Incorporation Of Silica Nanoparticles Research Articles

Reduction of calcium leaching in cement hydration process using nanomaterials

Continuous efforts are being made to understand the mineralogical and morphological properties of cement hydration at the early stages for speedy construction. Use of nanoparticles may provide faster kinetics due to their high surface/volume ratio. Spherical dispersed silica nanoparticles were prepared by employing the sol–gel method. Scanning electron microscope (SEM) and X-ray diffraction (XRD) studies revealed that the prepared nanoparticles are amorphous and uniform in size (∼50 nm). Further, these particles were incorporated into cement paste and investigated through SEM, XRD and thermogravimetric analysis techniques. Incorporation of silica nanoparticles into cement paste improved the microstructure of the paste, and calcium leaching is significantly reduced as silica nanoparticles react with calcium hydroxide (CH) and probably form an additional calcium–silicate–hydrate (C–S–H) gel. It was found that the CH content in the silica nanoparticle incorporated cement paste reduced by ∼86% at 1 day and up to ∼62% at 28 days of the hydration process. The XRD studies revealed that the addition of 2·5% (w/w) silica nanoparticle powder was found to be optimal to significantly digest the CH. Morphological features as studied through SEM showed that the microstructure of silica nanoparticle incorporated cement paste becomes significantly denser, and a more compact C–S–H gel is formed, thereby improving the mechanical properties of the resulting cement paste. Insight and tuning of cement based materials at nanolevel may thus greatly help in achieving ultrahigh performance concrete for durable and sustainable construction.

Amino-functionalized monolithic spin-type columns for high-throughput lectin affinity chromatography of glycoproteins

Hydrophilic poly(ethylene glycol)-based monoliths were synthesized in the spin-tip format for high-throughput applications via pulsed electron beam irradiation. Monoliths with a homogeneous porous structure and a total porosity of 69% were obtained. The cross-linked polymeric structure was further mechanically stabilized via the incorporation of silica nanoparticles. Amino-functionalization of the monoliths was accomplished by a straightforward, water-based, one-step approach that entailed the electron-beam irradiation-induced grafting of poly(allylamine). The amine functionalized spin columns showed very low unspecific protein adsorption and were successfully applied as adsorbents in lectin affinity chromatography for the purification of ovalbumin. The novel columns also outperformed a commercially available system.

An in situ polymerization approach for the synthesis of superhydrophobic and superoleophilic nanofibrous membranes for oil–water separation

Superhydrophobic and superoleophilic nanofibrous membranes exhibiting robust oil-water separation performance were prepared by a facile combination of electrospun cellulose acetate (CA) nanofibers and a novel in situ polymerized fluorinated polybenzoxazine (F-PBZ) functional layer that incorporated silica nanoparticles (SiO(2) NPs). By employing the F-PBZ/SiO(2) NPs modification, the pristine hydrophilic CA nanofibrous membranes were endowed with a superhydrophobicity with the water contact angle of 161° and a superoleophilicity with the oil contact angle of 3°. Surface morphological studies have indicated that the wettability of resultant membranes could be manipulated by tuning the surface composition as well as the hierarchical structures. The quantitative hierarchical roughness analysis using the N(2) adsorption method has confirmed the major contribution of SiO(2) NPs on enhancing the porous structure, and a detailed correlation between roughness and solid-liquid interface pinning is proposed. Furthermore, the as-prepared membranes exhibited fast and efficient separation for oil-water mixtures and excellent stability over a wide range of pH conditions, which would make them a good candidate in industrial oil-polluted water treatments and oil spill cleanup, and also provided a new insight into the design and development of functional nanofibrous membranes through F-PBZ modification.

Recovery of alcohols from water using polydimethylsiloxane–silica nanocomposite membranes: Characterization and pervaporation performance

AbstractDifferent polydimethylsiloxane (PDMS) nanocomposite membranes were synthesized by incorporating various contents of nanosized silica particles to improve the PDMS pervaporation (PV) performance. A uniform dispersion of silica nanoparticles in the PDMS membranes was obtained. The nanocomposite membranes were characterized morphologically by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that surface roughness increases by incorporating silica, and this decreases absorption of penetrants on the membrane. Swelling studies showed that the presence of silica nanoparticles into the PDMS membranes decreases degree of swelling, which can be attributed to rigidification of the PDMS matrix. Additionally, the results revealed that helium permeability decreases through the nanocomposite membranes, due to the more polymer chains packing. Effects of silica on recovery of isopropanol (IPA) from water mixtures were also investigated. Based on the results, incorporating silica nanoparticles promotes significantly the PDMS membrane selectivity because the polymer chains are rigidified and also the polymer free volume decreases. However, permeation flux decreases as diffusion of the penetrants reduces in the presence of silica nanoparticles within the PDMS membranes. As PV performance depends on operating conditions, effects of feed composition, and temperature were also studied. Moreover, recoveries of IPA, ethanol, and methanol from water mixtures were compared using the PDMS‐silica nanocomposite membranes. The results demonstrated that polarity and solubility of alcohols affect permeation flux and selectivity resulting in the higher permeation flux and selectivity for IPA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Efficient desulfurization by polymer–inorganic nanocomposite membranes fabricated in reverse microemulsion

The sulfur in gasoline will convert to SO2 after combustion under high temperature, which adversely affects human health and the environment. Membrane technique in particular pervaporation offers a number of potential advantages over conventional FCC gasoline desulfurization processes. The present study focuses on the performance enhancement of PDMS membrane by incorporating silica nanoparticles. Specifically, silica nanoparticles formed by the catalysis and templating of protamine in w/o reverse microemulsion are in situ embedded into PDMS bulk matrix, endowing the resultant oleophilic nanocomposite membranes with appropriate free volume properties and superior separation performance. Through the rational manipulation of biomimetic mineralization at water–oil interface, silica particles with uniform size are acquired. Following this protocol, by introducing organic PDMS oligomers into the oil phase, PDMS–SiO2 nanocomposite membranes are prepared in a facile way. The resultant nanocomposite membranes display superior permeability and permselectivity in the pervaporative desulfurization using thiophene/n-octane binary mixture as model gasoline, for example, under the condition of 500ppm sulfur in feed (40L/h) at 30°C, an enrichment factor of 4.83–5.82 with a normalized permeation rate of 6.61–10.76×10−5kgm/m2h is acquired.

Poly(vinyl chloride‐co‐vinyl acetate‐co‐maleic anhydride)/silica nanocomposites derived from in situ suspension polymerization

AbstractPoly(vinyl chloride‐co‐vinyl acetate‐co‐maleic anhydride) (PVVM)/silica nanocomposites were prepared by the suspension radical copolymerization of the monomers in the presence of fumed silica premodified with γ‐methylacryloxypropl trimethoxy siliane. Morphological observation showed that the silica particles of nanometer scale were well dispersed in the copolymer matrix of the nanocomposites films, whereas silica particles tended to agglomerate in the composites films prepared by the solution blending of PVVM with silica. The experimental results show that the thermal stability, glass‐transition temperature, tensile strength, and Young's modulus were significantly enhanced by the incorporation of silica nanoparticles. The enhancement of properties was related to the better dispersion of silica particles in polymer matrix and the interaction between the polymer chains and the surfaces of the silica particles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Thermoplastic polyurethane/silica nanocomposite fibers by electrospinning

AbstractThermoplastic polyurethane/silica nanocomposite fibers with good mechanical properties were prepared by electrospinning, using colloidal silica as the source of silica and dimethyl formamide as the solvent. The fiber morphology was examined by field emission scanning electron microscopy. The average fiber diameter is about 0.8 μm with 0–10 wt % silica, and silica nanoparticles were observed on all fiber surfaces. X‐ray photoelectron spectroscopy analysis of Si in combination with transmission electron microscopy observation suggest that silica nanoparticles have a fairly uniform distribution in the fibers rather than enriching on the fiber surfaces. Tensile tests show that the incorporation of silica nanoparticles can bring about a significant reinforcing effect without decreasing the ductility. The reinforcing effect is further confirmed by dynamic mechanical analysis. The thermoplastic polyurethane/silica composite fiber mats can adsorb gold nanoparticles after further treatment with 3‐aminopropyltriethoxysilane, demonstrating that the composite fibers could be used as functional fibers by using the properties of silica nanoparticles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Morphology and rheology of poly(l-lactide)/polystyrene blends filled with silica nanoparticles

The successful development of co-continuous structure from poly(l-lactide) (PLLA) blends by melt mixing with lower PLLA content is highly desired in preparing macroporous biomaterials. However, the low viscosity of PLLA makes it difficult to prepare co-continuous PLLA blends at low PLLA concentration. In this study, hydrophilic silica nanoparticle is adopted to control the morphology of co-continuous polystyrene (PS)/PLLA blends. The influence of nanoparticle concentration on the co-continuity intervals and rheological properties of PS/PLLA blends are examined. The morphological stability of blends against melt annealing is also determined and discussed with a conceptual coarsening model for co-continuous structure. The results demonstrate that the incorporation of silica nanoparticles into PS/PLLA blends can be used to prepare macroporous PLLA structure with controllable pore size at lower PLLA content.

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.

Fabrication of superhydrophobic cotton fabrics by silica hydrosol and hydrophobization

Superhydrophobic cotton fabrics were prepared by the incorporation of silica nanoparticles and subsequent hydrophobization with hexadecyltrimethoxysilane (HDTMS). The silica nanoparticles were synthesized via sol–gel reaction with methyl trimethoxy silane (MTMS) as the precursor in the presence of the base catalyst and surfactant in aqueous solution. As for the resulting products, characterization by particle size analyzer, scanning electron microscopy (SEM), scanning probe microscopy (SPM), X-ray photoelectron spectroscopy (XPS), and thermal gravimetric analysis (TGA) were performed respectively. The size of SiO2 nanoparticles can be controlled by adjusting the catalyst and surfactant concentrations. The wettability of cotton textiles was evaluated by the water contact angle (WCA) and water shedding angle (WSA) measurements. The results showed that the treated cotton sample displayed remarkable water repellency with a WCA of 151.9° for a 5μL water droplet and a WSA of 13° for a 15μL water droplet.

Co-cross-linking Silk Matrices with Silica Nanostructures for Robust Ultrathin Nanocomposites

We report on a novel assembly approach to fabricate ultrathin robust freely standing nanocomposite membranes. The materials are composed of a pre-cross-linked silk fibroin matrix with incorporated silica nanoparticles with silsesquioxane cores (POSS) or clay nanoplatelets. These reinforced silk membranes have enhanced mechanical properties as compared to traditional silk-based nanocomposites reported previously. Up to 6-fold and 8-fold increase in elastic modulus and toughness, respectively, were found for these nanocomposites. In contrast, traditional LbL-assembled nanocomposites showed only a 3-fold increase in mechanical strength. The silk nanocomposites obtained also revealed excellent optical transparency in the visible region especially if reinforced with POSS nanoparticles, which suggests their utility as low cost, nontoxic, and easily scalable reinforced biomaterials for mechanically demanding applications.

Fabrication of poly(ethylene glycol)‐based hydrogels entrapping enzyme‐immobilized silica nanoparticles

AbstractIn this study, we immobilized enzymes by combining covalent surface immobilization and hydrogel entrapment. A model enzyme, glucose oxidase (GOX), was first covalently immobilized on the surface of silica nanoparticles (SNPs) via 3‐aminopropyltriethoxysilane (APTES), and the resultant SNP‐immobilized enzyme was physically entrapped within photopolymerized hydrogels prepared from two different molecular weights (MWs) (575 and 8000 Da) of poly(ethylene glycol)(PEG). The hydrogel entrapment resulted in a decrease in reaction rate and an increase in apparent Km of SNP‐immobilized GOX, but these negative effects could be minimized by using hydrogel with a higher MW PEG, which provides higher water content and larger mesh size. The catalytic rate of the PEG 8000 hydrogel was about ten times faster than that of the PEG 575 hydrogel because of enhanced mass transfer. Long‐term stability test demonstrated that SNP‐immobilized GOX entrapped within hydrogel maintained more than 60% of its initial activity after a week, whereas non‐entrapped SNP‐immobilized GOX and entrapped GOX without SNP immobilization maintained less than 20% of their initial activity. Incorporation of SNPs into hydrogel enhanced the mechanical strength of the hydrogel six‐fold relative to bare hydrogels. Finally, a hydrogel microarray entrapping SNP‐immobilized GOX was fabricated using photolithography and successfully used for quantitative glucose detection. Copyright © 2009 John Wiley & Sons, Ltd.

Preparation and characterization of polymer/silica nanocomposites via double in situ miniemulsion polymerization

Polymer/SiO2 nanocomposite microspheres were prepared by double in situ miniemulsion polymerization in the presence of methyl methacrylate, butyl acrylate, γ-methacryloxy(propyl) trimethoxysilane, and tetraethoxysilane (TEOS). By taking full advantage of phase separation between the growing polymer particles and TEOS, inorganic/polymer microspheres were fabricated successfully in a one-step process with the formation of SiO2 particles and the polymerization of organic monomers taking place simultaneously. The morphology of nanocomposite microspheres and the microstructure, mechanical properties, thermal properties, and optical properties of the nanocomposite films were characterized and discussed. The results showed that hybrid microspheres had a raspberry-like structure with silica nanoparticles on the shells of polymer. The silica particles of about 20 nm were highly dispersed within the nanocomposite films without aggregations. The transmittance of nanocomposite film was comparable to that of the copolymer film at around 70–80% from 400 to 800 nm. The mechanical properties and the fire-retardant behavior of the polymer matrix were improved by the incorporation of silica nanoparticles. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3128–3134, 2010

Preparation and Characterization of Chitosan/SiO<SUB>2</SUB> Composite Films

Composite films made from chitosan, plasticizer, and incorporated silica nanoparticles were evaluated for their mechanical properties, thermal stability, water permeability, and surface characteristics. The influence of the chitosan amino group protonation upon the observed silica effects was also analyzed. Only slight differences between most of the properties of composite films and those of the biopolymer alone were observed. The lack of complete and uniform dispersion of the silica particles within the biopolymer matrix and the absence of relevant polymer-filler interactions in such composite membranes lead to a low level of interaction between the filler and the polymer, and only a reduced effect of the filler on the film properties. The silica effects worthy to mention are the decrease in Young's modulus and the increase in film elongation, and the slight influence on surface hydrophobicity and water vapour permeability, which were dependent on the neutralization pos-treatment process.

Fabrication of Triacetylcellulose−SiO2 Nanocomposites by Surface Modification of Silica Nanoparticles

We have successfully fabricated triacetylcellulose (TAC) polymer-silica nanocomposite films having up to 40 wt % of incorporated silica nanoparticles by deliberately designing a surface ligand that has a structure similar to that of polymer repeating units and effectively modifying the surface of silica nanoparticles through chemical bonding. Cross-sectional TEM analysis reveals no significant aggregation in all TAC-silica nanocomposite films. Thermal analysis results suggested that TAC-silica nanocomposites had higher T(g) and T(c) values as compared to pure TAC, and the increase in T(g) and T(c) was affected by the silica content. The transparency of all the nanocomposite films was over 80% in the visible range, confirming the excellent compatibility of nanoparticles with TAC. In this study, we enhance the interaction between nanoparticles and polymer matrices by modifying the surface of nanoparticles with a ligand that has a structure similar to that of polymer repeating units. It is expected that this method can be applied to other polymer systems to develop useful nanocomposites.

Large Strain and Fracture Properties of Poly(dimethylacrylamide)/Silica Hybrid Hydrogels

The synthesis and mechanical characterization of novel, tough poly(N,N-dimethylacrylamide) (PDMA)−silica hydrogel hybrids are presented to understand the role played by strong physical interactions between silica nanoparticles and the PDMA polymer on the properties of chemically cross-linked highly swollen PDMA networks. A detailed comparison of the hybrids with unmodified PDMA gels indicates that the incorporation of silica nanoparticles in the hydrogel increases the compression strength and the fracture toughness of notched samples up to an order of magnitude while increasing its modulus by a factor of 6 with a volume fraction of particles of the order of only 7%. The hybrid gels present a strain-dependent hysteresis but no permanent damage or residual strain upon unloading even after repeated cycling, a very unique property for such tough hydrogels. The reason for this exceptional increase in toughness is attributed mainly to the combined effect of breakable silica/polymer bonds and of a wide distribution of elastic chain lengths.

Poly(methyl methacrylate)/silica nanocomposite fibers by electrospinning

AbstractUniform poly(methyl methacrylate) (PMMA)/silica nanocomposite fibers containing up to 20 wt % silica were prepared by electrospinning. The electrospun solutions were prepared by mixing a solution of PMMA in dimethyl formamide (DMF) with colloidal silica in methyl ethyl ketone (MEK). The average fiber diameter decreases from 2.49 μm to 1.69 μm when 20 wt % silica is incorporated as a result of considerably increased solution conductivity, although the solution viscosity increases significantly, which should result in opposite effect. Thinner fibers (down to 350 nm) can be obtained by changing DMF/MEK proportion and by the addition of an ammonium salt. Nano‐sized silica particles (10–40 nm) distributes homogeneously in the fibers, as revealed by transmission electron microscopy. Furthermore, the incorporation of silica nanoparticles can change the thermal properties and surface wettability of the fiber mats. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1211–1218, 2009

Thermal decomposition behavior of poly(ethylene 2,6‐naphthalate)/silica nanocomposites

AbstractPoly(ethylene 2,6‐naphthalate) (PEN) nanocomposites reinforced with silica nanoparticles were prepared by direct melt compounding. Dynamic thermogravimetric analysis was conducted on the PEN/silica nanocomposites to clarify the effect of silica nanoparticle on the thermal decomposition behavior of the resultant nanocomposites. There is a significant dependence of thermal decomposition behavior for PEN/silica nanocomposites on the content of silica nanoparticles and heating rate. The variation of the activation energy for thermal decomposition reflected the improvement of the thermal stability of the PEN/silica nanocomposites. The unique characteristics of silica nanoparticles resulted in physical barrier effect against the thermal decomposition, leading to the enhancement of the thermal stability of the PEN/silica nanocomposites. The incorporation of silica nanoparticles into the PEN matrix increased the storage modulus of the PEN/silica nanocomposites and made it possible for them to sustain higher modulus at higher temperature relative to pure PEN. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers

Enhancement of the gas separation properties of polybenzimidazole (PBI) membrane by incorporation of silica nano particles

In the present work, the effect of silica nano particles on the permeability of CO 2, CH 4 and N 2 gases in polybenzimidazole (PBI) membranes has been studied. Silica particles were prepared via the sol–gel method through the hydrolysis of tetraethoxysilane (TEOS). PBI and PBI–silica hybrid membranes were prepared by thermal phase inversion method. Scanning electron microscopy (SEM), X-ray diffraction and FTIR analyses were employed in order to characterize the PBI and PBI–silica composite membranes. The obtained SEM micrographs confirmed the nano-scale distribution of silica particles in the polymer matrix. Gas permeation experiments showed an increase in the solubility and a corresponding reduction in the diffusivity of the gases through the membranes by increasing the silica content in the polymer matrix; consequently, the permeability of the condensable CO 2 and CH 4 gases were enhanced whereas that of non-condensable N 2 gas significantly decreased upon increasing the silica content of the nano-composite membranes. The permeability of CO 2 and its selectivity over N 2 was increased from 0.025 Barrer and 3.5 in pure PBI to 0.11 Barrer and 71.3 in the nano-composite containing 20 wt% of the silica particles. There was a strong correlation between the solubility coefficients and condensability of the gases, as well as the diffusion coefficient of the penetrants and their kinetic diameter. Higuchi model fitted fairly well with the experimental results concerning the permeability of nitrogen gas in nanocomposite membranes, supposing the K H = 3.8.

Poly (butylene terephthalate)/silica nanocomposites prepared from cyclic butylene terephthalate

Poly (butylene terephthalate) (PBT)/silica nanocomposites were compounded from cyclic butylene terephthalate (CBT) resin with very low melt viscosity via high-speed stirring and subsequent in situ polymerization. The effect of silica nanoparticles on the properties of CBT and its polymer composites has been studied. It was shown that the well-dispersed silica nanoparticles, even in small content (1–2 wt.%), result in the dramatic extension of the polymerization process of CBT resin. The flexural properties of polymerized PBT nanocomposites, including modulus, yield strength and failure strain, was improved significantly with the incorporation of silica nanoparticles.