Nanometric Silica Particles Research Articles

Development of nanohybrid dental composite containing mesoporous carrier silica particles: Synthesis particles, determination of fluoride adsorption capacities, and addition of the composite

AbstractMesoporous, nanometric silica particles that can serve both as carrier and filler for fluoride were synthesized, and their release properties were later investigated. The flexural and compressive strengths performances of organic matrix and composite materials were evaluated using the tests defined in BS EN ISO 4049. From the Brunauer–Emmett–Teller results of the synthesized mesoporous silica particles, mesoporous SiO2 particles‐6 (MSP‐6) was preferred because it fits the MSP‐6 Type V isotherm model and has a highly mesoporous structure. The saturation points of MSP‐6 and R709 silica particles in terms of fluoride were determined as 180 min for MSP‐6 and 120 min for R709, respectively. The strength of composites prepared after the treatment of surface‐modified R709 silica particles with fluoride solution decreased, an increase was observed in the composites prepared after MSP‐6 particles were treated with fluoride solution. The porous silica particles caused a slight increase in the compressive strength of the composites. The standard deviations of the compression values of the fluorine‐containing composites F/R709 and F/MSP‐6 are quite low. The microhardness values of R709, F/R709, MSP6 and F/MSP6 samples were determined as 82.1 ± 8.59, 247.67 ± 12.32, 131.03 ± 10.98, and 218.8 ± 11.24, respectively. Especially considering the effect of chewing force the surface hardness of the composite is also directly related to the compressive strength. The increase in the compressive strength of the samples treated with fluoride confirms this result. A high rate of mesoporous structure silica particles was synthesized and could serve both as a carrier for fluoride and as a filler required by the material.

PI-SiO<sub>2</sub>/NiI<sub>2</sub> colorimetric humidity sensor with fast response and recovery

The organic-inorganic hybrid colorimetric humidity sensor which can obtain environmental humidity by electrical signals and color changes has broad application prospects in the field of humidity monitoring because of its high feature color discrimination, excellent stability, and simple preparation process. However, its long response-recovery time is generally not conducive to real-time humidity monitoring. In this paper, nanometer silica particles are doped into polyimide(PI)-nickel(II) iodide(NiI<sub>2</sub>) organic-inorganic hybrid materials to fabricate PI-SiO<sub>2</sub>/NiI<sub>2</sub> composite films and colorimetric humidity sensors. Then their surface morphologies and humidity sensing properties are studied. It is found that PI-SiO<sub>2</sub>/NiI<sub>2</sub> film possesses a honeycomb-like surface morphology, the humidity sensitivity of PI-SiO<sub>2</sub>/NiI<sub>2</sub> colorimetric humidity sensor is better than that of other NiI<sub>2</sub> based humidity sensors, its characteristic color is distinct in a range of 11%–97% RH humidity, and the humidity response time of the PI-SiO<sub>2</sub>/NiI<sub>2</sub> colorimetric humidity sensor is less than 1.5 s, and the recovery time is less than 18 s. The research result indicates that the doping of nanometer silica particles can effectively improve response-recovery properties of the organic-inorganic hybrid colorimetric humidity sensor, which is helpful in improving the performance of the sensor.

How Surface Properties of Silica Nanoparticles Influence Structural, Microstructural and Biological Properties of Polymer Nanocomposites

The aim of this work was to study effect of the type of silica nanoparticles on the properties of nanocomposites for application in the guided bone regeneration (GBR). Two types of nanometric silica particles with different size, morphology and specific surface area (SSA) i.e., high specific surface silica (hss-SiO2) and low specific surface silica (lss-SiO2), were used as nano-fillers for a resorbable polymer matrix: poly(L-lactide-co-D,L-lactide), called PLDLA. It was shown that higher surface specific area and morphology (including pore size distribution) recorded for hss-SiO2 influences chemical activity of the nanoparticle; in addition, hydroxyl groups appeared on the surface. The nanoparticle with 10 times lower specific surface area (lss-SiO2) characterized lower chemical action. In addition, a lack of hydroxyl groups on the surface obstructed apatite nucleation (reduced zeta potential in comparison to hss-SiO2), where an apatite layer appeared already after 48 h of incubation in the simulated body fluid (SBF), and no significant changes in crystallinity of PLDLA/lss-SiO2 nanocomposite material in comparison to neat PLDLA foil were observed. The presence and type of inorganic particles in the PLDLA matrix influenced various physicochemical properties such as the wettability, and the roughness parameter note for PLDLA/lss-SiO2 increased. The results of biological investigation show that the bioactive nanocomposites with hss-SiO2 may stimulate osteoblast and fibroblast cells’proliferation and secretion of collagen type I. Additionally, both nanocomposites with the nanometric silica inducted differentiation of mesenchymal cells into osteoblasts at a proliferation stage in in vitro conditions. A higher concentration of alkaline phosphatase (ALP) was observed on the material modified with hss-SiO2 silica.

Synthesis of nanometric silica particles via a modified Stöber synthesis route

In this paper we describe a simple modification of the classic Stöber reaction enabling a high temperature synthesis of nanometric silica particles with diameters less than 100nm in sealed reaction tubes. This could be reached due to the replacement of the basic catalyst ammonia by ethanolamine. Thus, high temperature synthesis up to 80°C can be run without facing the risk of bubble formation inside the reaction tube. The modified synthesis route enables the synthesis of spherical silica nanoparticles with mean diameters between 28 and 647nm and standard deviations less than 10% as well as smooth surface structures. This work deals with basic studies on the use of ethanolamine for the synthesis of silica nanoparticles in alkaline media in sealed reaction tubes under ambient pressure. These include experiments on the adjustment of the particle size depending on the composition of the reaction solution and the temperature. In addition, reaction kinetics of the particle formation process are monitored as a function of temperature and the influence of the mixing time on the particle size is investigated.

Spray-dried encapsulated starch and subsequent synthesis of carbon-silica core-shell micro-granules

Encapsulation is a widely used method to preserve core material from environmental influences and for controlled release of the core material. Here, we demonstrate a fast and facile method to prepare such core-shell microgranules by encapsulating starch with nanometric silica particles using spray drying. The virgin spray dried powder contained silica at shell and starch at the core. The powder granules were pyrolyzed to convert the virgin encapsulated starch granules into carbon-silica core-shell microgranules. The mesoscopic structure of the synthesized microgranules was probed by electron microscopy, scattering techniques and infrared spectroscopy.

Colloidal liquid aphrons directed growth of sol–gel silica exhibiting bimodal porosities

We report a new method to prepare bimodally porous, macroporous–mesoporous silica materials utilizing TEOS co-constructed template with colloidal liquid aphrons (CLAs). The macroporous and mesoporous texture of obtained silica is characterized using a combination of fluorescence microscopy, SEM, TEM, and nitrogen volumetric adsorption analysis. The appearance of macropores is attributed to the interfacial confined hydrolysis–condensation of silica source where as the mespore formation is consistent with the pores resulting from the compact packing of nanometer silica particles under weak base-catalysed reaction condition. This bimodally porous silica materials can be prepared either as monoliths or ascisolated spherical particles by adjusting the TEOS concentration in the oil phase.

Sintering process of amorphous SiO 2 nanoparticles investigated by AFM, IR and Raman techniques

We report an experimental investigation on the effects of thermal treatments at different temperatures (room—1270 K) and for different duration (0–75 h) on amorphous silica nanoparticles ( fumed silica) in powder tablet form. Three types of fumed silica are considered, comprising nearly spherical particles of 40 nm, 14 nm and 7 nm mean diameter. The experimental techniques used here are Raman and infrared absorption (IR) spectroscopy together with atomic force microscopy (AFM). Raman and IR spectra indicate that the structure of nanometer silica particles is significantly different with respect to that of a bulk silica glass. In particular, the main differences regard the positions of the IR band peaked at about 2260 cm −1, the Raman R-band peaked at about 440 cm −1 and the intensity of the D1 and the D2 Raman lines, related to the populations of 4- and 3-membered rings, respectively. Our data also indicate that, under thermal treatments, the structure of fumed silica samples is significantly changed, gradually relaxing towards that pertaining to ordinary bulk silica. These changes are interpreted here on the basis of the morphological information provided by the AFM measurements and assuming a two-shell structure for the fumed silica primary particles.

Sensitivity enhancement using nanometer silica particles on the surface of a quartz cell in mercury and selenium determination by vapor generation atomic absorption spectrometry

The sensitivity of on-line vapor generation atomic absorption spectrometry of mercury and selenium was improved by using a new atom trap technology. The inner wall of a T-shaped quartz tube was coated with nanometer SiO2 so increase the residence time of the analyte atoms in the light path. The linear range of the calibration plots thus was increased to a range from 5.0 to 150 ng mL−1 for mercury, and from 4.5 to 100 ng mL−1 for selenium. The detection limits are 0.9 ng mL−1 for Hg and 1.0 ng mL−1 for Se which is a 2-fold improvement. The technique was applied to the determination of Hg and Se in herbs and hair.

Nanostructured hybrid networks based on highly fluorinated acrylates

A dual-curing process is described for obtaining highly fluorinated acrylic networks containing nanosilica. The new materials showed improved hardness, while maintaining the hydrophobicity of the fluorinated polymer. They were obtained by UV-curing a suitable mixture of a perfluoropolyetherurethanediacrylate and alkoxysilanes, followed by a thermal treatment during which the sol–gel process took place. The obtained crosslinked networks had a complex morphology: nanometric silica particles were formed, as observed by TEM, and embedded in a biphasic crosslinked matrix made of perfluoropolyether domains and of copolymeric crosslinked domains containing the polyurethane acrylic units and siloxane chains formed by the alkoxides condensation.

Polymer-ceramic nanocomposites for applications in the bone surgery

The subject of this work was preparation and investigation of properties of a nanocomposite material based on polymer matrix modified with nanometric silica particles (SiO2). The composite matrix consisted of resorbable P(L/DL)LA polymer with certified biocompatibility. Nanometric silica was introduced into the matrix by means of ultrasonic homogenisation and/or mechanical stirring. The silica was introduced directly e.g. as nanoparticles or inside calcium alginate fibres which contained 3 wt.% of amorphous SiO2. Proper dispersion of nano-filliers was confirmed by means of thermal analysis (TG/DTA, DSC). It was observed, that the presence of inorganic nanoparticles influenced several surface parameters of the nanocomposites i.e. hydrophility (a decrease of surface energy) and topography (both in micro- and nano-scale). Additionally, the nanocomposites exhibited enhanced mechanical properties (Young's modulus, tensile strength) compared to the pure polymer. The nanocomposites were bioactive materials (SBF/3 days/37oC). Biological tests (MTT test) showed a good viability of human osteoblasts (hFOB 1.19) in contact with the nanocomposites surface. Results of preliminary biological tests carried out with the use of mother cells extracted from human bone marrow showed that the nanocomposites may provide differenation of bone cells.

Structure of interacting aggregates of silicananoparticles in a polymer matrix: small-angle scattering and reverse Monte Carlo simulations

Reinforcement of elastomers by colloidal nanoparticles is an important application where microstructure needs to be understood—and, if possible, controlled—if one wishes to tune macroscopic mechanical properties. Here, the three-dimensional structure of large aggregates of nanometric silica particles embedded in a soft polymeric matrix is determined by small angle neutron scattering. Experimentally, the crowded environment leading to strong reinforcement induces a strong interaction between aggregates, which generates a prominent interaction peak in the scattering. We propose to analyze the total signal by means of a decomposition in a classical colloidal structure factor describing aggregate interaction and an aggregate form factor determined by a reverse Monte Carlo technique. The result gives new insight to the shape of aggregates and their complex interaction in elastomers. For comparison, fractal models for aggregate scattering are also discussed.

Effect of the dispersion of nanometric silica particles on the thermal stability of a nanostructured iron based powder

An iron based powder has been mechanically ground with nanometric silica particles in order to increase the thermal stability of the nanostructure. The powder has been annealed at different temperatures between 200 and 750 °C. Microhardness tests revealed that without the addition of SiO 2, the hardness is constant up to 400 °C, whereas the dispersion of SiO 2 keeps a constant hardness value up to 600 °C. A similar trend has been obtained for the microstructural parameters (crystalline domain size and dislocation density) obtained by a line profile analysis of the XRD spectra; the powders lose the nanostructure after annealing at 600 °C for the material without SiO 2 and above 750 °C with SiO 2 addition. Thermal analysis has been used to calculate the activation energy of the grain growth process and to extrapolate the temperature at which the powder could be sintered, without losing nanostructure, by spark plasma sintering (SPS). Preliminary attempts of sintering by SPS seem to confirm the indication obtained by the present work.

An optimized sol–gel synthesis of stable primary equivalent silica particles

An optimized synthesis of nanometer silica particles via hydrolysis and condensation of tetraethylorthosilicate (TEOS) is described. At the optimum experimental conditions, homogeneous and stable silica nanoparticles with mean particles size of 7.1 ± 1.9 nm were obtained. The particle size is in a good agreement with primary particles. The size, size distribution (SD) and the yield of silica were controlled by the concentration of the reactants, ammonia feed rate, temperature and mixing mode. The increase in TEOS concentration resulted in bigger and multi-model distributed powder, while high temperature and magnetic agitation produced a highly aggregated powder. However, higher H 2O/TEOS ratio and lower ammonia concentration at slower feed rate produced particles in the range of 10–14 nm. It was also found that the concentration of silanol group increased significantly with the decrease in particle size, especially below 40 nm. The optimized technique developed is simple and reproducible, affording a high yield of ∼75% of nanometer silica in a primary size range.

Relationship between the polymer/silica interaction and properties of silica composite materials

AbstractCast film composites have been prepared from aqueous polymer solutions containing nanometric silica particles. The polymers were polyvinyl alcohol (PVA), hydroxypropylmethylcellulose (HPMC) and a blend of PVA‐HPMC polymers. In the aqueous dispersions, the polymer–silica interactions were studied through adsorption isotherms. These experiments indicated that HPMC has a high affinity for silica surfaces, and can adsorb at high coverage; conversely, low affinity and low coverage were found in the case of PVA. In the films, the organization of silica particles was investigated through transmission electron microscopy (TEM) and small‐angle neutron scattering (SANS). Both methods showed that the silica particles were well‐dispersed in the HPMC films and aggregated in the PVA films. The mechanical properties of the composite films were evaluated using tensile strength measurements. Both polymers were solid materials, with a high‐elastic modulus (65 MPa for HPMC and 291 for PVA) and a low‐maximum elongation at break (0.15 mm for HPMC and 4.12 mm for PVA). In HPMC films, the presence of silica particles led to an increase in the modulus and a decrease in the stress at break. In PVA films, the modulus decreased but the stress at break increased upon adding silica. Accordingly, the polymer/silica interaction can be used to tune the mechanical properties of such composite films. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1134–1146, 2006

Effects of ammonia/silica molar ratio on the synthesis and structure of bimodal mesopore silica xerogel

A surfactant-templated silica xerogel with high pore volume, high porosity and narrow bimodal mesopore size distribution (designated as BMS) was synthesized by a judiciously controlled two-phase sol–gel processing under basic conditions. The properties of BMS silica mesostructure and the effect of ammonia/silica molar ratio on the resultant silica structure and morphology were assessed using various analytical techniques such as XRD, 29Si MAS NMR, SEM, TEM, TG-DTA and N 2 adsorption measurements. It is found that BMS silica xerogel consists of the packing of the micelle-encapsulated nanometer silica particles in the 20–40 nm range, depending upon the ammonia/silica molar ratio, and shows both an intraparticle framework mesopore resulting from the surfactant removal and a textural mesopore resulting from the interparticle voids, which can be adjusted in the 12.6–34.8 nm range by varying just the ammonia/silica molar ratio. The textural pore volumes for all BMS silica can be two or more times as large as the framework pore volumes, and the fill of a certain amount of surfactant between interparticle voids in as-synthesized BMS silica xerogel may play a crucial role for the formation, stability and ordering of textural mesoporosity. A fast hydrolysis and slow condensation process is beneficial to the formation of BMS silica mesostructure. Following a gradual increase of ammonia/silica molar ratio, thus an increase of condensation rate, the mesostructure evolution of the resultant silica products obtained from a bimodal mesopore via a disordered mesopore to a well-defined ordered hexagonal mesopore MCM-41 was observed.

Shear induced gelation of colloidal dispersions

Nanometric silica particles, dispersed in water, have been bridged into long necklaces by adsorbing macromolecules of poly(ethylene oxide). At high coverage of particles by macromolecules the necklaces repel each other and the dispersions are homogeneous solutions; at low coverage the necklaces bind to each other and a concentrated phase separates from excess water. It is reported here that shear induced gelation and shear induced flocculation are observed near the boundary of the phase separation region. The structures of these dispersions under shear have been observed through small angle neutron scattering. It has been found that, above a critical shear rate, the necklaces connect to each other to form threadlike objects which align along the velocity. At higher shear these objects associate sideways to form three-dimensional flocs.

Preparation of silica nanoparticles from sodium orthosilicate in inverse microemulsions

Sodium orthosilicate has been used to synthesize nanometer silica particles (5–20 nm) in water-in-oil microemulsion systems containing cyclohexane and a mixture of non-ionic surfactants, without using a cosurfactant. The particle sizes of silica formed in the microemulsion systems were affected by the pH and the concentration of sodium orthosilicate. Spherical silica particles formed in a wide range of pH (2–11) can easily be observed by transmission electron microscopy. Silica particles produced under basic conditions were more uniform in size, but larger specific surface areas (350–400 m2 g−1) of the calcined silica powders were only obtained from samples prepared in an acidic medium.

Transmission electron microscopy observations of composite polymer colloid nucleated by functionalized silica

AbstractIn this work, functionalized nanometric silica particles were engaged in emulsion polymerization of ethyl acrylate. The morphological characterization of this composite material was performed by transmission electron microscopy (TEM) and small angle X‐ray scattering (SAXS). We were particularly interested in the state of encapsulation of the silica particles and their distribution in the latex film. Initialy, we successively studied both components of the composite: polymer beads and silica particles differ by their size and also by their contrast. In addition, it was possible to perfrom dark field TEM to study this system of two amorphous phases because their respective amorphous halos are not too close. Hence, we investigated the colloid material in aqueous media and after film formation. Although no ideal encapsulation is observed in the colloid in aqueous media, the distribution of silica in the latex film is good. SAXS results are in good agreement with TEM observations.