Organic-inorganic hybrid superhydrophobic surfaces using methyltriethoxysilane and tetraethoxysilane sol-gel derived materials in emulsion

By applying alkaline-catalyzed co-hydrolysis and copolycondensation reactions of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) in organic siloxane modified polyacrylate emulsion (OSPA emulsion), we are able to demonstrate the potential for developing a sol-gel derived organic-inorganic hybrid emulsion for a superhydrophobic surface research. TEOS and MTES derived sol-gel moieties can be designed for a physical roughness and hydrophobic characteristic (Si-CH₃) of the hybrid superhydrophobic surface, while OSPA emulsion can be endowed for good film-forming property. The effect of formulation parameters on superhydrophobicity and film-forming property was analyzed. The water contact angle (WCA) on the sol-gel derived hybrid film is determined to be 156°, and the contact angle hysteresis is 5° by keeping the mole ratio of TEOS:MTES:C₂H₅OH:NH₃·H₂O:AMP-95 at 1:4:30:10:0.63 and the mass percentage of OSPA emulsion at 25%. The nanoparticle-based silica rough surface is observed as the mole ratio of MTES/TEOS at 4:1. The sol-gel derived organic-inorganic hybrid emulsion shows remarkable film-forming property when the mole ratio of MTES/TEOS reaches or exceeds 4:1. With the primer coating, the performance of superhydrophobic film achieve actual use standard. It reveals that this new procedure is an effective shortcut to obtain a superhydrophobic surface with potential applications.     

Fabrication of superhydrophobic wood surface by a sol-gel process

The superhydrophobic wood surface was fabricated via a sol-gel process followed by a fluorination treatment of 1H, 1H, 2H, 2H- perfluoroalkyltriethoxysilanes (POTS) reagent. The crystallization type of silica nanoparticles on wood surface was characterized using X-ray diffraction (XRD), the microstructure and chemical composition of the superhydrophobic wood surface were described by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), the bonding force between the silica nanoparticles and POTS reagent was analyzed by Fourier transform infrared spectroscopy (FT-IR) and the superhydrophobic property of the treated sample was measured by contact angle (CA) measurements. An analytical characterization revealed that nanoscale silica spheres stacked uniformly over the wood surface, and with the combination of the high surface roughness of silica nanoparticles and the low surface free energy film of POTS on wood surface, the wood surface has turned its wetting property from hydrophilic into superhydrophobic with a water contact angle of 164° and sliding angle less than 3°.     

Rapid fabrication of superhydrophobic surfaces on copper substrates by electrochemical machining

Hierarchical micrometer-nanometer-scale binary rough structures were fabricated on copper substrates by electrochemical machining in a neutral NaCl electrolyte. The rough structures are composed of the micrometer scale potato-like structures and the nanometer scale cube-like structures. After modified by the fluoroalkylsilane, the copper surfaces reached superhydrophobicity with a water contact angle of 164.3° and a water tilting angle less than 9°. This method has a high processing efficiency which can take just 3 s to fabricate the roughness required by the superhydrophobic surface. The effect of the processing time on wettability of the copper surfaces was investigated in this paper. The possible mechanism of the formation of the hierarchical roughness was also proposed, and the wettability of the copper surfaces was discussed on the basis of the Cassie-Baxter theory.     

Fabrication of superhydrophobic surfaces on aluminum

A superhydrophobic surface was prepared on aluminum substrate. Anodization and low-temperature plasma treatment were used to create micro-nano-structure and subsequently trichlorooctadecyl-silane modified the rough surface. The result shows that the water static contact of the aluminum surface after anodization and modification by trichlorooctadecyl-silane reaches to 152.1°. A rougher surface with some micro-nano-pores and small mastoids along the edges of pores was generated when low-temperature plasma treatment was applied to anodized aluminum film, resulting in water static contact angle up to 157.8°.     

Preparation of transparent BN films with superhydrophobic surface

A novel approach was investigated to obtain the superhydrophobicity on surfaces of boron nitride films. In this method boron nitride films were deposited firstly on Si(1 0 0) and quartz substrate using a radio frequency (RF) magnetron sputtering system, and then using CF₄ plasma treatment, the topmost surface area can be modified systematically. The results have shown that the water contact angle on such surfaces can be tuned from 67° to 159°. The films were observed to be uniform. The surfaces of films consist of micro-features, which were confirmed by Atomic Force Micrograph. The chemical bond states of the films were determined by Fourier Transform Infrared (FTIR) Spectroscopy, which indicate the dominance of B-N binding. According to the X-ray Photoelectron Spectroscopy analysis, the surface of film is mainly in BN phase. The micro-feature induced surface roughness is responsible for the observed superhydrophobic nature. The water contact angles measured on these surfaces can be modeled by the Cassie's formulation.     

Superhydrophobic properties of a hierarchical structure using a silicon micro-tip array decorated with ZnO nanowires

In this study, wetting properties of a hierarchical structure using a silicon micro-tip array covered with ZnO nanowire are characterized, and compared with hierarchical structures composed of micro-pillars for micro-scale roughness. The superhydrophobicity of a surface can be efficiently enhanced by using a micro-tip array, compared with a micro-pillar structure, because a micro-tip structure with high aspect ratio and small apex radius can significantly reduce fractions of liquid droplet area in contact, maintaining the droplet in the regime of the Cassie state. The micro-tip array was simply fabricated by combining anisotropic and isotropic silicon etching processes with one-step photolithography and a single etch mask. The measured height and aspect ratio of the fabricated micro-tip was around 40 μm and 8, respectively, when the center-to-center distance between micro-tips was 30 μm. The maximum CA on the hierarchical surface using the micro-tip array was measured to be 165.0 ± 2.3° with a period of 30 μm, while the hierarchical surface using the micro-pillar array showed the maximum CA of 158.6 ± 1.1° with 20 μm-diameter and 70 μm-gap between micro-pillars. The smallest CAH on the hierarchical micro-tip array was measured to be 5.0 ± 0.3° for the center-to-center distance between micro-tips of 30 μm.     

Wetting mode transition of nanoliter scale water droplets during evaporation on superhydrophobic surfaces with random roughness structure

During evaporation, shape changes of nanoliter-scale (80-100 nL) water droplets were evaluated on two superhydrophobic surfaces with different random roughness (nm-coating, μm-coating). The square of the contact radius and the square of the droplet height decreased linearly with evaporation time. However, trend changes were observed at around 170 s (nm-coating) and around 150 s (μm-coating) suggesting a wetting mode transition. The calculated droplet radii for the wetting mode transition from the average roughness distance and the average roughness height of these surface structures were approximately equal to the experimental values at these trend changes. A certain level of correlation between the roughness size and droplet radius at the wetting mode transition was confirmed on surfaces with random roughness.     

Facile fabrication of large-scale stable superhydrophobic surfaces with carbon sphere films by burning rapeseed oil

Stable anti-corrosive superhydrophobic surfaces were successfully prepared with the carbon nanosphere films by means of depositing the soot of burning rapeseed oil. The method is extremely cheap, facile, time-saving and avoided any of the special equipments, special reagents and complex process control. The method is suitable for the large-scale preparation of superhydrophobic surface and the substrate can be easily changed. The as-prepared surfaces showed stable superhydrophobicity and anti-corrosive property even in many corrosive solutions, such as acidic or basic solutions over a wide pH range. The as-prepared superhydrophobic surface was carefully characterized by the field emission scanning electron microscopy and transmission electron microscope to confirm the synergistic binary geometric structures at micro- and nanometer scale. This result will open a new avenue in the superhydrophobic paint research with these easily obtained carbon nanospheres in the near future.     

A new model for thermodynamic analysis on wetting behavior of superhydrophobic surfaces

Superhydrophobic surfaces have shown inspiring applications in microfluidics, and self-cleaning coatings owing to water-repellent and low-friction properties. However, thermodynamic mechanism responsible for contact angle hysteresis (CAH) and free energy barrier (FEB) have not been understood completely yet. In this work, we propose an intuitional 3-dimension (3D) droplet model along with a reasonable thermodynamic approach to gain a thorough insight into the physical nature of CAH. Based on this model, the relationships between radius of three-phase contact line, change in surface free energy (CFE), average or local FEB and contact angle (CA) are established. Moreover, a thorough theoretical consideration is given to explain the experimental phenomena related to the superhydrophobic behavior. The present study can therefore provide some guidances for the practical fabrications of the superhydrophobic surfaces.     

A novel method to fabricate superhydrophobic surfaces based on well-defined mulberry-like particles and self-assembly of polydimethylsiloxane

A superhydrophobic surface was obtained by combining application of CaCO₃/SiO₂ mulberry-like composite particles, which originated from violent stirring and surface modification, and self-assembly of polydimethylsiloxane. Water contact angle and sliding angle of the superhydrophobic surface were measured to be about 164 ± 2.5° and 5°, respectively. The excellent hydrophobicity is attributed to the synergistic effect of micro-submicro-nano-meter scale roughness (fabricated by composite particles) and the low surface energy (provided by polydimethylsiloxane). This procedure makes it possible for widespread applications of superhydrophobic film due to its simplicity and practicability.     

Preparation and characterization of slice-like Cu2(OH)3NO3 superhydrophobic structure on copper foil

Superhydrophobic structure was prepared on copper foil via a facile solution-immersion method. Thus slice-like Cu₂(OH)₃NO₃ crystal was prepared on the surface of the copper foil by sequential immersing in an aqueous solution of sodium hydroxide and cupric nitrate. And the superhydrophobic structure was obtained by modifying the slice-like Cu₂(OH)₃NO₃ crystal with 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS-17). The morphologies, chemical compositions and states, and hydrophobicity of the surface-modifying films on the copper foil substrates were analyzed by means of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and water contact angle measurement. Moreover, the thermal stability of the slice-like structure was also evaluated using thermogravimetric analysis (TGA). It was found that roughening of the copper foil surface helped to increase the hydrophobicity to some extent, but no superhydrophobicity was obtained unless the slice-like Cu₂(OH)₃NO₃ crystal formed on the Cu substrate was modified with 1H,1H,2H,2H-perfluorodecyltriethoxysilane. Besides, the superhydrophobicity of the FAS-17-modified slice-like Cu₂(OH)₃NO₃ structure was closely related to the surface morphology. And this hydrophobic structure retained good superhydrophobic stability at elevated temperature and in long-term storage as well, which should be critical to the application of Cu-matrix materials in engineering.     

Superhydrophobic surfaces fabricated by microstructuring of stainless steel using a femtosecond laser

Fabrication of superhydrophobic surfaces induced by femtosecond laser is a research hotspot of superhydrophobic surface studies nowadays. We present a simple and easily-controlled method for fabricating stainless steel-based superhydrophobic surfaces. The method consists of microstructuring stainless steel surfaces by irradiating samples with femtosecond laser pulses and silanizing the surfaces. By low laser fluence, we fabricated typical laser-induced periodic surface structures (LIPSS) on the submicron level. The apparent contact angle (CA) on the surface is 150.3°. With laser fluence increasing, we fabricated periodic ripples and periodic cone-shaped spikes on the micron scale, both covered with LIPSS. The stainless steel-based surfaces with micro- and submicron double-scale structure have higher apparent CAs. On the surface of double-scale structure, the maximal apparent CA is 166.3° and at the same time, the sliding angle (SA) is 4.2°.     

Fabrication of an intelligent superhydrophobic surface based on ZnO nanorod arrays with switchable adhesion property

The superhydrophobic ZnO surface possessing water adhesive reversibility is fabricated by a facile method. The as-prepared surface is low adhesive; however, after being irradiated by UV light through a photomask, it becomes highly adhesive. A water droplet can suspend on the irradiated surface. Further annealing the irradiated surface, water droplets can roll on the surface again. Reversible transition between the high adhesive pinning state and low adhesive rolling state can be realized simply by UV illumination and heat treatment alternately. The adhesion transition is attributed to the adsorption/desorption of surface hydroxyl groups and the organic chains rearrangement on the top surfaces of ZnO.     

Fabrication of superhydrophobic surfaces based on ZnO-PDMS nanocomposite coatings and study of its wetting behaviour

Superhydrophobic surfaces based on ZnO-PDMS nanocomposite coatings are demonstrated by a simple, facile, time-saving, wet chemical route. ZnO nanopowders with average particle size of 14 nm were synthesized by a low temperature solution combustion method. Powder X-ray diffraction results confirm that the nanopowders exhibit hexagonal wurtzite structure and belong to space group P63mc. Field emission scanning electron micrographs reveal that the nanoparticles are connected to each other to make large network systems consisting of hierarchical structure. The as formed ZnO coating exhibits wetting behaviour with Water Contact Angle (WCA) of ∼108°, however on modification with polydimethylsiloxane (PDMS), it transforms to superhydrophobic surface with measured contact and sliding angles for water at 155° and less than 5° respectively. The surface properties such as surface free energy (γ_p), interfacial free energy (γ_pw), and the adhesive work (W_pw) were evaluated. Electron paramagnetic resonance (EPR) studies on superhydrophobic coatings revealed that the surface defects play a major role on the wetting behaviour. Advantages of the present method include the cheap and fluorine-free raw materials, environmentally benign solvents, and feasibility for applying on large area of different substrates.     

A novel method for the synthesis of polystyrene-graft-silica particles using random copolymers based on styrene and triethoxyvinylsilane

In the present research, random copolymers based on triethoxyvinylsilane (TEVS) and styrene (St) are synthesized and structurally characterized. According to the reactivity ratios of the monomers determined by infrared analysis; St tends to form blocks whilst TEVS is expected to be incorporated as isolated units. A sample of poly(styrene-co-triethoxyvinylsilane) synthesized at low conversion using a monomer feeding ratio St:TEVS of 2:3 was used as macrosilane in the synthesis of polystyrene-g-silica particles. The grafting reaction was confirmed by infrared spectroscopy, thermogravimetric analysis and by the evaluation of the morphological characteristics of the hybrid particles.     

Fabrication of superhydrophobic silica-based surfaces with high transmittance by using tetraethoxysilane precursor and different polymeric species

The preparation of superhydrophobic silica-based surfaces via the sol-gel process through the addition of different polymeric species into the precursor solution was done in this study. The surface roughness of the films was obtained by removing the organic polymer at a high temperature, and then the hydrophobic groups were bonded onto the films with a monolayer by chemical reaction with hexamethyldisilazane (HMDS). The characteristic properties of the as-prepared films were analyzed by contact angle measurements, scanning electron microscopy (SEM), atomic force microscopy (AFM), nitrogen adsorption/desorption, and UV-vis scanning spectrophotometer. The experimental results revealed that the superhydrophobic thin films with high transmittance could easily be prepared using polypropylene (PPG), polyethylene (PEG), and poly(vinylpyrrolidone) (PVP). Surface roughness and pore size were enhanced using PPG polymeric species. The distribution of pore size was from the microporous to the mesoporous and marcoporous regions. In addition, the contact angles of the rough surfaces prepared at 500 °C without modification of HMDS were smaller than 5° but larger than 156° after modified by HMDS.     

面向微穿孔板吸声结构和吸声特性混合设计的软件平台

微穿孔板吸声结构是由微穿孔板与板后空腔组成的共振吸声结构,被认为是继多孔吸声材料之后发展起来的最有吸引力的吸声结构,其吸声特性与结构参数孔径d、板厚t、孔距b及空腔深度D有关,如何按需设计一个有效的微穿孔板吸声结构已成为目前研究的热点。本文从微穿孔板吸声结构和吸声特性混合设计的角度出发,使用面向对象的编程语言C++开发了微穿孔板吸声结构设计平台。与以往设计方法不同,本文开发的软件平台综合考虑了结构参数和吸声特性参数两方面的限制,根据实际应用要求平衡微穿孔板吸声结构的最大吸声系数与吸声带宽之间的制约关系,并以饱满的吸声曲线为目标,提供满足混合设计要求的优化结构参数。     

Preparation of low density TiO2/poly (methyl methacrylate) composite particles by emulsifier-free emulsion polymerization

Based on the 3-(trimethoxysilyl) propylmethacrylate (MPS) modified TiO₂ particles, the TiO₂/poly (methyl methacrylate) (PMMA) composite particles have been prepared successfully via emulsifier-free emulsion polymerization in water. A facile floating-sinking method is proposed to roughly evaluate the composite particles’ density. Chemical component of obtained composite particles was identified by Fourier transform infrared spectra (FTIR). The morphology and grain size of the composite particles were investigated by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Thermal analysis of the composite particles was measured by differential thermal analysis-thermo gravimetric analysis (DTA-TGA). The zeta potential and electrophoretic mobility of composite particles with suitable density in water was measured by dynamic light scattering (DLS).     

Easy fabrication of large-size superhydrophobic surfaces by atmospheric pressure plasma polymerization with non-polar aromatic hydrocarbon in an in-line process

We report on the formation of superhydrophobic surfaces on glass by plasma polymerization with non-polar aromatic hydrocarbon, at atmospheric pressure, in an in-line process. The glass was simply treated by radio frequency (RF) plasma with a mixture of toluene and hexamethyldisiloxane (HMDSO). The hydrophobicity of the sample surfaces increase with increasing plasma treatments; contact angles of 150° for water droplets are achieved. It is attributed mainly to its high content of non-polar hydrophobic phenyl groups and its rough surface.     

Experimental and theoretical evaluation of wettability on micro/nano hierarchically engineered surfaces based on robust micro-post-arrayed- and highly ordered nano-rippled-structures

This paper reports a simple approach for demonstrating a micro/nano hierarchical surface, ensuring both geometrical regularity and mechanical stability, for improving the hydrophobicity. The proposed dual-scale hierarchical surfaces were realized simply by combining the highly self-ordered ripple-like nano patterns with the robust micro-post arrays, based on the cost-effective nonlithographic chemical oxidation process and well-established microfabrication technologies. The wettability of the proposed nano-scale mono- and micro/nano dual-roughened surfaces was evaluated by measuring the apparent contact angles (ACAs), and analyzed theoretically with analytic models based on the Wenzel, Cassie, and combined wetting theories. Through experimental and theoretical observations, it was found that the proposed micro/nano hierarchical structures can improve the wetting property and the superhydrophobic robustness of high- and low-density micro-post arrayed surfaces, respectively.