Aggregation Of Silica Particles Research Articles

Experimental analysis of Algerian diatomaceous earth aimed at silicon extraction

Silicon, primarily derived from silica, plays a crucial role in creating glass, ceramics, and heat-resistant materials, making it indispensable across various industrial sectors. Moreover, it is fundamental in the manufacturing of semiconductors and electronic components. The main goal of our project is to study diatomite, particularly from Algerian deposits, such as western diatomite in order to extract silicon to achieve this, we will conduct experiments using electron microscopy and X-Ray Diffraction (XRD). These analyses highlight the significance of chemical methods in silicon extraction. Our focus is primarily on improving our study by examining the impact of various parameters, notably the use of acid cleansings, on the final product. These parameters are chosen based on the complex chemical reactions governing the aggregation of silica particles in the solution.

AC-assisted deposition of aggregate free silica films with vertical pore structure.

Silica thin films with vertical nanopores are useful to control access to electrode surfaces and may act as templates for growth of nanomaterials. The most effective method to produce these films, electrochemically assisted surfactant assembly, also produces aggregates of silica particles. This paper shows that growth with an AC signal superimposed onto the potential avoids the aggregates and only very small numbers of single particles are found. This finding is linked to better control of the diffusion field of hydroxide ions that are responsible for particle growth. The resultant films are smooth, with very well-ordered hexagonal pore structures.

Homopolymer-Assisted Fusions of Polymer Brushes and Block Copolymer Vesicles

The applications of materials are closely associated with surface structures and properties. Surface coassembly of block copolymers (BCPs) and polymer brushes is an effective method to fabricate surface structures with tunable properties. The surface coassembly approach not only provides a method for the fabrication of surface structures but also provides a method for the synthesis of hybrid materials with hierarchical nanostructures. In this research, polystyrene (PS)-assisted fusions of PS brushes on silica particles and BCP vesicles in a surface coassembly process are studied. The concentrations of BCP and PS homopolymer are two key parameters in the fusion process. When the BCP concentration is held constant at 3 mg/mL, with an increase in PS concentration, aggregation of silica particles and the fusions of polymer brushes and BCP vesicles are observed. When the BCP concentration is kept at 8 mg/mL, large hybrid compound structures composed of silica particles and the fused vesicles are formed. In the surface coassembly process, the addition of PS leads to an increased volume percentage of the solvophobic component in the system. To reduce the surface energy and the unfavorable contact between the solvent and PS, silica particles with PS brushes and BCP vesicles are fused into large compound structures. A variety of hybrid materials with hierarchical macro-/mesostructures can be fabricated by using this method.

Structuring Edible Oils With Fumed Silica Particles

Organogels are often made from solutions of proteins, polymers or fatty acids in oil. The macromolecular species crystallise, or assemble, into mesh structures that inhibit oil flow. This review focuses on using fumed silica nanoparticles as an alternative structuring agent. Fumed silica particles have a unique, branched morphology that means the particles aggregate into three-dimensional, interconnected networks. Two key aspects for formulating edible oleogels are addressed. Advances in our understanding of fumed silica particle aggregation in oil that point towards strategies for tuning the rheological properties of oleogels are examined. Secondly, the factors likely to affect the lipolysis of oils structured used fumed silica particles, and hence the bioavailability of ingredients loaded into the gels, are discussed. The next challenge for these promising materials is to target suitable applications for their use as fat replacement in foods.

Determination of the fate and biological responses of food additive silica particles in commercial foods.

Synthetic amorphous silica (SAS) is widely added to commercial foods as an anticaking agent. Concern about the potential application of nanosized silica in foods has increased as nanomaterials are not intended for use as food additives. This study evaluated the particle size distributions and biological responses of food additive SAS. An accurate, sensitive, and cost-effective analytical method for probing SAS was established, and quantitative analysis of its presence in commercial foods was performed. The results demonstrate that food additive SAS is an aggregated material composed of nanosized particles with nanosized aggregates of silica particles identified in commercial foods. Food additive SAS did not exhibit acute cytotoxicity compared to both general-grade nano (G-nano) and bulk (G-bulk) silica. Moreover, intestinal transport amounts of food additive SAS were significantly lower than for G-nano. Taken together, we find that food additive SAS does not exhibit acute toxicity resulting from nanosized materials.

Surface Energy Mapping of Modified Silica Using IGC Technique at Finite Dilution.

The reinforcing silica filler, which can be more than 40% of an elastomer composite, plays a key role to achieve the desired mechanical properties in elastomer vulcanizates. However, the highly hydrophilic nature of silica surface causes silica particle aggregation. It remained a challenge for many tire manufacturers when using silica-filled elastomer compounds. Here, the silica surface energy changes when the surface is modified with coupling or noncoupling silanes; coupling silanes can covalently bond the silica to the elastomers. The surface energy of silica was determined using inverse gas chromatography (IGC) at finite dilution (FD-IGC) and found to be reduced by up to 50% when the silica surface was silanized. The spatial distribution of silica aggregates within the tire matrix is determined by transmission electron microscopy (TEM) and a direct correlation between aggregate size (silica microdispersion) and work of cohesion from IGC is reported, highlighting surface energy and work of cohesion being excellent indicators of the degree of dispersion of silica aggregates.

Enzyme immobilization using two processing methods onto silica core-shell particles

Two methods of enzyme immobilization onto silica core-shell particles were developed. The first method involved the immobilization of Candida rugosa lipase inside a previously synthesized mesoporous silica layer (deposited at 80°C) surrounding a dense silica core. To prevent lipase leakage from the support, an outer mesoporous silica layer was deposited at 40°C around the first silica layer containing the immobilized lipase. The deposition of the second layer was performed at a relatively lower temperature, to prevent thermal inactivation of the immobilized enzyme. The internal silica layer was obtained by assembling primary silica nanoparticles generated from highly basic sodium silicate solution at 80°C on the surface of poly (diallyldimethylammonium chloride) (PDDA) functionalized silica core particles. The average shell thickness and pore size of the internal silica layer was ∼60nm and 24nm, respectively. The effect of process parameters on generation and aggregation of silica nanoparticles prepared from highly basic sodium silicate solution was also investigated. The aggregation of silica particles generated at 40°C and 80°C took place after 840s and 570 of reactions, respectively. The immobilization efficiency of lipase on the mesoporous silica monolayer was 80%. A decline of immobilized lipase activity was approximately 6 times after 10 reaction cycles due to lipase leakage from the monolayered shell. An outer mesoporous silica layer was deposited at 40°C onto the surface of previously PDDA-functionalized monolayered silica core-shell particles containing the immobilized lipase. The average thickness and pore size of outer mesoporous silica layer was ∼60nm and 17nm, respectively. The activity of lipase immobilized inside the bilayered shell was further reduced due to diffusion resistance within the outer silica layer and PDDA layer however, it was retained for the next reaction cycles.The pore size of mesoporous silica layer obtained at 80°C was insufficient to allow invertase immobilization. Thus, the second method for the immobilization of invertase was developed. It involved the preparation of the mesoporous silica layer simultaneously with invertase immobilization at 40°C. The immobilized invertase showed decreased activity, but it was not hampered by substrate inhibition, as in the case of the free enzyme, due to the location of the enzyme inside the mesoporous silica layer, where the mass transfer resistance for the substrate to the enzyme active site was present.

Fractal aggregation in silica sols in basic tetraethoxysilane/ethanol/water solutions by small-angle neutron scattering

Abstract Conventional small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS) are applied in the combined analysis of aggregated silica particles formed in basic tetraethoxysilane/ethanol/water solutions. The scattering is followed for different water/TEOS molar ratios to make a self-consistent description of fractal and size characteristics of the developed aggregates.

Probing particle heteroaggregation using analytical centrifugation.

The controlled aggregation of colloidal particles is not only a widespread natural phenomenon but also serves as a tool to design complex building blocks with tailored shape and functionalities. However, the quantitative characterization of such heteroaggregation processes remains challenging. Here, we demonstrate the use of analytical centrifugation to characterize the heteroaggregation of silica particles and soft microgels bearing similar surface charges. We investigate the attachment as well as the stability of the formed heteroaggregates as a function of particle to microgel surface ratio, microgel size and the influence of temperature. The attachment of microgels onto the colloidal particles induces a change in the sedimentation coefficient, which is used to quantitatively identify the number of attached microgels. We corroborate the shift in sedimentation coefficient by computer simulations of the frictional properties of heteroaggregates via a modified Brownian dynamic algorithm. The comparison between theoretical investigations and experiments suggest that the microgels deform and flatten upon attachment.

One-Step Aqueous Spraying Process for the Fabrication of Omniphobic Fabrics Free of Long Perfluoroalkyl Chains.

We report on a simple and versatile method for the preparation in one-step of omniphobic textiles, using only aqueous suspensions of silica particles and polyurethane devoid of long perfluoroalkyl chains (C8) that are now legally-banned because of severe environmental concerns. The omniphobic coatings can be applied on different substrates including fabrics, can resist acidic and basic conditions and a moderate number of washing cycles, and repel liquids such as n-octane, dodecane, hexadecane, ethylene glycol, glycerol, olive oil, and water. Analysis of the wetting properties of coated fabrics indicates that the liquid repellence results from the trapping of air in the re-entrant roughness created by aggregates of silica particles, together with the low surface tension of the polyurethane which bears legally accepted short perfluoroalkyl chains (C4). Our study is a significant step forward toward achieving more environmentally-friendly and robust omniphobic textiles.

Aggregation Mechanisms of Silica Particles in the Sol–Gel Synthesis of Promoted Silver Catalysts

As found using in situ small-angle X-ray scattering (SAXS), a porous structure consisting of compact particles with sizes from 2 to 8 nm was formed as a result of the sol–gel synthesis of silicate, silicate–phosphate, and silicate–phosphate–silver gels from tetraethoxysilane. It was established that the aggregation of silica particles in the presence of nitric acid proceeds according to a coalescence mechanism. The presence of phosphoric acid in the system changes the mechanism of aggregation for Ostwald ripening. The introduction of silver nitrate into the system does not significantly affect the size of silica particles and the mechanism of their aggregation.

Microcellular silicone rubber foams: The influence of reinforcing agent on cellular morphology and nucleation

A series of microcellular silicone rubber foams were prepared by supercritical carbon dioxide (scCO2). The effect of reinforcing agent (silica) on the rheological behavior, cellular morphology and nucleation of silicone rubber composites was investigated. The results show that the silica not only acts as reinforcing agent but also plays an important role in the cellular nucleation. When the content of silica increases from 40 phr to 70 phr, the range of the calculated surface tension of silicon rubber composites/scCO2 (γmix) and radius of the critical nucleus (r*) are 158.95∼1,092.74 nN/m and 14.45–99.34 nm, respectively. Meanwhile, aggregated silica has good heterogeneous nucleation as the diameter of aggregated silica particles is approximate to twice r*. The smallest cell diameter and the highest cell density of the silicone rubber foam can reach to 708 nm and 1.02 × 1011 cells/cm3, which indicate that the silicone rubber nanofoams can be obtained by means of the supercritical foaming technology. POLYM. ENG. SCI., 59:5–14, 2019. © 2018 Society of Plastics Engineers

Formation of Silica-Lysozyme Composites Through Co-Precipitation and Adsorption

Interactions between silica and proteins are crucial for the formation of biosilica and the production of novel functional hybrid materials for a range of industrial applications. The proteins control both precipitation pathway and the properties of the resulting silica-organic composites. Here we present data on the formation of silica-lysozyme composites through two different synthesis approaches (co-precipitation vs. adsorption) and show that the chemical and structural properties of these composites, when analyzed using a combination of synchrotron-based scattering (total scattering and SAXS), spectroscopic, electron microscopy and potentiometric methods vary dramatically. We document that while lysozyme was not incorporated into nor did its presence alter the molecular structure of silica, it strongly enhanced the aggregation of silica particles due to electrostatic and potentially hydrophobic interactions, leading to the formation of composites with characteristics differing from pure silica. The differences increased with increasing lysozyme content for both synthesis approaches. Yet, the absolute changes differ substantially between the two sets of composites, as lysozyme did not just affect aggregation during co-precipitation but also particle growth and likely polymerization during co-precipitation. Our results improve the fundamental understanding of how organic macromolecules interact with dissolved and nanoparticulate silica and how these interactions control the formation pathway of silica-organic composites from sodium silicate solutions, a widely available and cheap starting material.

Investigating the interrelationship of superhydrophobicity with surface morphology, topography and chemical composition in spray-coated polyurethane/silica nanocomposites

A one-step and efficient method, based on the spray-coating technique, was proposed to impart superhydrophobicity to an intrinsically hydrophilic polymer. The main aim is to establish correlations among surface morphology, topography and chemical composition of superhydrophobic surfaces. Introduction of non-solvent changed the ordered honeycomb-like morphology to an unordered strand-like morphology. Moreover, the concurrent addition of non-solvent and nanoparticles has led to a unique hierarchical morphology where silica nanoparticles decorated the PU strand-like structure resulting in a very high WCA value (160°) and very low sliding angle (<2°). The topography results were utterly in conformity with those attained by the morphological analysis, and both qualitative and quantitative descriptions were given. It was found that the uniformity of the roughened structure plays a crucial role in superhydrophobicity. Moreover, the aggregation of silica particles at the surface layer of the coatings was also influential which was further confirmed by X-ray photoelectron spectroscopy results.

Synthesis of silica particles from rice straw waste using a simple extraction method

The purpose of this study was to synthesize silica particles from rice straw waste using a simple extraction method. The experiment was conducted by heating and extracting rice straw waste into basic solution. To get silica particles, the extracted solution was then put into acid solution and heated to remove the remained solvent. The experimental results showed that the aggregated silica particles with sizes of about 200 nm were successfully produced. The XRD and FTIR analysis showed that the final product was silica and free of graphite. However, we found that some KCl component in the final product in which this was possibly from the use of KOH as the extraction agent. Therefore, further studies are still required to synthesize high purity silica particles from rice straw waste.

Facile Preparation of Stable Superhydrophobic Coatings on Wood Surfaces using Silica-Polymer Nanocomposites

Superhydrophobic organic-inorganic composite nanocoatings were fabricated on the intrinsically heterogeneous surfaces of wood using silica-polymer hybrid materials, which were prepared through sol-gel chemistry using tetraethoxysilane (TEOS) as an inorganic precursor and hexadecyltrimethoxysilane (HDTMS) as an organic modifier. The long-chain HDTMS acts not only as a hydrophobic agent to lower the surface free energy of the silica particles but also as a bonding agent to aggregate the nanoparticles by polymerization. The degree of aggregation of the silica particles in the coating can be controlled by adjusting the initial concentration of HDTMS, and hence the surface morphology and roughness of the coated wood are tuned. When the concentration of HDTMS reaches a critical level, the formed aggregates of silica particles in combination with the inherent microscale roughness of wood appear to create hierarchical micro/nanostructures on the wood substrate, allowing for the generation of superhydrophobicity. The silica-polymer hybrid coatings on the wood surface are robust enough to withstand high humidity as well as strong acid and alkali whilst retaining its superhydrophobicity. The coatings also exhibit satisfactory durability against water leaching without significantly changing its hydrophobicity, highlighting their potential for outdoor applications.

Large-scale synthesis of monodisperse microporous silica nanoparticles by gradual injection of reactants

Monodisperse microporous silica particles were prepared in high yield, by the gradual injection of tetramethoxysilane (TMOS) and template molecules into the reaction system. This resulted in continuous nucleation. The dilute TMOS concentration suppressed silica particle aggregation. The diameters of the microporous silica particles were 100–130 nm. The narrow size distribution resulted from larger particles experiencing smaller growth rates, despite the continuous nucleation occurring during TMOS injection. This method has potential in the industrial-scale preparation of monodisperse silica particles.

Superhydrophobic surfaces with near-zero sliding angles realized from solvent relative permittivity mediated silica nanoparticle aggregation

Superhydrophobic surfaces with near-zero sliding angles are generated by solvent ε-mediated silica particle aggregation and formation of multi-scale roughness.

Spin Contrast Variation Study of Fuel-efficient Tire Rubber

The scattering length of a proton against a polarized neutron depends strongly on the polarization of proton spins (PH). This dependence can be utilized for contrast variation in small angle neutron scattering (SANS). We applied this spin contrast variation technique to a silica-filled SBR rubber specimen, which is widely used for tread rubber of fuel-efficient tires. For realizing high PH, we used dynamic nuclear polarization (DNP) technique, in which large polarization of electron spin at low temperature and high magnetic field is transferred to proton spin by microwave irradiation with a tuned frequency. As this electron spin source, we doped stable radical TEMPO (2,2,6,6-tetramethyl piperidine 1-oxyl) into the rubber sample by use of a vapor sorption technique. For the TEMPO-doped rubber sample, SANS measurements were conducted at PH = −20%, 0%, and +13%, with almost fully polarized neutron beam %) with its wavelength of 6.5±0.6 Å. The SANS profile clearly changed as a function of PH, which can be explained by the PH dependence of the neutron scattering length densities of the main three components (SBR, silica and zinc oxide). By a linear transformation of the profiles obtained at the three different PH values, we successfully determined the partial scattering function of silica, which reflects the aggregation of silica particles.

Hybrid thin films derived from UV-curable acrylate-modified waterborne polyurethane and monodispersed colloidal silica

Hybrid thin films containing nano-sized inorganic domains were synthesized from UV-curable acrylate-modified waterborne polyurethane (WPU-AC) and monodispersed colloidal silica with coupling agent. The coupling agent, 3- (trimethoxysilyl)propyl methacrylate (MSMA), was bonded onto colloidal silica first, and then mixed with WPU-AC to form a precursor solution. This precursor was spin coated, dried and UV-cured to generate the hybrid films. The silica con- tent in the hybrid thin films was varied from 0 to 30 wt%. Experimental results showed the aggregation of silica particles in the hybrid films. Thus, the silica domain in the hybrid films was varied from 30 to 50 nm by the different ratios of MSMA- silica to WPU-AC. The prepared hybrid films from the crosslinked WPU-AC/MSMA-silica showed much better thermal stability and mechanical properties than pure WPU-AC.