On the surface roughness and hydrophobicity of dual-size double-layer silica nanoparticles

An array of double-layer silica nanoparticles with two different length scales was introduced onto the glass substrates for investigating the effect of surface morphology on wettability. Silica nanoparticles of 7, 12, 20, and 40 nm in diameters were individually functionalized using 3-aminopropyltriethoxysilane or 3-glycidoxypropyltrimethoxysilane. Silica nanoparticles functionalized with the complementary amine and epoxy groups were deposited alternately on glass surfaces to obtain durable and covalently bound dual-size double-layer silica nanoparticle coatings. Order of the deposition of nanoparticles for the fabrication of dual-size double-layer coatings was found to be the most determinant factor on surface roughness and hence the wettability. Deposition of the bigger nanoparticles on top of smaller ones resulted in rougher surfaces and consequently higher hydrophobicity. Based upon these findings, it is now possible to fine-tune surface roughness and subsequent wettability by controlling the size ratio of dual-size double-layer silica nanoparticles.     

Preparation and wettability examinations of transparent SiO2 binder-added MgF2 nanoparticle coatings covered with fluoro-alkyl silane self-assembled monolayer

SiO2-added MgF2 nanoparticle coatings with various surface roughness properties were formed on fused silica-glass substrates from autoclaved sols prepared at 100-180 °C. To give it hydrophobicity, we treated the samples with fluoro-alkyl silane (FAS) vapor to form self-assembled monolayers on the nanoparticle coating and we examined the wettability of the samples. The samples preserved good transparency even after the FAS treatment. The wettability examination revealed that higher autoclave temperatures produced a larger average MgF2 nanoparticle particle size, a larger surface roughness, and a higher contact angle and the roll-off angle.     

Fabrication and characterization of transparent superhydrophilic/superhydrophobic silica nanoparticulate thin films

The realization of transparent and superhydrophilic/superhydrophobic surfaces by silica nanoparticulate thin films was exploited in this work. An aqueous electrostatic layer-by-layer assembly process was utilized to fabricate nanoparticulate thin films with adhesion/body/top layer structure on glass substrates by using SiO₂ nanoparticles and polyelectrolytes. The effects of volume ratio of differently sized silica nanoparticle solutions for the body layer deposition on transmittance in visible light region and surface wettability of the nanoparticulate thin films were systematically studied. The experimental results revealed that both optical transparency and superhydrophobicity/superhydrophilicity can be achieved on the same SiO₂ nanoparticulate thin film by using appropriate volume ratios of differently sized silica nanoparticle solutions for body layer deposition, and with and without silane treatment in the fabrication process. The high contrast of wettability that can be achieved by this way suggests the possibility of the creation of superhydrophilic/superhydrophobic patterning and superhydrophilic-superhydrophobic gradient on the same surfaces.     

Synthesis of monodisperse fluorinated silica nanoparticles and their superhydrophobic thin films

Monodispersive silica nanoparticles have been synthesized via the Sto?ber process and further functionalized by adding fluorinated groups using fluoroalkylsilane in an ethanolic solution. In this process, six different sizes of fluorinated silica nanoparticles of varying diameter from 40 to 300 nm are prepared and used to deposit thin films on aluminum alloy surfaces using spin coating processes. The functionalization of silica nanoparticles by fluorinated group has been confirmed by the presence C-F bonds along with Si-O-Si bonds in the thin films as analyzed by Fourier transform infrared spectroscopy (FTIR). The surface roughnesses as well as the water contact angles of the fluorinated silica nanoparticle containing thin films are found to be increased with the increase of the diameter of the synthesized fluorinated silica nanoparticles. The thin films prepared using the fluorinated silica nanoparticles having a critical size of 119 ± 12 nm provide a surface roughness of ～0.697 μm rendering the surfaces superhydrophobic with a water contact angle of 151 ± 4°. The roughness as well as the water contact angle increases on the superhydrophobic thin films with further increase in the size of the fluorinated silica nanoparticles in the films.     

镁合金超疏水表面制备的研究进展

利用超疏水表面可望减少材料与液体介质的直接接触来提高材料的耐蚀性能,在制备自清洁表面等方面得到了广泛研究。超疏水表面一般通过构造一定表面粗糙度和用低表面自由能物质修饰表面而成。在简要概括固体表面润湿性理论的基础上,针对镁合金的特点,综述了当前镁合金上超疏水表面制备的最新进展,并讨论了提高其性能的可能途径和未来的发展方向。     

Effect of reflow temperature and substrate roughness on wettability,IMC growth and shear strength of SAC387/Cu bonds

The effect of reflow temperature and substrate surface roughness on wettability, intermetallics and shear strength of Sn–3.8Ag–0.7Cu solder alloy on copper (Cu) substrate was studied. It was found that increase in reflow temperature and substrate surface roughness improved the wettability of solder alloy. The size of needle shaped Cu₆Sn₅ IMCs (intermetallic compounds) increased with increase in temperature. The morphology of IMCs transformed from long to short needles with increase in substrate roughness. Shear strength and shear energy of the solder bond on rough Cu surfaces were found to be higher than that on smooth Cu surfaces. However, the sheared surfaces of the solder bond on rough Cu surface exhibited a transition ridge characterised by sheared IMCs whereas solder bond on smooth Cu surfaces exhibited completely ductile failure. Although, rough surface exhibited higher shear strength and shear energy, smoother surface is preferable due to its predominant bond failure in the solder matrix.     

Wetting behaviour of laser textured Ti3SiC2 surface with micro-grooved structures

In the present paper, micro-grooved Ti₃SiC₂ surfaces with different roughness were fabricated by pulsed laser processing. The surface topography and chemical composition of smooth and micro-grooved surfaces were characterised. The wetting behaviours of smooth and micro-grooved Ti₃SiC₂ surfaces such as static contact angle, anisotropic wettability and contact angle evolution versus time were investigated. The experimental results show that micro-grooved structures can be efficiently fabricated on Ti₃SiC₂ surface by laser processing. The contact angle of micro-grooved surface was increased by 64.2° compared with that of smooth surface. The difference values of contact angles between perpendicular and parallel direction were <?10°. The wetting state of droplet on textured surface was close to Cassie–Baxter model.     

Transforming an intrinsically hydrophilic polymer to a robust self-cleaning superhydrophobic coating via carbon nanotube surface embedding

A single-step method, including surface embedding of nanoparticles into a polymer matrix, was employed to fabricate superhydrophobic thermoplastic polyurethane (TPU)/carbon nanotube (CNT) nanocomposite coatings. The main aim was to prove that surface roughness plays a more important role in designing superhydrophobic surfaces as compared with the surface energy. Therefore, TPU was used as the model hydrophilic polymer and CNTs were employed as non-hydrophobic nanoparticles. It was found that, at a certain pressing time, CNTs form an efficient hair-like morphology which is able to highly enclose air within its as-formed pores leading to superhydrophobic behavior. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and confocal microscopy were utilized for characterization of samples. SEM and confocal microscopy results proved that surface roughness played the key role in the final wettability behavior. Based on XPS results, it was also found that a very long pressing time led to partial migration of TPU macromolecules into the CNTs' pores, and hence, superhydrophobicity was reduced. The effects of mechanical abrasion and nanoparticle type on wettability behavior of samples were evaluated as well. In conclusion, it is suggested that surface roughness factor should be highly considered in designing superhydrophobic nanocomposite coatings rather than surface energy.     

Characterization of silica-coated Ag nanoparticles synthesized using a water-soluble nanoparticle micelle

This article describes the synthesis of silica-coated Ag nanoparticles using a water-soluble nanoparticle micelle under basic conditions. Monodispersed Ag nanoparticles with a mean particle size of 7 nm were synthesized using AgNO₃ in the presence of ascorbic acid as a reducing agent. The Ag nanoparticles were easily re-dispersed into an aqueous solution by surface adsorption of surfactant molecules, indicating formation of water-soluble nanoparticle micelles. Silica-coated Ag nanoparticles ranging in size from 50 to 100 nm were obtained by controlling the surfactant, Ag nanoparticle and tetraethylortho silicate (TEOS) concentrations. Adsorbed surfactant monolayers on Ag nanoparticles were used as a template for the silica shell because of the hydrophobicity of TEOS. In all cases, the size of the resulting particles increased linearly as these concentrations increased. Based on transmission electron microscopy, all the Ag nanoparticles were completely covered with a silica shell. In most samples, however, Ag nanoparticle size increased from 7 to 50 nm due to evaporation of hexane by heating. Although mean particle size of silica-coated Ag nanoparticles was drastically altered, characteristic absorption peaks were observed at approximately 410 nm.     

Wettability control by laser texturing process generating localized gold nanoparticles on polymeric thin films

In this work a new approach is introduced for surface properties control by laser texturing process. By UV laser irradiation, we are able to control the surface wettability of a chitosan polymeric film in which is introduced a chloroauric acid salt by immersion. Specifically the UV irradiation is responsible for the creation of gold nanoparticles at the irradiated surface of the polymeric film. This photolytic process allows us to localize and design accurately surface patterns and moreover to tune metallic particle size in the range of nanoscale. After the characterization of our gold textured surfaces by atomic force and scanning electron microscopies, we demonstrate the link between wettability surface properties and gold nanoparticles size. The experimental results indicate the influence of the laser intensity, the irradiation time and the polymer film thickness (by increasing the gold concentration) on the gold nanoparticle density and size.     

Effect of temperature and substrate surface texture on wettability and morphology of IMCs between Sn–0.7Cu solder alloy and copper substrate

In the present work, the effect of soldering temperature (270 and 298?°C) and substrate surface texture (0.02 and 1.12?μm) on wetting characteristics and morphology of intermetallic compounds (IMCs) between Sn–0.7Cu lead-free solder on copper substrates was investigated. It was found that increase in temperature and substrate surface roughness improved the wettability of solder alloy. However, the effect of surface roughness on wettability was significant as compared to that of temperature. The spreading of solder alloy was uniform on smooth substrate, whereas spreading of the alloy on rough substrate resulted in an oval shape. The morphology of IMCs transformed from long needle shaped to short and thick protrusions of IMCs with increase in surface roughness of the substrate. Needle shaped and thick protruded intermetallics formed at the solder/Cu interface were identified as Cu₆Sn₅ compounds. The formation of Cu₃Sn IMC was observed only for the spreading of solder alloy at 298?°C which contributed to improvement in the wettability of solder alloy on both smooth and rough substrate surfaces.     

Molecular dynamics simulation of the forces between colloidal nanoparticles in Lennard–Jones and <Emphasis Type="Italic">n</Emphasis>-decane solvent

Molecular-dynamics is utilized to simulate solvation forces between two nanoparticles immersed in two different solvents: Lennard–Jones spheres and and n-decane. Three different sizes and shapes of solvophilic nanoparticles are investigated. Nanoparticles in the Lennard–Jones liquid exhibit solvation forces that oscillate between attraction and repulsion as the nanoparticle separation increases. The magnitude of these solvation forces increases with particle size and depends on particle shape, consistent with the Derjaguin approximation. When n-decane is the solvent, the solvation forces are negligible for small nanoparticles, with sizes comparable to the end-to-end distance of all-trans decane. The solvation forces oscillate between attraction and repulsion for sufficiently large nanoparticles in decane—however the Derjaguin approximation does not appear to be effective at describing the dependence of nanoparticles forces on nanoparticle size and shape when decane is the solvent. For both the Lennard–Jones and n-decane solvents, it is apparent that the force profiles are influenced by the surface roughness of the nanoparticles. These factors should be taken into account in efforts to engineer colloidal suspensions.     

Roughness-enhanced thermal-responsive surfaces by surface-initiated polymerization of polymer on ordered ZnO pore-array films

The correlation between stimuli-responsive wettability switching and surface morphology of poly(N-isopropylacrylamide) (PNIPAm)-modified ZnO pore-array surface is studied. PNIPAm is grafted to the ZnO pore-array surface by surface-initiated polymerization. The effects of thickness of the PNIPAm layer and surface morphology on the thermally responsive switching behavior of the PNIPAm-modified films were studied considering the influences 3D capillary effect (Wenzel's model) and air trapping effect (Cassie's model). The air trapping effect can be controlled by the pore size, amount of grafted PNIPAm polymer, and shape of the pore edge. The surface roughness and expanded pore edge with mushroom-like texture of S2 film amplify the thermally responsive wettability switching between hydrophilicity and hydrophobicity. When the pore structure is completely filled, the switching properties get lower. The thermally responsive switching behavior is enhanced with increasing molecular chain length of the PNIPAm. By controlling the ZnO pore-array structure and the amount of grafted PNIPAm layer, the S2 film shows excellent reversibility for more than 3 cycles and a quick transformation between hydrophilicity and hydrophobicity.     

Microscale bone grinding temperature by dynamic heat flux in nanoparticle jet mist cooling with different particle sizes

Nanoparticle jet mist cooling (NJMC) is an effective solution to prevent heat injuries in clinical neurosurgery bone grinding. A simulation study on temperature field of microscale bone grinding was performed to discuss the effect of nanoparticle size on heat convection during this cooling method by the dynamic heat flux density model. Such dynamic heat flux density model was established through real-time acquisition of grinding force signals. Results showed that given the real-time dynamic heat flux, workpiece surface temperature changes with time. Nanofluids using 30?nm nanoparticles show the largest heat convection coefficient (1.8723?W/mm²?·?K) and the lowest average surface temperature followed by nanofluids of 50, 70, and 90?nm nanoparticles successively. An experimental verification using fresh bovine femur was conducted with 2% (volume fraction) of different sizes of Al₂O₃ nanoparticles. The simulated temperature under dynamic heat flux comes close to the actual measured temperature. Under testing conditions, temperature under mist cooling is 33.6°C, temperatures under NJMC using nanofluids (30, 50, 70, and 90?nm) are 21.4, 17.6, 16.1, and 8.3% lower, respectively. This result confirmed the positive correlation between the average workpiece surface temperature and nanoparticle size. Experimental results agreed with theoretical analysis, verifying the validity of theoretical modeling.     

Scaling properties of mortar fracture surfaces

Scaling properties of mortar crack surfaces are studied from mode I fracture specimens of six different sizes. Fracture surfaces initiated from a straight notch exhibit an anomalous dynamic scaling which involves two independent roughness indices: the universal local roughness exponent ζ_loc ≈ 0.8 and the global roughness exponent, estimated to ζ ≃ 1.35. We show that there exists a linear relationship between the specimen size and the maximum self-affine correlation length inducing a size effect on the roughness magnitude at saturation and this especially for the smallest length scales. Finally, we argue that anomalous roughening could be an inheritance of the changes in long range elastic interactions which take place in the fracture process zone of quasibrittle materials.     

CeO2 nanocrystals: Seed-mediated synthesis and size control

This work reports on seed-mediated synthesis and size control of monodispersed CeO₂ nanoparticles. CeO₂ nanoparticles of mean size smaller than 2 nm were first prepared by a simple mixing of aqueous solution of cerium (IV) sulfate and ammonia solution at ambient conditions. Using these as-prepared fine particles as the tiny seeds, tunable sizes of CeO₂ nanoparticles were achieved via a facile hydrothermal treatment. All samples were characterized by X-ray diffraction (XRD), infrared (IR) spectroscopy, UV-vis spectroscopy, and thermogravimetric analysis (TGA). It is shown that in comparison with other inorganic cerium salts such as cerium (III) nitrates, cerium (IV) sulfate appears more suitable for forming CeO₂ nanoparticles at room temperature. Sulfate groups are strongly thermodynamically adsorbed on CeO₂ nanoparticle surfaces. The formation mechanism, surface hydration and sulfation characteristics of the resulting CeO₂ nanoparticles are also discussed.     

Hydrophobic properties of polytetrafluoroethylene thin films fabricated at various catalyzer temperatures through catalytic chemical vapor deposition using a tungsten catalyzer

Using the catalytic chemical vapor deposition (Cat-CVD) method, polytetrafluoroethylene (PTFE) thin films were fabricated on Si(100) substrates at various catalyzer temperatures, using a tungsten catalyzer, and Fourier transform infrared (FTIR) spectroscopy and X-ray photoemission spectroscopy (XPS) were used to confirm the fabrication of the films. An atomic-force microscope (AFM) and a scanning electron microscope (SEM) were employed to study the correlation between the wettability and surface morphology of the samples. It was found that the wettability of the PTFE thin films fabricated via Cat-CVD is strongly correlated with the sizes of the film surfaces' nanoprotrusions, and that superhydrophobic PTFE thin-film surfaces can be easily achieved by controlling the sizes of the nanoprotrusions through the catalyzer temperature. The comparison of the wettability values and surface morphologies of the films confirmed that nanoscale surface roughness enhances the hydrophobic properties of PTFE thin films. Further, the detailed analysis of the films' surface morphologies from their AFM images with the use of the Wenzel and Cassie models confirmed that the nanoscale surface roughness enhanced the hydrophobic property of the PTFE films. Further, the variations of the wettability of the PTFE thin films prepared via Cat-CVD are well explained by the Cassie model. It seems that the increase in the trapping air and the reduction of the liquid-solid contact area are responsible for the superhydrophobicity of the PTFE thin films prepared via Cat-CVD.     

Air plasma treatment of copper sheets using Diffuse Coplanar Surface Barrier Discharge

The treatment of copper sheets by atmospheric-pressure air plasma generated using the Diffuse Coplanar Surface Barrier Discharge was studied. The surface free energy measurements indicated a significant increase of the wettability after several seconds of plasma exposure. The atomic force microscopy technique revealed a relatively small increase of the surface roughness due to the plasma treatment. The observed increase of wettability, the influence of air humidity on treatment efficiency and the hydrophobic recovery of the plasma treated surfaces were studied by the x-ray photoelectron spectroscopy. A generation of surface -NO_x groups in humid air plasma was observed.     

Hydrophobicity study of polytetrafluoroethylene nanocomposite films

In the present work, inorganic fullerene-like tungsten disulfide (IF-WS₂) nanoparticles have been incorporated into polytetrafluoroethylene films using aerosol-assisted deposition process. The hydrophobic behavior of the nanocomposite film has been investigated and the result shows that the hydrophobicity of PTFE films can significantly be improved with the incorporation of IF-WS₂ nanoparticles. An oblate spheroid model which takes into the consideration of surface roughness effect has been proposed, to simulate the hydrophobic behavior, based on the surface roughness and peak density of the nanocomposite films. This hydrophobic model can provide a useful guideline to describe and predict the hydrophobicity of nanocomposite films, from the input of parameters such as surface energy, roughness and liquid properties.     

Facile tuning of superhydrophobic states with Ag nanoplates

GaAs wafers have been decorated with Ag nanoplates through direct galvanic reaction between aqueous AgNO₃ solutions and GaAs, resulting in Ag nanoplate/GaAs composite surfaces with varying hydrophobocity after the Ag nanoplates are coated with self-assembled monolayers of alkyl thiol molecules. By carefully controlling the reaction conditions, such as growth time and concentration of the AgNO₃ solution, the size, thickness, and surface roughness of the individual Ag nanoplates can be tuned in order to produce different topographic structures and roughness of the composite surfaces, which in turn infl uences the hydrophobicity of the surfaces. The as-synthesized composite surfaces have been found to exhibit various levels of hydrophobicity and different wetting states such as the Wenzel wetting state, Cassie impregnating wetting state, and Cassie nonwetting state. The relationship between surface structure and hydrophobic state is also discussed. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com