Hydrophilic Fumed Silica Research Articles

Revealing the correlation between the performance of silica-based DAC adsorbents and their pore natures

Direct air capture (DAC) technology is a potential carbon negative process, which can effectively reduce the emission of carbon dioxide (CO2) in the atmosphere. Amine-functionalized porous materials are promising because of their high ratio of accessible amino groups and fast adsorption/desorption kinetics. This work reveals the correlation between the specific surface area, pore radius, and pore volume of the silica-based DAC adsorbents and their CO2 adsorption capacity and adsorption rate. Four typical silica-based DAC adsorbent materials loaded with polyethylenimine (PEI) were studied, including hydrophilic fumed silica (HFS), Santa Barbara Amorphous-15 (SBA-15), Mobil Crystalline Materials-41 (MCM-41), and silica gel (SG). It is observed that when the PEI loading is constant, adsorbent materials with larger specific surface area, larger pore radius, and larger pore volume tend to show the higher adsorption capacity and faster adsorption-desorption rate. Humidity is beneficial for the CO2 capture capacity, but it slows down the CO2 uptake rate at the same time. The capacity of 50%PEI@SBA-15 adsorbent can reach to 3.24 mmol/g under 90% relative humidity (RH). Supports with small pore radius tend to have unfavorable performance at dry conditions. After the inlet gas is humidified, the CO2 capacity of the MCM-41 material is enhanced greatly, from 0.91 mmol/g to 2.92 mmol/g. This work provides guiding principle for synthesizing appropriate adsorbents with higher DAC capacity, higher adsorption and desorption rate at ambient conditions.

Myristic acid-tetradecanol-capric acid ternary eutectic/SiO2/MIL-100(Fe) as phase change humidity control material for indoor temperature and humidity control

Building materials with the dual function of temperature and humidity regulation can improve people's living comfort and reduce energy consumption. In this work, a simple and convenient strategy for building a comfortable indoor temperature and humidity environment was proposed. The phase change humidity control material (PCHCM) was prepared by the mixing of form-stable composite phase change material (CPCM) as temperature-control component and hygroscopic MIL-100(Fe) as humidity-control component. In PCHCM, the CPCM was obtained by molten recombination of myristic acid, tetradecanol, and capric acid (MA-TD-CA) as phase change material and hydrophilic fumed silica (SiO2) as porous carrier, and MIL-100(Fe) was synthesized by low-temperature solution method. Thermal analysis indicated that, under the optimized mass ratio of 28.8%MA-61.2%TD-10%CA, the CPCM containing 30 % SiO2 could effectively prevent the leakage of ternary eutectic, with a suitable phase change temperature and enthalpy (21.74 °C, 96.70 J·g−1). The thermal and wet performance evaluation confirmed that the PCHCMs containing 40–50 % CPCM had human body comfortable phase change temperature (26.96–27.26 °C) and high saturation adsorption capacity (0.179–0.205 g/g) at 60 % RH as well as outstanding thermal and wet cycle reliability, indicating the novel MA-TD-CA/SiO2/MIL-100(Fe) PCHCM has broad application potential in room temperature and humidity control and building energy conservation.

Novel Bioequivalent Tablet of Solifenacin Succinate Prepared Using Direct Compression Technique for Improved Chemical Stability.

We designed a bioequivalent tablet form of solifenacin succinate (SOL) with an improved storage stability using a direct compression (DC) technique. An optimal direct compressed tablet (DCT) containing an active substance (10 mg), lactose monohydrate, and silicified microcrystalline cellulose as diluents, crospovidone as a disintegrant, and hydrophilic fumed silica as an anti-coning agent was constructed by evaluating the drug content uniformity, mechanical properties, and in vitro dissolution. The physicochemical and mechanical properties of the DCT were as follows: drug content 100.1 ± 0.7%, disintegration time of 6.7 min, over 95% release within 30 min in dissolution media (pH 1.2, 4.0, 6.8, and distilled water), hardness > 107.8 N, and friability ~0.11%. The SOL-loaded tablet fabricated via DC showed an improved stability at 40 °C and RH 75%, exhibiting markedly reduced degradation products compared to those fabricated using ethanol or water-based wet granulation or a marketed product (Vesicare®, Astellas Pharma). Moreover, in a bioequivalence study in healthy subjects (n = 24), the optimized DCT offered a pharmacokinetic profile comparable to that of the marketed product, with no statistical differences in the pharmacokinetic parameters. The 90% CIs for the geometric mean ratios of the test to the reference formulation for the area under the curve and the maximum drug concentration in plasma were 0.98-1.05 and 0.98-1.07, respectively, and satisfied the FDA regulatory criteria for bioequivalence. Thus, we conclude that DCT is a beneficial oral dosage form of SOL with an improved chemical stability.

Fabrication and thermal properties of CaCl2·6H2O–CO(NH2)2/SiO2 as room-temperature shape-stable composite PCM for building thermal insulation

The combination of room-temperature phase change materials (PCMs) and building materials can reduce the energy consumption of heating equipment and improve indoor thermal comfort. In this paper, the novel CaCl2·6H2O–CO(NH2)2/SiO2 room-temperature shape-stable composite PCM was fabricated by melt-blending method with CaCl2·6H2O as the basic PCM, CO(NH2)2 as the phase change temperature regulator and hydrophilic fumed silica (SiO2) as the carrier. The temperature-regulating effect of CO(NH2)2 on CaCl2·6H2O and the shape-stabilizing effect of SiO2 on CaCl2·6H2O–CO(NH2)2 PCM were emphatically analyzed. The results revealed that the obtained composite PCM with 6% CO(NH2)2 and 20% SiO2 possessed a favorable form-stability, relatively high enthalpy (114.3 J g-1) and appropriate phase change temperature (21.03 °C) which decreased by 7.81 °C compared with pure CaCl2·6H2O (28.84 °C). Furthermore, its small supercooling degree (0.259 °C), low thermal conductivity (0.3667 W·m-1·K-1) as well as the excellent cyclic reliability and thermal stability indicated that the composite PCM has good thermodynamic properties, enabling its application for indoor building thermal insulation and even some other areas.

Synthesis of Ag(I)@Fum−Pr−Pyr−Benzimidazole and Its Optical and Catalytic Activities in Click Reactions

AbstractA hydrophilic fumed silica was used as a support and modified by benzimidazole scaffold, which can be chelate with silver as a highly selective and sensitive receptor to the successive detection of Ag+ ion. Fluorescence properties of Fum−Pr−Pyr−Benzimidazole were verified by the addition of various cations in an aqueous medium, and its high selectivity and sensitivity toward Ag+ ion was observed. Silver ion was placed onto the Fumed‐SiO2 to prepare Ag(I) @Fum−Pr−Pyr−Benzimidazole catalyst using in click chemistry. A number of characterization analyses were used, including FT‐IR, SEM, BET, and EDX, to prove that the Pr‐Pyr‐Benzimidazole and Ag (I) were homogeneously distributed on the fumed‐silica. EDX and SEM analysis were used to characterize the active component distribution.

Influence of different fumed silica as thixotropic additive on carbonyl particles magnetorheological fluids for sedimentation effects

The present work reports the influence of different types of surface area, hydrophobic, and hydrophilic fumed silica mixed in silicone oil as a thixotropic additive on carbonyl particles based magnetorheological fluids (MRFs) were prepared. Scanning electron microscopy analysis confirms the fumed silica particles attached to the surfaces of CIPs. The vibrating sample magnetometer result shows the MRF4 and 5 have a better magnetic saturation value of 30.12 emu/gm and 40.12 emu/gm, respectively. The experimental rheological flow curve behaviours are investigated using the magnetorheometer. The Herschel–Bulkley rheological model is found to be in good agreement with the experimental curves and suggested shear thinning property is observed. The results showed that the hydrophilic silica with larger surface area type presented (i.e.MRF 4 and 5) better magnetorheological fluid characteristics in terms of shear stress, with a high value of dynamic yield stress, and have much-improved sedimentation ratio up to seven days.

Hypervelocity Impacts on Honeycomb Core Sandwich Panels Filled with Shear Thickening Fluid

The use of honeycomb core sandwich panels filled with a shear thickening fluid (STF) as a component of spacecraft micrometeoroid/orbital debris (MMOD) shielding was investigated using hypervelocity impact (HVI) testing. Incorporating a STF into shielding has the potential to reduce damage to the core and the likelihood of back-side facesheet perforation in the event of a HVI. The sandwich panels tested consisted of 1.27 cm thick hexagonal aluminum honeycomb core bonded between 0.064 cm thick aluminum facesheets. The STF displayed a marked rise in viscosity with increasing shear rate above a critical shear rate. It was based on low molecular weight polyethylene glycol (PEG) and hydrophilic fumed silica. Sandwich panel target specimens filled with the STF were subjected to HVIs by 1 mm diameter stainless steel spheres at nominal temperatures of -80°C or 21°C with nominal impact velocities of 4.8 km/s or 6.8 km/s. Additional specimens filled with PEG only were also impacted for comparison.Visual inspections and X-ray computerized tomography were used to assess impact damage. All of the panels experienced perforation of the impacted facesheet, facesheet bulging, localized delamination, and the formation of a cavity in the damaged core. STF-filled panels sustained significantly less damage than PEG-filled panels. None of the STF-filled panels were completely perforated during impact. In contrast, one of the PEG-filled panels impacted at the peak velocity was perforated. The remaining PEG-filled panel sustained substantially more honeycomb core damage and facesheet-core delamination compared to an analogous STF-filled panel. Sandwich panels filled with the STF provide superior HVI mitigation in comparison to panels filled with a Newtonian fluid (i.e., PEG). These experiments show that incorporation of STFs into MMOD shielding components has the potential to dramatically improve the HVI penetration resistance over a broad range of impact velocities and temperatures.

Effect of the silica nanofiller on the properties of castor oil-based waterborne polyurethane hybrid dispersions based on recycled PET waste

The paper describes the chemical depolymerization of the polyethylene terephthalate (PET) waste from postconsumer soft drink bottles and a search for the way to use this product. The depolymerized oligoester obtained from glycolysis of PET waste using tiethylene glycol was transesterified with castor oil which resulted in the formation of hydroxyl-functional polyester polyol, with hydroxyl value of 391 mg KOH g−1. In the presented paper, series of castor oil-based waterborne polyurethane (CPU)/silica hybrid dispersions were prepared using dimethylolpropionic acid as an ionic center. The polyurethane prepolymers with pendent castor oil groups were prepared first, and then different concentrations of hydrophilic fumed silicas (0, 0.5, 0.75, 1.0 and 2.0 wt%) were added. For waterborne polyurethane dispersions of hydrophilic fumed silica with the surface area (50 ± 15 m2/g) and a primary particle size of 40 nm in the polymer matrix, ultrasound waves were used. The hybrid dispersions were prepared by adding the required amount of triethylamine and water. The molecular structures and mass of glycolyzed PET oligoesters, castor oil-based polyol and castor oil-based polyurethane–silica hybrid dispersions were estimated by FTIR method and gel permeation chromatography.The incorporation effect of SiO2 nanoparticles into the PU matrix on the thermal and mechanical properties of resulting polyurethane films has been examined by Fourier transform infrared spectroscopy (FTIR), thermogravimetry analysis, differential scanning calorimetry (DSC), SEM microscope, and measurement of the coatings properties. The DSC data results suggest that hard segment glass temperature decreases, but mixed-phase glass transition temperature increases with increasing SiO2 content. The FTIR deconvolution result of the degree of phase separation between oxide nanoparticles and hard segment supports to the DSC analysis. The addition of silica oxide caused the increase in the thermal stability. The T10% and T50% of CPU films (the temperatures where 10 and 50% weight loss occurred) increased with increasing the SiO2 content. UV–Vis spectrophotometry showed that introduction of nanosilica particles into polyurethane enhanced the shielding property of obtained films for UV light. The hardness, adhesion, and gloss quality of the polyurethane films were also determined considering the effect of the phase separation and the SiO2 content, so this paper confirmed the suitability of using these castor oil-based waterborne polyurethane/silica hybrid dispersions as new materials with high-performance coatings materials.

Influence of the surface properties of nano-silica on the dispersion and isothermal crystallization kinetics of PHB/silica nanocomposites

The effects of the surface properties of several silica nanoparticles (NPs) on the dispersion and isothermal crystallization kinetics of poly(3-hydroxybutyrate) (PHB) nanocomposites were investigated by the techniques of transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Bare and PEGylated sol-gel silica NPs were synthesized and commercially available hydrophobic and hydrophilic fumed silica NPs were used to prepare the PHB/silica nanocomposites containing ≤5 wt% silica. Among these 4 types, PEGylated silica NPs were best dispersed in PHB matrix as evidenced by TEM images. Values of the Avrami exponent, n = 2.2 ± 0.2 for all the PHB/silica nanocomposites, indicated that the mechanism of the crystallization of PHB was not altered by the introduction of various silica NPs. However, the crystallization rate of PHB in the nanocomposites was significantly decreased by the introduction of PEGylated silica because the rearrangement of the PHB polymer chains during crystallization was limited by the interaction and chain entanglement between PHB and the grafted PEG on silica.

Photoluminescence of silica monoliths prepared from cold sintering of nanometric aerosil precursors under high pressure

Blue photoluminescent silica monoliths were obtained by cold sintering of nanosized precursors under high pressure. The samples were prepared from hydrophobic and hydrophilic fumed silica AEROSIL® precursors which were placed inside a soft capsule of hBN and pressed at 7.7GPa. Practically no photoluminescence (PL) emission was observed for the nanometric powdered precursors while a relatively intense emission was measured for the sintered monoliths, which was dependent on the excitation wavelength (2.47–5.63eV). The emission was observed in the range between 2.0 and 3.5eV for all samples with the peak at ~2.7eV for excitation between 3.26–3.44eV. The blue band is probably related to the defects produced during the cold sintering process related to plastic deformation and internal stress of the monolith. The intensity of PL spectra of the monoliths obtained from the hydrophilic precursor (A200) was higher than the intensity of the spectra observed for the monoliths obtained from hydrophobic precursors (R974, R816 and R812) probably due to the presence of the carbon groups at the surface of the hydrophobic precursors, hindering the cold sintering process.

Dopamine/Silica Nanoparticle Assembled, Microscale Porous Structure for Versatile Superamphiphobic Coating.

Artificial superamphiphobic surfaces, which could repel both water and low surface tension organic liquids, have been limited to particular kinds of materials or surfaces thus far. In this work, a kind of microscale porous coating was developed. Taking dopamine and hydrophilic fumed silica nanoparticles as initial building blocks, microscale porous coating was constructed via ice templation. Polydopamine bound silica nanoparticles together to form a porous structure network and rendered the coating to have potential for further postfunctionalization. After two-step CVD, the microscale porous coating changes from superhydrophilic to superamphiphobic, exhibiting super-repellency to droplets with surface tension of 73-23 mN/m. The influences of concentration of initial dopamine, hydrophilic fumed silica nanoparticles, and dry conditions on the formation of the porous structure have been studied to optimize the conditions. Coatings with different pore sizes and pore heights have been fabricated to discover the relationship between the structure parameters and the repellency of the porous coatings. Only with optimal pore size and pore height can the porous coating display superamphiphobicity. Compared with nanoscale, the microscale structure favors the achievement of superamphiphobicity. Given the outstanding adhesive ability of polydopamine, the superamphiphobic coatings have been successfully applied to various materials including artificial materials and natural materials.

Morphological hysteresis in immiscible PIB/PDMS blends filled with fumed silica nanoparticles

The morphological hysteresis behavior of immiscible polymer blend reflects the dependence of their steady-state morphology on the shear protocol applied. In this work, the influences of hydrophobic and hydrophilic fumed silica nanoparticles on the morphology hysteresis behavior of immiscible polyisobutylene (PIB)/polydimethylsiloxane (PDMS) (10/90) blends under simple shear flow were investigated by using optical shear technique. Compared with particle-free blend, the morphology hysteresis zone of filled blends was found to be expanded by the addition of hydrophobic or hydrophilic fumed silica nanoparticles. It was found that the expansion of the morphology hysteresis zone in hydrophobic nanoparticle-filled blend stemmed from the suppression of droplet coalescence. However, the expansion in the morphological hysteresis zone for hydrophilic nanoparticle-filled blend, which was less noticeable, might originate from the more difficult breakup of PIB droplets upon the addition of nanoparticles.

A rheological study on temperature dependent microstructural changes of fumed silica gels in dodecane

The effect of temperature on colloid systems of hydrophobic and hydrophilic fumed silica in dodecane was investigated mainly by means of dynamic rheology. Dynamic frequency sweeps showed frequency-independent elastic modulus (G′), indicating the presence of gel networks in both dispersions. Dynamic temperature sweeps consisting of a heating and cooling cycle were also conducted. For the hydrophobic fumed silica gel, G′ slowly decreased with rising temperature owing to the increased particle mobility and decreased strength of hydrogen bonds due to the higher thermal energy. However, the hydrophilic fumed silica gel showed a rather unusual temperature dependent behavior involving a transition temperature (Tc) and an irreversible increase in G′ during the cooling cycle. This unusual behavior was believed to be related to the restructuring of nanoparticle chain aggregates (NCA) of fumed silica in gels as also revealed by FTIR results. Further analysis on this behavior showed that elevated temperature tended to increase the fractal dimension (Df) of aggregates, resulting in more compact NCAs and thereby a denser gel network with a higher G′. These results suggest that temperature is an important external variable that can be regarded as an optional simple way to tailor the viscoelastic properties and to control the microstructure of colloidal systems such as fumed silica dispersions in dodecane.

In situ formation of nanoparticles upon dispersion of melt extrudate formulations in aqueous medium assessed by asymmetrical flow field-flow fractionation

In recent years melt extrudates (e.g. Meltrex ®) have proven to be a promising formulation tool for poorly water-soluble and poorly bioavailable drugs. During the hot-melt extrusion process solid dispersions are formed. For several of these formulations improved bioavailabilities have been reported; the mechanism behind, however is still not very well understood. The aim of this study was to investigate whether solid dispersions prepared by melt extrusion upon dispersion in aqueous medium form particles and/or supramolecular assemblies. The formulation investigated here contained the human immunodeficiency virus (HIV) protease inhibitors lopinavir and ritonavir, polyvinylpyrrolidone–vinyl acetate copolymer (Kollidon ® VA64), sorbitan monolaurate (Span ® 20) and hydrophilic fumed silica (Aerosil ® 200). The aqueous dispersions originating from both, API-containing and placebo formulation were investigated using photon correlation spectroscopy (PCS) and asymmetrical flow field-flow fractionation (AsFlFFF) with subsequent online multi-angle light-scattering (MALS) particle size analysis. The content of both APIs in the AsFlFFF-fractions was quantified using high performance liquid chromatography–mass spectrometry. PCS indicated sub-micron particles. AsFlFFF revealed the co-existence of up to three different types of colloidal to nanoparticulate assemblies in the aqueous dispersions. Even though a complete resolution of the composition of the sub-fractions could not be achieved, the following types could be clearly distinguished: The first fraction eluting from AsFlFFF, appears to be colloidal polymer. Only marginal amounts of the APIs were found associated with the polymer. Secondly, API-rich nanoparticles eluted. Thirdly, nanoparticulate assemblies assigned to sorbitan monolaurate and/or hydrophilic fumed silica were identified. A limited amount of drug was found associated with this fraction. Using AsFlFFF–MALS the size of particles in fractions could be determined. From this experience AsFlFFF is regarded as promising technique for investigation of particles/structures originating during dispersion of melt extrudates in aqueous medium in terms of size and type of nanoparticles and their API-content.

The effect of hydrophobic and hydrophilic fumed silica on the rheology of magnetorheological suspensions

We investigate magnetorheological fluids (MRFs) prepared with carbonyl iron powder and different types of hydrophobic and hydrophilic fumed silica. The rheological properties of the MRF suspensions were investigated with and without an applied magnetic field. The MRF samples prepared with hydrophobic silicas presented a more pronounced thixotropic effect and a higher recovery rate than those prepared with hydrophilic silicas. The application of a magnetic field to all the MRFs samples investigated leads to an increase in the viscosity and the thixotropic effect. MRF prepared with hydrophobic silicas presented smaller values of the viscosity than those prepared with hydrophilic silicas. At low applied magnetic fields, the type of the silica used to prepare the MRF leads to noticeable differences in the shear stress. However, these differences disappear at high magnetic fields. The results obtained showed that MRF samples prepared with the hydrophobic silica with the biggest particle diameter presented bett...

Sulfonated poly(arylene ether sulfone)–silica nanocomposite membrane for direct methanol fuel cell (DMFC)

Inorganic nanoparticles in nanocomposite membranes significantly affect the characteristics of those membranes, such as proton and methanol transport behavior, membrane durability, and electrochemical single cell result. Therefore, the inorganic nanoparticles should be deliberately chosen to fabricate composite membranes with desirable properties for DMFC. In this study, sulfonated poly(arylene ether sulfone) (SPAES) and hydrophilic fumed silica (SiO 2) were used as a polymer matrix and an inorganic nanoparticle, respectively. The SiO 2 nanoparticles have various surface areas (150, 200, 300, and 380 m 2 g −1) and average particle sizes (7, 12, and 14 nm). The SiO 2 nanoparticles are evenly dispersed in the SPAES matrix by aid of a non-ionic surfactant (Pluronics ® L64). Interestingly, SiO 2 particles with a high surface area and small particle size showed the best results: high proton conductivity, long membrane life time under oxidative conditions, good dimensional stability, outstanding single cell performance, and reduced methanol crossover. Moreover, SiO 2 content plays an important role in membrane microstructures and membrane properties such as proton conductivity and methanol barrier behavior. An excessive SiO 2 content caused a large aggregation of SiO 2 particles, leading to the deterioration of mechanical properties in nanocomposite membranes. In the present study, optimal SiO 2 content for maximizing the fuel cell performance of current nanocomposite membranes was ca. 2 wt.%.

Rheological behavior of hydrophilic silica dispersion in polyethylene glycol

AbstractThe rheological properties of hydrophilic fumed silica dispersed in polyethylene glycol (PEG) were investigated. The dispersion was prepared by dispersing the fumed silica in PEG with various concentrations. The reversible sol–gel transition was observed over 5 wt % of silica concentration as a function of temperature. The gelation temperature was found to depend on the applied shear stress and silica concentration, and the high shear stress was found to lead to the decrease of sol–gel transition temperature of the dispersion with the same silica concentration. As the silica concentration increases, the sol–gel transition shifts to the lower temperature. © 2006 Wiley Periodicals, Inc. J Apple Polly Sci 103: 2481–2486, 2007

Composite gel electrolytes based on poly(methylmethacrylate) and hydrophilic fumed silica

Transparent and highly conducting (10 −3 S cm −1) composite gel electrolytes (cges) based on poly(methylmethacrylate) (PMMA) with 1 M LiClO 4 in propylene carbonate (PC) and hydrophilic fumed silica (SiO 2) added in different proportions up to 5 wt.% as the constituents were prepared. The unique property of the aggregates of surface hydroxyl groups of hydrophilic fumed silica to link together through hydrogen bonding to form a network and the interactions between various constituents, probed by FTIR spectroscopic technique, have revealed to control both the transport and rheological properties of the cges. The high mechanical and electrochemical stability of these cges makes them potential candidates as electrolytes in “All Solid State Electrochromic Windows” (ECWs). Detailed room temperature conductivity and viscosity measurements correlated to FTIR spectroscopic analysis of cges along with their optical and electrochemical investigations is reported in the present paper.

The performance of oxygen sensing films with ruthenium-adsorbed fumed silica dispersed in silicone rubber

Oxygen sensing films were prepared by adsorbing the tris(4,7-diphenyl-1,10-phenanthroline)ruthenium dye onto high surface area hydrophilic fumed silica and dispersing the ruthenium-loaded silica in a silicone rubber support. These sensing films possess desirable properties including higher luminescence intensity, larger response towards oxygen and more linear Stern–Volmer calibration curves than films prepared by simple mixing of the ruthenium dye with silicone rubber. However, the response time of these silica-containing films in the recovery cycle is ca. 30–50% longer than the films without silica.