 2003;42:800-802. DOI: 1433-7851/03/4207-0802
Li. A., Sun. H. X., Tan. D. Z., Fan. W. J., Wen. S. H.,Qing. X. J., Li. G. X., Superhydrophobic conjugated microporous polymers for separation and adsorption Energy & Environmental Science. 2011;4:2062-2065. DOI: 10.1039/C1EE01092A
Weng. J. C., Chang. C. H., Peng. C. W., Chen. S. W., Yeh. J. M.,. Advanced anticorrosive coatings prepared from the mimicked xanthosoma sagittifolium-leaf-like electroactive epoxy with synergistic effects of superhydrophobicity and redox catalytic capability. Chemistry of Materials. 2011;23:2075-2083. DOI: dx.doi.org/10.1021/cm1030377
Lee. W., Jin. M. K, Yoo. W. C, Lee. J. K.,. Nanostructuring of a polymeric substrate with well-defined nanometer-scale topography and tailored surface wettability. Langmuir. 2004;20:7665-7669. DOI: 10.1021/la049411
Wang. Y., Wang. M., Ge. X.,. Fabrication of superhydrophobic three-dimensionally ordered macroporous polytetrafluoroethylene films and its application. Langmuir. 2014;30:10804−10808. DOI: dx.doi.org/10.1021/la502866h
Li. J., Fu. J., Cong. Y., Wu. Y., Xue. L., Han. Y.,. Macroporous fluoropolymeric films templated by silica colloidal assembly: a possible route to super-hydrophobic surfaces. Applied Surface Science. 2006;252:2229-2234. DOI: 10.1016/j.apsusc.2005.03.224
Pan. L., Pu. L., Shi. Y., Song. S, Xu. Z., Zhang. R., Zheng. Y.,Synthesis of polyaniline nanotubes with a reactive template of manganese oxide. Advanced Materials. 2007;19:461-464. DOI: 10.1002/adma.200602073
Zhang. Z., Sui. J., Zhang. L., Wan. M., Wei. Y., Yu. L.,Synthesis of polyaniline with a hollow, octahedral morphology by using a cuprous oxide template. Advanced Materials. 2005;17:2854-2857. DOI: 10.1002/adma.200501114
Bormashenko. E., Stein. T., Whyman. G., Bormashenko. Y, Pogreb. R.,Wetting properties of the multiscaled nanostructured polymer and metallic superhydrophobic surfaces. Langmuir. 2006;22:9982-9985. DOI: 10.1021/la061622m
Zhong. W., Li. Y., Wang. Y., Chen. X., Wang. Y., Yang. W.,Superhydrophobic polyaniline hollow bars: constructed with nanorod-arrays based on self-removing metal-monomeric template. Journal of Colloid and Interface Science. 2012;365:28-32. DOI: 10.1016/j.jcis.2011.08.083
Sun. C., Ge. L. Q., Gu. Z.,Fabrication of super-hydrophobic film with dual-size roughness by silica sphere assembly. Thin Solid Films. 2007;515:4686-4690. DOI: 10.1016/j.tsf.2006.11.027
Li. Y., Cai. W., Cao. B., Duan. G., Sun. F., Li. C., Jia. L.,Two-dimensional hierarchical porous silica film and its tunable superhydrophobicity. Nanotechnology. 2006;17:238-243. DOI: 10.1088/0957-4484/17/1/040
Kannarpady. G. K., Khedir. R. K., Ishihara. H., Woo. J., Oshin. O. D.,Controlled growth of self-organized hexagonal arrays of metallic nanorods using template-assisted glancing angle deposition for superhydrophobic applications. Appl. Mater. Interfaces. 2011;3:2332-2340. DOI: x.doi.org/10.1021/am200251n
Sas. I., Gorga. R. E., Joines. J. A., Thoney. K. A.,Literature review on superhydrophobic self-cleaning surfaces produced by electrospinning. Journal of Polymer Science Part B: Polymer Physics. 2012;50:824-845. DOI: 10.1002/polb.23070
Jiang. L., Zhao. Y., Zhai. J.,. A Lotus-leaf-like superhydrophobic surface: a porous microsphere/nanofiber composite film prepared by electrohydrodynamics. Angewandte Chemie International Edition. 2004;43:4338-4341. DOI: 10.1002/anie.200460333
Lin. J., Cai. Y., Wang. X., Ding. B., Yu. J., Wang. M.,Fabrication of biomimetic superhydrophobic surfaces inspired by lotus leaf and silver ragwort leaf. Nanoscale. 2011;3:1258-1262. DOI: 10.1039/c0nr00812e
Wang. S., Li. Y., Fei. X., Sun. M., Zhang. C., Li. Y., Yang. Q., Hong. X.,Preparation of a durable superhydrophobic membrane by electrospinning poly (vinylidene fluoride) (PVDF) mixed with epoxy-siloxane modified SiO2 nanoparticles: a possible route to superhydrophobic surfaces with low water contact angle. Journal of Colloid and Interface Science. 359;2011:380-388.
Xiang. H., Zhang. L., Wanga. Z., Yu. X., Long. Y., Zhang. X., et al.,Multifunctional polymethylsilsesquioxane (PMSQ) surfaces prepared by electrospinning at the sol-gel transition: superhydrophobicity, excellent solvent resistance, thermal stability and enhanced sound absorption property. Journal of Colloid and Interface Science. 2011;359:296-303. DOI: 10.1016/j.jcis.2011.03.076
Ma. M., Hill. R. M., Lowery. J. L., Fridrikh. S. V., Rutledge. G. C.,Electrospun poly(styrene-block-dimethylsiloxane) block copolymer fibers exhibiting superhydrophobicity. Langmuir. 2005;21:5549-5554. DOI: 10.1021/la047064y
Nuraje. N., Khan. W. S., Lei. Y., Ceylan. M., Asmatulu. R., Superhydrophobic electrospun nanofibers. Journal of Material Chemistry A. 2013;1:1929-1946. DOI: 10.1039/C2TA00189F
Zhan. N., Li. Y., Zhang. C., Song. Y., Wang. H., Sun. L., A novel multinozzle electrospinning process for preparing superhydrophobic PS films with controllable bead-on-string/microfiber morphology. Journal of Colloid and Interface Science. 2010;345:491-495. DOI: 10.1016/j.jcis.2010.01.051
Ma. M., Hill. R. M.,Superhydrophobic surfaces. Current Opinion in Colloid & Interface Science. 2006;11:193-202. DOI: 10.1016/j.cocis.2006.06.002
Ding. B., Ogawa. T., Kim. J., Fujimoto. K., Shiratori. S.,Fabrication of a super-hydrophobic nanofibrous zinc oxide film surface by electrospinning. Thin Solid Films. 2008;516:2495-2501. DOI: 10.1016/j.tsf.2007.04.086
Tang. H., Wang. H., He. J.,. Superhydrophobic titania membranes of different adhesive forces fabricated by electrospinning. Journal of Physical Chemistry C. 2009;113:14220-14224. DOI: 10.1021/jp904221f
Wang. S., Liu. Q., Zhang. Y., Wang. S., Li. Y., Yang. Q., Song. Y., Preparation of a multifunctional material with superhydrophobicity, superparamagnetism, mechanical stability and acids-bases resistance by electrospinning. Applied Surface Science. 2013;279:150- 158. DOI: 10.1016/j.apsusc.2013.04.060
Rabenau. A.,The role of hydrothermal synthesis in preparative chemistry. Angewandte Chemie International Edition. 24;1985:1026-1040. DOI: 10.1002/anie.198510261
Liu.X., He. J.,. One-step hydrothermal creation of hierarchical microstructures toward superhydrophilic and superhydrophobic surfaces. Langmuir. 2009;25:11822-11826. DOI: 10.1021/la901426r
Wang. S., Wang. C., Liu. C., Zhang. M., Ma. H., Li. J.,Fabrication of superhydrophobic spherical-like α-FeOOH films on the wood surface by a hydrothermal method. Colloids and Surfaces A: Physicochemical Engineering Aspects. 2012;403:29-34. DOI: 10.1016/j.colsurfa.2012.03.051
Xiao. C., Yan. J., Li. T.,Fabrication and superhydrophobic property of ZnO micro/nanocrystals via a hydrothermal route. Journal of Nanomaterials. 2014;2014:680592. DOI: 10.1155/2014/680592
Li. L., Zhang. Y., Lei. J, He. J., Lv. R., Li. R., Pan. F.,A facile approach to fabricate superhydrophobic Zn surface and its effect on corrosion resistance. Corrosion Science. 2014;85:174-182. DOI: 10.1016/j.corsci.2014.04.011
Li. L, Zhang. Y, Lei. J, He. J, Lv. R., Li. N., et al.,Water-only hydrothermal method: a generalized route for environmentally-benign and cost-effective construction of superhydrophilic surfaces with biomimetic micronanostructures on metals and alloys. Chemical Communications.2014;50:7387-7554. DOI: 10.1039/c4cc00012a
Guo. Z., Chen. X., Li. J., Liu. J. H., Huang. X.J.,ZnO/CuO hetero-hierarchical nanotrees array: hydrothermal preparation and self-cleaning properties. Langmuir. 2011;27:6193-6200. DOI: 10.1021/la104979x
Hao. X., Wanga. L., Lv. D., Wang. Q., Li. L., He. N, et al.,Fabrication of hierarchical structures for stable superhydrophobicity on metallic planar and cylindrical inner surfaces. Applied Surface Science. 2015;325:151-159. DOI: 10.1016/j.apsusc.2014.11.014
Shen. Y., Tao. H., Chen. S., Zhu. L., Wang. T., Tao. J.,Icephobic/anti-icing potential of superhydrophobic Ti6Al4V surfaces with hierarchical textures. RSC Advances. 2015;5:1666-1672. DOI: 10.1039/c4ra12150c
Latthe. S. S., Gurav. A. B., Maruti. C. S., Vhatkar. R. S.,Recent progress in preparation of superhydrophobic surfaces: a review. Journal of Surface Engineered Materials and Advanced Technology. 2012;2:76-94. DOI: 10.4236/jsemat.2012.22014
Zhang. X., Jin. M., Liu. Z, Tryk. D. A., Nishimoto. S.,Superhydrophobic TiO2 surfaces: preparation, photocatalytic wettability conversion, and superhydrophobic-superhydrophilic patterning. Journal of Physical Chemistry C. 2007;111:14521-14529. DOI: 10.1021/jp0744432
Rao. A. V., Haranath. D.,Effect of methyltrimethoxysilane as a synthesis component on the hydrophobicity and some physical properties of silica aerogels. Microporous and Mesoporous Materials. 1999;30:267-273. DOI: 10.1016/S1387-1811(99)00037-2
Rao. A. V., Gurav. A. B., Latthe. S. S., Vhatkar. R. S., Imai. H., et al.,Water repellent porous silica films by sol-gel dip coating method. Journal of Colloid and Interface Science. 2010;352:30-35. DOI: 10.1016/j.jcis.2010.08.003
Lakshmi. R. V., Basu. B. J.,Fabrication of superhydrophobic sol-gel composite films using hydrophobically modified colloidal zinc hydroxide. Journal of Colloid and Interface Science. 2009;339:454-460. DOI: 10.1016/j.jcis.2009.07.064
Shang. S. M., Li. Z., Xing. Y., Xin. J. H., Tao. X. M.,Preparation of durable hydrophobic cellulose fabric from water glass and mixed organosilanes. Applied Surface Science. 2010;257:1495-1499. DOI: 10.1016/j.apsusc.2010.08.081
Pan. C., Shen. L., Shang. S., Xing. Y.,Preparation of superhydrophobic and UV blocking cotton fabric via sol-gel method and self-assembly. Applied Surface Science. 2012;259:110-117.
Han. J. T., Lee. D. H, Ryu. C. Y., Cho. K.,Fabrication of superhydrophobic surface from a supramolecular organosilane with quadruple hydrogen bonding. Journal of American Chemical Society. 2004;126:4796-4797. DOI: 10.1021/ja0499400
Srivastava. S., Nicholas. A. K.,Composite layer-by-layer (LBL) assembly with inorganic nanoparticles and nanowires. Accounts of Chemical Research. 2008;41:831-1841. DOI: 10.1021/ar8001377
Isimjan. T. T., Wang. T., Rohani. S.,. A novel method to prepare superhydrophobic, UV resistance and anti-corrosion steel surface. Chemical Engineering Journal. 2012;210:182-187. DOI: 10.1016/j.cej.2012.08.090
Sunny. S., Vogel. N., Howell. C.,Vu. T. L., Aizenberg. J.,Lubricant-infused nanoparticulate coatings assembled by layer-by-layer deposition. Advanced Functional Materials. 2014;6658-6667.24. DOI: 10.1002/adfm.201401289
Shi. F., Wang. Z., Zhang. X.,Combining a layer-by-layer assembling technique with electro chemical deposition of gold aggregates to mimic the legs of water striders. Advanced Materials. 2005;17:1005-1009. DOI: 10.1002/adma.200402
Amigoni. S., Givenchy. E. T., Dufay. M., Guittard. F.,Covalent layer-by-layer assembled superhydrophobic organic-inorganic hybrid films. Langmuir. 2009;25:11073-11077. DOI: 10.1021/la901369f
Quinn. J. F., Angus. P. R. J., Georgina. K. S., Alexander. N. Z., Caruso. F.,Next generation, sequentially assembled ultrathin films: beyond electrostatics. Chemical Society Reviews. 2007;36:707-718. DOI: 10.1039/b610778h
Huang. H., Zacharia. N. S.,Layer-by-layer rose petal mimic surface with oleophilicity and underwater oleophobicity. Langmuir. 2015;31:714-720. DOI: 10.1021/la504095k
Tsai. H., Lee. Y.,. Facile method to fabricate raspberry-like particulate films for superhydrophobic surfaces. Langmuir. 2007;23:12687-12692. DOI: 10.1021/la702521u
Li. Y.,Chen. X., Li. Q., Song. K., Wang. S., Chen. X., et al.,Layer-by-layer strippable Ag multilayer films fabricated by modular assembly. Langmuir. 2014;30:548−553. DOI: 10.1021/la4045557
Liu. H., Feng. L., Zhai. J, Jiang. L., Zhu. D., reversible wettability of a chemical vapor deposition prepared ZnO film between superhydrophobicity and superhydrophilicity. Langmuir. 2004;20:5659-5661. DOI: 10.1021/la036280o
Liu. H., Feng. L., Zhai. J, Jiang. L., Zhu. D. Reversible wettability of a chemical vapor deposition prepared ZnO film between superhydrophobicity and superhydrophilicity. Langmuir. 2004;20:5659-5661.
Kamal. S.A. A., Ritikos. R., Rahman. S. A.,Wetting behaviour of carbon nitride nanostructures grown by plasma enhanced chemical vapour deposition technique. Applied Surface Science. 2015;328:146-153. DOI: 10.1016/j.apsusc.2014.12.001
Rezaei. S., Manoucheri. I., Moradian. R., Pourabbas. B.,One-step chemical vapor deposition and modification of silica nanoparticles at the lowest possible temperature and superhydrophobic surface fabrication. Chemical Engineering Journal. 2014;252:11-16. DOI: 10.1016/j.cej.2014.04.100
Coclite. A. M., Shi. Y., Gleason. K. K.,Controlling the degree of crystallinity and preferred crystallographic orientation in poly-perfluorodecylacrylate thin films by initiated chemical vapor deposition. Advanced Functional Materials. 2012;22:2167-2176. DOI: 10.1002/adfm.201103035
Dong. X., Chen. J., Ma. Y., Wang. J., Chan-Park. M. B.,Liu. X., et al.,Superhydrophobic and superoleophilic hybrid foam of graphene and carbon nanotube for selective removal of oils or organic solvents from the surface of water. Chemical Communications. 2012;48:10660-10662. DOI: 10.1039/C2CC35844A
Singh. E., Chen. Z., Houshmand. F., Ren. W., Peles. Y., Cheng. M., Koratkar. N.,Superhydrophobic graphene foams. Small. 2013;9:75-80. DOI: 10.1002/smll.201201176
Lee. C. H., Johnson. N., Drelich. J., Yap. Y. K.,The performance of superhydrophobic and superoleophilic carbon nanotube meshes in water-oil filtration. Carbon. 2011;49:669-676. DOI: 10.1016/j.carbon.2010.10.016
Yang. R., Gleason. K. K.,Ultrathin antifouling coatings with stable surface zwitterionic functionality by initiated chemical vapor deposition (iCVD). Langmuir. 2012;28:12266−12274. DOI: 10.1021/la302059s
Bittencourt. J. A., Fundamentals of plasma physics. Springer, New York; 2014
Popov. A. O., High density plasma sources. Matsushita Electric Works, Woburn; 1996
Francombe. H. M., Plasma sources for thin film deposition and etching. Academic Press, London; 1994
Ostrikov. K. K., Xu. S., Plasma-aided nanofabrication: from plasma sources to nanoassembly. Wiley-VCH, Weinheim; 2007
Akinoglu. M. E., Morfa. J. A., Giersig. M., Understanding anisotropic plasma etching of two-dimensional polystyrene opals for advanced materials fabrication. Langmuir. 2014;30:12354-12361. DOI: 10.1021/la500003u
Barshilia. C. H., Gupta. N., Superhydrophobic polytetrafluoroethylene surfaces with leaf-like micro-protrusions through Ar + O2 plasma etching process. Vacuum. 2014;99:42-48. DOI: 10.1016/j.vacuum.2013.04.020
Zylka. P., On the surface performance of superhydrophobic silicone rubber specimens fabricated by direct replica method. IEEE Transactions on Dielectrics and Electrical Insulation. 2014;21:1183-1188. DOI: 10.1109/TDEI.2014.003843
Checco. A., Rahman. A., Black. T. C., Robust superhydrophobicity in large-area nanostructured surfaces defined by block-copolymer self assembly. Advanced Materials. 2014;26:886-891. DOI: 10.1002/adma.201304006
Cai. C. Y., Lin. A. K. Y., Yang. H., Superhydrophobic anti-ultraviolet films by doctor blade coating. Applied Physics Letters. 2014;105:201913. DOI: 10.1063/1.4902547
Vourdas. N., Tserepi. A., Gogolides. E., Nanotextured super-hydrophobic transparent poly(methyl methacrylate) surfaces using high-density plasma processing. Nanotechnology. 2007;18:125304. DOI: 10.1088/0957-4484/18/12/125304
Mundoa. R., Benedictis. V., Palumbo. F., d’Agostino. R., Fluorocarbon plasmas for nanotexturing of polymers: a route to water-repellent antireflective surfaces. Applied Surface Science. 2009;255:5461-5465. DOI: 10.1016/j.apsusc.2008.09.020
Balu. B., Breedveld. V., Hess. W. D., Fabrication of “roll-off” and “sticky” superhydrophobic cellulose surfaces via plasma processing. Langmuir. 2008;24:4785-4790. DOI: 10.1021/la703766c
Coulson. S. R:, Woodward. I., Badyal. J. P. S., Super-repellent composite fluoropolymer surfaces. J. Phys. Chem. B 2000;104:8836-8840. DOI: 10.1021/jp0000174
Ruiz. A., Valsesia. A., Ceccone. G., Gilliland. D., Colpo. P., Rossi. F., Fabrication and characterization of plasma processed surfaces with tuned wettability. Langmuir. 2007;23:12984-12989. DOI: 10.1021/la702424r
Ji. Y. Y., Kim. S. S., Kwon. O. P., Lee. S. H., Easy fabrication of large-size superhydrophobic surfaces by atmospheric pressure plasma polymerization with non-polar aromatic hydrocarbon in an in-line process. Applied Surface Science. 2009;255:4575-4578. DOI: 10.1016/j.apsusc.2008.12.002
Satyaprasad. A., Jain. V., Nema. S. K., Deposition of superhydrophobic nanostructured Teflon-like coating using expanding plasma arc. Applied Surface Science. 2007;253:5462-5466. DOI: 10.1016/j.apsusc.2006.12.085
Yang. S. H., Liu. C. H., Hsu. W. T., Chen. H., Preparation of super-hydrophobic films using pulsed hexafluorobenzene plasma. Surface and Coatings Technology. 2009;203:1379-1383. DOI: 10.1016/j.surfcoat.2008.11.007
Teare. D. O. H., Spanos. C. G., Ridley. P., Kinnmond. E. J., Roucoules. V., Pulsed plasma deposition of super-hydrophobic nanospheres. Chemistry of Materials. 2002;14:4566-4571. DOI: 10.1021/cm011600f