Fabrication and characterization of superhydrophobic silica nanotrees

Superhydrophobic silica nanotrees were obtained by sol–gel method with hybrid silica sol and jelly-like resorcinol formaldehyde resin. Rough surfaces were obtained by removing the organic polymer at high temperature. After the films with rough surface were modified by trimethylchlorosilane (TMCS), the wettability of the film changed from superhydrophilic to superhydrophobic. The surface roughness of the silica nanotrees film is about 20 nm, and it is transparent and superhydrophobic with a water contact angle higher than 150°.     

Fabrication of highly transparent superhydrophobic coatings from hollow silica nanoparticles

We herein report a simple and effective method to fabricate excellent transparent superhydrophobic coatings. 3-Aminopropytriethoxysilane (APTS)-modified hollow silica nanoparticle sols were dip-coated on slide glasses, followed by thermal annealing and chemical vapor deposition with 1H,1H,2H,2H-perfluorooctyltrimethoxysilane (POTS). The largest water contact angle (WCA) of coating reached as high as 156° with a sliding angle (SA) of ≤2° and a maximum transmittance of 83.7%. The highest transmittance of coated slide glass reached as high as 92% with a WCA of 146° and an SA of ≤6°. A coating simultaneously showing both good transparency (90.2%) and superhydrophobicity (WCA: 150°, SA: 4°) was achieved through regulating the concentration of APTS and the withdrawing speed of dip-coating. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) were used to observe the morphology and structure of nanoparticles and coating surfaces. Optical properties were characterized by a UV-visible spectrophotometer. Surface wettability was studied by a contact angle/interface system. The effects of APTS concentration and the withdrawing speed of dip-coating were also discussed on the basis of experimental observations.     

Fabrication of compact silver nanoshells on polystyrene spheres through electrostatic attraction

Nanoshells composed of close-packed silver nanocrystals have been fabricated on polystyrene spheres via direct electrostatic attraction at appropriate pH; the thickness and roughness of the shell can be readily controlled through a layer-by-layer technique.     

Surface-anisotropic polystyrene spheres by electroless deposition

Surfaces of sulfate-terminated polystyrene microspheres are anisotropically modified with silver nanoparticles covering 20-50% of the sphere surface using electroless deposition. A PDMS templating method is employed. Silver nanoparticles are found to deposit uniformly onto the exposed sphere surfaces. The deposition is diffusion-controlled and the nanoparticles adhere strongly to the polystyrene particles despite extensive exposure to ultrasonication. Silver content is confirmed by EDAX analysis. The final silver coverage is controlled via the PDMS pre-curing conditions.     

Fabrication of polystyrene/upconversion nanocrystals nanocomposite spheres through in situ dispersion polymerization

This paper presents a feasible and efficacious procedure to synthesize polystyrene/upconversion nanocrystals (PS/UCNCs) nanocomposite spheres with raspberry-like structure via an in situ dispersion polymerization technique. During this process, polyacrylic acid (PAA) as stabilizer plays the key role in adsorbing UCNCs, including NaYF(4):Yb(3+)-Er(3+), NaYF(4):Yb(3+)-Tm(3+) and NaYF(4):Yb(3+)-Ho(3+) onto the PS surfaces. TEM and SEM images confirmed the raspberry-like morphology of the obtained nanocomposite spheres. The effect of synthetic conditions, for instances, PAA amount, type and concentration of UCNCs on the structure and fluorescence of the PS/UCNCs nanocomposite spheres were studied in detail.     

Highly transparent superhydrophobic thin film with low refractive index prepared by one-step coating of modified silica nanoparticles

An easy and effective method to prepare superhydrophobic thin film has been developed. The film with optically transparent and low refractive index was composed by one-step coating with modified silica nanoparticles. The silica nanoparticles were prepared by sol–gel process of hydrolysis and condensation of alkoxysilane compounds and then surface modification silica nanoparticles, 50 ± 10 nm, were accomplished using methoxytrimethylsilane (MOTMS). Water contact angle of film increased with the weight of MOTMS of silica sol. When the weight of MOTMS was optimized, the water contact angle and sliding angle of film were 152.8° and less than 10°, respectively. The transmittance of film was also increased as compared to the un-coated microscope glass slide, from 91 to 93.5 %. The refractive index of the film was approximately 1.09 as measured by ellipsometer. The superhydrphobic thin film was also successfully made by using spray coating and the water contact angle of this film was more than 160°. Surface morphology of difference coating methods, dip and spray, were studied. Our result suggests that the film can be applied for superhydrophobicity and optical applications.     

Fabrication linalool-functionalized hollow mesoporous silica spheres nanoparticles for efficiently enhance bactericidal activity

To develop a novel food preservation technology for efficiently enhance bactericidal activity in a long term, hollow mesoporous silica spheres (HMSS) with regular nanostructures were applied to encapsulate natural organic antimicrobial agents. The chemical structures, morphologies and thermal stabilities of linalool, HMSS and linalool-functionalized hollow mesoporous silica spheres (L-HMSS) nanoparticles were evaluated by polarimeter, field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), fourier transform infrared (FT-IR), thermal gravimetric analyzer (TGA), nitrogen adsorption-desorption, zeta potential and small angle X-ray diffraction (SXRD). The results show that the linalool was successfully introduced into the cavities of HMSS, and the inorganic host exhibited a high loading capacity of about 1500 mg/g. In addition, after 48 h of incubation, the minimum bactericidal concentrations (MBC) of L-HMSS against Escherichia coli (E. coli), Salmonella enterica (S. enterica) and Staphylococcus aureus (S. aureus), Listeria monocytogenes (L. monocytogenes) were decreased to be 4 (< 5) mg/mL and 8 (< 10) mg/mL, respectively. These results revealed linalool-functionalized hollow mesoporous spheres could efficiently improve the bactericidal activities of the organic component. Furthermore, SEM images clearly showed that L-HMSS indeed had an extremely inhibitory effect against gram-negative (E. coli) and gram-positive (S. aureus) by breaking the structure of the cell membrane. This research is of great significance in the application of linalool in nano-delivery system as well as food industry.     

Fabrication of hollow silica spheres using droplet templates derived from a miniemulsion technique

Hollow silica spheres have been successfully fabricated by means of a miniemulsion technique, in which miniemulsion droplets of tetraethoxysilane (TEOS) and octane were prepared with cetyltrimethylammonium bromide as a surfactant and hexadecane as a costabilizer and used as templates. As the TEOS diffused out from the droplets, it was hydrolyzed and condensed to form a silica shell at the oil/water interface. In this way, hollow silica spheres could be obtained directly since the miniemulsion droplets of octane could be evaporated very easily during the reaction process or the drying process; neither an additional dissolution nor a calcination process or additional surface modification of the templates were needed.     

Facile fabrication of hollow silica and titania microspheres using plasma-treated polystyrene spheres as sacrificial templates

By means of a plasma technique, the surfaces of monodisperse polystyrene (PS) colloids have been modified with hydroxyl groups. Using these surface-modified PS colloids as sacrificial templates, we have fabricated silica-coated PS colloids (PS@silica) and titania-coated PS colloids (PS@titania) composite microspheres as well as hollow and mesoporous silica and titania microspheres. This process not only demonstrated a facile, low-cost, environmentally benign way to fabricate hollow oxides structures but also offered a feasible alternative to the preparation of polymer/inorganic oxide composites by templating against the polymer substrate with hydrophobic surfaces.     

Synthesis of silica hollow spheres assisted by ultrasound

A simple and effective method for synthesizing silica hollow spheres is presented. The synthesis utilizes vesicles from oppositely charged surfactants sodium dodecyl sulfate (SDS) and tetrapropylammonium bromide (TPAB) aqueous solution as template for the silica growth. Tetraethyl orthosilicate (TEOS) is added to the vesicular template as a precursor for the silica formation. Ultrasound was employed to accelerate the formation of vesicles template. The morphology of the silica spheres is uniform and well-defined (diameter: 200 nm-5 microm, wall thickness: 50 nm). The product was also characterized by FTIR, TG-DTA, N2 adsorption. TEM images reveal that the spheres have structure stability after calcinations at 550 degrees C.     

Fabrication of silica nanoparticles and hollow spheres using ionic liquid microemulsion droplets as templates

Silica products with two different morphologies were synthesized using nonaqueous ionic liquid microemulsion droplets as templates. The morphologies of the obtained products were characterized by both transmission electron microscopy (TEM) and scanning electron microscopy (SEM). By adjusting the reaction conditions, ellipsoidal nanoparticles were formed under acidic conditions, while hollow silica spheres were obtained under alkaline conditions. It is demonstrated that the size distribution of hollow silica spheres was narrower than that of the ellipsoidal nanoparticles. The various vibration modes of different functional groups in the silica materials were revealed by Fourier transform infrared (FTIR) spectroscopy. The two samples were both shown to be amorphous, not crystalline by X-ray diffraction (XRD). A simple diagram of the formation process including the hydrolysis and condensation reactions is given. Furthermore, a probable mechanism for the formation of silica materials under acidic or alkaline conditions is presented, which may be helpful for better understanding the different silica materials obtained under different conditions.     

Fabrication of superhydrophobic surfaces of n-hexatriacontane

Superhydrophobic surfaces of n-hexatriacontane were fabricated in a single-step process. The low surface energy of n-hexatriacontane together with the randomly distributed micro- and nanoscale roughness features guarantees very large contact angles and a small roll-off angle for water drops. The advantage of n-hexatriacontane superhydrophobic surfaces is their stability in the sense that they are impervious to chemical reactions and retain their wetting characteristics over a long period of time, as confirmed by XPS analysis and contact angle measurements.     

Colloidal crystals formed by aqueous suspensions of monodispersed silica, polystyrene, and poly(methyl methacrylate) colloidal spheres

Colloidal crystals consisted of silica, polystyrene, and poly(methyl methacrylate) monodispersed suspensions; deionized sufficiently in water at the same condition; were formed; and their properties were compared changing sphere diameter and volume fraction systematically. The size of these colloidal crystals was maximized at their critical sphere concentration irrespective of their sphere size. The Bragg peak wavelengths of these colloidal crystals were uniquely determined only by the sphere diameter and volume fraction for all kinds of colloidal spheres used in this work. The larger the sphere volume fraction, the larger the crystal growth rates, and there were no significant differences among the colloidal spheres. The rigidity of colloidal crystals increased in proportion to the number density of spheres. Consequently, the crystallization mechanism and properties of colloidal crystals formed by these spheres are not dependent on the kind of spheres, but they are dependent only on the sphere diameter and number density.     

Antibacterial fluorinated silica colloid superhydrophobic surfaces

A superhydrophobic xerogel coating synthesized from a mixture of nanostructured fluorinated silica colloids, fluoroalkoxysilane, and a backbone silane is reported. The resulting fluorinated surface was characterized using contact angle goniometry, scanning electron microscopy (SEM), and atomic force microscopy (AFM). Quantitative bacterial adhesion studies performed using a parallel plate flow cell demonstrated that the adhesion of Staphylococcus aureus and Pseudomonas aeruginosa was reduced by 2.08 ± 0.25 and 1.76 ± 0.12 log over controls, respectively. This simple superhydrophobic coating synthesis may be applied to any surface, regardless of geometry, and does not require harsh synthesis or processing conditions, making it an ideal candidate as a biopassivation strategy.     

Fabrication of superhydrophobic surfaces by self-assembly and their water-adhesion properties

The self-assembled films of methyloctyldimethoxysilane (MODMS) and fluorooctylmethyldimethoxysilane (FODMS) were prepared on silicon surfaces and evaluated with AFM, water contact angle measurement, and X-ray photoelectron spectroscopy. Superhydrophobic surfaces were obtained by cooperation of MODMS and FODMS self-assembly with surface roughening. The results showed that preparing closely packed self-assembled films and fabricating surface nanometer-scale and micrometer-scale binary roughness can achieve superhydrophobic films with a water contact angle larger than 156 degrees. The difference between solution deposition and chemical vapor deposition is also investigated. Moreover, superhydrophobic surfaces created with MODMS and FODMS show the different water-adhesion effects, which could have great significance on liquid microtransport in microfluid devices.     

Hollow titania spheres with movable silica spheres inside

We demonstrate a flexible method for preparing hollow TiO2 nanospheres with movable silica nanoparticles inside (HTNMSNs). In this method, we used monodisperse silica--polystyrene core--shell nanospheres (SiO2-PS-CSNs) sulfonated as templates and prepared the composite shell consisting of TiO2 and sulfonated polystyrene (SPS) through adsorbing or depositing tetrabutyl titanate gel into the SPS shell. Finally the HTNMSNs were obtained after removal of all polymers in the composite nanospheres by dissolution or calcinations. We investigated the dependence of the morphologies of HTNMSNs on the thickness of PS shells and the size of SiO2 cores and prepared rare earth doped HTNMSNs by a sol-gel process.     

Fabrication of uniform magnetic nanocomposite spheres with a magnetic core/mesoporous silica shell structure

A novel kind of magnetic core/mesoporous silica shell nanospheres with a uniform particle diameter of ca. 270 nm was synthesized. The inner magnetic core endues the whole nanoparticle with magnetic properties, while the outer mesoporous silica shell shows high enough surface area and pore volume. The synthesized material is expected to be applied to targeted drug delivery and multiphase separation. The storage and release of ibuprofen into and from the pore channels of the mesoporous silica shell, as a typical example, are demonstrated.