Confinement effect and spreading of water into microchannels fabricated on the VACNT surfaces

An easy and fast method to produce microchannels on the vertically aligned multiwalled carbon nanotube (VACNT) surfaces is described. Alternating superhydrophilic and superhydrophobic channels were built on VACNT films, using oxygen plasma functionalization and CO₂ laser treatment, respectively. A combined effect of wettability and capillary forces promotes an effective spreading, and confinement of water microdroplets on the superhydrophilic channels.     

Preparation of superhydrophobic surfaces by cauliflower‐like polyaniline

Cauliflower‐like polyaniline (PANI) was successfully prepared using an interfacial polymerization method. By modification with polydimethylsiloxane (PDMS) using chemical vapor deposition method, the surface wettability of cauliflower‐like PANI can be tailored to be superhydrophobic with a water contact angle of 160.4°. The deposition of the low‐surface‐energy silicon coating originated from PDMS pyrolysis on the cauliflower‐like PANI was confirmed by X‐ray photoelectron spectroscopy and Fourier Transform Infrared Spectroscopy. The changes in thermal stability and conductivity of the as‐prepared PANI before and after PDMS treatment were also investigated by thermogravimetric analysis and using a four‐probe method. Compared with nanofiber‐shaped PANI by electrodepositing polymerization, the PDMS‐treated cauliflower‐like PANI has superior surface wettability. Our study may open a new way for fabrication of superhydrophobic surfaces by developing novel nanostructured PANI. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39767.     

Wettability modification of zirconia by laser surface texturing and silanization

This paper presents the modification of wettability by nanosecond laser surface textured followed by silanization to fabricate the superhydrophobic zirconia surface. Surface modification by varying the pitch between channels leads to micro-channel and micro-grid pattern with different surface roughness. The generated morphological and metallurgical modifications of the surface are measured by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Numerous micro-pits and cracks in the laser-treated areas can be observed from SEM, which indicates crack propagation dominating the process of laser ablation of zirconia. The surface is superhydrophilic with laser-texturing instantly, whose wettability is modified over time. By analyzing the XPS, carbon content, especially C-C (H) groups, is important for the time-dependent wettability. The hydrophobicity of all laser-textured surfaces is improved after silanization. Laser texturing with smaller pitch (50 μm and 70 μm) leads to superhydrophobic surfaces after silanization, which may be due to the modification of physicochemical properties of substrate by very rapid local heating and cooling on the thick surface layer. Overall, the investigations indicate that wettability modifications can be attributed to the surface's microstructure, which depend on laser processing parameters, and chemical composition, especially in terms of −CF₃, −CF₂, and C-C (H).     

Superhydrophobic to superhydrophilic wettability transition of functionalized SiO2 nanoparticles

The superhydrophobic and superhydrophilic surfaces and their transitions are of great interest for the production of self-cleaning, anti-biofouling, or corrosion-resistant materials. This work reports the wettability transition from superhydrophobic to superhydrophilic SiO₂ nanoparticles functionalized with 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (POTS) and induced by temperature. The functionalization of these nanoparticles was confirmed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy. The functionalization of SiO₂ nanoparticles with POTS resulted in superhydrophobic surfaces with water contact angles up to 157°. A sudden transition to superhydrophilic behavior with water contact angles (WCA) below 5° was observed when the sample was heat-treated at 500 °C, despite the presence of fluorine on the surface of these nanoparticles, as confirmed by XPS and transmission electron microscopy. XPS suggested that the transition was caused by the change in orientation of the fluoroalkyl molecules and its partial decomposition due to the loss of the –CF₃ group, resulting in shorter chains with a tail-end group with C–O bonds, which promoted the superhydrophilicity.     

Reversibly light-switchable wettability between superhydrophobicity and superhydrophilicity of hybrid ZnO/bamboo surfaces via alternation of UV irradiation and dark storage

Functional bamboo surfaces with reversibly tunable wettability have become much sought after because of their usefulness in sustainable material protection strategies and industrial applications. In this paper, the hybrid ZnO/bamboo surfaces with reversibly light-switchable wettability between superhydrophobicity and superhydrophilicity were successfully prepared via a hydrothermal method at low temperature. The bamboo substrates served as adhesion, and the well-aligned ZnO nanosheet arrays (WZNA) were deposited on the bamboo surfaces after a hydrothermal process. A subsequent chemical treatment with octadecyltrichlorosilane (OTS) led to a superhydrophobic surface with a water contact angle (WCA) up to 153°. Under UV irradiation, the WCA decreased gradually, and the surface eventually became superhydrophilic because of hydroxyl absorption on the ZnO surfaces. The wetting behavior of the WZNA can be reversibly switched between superhydrophilic and superhydrophobic via alternation of UV exposure for 12 h and dark storage for 10 days.     

Fabrication and application of superhydrophilic surfaces: a review

Extreme wetting behaviors have been the subject of numerous studies in recent decades. Superhydrophilic surfaces with water contact angle lower than 5° is one of the most exciting research areas which has attract much attention. The ultrafast drying of such surfaces can provide outstanding properties such as antifogging, evaporative cooling, self-cleaning, and others. We review here the basic strategies and recent progress in fabricating superhydrophilic surfaces. And smart surfaces combining superhydrophilic and superhydrophobic abilities are highlighted, including surfaces with stimuli reversible wettability, patterning wettability, and gradient wetting. We also provide insights into the applications of the highly wettable surfaces, especially in devising new potentials.     

Superhydrophobic-superhydrophilic binary micropatterns by localized thermal treatment of polyhedral oligomeric silsesquioxane (POSS)-silica films

Surfaces patterned with alternating (binary) superhydrophobic-superhydrophilic regions can be found naturally, offering a bio-inspired template for efficient fluid collection and management technologies. We describe a simple wet-processing, thermal treatment method to produce such patterns, starting with inherently superhydrophobic polysilsesquioxane-silica composite coatings prepared by spray casting nanoparticle dispersions. Such coatings become superhydrophilic after localized thermal treatment by means of laser irradiation or open-air flame exposure. When laser processed, the films are patternable down to ～100 μm scales. The dispersions consist of hydrophobic fumed silica (HFS) and methylsilsesquioxane resin, which are dispersed in isopropanol and deposited onto various substrates (glass, quartz, aluminum, copper, and stainless steel). The coatings are characterized by advancing, receding, and sessile contact angle measurements before and after thermal treatment to delineate the effects of HFS filler concentration and thermal treatment on coating wettability. SEM, XPS and TGA measurements reveal the effects of thermal treatment on surface chemistry and texture. The thermally induced wettability shift from superhydrophobic to superhydrophilic is interpreted with the Cassie-Baxter wetting theory. Several micropatterned wettability surfaces demonstrate potential in pool boiling heat transfer enhancement, capillarity-driven liquid transport in open surface-tension-confined channels (e.g., lab-on-a-chip), and select surface coating applications relying on wettability gradients. Advantages of the present approach include the inherent stability and inertness of the organosilane-based coatings, which can be applied on many types of surfaces (glass, metals, etc.) with ease. The present method is also scalable to large areas, thus being attractive for industrial coating applications.     

Preparation and characterization of superhydrophobic surface based on polydimethylsiloxane (PDMS)

Biomimetic superhydrophobic surfaces exhibit excellent self-cleaning properties due to their special micro/nano-scale binary structures. In order to prepare the superhydrophobic surface of the polydimethylsiloxane (PDMS), a facile fabrication method for replicating micro/nano-scale binary aluminium structures into PDMS is presented. The microscopic morphology, composition, surface roughness (Ra) and wettability of the sample surface were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, roughness measurement equipment and contact angle meter respectively. Based on the measurements of the contact angles of deionized water (DI water) and ethanediol, surface free energies of the coatings were estimated according to the Owens two-liquid method. The superhydrophobic PDMS exhibited lower surface free energy than flat PDMS with a DI water contact angle (WCA) of 165°. The surface roughness (Ra) increased with the increasing of etching time in the range 0–80?min, and then decreased with the change of etching time, similar to the variation of contact angle with etching time. Moreover, the prepared surface had different micro-morphologies and its wettability was changed by regulating the chemical etching time. In addition, the superhydrophobic PDMS also showed good self-cleaning properties and the bouncing effect of the water droplets.     

Controlling the surface wettability of poly(sulfone) films by UV‐assisted treatment: benefits in relation to plasma treatment

Hydrophilic and superhydrophilic surfaces of poly(sulfone) (PSU) thin films were prepared by UV irradiation in the presence of O₂ or acrylic acid (AA) vapor. Treated surfaces were then investigated by water contact angle measurements, Fourier transformed IR spectroscopy in attenuated total reflectance mode (FTIR‐ATR), X‐ray photoelectron spectroscopy (XPS), near‐edge X‐ray absorption fine structure (NEXAFS) and AFM. Water contact angle values of treated PSU films using either O₂ or AA vapor as the reactive atmosphere reached about 6° after more than 120 min of irradiation. FTIR‐ATR, XPS and NEXAFS analysis showed incorporation of oxygenated groups onto the surface that led to its hydrophilic characteristics. In addition, when AA vapor was used as the reactive atmosphere, a photopolymerization process of poly(acrylic acid) onto the surface of the PSU was observed. AFM analysis showed a very low level of roughness after the treatments. A comparison of UV‐assisted surface modifications of PSU films with traditional plasma treatments showed excellent qualitative agreement between the two techniques. Our results show that UV‐assisted treatments in the presence of AA vapor or O₂ are efficient ways of controlling the surface wettability and functionalities grafted on the surface of PSU films. This treatment can be considered as a permanent dry grafting method that resists aging and uses a simple experimental setup. © 2012 Society of Chemical Industry     

Fabrication of superhydrophilic surface on copper substrate by electrochemical deposition and sintering process

Superhydrophilic surfaces were fabricated on copper substrates by an electrochemical deposition and sintering process. Superhydrophobic surfaces were prepared by constructing micro/nano-structure on copper substrates through an electrochemical deposition method. Conversion from superhydrophobic to superhydrophilic was ob-tained via a suitable sintering process. After reduction sintering, the contact angle of the superhydrophilic sur-faces changed from 155° to 0°. The scanning electron microscope (SEM) images show that the morphology of superhydrophobic and superhydrophilic surfaces looks like corals and cells respectively. The chemical composi-tion and crystal structure of these surfaces were examined using energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). The results show that the main components on superhydrophobic surfaces are Cu, Cu2O and CuO, while the superhydrophilic surfaces are composed of Cu merely. The crystal structure is more inerratic and the grain size becomes bigger after the sintering. The interfacial strength of the superhydrophilic surfaces was investigated, showing that the interfacial strength between superhydrophilic layer and copper substrate is considerably high.     

A facile preparation of the superhydrophobic polydimethylsiloxane materials and its performances based on the supercritical fluid foaming

The supercritical foaming (SCF) method was proposed to conveniently fabricate superhydrophobic polydimethylsiloxane (PDMS) surface. The effect of foaming parameters on the cellular structure, wettability, mechanical properties and thermal properties was investigated. This work indicates that the microstructure plays an important role in the superhydrophobicity of the PDMS materials. When the cell size and cell wall size, respectively, reach to 103.6 and 29.7 μm, the water contact angle (WCA) of the microcellular PDMS foams can achieve the maximum value 158°, and the air occupies about 90.6% of the contact areas. Meanwhile, the tensile strength of superhydrophobic PDMS materials can reach to 0.81 MPa, indicating that the superhydrophobic PDMS materials are useful. Moreover, the superhydrophobic PDMS materials show good thermal stability and excellent adiabatic property. And the method is simple and convenient, which can be used for the preparation of the superhydrophobic surfaces.     

Surface,Biocompatible and Hemocompatible Properties of Meta‐Amorphous Titanium Oxide Film

This study involved modification of the surface of Ti by micro‐arc oxidation (MAO). A rough and porous oxide film with good wettability was formed on the Ti surface. This MAO‐treated film exhibited a meta‐amorphous structure comprising crystalline anatase and rutile TiO₂ as well as amorphous phases. In addition, the incorporation of Ca and P in the MAO‐treated film was induced by micro‐arc discharge. The biological responses of the MAO‐treated surfaces were evaluated by observing the adhesion of MG63 osteoblast‐like cells and platelets. The MAO‐treated Ti had a considerably better biocompatibility and blood compatibility than untreated Ti.     

Thermo-responsive surface wettability on a pristine carbon nanotube film

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

Physical,mechanical, and biocompatibility evaluation of three different types of silicone rubber

Silicone rubber as a valuable biomaterial is widely used in medical applications, but its surface properties and low wettability make serious problems in long‐term implants. This work was undertaken to evaluate the biocompatibility of modified silicone rubber using two different techniques. A blend of poly(acrylamide) and silicone rubber was compared with virgin silicone surfaces as well as with those modified by laser treatment. Physical and mechanical properties of the samples were examined using different techniques. The hydrophilicity of the silicone rubber increased with increasing hydrogel content and decreased as a result of laser treatment. Both fibroblast cell (L929) and platelet behavior in contact with these surfaces were evaluated in vitro. The morphology of fibroblast cells that adhered to the blends was similar to the control. In contrast, on the laser‐treated surfaces fibroblast cells showed different proliferation. On the other hand, fewer platelets adhered to the laser‐treated surface than adhered to the blend and the unmodified PDMS surfaces. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2522–2529, 2003     

Fabrication of superhydrophobic transparent cyclic olefin copolymer (COC)-SiO2 nanocomposite surfaces

A superhydrophobic cyclic olefin copolymer (COC) nanocomposite coating was produced with a very simple and easy method. Self-cleaning superhydrophobic COC surfaces were obtained by only adding surface hydrophobized SiO₂ nanoparticles by dip coating method. The influence of concentration of SiO₂ and the coating temperatures on the wettability of the surfaces were investigated. The surface wettability of the coatings was examined with the contact angle measurements and the surface roughness and morphology were analyzed by using atomic force microscope and scanning electron microscopy analysis. Surfaces with certain amounts of COC and SiO₂ showed superhydrophobic character with high water contact angle of 169⁰. Also, the obtained superhydrophobic surfaces show superior water repellent, high transparency, and self-cleaning characteristics.     

Robust polymer incorporated TiO2-ZrO2 microsphere coatings by electrospraying technique with excellent and durable self cleaning,antibacterial and photocatalytic functionalities

The applications of self-cleaning coatings on large scale are limited due to their poor durability, remnants of hazardous by-products and lack of biocompatibility. We propose to solve this problem by developing TiO₂-ZrO₂ composite-based self cleaning coatings. In order to achieve this task another important aspect was to select biocompatible polymers poly (methyl methacrylate) and pluronic F-127 (PF-127) as they can enhance the self-cleaning capability of TiO₂-ZrO₂ which itself is biocompatible and endowed with anti-bacterial capability. The selection of a preparation technique that could produce coatings mimicking the nature has also been important and hence Electrospraying technique was selected as the processing method. The samples were then characterized using various techniques like field emission scanning electron microscopy, X-ray diffraction, high resolution transmission electron microscopy, Brunauer–Emmett–Teller analysis, and so forth to fathom the interlink between observed properties and morphology. High quality superhydrophobic and superhydrophilic films have been generated and the surfaces were modulated by the addition of tri-block co-polymer which was found to provide swapping of superhydrophobic nature to superhydrophilic nature. The integration of superhydrophobic, superhydrophilic, photocatalytic and antibacterial properties in the prepared microsphere coatings is a unique achievement and may interest those in the quest for self-cleaning materials for antibacterial coatings in mitigating surgical site infections, medical implants, coronary stent surfaces, and so forth.     

Physicochemical and biological evaluation of plasma‐induced graft polymerization of acrylamide onto polydimethylsiloxane

Polydimethylsiloxane (PDMS) rubbers exhibit good mechanical properties for biomedical and industrial applications, but their inherently high hydrophobicity limits biomedical applications of this material despite its favorable mechanical properties. In this work, surface modification of PDMS by radio‐frequency glow discharge and subsequently graft polymerization of acrylamide was studied. PAAm‐grafted, oxygen plasma‐treated, and control (untreated) PDMS rubbers were characterized using attenuated total reflectance Fourier transform infrared, scanning electron microscopy, dynamic mechanical thermal analyses, zeta potential, and contact angle techniques. Fibroblast (L929) cell attachment and growth onto these surfaces were examined by optical microscopy. The data from in vitro assays showed that cell attachment onto control surface was very negligible while significant cell attachment and growth was observed onto oxygen plasma‐treated and PAAm‐grafted PDMS surfaces. The method developed in this work offers a convenient way of surface modifications of biomaterials to improve attachment of cells onto substrates. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Superhydrophobic/superhydrophilic micropatterning on a carbon nanotube film using a laser plasma-type hyperthermal atom beam facility

Superhydrophobic/superhydrophilic micropatterning on a carbon nanotube (CNT) film has been achieved using a laser plasma-type hyperthermal atom beam facility, which produces a small amount of damage and generates a highly anisotropic beam. Fluorination and oxidation on CNT films by exposure to fluorine-atom and oxygen-atom beams caused superhydrophobic and superhydrophilic surfaces, respectively, while maintaining the as-grown fibrous forms of the CNT films. Micropatterned oxidation on CNT films without using photoresists created superhydrophilic microdots and microchannels.     

Wettability control on vertically-aligned multi-walled carbon nanotube surfaces with oxygen pulsed DC plasma and CO2 laser treatments

This work presents a method to obtain control on wettability of vertically-aligned multi-walled carbon nanotube surfaces, using oxygen pulsed directly current plasma and CO₂ laser irradiation. Superhydrophilic surfaces were obtained by the oxygen pulsed DC plasma treatment to incorporate polar groups on VACNT. The CO₂ laser was used to irradiate the functionalized samples, at different power levels, in order to restore the superhydrophobic characteristic. Evaluation of polar and dispersive components of superficial energy was performed by Owens and Wendt method.     

Simultaneous graft copolymerization of 2‐hydroxyethyl methacrylate and acrylic acid onto polydimethylsiloxane surfaces using a two‐step plasma treatment

Acrylic acid (AAc) and 2‐hydroxyethyl methacrylate (HEMA) mixtures were simultaneously grafted onto the surfaces of polydimethylsiloxane (PDMS) films using a two‐step oxygen plasma treatment (TSPT). The first step of this method includes: oxygen plasma pretreatment of the PDMS films, immersion in HEMA/AAc mixtures, removal from the mixtures, and drying. The second step was carried out by plasma copolymerization of preadsorbed reactive monomers on the surfaces of dried pretreated films. The effects of pretreatment and polymerization time length, monomer concentration, and ratio on peroxide formation and graft amount were studied. The films were characterized by attenuated total reflection Furrier transformer infrared (ATR‐FTIR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), zeta potential, surface tension, and water contact angle measurements. The ATR‐FTIR spectrum of the modified film after alkaline treatment showed the two new characteristic bands of PHEMA and PAAc. Both increase the polar part of surface tension (γ_p) after grafting and the evaluation of surface charge at pH 1.8, 7, and 12 confirmed the presence of polar groups on the surface of grafted films with a mixture of HEMA/AAc. Morphological studies using both AFM and SEM evaluation illustrated various amounts of grafted copolymer on the surface of PDMS films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007