Silica Nanoparticles In Solution Research Articles

Facile formation of nanoparticle patterns by water induced flow of a polymer thin film

In general, techniques of particle arrays on polyelectrolyte multilayers involve complex and inefficient steps. Here, we present a simple yet robust method for fabricating ordered two-dimensional nanoparticle arrays on polyelectrolyte multilayers via water induced flow of multilayer films. The process is easy and repeatable without the requirement of complicated surface preparation or chemical modification. By droplet evaporation of silica or other functional nanoparticle solutions on a patterned PDMS stamp, nanoparticle arrays on polyelectrolyte multilayer film surfaces will occur when the PDMS stamp contacts with polyelectrolyte multilayers. This work provides a facile and efficient approach to fabricate colloidal nanoparticle or other functional nanoparticle arrays on polyelectrolyte multilayers which are potentially useful for sensor materials, biomaterials and so on.

Supramolecular associates of double-decker lanthanide phthalocyanines with macromolecular structures and nanoparticles as the basis of biosensor devices

The electronic-spectroscopy technique is used to study the properties of solutions of double-decker diphthalocyanine complexes of lanthanides LnPc2 (Ln = Ho, Er, Yb, Lu) in chloroform, dimethylformamide, water-micellar systems, solutions of proteins, and polymers, as well as on the surface of silica nanoparticles. In all the studied systems, a correlation is established between the positions of maxima of absorption bands of LnPc2 and the ionic radius of the complexing metal. Redox processes determined by the nature of the solubilizer are detected in supramolecular associates of LnPc2 with macrocompounds and nanoparticles. Finally, prototypes of sensor systems are suggested for determination of albumin and silica nanoparticles in solutions. Films of polyvinyl pyrrolidone and polyvinyl alcohol containing LuPc2 and YbPc2 are obtained, for which sensor response to albumin and nanosilica is also established. On the whole, the results show good prospects for development of sensor devices based on the studied systems.

Silica-based nanofibers for electrospun ultra-thin layer chromatography

Nanofibrous silica-based stationary phases for electrospun ultra-thin layer chromatography (E-UTLC) are described. Nanofibers were produced by electrospinning a solution of silica nanoparticles dispersed in polyvinylpyrrolidone solutions to create composite silica/polymer nanofibers. Stationary phases were created from as-spun nanofibers, or the nanofibers were heated either to crosslink the polyvinylpyrrolidone or to calcine and selectively remove the polymer. As-spun, crosslinked, and calcined nanofibers with similar mat thicknesses (23–25μm) were evaluated as stationary phases for E-UTLC separations of laser dyes and amino acids and compared to commercial silica TLC plates. As-spun nanofiber plates offered fast mobile phase velocities, but like other polymer-based nanofibers, separations were only compatible with techniques using nonsolvents of the polymer. Crosslinked nanofibers were not as limited in terms of chemical stability, but separations produced tailed spot shapes. No limitations in terms of mobile phases, analyte solvents, and visualization techniques were observed for calcined nanofibers. Highly efficient separations of amino acids were performed in 15mm on calcined nanofiber plates, with observed plate heights as low as 8.6μm, and plate numbers as large as 1400. Additional alignment of the nanofibers provided shorter analysis times but also larger spot widths. The extension of stationary phases to silica-based nanofibers vastly expands the range of mobile phases, analyte solvents, and visualization techniques which can be used for E-UTLC separations.

Effect of incorporation route on dispersion of mesoporous silica nanospheres in cement mortar

It was shown that the uniform dispersion of nanoparticles into a cement matrix is a key issue in their application in the field. Therefore, here we compare two methods of incorporation of mesoporous silica nanospheres into cement using acetone (method A) or water (method B) as a dispersant, to reveal its influence on the mechanical properties of the formed composite. It was proven that in both cases, small amounts of silica nanoparticles agglomerates does not affect the mechanical properties of the cement mortars. However, the addition of mesoporous silica nanospheres to cement in an acetone solution is more effective and results in higher compressive and flexural strength than the sample of the composite formed from water solution of silica nanoparticles and cement.

Controlled etching of internal and external structures of SiO2 nanoparticles using hydrogen bond of polyelectrolytes.

We have demonstrated a novel strategy for the synthesis of mesoporous silica nanoparticles (MSNPs) using a surfactant-free method under ambient conditions. By the simple addition of an amine-based polymer (polyethylenimine; PEI) with a high molecular weight to a silica nanoparticle (SNP) solution, two types of MSNPs, including rambutan-like MSNPs (R-MSNPs) and hollow MSNPs (H-MSNPs), were produced. The structural changes of the MSNPs were systematically studied using various reaction conditions (reaction time, molar ratio and molecular weight of PEI, etc.) and were observed using electron microscopic techniques. The formation mechanisms of both MSNPs were carefully investigated using XPS, Raman, and IR spectroscopies. Because the synthesized MSNPs are highly porous materials that contain internal organic/inorganic networks, we investigated the removal/adsorption properties of these MSNPs with respect to pollutants toward possible future use in environmental remediation applications. The H-MSNPs exhibited better environmental remediation capabilities relative to the R-MSNPs because PEI is present between the cobweb-like internal structures of the H-MSNPs, thereby providing a significant number of reaction sites for the adsorption of pollutants. The approach presented here can also be used as a direct method for the preparation of intraconnected networks within the substructures.

The impact of silica nanoparticles on the performance of polymer solution in presence of salts in polymer flooding for heavy oil recovery

Due to role of polymer in increasing sweep efficiency during oil recovery, much attention has been paid to the using polymer solutions in enhanced oil recovery methods. In spite of the existence of the great researches in this area, the role of nanoparticles in modification of the polymer performance in the presence of salts has not been examined before. Furthermore, there is no information about how the dispersed silica nanoparticles affect the heavy oil recovery during the polymer flooding in the presence of divalent cations. In this study, a series of polymer flooding experiments are performed in a quarter five-spot glass micromodel saturated with heavy oil. Solutions of polyacrylamide and dispersed silica nanoparticles in polyacrylamide (DSNP) with different salinities are used as the injectants to examine the effect of silica nanoparticles on the polyacrylamide performance in the presence of salts during polymer flooding of heavy oil, the oil recovery values were measured in different salinities. Furthermore, viscosity measurements are performed to help analyzing the results of polymer flooding tests. The oil recovery is measured via analysis of the continuously captured images during the displacement. Also, microscopic monitoring is used to analyze the distribution of residual heavy oil and polymer solution at the pore level. The results showed that the oil recovery decreases by increasing the salt concentration during the polyacrylamide flooding whereas in case of flooding with suspension of silica nanoparticles in polyacrylamide, decreasing rate in oil recovery is lower. The results of viscosity measurements showed that increasing the salt concentration lowers the viscosity of polyacrylamide solution to a minimum value which at higher values salts had a reverse effect and increased solution viscosity. Moreover, viscosity of silica nanosuspension in polyacrylamide was higher than that of polyacrylamide solution at the same salinity. This increase in viscosity becomes more noticeable by increasing the silica nanoparticles concentration. Finally oil recovery values versus injectant viscosity were plotted for different condition of salinity which confirmed the previous results, it means oil recovery was increased wherever injectant viscosity has been increased.

Nanoparticle solutions as adhesives for gels and biological tissues

Adhesives are made of polymers because, unlike other materials, polymers ensure good contact between surfaces by covering asperities, and retard the fracture of adhesive joints by dissipating energy under stress. But using polymers to 'glue' together polymer gels is difficult, requiring chemical reactions, heating, pH changes, ultraviolet irradiation or an electric field. Here we show that strong, rapid adhesion between two hydrogels can be achieved at room temperature by spreading a droplet of a nanoparticle solution on one gel's surface and then bringing the other gel into contact with it. The method relies on the nanoparticles' ability to adsorb onto polymer gels and to act as connectors between polymer chains, and on the ability of polymer chains to reorganize and dissipate energy under stress when adsorbed onto nanoparticles. We demonstrate this approach by pressing together pieces of hydrogels, for approximately 30 seconds, that have the same or different chemical properties or rigidities, using various solutions of silica nanoparticles, to achieve a strong bond. Furthermore, we show that carbon nanotubes and cellulose nanocrystals that do not bond hydrogels together become adhesive when their surface chemistry is modified. To illustrate the promise of the method for biological tissues, we also glued together two cut pieces of calf's liver using a solution of silica nanoparticles. As a rapid, simple and efficient way to assemble gels or tissues, this method is desirable for many emerging technological and medical applications such as microfluidics, actuation, tissue engineering and surgery.

Dynamics of Hybrid Poly(acrylamide-co-N,N-dimethylacrylamide) Hydrogels Containing Silica Nanoparticles Studied by Dynamic Light Scattering

Nanohybrid gels based on poly(acrylamide-co-N,N-dimethylacrylamide), P(AAm-co-DMA), and colloidal silica nanoparticles were synthesized by radical polymerization, and the influence of hydrogen bonding between DMA and silica nanoparticles on the dynamics of the network and the nanoparticles were studied by dynamic light scattering. As previously reported, in the case of polyacrylamide homopolymer, PAAm, which have no hydrogen bonding with silica, we observed two decay modes in the hybrid gels, a gel mode and a Brownian diffusion mode of silica nanoparticles. When we increased the DMA weight fraction (or physical cross-link density), we observed (1) a higher scattered light intensity than the silica suspension and the gel without silica, (2) an increased plateau value of the autocorrelation function, (3) a slowing down of the silica diffusion mode, and (4) no influence on the gel mode. These results, compared with those of the mixtures of the linear PDMA and silica nanoparticles in solution (showing an increase in the scattered light intensity and in the hydrodynamic radius), indicate that the P(AAm-co-DMA) hybrid gels have a more heterogeneous structure due to the adsorption of the polymer on the silica nanoparticles, and that the silica nanoparticles, trapped in the network due to the adsorption of the polymer, show a cage dynamics in the network. The local viscoelastic properties probed by the bound nanoparticles are discussed.

Silica nanoparticle-based films on titanium substrates with long-term superhydrophilic and superhydrophobic stability

We report the fabrication of stable superhydrophilic and superhydrophobic surfaces on titanium substrates using simple methods. Sandblasting the titanium surface to generate microscale roughness, followed by dip-coating in a colloidal silica nanoparticle solution to generate nanoscale roughness and a hydrophilic surface chemistry, produces a superhydrophilic surface. Further chemical modification with a several-nanometer-thick low surface energy fluorinated carbon film renders the surface superhydrophobic. The wettability of these superhydrophilic and superhydrophobic surfaces display a high degree of stability, as both surfaces retain their wetting properties for at least 54 days under multiple wetting/de-wetting cycles. Furthermore, the superhydrophilic surfaces retain their wetting properties in excess of 25 months after storage in ambient atmosphere. Due to their long-term wetting stability and ease of fabrication, these surfaces have potential applications in a variety of fields, including biomedical fields where titanium is widely used.

An Experimental Investigation of Silica Nanoparticles Effect on the Rheological Behavior of Polyacrylamide Solution to Enhance Heavy Oil Recovery

The use of polymer flooding as one of enhanced oil recovery methods has recently increased. The occurrence of high shear rates in reservoir and near well bore through perforation nozzles during polymer flooding cause shear degradation of polymers and therefore polymer viscosity has decreased. Rheological behavior of polymer solution in different conditions of oil reservoir is one of the key factors to develop use of polymer solutions. A few researches are available regarding improving rheological behavior of polymeric solution. In this study, to investigate the effect of nanoparticles on rheological behavior of polymer solutions two samples were prepared: polyacrylamide solution in water and suspension of silica nanoparticles in polyacrylamide solution. The sample viscosities in different shear rates were measured. The best rheology models were developed to state rheological behavior of prepared samples and the measured data were compared to power law model. An increase in the viscosity of the suspension solution with respect to polymer solution in different shear rates was observed. Rheological analysis showed that power law model is a good rheology model to demonstrate rheological behavior of suspension in low and medium shear rates and is an acceptable model for polymer solution in low shear rates. Two types of flooding test were performed in a glass micromodel: flooding by polyacrylamide solution and suspension of silica nanoparticles in polyacrylamide solution. The results of flooding test showed a 10% increase in oil recovery for nanosuspension solution in comparison with polymer solution after one pore volume fluid injection.

Aggregation kinetics and shear rheology of aqueous silica suspensions

The kinetics of aggregation of silica nanoparticle solutions as a function of NaCl and silica concentrations is studied experimentally and theoretically. Silica nanoparticles form fractal aggregates due to the collapse of the electrical double layer at high salt concentrations and resulting reduction in stabilizing repulsive force. We propose a convenient model to describe the aggregation of silica nanoparticles and the growth of their aggregate size that depends on particle size and concentration and salt concentration. The model agrees well with experimental data. The aggregation of silica nanoparticles also affects the rheology of the suspension. We propose an equilibrium approach for sediment volume fraction to determine the maximum effective packing fraction. The results for the relative viscosity of silica aggregates agree well with the proposed viscosity model, which also collapses onto a single master curve.

One-Step Index-Tunable Antireflection Coatings from Aggregated Silica Nanoparticles

We demonstrate a method for producing thickness- and refractive index-tunable antireflection coatings utilizing a one-step spin coating procedure with silica nanoparticle solutions. Aging nanoparticle solutions under controlled pH and temperature induces aggregation, allowing precise control of the porosity and refractive index of the spin-processed coating. Coating thickness measurements as a function of solution aging time and temperature allow for determination of the activation energy of the reaction-limited aggregation process. We demonstrate optimization of the antireflection effect for a single-layer silica nanoparticle coating on glass, and suggest that the aggregation method may be generalized to various other nanoparticle-based assemblies.

Phase behavior and rheological characterization of silica nanoparticle gel

Preferential injection into high permeability thief zones or fractures can result in early breakthrough at production wells and large unswept areas of high oil saturation, which impact the economic life of a well. A variety of conformance control techniques, including polymer and silica gel treatments, have been designed to block flow through the swept zones. Over a certain range of salinities, silica nanoparticle suspensions form a gel in bulk phase behavior tests. These gels have potential for in situ flow diversion, but in situ flow tests are required to determine their applicability. To determine the appropriate scope of the in situ tests, it is necessary to obtain an accurate description of nanoparticle phase behavior and gel rheology. In this paper, the equilibrium phase behavior of silica nanoparticle solutions in the presence of sodium chloride (NaCl) is presented with four phase regions classified as a function of salinity and nanoparticle concentration. Once the gelation window was clearly defined, rheology experiments of silica nanoparticle gels were also carried out. Gelation time decreases exponentially as a function of silica concentration, salinity, and temperature. Following a power law behavior, the storage modulus, G′, increases with particle concentration. Steady shear measurements show that silica nanoparticle gels exhibit non-Newtonian, shear thinning behavior. This comprehensive study of the silica nanoparticle gels has provided a clear path forward for in situ tests to determine the gel’s applicability for conformance control operations.

Condensation of silica nanoparticles on a phospholipid membrane

The structure of the transient layer at the interface between air and the aqueous solution of silica nanoparticles with the size distribution of particles that has been determined from small-angle scattering has been studied by the X-ray reflectometry method. The reconstructed depth profile of the polarizability of the substance indicates the presence of a structure consisting of several layers of nanoparticles with the thickness that is more than twice as large as the thickness of the previously described structure. The adsorption of 1,2-distearoyl-sn-glycero-3-phosphocholine molecules at the hydrosol/air interface is accompanied by the condensation of anion silica nanoparticles at the interface. This phenomenon can be qualitatively explained by the formation of the positive surface potential due to the penetration and accumulation of Na+ cations in the phospholipid membrane.

Fabrication and characterization of transparent superhydrophilic/superhydrophobic silica nanoparticulate thin films

The realization of transparent and superhydrophilic/superhydrophobic surfaces by silica nanoparticulate thin films was exploited in this work. An aqueous electrostatic layer-by-layer assembly process was utilized to fabricate nanoparticulate thin films with adhesion/body/top layer structure on glass substrates by using SiO2 nanoparticles and polyelectrolytes. The effects of volume ratio of differently sized silica nanoparticle solutions for the body layer deposition on transmittance in visible light region and surface wettability of the nanoparticulate thin films were systematically studied. The experimental results revealed that both optical transparency and superhydrophobicity/superhydrophilicity can be achieved on the same SiO2 nanoparticulate thin film by using appropriate volume ratios of differently sized silica nanoparticle solutions for body layer deposition, and with and without silane treatment in the fabrication process. The high contrast of wettability that can be achieved by this way suggests the possibility of the creation of superhydrophilic/superhydrophobic patterning and superhydrophilic–superhydrophobic gradient on the same surfaces.

Chemically Modified (Nano)Silica as Sensitive Material for Arginine and Lysine

Silica has been derivatized with aminopropyl groups which subsequently have been chemically modified with N-methoxy-2,6-dinitroaniline derivatives to yield a solid which changes its color in the presence of arginine or lysine, from yellow to blue. Other amino-acids (such as glycine, valine, cysteine, cystine, alanine, phenylalanine, histidine) do not showed this behavior. The same procedure may be applied to silica nanoparticles. The new materials were characterized by UV–Vis, IR, and TEM. Visible spectra of a water solution of derivatives silica nanoparticles in absence (dash line) and in the presence of arginine or lysine (solid line).

Forces between functionalized silica nanoparticles in solution

To prevent the flocculation and phase separation of nanoparticles in solution, nanoparticles are often functionalized with short chain surfactants. Here we present fully atomistic molecular dynamics simulations which characterize how these functional coatings affect the interactions between nanoparticles and with the surrounding solvent. For 5-nm-diameter silica nanoparticles coated with poly(ethylene oxide) (PEO) oligomers in water, we determined the hydrodynamic drag on two approaching nanoparticles moving through solvent and on a single nanoparticle as it approaches a planar surface. In most circumstances, macroscale fluid theory accurately predicts the drag on these nanoscale particles. Good agreement is seen with Brenner's analytical solutions for wall separations larger than the soft nanoparticle radius. For two approaching coated nanoparticles, the solvent-mediated (velocity independent) and lubrication (velocity-dependent) forces are purely repulsive and do not exhibit force oscillations that are typical of uncoated rigid spheres.

Ion-size effect at the surface of a silica hydrosol

Using synchrotron x-ray reflectivity, I studied the ion-size effect for alkali ions (Na(+), K(+), Rb(+), and Cs(+)), with densities as high as 4x10(18)-7x10(18) m(-2), suspended above the surface of a colloidal solution of silica nanoparticles in the field generated by the surface electric-double layer. I found that large alkali ions preferentially accumulate and replace smaller ones at the surface of the hydrosol, a result qualitatively agreeing with the dependence of the Kharkats-Ulstrup single-ion electrostatic free energy on the ion's radius.

Electrospun Silica—Polybenzimidazole Nanocomposite Fibers

AbstractA new route for the manufacturing of silica/poly(benzimidazole) (PBI) nanocomposites fibers is described. PBI was synthesized via melt polycondensation and polycondensation in poly(phosphoric acid). Solutions of PBI and silica nanoparticles in N,N‐dimethylacetamide (DMAc) were electrospun to fibers and non‐wovens. The resulting materials were analyzed by ATR‐IR spectroscopy, small‐angle X‐ray scattering (SAXS) and nitrogen sorption measurements. The non‐wovens could be processed towards dense, cross‐linked membranes by hot pressing and treatment with p‐xylylene dichloride.magnified image

Nanosized Polymer Particle-facilitated Preparation of Mesoporous Silica Particles Using a Spray Method

Abstract Spherical silica particles with large mesopores and controlled particle size in the submicron range were prepared using a mixed solution of silica nanoparticles and nanosized polymer particle as a template via spray routes.