Addition Of Silica Nanoparticles Research Articles

Ceramic Microbeads as Adsorbents for Purification Technologies with High Specific Surface Area, Adjustable Pore Size, and Morphology Obtained by Ionotropic Gelation

In this study, we present an ionotropic gelation route for obtaining porous alumina/silica microbeads (MBs) with tailorable morphology, specific surface area (SBET), and pore size, which can directly be sintered into porous, monolithic adsorbents (MAds). After sintering, SBETs from 20 m2/g up to 70 m2/g with open porosities up to 90% could be achieved depending on the silica nanoparticle addition. Due to the significantly increased SBET, a more than 100‐fold faster uptake of model dye molecules was obtained. Pore sizes ranged between 13 and 184 nm with adjustable mono‐ and bimodal size distributions. Depending on silica content and sintering temperature, the MBs were also found to be chemically stable in technologically relevant solvents such as water, acetone, acetonitrile, hydrochloric acid, and methanol for at least 1 week except for sodium hydroxide. By adjusting the processing parameters, spherical, fibrous or irregular microbead morphologies could be obtained. The same route was also successfully applied for obtaining calcium phosphate, titania, and zirconia microbeads. The presented straight‐forward ionotropic gelation route is basically applicable to any other ceramic material and therefore extremely versatile. The obtained MBs and MAds can be further adapted to any type of environmental or biotechnological purification process by additional functionalization steps.

Thermally stable and photocatalytically active titania for ceramic surfaces

The most photocatalytically active titania modification anatase must be stabilised to achieve high photocatalytic activity in ceramic processes at temperatures above 1000 °C. Thermally stable TiO 2 powders were prepared by the addition of silica and boehmite nanoparticles and deposited on corundum substrates and lead-free glazes. The powders and coatings were fired at increasing temperatures, and stabilisation of the anatase phase was achieved up to 1200 °C. In general, thermal stability was found to be lower when coated on substrates compared to the powder alone, and the extent of reduction depended on the chemical composition of the substrate. Only a slight modification of the titania electronic structure was found, indicating only weak interactions between silica and titania. Based on these results it is possible to assume an amorphous silica and alumina shell encases the titania particles which prevents grain growth and the anatase to rutile phase transformation.

Addition of silica nanoparticles to tailor the mechanical properties of nanofibrillated cellulose thin films

Over the last decade, the use of nanocellulose in advanced technological applications has been promoted both due the excellent properties of this material in combination with its renewability. In this study, multilayered thin films composed of nanofibrillated cellulose (NFC), polyvinyl amine (PVAm) and silica nanoparticles were fabricated on polydimethylsiloxane (PDMS) using a layer-by-layer adsorption technique. The multilayer build-up was followed in situ by quartz crystal microbalance with dissipation, which indicated that the PVAm–SiO2–PVAm–NFC system adsorbs twice as much wet mass material compared to the PVAm–NFC system for the same number of bilayers. This is accompanied with a higher viscoelasticity for the PVAm–SiO2–PVAm–NFC system. Ellipsometry indicated a dry-state thickness of 2.2 and 3.4nm per bilayer for the PVAm–NFC system and the PVAm–SiO2–PVAm–NFC system, respectively. Atomic force microscopy height images indicate that in both systems, a porous network structure is achieved. Young’s modulus of these thin films was determined by the Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM) technique. The Young’s modulus of the PVAm/NFC films was doubled, from 1 to 2GPa, upon incorporation of silica nanoparticles in the films. The introduction of the silica nanoparticles lowered the refractive index of the films, most probably due to an increased porosity of the films.

Preparation of Silica Nanoparticles and its Beneficial Role in Cementitious Materials

Spherical silica nanoparticles (n-SiO2) with controllable size have been synthesized using tetraethoxysilane as starting material and ethanol as solvent by sol-gel method. Morphology and size of the particles was controlled through surfactants. Sorbitan monolaurate, sorbitain monopalmitate and sorbitain monostearate produced silica nanoparticles of varying sizes (80-150 nm), indicating the effect of chain length of the surfactant. Increase in chain length of non-ionic surfactant resulted in decreasing particle size of silica nanoparticles. Further, the size of silica particles was also controlled using NH3 as base catalyst. These silica nanoparticles were incorporated into cement paste and their role in accelerating the cementitious reactions was investigated. Addition of silica nanoparticles into cement paste improved the microstructure of the paste and calcium leaching is significantly reduced as n-SiO2 reacts with calcium hydroxide and form additional calcium-silicate-hydrate (C-S-H) gel. It was found that calcium hydroxide content in silica nanoparticles incorporated cement paste reduced ∼89% at 1 day and up to ∼60% at 28 days of hydration process. Synthesized silica particles and cement paste samples were characterized using scanning electron microscopy (SEM), powder X-ray diffraction (XRD), infrared spectroscopy (IR) and thermogravimetric analysis (TGA).

Hard-templating synthesis of mesoporous carbon spheres with controlled particle size and mesoporous structure for enzyme immobilization

Mesoporous carbon spheres (MCSs) with controlled particle size and pore structure were synthesized via a combined hard templating and sol–gel processing within water-in-oil emulsions, using resorcinol–formaldehyde polymer as carbon precursor and colloidal silica nanoparticles as hard templates. The addition of silica nanoparticles in polymer sol not only served as the pore structure reagents but also shortened the gelation time, making it easy to control the emulsion process. The sphere size of MCSs can be controlled in the range from 10 to 500 μm by changing the emulsification conditions. The pore structure of MCSs can be tuned by adjusting the mass ratio of resorcinol–formaldehyde polymer to silica nanoparticles and the diameter of silica nanoparticles. The as-prepared MCSs possessed large surface area (>600 m 2 g −1), large pore volume (>1 cm 3 g −1) and a narrow pore size distribution replicated from the silica nanoparticles used. These MCSs exhibited extraordinary high adsorption capacities (ca. 1100 mg g −1) for α-Chymotrypsin (Chy) in solution. Due to their well-developed pore structure and the controllable pore size, as well as the unique shape and good affinity to biomolecules, the as-prepared MCSs should have a good potential in enzyme immobilization.

High compressive strength of home waste and polyvinyl acetate composites containing silica nanoparticle filler

Simple mixing and hot pressing methods were used to make composites from home waste—in particular, paper and dry leaves—using polyvinyl acetate (PVAc) as an adhesive and silica nanoparticles as filler. The optimum composition for the strongest composites, in terms of compressive strength, had a mass ratio of silica nanoparticles/PVAc/(paper + dry leaves) of 3:80:280. With this mass ratio, a compressive strength of 68.50 MPa was obtained for samples prepared at a pressing temperature of 150°C, pressing pressure of 100 MPa, and pressing time of 20 min. The addition of silica nanoparticles increased the compressive strength by about 50%, compared with composites made without the addition of nanosilica (45.60 MPa). Higher compressive strength was obtained at a higher pressing pressure. At a pressing pressure of 120 MPa, pressing temperature of 150°C, and pressing time of 20 min, a compressive strength of 69.10 MPa was obtained. When the pressing time was increased to 45 min at a pressing pressure of 120 MPa, a compressive strength of 84.37 MPa was measured. A model was also proposed to explain the effects of pressing pressure and pressing time on compressive strength. The model predictions were in good agreement with the experimental data.

Optimizing the incorporation of silica nanoparticles in polysulfone/poly(vinyl alcohol) membranes with response surface methodology

AbstractThe addition of silica nanoparticles and poly(vinyl alcohol) (PVA) to polysulfone (PSF) membranes was used to modify the membrane morphology and enhance membrane performance. The central composite design of the response surface methodology was used to predict the maximum permeability and real salt rejection (Rreal) of the PSF membranes. The factors affecting the permeability and Rreal values of the PSF membranes were the silica (0–12 wt % PSF) and PVA (0–2 wt % PSF) contents. The optimized responses, membrane permeability, and Rreal obtained experimentally were 61.9260 L m−2 h−1 bar−1 and 97.5850%, respectively, with deviation from the predicted values of 34.72 and 15.84%, respectively. In the further characterization, the contact angle results showed that PVA was important in stabilizing the nanoparticle surfaces to prevent agglomeration in the polymeric matrix. The tensile strength test confirmed that the addition of silica nanoparticles improved the mechanical strength of the PSF membranes. However, the addition of PVA had a weakening effect on the mechanical strength of the PSF membranes. The addition of silica nanoparticles and PVA affected the typical asymmetric structures of the PSF membrane less, as shown in the scanning electron micrographs. This may have been due to the good incorporation of additives in the PSF membranes, as observed from the energy‐dispersive X‐ray and Fourier transform infrared spectroscopy results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 Liver Transpl, 2011. © 2011 AASLD.

The role of interfacial interactions on the glass-transition and viscoelastic properties of silica/polystyrene nanocomposite

Filler surface properties and polymer–filler interactions have dominate influence on viscoelastic behavior of polymeric matrix composites. When the filler–filler spacing is on the order of the polymeric matrix molecular size, fillers may agglomerate through direct short-range interactions, also by overlapping of interfacial layers of neighboring fillers. In this work the effect of interfacial layer on the viscoelastic properties of silica/polystyrene composite was investigated. The Si/Ps nanocomposites were prepared by solution mixing method, and dynamic rheometry was employed to determine the viscoelastic behavior in the melt state. Experimental results show that, addition of silica nanoparticles to polystyrene matrix would increase the glass-transition temperature of polymer. This increasing will be accelerated by presence of nanoparticles with more filler–polymer adhesion energy, because of more interfacial layer volume fraction. It is helpful in evaluating the volume fraction and equivalent thickness of interfacial layer in polymer nanocomposites. Likewise it is shown that, the dynamic moduli of nanocomposite is enhanced associated with the increase in the glass-transition temperature. This study implies that the main source of increment in both dynamic modulus and glass-transition temperature of polymer nanocomposites is the presence of the immobilized interfacial layer and the secondary filler network.

A facile approach to fabricate porous nylon 6 nanofibers using silica nanotemplate

AbstractPorous Nylon 6 nanofibers were prepared using silica nanoparticles as the template. Firstly, Nylon 6/silica composite nanofibers were prepared as precursors by electrospinning Nylon 6 solutions containing different contents of silica nanoparticles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the surface morphology and the inner structure of composite nanofibers; where it was found that silica nanoparticles were distributed both inside and on the surface of nanofibers. Analytical techniques [Fourier transform infrared (FTIR), differential scanning calorimetry, thermal gravimetric analysis (TGA), and wide‐angle X‐ray diffraction) were used to study the structure and properties of these composite nanofibers. The glass transition, melting, and crystallization processes of the fibers were affected by the addition of silica nanoparticles. Secondly, porous Nylon 6 nanofibers were obtained by removing silica nanoparticles via hydrofluoric acid treatment. The removal of silica nanoparticles was confirmed using FTIR and TGA tests. SEM and TEM observations revealed the formation of the porous structure in these nanofibers. After the formation of the porous structure, Brunauer–Emmett–Teller specific surface areas of nanofibers were increased as compared to solid Nylon 6 and composite nanofibers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Negative Electrorheological Behavior in Suspensions of Inorganic Particles

An investigation is described on the electric-field-induced structures in colloidal dispersions. Both rheological determinations and direct microscopic observations are used with that aim. The starting point of this study is the so-called electrorheological (ER) effect, consisting of the mechanical reinforcing of a fluid or suspension due to formation of chains of molecules or particles after being polarized by the action of the field. One macroscopic manifestation of this phenomenon is the transformation of the fluid from a typically Newtonian behavior to a viscoelastic material, with finite yield stress and high elastic modulus. The systems investigated were suspensions of elongated goethite (β-FeOOH) particles in silicone oils with varying amounts of silica nanoparticles. The results showed the rather unusual behavior known as "negative ER effect", which can be best described by saying that the application of an electric field reduces the yield stress and the elastic modulus, that is, produces destruction of structures rather than their build up. The negative behavior is also found for suspensions of other inorganic powders, including hematite and quartz. On the contrary, the usual positive ER response is found for suspensions of cellulose and montmorillonite clay. The same happens if goethite suspensions are prepared in high volume fractions, high-viscosity fluids, or both. All of the results found are compatible with the so-called interfacial model of electrorheology: the reduction of the yield stress of goethite suspensions when the applied field is high enough is the consequence of particle migration toward the electrodes because of charge injection and subsequent electrophoresis. The migration leaves the gap between the electrodes devoid of particles and explains the decrease in yield stress. The addition of silica nanoparticles contributes to reduce the strength of this effect by hindering the charging and making it necessary to increase the field strength to observe the negative effect. The model appears to also be applicable to cellulose, although the positive response found for such particles is explained by their large size: larger diameters bring about larger attraction forces between particles, leading to a tendency to produce strong aggregates. This is likely to occur in suspensions of colloids which, because of their relatively high electrical conductivity, tend to acquire charge even in such nonpolar liquids as silicone oils.

Enhanced ionic conductivity in nano-composite solid polymer electrolyte: (PEG) x LiBr: y(SiO2)

In this paper, we report an enhancement in ionic conductivity in a new nano-composite solid polymer electrolyte namely, (PEG) x LiBr: y(SiO2). The samples were prepared, characterized, and investigated by XRD, IR, NMR, and impedance spectroscopy. Conductivity as a function of salt concentration shows a double peak. Five weight percent addition of silica nanoparticles increases the ionic conductivity by two orders of magnitude. Conductivity exhibits an Arrhenius type dependence on temperature. IR study has shown that the existence of nanoparticles in the vicinity of terminal O―H group results in a shift in IR absorption frequency and increase in amplitude of vibration of the terminal O―H group. This might lead to an enhancement in conductivity due to increased segmental motion of the polymer. 7Li NMR spectroscopic studies also seem to support this. Thus addition of nanoparticle inert fillers still seems to be a promising technique to enhance the ionic conductivity in solid polymer electrolytes.

Cycloolefin copolymer/fumed silica nanocomposites

AbstractWe prepared cycloolefin copolymer (COC)/fumed silica nanocomposites by melt compounding to study the effect of the filler dimensions (filler surface area) on the physical properties, with particular attention to their thermal, mechanical, and optical behaviors. Thermogravimetric analysis revealed a positive contribution of silica nanoparticles to the thermal degradation resistance of COC, as the decomposition temperature of the nanofilled samples increased by 40°C with respect to that of the unfilled matrix. Dynamic mechanical thermal analysis and quasi‐static tensile tests of the nanocomposites evidenced a slight stiffening effect, proportional to the nanofiller surface area, without any reduction in the fracture toughness. Creep resistance of the nanocomposites was increased by the addition of silica nanoparticles, especially when high‐surface‐area nanoparticles were used. The positive effect of the nanoparticles on the viscoelastic and fracture behavior was related to the uniform dispersion of silica aggregates in the matrix. Ultraviolet–visible spectrometry measurements evidenced that the original transparency of neat COC was practically maintained after the addition of silica nanoparticles. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

The effect of silica nanoparticles and carbon nanotubes on the toughness of a thermosetting epoxy polymer

AbstractSilica nanoparticles and multiwalled carbon nanotubes (MWCNTs) have been incorporated into an anhydride‐cured epoxy resin to form “hybrid” nanocomposites. A good dispersion of the silica nanoparticles was found to occur, even at relatively high concentrations of the nanoparticles. However, in contrast, the MWCNTs were not so well dispersed but relatively agglomerated. The glass transition temperature of the epoxy polymer was 145°C and was not significantly affected by the addition of the silica nanoparticles or the MWCNTs. The Young's modulus was increased by the addition of the silica nanoparticles, but the addition of up to 0.18 wt % MWCNTs had no further significant effect. The addition of both MWCNTs and silica nanoparticles led to a significant improvement in the fracture toughness of these polymeric nanocomposites. For example, the fracture toughness was increased from 0.69 MPam1/2 for the unmodified epoxy polymer to 1.03 MPam1/2 for the hybrid nanocomposite containing both 0.18 wt % MWCNTs and 6.0 wt % silica nanoparticles; the fracture energy was also increased from 133 to 204 J/m2. The mechanisms responsible for the enhancements in the measured toughness were identified by observing the fracture surfaces using field‐emission gun scanning electron microscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Improving the Thermal Behavior of Poly(propylene) by Addition of Spherical Silica Nanoparticles

AbstractSpherical silica nanoparticles were mixed with a PP matrix and the thermal behavior of the nanocomposites was studied. The nanocomposites presented drastic improvements in the degradation behavior under thermo‐oxidative conditions, showing complex multistep processes. Under inert conditions the improvements were lower. Our results indicate that mechanisms based on the labyrinth effect, nanoconfinement or trapping model, are not able to explain the whole enhanced thermal stability in these nanocomposites. Moreover, the high specific area of the nanoparticles (≈70 m2 · g−1) indicates that processes based on the adsorption of volatile polar products coming from the oxidative degradation mechanism are plausible.magnified image

The Addition of Silica Nanoparticles with Different Sizes for a Silica Film on Stainless Steel without Crack Formation

Inorganic protective silica film was tried on the surface of stainless steel using a sol-gel chemical route where tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES) were used. In the coating solution silica nanoparticles with different sizes were mixed. Then the film was deposited on the stainless steel substrate. It was intended that by mixing the small and the large particles at the same time a sufficient consolidation of the film was possible because of the high surface activity of the small nanoparticles and a modest silica film would be obtained with a low temperature heat treatment at as low as 200 °C. The prepared film showed enhanced adhesion when compared with a silica film without nanoparticle additions. The films also showed improved protect-ability against corrosion. Scanning electron microscopy (SEM), scratch test, potentiodynamic polarization scan and electrochemical impedance analysis were also used to characterize the films.

Silica–collagen bionanocomposites as three-dimensional scaffolds for fibroblast immobilization

Silica-collagen bionanocomposite hydrogels were obtained by addition of silica nanoparticles to a protein suspension followed by neutralization. Electron microscopy studies indicated that larger silica nanoparticles (80 nm) do not interact strongly with collagen, whereas smaller ones (12 nm) form rosaries along the protein fibers. However, the composite network structurally evolved with time due to the contraction of the cells and the dissolution of the silica nanoparticles. When compared to classical collagen hydrogels, these bionanocomposite materials showed lower surface contraction in the short term (1 week) and higher viability of entrapped cells in the long term (3 weeks). A low level of gelatinase MMP2 enzyme expression was also found after this period. Several proteins involved in the catabolic and anabolic activity of the cells could also be observed by immunodetection techniques. All these data suggest that the bionanocomposite matrices constitute a suitable environment for fibroblast adhesion, proliferation and biological activity and therefore constitute an original three-dimensional environment for in vitro cell culture and in vivo applications, in particular as biological dressings.

One-pot synthesis of organo-functionalized monodisperse silica particles in W/O microemulsion and the effect of functional groups on addition into polystyrene

The direct synthesis from TEOS and organosilanes is carried out in W/O microemulsion in order to prepare monodisperse functionalized silica nanoparticles. The well monodisperse particles are obtained successfully from a wide range of concentration of 3-aminopropyltriethoxysilane (APTES), 3-mercaptopropyltrimethoxysilane (MPTMS), phenyltrimethoxysilane (PTMS), vinyltriethoxysilane (VTES) and 3-cyanoethyltriethoxysilane (CETES) in the solution of TEOS and polyoxyethylene nonylphenol ether (NP-5). The particle size can be controlled without widening the distributions. On the other hand, the direct synthesis with these organosilanes and TEOS by conventional Stöber method using no surfactant provides colloidal solutions with DLS plots with wide or bimodal dispersions. NP-5 is removed by washing the colloids with DEGDEE and the decline of IR absorptions due to the benzene ring stretching is observed. The resultant colloidal powder is occluded into polystyrene by the polymerization of styrene monomer in the presence of these functionalized silica nanoparticles. The heat resistance of modified polystyrene is investigated by TG–DTA in dry air. The position of DTA peak due to combustion of the polymer is shifted to a higher temperature with the addition of silica nanoparticles. The considerably large shift is found in silica nanoparticles prepared with VTES and PTMS, whose difference is higher than that by the addition of simple silica nanoparticle with no functional groups.

The morphology of immiscible PDMS/PIB blends filled with silica nanoparticles under shear flow

The influence of surface nature (hydrophobic and hydrophilic) and concentration of silica nanoparticles on the coalescence behavior of immiscible polydimethylsiloxane (PDMS)/polyisobutylene (PIB) (90/10) blends under simple low-rate shear flow were investigated via optical shear technique. It was found that the coalescence of PIB droplets in PDMS matrix was suppressed efficiently by incorporating hydrophobic silica nanoparticles, and a constant droplet size was obtained at high particle contents. The addition of a small amount (<0.4 wt.%) of hydrophilic silica nanoparticles also decreased the size of PIB droplets. Clusters of small PIB droplets were formed at low filler concentration. When the filler concentration exceeded 0.8 wt.%, the clusters of PIB drops disappeared and elongated PIB threads with large size were formed, which suggest that the coalescence of PIB droplets was promoted. The results indicate that the discrepancy in the morphology evolution of PDMS/PIB blends upon the addition of silica nanoparticles is controlled not only by the surface chemistry of nanoparticles but also by their concentration in the blends.

Nanotechnology and Concrete

The structure of cement derivatives (cement-based materials) is complex and not fully understood. They are formed by self-assembly of different chemical species in a specific way to form basic building blocks (or units); the size of these units is on the order of a few nanometers. After they are formed, these basic units arrange themselves into larger units, still nano-metric in size, which constitute the cementitious matrix. The distinctive macroscopic properties of cementitious materials arise from their unique structural arrangement. This paper is an introduction to the results obtained by the Centre for Nanomaterials Applications in Construction over the past 5 years. The approach used in this study is a combination of experimental and numerical (multiscale simulation) techniques. On the one hand, the study shows how the addition of nanosilica particles can modify the mechanical properties of the cement matrix as well as its resistance to the calcium leaching process. On the other hand, the study illustrates how computational modeling is a valuable tool for gaining insight into the complex calcium silicate hydrate nanostructure and for designing improved cementitious materials.

Lithium-functionalised silicananoparticles for enhanced ionic conductivity in an organic ionic plastic crystal

Addition of silica nanoparticles functionalised with lithium propane sulfonate to the organic ionic plastic crystal N-ethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide ([C2mpyr][NTf2]) results in a significant increase in ionic conductivity. Analysis of these nanocomposites by impedance spectroscopy, NMR, positron annihilation lifetime spectroscopy (PALS) and Raman spectroscopy suggests that this is the result of higher matrix mobility due to an increase in defect size and concentration. The effect of these functionalised nanoparticles is compared to that previously observed for unfunctionalised nanoparticles in the lithium-doped and pure plastic crystal.