Fluoroalkylsilane Modification Research Articles

Fabrication of highly oleophobic and superhydrophobic surfaces on microtextured Al substrates

Theoretical calculations suggest that creating highly oleophobic surfaces would require a surface energy lower than that of any known materials. In the present work, we demonstrate microtextured Al substrate surfaces with vein-like micro-/nanostructures displaying apparent contact angles of >120°, even with nitromethane (surface tension γl = 37 mN m−1). The Al substrate was microtextured by a chemical solution mixed by zinc nitrate hexahydrate, hexamethyltetramine and a little hydrofluoric acid. A fluoroalkylsilane agent was used to tune the surface wettability. The Al substrates were microtextured by vein-like micro-/nanostructures and generated a solid/liquid/vapour composite interface. Combined with fluoroalkylsilane modification, the Al surfaces resulted in an oleophobicity with contact angle of 126·3° for nitromethane (152·7° for diethylene glycol and γl = 45·2 mN m−1). In addition, the Al surfaces demonstrated a low rolling off angle with <6° even for diethylene glycol. However, the nitromethane droplet favoured to pin on the sample surface even when the sample stage is tilted to 90°. It is noted that this highly oleophobic behaviour is induced mainly by topography, which forms a composite surface of air and solid with oil drop sitting partially on air. The results are expected to promote the study on self-cleaning applications, especially in the condition with oil contaminations.

Fabrication of superhydrophobic surfaces with hierarchical rough structures on Mg alloy substrates via chemical corrosion method

Superhydrophobic surfaces are commonly fabricated by a combination of hierarchical rough structures and low surface energy materials. The hierarchical rough structures of micrometre-scale lump-like structures and sub-micrometre-scale concave–convex structures were firstly and directly fabricated on the surfaces of magnesium (Mg) alloy plates by a simple chemical corrosion. Then, chemical modification with fluoroalkylsilane (FAS) and stearic acid was employed to decrease surface energy. Effect of the composition of chemical corrosive solution on the surface morphology was also studied. Results show that a good superhydrophobic surface on Mg alloy substrates with a 163.4° static water contact angle and 8° rolling angle was obtained via chemical corrosion and FAS modification. The chemicals NiSO4 and NaH2PO2 are both essential to fabricate the hierarchical rough structures needed by the superhydrophobic surfaces.

Tailoring the wettability of nanocrystalline TiO2 films

The water contact angle (WCA) of nanocrystalline TiO2 films was adjusted by fluoroalkylsilane (FAS) modification and photocatalytic lithography. FAS modification made the surface hydrophobic with the WCA up to ∼156°, while ultraviolet (UV) irradiation changed surface to hydrophilic with the WCA down to ∼0°. Both the hydrophobicity and hydrophilicity were enhanced by surface roughness. The wettability can be tailored by varying the concentration of FAS solution and soaking time, as well as the UV light intensity and irradiation time. Additionally, with the help of photomasks, hydrophobic–hydrophilic micropatterns can be fabricated and manifested via area-selective deposition of polystyrene particles.

Facile fabrication of flexible magnetic nanohybrid membrane with amphiphobic surface based on bacterial cellulose

Flexible magnetic membranes based on bacterial cellulose (BC) with amphiphobicity were prepared firstly by the in situ synthesis of the Fe3O4 nanoparticles on the BC nanofibers and then the fluoroalkyl silane (FAS) modification. X-ray diffraction (XRD) patterns indicated the Fe3O4 nanoparticles had a spinel structure and field emission scanning electron microscopy (FE-SEM) revealed the Fe3O4 nanoparticles were homogeneously deposited on the BC nanofibers. FT-infrared (FTIR) spectra and energy-dispersive spectrum (EDS) demonstrated the presence of FAS. After FAS modification on the magnetic BC membrane prepared by the in situ synthesis of the Fe3O4 nanoparticles, the surface wettability of BC membrane was converted from amphiphilicity to amphiphobicity. The fluorinated membrane with appropriate roughness showed the highest water contact angle (WCA) of 130° and oil contact angle (OCA) of 112°. Additionally, the magnetometric measurements revealed that the membranes exhibited the superparamagnetic behavior and can be magnetically actuated. Magnetically responsive BC membrane with hydrophobic and lipophobic surface would have potential applications in electronic actuators, magnetographic printing, information storage, electromagnetic shielding coating and anti-counterfeit.

Nanoparticle decorated fibrous silica membranes exhibiting biomimetic superhydrophobicity and highly flexible properties

Inspired by the self-cleaning lotus leaf, here we report the fabrication of flexible fluorinated silica nanofibrous membranes with biomimetic non-wettable surfaces by electrospinning blend solutions of poly(vinyl alcohol) (PVA) and silica gel in the presence of silica nanoparticles, followed by calcination and fluoroalkylsilane (FAS) modification. The resultant silica nanofibers exhibited a lotus-leaf-like structure with numerous nanoparticles decorated on the fiber surfaces due to the rapid phase separation in electrospinning and calcination processing. The content of silica nanoparticles incorporated into the fibers proved to be the key factor affecting the fiber surface morphology and wettability. The fluorinated silica fibrous membranes containing 38.8 wt% silica nanoparticle showed the highest water contact angle (WCA) of 155°, oil contact angle (OCA) of 143°, orange juice contact angle (OJCA) of 142°, and milk contact angle (MCA) of 137°. Additionally, the fluorinated silica membranes exhibited good flexibility and the flexibility was also characterized by KES-FB2S. We believe that this new class of inorganic membranes is particularly promising for the development of high-temperature filtration, novel easy-clean coatings, and even flexible electronics.

Tribological performance of fluoroalkylsilane modification of sol–gel TiO2 coating

This paper explores the possibility of making coatings with super friction-reducing and wear protection properties by using both sol–gel and self-assembling techniques. The thin film of TiO2 was firstly prepared on glass substrates via a sol–gel method, followed by sintering at 480°C. The self-assembled monolayer of Fluoroalkylsilane (FAS) were then prepared on TiO2 thin film to obtain TiO2–FAS dual-layer film. The contact angle measurement and X-ray photoelectron spectroscopy were used to determine the wetting behavior and chemical structure of films, respectively. The friction behavior of films sliding against a steel ball was examined on a macro friction and wear tester. It is shown that FAS is strongly adsorbed on sol–gel derived TiO2 thin film, making it strongly hydrophobic. Good friction-reducing and wear protection behavior is observed for the glass substrate after duplex surface-modification with sol–gel TiO2 and top layer of FAS.

Fabrication of Superhydrophobic Surfaces on Al Substrates for Anti-Adhesion and Self-Cleaning Applications

Superhydrophobic surfaces, which have anti-adhesion and self-cleaning properties, were fabricated on Al substrates. The self-cleaning surface was prepared by two steps: firstly, a chemical solution method was used to create the surface roughness with disorderly veins micronanostructures. Secondly, fluoroalkylsilane was deposited on the rough surface to lower its surface energy. The combination of veins micronanostructures and fluoroalkylsilane modification gave the surface a superhydrophobicity with static water contact angle of 166° and sliding angle of smaller than 1°. Additionally, the surface showed a strong anti-adhesion with water and a satisfied self-cleaning property. Water droplets easily rolled off the surface and picked up dirt and debris with them. The surfaces obviously corresponded to Cassie (not Wenzel) -model. Air entrapped within the veins microstructures greatly increases the air/water interface, effectively preventing the penetration of water into the grooves, and finally exhibiting the self-cleaning property. The results will greatly extend Al substrates for specific functions such as water-repellence, self-cleaning and anti-fouling.

Superoleophobic and Superhydrophobic Surfaces from Microtextured ZnO-Based Surfaces on Si Substrate

Theoretical calculations suggest that creating superoleophobic surfaces would require a surface energy lower than that of any known materials. In the present work, we demonstrate micronanostructured ZnO-based surfaces displaying apparent contact angles (CA) greater than 150, even with hexadecane (surface tension l = 27.5 mN/m). The specific ZnO microtextures were fabricated by a chemical solution method, and fluoroalkylsilane (FAS) was then used to tune the surface wettability. The combination of ZnO microtextures and FAS modification resulted in a superoleophobicity with CA for hexadecane was 154.6 (161.9 for diethylene glycol (l = 45.2 mN/m). This apparent superoleophobic behavior was induced on intrinsically oleophilic materials mainly by topography (i.e. the specific ZnO microtextures), which form a composite surface of air and solid with oil drop sitting partially on air. Such special wetting state is a metastable Cassie state. The results are expected to promote the study on self-cleaning applications, especially in the condition with oil contaminations.

Amphiphobic Nanofibrous Silica Mats with Flexible and High-Heat-Resistant Properties

In this study, for the first time, we fabricated flexible, high-heat-resistant, and amphiphobic mats by (fluoroalkyl)silane (FAS) modification of electrospun pure silica nanofibrous mats. The inorganic silica nanofibrous mats were obtained via electrospinning the blend solutions of poly(vinyl alcohol) (PVA) and silica gel, followed by calcination to remove the organic component. The PVA/silica and silica fibers were found to be randomly oriented as nonwoven mats with fiber diameters in the range of 150−500 nm. After the FAS modification, the surface wettability of the silica mats was converted from amphiphilic to amphiphobic. The fluorinated mat with the bead-on-string structure showed the highest water contact angle (WCA) of 154° and oil contact angle (OCA) of 144°. Additionally, the fluorinated inorganic fibrous mats exhibited a high heat resistance; they kept their hydrophobicity (WCA of 138°) and oleophobicity (OCA of 132°) even after the annealing treatment at 450 °C for 30 min. Potential application...

A cauliflower-like gold structure for superhydrophobicity

We present a two-step route to produce a hierarchical cauliflower-like gold structure that involves the adsorption of gold nanoparticles described by the random sequential adsorption (RSA) model, followed by the electrochemical growth on the surfaces of the primary gold nanoparicles. The structure was confirmed using scanning electron microscopy (SEM), energy dispersive spectrometer analysis (EDS), and X-ray diffraction (XRD). After fluoroalkylsilane modification, the cauliflower-like structured surface exhibits a high contact angle and a low sliding angle.

STICKY AND SLIPPY: TWO HYDROPHOBIC STATES TRANSITION OF ZnO HIERARCHICAL FILMS BY FLUOROALKYLSILANE MODIFICATION

ZnO films with hierarchical structures were prepared in an aqueous solution of zinc nitrate, hexamethylenetetramine and hydrofluoric acid. They demonstrated superhydrophobicity and two superhydrophobic states conversion from sticky to slippy after they were modified by fluoroalkylsilane (FAS) self-assemble layers. Before FAS modification, ZnO hierarchical structures, having sphere-like microstructures with nano-petals, showed water contact angle of 151° and a sticky behavior: water droplets rest on such surface did not slide when the surface was tilted to any angle or even upside down, indicating a strong adhesion between water and the surface. However, after FAS modification, ZnO films showed an increase of water contact angle up to 164° and a large difference in dynamic wetting properties: water droplets moved spontaneously and hardly came to rest even on a horizontal surface. The transition from sticky ("Wenzel's state") to slippy ("Cassie's state") resulted from surface free energy change from high to low. The results also confirm that the low enough surface energy, cooperating with surface roughness, is crucial in making Cassie's state superhydrophobicity. The realization of conversion from sticky to slippy is of importance for further understanding wetting properties and applications of ZnO micronanostructures.

Fabrication of a super-hydrophobic nanofibrous zinc oxide film surface by electrospinning

We report a new approach for fabricating a super-hydrophobic nanofibrous zinc oxide (ZnO) film surface. The pure poly(vinyl alcohol) (PVA) and composite PVA/ZnO nanofibrous films can be obtained by electrospinning the PVA and PVA/zinc acetate solutions, respectively. After the calcination of composite fibrous films, the inorganic fibrous ZnO films with a reduced fiber diameter were fabricated. The wettability of three kinds of fibrous film surfaces were modified with a simple coating of fluoroalkylsilane (FAS) in hexane. The resultant samples were characterized by field emission scanning electron microscopy (FE-SEM), water contact angle (WCA), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). It was found that the pure PVA fibrous films maintained the super-hydrophilic surface property even after the FAS modification. Additionally, the WCA of composite fibrous films was increased from 105 to 132° with the coating of FAS. Furthermore, the surface property of inorganic ZnO fibrous films was converted from super-hydrophilic (WCA of 0°) to super-hydrophobic (WCA of 165°) after the surface modification with FAS. Observed from XPS data, the hydrophobicity of FAS coated various film surfaces were found to be strongly affected by the ratio of fluoro:oxygen on the film surfaces.

Fabrication of Highly Antireflective Silicon Surfaces with Superhydrophobicity

Highly antireflective porous silicon surfaces with superhydrophobicity were obtained by means of chemical etching and fluoroalkylsilane self-assembly. The results show that wettability and reflectivity of these surfaces strongly depend on the etching method and the resultant surface morphology. All of the four resultant porous silicon surfaces by alkaline etching, acidic etching, thick Pt-assisted acidic etching, and thin Pt-assisted acidic etching can reduce reflectance, but the efficiency differs greatly. Except for the alkaline etching, the porous silicon surfaces produced by the other three etching methods can reach superhydrophobicity after fluoroalkylsilane modification. These differences are due to the different surface morphology and roughness. Moreover, the porous silicon surface produced by thin Pt-assisted acidic etching presents abundant holes and particles with diameters ranging from nanometers to submicrometers. This morphology enables the porous silicon surface to own a very low reflectance value that is averaged to be about 3% over the whole experimental photon wavelength spanning 300-800 nm.

Electrochemical Deposition of Conductive Superhydrophobic Zinc Oxide Thin Films

A simple method of electrochemical deposition was adopted to prepare conductive hydrophobic zinc oxide (ZnO) thin films. The surface structures were characterized by sanning electron microscopy (SEM) and atomic force microscopy (AFM). Wettability studies revealed that the surface of the as-prepared thin films showed a contact angle (CA) for water of 128.3 ± 1.7°, whereas the superhydrophobic surface with a water contact angle of 152.0 ± 2.0° was obtained by (fluoroalkyl)silane modification. The superhydrophobic conductive thin films materials may have potential use such as microfluidic devices in the future. It is likely that other oxide materials may be similarly prepared by this method.