Types Of Silica Nanoparticles Research Articles

Adsorption and release of biocides with mesoporous silica nanoparticles

In this proof-of-concept study, an agricultural biocide (imidacloprid) was effectively loaded into the mesoporous silica nanoparticles (MSNs) with different pore sizes, morphologies and mesoporous structures for termite control. This resulted in nanoparticles with a large surface area, tunable pore diameter and small particle size, which are ideal carriers for adsorption and controlled release of imidacloprid. The effect of pore size, surface area and mesoporous structure on uptake and release of imidacloprid was systematically studied. It was found that the adsorption amount and release profile of imidacloprid were dependent on the type of mesoporous structure and surface area of particles. Specifically, MCM-48 type mesoporous silica nanoparticles with a three dimensional (3D) open network structure and high surface area displayed the highest adsorption capacity compared to other types of silica nanoparticles. Release of imidacloprid from these nanoparticles was found to be controlled over 48 hours. Finally, in vivo laboratory testing on termite control proved the efficacy of these nanoparticles as delivery carriers for biopesticides. We believe that the present study will contribute to the design of more effective controlled and targeted delivery for other biomolecules.

Synthesis and study of properties of dental resin composites with different nanosilica particles size

Objectives The aim of this work was the synthesis of light-cured resin nanocomposites using nanosilica particles with different particle size and the study of some physical–mechanical properties of the composites. Methods Various types of silica nanoparticles (Aerosil) with average particle size of 40, 20, 16, 14, and 7 nm, used as filler were silanized with the silane 3-methacryloxypropyl-trimethoxysilane (MPS). The total amount of silane used was kept constant at 10 wt% relative to the filler weight to ensure the complete silanization of nanoparticles. The silanizated silica nanoparticles were identified by FT-IR spectroscopy and thermogravimetric analysis (TGA). Then the silanized nanoparticles (55 wt%) were mixed with a photoactivated Bis-GMA/TEGDMA (50/50 wt/wt) matrix. Degree of conversion of composites was determined by FT-IR analysis. The static flexural strength and flexural modulus were measured using a three-point bending set up. The dynamic thermomechanical properties were determined by dynamic mechanical analyzer (DMA). Sorption, solubility and volumetric change were determined after storage of composites in water or ethanol/water solution 75 vol% for 30 days. The TGA for composites was performed in nitrogen atmosphere from 30 to 700 °C. Results As the average silica particle size decreases, the percentage amount of MPS attached on the silica surface increases. However, the number of MPS molecules attached on the silica surface area of 1 nm 2 is independent of filler particle size. As the average filler particles size decreases a progressive increase in the degree of conversion of composites and an increase in the amount of sorbed water is observed. Significance The prepared composites containing different amount of silica filler, with different particle size, but with the same amount of silanized silica and organic matrix showed similar flexural strength and flexural modulus, except composite with the lowest filler particle size, which showed lower flexural modulus.

Smartly designed photoreactive silica nanoparticles and their reactivity

Monodisperse, colloidal silica nanoparticles (NPs) are being widely investigated due to a variety of applications in various fields of chemistry. Many works utilize incorporation of various functional groups to silica NPs for their further modifications. However, at present no benzophenone (BPh) or phenyl azide (PA) containing silica NPs exist. Upon UV irradiation BPh and PA form highly reactive species that react with any organic material. Here we present a convenient method for the preparation of novel hybrid photoreactive silica NPs (denoted as SiO2@photoreactive group) prepared by co-condensation of photoreactive organosilanes and tetraethyl orthosilicate (TEOS) to obtain SiO2@PA and SiO2@BPh NPs. The reactivity of these two types of silica NPs is compared to that of perfluorinated phenyl azide (PFPA) based SiO2 NPs. The reactivity evaluation is carried out by the reaction of the three types of SiO2 NPs with highly inert poly(2-chloro-paraxylelene) films. It is found that, in contrast to what is stated in the literature, PA is much more reactive than PFPA, when dealing with solid state photochemical reactions. Next, photoreactive silica NPs on polymer films are used as an intermediate functional phase for a second modification step using silane-based chemistry. A successful incorporation of amine functionality onto silica NPs is achieved by their reaction with 3-aminopropyltriethoxysilane (APTES) and is verified by fluorescence microscopy. This strategy provides a general and versatile route to efficient functionalization of silica by light.

Competing effects of silanol surface concentration and solvent dielectric constant on electrostatic layer-by-layer assembly of silica nanoparticles on gold

Two types of silica nanoparticles having differing concentrations of ionizable surface groups are used to investigate the interplay between nanoparticle surface charge and solvent dielectric constant in nanostructure development during layer-by-layer assembly with a cationic polyacrylamide. Zeta ( ζ) potential measurements are used to determine the extent of silanol dissociation with pH. For 19-nm-diameter X-Tec 3408 silica nanoparticles from Nano-X GmbH (NanoX), complete dissociation yields a ζ-potential value of about −44 mV and occurs between pH 5 and 6 in 50% ethanol-in-water mixture by volume. By contrast, 65-nm-diameter polishing silica from Electron Microscopy Supply (EMS) has a ζ potential that does not equilibrate even up to pH 7 with a value of −59 mV under otherwise similar solution conditions. The more negative zeta potential at a given pH is found to substantially reduce nanoparticle adsorption. This behavior is opposite that observed when the dielectric constant of the suspension is decreased, independent of particle size. Nanoparticle surface chemical heterogeneity is discussed as a plausible explanation for such seriously discrepant behavior and the effects on multilayer electrical contact resistance for proton-exchange membrane (PEM) fuel-cell coating applications are presented.

Sonochemical synthesis and rheological properties of shear thickening silica dispersions

A sonochemical method has been developed to synthesize shear thickening fluid. This shear thickening fluid (STF) is composed of hard silicon dioxide nanoparticles and polyethylene glycol (PEG) liquid polymer. The combination of flow-able and hard components at a particular composition, results a material with remarkable rheological properties that is suitable for liquid body armor applications. In the present study nine types of STF’s have been synthesized with two different types of silica nanoparticles (15 nm and 200 nm) and polyethylene glycol at various weight fractions using a high intensity ultrasonic irradiation. The resultant STF samples were tested for their rheological and thermal properties. The advantages and disadvantages of this process have been discussed.

Storage and release of solutes and microalgae from water-in-oil emulsions stabilized by silica nanoparticles

Water-in-oil (W/O) emulsions using crop oils and stabilized by surface modified silica nanoparticles and polymeric surfactants appear to be a promising approach for storing and delivering microorganisms to aqueous environments. In these systems cells are contained within the internal phase of the emulsion. We examined two types of silica nanoparticles for stabilizing Chlorella vulgaris in W/O emulsions and release kinetics upon delivery to water. C. vulgaris was selected because of its potential for nutritional and industrial applications. We also examined the effects of silica nanoparticles on the release of a model solute NaCl. Surface modification of the nanoparticles and concentration of nanoparticles in the continuous phase had significant effects on the release of NaCl while only surface modification had an effect on the release of cells. Increasing the hydrophobicity of the nanoparticles significantly reduced the level of cell release and rate of solute release suggesting emulsion properties could be tailored to achieve the controlled release of cells and solute upon delivery.

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) nanocomposites with optimal mechanical properties

With the ultimate goal to design renewable polymer nanocomposites with optimal mechanical properties, this study reports an investigation of structure–property relationships for a model system – silica/ poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHx) nanocomposites. Two molecular weights of PHBHx (Mw ¼ 903,000 g/mol and Mw ¼ 633,000 g/mol) and two types of silica nanoparticles (nominally spheres and fibers according to the manufacturer) were used to prepare the nanocomposites. Smallangle X-ray scattering shows that the sphere and fiber nanoparticles had similar surface areas and primary particle size, but differed in degree of aggregation of the primary particles. The thermal stability of the PHBHx matrix was slightly improved by the addition of nanofillers. Simultaneous improvement of both stiffness and toughness was observed at 1-wt% loading for the higher molecular weight matrix. The more highly aggregated SiO2 fibers had a greater toughening effect than the SiO2 spheres. Compared to the unfilled polymer matrix, a 30% increase in Young’s modulus and 34% increase in toughness were obtained for the 1-wt% SiO2 fiber/PHBHx072 nanocomposite. The addition of SiO2 spheres to PHBHx072 resulted in the same increase in Young’s modulus (30%) but a smaller increase (11%) in toughness. The dramatic increases in modulus for PHBHx072 cannot be explained on the basis of two-component micromechanical models. Apparently the filler alters the character of the semicrystalline matrix. When the loading was 3 wt% and above, Young’s modulus continued to increase, but the strain at break and toughness decreased. The ultimate strength did not change compared with the unfilled polymer. In order to understand the mechanical properties observed, the thermal behavior, spherulitic morphology and the deformation mechanisms of the nanocomposites and the dispersion state of the nanofillers were studied. We found that a high molecular weight of the polymer matrix, weak interfacial adhesion and a good dispersion of the nanofillers are necessary to improve toughness and stiffness simultaneously. 2009 Elsevier Ltd. All rights reserved.

Enhanced stab resistance of armor composites with functionalized silica nanoparticles

Traditionally shear thickening fluid (STF) reinforced with Kevlar has been used to develop flexible armor. At the core of the STF-Kevlar composites is a mixture of polyethylene glycol (PEG) and silica particles. This mixture is often known as STF and is consisted of approximately 45 wt % PEG and 55 wt % silica. During rheological tests, STF shows instantaneous spike in viscosity above a critical shear rate. Fabrication of STF-Kevlar composites requires preparation of STF, dilution with ethanol, and then impregnation with Kevlar. In the current approach, nanoscale silica particles were dispersed directly into a mixture of PEG and ethanol through a sonic cavitation process. Two types of silica nanoparticles were used in the investigation: 30 nm crystalline silica and 7 nm amorphous silica. The admixture was then reinforced with Kevlar fabric to produce flexible armor composites. In the next step, silica particles are functionalized with a silane coupling agent to enhance bonding between silica and PEG. The performance of the resulting armor composites improved significantly. As evidenced by National Institute of Justice spike tests, the energy required for zero-layer penetration (i.e., no penetration) jumped twofold: from 12 to 25 J cm2/g. The source of this improvement has been traced to the formation of siloxane (Si-O-Si) bonds between silica and PEG and superior coating of Kevlar filaments with particles. Fourier transform infrared, x-ray photoemission spectroscopy, and scanning electron microscopy studies were performed to examine chemical bonds, elemental composition, and particle dispersion responsible for such improvement. In summary, our experiments have demonstrated that functionalization of silica particles followed by direct dispersion into PEG resulted in superior Kevlar composites having much higher spike resistance.

Synthesis of novel silica-polyamide nanocomposite membrane with enhanced properties

A synthesis method of polyamide nanocomposite film of about 400–800 nm thickness coated over porous polysulfone support via interfacial polymerization to produce thin film nanocomposite membrane with enhanced properties is described here. Two types of nanocomposite films were prepared by incorporating two types of silica nanoparticles in situ into the polyamide films, one was commercially available LUDOX ® HS-40 of which the particle size is about 16 nm and the other has the size of about 3 nm which was synthesised in our laboratory from hydrolysis of tetraethyl orthosilicate (TEOS) in acidic medium. The nanocomposite membranes exhibit superior thermal stability than the pure polyamide membranes; and in both the nanocomposite types, the best membrane performance in terms of separation efficiency and productivity flux was observed in the membrane with a certain amount of silica loading. Higher silica loading into the polymer resulted into a thicker nanocomposite membrane film formation; and at the same time these nanocomposite membranes have relatively large pore sizes as well as higher pore number density, as determined by the analysis of membrane permeation data of aqueous solutions of organic solutes and sodium chloride at pressures ranging from 50 to 400 psig. Depending on the silica content, the average pore radii membranes vary from smaller radius of 0.34 nm to fairly a larger radius of 0.73 nm.

Characterization of physical structure of silica nanoparticles encapsulated in polymeric structure of polyamide films

Polyamide nanocomposite films were prepared from nanometer sized silica particles and trimesoyl chloride– m-phenylene diamine based polyamides. The type of silica nanoparticles used is commercial LUDOX ® HS-40 and the particle size characterized by the radius of gyration ( R g ) is about 66 Å. The immediately prepared films were easily broken into particles to form colloidal-like dilute suspension of the silica–polyamide composite particles in D 2O–H 2O solutions for SANS measurements, that in this dilute system SANS data the complication of scattering data from the interacting particles is minimized. At about 60% D 2O of the sample solution, the silica is contrasted out, therefore the SANS profiles are predominantly from the organic polyamide scattering. The SANS profile of the sample solutions measured at 90% D 2O clearly indicates scattering from both silica and polymer. The scattering heterogeneities for two-phase system were evident from the validity of the Debye–Bueche expression in case of the nanocomposite with high silica loading. At limited silica loading of the nanocomposite, interaction between the silica and polymer chains forming core–shell morphology was observed. The transport properties of the membranes made from the nanocomposite films were measured on a batch type test kit with an aqueous solution of 500 ppm dioxane concentration at pressures ranging from 50 to 200 psig, and correlated to their composite structure.

Ultra-water-repellent surface: fabrication of complicated structure of SiO2 nanoparticles by electrostatic self-assembled films

Ultra-water-repellent surface requires a high surface roughness and low surface energy. We designed surface complicated microstructure of SiO 2 nanoparticles by using electrostatic self-assembly process. The films that were prepared by the alternate adsorption of poly(allylamine hydrochloride), SiO 2 nanoparticles mixture solution and poly(acrylic acid) on the substrates were very complicated in surface structure. After surface hydrophobic treatment by dichlorodimethylsilane, the film surface showed a contact angle of larger than 160° for water droplets. The value was much larger compared with the contact angle on silicon wafer treated by dichlorodimethylsilane. The difference was strongly dependent on the surface structure. In this paper, we changed deposition conditions to fabricate the water-repellent surfaces with various surface structures by using three types of silica nanoparticles, and we found that the nanoscale structure was very important for the ultra-water-repellency.

Ultra-water-repellent surface: fabrication of complicated structure of SiO2 nanoparticles by electrostatic self-assembled films

Ultra-water-repellent surface requires a high surface roughness and low surface energy. We designed surface complicated microstructure of SiO2 nanoparticles by using electrostatic self-assembly process. The films that were prepared by the alternate adsorption of poly(allylamine hydrochloride), SiO2 nanoparticles mixture solution and poly(acrylic acid) on the substrates were very complicated in surface structure. After surface hydrophobic treatment by dichlorodimethylsilane, the film surface showed a contact angle of larger than 160° for water droplets. The value was much larger compared with the contact angle on silicon wafer treated by dichlorodimethylsilane. The difference was strongly dependent on the surface structure. In this paper, we changed deposition conditions to fabricate the water-repellent surfaces with various surface structures by using three types of silica nanoparticles, and we found that the nanoscale structure was very important for the ultra-water-repellency.

Electrooptic properties of liquid crystals filled with silica nanoparticles of different sorts

In this work we investigate electrooptic properties of nematic liquid crystal (LC) E7 from Merck filled with two types of silica nanoparticles (NPs). The particles of these types are of similar size and shape, however, they are made by different methods. The NPs of the first type, aerosil (A), are prepared by a high-temperature hydrolysis of chlorosilanes. The second type of NPs, based on hydrolysis and controlled precipitation of tetraethylorthosilicate in alcohol, yields monodispersed NP (MNPs) of silica. Transmittance versus applied voltage curves of the suspension layers are measured and analyzed. Our results show a strong dependence of the electrooptic properties on the particle preparation method. The contrast ratio (CR) 61:1 of LC-A suspension is achieved at relatively low A content (17 wt %). Unlike it, the value of the CR of LC-MNP suspensions is low (about 2:1) even at 30 wt % of MNPs in the mixture. Both types of suspensions show electrooptic memory. The maximum of the memory efficiency of LC-A suspensions is detected at 4 wt % of A, while for LC-MNP suspensions the maximum is achieved at 15 wt % of MNPs. The difference in the results for the LC-A and LC-MNP series of composites is caused by much stronger aggregation of MNPs compared with A in the LC matrix. Moreover, reactive particle fusion and formation of silica microcrystallites substantially enhances the effect caused by MNP aggregation. These processes deteriorating electrooptic performance may be stabilized by introduction of a polymer network in LC-MNP suspensions.