Effect of deposition parameters on the wettability and microstructure of superhydrophobic films with hierarchical micro-nano structures

Superhydrophobic films with hierarchical micro-nano structures were deposited on glass substrates by solution immersion method from a solution containing cobalt chloride, urea and cetyl trimethyl ammonium bromide (CTAB). Subsequently the films were hydrophobized with a low surface energy material like octadecanoic acid under ambient conditions resulting in superhydrophobic surfaces with water contact angle (WCA) of about 168° and contact angle hysteresis of 1°. The effect of deposition parameters such as solution composition, temperature, deposition time and alkanoic acid treatment on surface morphology and wettability of the films was studied. Mechanism of formation of cobalt chloride carbonate hydroxide film is discussed. Addition of CTAB to the solution resulted in a change in the surface morphology of the deposited films with flower-like structures. The wettability of films obtained under different process conditions was correlated to surface roughness using Wenzel and Cassie models.     

Fabrication of optically active flexible polymer films with embedded chain-like arrays of silver nanoparticles

We report a straightforward method for preparation of freestanding transparent polymer film containing 2D silver nanoparticle arrays and possessing polarization-sensitive optical properties.     

Electrochemical synthesis of silver polyhedrons and dendritic films with superhydrophobic surfaces

Single-crystalline Ag dendrites are grown on a Ni/Cu substrate by using a simple templateless, surfactantless electrochemical technique. Controlling only the applied potential causes a change in the deposited silver morphology from polyhedrons to dendrites. Microstructure characterization suggests that preferential growth along the 211 directions by the oriented attachment of Ag nanocrystals leads to the formation of Ag dendrites, which are composed of trunks, branches, and leaves. Modifying as-grown Ag dendritic film with a thickness of about 10 microm with a self-assembled monolayer of n-dodecanethiol yields a superhydrophobic surface with a contact angle of 154.5 +/- 1.0 degrees and a tilt angle lower than 2 degrees.     

Fabrication of hierarchical ZnO architectures and their superhydrophobic surfaces with strong adhesive force

Grid-structured ZnO microsphere arrays assembled by uniform ZnO nanorods were fabricated by noncatalytic chemical vapor deposition, taking advantage of morphologies of alumina nanowire pyramid substrates and ZnO oriented growth habits. Every ZnO microsphere (similar to the micropapilla on a lotus leaf surface) is assembled by over 200 various oriented ZnO nanorods (similar to the hairlike nanostructures on mircopapilla of a lotus leaf). This lotus-leaf-like ZnO micro-nanostructure films reveal superhydrophobicity and ultrastrong adhesive force to liquid. The realization of this hierarchical ZnO nanostructure film could be important for further understanding wettability of biological surfaces with micro-nanostructure and application in microfluidic devices.     

Fabrication of hollow spheres and thin films of nickel hydroxide and nickel oxide with hierarchical structures

Hollow spheres and thin films of Ni(OH)(2) and NiO with unusual form and hierarchical structures have been synthesized by a simple solution chemistry method. First, in situ formed Ni(OH)(2) nanoflakelets organized on the surface of styrene-acrylic acid copolymer (PSA) latex particles to form core/shell structures. Ni(OH)(2) hollow shells built up with nanoflakelets were obtained after subsequent removal of the core latex particles by dissolving PSA latex in toluene; the removal of the cores by calcinations would result in NiO hollow shells, also with hierarchical structures. BET calculation showed the surface area of the NiO hollow spheres was 156 m(2)/g. The nanoflakelets could also organize themselves into thin films with hierarchical structures. It is anticipated that these novel structures will have some unique applications in Ni-based batteries and other potentials.     

Fabrication of polyaniline with hierarchical structures in alkaline solution

Nanosheet- or nanorod-based microspheres and nanorod-based microrods of polyaniline (PANI) with hierarchical structures were successfully prepared by oxidation polymerization of aniline in alkaline solution. Temperature was found to have important influence on the morphology of PANI hierarchical structures and their building blocks. The concentration of alkali (NaOH) could be used to guide the morphological evolution of PANI, from leaf-like structures to nanosheet-based particles, and to nanorod-based microspheres and nanorod-based microrods with increasing concentration of NaOH in synthesis. The chemical structures of product were characterized by FTIR, UV-vis spectra and XRD, and its solubility was also studied in this report.     

Fabrication of superhydrophobic sponge with hierarchical structure and application for oil/water separation

Oil/water separation polyurethane sponge with hierarchically structured surface similar to the chemical/topological structures of lotus leaf has been successfully developed by combining mussel-inspired one-step copolymerization approach. The chemical structure, surface topography, and surface wettability of the sponge were characterized by FTIR, SEM, and contact angle experiments, respectively. The results showed that as-prepared sponge exhibited high oil absorption rate because of the expansion in oil and collapse in water of the polymer molecular brushes. Meanwhile, it also possessed high absorption capacity (20 times of the self-weight), high oil retention (93.7%), and good recyclability. It had excellent potential in practical applications.     

Importance of hierarchical structures in wetting stability on submersed superhydrophobic surfaces

Submersed superhydrophobic surfaces exhibit great potential for reducing flow resistance in microchannels and drag of submersed bodies. However, the low stability of liquid-air interfaces on those surfaces limits the scope of their application, especially under high liquid pressure. In this paper, we first investigate the wetting states on submersed hydrophobic surfaces with one-level structure under hydrostatic pressure. Different equilibrium states based on free-energy minimization are formulated, and their stabilities are analyzed as well. Then, by comparison with the existing numerical and experimental studies, we confirm that a new metastable state, which happens after depinning of the three-phase contact line (TCL), exists. Finally, we show that a strategy of using hierarchical structures can strengthen the TCL pinning of the liquid-air interface in the metastable state. Therefore, the hierarchical structure on submersed surfaces is important to further improve the stability of superhydrophobicity under high liquid pressure.     

Fabrication of hierarchical structures by unconventional two-step imprinting

We present a simple sequential imprinting lithography method to fabricate micro/nanoscale hierarchical structures. This method involves hot embossing and capillary force lithography with two stamps of different microscales, which avoids using nanoscale stamps. By varying the experimental conditions in the capillary force lithography process, the morphology of the resulting structures can be controlled. This method may provide a facile and low-cost route for fabricating large area patterns of hierarchical structures.     

Fabrication of superhydrophobic surface by hierarchical growth of lotus-leaf-like boehmite on aluminum foil

Hierarchical growth of boehmite film on the aluminum foil was carried out via a facile solution-phase synthesis route. The resultant film is composed of three-dimensional microprotrusions assembled from well aligned nanoneedles. Such dual scale micro-/nanostructures are highly similar with those of lotus leaves. The resultant surface after hydrophobization exhibits a water contact angle of 169° and a sliding angle of ～4° for a 5 μL droplet, which is ascribed to the combination of the dual scale roughness at the micro- and nanometer scale and the low surface energy of stearic acid coating. The obtained film possesses relatively good adhesion to the aluminum substrate and keeps superhydrophobicity after the ultrasonic treatment or long-term storage in spite of the partial loss of it superhydrophobic ability after abrasion test.     

Hydrocarbon versus fluorocarbon in the electrodeposition of superhydrophobic polymer films

To elaborate on superhydrophobic surfaces, we report the electrochemical synthesis, surface morphology, and wettability of hydrocarbon conductive polymer films obtained by the electrodeposition of polythiophene, poly(3,4-ethylenedioxythiophene) (i.e., PEDOT), and poly(3,4-ethylenedioxypyrrole) (i.e., PEDOP) derivatives. Highly hydrophobic films were obtained from n-C(14)H(29) and n-C(8)H(17) chains in the cases of polythiophenes and PEDOP, respectively. By contrast, superhydrophobic films were formed by the deposition of PEDOT substituted with n-C(10)H(21) chains (PEDOT-methyl undecanoate): static contact angle ≈ 160.6°, hysteresis ≈ 2°, and sliding angle ≈ 3°. Their surface properties were compared to those of previously reported fluorinated analogues. The water-repellent properties of PEDOT-methyl undecanoate were similar to the best surface properties obtained with fluorinated monomers. Even if the main approach for the chemical factor to build up superhydrophobic surfaces is via a coating of a fluorinated compound, this work confirms that the formation of fractal surfaces is able to achieve super-anti-wetting properties within a hydrocarbon series (less expensive with a favorable ecotoxic approach), and it opens a new path to bioinspired surfaces.     

Optical properties of plasma polymer films with encapsulated silver particles

Plasma polymer thin films with encapsulated small metal particles were prepared by simultaneous plasma polymerization and metal evaporation. Based on transmission electron microscope (TEM) micrographs, particle size and shape were analysed on films with continuously varying filling factor. Thermal annealing causes dramatic changes of the particle size and shape. The optical (UV, VIS, NIR) properties of the films were determined by the UV-absorption of the plasma polymer and by the plasma resonance absorption of the metal particles. The changes in the transmission spectra during thermal annealing were simulated with different effective medium theories. The calculated transmission spectra were fitted to the experimental spectra.     

Fabrication of flower-like silver structures through anisotropic growth

Using a simple chemical reaction, a new nanostructure of silver, which we call a "flower-like silver structure", is produced. The flower-like silver structure consists of a silver core and many rod-like tips protruding out in three dimensions. Besides common face-centered-cubic (FCC) phase of silver, there exists hexagonal-close-packed (HCP) phase in these tips. The appearance of HCP silver is the result of rapid growth of silver nuclei when using CH(2)O or C(2)H(4)O as the reducing agent. The formation of the rod-like tips is caused by the anisotropic growth determined by the HCP phase and the directing role of formic acid, which is the oxidation product of CH(2)O. It is also found that the concentration of reactants, the kind of reducing agents and the sequence of adding reactants can influence the morphology and phase constitution of the final products.     

Fabrication of superhydrophobic surfaces with hierarchical structure through a solution-immersion process on copper and galvanized iron substrates

Superhydrophobic surfaces were obtained on copper and galvanized iron substrates by means of a simple solution-immersion process: immersing the clean metal substrates into a methanol solution of hydrolyzed 1H,1H,2H,2H-perfluorooctyltrichlorosilane (CF3(CF2)5(CH2) 2SiCl3, FOTMS) for 3-4 days at room temperature and then heated at 130 degrees C in air for 1 h. Both of the resulting surfaces have a high water contact angle (CA) of larger than 150.0 degrees as well as a small sliding angle (SA) of less than 5 degrees . The formation and structure of the superhydrophobic surfaces were characterized by means of scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectrometry (EDX). SEM images showed that both of the resulting surfaces exhibited special hierarchical structure. The special hierarchical structure along with the low surface energy leads to the high surface superhydrophobicity.     

Controllable superhydrophobic and lipophobic properties of ordered pore indium oxide array films

Using the polystyrene (PS) colloidal monolayers as templates, ordered indium oxide pore array films with different morphologies were prepared by sol-dipping method. These porous films took on hydrophilicity, however, after chemical modification, such pore array films displayed both superhydrophobicity and lipophobicity due to rough surface and low surface free energy materials on their surfaces. Interestingly, with increase of the pore size in the films, the superhydrophobicity could be controlled and was gradually enhanced due to the corresponding increase of roughness caused by nanogaps produced by the thermal stress in the annealing process with increase of film thickness.     

Concentric-ringed structures in polymer thin films

Novel polymer crystalline structures containing micrometer-sized concentric rings (or bands) were observed in thin poly(bisphenol A hexane ether) (BA-C6) films. The origin of the banded structures was found to be different from that of traditional banded spherulites in polymer systems. Analyses based on optical microscopy (OM) and atomic force microscopy (AFM) revealed that the banded structures contained alternating ridge and valley bands of polymer crystals in the flat-on orientation. No lamellar twisting was observed within the concentric-ringed structures, which were developed as a result of the formation of a depletion zone during crystallization. The formation of a depletion zone was determined to be caused by the specific volume decrement between the crystal and the melt and by the diffusion of polymer chains to the fold surfaces of the flat-on lamellae. The height of the ridges and the interband widths could be adjusted by controlling the diffusion rate. Time-of-flight secondary ion mass spectrometry ion images showed higher concentrations of low-molecular-weight polymer chains on the surfaces of the ridges than in the valleys.     

Synthesis and morphogenesis of organic polymer materials with hierarchical structures in biominerals

Synthesis and morphogenesis of polypyrrole (PPy) with hierarchical structures from nanoscopic to macroscopic scales have been achieved by using hierarchically organized architectures of biominerals. We adopted biominerals, such as a sea urchin spine and nacreous layer, having hierarchical architectures based on mesocrystals as model materials used for synthesis of an organic polymer. A sea urchin spine led to the formation of PPy macroscopic sponge structures consisting of nanosheets less than 100 nm in thickness with the mosaic interior of the nanoparticles. The morphologies of the resultant PPy hierarchical architectures can be tuned by the structural modification of the original biomineral with chemical and thermal treatments. In another case, a nacreous layer provided PPy porous nanosheets consisting of the nanoparticles. Conductive pathways were formed in these PPy hierarchical architectures. The nanoscale interspaces in the mesocrystal structures of biominerals are used for introduction and polymerization of the monomers, leading to the formation of hierarchically organized polymer architectures. These results show that functional organic materials with complex and nanoscale morphologies can be synthesized by using hierarchically organized architectures as observed in biominerals.     

Transformation of hydrophobic surface into superhydrophobic surface by interfacial flower like silver films

Fabrication of superhydrophobic surface was achieved by electroless deposition of silver film and subsequent immersion into a mixture of stearic acid and cysteamine. The resultant superhydrophobic surface with flower and fall‐leaves like structure showed lotus leaf effect with the water contact angle of about 154° making copper surface water repellant. Copyright © 2014 John Wiley & Sons, Ltd.     

Facial fabrication of superhydrophobic cellulose film with hierarchical morphologies

Hierarchical CuO spheres were firstly grown on the surface of cellulose film, and then stearic acid (STA) was utilized to decrease surface energy. The cupric ions fixed on the cellulose film transferred to one side and reacted with STA forming cupric stearates. The cupric stearates then self-assembled into nanobelts/nanoribbons and spread over the film, which induces to form hierarchical morphologies. Both sides of CuO modified film are black and superhydrophilic in air; after modification with STA, the film becomes superhydrophobic for both sides, whereas one side is blue and the other side is black showing different morphologies. Water contact angles (WCAs) of the superhydrophobic film for both black and blue sides are 153.9 ± 0.6° and 153.5 ± 0.8°, respectively. Sliding angles (SAs) for both sides are lower than 9.5°, indicating non-sticking superhydrophobic state. More importantly, the superhydrophobic cellulose–CuO–STA film is still superhydrophobic under hydrodynamic impact or pH of 3–11.