Silica Particle Size Research Articles

The influence of fumed silica content and particle size in poly (amide 6-b-ethylene oxide) mixed matrix membranes for gas separation

Abstract Mixed-matrix membranes (MMMs) comprised of poly (amide 6-b-ethylene oxide) (PEBAX) as continuous phase and fumed silica (FS) as dispersed phase were prepared to separate CO2 and CH4. The influences of FS nanoparticle size and weight percentage on the phase behavior and microstructure of the prepared MMMs were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo-gravimetric analysis (TGA), differential scanning calorimeter (DSC) and tensile testing. The performance of the prepared MMMs was characterized by single gas permeation measurement of CO2, N2 and CH4 (at 25 °C). The effects of feed pressure on the gas separation performance of the membranes were also investigated. Generally, PEBAX-FS MMMs showed higher CO2 permeability and selectivity (α) than the pure PEBAX membrane. Adding 10 wt% of 7 nm FS nanoparticles to the PEBAX matrix led to significant improvement in the CO2 permeability (∼4 times), CO2/CH4 and CO2/N2 selectivity (∼2 times) compared to the pure PEBAX membrane. The CO2/CH4 and CO2/N2 selectivity for these membranes were also about 64.8% and 45.3% higher than those of MMMs containing 10 wt% of larger FS nanoparticles (16 nm). This was attributed to the higher surface to volume ratio of smaller FS nanoparticles which can provide higher interactions with polymeric matrix and CO2 gas.

Development of silica-enriched cement-based materials with improved aging resistance for application in high-temperature environments

Understanding the effects of high temperature (HT) and high pressure (HP) conditions on the microstructure of cement-based materials is critical to the construction and safe operation of deep oil and gas wells. Under such conditions, the persistence of calcium-silicate-hydrate (C-S-H) gel is compromised by ongoing crystallization that, if not controlled, may adversely affect the durability of the cement sheath. This work investigates the effect of silica content >35% by-weight-of-cement (BWOC), silica particle size, and solid volume fraction (SVF) on the microstructure and phase composition of cement-silica blends cured hydrothermally at 200 °C and 20.7 MPa. The results of X-ray diffraction and electron microprobe analysis revealed significant impact of these three mix design parameters on the final phase assembly, and on the conversion rate of semi-crystalline C-S-H to gyrolite and 11 Å tobermorite. Incorporation of more fine siliceous material suppressed dissolution of coarse silica particles, resulting in a matrix with improved homogeneity and dominated by fine gel pores. Mixes with lower SVF showed greater formation of 11 Å tobermorite, a higher degree of crystallinity and/or greater crystallite size. Prolonged HTHP curing of all systems (up to three months in this study), irrespective of the initial SVF, increased the fraction of capillary pores, indicating void coalesce caused by crystal growth. However, we find that this coarsening is less pronounced in systems with less pore space available for crystallization.

Adsorption of benzyldimethyldodecylammonium bromide on silica nanoparticles in water

Adsorption of the cationic surfactant benzyldimethyldodecylammonium bromide (BDDABr) on silica nanoparticles with ~ 12 and 31 nm in size (denoted as S-SiO2 and L-SiO2, respectively) is investigated at various solid dosages (Cs, 10–40 g/L), pH (3–10), and temperature (T, 298–308 K). No Cs-effect is observed in the adsorption. However, it is interestingly found that, besides pH and T, the size of the silica particles has an obvious influence on the adsorption. The adsorption may show the Langmuir type (L-type), S-type, and “double plateau” type (LS-type) isotherms, depending on silica particle sizes and pH. Increasing pH may lead to a change in the isotherm types from S-type through LS-type to L-type. The S-type and LS-type isotherms can be adequately described using the one-step and two-step surface micellization models, respectively. The affinity of the S-SiO2 toward BDDABr is lower than that of the L-SiO2, consistent with the dissociation tendency of their surface hydroxyl groups.

Influence of Silica Size on Properties of Poly[(Butylene Succinate)‐Co‐Adipate]/Butyl‐Etherified High‐Amylose Starch Blend Composites

In this study, hydrophilic microsilica and nanosilica particles are dispersed in poly[(butylene succinate)‐co‐adipate]/butyl‐etherified high‐amylose starch (PBSA/BHAS) blends in order to stabilize the morphology by refining the droplet sizes of BHAS phase. The composites are prepared through melt processing in a batch mixer at varying screw speeds. Scanning and transmission electron microscopy studies confirmed the dispersion and localization of microsilica particles in the PBSA matrix and nanosilica particles in the dispersed BHAS phase. The increase in the screw speed promoted migration of some microsilica particles from the PBSA matrix to the dispersed BHAS phase, while nanosilica particles are mostly localized in the BHAS phase at both screw speeds. This led to changes in viscosity ratios that resulted in a variation in the morphology development. In conclusion, PBSA/BHAS blend composites containing both micro‐ and nanosilica particles are studied and a correlation between the silica particle sizes, localization, and the final properties was established.

Analysis of methods of regulation of silicon dioxide particles size obtained by the Stober method

The object of research is the method of synthesis of silicon dioxide nanoparticles, namely the Stober method. Synthesis of particles with the help of the Stober process is an example of a sol-gel method, one of the most practical and controlled methods for obtaining controlled size nanoparticles, shapes and morphologies. The Stober method is a classical approach to the synthesis of silica nanoparticles, but in existing works there is no systematic approach to establishing a connection between such reaction parameters as the concentration of components, temperature and time of the process. During the research, various types of information retrieval and information research were used. As a result of this work, a survey is obtained that is able to solve the problem of systematizing the influence of these parameters under the conditions of the Stober process. Methods for regulating the size of silica particles are considered, namely, a change in: a temperature in a sufficiently wide range from 5 ºC to 65 ºC; TEOS/H2O/NH3 concentration; quantity and thermodynamic quality of the solvent, as well as the effect of the reaction time. The influence of these parameters is considered not only from the point of view of changing the unit parameter, but also in combination with the others. The regularities of the particle diameter variation for the main synthesis conditions are established. The ways of particle synthesis by the Stober method from hundreds of nanometers to micrometers are shown. It is shown that for the synthesis of particles with minimal dimensions, a decrease in the concentration of the reacting components will be necessary: TEOS, H2O and NH3. This makes it possible to reduce the rate of hydrolysis and condensation processes, as well as the solubility of the intermediate Si(OC2H5)4-X(OH)X], which determines the absence of supersaturation during nucleation. The determining factors for this decrease are the increased synthesis temperature and the use of more polar solvents. The results of the work can be used to control the synthesis of silicon dioxide nanoparticles for various applications, from catalytic systems to functional fillers of materials and in particular to the creation of superhydrophobic structures.

Controlling morphology and particle size of hollow poly(styrene-divinylbenzene) microspheres fabricated by template-based method

Hollow poly(styrene–divinylbenzene) (P(S-DVB)) microspheres were fabricated via template-based method including synthesis of silica particles by sol-gel method, preparation of silica/P(S-DVB) particles by dispersion polymerization and chemical etching of silica cores by NaOH solution. TEM, FTIR and TG analyses confirmed that the hollow P(S-DVB) microspheres were successfully obtained. The morphology of hollow P(S-DVB) microspheres could be controlled by adjusting the amounts of DVB, AIBN and VTES, and the round-ball-like hollow P(S-DVB) microspheres were fabricated when the amount of DVB, AIBN and VTES was 30.0 wt%, 5.0 wt% and 30.0 vol% respectively. Both the size of silica particles and amount of monomers were regarded as the two key factors to control the particle size of the round-ball-like hollow P(S-DVB) microspheres.

Pneumothorax in the cases of silicosis in southern part of Rajasthan

Background: Silicosis is an occupational lung disease caused by inhalation of dust containing crystalline silica particles of size 0.5-5 microns in diameter. It commonly occurs in workers involved in quarrying, mining, sandblasting, tunneling, foundry work and ceramics. Pneumothorax is one of the complications of silicosis. The occurrence of pneumothorax in a patient with silicosis is a rare event, but it may be fatal. The incidence of secondary spontaneous pneumothorax (SSP) in silicosis as such is not known. This study aims to report the cases of secondary spontaneous pneumothorax in patients of silicosis in Southern part of Rajasthan.Methods: 50 patients of silicosis established by historical, clinical evaluation and radiological evidence with increased dyspnoea were included in the study. In all patients Chest X ray was done immediately.Results: Among 50 patients of silicosis with increased dyspnoea, Chest X ray showed pneumothorax in 20 patients of which 4 had bilateral pneumothorax, 7 had right pneumothorax and 9 had left pneumothorax. The mean duration of exposure to silica particles was 10 years (5 to 15 years). All the patients had various degrees of dyspnoea and chest pain. Tube thoracostomy was performed in 15 patients while 5 patients were managed conservatively with oxygen and bronchodilators.Conclusions: Our study showed an increased incidence of secondary pneumothorax in silicosis patients. The occurrence of pneumothorax, though rare in silicosis is a potentially life-threatening complication and may cause serious morbidity and mortality. The patients of silicosis who develop sudden onset of dyspnoea should be promptly investigated for this complication.

Separation of different-sized silica nanoparticles using asymmetric flow field-flow fractionation by control of the Debye length of the particles with the addition of electrolyte molecules

Asymmetric flow field-flow fractionation (AF4) is widely used in nanotechnology to fractionate objective size from samples with wide size distributions. Essentially, the size separation of nanoparticles by AF4 is based on the diffusivity/size of the objects; however; we found unexpected results when using AF4 for the separation of different-sized silica nanoparticles. Using pure water as the carrier liquid in the AF4 assessment, silica nanoparticles of 50 and 100nm were eluted out at almost the same retention time because of the cooperative diffusion derived by larger amounts of particles. After reducing the total concentration of silica particles, since the interaction between silica particles decreased with decreasing number of particles, better separation of the two different-sized silica nanoparticles was obtained. Furthermore, in order to reduce the electrostatic interaction between silica particles, electrolyte molecules (sodium dodecyl sulfate: SDS) were added to the carrier liquid, resulted that the excellent separation of 50 and 100nm sized silica particles was achieved using 0.005mg/mL of SDS aqueous solution as the carrier liquid. However, it was surprisingly observed that the zeta-potential of particles and membrane were not changed at all after addition of SDS into aqueous carrier. A theoretical estimation using the zeta-potential assessment and DLVO (Derjaguin-Landau-Verwey-Overbeek) theory indicated the Debye length of silica particles is the most important factor to induce appropriate separation of silica particles using AF4. Namely, the cooperative diffusion of different sizes of silica nanoparticles were suppressed by the change of the effective distance of the electrostatic interaction between particles (Debye length of particles). Although there are many studies focused on membrane-particle interactions or loading sample concentration effect in AF4 separation supported by the obvious change of zeta potential of particles by adding electrolyte, this study clearly demonstrates that not only diffusivity/size and zeta potentials of particle/membrane, but also Debye length of particles as well as that of the membrane significantly contribute to determining the appropriate separation conditions for AF4 assessment of nanomaterials.

A novel low-cost method of silica aerogel fabrication using fly ash and trona ore with ambient pressure drying technique

Highly porous and hydrophobic silica aerogel is fabricated using fly ash and trona ore as the starting materials and the cost-effective ambient pressure drying technique. The optimal calcination parameters are determined as temperature of 850°C, holding time of 2h, and the trona ore/fly ash mass ratio of 1.4. The CO2 release mechanism during calcination is proposed and has been verified by the Thermogravimetric and Differential Scanning Calorimetry analysis (TG/DSC) and X-ray fluorescence (XRF) technique. The hydrogel is derived from reacting the calcination mixture with sulphuric acid solution, followed by filtration. The impurities can be effectively removed through water washing and solvent exchange processes. No ion exchange resin is used in this preparation method, and thus it is a safe, inexpensive and much more straightforward process. In order to minimize drying shrinkage, the hydrogel is first transformed into an alcogel by soaking in ethanol, after which the alcogel is surface modified with the hexane/ethanol/trimethylchlorosilane (hexane/ethanol/TMCS) mixture solution. It has been observed that the specific surface area, BJH desorption pore volume, and BJH desorption average pore diameter all first increase and then decrease so that reach to the maximum values once the heat treatment temperature approaches 500°C due to the oxidation of CH3 groups on the silica skeleton surface. The final product presents special characteristics including: (1) high thermal stability for maintaining hydrophobicity up to 476°C, (2) contact angle of the as-dried silica aerogel as high as 151°, (3) silica particle size of ca. 3–6nm, agreeing well with the model as reported, (4) and the 500°C heat treated sample possessing a large specific surface area of 856.2m2/g, a large pore volume of 2.92cm3/g, and a BJH desorption average pore diameter of 17.1nm. The proposed inexpensive approach produces silica aerogel with superior properties and is a scalable-manufacturing method for large-scale industrial production.

Silica aerogels formed from soluble silicates and methyl trimethoxysilane (MTMS) using CO2 gas as a gelation agent

Silica aerogel has been formed using CO2 gas as the gelation agent through the low-cost ambient pressure drying technique. With water wash and the following solvent exchange process for Na+ removal, this synthesis route has no ion exchange resin used and becomes more straightforward. In order to reduce the silica particle and pore sizes, different hydrolysis-condensation rate control agents including dimethylformamide (DMF), methyltriethoxysilane (TMES), Glycerol and methyltrimethoxylsilane (MTMS) have been applied to modify the structural groups of silica network. Results show that MTMS is the most effective control agent and the optimized MTMS/silica sol volume ratio has been found at 1% by testing the specific surface area of the aerogel. In addition, the effects of chlorotrimethylsilane (TMCS) amount and the calcining temperature on the physicochemical properties of the aerogel have been also investigated. When the TMCS/silica sol volume ratio is 0.4, Thermogravimetric and Differential Scanning Calorimetry analysis (TG/DSC) measurement shows that there is an apprent exothermic peak at calcining temperture of 420°C, caused by the transformation of Si-CH3 group to Si-OH group. X-ray photoelectric spectroscopy (XPS) results show that the percentages of Si-C(-H) bonds with binding energy of 102.4eV have decreased from 25.5% to 7.2% after 420°C calcining. The contact angle of the as-dried aerogel is as high as 154° and dramatically decreases to ca. 109° after calcining at 450°C. The pore volume and BET specific surface area both increase first and then decrease with the increase of calcining temperature, and the pore volume reaches the maxmium of 1.45cm3/g at 400°C and it confirms Si-CH3 group release. This study offers a new facile route to the synthesis of silica aerogel and presents a promising way of the cost-effective large-scale manufacturing.

Synthesis of core-shell silica spheres with tunable pore diameters for HPLC

Core-shell silica particles with fibrous shell structure and tunable pore size were prepared by using a dul-template method. The pore size of the core-shell silica particles was affected greatly by the amount of octadecylamine, which as used as cosurfactant. The pore size could be enlarged from 7.1nm to 22.3nm while keeping the unique fibrous shell structure. After derivatized with C18, the separation performances of these particles with a wider pore size were investigated. The column efficiency was as high as 219,789 plates m−1 for dimethylnaphthalene. Baseline separation of proteins ranging in size from 12 to 66kD was achieved within 5min. The separation results demonstrate that the synthesized core-shell silica particles would be a promising packing material in the rapid and high-resolution separation of both small solutes and macromolecules.

Tailoring the size and microporosity of Stöber silica particles

The influence exerted by addition of [3-(methacryloyloxy) propyl]trimethoxysilane (MPTMOS) on the porosity and size of silica particles synthesized in a water-ethanol-ammonia-tetraethoxysilane (TEOS) mixture by the Stöber-Fink-Bohn method with the subsequent calcination in oxygen at 400 °C was studied. A set of particles was synthesized at the same relative amounts of the starting reagents and at the same temperature of the reaction mixture. It was shown that as the amount of MPTMOS in the TEOS + MPTMOS precursor is raised from 0 to 12.5 mol%, the final size of the resulting SiO2 particles decreases from ∼400 to ∼10 nm, which is presumably due to the increase in the number of nucleation centers by several orders of magnitude. It was found that the particles have micropores, which are presumably formed upon removal of methacryloyloxypropyl groups by calcination. As the MPTMOS:TEOS molar ratio is raised, the micropore volume and the apparent specific surface area of the particles first grow and reach values of 0.15 сm3 g−1 (350 m2 g−1), and then decrease to 0.05 сm3 g−1 (100 m2 g−1) because the particle size (∼10 nm) becomes comparable with the pore size (1–2 nm). Upon addition of one more porogen, cetyltrimethylammonium bromide (CTAB), to the reaction mixture, the micropore volume and the apparent specific surface area of the particles substantially increase to become 0.25 cm3 g−1 and 600 m2 g−1, correspondingly, and the particle size rises to 50 nm. Probably, mesopores formed upon oxidation of CTAB micelles and micropores are mutually connected and form a common network within the particles. The total pore volume and the specific surface area of the particles determined by BET reach values of 1.05 cm3 g−1 and 1200 m2 g−1, respectively.

Simultaneous control of size and surface functionality of silica particle via growing method

Although silane treatment has been studied asa simple and powerful tool to modify the surface of silica particle, there are still several difficulties in terms of controlling surface functionality and size of nanoparticles. Here we develop a growing method to overcome above drawback. The method was processed by continuously injecting precursor using syringe pump. According to the continuous injection, the concentration of precursors in media are properly controlled, and then the continuous injection of precursor promotes the growth of silica particles. When the functional silanes (silane coupling agents) are used, the method can control the amount of surficial functional groups on the silica particle, and can adjust diameter of the particle simultaneously. Furthermore, well-controlled functional silica particles made by growing method are used for catalytic reaction, Knoevenagel reaction, asa solid state catalyst.

Nano-structured platinum group metal-free catalysts and their integration in fuel cell electrode architectures

The novel platinum group metal-free (PGM-free) catalyst for the oxygen reduction reaction (ORR) is synthesized by a modified sacrificial support method (SSM). The catalyst chemical/surface composition is studied by X-ray photoelectron spectroscopy, and the morphology of the material is observed using both HR-SEM and HR-TEM, demonstrating the open-frame, self-supported catalysts. This new catalyst’s electrochemical performance is evaluated by polarization curves and has behaviour comparable to the state-of-the-art PGM-free catalysts. Meso-structure imaging shows pores on the order of 100nm, the mean size of the individual silica particles in the sacrificial support. For the first time, PGM-free catalyst layer (CL) morphology in a membrane electrode assembly (MEA) is studied in detail by combined nano- and micro X-ray computed tomography (CT) and interpretational modelling. The highly inhomogeneous, high-tortuosity, through-thickness structure of the CL is observed with micro-CT. The nano-CT method for these thick PGM-free electrodes is not sufficient to capture the full through-thickness morphology of these electrodes. Water retention curves suggest water pooling at the MEA components’ interfaces and significant dependence of capilary pressure and saturation on through-thickness location. This study is the first of its kind to identify morphology-dependent transport losses in the thick PGM-free electrodes using scale-bridging between meso-, micro-, and macro.

An analytical model for the control of silica grout penetration in natural groundwater systems

Over the last three decades, colloidal silica has been investigated and more recently adopted as a low viscosity grouting technology (e.g. for grouting rock fractures within geological disposal facilities nuclear waste). The potential of colloidal silica as a favourable grouting material exists due to: its initial low viscosity; its low hydraulic conductivity after gelling (of the order of 10−7cm/s); the very low injection pressures required; its controllable set/gel times (from minutes to several days); the fact it is environmentally inert; its small particle size (less than hundreds of nanometres) and its cost-effectiveness. Despite the documented success of colloidal silica based grouts for hydraulic barrier formation, research has not translated into widespread industrial use. A key factor in this limited commercial uptake is the lack of a predictive model for grout gelling which controls grout penetration: whilst data are available to underpin design of a grouting campaign in laboratory conditions, little research has been done to underpin applications in natural environments. Here we develop and validate an analytical model of colloidal silica gelling in groundwaters with varying pH and background electrolyte concentrations. This paper presents an analytical model that accounts for changes in pH, electrolyte concentration, cation valency and molar mass, silica particle size and silica concentration giving predictive capability without the need for site-specific calibration. The model is validated against experimental observations for gel times of 32–766min, the model accurately predicts the log(gel time) with an average error of 4% which corresponds to an R2 value of 0.96.The model is then applied to a hypothetical case study to demonstrate its use in grout design, based on published in-situ groundwater data from the Olkiluoto area of Finland. The model successfully predicts the required accelerator concentration to achieve a grout gel time of approximately 50min, taking into account the cations already present within the synthetic groundwater.

Spray drying of amorphous ibuprofen nanoparticles for the production of granules with enhanced drug release

This work investigates formulation strategies for the production of pharmaceutical powders out of precipitated API (active pharmaceutical ingredient) nanoparticles. In order to accomplish this challenge, composite granules were designed via two distinct formulation strategies with the final goal of producing pharmaceutical powders with enhanced bioavailability. On the one hand, lactose granules were prepared by embedding secluded ibuprofen nanoparticles (particle size of ibuprofen: 100nm) in a lactose matrix via spray drying. On the other hand, silica granules were obtained by encasing ibuprofen nanoparticles in a nanoparticulate silica shell (primary particle size of silica: 40nm). Afterwards, granules were analysed by means of dissolution tests with a view to comparing different loading procedures regarding drug release. Furthermore, differential scanning calorimetry (DSC) measurements were used to prove the solid state, amorphous or crystalline, of APIs. Additionally, scanning electron microscopy (SEM) images enabled to characterize the morphology of the granules.

Effect on Aluminium Metal Matrix Composite Reinforced with Nano Sized Silica Particles

In recent times, it could be observed that metal matrix composites receive considerable importance on account of improved properties compared to unreinforced alloys which includes high specific strength, specific modulus, damping capacity and good wear resistance. Interest in composites containing low density and low cost reinforcements has been since growing. Among various discontinuous particulate, silica is one of the most inexpensive and low density reinforcement available in large quantities. Hence, composites with aluminium oxide as reinforcement after the in-situ reaction of aluminium and silica are likely to overcome the cost barrier for wide spread applications in automotive and small engine applications. It is therefore expected that the incorporation of aluminium oxide particles in aluminium alloy will improve the mechanical properties of base material that will see increased usage in aircraft application due to reduced weight. In this research an effect on aluminum matrix composite reinforced with nano sized silica particles with different weight percentage was carried out. From the results it was found that the composites with 4 to 6wt% particle volume fraction to be the best with good tensile strength, yield stress and percentage elongation.

Exhaled Breath Condensate: A Novel Matrix for Biological Monitoring to Assess Occupational Exposure to Respirable Crystalline Silica.

Biological monitoring (BM) is a useful way of determining overall exposures to chemical substances; however, in the case of respirable crystalline silica (RCS), this has not been analytically feasible in conventional biological matrices. The aim of this study was to investigate the utility of exhaled breath condensate (EBC) as a potential biological matrix in which to determine exposure to RCS. A small pilot study was undertaken collecting EBC from six quarry workers and six occupationally unexposed persons; the samples were analysed using both single particle inductively coupled plasma mass spectrometry (spICP-MS) and transmission electron microscopy (TEM). The results showed that EBC obtained from the occupationally unexposed persons exhibited low background levels of dissolved silica whilst silica particles of various sizes were present in samples from quarry workers. This is the first study to report EBC as a potential biological matrix that allows differentiation of RCS concentrations between samples from workers and occupationally unexposed controls. The results shown here confirm the presence of RCS in EBC by both spICP-MS and TEM. However, there are difficult analytical challenges still to be overcome before this can be used as a BM method to determine workplace exposure, these are currently being investigated.

Preparation and characterization of monodisperse silica nanoparticles via miniemulsion sol–gel reaction of tetraethyl orthosilicate

Monodisperse silica nanoparticles were prepared via miniemulsion sol–gel reaction of tetraethyl orthosilicate (TEOS). Hexadecane (HD) or hexadecyltrimethoxysilane was used as costabilizer to effectively retard the Ostwald ripening process involved in TEOS miniemulsion. The Ostwald ripening behavior was characterized by dynamic light scattering (DLS), and it was adequately described by the modified Kabal’nov equation. The miniemulsion sol–gel reaction of TEOS/HD with a volume fraction (φ c) of 0.024 at 80 °C is stable in the pH range 6–10. By contrast, gelation of reacting miniemulsions occurs at 70 and 100 min at pH 4 and 5, respectively. The weight-average silica particle size (d w) of colloidal products prepared at 80 °C and pH 7 decreases from 59 to 36 nm with low polydispersity index (PDI, in the range 1.02–1.03), determined by transmission electron microscopy, when the φ c of HD increases from 0.024 to 0.23. At constant φ c (0.024), the resultant silica nanoparticles show larger d w (83 nm) and PDI (1.35) for the TEOS/HD system at pH 10 as compared to the counterpart of pH 7. Furthermore, for the TEOS/HD system at pH 7 and low φ c (0.024), d w increases significantly with temperature being increased from 25 to 80 °C. By contrast, the effect of temperature on silica nanoparticle size becomes insignificant when a high level of HD (φ c = 0.23) is used. Zeta potential measurements and field emission scanning electron microscopy were used to characterize the surface charge density and morphology of resultant silica nanoparticles.

Effect of steric hindrance on surface wettability of fine silica powder modified by n- or t-butyl alcohol

Fumed silica is an important industrial material, which is widely used in medical, cosmetic, and electronic products. One important industrial application of the fumed silica powder is using it as fillers, which are key materials for reinforcing the high-performance/high-functional industrial products. However, the use of fumed silica as filler is limited to micrometer or millimeter sized particles, because nanometer sized silica particles tend to aggregate. In this study, the surface of fine silica powder is modified with n- and t-butyl alcohols, which exhibit different steric hindrance effects. The surface wettability of each modified silica powders is determined in two ways: macroscopic and microscopic wettability. Macroscopic wettability refers to preference dispersion test and microscopic wettability refers to evaluation of the molecular level by Fourier transform infrared spectroscopy (FT-IR). The modification ratio of each sample is confirmed by thermogravimetry-differential thermal analysis (TG-DTA), and the hydrophobicity of these modified silica powders is evaluated by the preference dispersion test. Molecular level evaluation of surface wettability by FT-IR confirms an obvious structural difference due to the steric hindrance of the n- and t-butoxy groups on the surface of silica. In addition, a correlation between macroscopic and microscopic evaluation results for the surface wettability of modified silica powders is confirmed.