Surface Modification of Nanometer Silica by N, N'-dicyclohexyl- carbodiimide Mediated Amidation

A potentially versatile procedure for surface modification of nanometer silica is illustrated by N, N-dicyclohexylcarbodiimide (DCC) mediated amidation of stearic acid.

GRAFTING OF POLYSTYRENE ONTO A NANOMETER SILICA SURFACE BY MICROEMULSION POLYMERIZATION

The grafting of polystyrene onto a nanometer silica surface by microemulsion polymerization is described. Silica was functionalized with 3-methacryloxypropyltrimethoxysilane coupling agent before polymerization. A mixture of ionic and non-ionic surfactants as well as water-soluble and oil-soluble initiators were used. The effect of the amount of silica and ionic surfactant on the graft polymerization was studied. The graft polymerization procedure for styrene was also applied to methyl methacrylate, Composite particles with a core-shell structure were obtained and the yield and grafting efficiency of monomer were high.

Mesoporous silica rods with cone shaped pores modulate inflammation and deliver BMP-2 for bone regeneration

Biomaterials with suitable osteoimmunomodulation properties and ability to deliver osteoinductive biomolecules,such as bone morphogenetic proteins,are desired for bone regeneration.Herein,we report the development of mesoporous silica rods with large cone-shaped pores(MSR-CP)to load and deliver large protein drugs.It is noted that those cone-shaped pores on the surface modulated the immune response and reduced the pro-inflammatory reaction of stimulated macrophage.Furthermore,bone morphogenetic proteins 2(BMP-2)loaded MSR-CP facilitated osteogenic differentiation and promoted osteogenesis of bone marrow stromal cells.In vivo tests confirmed BMP-2 loaded MSR-CP improved the bone regeneration performance.This study provides a potential strategy for the design of drug delivery systems for bone regeneration.

Low-cost preparation of mesoporous silica with high pore volume

Mesoporous silica materials with high pore volume were successfully prepared by the chemical precipitation method, with water glass and a biodegradable nonionic surfactant polyethylene glycol （PEG）. The obtained materials were characterized by transmission electron microscopy （TEM）, scanning electron microscopy （SEM）, thermo gravimetric analyzer and differential scanning calorimetry （TG-DSC）, nitrogen adsorption-desorption measurements, and X-ray diffraction （XRD）. The results showed that the changes of the pore parameters depended on both the surfactant content and heat treatment temperature. When the content of PEG was 10wt% and the obtained PEG/SiO2 composite was heated at 600℃, the mesoporous silica with a pore volume of 2.2 cma/g, a BET specific surface area of 361.55 m^2/g, and a diameter of 2-4 μm could be obtained. The obtained mesoporous silica materials have potential applications in the fields of paint and plastic, as thickening, reinforcing, and flatting agents.

Microstructure of β-Dicalcium Silicate after Accelerated Carbonation

The present work presents the microstructure of β-Ca_2SiO_4(β-C_2S) after accelerated carbonation. The synthesis procedure of β-C_2S was examined first, and the crystalline and amorphous structure, the distribution and the pore structure of β-C_2S carbonation products were also determined by X-ray diffraction(XRD) quantitative analysis, simultaneous thermal analyzer(TG/DTA), Fourier transform-infrared spectroscopy(FT-IR), high resolution ^(29)Si magic angle spinning nuclear magnetic resonance(^(29)Si NMR), N_2-sorption techniques, and scanning electron microscopy(SEM), respectively. Test results indicate that carbonation products are dramatically formed in the initial 2 h. The main carbonation products are crystalline calcite and amorphous three-dimensional network silica gels, which contain nanometer-sized pores. The calcite, silica gels and un-carbonated β-C_2S are distributed hierarchically.

Synthesis and Characterization of Bimodal Mesoporous Silica

Mesoporous silica with controllable bimodal pore size distribution was synthesized with cetyltrimethylammonium bromide （CTAB） as chemical template for small mesopores and silica gel as physical template for large mesopores. The structure of synthesized samples were characterized by Fourier transform infrared （FT-IR） spectroscopy, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and N2 adsorption-desorption measurements. The experimental results show that bimodal mesoporous silica consists of small mesopores of about 3 nm and large mesopores of about 45 nm. The small mesopores which were formed on the external surface and pore walls of the silica gel had similar characters with those of MCM-41, while large mesopores were inherited from parent silica gel material. The pore size distribution of the synthesized silica can be adjusted by changing the relative content of TEOS and silica gel or the feeding sequence of silica gel and NH4OH.

Sulfate Attack Resistance of Air-entrained Silica Fume Concrete under Dry-Wet Cycle Condition

Based on the erosion resistant coefficient,the effects of water-cement ratio,air-entrained,silica fume content and sand ratio on the sulfate attack resistance of air-entrained silica fume concrete were studied by orthogonal experiments in order to explore its sulfate attack resistance under dry-wet condition.A more significant model of concrete resistance to sulfate attack was also established,thus this work provided a strategy reference for quantitative design of sulfate attack resistant concrete.The experimental results show that dry-wet cycle deteriorates the concrete resistance to the sulfate attack,and leads to the remarkable declines of concrete strength and sulfate resistance.Air bubbles in the air-entrained silica fume concrete lower and delay the damage resulted from the crystallization sulfate salt.However this delay gradually disappears when most of the close bubbles are breached by the alternative running of the sulfate salt crystallization and the permeating pressure,and then the air bubbles are filled with sulfate salt crystallization.The concrete is provided with the strongest sulfate resistance when it is prepared with the 0.47 water-binder ratio,6.0% air-entrained,5% silica fume and 30% sand ratio.The erosion resistant coefficients K80 and K150 of this concrete are increased by 9%,7%,9%,and 5% respectively as compared with those of concretes without silica fume and air entraining.

Synthesis of Nanometer-sized Mesoporous Oxide Spheres

A few hundreds nanometer-sized mesoporous silica and alumina spheres were synthesized in organic solvents. The impacts of ammonia, N, N-dimethylformamide (DMF) and stirring speed were also investigated.

Biopolymer Entering into and Escaping from a Nanometer Pore

We theoretically investigated negative entropy S of biopolymer which passes through a nanometer pore（such as a-hemolysin）, especially entering process and escaping process, on the basis of which we also studied biopolymer entering-pore time rent, biopolymer entering mean velocity Vent, biopolymer escaping-pore time resc, and biopolymer escaping mean velocity vesc, respectively. Our results illustrate that the entering and escaping processes of biopolymer depend on its negative entropy, and entering process is more difficult than escaping process for biopolymer translocation. This tremendous difference between the two processes will offer a useful engineering hint for single macromolecule identification.

A comparative study of drying techniques on the morphology of porous silica gels synthesized via sol-gel process

The effect of drying techniques on the microstructure,morphology and pore structure of porous silica gels was studied in the paper.The gels were prepared by using sol-gel process and different drying routes:freeze-drying (FD),low pressure drying (LPD),high temperature drying (HTD) and chemical modification & ambient drying (CMD) techniques.Observation under pore distribution and structural properties showed that CMD technique leads to homogenous mesoporous silica material with specific surface area of 745 m2/g,and the average pore size around 20 nm,while LPD and HTD result in loosely packed particles with non-isotropic aggregation pattern.The specific surface areas of LPD and HTD samples are 419 and 513 m2/g respectively,and the pore size distribution of the samples are observed distributing widely in range of 10-100 nm.Freeze drying method is a new but prospective way to prepare mesoporous silica.The specific area of FD sample is around 500 m2/g.By the comparison for the properties of the gels,this paper wants to induce a further interest in finding a proper method to synthesize the porous silica gels for low price use.

Preparation of Silica Radiation Pore and Its Application as Antimicrobial Carrier

Hollow silica nanospheres with radical pore on the surfaces were prepared using the assemblies of valine amphiphilic small molecule and benzene as double-templates through sol-gel method in tetramethylammonium hydroxide(25wt%)solution at the stirring rate of 1000 rpm.There are a lot of vertical pores on the surfaces of the hollow spheres after removing the templates in Muffle furnace at 550℃for 5 h.The sample was characterized using field-emission scanning electron microscopy,transmission electron microscopy,Brunauer-Emmett-Teller(BET),X-ray diffraction,etc.The diameter,the vertical pore size of the nanospheres and the BET surface areas are 30-100 nm,4.2 nm,and 570.5 m2/g,respectively.Because the high porosity and specific surface area,this kind of hollow sphere is the excellent antimicrobial carrier.The antibacterial activities of the silica nanospheres were evaluated by using a bacterial growth inhibitory assay.The experimental results show that the silica hollow spheres loaded with Ag+have a good bactericidal effect.

Monodisperse Ultra-Large-Pore Silica Coated Polystyrene Core-Shell Microbeads via Layer-by-Layer Assembly for Nano-Micro Composite

Polystyrene （PS） @SiO2 core-shell microbeads with large pore and large particle size were prepared via layer-by-layer（LBL）assembly technique for potential applications in nano-micro composites. Negative silica nanoparticles synthesized via modified St6ber method and cationic poly （diallyldimethylammonium chloride） were alternately adsorbed on the surface of microbeads. Zeta potential, size, and morphology of the microbeads were monitored during LBL assembly process to ensure the successful deposition of silica nanoparticles. The porous shell was characterized using nitrogen adsorption and desorption analyses, and the surface area, volume and diame- ter of the pores were derived. It is found that the porous shell thickness and the pore size can be tuned by changing the coating times of silica nanoparticles. Finally, PS@SiO2 core-shell microbeads with 5 grn PS solid core and 350 nm mesoporous shell （mean BJH pore diameter is ~27 nm） were used to load CdSe/ZnS quantum dots （QDs）. The fluorescence microscopic image and the optical amplification of the QDs-embedded microbeads （QDBs） indicate that the as-prepared core-shell microbeads can provide adequate space for QDs and may be useful for further application of nano-micro composites.

Effect of Nano Silica on Hydration and Microstructure Characteristics of Cement High Volume Fly Ash System Under Steam Curing

The influences of nano silica (NS) on the hydration and microstructure development of steam cured cement high volume fly ash (40 wt%, CHVFA) system were investigated. The compressive strength of mortars was tested with different NS dosage from 0 to 4%. Results show that the compressive strength is dramatically improved with the increase of NS content up to 3%, and decreases with further increase of NS content (e g, at 4%). Then X?ray diffraction (XRD), differential scanning calorimetry-thermogravimetry (DSCTG), scanning electron microscope (SEM), energy disperse spectroscopy (EDS), mercury intrusion porosimeter (MIP) and nuclear magnetic resonance (NMR) were used to analyze the mechanism. The results reveal that the addition of NS accelerates the hydration of cement and fly ash, decreases the porosity and the content of calcium hydroxide (CH) and increases the polymerization degree of C-S-H thus enhancing the compressive strength of mortars. The interfacial transition zone (ITZ) of CHVFA mortars is also significantly improved by the addition ofNS, embodying in the decrease of Ca/Si ratio and CH enrichment of ITZ.

Porous Properties of Nano-fibriform Silica from Natural Chrysotile

With the TEM and physical gas adsorption techniques, porous properties of nano-ribriform silica （MLD： 92.73%） from natural chrysotile are studied in this paper. The results indicate that porous nano-fibriform silica results from brucite octahedral sheets of nature chrysotile dissolved completely and Si-O tetrahedral sheets collapsed by acid leaching. Its length is at a micron or nanometer scale. There are two types of pores： pores among neighboring fibers and pores in nanoriber. These pores （less than 6.5 nm in diameter, mostly 2.1 nm and 3.8 nm） all belong to mesopores. The pores in fibers consist of those among SiO2 particles, those among aggregates, remnant nanotubes and capillary tubes. Nanoribriform silica proves better than the traditional silica as a carrier of catalyzer and a filler for reinforce rubber and plastics.

Experiment on the silica sol imbibition of low-permeability rock mass:With silica sol particle sizes and rock permeability considered

It’s a universal engineering problem to seal micro-cracks of low-permeability argillaceous rock mass by grouting in the fields of civil engineering and mining.This paper achieved the grouting sealing of lowpermeability artificial rocks with the permeability of 0.1–40 mD by adopting silica sol imbibition grouting.The variation characteristics of particle size,viscosity,and contact angle of silica sol during solidification and the pore size distribution of low-permeability artificial rocks were measured,and spontaneous imbibition tests of the artificial rocks were carried out.Finally,combined with the imbibition theory,percolation theory,and fracture medium grouting principle,the silica sol imbibition mechanism of lowpermeability rocks and soil was discussed.The results show that:(1)Silica sol can be injected into artificial rocks with the minimum permeability of 0.1 mD through spontaneous imbibition;(2)The particle size increase of silica sol leads to decreased wettability,affinity,and injectability in grouting materials;and(3)In the range of 0.1–40 mD,the grout absorption first increases and then decreases with increased permeability.The number of large pores and fractures in the rock mass is related to injectability,and the number of small and medium pores is related to the internal driving force of imbibition.This study provides a theoretical basis for silica sol grouting sealing of low-permeability argillaceous rocks and is,therefore,an important reference for application.

INVESTIGATION OF THE INTERACTIONS BETWEEN WATER AND MODIFIED SILICA GEL BY IGC AND TPD

In this work, the thermodynamic parameters for the adsorption of water vapor on untreated silica gel and silica gel treated with hygroscopic salts and silane coupling agent were determined by lnverse Gas Chromatography （IGC） in the infinite dilution region. The desorption activation energies of the water vapor on virgin and modified silica gels were estimated by using the Temperature Programmed Desorption （TPD） technique. The interactions between the water and the virgin and modified silica gels were discussed. Results showed that the thermodynamic parameters and desorption activation energy of water vapour on the silica gels increase with decreasing pore size and increasing the surface hydrophilic properties. The desorption activation energy of virgin and modified silica gels was found to increase with increasing the thermodynamic parameters. The larger the adsorption parameters and the desorption activation energy were, the interactions between water and virgin and modified silica gels were.

Synthesis of silica powder with high pore volume by skeleton reinforcement

In this paper,a method composed of gelation of basic skeleton(first step)and skeleton reinforcement process(second step)was introduced to synthesize silica powder with high pore volume through the reaction between water glass and sulfuric acid.No organic solvents were involved in the entire preparation process and the final product was collected by spray drying.The effect of concentration of base solution,gelation point p H value and skeleton reinforcement time on the BET specific surface area and pore volume of the prepared silica powder were investigated intensively.The results show that,a basic skeleton with good dispersibility and high porosity was obtained when the concentration of base solution was 0.1 mol·L^(-1) and the gelation p H value reached 6.5.Then the basic skeleton grew into a more uniform porous structure after 30 min skeleton reinforcement.Under these optimum conditions,silica powder prepared by skeleton reinforcement method had a BET specific surface area of 358.0 m^(2)·g^(-1),and its pore volume reached 2.18 cm^(3)·g^(-1),which was much higher than that of prepared by skeleton-free method(1.62 cm^(3)·g^(-1))and by direct gelation method(0.31 cm^(3)·g^(-1)).

Effect of Silica Fume on Early Performance of Precast Concrete with Early Strength Agents

The effect of silica fume on the early performance of precast concrete with an early strength agent was investigated.The ternary compounding technique of silica fume,fly ash and early strength agent were used to examine the compressive strength,heat of hydration,hydration products,and microstructures of the precast concrete.The experimental results showed that the optimum amount of silica fume in the precast concrete was 9%.Silica fume filled the fine pores between the cement particles.However,the cement hydration was mainly influenced by the waterto-cement ratio and cement particle size.As the hydration reaction continued,silica fume provided more nucleation sites,and the characteristic volcanic ash reaction increased both the hydration degree and hydration rate of the early strength agent doped cementitious materials.

Effect of Pore Size on Properties of Highly Porous Silica Ceramic Foams for Heat Insulation

Highly porous silica ceramics with different pore sizes were fabricated by adjusting the mixed surfactants addition.The effect of the pore size on the cold compressive strength and the thermal conductivity of the ceramics was researched.The results show that the smaller pore size can improve the compressive strength and the thermal conductivity.With the mixed surfactants addition increasing from 0.1 mass%to 0.4 mass%,the porosity is close,in the range of 88.10%-88.31%,and the average pore size decreases from 190μm to 97μm;the compressive strength is enhanced from 2.97 MPa to 3.55 MPa;and the thermal conductivity decreases from 0.104 W·m-1·K-1 to 0.089 W·m-1·K-1.

The effect of silica nanoparticle aggregates on wax dissolution in diesel oil

In recent years, silica nanoparticle aggregates （SNPAs） have been used to decrease the injection pressure of wells in low permeability reservoirs achieving good results. In order to study the mechanisms for reduction in the injection pressure of low permeability wells by the SNPA-diesel oil system injection, the microstructure of SNPAs was observed with a transmission electron microscope （TEM）. The particle size distribution of SNPAs was also measured by the laser scattering method. The viscosities of diesel oil and SNPA-diesel oil system were measured with a capillary viscometer. The effect of SNPAs on the solubility of wax in the diesel oil was experimentally studied. The influencing factors, including temperature and SNPA concentration in diesel oil, on wax solubility were analyzed. A pore-throat film displacement model （PTFDM） was built for mechanism explanation. The microstructure and size distribution analyses show that the SNPAs are in the nanometer size range. The viscosity of the SNPA-diesel oil system is lower than that of the diesel oil. The solubility of wax in the diesel oil increases greatly due to SNPA addition, the solubility ratio reaches 7.5. The solubility of wax in diesel oil increases with increases in the concentration of SNPAs in the diesel oil and with the temperature. It is proved that the addition of SNPAs to diesel oil helps remove the wax deposited near the wellbore. This maybe one of the main mechanisms for injection pressure decreases in low permeability reservoirs.