Layer Of Silica Nanoparticles Research Articles

Preparation of villus-like PMMA/silica hybrids via surface modification and wet grinding

A novel method to prepare inorganic–organic hybrid with villus-like morphology comprising a layer of silica nanoparticles adsorbed on polymethylmethacrylate (PMMA) microsphere was presented in this article. At first, silica nanoparticles were surface treated with vinyltriethoxysilane (VTEOS), and then a wet grinding process with VTEOS as the dispersing agent was utilized to prevent the aggregation of nanoparticles. Zeta-potential measurements confirmed that the surface charge of these milled silica is negative. On the other hand, positively charged PMMA was prepared by adsorption of 2-(methacryloyloxy) ethyl-trimethyl ammonium chloride (METMAC) on as-synthesized PMMA beads. Owing to the electrostatic interaction, the negatively charged silica particles were coated directly on the surface of positively charged PMMA microspheres. The hybrid is fully covered by a layer of silica and the silica content is 18.5%. From our results, it is evident that the villus silica layer adhered on the PMMA bead surfaces and it significantly enhanced the thermal stability of the hybrid microspheres. The characteristics and morphologies of the silica particles, PMMA beads and the resulting PMMA/silica hybrids were investigated by SEM, TEM, FESEM, EDS, FTIR, TGA, and aging analysis.

Fabrication of Fast‐Absorbing and Quick‐Drying Wool Fabrics with Good Washing Durability

The quick and the dry: Fast-absorbing and quick-drying wool fabrics with good washing durability are fabricated by functionalizing reactive siloxane monolayer on wool fiber surface, followed by grafting an ultrathin silica nanoparticles layer using an in situ growth method. The new properties are maintained even after washing 20 times because of the strong immobilization between the wool fiber and the ultrathin silica nanoparticles through siloxane bonding.

Viscoelastic properties of silica nanoparticle monolayers at the air-water interface

We have investigated the rheological behaviour of silica nanoparticle layers at the air-water interface. Both compressed and deposited layers have been studied in Langmuir troughs and with a bicone rheometer. The compressed layers are more homogeneous and rigid, and the elastic response to continuous, step and oscillatory compression are similar, provided the compression is fast enough and relaxation is prevented. The deposited layers are less rigid and more viscoelastic. Their shear moduli deduced from the oscillatory uniaxial compression are much smaller than those deduced from pure shear deformation suggesting that the effective shear rate is smaller than expected in the compression measurements.

Covalent Layer-by-Layer Assembled Superhydrophobic Organic−Inorganic Hybrid Films

Using the concept of covalent layer-by-layer assembly (covalent LbL), used until now for the elaboration of films from polymers or dendrimers, we have constructed hybrid organic/inorganic surfaces by alternating different layers of amino-functionalized silica nanoparticles (295 nm diameter) and epoxy-functionalized smaller silica nanoparticles (20 nm diameter). The so-realized macromolecular edifice leads to a hierarchical integration of nanoscale textures. Then hydrophobization of the last layer of amino-functionalized silica particles was carried out by grafting a new designed highly fluorinated aldehyde, creating a monomolecular layer via the formation of an imine function. Five highly fluorinated surfaces were built, and their water-repellent abilities were directly correlated to the surface topologies (i.e., the number of layers of silica nanoparticles and their organization on the glass support). The hydrophobicity increased with the number of layers and stable highly water-repellent surfaces (static contact angle with water of 150+/-3 degrees and a contact angle hysteresis of 12 degrees) were obtained with the alternation of nine layers. This result demonstrates the possibility to construct covalent LbL edifices with functionalized silica nanoparticles of different sizes and open this field for the elaboration of responsive, sensing, and therapeutic surfaces with improved film stability.

Chemical stability and phase distribution of all- trans-retinol in nanoparticle-coated emulsions

The influence of silica nanoparticle coating on the chemical stability and phase distribution of all- trans-retinol in submicron oil-in-water emulsions is reported. The chemical stability was studied as a function of UVA + UVB irradiation, and storage temperature (4 °C, ambient temperature, and 40 °C) for emulsions stabilised with lecithin and oleylamine as the initial emulsifier with and without silica nanoparticle layers. The chemical stability of all- trans-retinol was highly dependent on the emulsifier type and charge, with negligible influence of the initial loading phase of silica nanoparticles. A significant stability improvement (∼2-fold increase in the half-life of the drug) was observed by nanoparticle incorporation into oleylamine-stabilised droplets (i.e. electrostatically coated), with no considerable effect for partially coated lecithin-stabilised droplets. The chemical stability of all- trans-retinol incorporated into nanoparticle-coated emulsions was well-correlated to the phase distribution of the active agent, and the interfacial structure of emulsions as determined by freeze fracture-SEM. Specifically engineered nanoparticle layers can be used to enhance the chemical stability of active ingredients in emulsion carriers.

An ellipsometry study of silica nanoparticle layers at the water surface

We have studied silica nanoparticle layers spread at the air/water interface. The surface pressure of the layers has been determined in a Langmuir trough via two orthogonal Wilhelmy plates. We observed significant differences in surface pressure according to the preparation protocol: layers spread then compressed or layers obtained after successive spreading steps. We also studied the two types of layers by multiple angle of incidence ellipsometry. We introduce a two-layer model which enables us to evaluate the radius of interfacial aggregates and their contact angle with the air/water interface.

Fabrication of Transparent Capacitive Structure by Self-Assembled Thin Films

An approach to fabricating transparent electronic devices by using nanomaterial and nanofabrication is presented in this paper. A see-through capacitor is constructed from self-assembled silica nanoparticle layers that are stacked on the transparent substrate. The electrodes are made of indium tin oxide. Unlike the traditional processes used to fabricate such devices, the self-assembly approach enables one to synthesize the thin film layers at lower temperature and cost, and with a broader availability of nanomaterials. The vertical dimension of the self-assembled thin films can be precisely controlled, as well as the molecular order in the thin film layers. The shape of the capacitor is generated by planar micropatterning. The monitoring by quartz crystal demonstrates the steady growth of the silica nanoparticle multilayer. In addition, because the material synthesis and the device fabrication steps are separate, the fabrication is not affected by the harsh conditions required for the material synthesis. As a result, a clear pattern is allowed over a large area on the substrate. The prepared capacitive structure has an optical transparency higher than 92% over the visible spectrum. The capacitive impedance is measured at different frequencies and fit the theoretical results. As one of the fundamental components, this type of capacitive structure can serve in the transparent circuits, interactive media and sensors, as well as being applicable to other transparent devices.

Analysis of Surface Structure and Hydrogen/Deuterium Exchange of Colloidal Silica Suspension by Contrast-Variation Small-Angle Neutron Scattering

The microscopic surface structure and hydrogen/deuterium exchange effect were investigated by contrast-variation small-angle neutron scattering (CV-SANS) for three different-sized amorphous colloidal silica aqueous suspensions. The results show that the fraction of hydrogen/deuterium exchange per nanoparticle, phiH/D, strongly depends on the size of silica nanoparticles. This finding supports that the hydrogen/deuterium exchange occurs exclusively within a finite surface layer of silica nanoparticles, while the inner component remained unchanged. Detailed analyses of the scattering intensity functions led to the estimation of (1) phiH/D and (2) the thickness of the surface layer as functions of the particle radius. The surface layer thickness was found to increase from 18 to 35 A with decreasing the particle radius from 165 to 71.2 A. The surface area per unit weight of silica estimated with the CV-SANS results are comparable to those reported in the literature.

Nanoparticle layers controlling drug release from emulsions

The influence of interfacial layers of silica nanoparticles on the release kinetics of a model lipophilic drug (di-butyl-phthalate (DBP)) from polydimethylsiloxane droplets in water is reported. The nanoparticle layers are formed by self-assembly from solution and their structure is controlled by nanoparticle hydrophobicity and the solution conditions. For DBP loading levels resulting in released concentrations below the solubility limit, release is rapid from uncoated droplets whereas significant sustained release is facilitated by rigid interfacial layers of hydrophobic silica nanoparticles. Activation energies for release are in the range 580–630 kJ mol −1, which is ten times greater than for barriers introduced by typical polymeric stabilisers. In contrast, at higher DBP loading levels (total concentration greater than the solubility level), both hydrophilic and hydrophobic nanoparticle layers increase the rate and extent of dissolution compared with uncoated droplets and pure DBP solutions. Nanoparticle layers are shown to significantly influence the release kinetics of lipophilic drugs from oil in water emulsions: either sustained or enhanced release properties can be introduced depending on the nanoparticle layer type and drug loading level. Thus, nanoparticle layers may be engineered to facilitate a range of release behaviours and offer great potential in the delivery of poorly soluble drugs.

A localized surface plasmon resonance based immunosensor for the detection of casein in milk

In this research, a localized surface plasmon resonance (LSPR) immunosensor based on gold-capped nanoparticle substrate for detecting casein, one of the most potent allergens in milk, was developed. The fabrication of the gold-capped nanoparticle substrate involved a surface-modified silica nanoparticle layer (core) on the slide glass substrate between bottom and top gold layers (shell). The absorbance peak of the gold-capped nanoparticle substrate was observed at ∼520 nm. In addition, the atomic force microscopy (AFM) images demonstrated that the nanoparticles formed a monolayer on the slide glass. After immobilizing anti-casein antibody on the surface, our device, casein immunosensor, could be applied easily for the detection of casein in the raw milk sample without a difficult pretreatment. Under the optimum conditions, the detection limit of the casein immunosensor was determined as 10 ng/mL. Our device brings several advantages to the existing LSPR-based biosensors with its easy fabrication, simple handling, low-cost, and high sensitivity.

Superhydrophobic cotton fabric coating based on a complex layer of silica nanoparticles and perfluorooctylated quaternary ammonium silane coupling agent

A superhydrophobic complex coating for cotton fabrics based on silica nanoparticles and perfluorooctylated quaternary ammonium silane coupling agent (PFSC) was reported in this article. The complex thin film was prepared through a sol–gel process using cotton fabrics as a substrate. Silica nanoparticles in the coating made the textile surface much rougher, and perfluorooctylated quaternary ammonium silane coupling agent on the top layer of the surface lowered the surface free energy. Textiles coated with this coating showed excellent water repellent property, and water contact angle (CA) increased from 133° on cotton fabrics treated with pure PFSC without silica sol pretreatment up to 145°. The oil repellency was also improved and the contact angle of CH2I2 droplet on the fabric surface reached to 131°. In contrast, the contact angle of CH2I2 on the fabric surface treated with pure PFSC was only 125°.

Nanoparticle encapsulation of emulsion droplets

The overall aim of this study is to coat emulsion droplets with nanoparticles using a simple heterocoagulation process in aqueous dispersion and determine: the adsorption behavior and interfacial layer microstructure, droplet physical stability against flocculation and coalescence, and the release profile of a model lipophilic molecule (dibutylphtalate (DBP)) from within the droplets. Polydimethylsiloxane (PDMS) droplets were used as a model emulsion due to their colloidal stability in the absence of added stabilisers. Aerosil™ type silica nanoparticles with different hydrophobicity levels were used as the model nanoparticles. The adsorption behavior of silica nanoparticles at the droplet–water interface was studied using adsorption isotherms and SEM imaging. Adsorption of hydrophilic nanoparticles is weakly influenced by pH, but significantly influenced by salt addition, whereas for hydrophobically modified nanoparticles a balance of hydrophobic and electrostatic forces controls adsorption over a wide range of pH and salt concentrations. The coalescence kinetics (determined under coagulation conditions at high salt concentration) and the physical structure of coalesced droplets were determined from optical microscopy. Adsorbed layers of hydrophilic nanoparticles introduced a barrier to coalescence of ∼1 kT and form kinetically unstable droplet networks at high salt concentrations. The highly structured and rigid adsorbed layers significantly reduce coalescence kinetics. Significant sustained release of DBP can be achieved using rigid layers of hydrophobic silica nanoparticles at the interface. Activation energies for release are in the range 580–630 kJ mol −1, 10 times higher than for barriers introduced by Pluronic ® stabilisers.

The influence of void space on antireflection coatings of silica nanoparticle self-assembled films

This study investigates the deposition by ionic self-assembly of alternating silica nanoparticle and poly(allyamine hydrochloride) layers with the goal to create a single-material antireflection coating. The condition that the optical thickness of the film be equal to λ∕4 can be satisfied by depositing the requisite number of bilayers to obtain minimum reflectivity at the chosen wavelength. The second condition for antireflection, that the index of refraction of the film be equal to nc=n1n2, where n1 and n2 are the refractive indices of the media on each side of the film, requires that nc=1.22 for a film with air on one surface and glass (assuming n=1.50) on the other. Such a low index of refraction can be created in films consisting of nanoparticles if the proper volume fraction of void space exists in the film. In the wavelength range λ=350–700nm, minimum reflectivities of ⩾2.0%, ⩽0.2%, and ⩽0.2% were obtained with films created on both sides of a glass slide using 15, 45, and 85nm average diameter silica nanoparticles, respectively. The maximum transmittances for the corresponding films were 97%, ⩾98%, and ⩾97%. The minimum reflectance of films prepared with 15nm average diameter silica nanoparticles was limited by insufficient void volume in the films. The maximum transmittances of films prepared with 45 and 85nm average diameter silica nanoparticles were limited by diffuse scattering arising from the inhomogeneous morphology of the films. The extinction of normal incident light (=1−R−T, where R and T are the reflectance and transmittance, respectively) provides a measure of diffuse scattering for light with wavelength longer than the absorption edge of the film. It was found that the extinction is proportional to 1∕λ4 for λ>450nm suggesting that the mechanism for extinction at long wavelengths is Rayleigh scattering. The Rayleigh slope (diffuse scattering intensity versus 1∕λ4) increased with increasing diameter silica nanoparticles. For a given average diameter silica nanoparticle, the Rayleigh slope increased with increasing film thickness for films less than approximately 150nm thick, but did not depend on film thickness, within experimental scatter, for films that were thicker than 150nm. The results suggest that the source of Rayleigh scattering was not in the bulk of the film (such as, fluctuations in the index of refraction), but rather was primarily associated with surface roughness.

Zinc-embedded silica nanoparticle layer in a multilayer coating on a glass substrate achieves broadband antireflection and high transparency

A zinc-embedded silica (Zn-SiO2) nanoparticle layer has been applied as the outermost layer over the three-layer coating system, Zn-SiO2∕SiO2∕ITO (indium tin oxide), coated on a soda-lime glass substrate. The additional coating of the zinc-embedded nanoparticle layer over the 2-layer/glass, i.e., SiO2∕ITO∕glass system, yielded a significant diminution in reflectance, as well as an improved transmittance as compared to the 2-layer/glass system. Plausible mechanisms responsible for such phenomena are discussed. The application of the zinc-embedded silica nanoparticle layer to the multilayer coating system is shown to provide a flexible way to achieve a broadband antireflection and a high transmission.

Assembly of Nanoparticles into Hollow Spheres Using Block Copolypeptides

Various modes are being explored for the construction of functional materials out of nanoparticles. Despite these efforts, the assembly of nanoparticles remains challenging with respect to the requirement of multiple component organization on varying dimensions and length scales. We report here a room-temperature, wet chemical-based synthesis route in which silica and gold nanoparticles (∼10 nm) are cooperatively assembled with lysine−cysteine diblock copolypeptides into robust hollow spheres (diameter ∼ microns). The walls of the hollow spheres are composed of two distinct layers of silica and gold nanoparticles, and the hollow center is created without the use of a sacrificial core, emulsion phase, or hollow preformed substrate. Block copolypeptides designed with specific recognition sites for nanoparticles of various compositions provide a versatile approach for the hierarchical organization of nanoparticles into multidimensional composite arrays.