Nanosilica Sol Research Articles

Preparation and characterization of novel addition cured polydimethylsiloxane nanocomposites using nano-silica sol as reinforcing filler

A series of novel addition cured polydimethylsiloxane (PDMS) nanocomposites with various amounts of nano-silica sol were prepared via hydrosilylation for the first time. The influence of various amounts of nano-silica sol on the morphology, thermal behavior, mechanical and optical properties of these PDMS nanocomposites was studied in detail. It was found that with an increment in the amount of nano-silica sol the reinforcing effect of the nano-silica sol on the thermal and mechanical properties of the PDMS nanocomposites was very noticeable compared with the reference material. The prominent improvements in resistance to thermal degradation and mechanical properties can probably be attributed to the strong interaction of PDMS chains and uniformly dispersed particles resulting from the nano-silica sol. However, the transparency of the PDMS nanocomposites slightly decreased with an increment in weight fraction of nano-silica, compared with that of PDMS composite without nano-silica (Sol-0), which can probably be ascribed to an increasing size of the aggregated particles in the PDMS nanocomposites. The optimum amount of nano-silica sol for preparing novel addition curing PDMS nanocomposites was about 15 wt%. © 2015 Society of Chemical Industry

Nanocolloid cake properties determined from step‐up pressure filtration with single‐stage reduction in filtration area

A sophisticated method was developed for evaluating simultaneously and accurately both the average specific resistance and average porosity of the filter cake formed in unstirred dead‐end ultrafiltration of nanocolloids such as protein solution and nanosilica sol. In the method, a step‐up pressure filtration test was conducted by using a filter with a single‐stage reduction in the effective filtration area. The influence of the pressure drop across the cake on not only the average specific cake resistance but also on the average cake porosity of highly compressible filter cake was evaluated using only flux decline data in one dead‐end filtration test, taking advantage of the decrease in the cake thickness caused by the pressure increase. As a result, the cake properties were easily determined for a variety of nanocolloids. Constant pressure dead‐end ultrafiltration data obtained under various pressures and concentrations were well evaluated based on the method proposed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4426–4436, 2015

Thermal stability, mechanical and optical properties of novel addition cured PDMS composites with nano-silica sol and MQ silicone resin

A series of novel addition cured polydimethylsiloxane (PDMS) composites with a given weight amount of nano-silica sol were prepared using MQ silicone resin as reinforcing agent by hydrosilylation for the first time. Influences of the used amount of MQ silicone resin on morphology, thermal stability, mechanical and optical properties of these novel PDMS composites were mainly studied. It was found that thermal stabilities and transparencies of the novel PDMS composites with a given amount of nano-silica sol decreased with an increment in weight fraction of MQ silicone resin, as compared with that of PDMS composites without MQ silicone resin (SMQ-0), which were likely ascribed to an increasing amount of remained silanols and the increasing size of aggregated particles in PDMS composites, respectively. However, mechanical properties of the novel PDMS composites with a given weight of nano-silica sol were improved significantly with amount of MQ silicone resin increasing, especially their elongations at break, which were up to 10 times. This was a great breakthrough for PDMS composites. The prominent improvements in mechanical properties were probably attributed to strong interaction of PDMS chains and uniformly dispersed particles resulted from crosslink of MQ silicone resin and nano-silca sol. This strategy for preparing novel addition curing PDMS composites provides a guide method to develop high elastic PDMS composites with desirable properties in industry applications.

The effect of octamethylcyclotetrasiloxane (D4) addition on the structure and properties of film‐forming polyacrylate/silica core–shell composite particles

ABSTRACTThe film‐forming polyacrylate/silica core–shell nanocomposite particles with octamethylcyclotetrasiloxane (D4) were successfully synthesized via aqueous emulsion polymerization in the presence of a glycerol‐functionalized nano silica sol. The ring‐opening polymerization of D4 and the reaction with the glycerol‐functionalized nano silica particles before emulsion polymerization was the key procedure in this process. Transmission electron microscopy results showed that more nano silica particles tended to coat on the polyacrylate particles surface after the nano silica sols were modified with D4. The silica aggregation efficiency was increased from 90.9 to 98.6% when the amount of D4 used in the system was varied from 0 to 8.0 wt %. The transparency of the nanocomposite films was not compromised after D4 was incorporated into the system. The films of the nanocomposite particles with or without D4 both exhibited superior abrasive resistance. Furthermore, the water resistance and hydrophobicity of the films of these particles with D4 were also improved significantly. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42003.

Superhydrophobic and anti-icing properties at overcooled temperature of a fluorinated hybrid surface prepared via a sol-gel process.

A superhydrophobic surface with anti-icing performance has been the focus of research, but few studies have reported the effective and low cost strategy that met the requirements under overcooled conditions. In this article, the fluorinated sol-gel colloid coatings were simply prepared via hydrolytic condensation of nanosilica sol, methyltriethoxysilane (MTES) and 3-[(perfluorohexylsulfonyl)amino]propyltriethoxysilane (HFTES). The multi scale morphology and chemical composition of the artificial surfaces were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The influence of the surface roughness structure and fluorinated groups on the wettability and freezing delay time of the colloid surface under overcooled conditions were explored. As the HFTES content was higher than 6 wt%, the prepared colloid surface showed excellent superhydropobicity with a contact angle (CA) of about 166° at room temperature. The CA gradually reduced with the decrease of the temperature. Only the samples with high HFTES contents (above 30 wt%) exhibited special superhydrophobic and anti-icing properties under freeze temperature. Besides the surface roughness structure, the high fluoride enrichment on the surface plays a major role in the superhydrophobic and anti-icing properties under overcooled conditions.

Fabrication of Bioceramic Bone Scaffolds for Tissue Engineering

In this study, microhydroxyapatite and nanosilica sol were used as the raw materials for fabrication of bioceramic bone scaffold using selective laser sintering technology in a self-developed 3D Printing apparatus. When the fluidity of ceramic slurry is matched with suitable laser processing parameters, a controlled pore size of porous bone scaffold can be fabricated under a lower laser energy. Results shown that the fabricated scaffolds have a bending strength of 14.1 MPa, a compressive strength of 24 MPa, a surface roughness of 725 nm, a pore size of 750 μm, an apparent porosity of 32%, and a optical density of 1.8. Results indicate that the mechanical strength of the scaffold can be improved after heat treatment at 1200 °C for 2 h, while simultaneously increasing surface roughness conducive to osteoprogenitor cell adhesion. MTT method and SEM observations confirmed that bone scaffolds fabricated under the optimal manufacturing process possess suitable biocompatibility and mechanical properties, allowing smooth adhesion and proliferation of osteoblast-like cells. Therefore, they have great potential for development in the field of tissue engineering.

Nanosilica Sol Leads to Further Increase in Polyethylene Glycol (PEG) 1000-Enhanced Thermostability of β-Cyclodextrin Glycosyltransferase from Bacillus circulans

A major disadvantage of cyclodextrin production is the limited thermostability of cyclodextrin glycosyltransferase. The ability of combinations of nanosilica sol with polyethylene glycol (PEG) 1000 to enhance the thermostability of the β-cyclodextrin glycosyltransferase from Bacillus circulans was investigated. It was found that 10% PEG 1000 combined with 0.05% nanosilica sol could activate the β-cyclodextrin glycosyltransferase by 17.2%. Furthermore, 0.05% nanosilica sol leads to further increase in PEG 1000-enhanced thermostability of β-cyclodextrin glycosyltransferase. With the simultaneous addition of 10% PEG 1000 and 0.05% nanosilica into the enzyme solution, which was allowed to incubate for 60 min at 60 °C, 61.3% of β-cyclodextrin-forming activity could be retained, which was much higher than that with only 10% PEG 1000 added. Atomic force microscopy, fluorescence spectroscopy, and circular dichroism analysis indicated that silica nanoparticles helped PEG 1000 further protect the tertiary and secondary structures of β-cyclodextrin glycosyltransferase. This study provides an effective approach for improving the thermostability of cyclodextrin glycosyltransferase and related enzymes.

Synergistic Effect of Nanosilica Aerogel with Phosphorus Flame Retardants on Improving Flame Retardancy and Leaching Resistance of Wood

Nanosilica (Nano‐SiO2) sol fabricated by a sol‐gel process was introduced into wood modification with phosphorus flame retardants to improve the flame retardancy and leaching resistance of wood. The obtained materials were characterized by scanning electron microscopy and energy dispersive spectrometer (SEM‐EDS), thermogravimetric analysis (TGA), cone calorimetric (CONE), and infrared spectroscopy (FT‐IR). The residual rate of flame retardants before and after leaching was determinated by a leaching resistance. The results showed that the phosphorus flame retardants and SiO2 sol could reside in the poplar wood and are widely distributed in the vessels, pits, wood timber, and the spaces between wood cells of poplar substrate. TGA and CONE results indicated that the introduction of nano‐SiO2 aerogel with phosphorus flame retardants had a significantly synergistic effect on improving the flame retardancy and inhibiting the release of smoke and toxic gases. In addition, the leaching resistance test, combined with infrared analysis and EDS analysis, confirmed that the phosphorus flame retardants were able to be fixed by SiO2 aerogel in the wood.

Highly Populated and Nearly Monodispersed Nanosilica Particles in an Organic Medium and Their Epoxy Nanocomposites

An organic aminopropyl-functionalized nanosilica sol was synthesized in the presence of ethyl silicate, γ-(aminopropyl)triethoxysilane (KH550), and N,N-dimethylformamide (DMF) via a sol-gel technique and then used to prepare epoxy nanocomposites. Structure and morphology analyses of the obtained aminopropyl-functionalized nanosilicas were observed by dynamic light scattering (DLS), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM). TEM and DLS showed that modified nanosilicas with an average diameter of 30 nm dispersed homogeneously in DMF. The effects of the aminopropyl-functionalized nanosilica particles on the flexural modulus, impact strength, glass transition temperature (Tg), and bulk resistivity (ρv) of the epoxy nanocomposites were investigated. The toughening mechanisms and microstructures were determined in terms of the impact fracture surface morphology using scanning electron microscopy.

Acrylic acid grafted guargum–nanosilica membranes for transdermal diclofenac delivery

Green, hydrophobic device for controlled transdermal release of diclofenac sodium was designed from in situ nanosilica/acrylic acid grafted guargum membranes. Best grafting condition was assigned and nanocomposites were formed in situ using varying proportions of aqueous nanosilica sol. Nanocomposite/drug conjugates were formed by bringing down the medium pH from 9.0 to 7.0. The conjugates were characterized through infrared and solid state NMR spectroscopy, electron microscopy, hydro-swelling, surface contact angle, viscometry and biocompatibility. Most balanced property was exhibited by the membrane containing 1wt% nanosilica. It also had shown the highest encapsulation efficacy vis-à-vis slowest release as compared to others during experimentation in a Franz diffusion cell.

Effects of nanosilica addition on workability and compressive strength of Portland cement pastes

The effect of nano-size particles of amorphous silica (nanosilica) on the rheological behaviour and mechanical strength development of cementitious mixes is addressed. Mini-slump and rheometric tests were carried out on cement pastes made with three dose levels of nanosilica at different water/binder ratios. Cement paste workability resulted to be significantly lower than expected for the adopted water/binder ratios, as a consequence of instantaneous interactions between nanosilica sol and the liquid phase of cement pastes, which evidenced the formation of gels characterised by a significant water retention capacity. The resulting reduction of the mix workability was avoided by suitable addition procedures of superplasticizers. No appreciable improvement in the compressive strength development of cementitious mixes by nanosilica addition was observed, in contrast with some results from literature. This confirms conflicting experience on the problem, but some parameters affecting the strength development were identified and discussed.

Fabrication and Characterization of Polyorganosiloxane Superhydrophobic Film by Sol-Gel Method

The polyorganosiloxane superhydrophobic film was fabricated via a sol-gel process followed by nano-silica(SiO2) sol and new organo-siloxane reagent 1,1,1,3,5,5,5-heptamethyl-3-[2-(trimethoxysilyl)-ethyl]-tri-siloxane(in brief as HPTETOs), the chemical structure of the polyorganosiloxane superhydrophobic were described by Fourier transform infrared spectroscopy (FT-IR), the superhydrophobic property of the treated sample was measured by contact angle (CA) measurements. It revealed that nano-silica and polyorganosiloxane formed 3D hydrophobic groups on the film; the film has turned its wetting property from hydrophilic to superhydrophobic with water contact angle of 143.7°.

SWELLING DESWELLING STUDIES AFTER FREEZE–THAW TREATMENT OF NANOSILICA REINFORCED POLY (VINYL ALCOHOL)-BASED ORGANIC–INORGANIC HYBRID HYDROGEL

Aqueous nanosilica sol (particle size range: 9–13 nm, pH: 9.0) was added at various low concentration range (0.5–2 wt.%) into aqueous poly (vinyl alcohol) (PVA) of different molecular weight (98% hydrolyzed, 20 wt.%) (pH: 5.0) at room temperature under constant stirring to synthesize organic-inorganic hybrid hydrogels in presence of sodium lauryl sulphate as a silica dispersant. Buffer tablets were added to arrest the pH at 9.0 (to prevent any silica aggregation due to change in pH). The resultant hybrids were cast on Teflon sheets and dried in an oven at 50°C to drive out all the unbound water. Those films were then subjected to freese-thaw treatment continuously for 5 h. The freese-thawed films appeared opaque. The swelling-de swelling experiments with the hydrogels were carried out in distilled water at room temperature and consequently allowed to de-swell naturally. Those observations were correlated with the microstructures of the hybrid hydrogels.

Study on Preparation of Nano-Silicon Dioxide and the Influencing Factors of Particle Size Growth

Nano-silica sol with average particle size of 20-30nm has been prepared by the hydrolyzation method of elemental silicon powder with addition of MD-01. The influencing factors of nano-particle size growth such as reaction time, reaction temperature, dosages of sodium hydroxide and additive MD-01 were investigated in this paper, and the forming process of nano-silicon dioxide was also analysed.

Study on rheological behaviour of selfcrosslinkable acrylate emulsion with nanosilica sol by blending

A study on blending self-crosslinkable acrylate emulsion with nanosilica sol has been made to improve the paint film properties. Fourier transform infrared, differential scanning calorimetry and SEM are employed to characterise the film prepared by blending polyacrylic emulsion with nanosilica sol. The results of the rheological property show that the blended emulsions containing different silica sol contents are pseudoplastic fluid, and the apparent viscosity, consistency factor and zero shear viscosity increase in accordance with the content of the silica sol, but the emulsion flow index decreases. After being laid for 2 days, the apparent viscosity, consistency coefficient and zero shear viscosity of the emulsion increase, but the flow index is decreased in comparison with the emulsion with the same amount of silica sol without laying.

Preparation of waterborne epoxy acrylate/silica sol hybrid materials and study of their UV curing behavior

A novel waterborne epoxy acrylate (WEA) was synthesized using bisphenol A epoxy resin as basic resin (E-44), acrylic acid (AA) and maleic anhydride (MA) as modification agent. Nano-silica sol was synthesized by a sol–gel method using tetraethyl orthosilicate (TEOS) as precursor. The UV curable waterborne epoxy acrylate/silica sol hybrid materials were prepared by UV radiation, in which the synthesized WEA served as an organic polymer phase, and the nano-silica sol as an inorganic phase. 3-Trimethoxysilyl-propyl methacrylate (TMSPM) was selected as a coupling agent between the organic polymer phase and the inorganic phase. The influence of the photoinitiator amount and the curing time on the curing degree of the mixture system was investigated, and both the WEA coated film and the hybrid material coated film were characterized by Fourier transform infrared (FT-IR) spectra and thermogravimetry (TG) analysis. The experimental results showed that the maximum curing degree achieved was 88% gel content, the optimal photoinitiator amount was 3.5%, and curing time was 40 s. FT-IR analysis implied that WEA/silica sol hybrid materials were formed for the hybrid between WEA and TMSPM modification silica sol. TG analysis indicated that the decomposition temperature of WEA/silica sol hybrid material coated film was 33 °C higher than that of WEA coated film, which indicated that the addition of nano-silica sol improved the thermal stability of waterborne epoxy acrylate (WEA).

Nanosilica/PMMA composites obtained by the modification of silica nanoparticles in a supercritical carbon dioxide–ethanol mixture

Nanosilica/poly(methyl methacrylate) (PMMA) composites are used to improve the mechanical properties of neat PMMA polymer. In order to obtain superior mechanical properties, it is essential to achieve good bonding between the SiO2 nanoparticles and the PMMA matrix, which is typically achieved by coating silica nanoparticles with silane coupling agents. In this study, conventional and supercritical coating methods were investigated together with their influence on the mechanical properties of the obtained nanosilica/PMMA composites. The results indicate advantageous properties of nanosilica modified in the supercritical phase of carbon dioxide and ethanol in terms of particle size distribution, amount of coated silane, and dispersion in the PMMA matrix. Careful dispersion of the starting silica nanoparticles in ethanol at low temperatures in order to obtain a nanosilica sol plays an important role in deagglomeration, dispersion, and the coating process. The resulting nanosilica/PMMA composite containing nanoparticles obtained by supercritical processing of the nanosilica sol showed an increase in hardness by 44.6% and elastic modulus by 25.7% relative to neat PMMA, as determined using the nanoindentation technique. The dynamic mechanical analysis reveals that addition of nanoparticles as nanosilica sol and nanosilica gel enhances composite storage modulus by about 54.3 and 46.5% at 40 °C. At the same temperature, incorporation of modified silica nanoparticles with conventional method leads to an increase of 15.9% for the storage modulus, probably due to a large silica particle size and lower silane content in this sample.

Study on the Gel Aging of Nano Silica Sol Produced by a Y-shaped Reactor

Study on the Gel Aging of Nano Silica Sol Produced by a Y-shaped Reactor

PREPARATION OF HIGH-TEMPERATURE VULCANIZED SILICONE RUBBER OF EXCELLENT MECHANICAL AND OPTICAL PROPERTIES USING HYDROPHOBIC NANO SILICA SOL AS REINFORCEMENT

Hydrophobic nano silica sol (HNSS) was incorporated into polyvinylmethylsiloxane to prepare reinforced high-temperature vulcanized (HTV) silicone rubber. HTV silicone rubber filled with 40 phr HNSS showed excellent mechanical and optical properties: the tensile strength reached 11.7 MPa and the optical transmittance was higher than 90%. Possible reasons for reinforcement and transparency were discussed on the basis of the bound rubber percentage, total crosslink density, and SEM analysis. Our work suggests that HNSS is effective for reinforcement of HTV silicone rubber to endow excellent mechanical and optical properties.

Stabilization of dopamine in nanosilica sol–gel matrix to be used as a controlled drug delivery system

Sol–gel silica reservoirs were synthesized using tetraethoxysilane and functionalized with OH groups to stabilize dopamine into a ceramic matrix. The synthesis was made in air and N2 atmosphere. The dopamine–silica reservoirs were analyzed by FTIR spectroscopy, DTA–TGA and BET techniques. Nanostructured materials with a high specific surface area (500m2/g) and a mean pore size between 40 and 152Å were obtained. It was found that dopamine is entrapped and stabilized into the SiO2–OH matrix when the reservoirs are synthesized in N2 atmosphere.