Layer Of Silica Nanoparticles Research Articles

Self-cleaning behavior in polyurethane/silica coatings via formation of a hierarchical packed morphology of nanoparticles

In the current research, a hierarchical morphology comprising of packed assembly of nanoparticles was induced in thermoplastic polyurethane (TPU)/silica nanocomposite coatings in order to achieve self-cleaning behavior. Moderately hydrophilic behavior of TPU hinders its transforming to a superhydrophobic material. In the presented method, a very thin layer of silica nanoparticles is applied to the surface of TPU sheets under elevated temperature and pressure. As temperature and pressure of the process remain unchanged, processing time was considered as a main variable. Based on scanning electron microscopy and confocal microscopy results, it was found that at a certain processing time, nanoparticles can form an utterly packed morphology leading to a self-cleaning behavior. Once the process was prolonged, TPU macromolecules found the chance to migrate onto the coating's top layer due to the enhanced mobility of chains at high temperature. This observation was further proved by X-ray photoelectron spectroscopy analysis and cross-sectional morphology. The presented method has promising potentials in transforming intrinsically hydrophilic polymers into superhydrophobic materials with self-cleaning behavior.

A robust smart window: reversibly switching from high transparency to angle-independent structural color display.

A smart window is fabricated from a composite consisting of elastomeric poly(dimethylsiloxane) embedded with a thin layer of quasi-amorphous silica nanoparticles. The smart window can be switched from the initial highly transparent state to opaqueness and displays angle-independent structural color via mechanical stretching. The switchable optical property can be fully recovered after 1000 stretching/releasing cycles.

A facile spraying method for fabricating superhydrophobic leather coating

Abstract A facile spraying method was developed to fabricate superhydrophobic leather coating. The coating was obtained by spraying polyacrylate emulsion and followed by spraying ethanol dispersion of hydrophobic silica nanoparticles. The hydrophobicity of the obtained coating could be tuned by varying the number of spraying layers of hydrophobic silica nanoparticles. The coating was universal on other cellulose-based substrates.

Dilational rheology of spread and adsorbed layers of silica nanoparticles at the liquid-gas interface

This short review is devoted to recent achievements in studies of the dilational surface rheological properties of the systems containing complexes of silica nanoparticles with conventional surfactants. It is shown that there is a surfactant concentration range where the dynamic surface elasticity reaches extremely high values up to 1000 mN/m. This result can explain the formation of very stable foams and emulsions containing nanoparticles. In some surfactant concentration ranges the adsorption layer is characterized by a non-linear response to small compressions or expansions of the liquid surface. Possible causes of this behavior and the mechanism of main relaxation processes are briefly discussed.

Dilational Rheology of Spread and Adsorbed Layers of Silica Nanoparticles at the Liquid–Gas Interface

Dilational Rheology of Spread and Adsorbed Layers of Silica Nanoparticles at the Liquid–Gas Interface

Ordered multilayer silica-metal nanocomposites for second-order nonlinear optics

We use aerosol synthesis to fabricate ordered metal-silica nanocomposites consisting of alternating layers of pure silica and silica nanoparticles decorated with silver nanodots. These multilayer structures preserve the narrow plasmon resonance of the nanodots even for high optical densities and allow second-harmonic generation due to spontaneous symmetry breaking arising from the interfaces between silica and nanoparticle layers. Our concept opens up perspectives for complex structures for advanced optical applications.

Facile Preparation of Raspberry-Like Superhydrophobic Polystyrene Particles via Seeded Dispersion Polymerization

A simple and facile approach was developed to fabricate raspberry-like or snowman-like particles via seeded dispersion polymerization by just changing the ratio of second monomer styrene (St) to seeds in which poly(styrene-co-hydrolyzed-methacryloxypropyltrimethoxysilane) [P(St-co-MPS)] latex was used as seeds with hydrolyzed-MPS as a cross-linking agent. The morphologies of final products were confirmed by field-emission scanning electron microscopy and transmission electron microscopy. Interestingly, the seed part of snowman-like particles showed raspberry-like with adsorbing quantities of PS particles while the other part smooth. The formation mechanism of the raspberry-like particles was also discussed. The superhydrophobic surface with both the static contact angle of 158° and high adhesion to water could be achieved by the hydrophobization of the particulate film with octadecyltrimethoxysilane that was formed from the raspberry-like particles decorated by a thin layer of silica nanoparticles. Further, through encapsulating Ag nanoparticles within the surface, the obtained raspberry-like PS/Ag/SiO2 nanocomposite particles exhibited excellent antibacterial property simultaneously.

Bistable liquid crystal devices with nanoparticle-coated polyimide alignment films

Bistable hybrid-aligned nematic (HAN) liquid crystal devices (LCDs) with silica nanoparticle-coated polyimide alignment films were investigated. It was observed that the existence of the internal electric field produced from the triboelectrically charged silica nanoparticles layer and impurity ions in the LC reduced the total free energy of the HAN-LCD and stabilized the cell in the homeotropic state. The stable homeotropic state can be switched back to the HAN state by changing the ion distribution through a voltage pulse with proper polarity. The capability of controlling bistability through modification of ion density in the LC layer may have some applications, such as displaying a one-time password requiring a specific stable time.

Templated Nanopores for Robust Functional Surface Porosity in Poly(methyl methacrylate)

A novel "sink and etch" technique is used to generate stable surface nanoporosity in poly(methyl methacrylate). Layer-by-layer assembly is first used to conformally coat PMMA substrates with a uniform layer of silica nanoparticles. Thermal annealing is then applied to cause sinking and engulfment of the silica nanoparticles into the thermoplastic PMMA surface. By selectively etching away the layer of embedded silica nanoparticles, a conformal porous layer of inversely templated structure can be obtained in the PMMA surface. Characterization with atomic force microscopy shows that a variety of nanoporous surface morphologies can be achieved simply by controlling the duration and temperature of thermal annealing. The nanoporous surfaces consisting of either as assembled silica nanoparticles or templated inverse porosity in PMMA were compared in terms of their antireflective (AR) properties. Measuring AR properties provided a quantitative means to compare the stability of these porous AR surfaces before and after several cleaning cycles. Our results show that while both types of surface porosity can provide excellent AR properties (optimized for 300-400 nm), the porous layer generated by the "sink and etch" technique showed superior mechanical stability.

Ultrasound assisted deposition of silica coatings on titanium

We present a novel ultrasound assisted method for silica coating of titanium surfaces. The coatings are formed by “smashing” silica nanoparticles onto activated titanium surface in solution using intense ultrasonic field. Homogeneous silica coatings are formed by deposition of dense multiple layers of silica nanoparticles. Since the nanoparticles also grow during the reaction, the layers of the coatings have smaller particles on the substrate and larger particles towards the surface. The thickness of the coatings can be controlled with several experimental parameters. Silica layers with thickness over 200nm are readily obtained.

Selectively transparent and conducting photonic crystal solar spectrum splitters made of alternating sputtered indium-tin oxide and spin-coated silica nanoparticle layers for enhanced photovoltaics

Selectively-transparent and conducting photonic crystals (STCPCs) made of alternating layers of sputtered indium-tin oxide (ITO) and spin-coated silica (SiO2) nanoparticle films exhibit Bragg-reflectance peaks in the visible spectrum of 95% reflectivity and have a full width at half maximum that is greater than 200nm. At the same time, their conductive properties are comparable to that of solid sputtered ITO films. Moreover, the average transmission of the STCPCs in the pass-band can be increased to ∼88%, or within 3.3% of the bare glass slide they are fabricated on. Furthermore, we also show that these STCPCs can readily be fabricated on textured surfaces similar to those used for micromorph solar cells. In this context wave optics analysis shows that these STCPCs can be utilized as intermediate reflectors that boost the relative photo-current generated in textured micromorph cells by more than 20% over a broad range of incident angles.

Reorganization of Langmuir–Blodgett layers of silica nanoparticles induced by the low energy, high fluence ion irradiation

The Langmuir–Blodgett (LB) layers with different selforganization of small, medium, and large size silica nanoparticles, when exposed to the low energy, high fluence ion beam, show reorganization. The reorganization appears as the net effect between the forces caused by charging and by heating of particles, whereas the Coulomb repulsive force between the particles overcomes their adhesion to the Si substrate. The threshold force was estimated for the case of small thermal effects (solid particle on the solid substrate), of higher thermal effects (soft particle on the solid substrate), and of the strong thermal effects (soft particle on the soft substrate), as function of the ion fluence. The increase of fluence causes simultaneous decrease of the Coulomb repulsion and increase of adhesion, so that the mobility of particles decreases affecting the reorganization process. The reorganization depends on the ion fluence, but also on the initial selforganization of the LB layer, being different for the small, medium, and the large size particles. The hydroclusters of small particles become reorganized into “infinite” complex irregular chain-cluster; the small crystal-grains of medium size particles become rhombic and hexagonal clusters, while the 2D hexagonal crystals of large size particles become only slightly disturbed. The reorganization occurs until the increasing ion fluence reaches the reorganization-breakdown-threshold, and overwhelming thermal effects turn the process into particle destruction.

Properties of Fatty Amine–Silica Nanoparticle Interfacial Layers at the Hexane–Water Interface

The formation and properties of composite layers of silica nanoparticles and an oil-soluble (fatty) amine surfactant at the oil–water interface have been studied using interfacial tensiometry, rheology, and contact angle measurements to characterize the synergy between the particles and surfactant. The initially hydrophilic particles interact with the surfactant only at the water–hexane interface. Synergistic interactions are required for interface stabilization. A key result is that nanoparticle attachment is driven by surfactant adsorption at the liquid interface. Particles are efficiently bound to the interface once the adsorbed surfactant layer is close to saturation. Surfactant adsorption onto the particle surfaces optimizes the particle wettability and promotes particle aggregation into networks that enhance the viscoelasticity of the interface. The implications of these results for controlling the formation and kinetic stability of emulsions containing particles and surfactant are discussed.

Optical thin film filters of colloidal gold and silica nanoparticles prepared by a layer-by-layer self-assembly method

A novel fabrication method for optical thin film filters based on the self-organization of alternating layers of colloidal gold and silica nanoparticles (NP) is reported. The filter is designed to work in the deep-UV to visible spectral range. The spectral absorption peaks are tuned by three parameters: the organic capping ligand of the gold NPs (citrate, chitosan, poly (diallyl-dimethylammonium)-chloride or PDDA); the capping environment (bare, chitosan, or PDDA) of the silica NPs and the thickness of the film. Precise control of the transmission color (less than 1% color distance per layer), is achieved by changing the film thickness. Exploitation of the self-assembly process should lead to the facile production of highly reliable large area thin film optical filters at considerably lower costs.

Label-Free Detection of Leptin Antibody-Antigen Interaction by Using LSPR-Based Optical Biosensor

In the recent research, the development of optical biosensing devices has been focused on finding new method and technologies to exploit the optical properties of noble metal nanostructure, especially localized surface plasmon resonance (LSPR). In this study, we fabricated a LSPR-based label-free optical biosensor with the multi-spot gold-capped nanoparticle array (MG-NPA) biochip based on the deposition of a thin gold (Au) film on the silica nanoparticles layer with the simple process. The MG-NPA biochip used the silica nanoparticles as the core and a thin Au film as a shell on the surface. This structure can excite the LSPR signal easily with the high reproducibility. The anti-leptin antibody was immobilized on the surface of MG-NPA biochip, which could recognize only leptin antigen. The leptin antibody-antigen interaction was performed by the introduction of different concentration (1 pg/mL-100 microg/mL) of leptin antigen solutions for 1 h. The detection limit was found to be 100 pg/mL by using the anti-leptin antibody immobilized MG-NPA biochip. This LSPR-based label-free optical biosensor employing the MG-NPA biochip brings several advantages such as low cost, easy to fabricate, using a simple optical system and can be applied in a wide immunoassay with the similar antibody-antigen model.

Influence of the contact angle of silica nanoparticles at the air–water interface on the mechanical properties of the layers composed of these particles

We have studied the properties (surface pressure, compression and shear moduli, texture) of silica nanoparticle layers at the air–water interface. Particle hydrophobicity or, equivalently, the contact angle between particles, air and water, is the main factor that influences surface organization and surface elastic moduli. The surface layers are denser for particles of higher hydrophobicity. The compression and shear moduli, as well as the yield and melt strains, present a maximum for contact angles around 90°. The dependence of the mechanical properties on particle hydrophobicity is closely related to the foamability and stability of the foams made from dispersions.

Carbon nanotube-based symbiotic coaxial nanocables with nanosilica and nanogold particles as labels for electrochemical immunoassay of carcinoembryonic antigen in biological fluids

A feasible and practicable amperometric immunoassay strategy for sensitive screening of carcinoembryonic antigen (CEA) in human serum was developed using carbon nanotube (CNT)-based symbiotic coaxial nanocables as labels. To construct such a nanocable, a thin layer of silica nanoparticles was coated on the CNT surface by sonication and sol–gel methods, and then colloidal gold nanoparticles were assembled on the amino-functionalized SiO2/CNTs, which were used for the label of horseradish peroxidase-anti-CEA conjugates (HRP-anti-CEA-Au/SiO2/CNT). In the presence of analyte CEA, the sandwich-type immunocomplex was formed on an anti-CEA/Au/thionine/Nafion-modified glassy carbon electrode by using HRP-anti-CEA-Au/SiO2/CNTs as detection antibodies. To embody the advantages of the protocol, the analytical properties of variously modified electrodes were compared in detail on the basis of different nanolabels. Under optimal conditions, the cathodic peak currents of the electrochemical immunosensor were proportional to the logarithm of CEA concentration over the range from 0.01 to 12ngmL−1 in pH 5.5 HAc-NaAc containing 5mM H2O2. At a signal-to-noise ratio of 3, the detection limit (LOD) is 5pgmL−1 CEA. Intra- and inter-assay coefficients of variation were below 9.5%. Meanwhile, the selectivity and stability of the immunosensor were acceptable. In addition, the technique was evaluated by spiking CEA standards in pH 7.4 PBS and with 35 clinical serum specimens, receiving excellent accordance with results from commercially available electrochemiluminescent enzyme-linked immunoassay.

FePt grains for magnetic storage on layer of self-assembled silica nanoparticles

Abstract

Making silicananoparticle-covered graphene oxide nanohybrids as general building blocks for large-area superhydrophilic coatings

We report a facile strategy to synthesize silica nanoparticles-coated graphene oxide (GO-SiO2) nanohybrids in a water-alcohol mixture at room temperature. AFM observations revealed that silica nanoparticles with ca. 50 nm in size were densely and evenly covered on graphene oxide sheets. Due to the space layer of silica nanoparticles, micro-scale GO-SiO2 hybrid plates could be individually dispersed in water and polar organic solvents, promising good solution-based processibility. The growth process of GO-supported silica is traced by TGA and XRD measurements, showing that 24 hours is enough to achieve a fine cover effect for the disappearance of (002) diffraction peak of GO. Based on the high dense overlaying of silica nanoparticles, up to micro-scale silica sheets with thickness of ca. 8 nm were readily fabricated by burning GO-SiO2 at 650 °C in air. Likewise, a centimeter-scale semitransparent film of silica nanosheets was prepared by calcining a GO-SiO2 film. Interestingly, the GO-SiO2 nanohybrids exhibit excellent hydrophilic nature and can be directly applied as a general kind of building blocks to construct large-area superhydrophilic surfaces on arbitrary substrates (e.g., lotus leaf, ceramic tile and polypropylene) through the simple drop-coating method. Such a coating methodology paves the way for making large-area superhydrophilic surface without extra process treatments and damaging the intrinsic structure of substrates.

Rapid fabrication of core–shell silica particles using a multilayer-by-multilayer approach

Monodisperse silica core-shell particles with a high surface area and large pore size were rapidly prepared via a multilayer-by-multilayer (ML-b-ML) process, with 6-7 layers of silica nanoparticles deposited per coating cycle onto an oppositely charged polyelectrolyte in 0.1 M NH(4)NO(3) at pH 2.7. The resultant porous shells show much greater porosity compared to particles obtained by the traditional layer-by-layer process.