• Elastomers and Composites
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• v.53 no.3
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• pp.175-180
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• 2018

Solution-styrene-butadiene rubber (SSBR) composites were manufactured using four kinds of fillers: silica-silane coated carbon black (SC-CB) hybrid, starch-SC-CB hybrid, pure silica, and pure starch. The influence of filler type on the mechanical properties of the rubber matrix was studied in this work. SC-CB was prepared by silane-graft-coating using vinyl triethoxy silane and carbon black, which enhanced the dispersion effect between the rubber matrix and the filler, and improved the mechanical properties of the compounds. The morphology of the composites was observed by field-emission scanning electron microscopy (FE-SEM). The thermal decomposition behavior of the composites was determined by thermogravimetric analysis (TGA), and the crosslinking behavior of the composites was tested using a rubber process analyzer (RPA). The hardness, tensile strength, swelling ratio, and gas transmittance rate of the composites were evaluated according to ASTM. The test results revealed that with the addition of SC-CB, the hybrid fillers, especially those blended with silica, showed a better reinforcement effect, the highest hardness and tensile strength, and stable thermal decomposition behavior. This implies that the silica-SC-CB hybrid filler has a notable mechanical reinforcement effect on the SSBR matrix. Because of self-crosslinking during its synthesis, the starch-SC-CB hybrid filler produced the most dense matrix, which improved the anti-gas transmittance property. The composites with the hybrid fillers had better anti-swelling properties as compared to the neat SSBR composite, which was due to the hydrophilicity of silica and starch.

• Transactions on Electrical and Electronic Materials
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• v.17 no.3
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• pp.155-158
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• 2016

The effect of microsilica content modified with silicone-modified epoxy on electrical and mechanical properties of cycloaliphatic epoxy/microsilica system was investigated. The cycloaliphatic epoxy resin was diglycidyl 1,2-cyclohexanedicarboxylate and curing agent was an anhydride. Surface of microsilica was modified with silicone-modified epoxy. Electrical breakdown strength, the most important property for electrical insulation materials was tested. Tensile and flexural tests were also performed using universal testing machine (UTM). The microcomposite with 60 wt% microsilica shows maximum values in electrical breakdown strength.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.20-25
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• 2020

As nanoscience and nanotechnology advance, techniques for selective pattern growth have attracted significant attention. Silica nanoparticles (NPs) are used as a promising nanomaterials for bio-labeling, bio-imaging, and bio-sensing. In this study, silica NPs were synthesized by a sol-gel process using a modified Stöber method. In addition, the selective pattern growth of silica NPs was achieved by the surface functionalization of the substrate using a micro-contact printing technique of a hydrophobic treatment. The particle size of the as-synthesized silica NPs and morphology of selective pattern growth of silica NPs were characterized by FE-SEM. The contact angle by surface functionalization of the substrate was investigated using a contact angle analyzer. As a result, silica NPs were not observed on the hydrophobic surface of the OTS solution treatment, which was coated by spin coating. In contrast, the silica NPs were well coated on the hydrophilic surface after the KOH solution treatment. FE-SEM confirmed the selective pattern growth of silica NPs on a hydrophilic surface, which was functionalized using the micro-contact printing technique. If the characteristics of the selective pattern growth of silica NPs can be applied to dye-doped silica NPs, they will find applications in the bio imaging, and bio sensing fields.

• Journal of Sensor Science and Technology
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• v.15 no.5
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• pp.371-377
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• 2006

Nano porous, transparent silica aerogels monoliths were prepared under ambient drying (1 atm, $270^{\circ}C$) condition by the combination of sol-gel process and surface modification with subsequent heat treatment. Three kinds of solvent, n-hexane, n-heptane and xylene, were selected in the point view of low surface tension and vapor pressure in order to restrain a formation of cracks during drying. Crack-free silica aerogels with over 93 % of porosity and below $0.14g/cm^3$ of density were obtained by solvent exchange and surface modification under atmosphere condition. Optimum solvent was confirmed n-heptane among these solvents through estimation of FT-IR, TGA, BET and SEM. Modified silica aerogel exhibited a higher porosity and pore size compare to unmodified aerogels. Hydrophobicity was also controled by C-H and H-OH bonding state in the gel structure and heat treatment over $400^{\circ}C$ effects to the hydrophobicity due to oxidation of C-H radicals.

• Journal of Powder Materials
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• v.18 no.3
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• pp.269-276
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• 2011

The synthesis behavior of nanoporous silica aerogel in the macroporous ceramic structure was observed using TEOS as a source material and glycerol as a dry control chemical additive (DCCA). Silica aerogel in the macroporous ceramic structure was synthesized via sono-gel process using hexamethyldiazane (HMDS) as a modification agent and n-hexane as a main solvent. The wet gel with a modified surface was dried at $105^{\circ}C$ under ambient pressure. The addition of glycerol appears to give the wet gel a more homogeneous microstructure. However, glycerol also retarded the rate of surface modification and solvent exchange. Silica aerogel completely filled the macroporous ceramic structure without defect in the condition of surface modification (20% HMDS/nhexane at 36hr).

• Membrane Journal
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• v.14 no.3
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• pp.201-206
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• 2004

The stability of the prepared silica membrane by chemical vapor deposition (CVD) method in the HI-$H_2O$ gaseous mixture was evaluated aiming at the application for hydrogen iodide decomposition in the thermochemical IS process. Porous $\alpha$-alumina having pore size of 100 nm was modified by the different CVD temperature using tetraethoxysilane as the Si source. The CVD temperature was $700^{\circ}C$, $650^{\circ}C$, and $600^{\circ}C$. The $H_2$/H$_2$ selectivities of the modified membranes which were measured by single-component permeation experiment showed 43.2, 12.6, and 8.7 at $600^{\circ}C$ for the M1 (CVD temperature was $700^{\circ}C$), M2 (CVD temperature was $650^{\circ}C$) and M3 membranes (CVD temperature was $600^{\circ}C$), respectively. Stability experiment in the HI-$H_2O$ gaseous mixture was carried out at $450^{\circ}C$. The prepared silica membrane at $600^{\circ}C$ of CVD temperature was more stable than that at the other CVD temperature.

• Korean Chemical Engineering Research
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• v.48 no.5
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• pp.583-588
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• 2010

Esterification of free fatty acid with methanol to biodiesel was investigated in a batch reactor using various solid acid catalysts, such as polymer cation-exchanged resins with sulfuric acid functional group(Amberlyst-15, Dowex 50Wx8), acidic ionic liquids (ILs)-modified silica gels respectively with $-SO_3H$ and $-SO_2Cl$ functional group ($SiO_2-[ASBI][HSO_4]$, $SiO_2-[ASCBI][HSO_4]$) and grafted silica gels respectively with $-SO_3H$ and $-SO_2Cl$ functional group ($SiO_2-R-SO_3H$, $SiO_2-R-SO_2Cl$). The effects of reaction time, temperature, reactant concentration(molar ratio of methanol to oleic acid), and catalyst amount were studied. Allylimidazolium-based ILs on modified silica gels were superior to other tested solid acid catalysts. Especially, the performance of $SiO_2-[ASBI][HSO_4]$ (immobilized by grafting of 3-allyl-1-(4-sulfobutyl)imidazolium hydrogen sulfate on silica gel) was better than that of a widely known Amberlyst-15 catalyst at the same reaction conditions. A high conversion yield of 96% was achieved in the esterification reaction of the simulated cooking oil at 353 K for 2 h. The high catalytic activity of $SiO_2-[ASBI][HSO_4]$ was attributed to the presence of strong Brønsted acid sites from the immobilized functional groups. The catalyst was recovered and the biodiesel product was separated by simple processes such as decantation and filtration.

• Journal of Adhesion and Interface
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• v.17 no.1
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• pp.7-14
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• 2016

Epoxy composites with concentrations of 5-70 wt% of silica particles were prepared in order to improve mechanical property and poor thermal stability. The mechanical and thermal properties were investigated and compared to the corresponding properties of neat epoxy composite. Furthermore, the effects of silane compound treatment on silica particles were observed by the experimental results of the tensile strength, glass transition temperature, and thermal stability of epoxy composite. Tensile strength of epoxy composites was measured by universal testing machine (UTM) and after that, the structure and morphology analysis of epoxy nanocomposites were analyzed by field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS). The increased solid content of CA0030 particle improved the tensile strength of epoxy/ modified composites to give 30-50 MPa. The thermal expansion coefficients (CTE) of neat epoxy resin and epoxy/silica composites measured with a thermomechanical analyzer (TMA) showed that the incorporation of silica particles was helpful to reduce the CTE of neat epoxy resin.

• Applied Chemistry for Engineering
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• v.27 no.3
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• pp.299-306
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• 2016

In this study, new hydroxyapatite powder surface composites were investigated for protective effects against ultraviolet rays. Hydroxyapatite (HAp) is biocompatible and does not cause nebula phenomenon on skin. We investigated the surface modification of hydroxyapatite to improve UV block and skin usage. Dimethicone, lauroyl lysine, triethoxycaprylylsilane and silica were used as coating agents for the surface modification of HAp. To prepare the composite complex of the modified surface, the dimethicone, lauroyl lysine and triethoxycaprylylsilane were prepared by a dry process, and silica by a hydrothermal synthesis method. The HAp-silica was chosen as the best composite powder when measuring its sun protection levels. We investigated the characteristics of the surface of HAp-silica by SEM, particle size analyzer and energy dispersive spectrometry (EDS). Additionally, the stability in the formulation, UV block effect, and safety in BB creams were investigated. In conclusion, HAp-silica prepared by the modification of HAp complex surface improved the skin usage and UV block effect by enhancing the white cloudy phenomenon. These results indicate that HAp-silica may be used for UV block cosmetics.

• Computers and Concrete
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• v.26 no.3
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• pp.257-273
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• 2020

Concrete bond strength with steel re-bars depends on multiple factors including concrete-steel interface and mechanical properties of concrete. However, the hydration development of cementitious paste, and in turn the mechanical properties of concrete, are negatively affected by cold weather. This study aimed at exploring the concrete-steel bonding behavior in concrete cast and cured under freezing temperatures. Three concrete mixtures were cast and cured at -10 and -20℃. The mixtures were protected using conventional insulation blankets and a hybrid system consisting of insulation blankets and phase change materials. The mixtures comprised General Use cement, fly ash (20%), nano-silica (6%) and calcium nitrate-nitrite as a cold weather admixture system. The mixtures were tested in terms of internal temperature, compressive, tensile strengths, and modulus of elasticity. In addition, the bond strength between concrete and steel re-bars were evaluated by a pull-out test, while the quality of the interface between concrete and steel was assessed by thermal and microscopy studies. In addition, the internal heat evolution and force-slip relationship were modeled based on energy conservation and stress-strain relationships, respectively using three-dimensional (3D) finite-element software. The results showed the reliability of the proposed models to accurately predict concrete heat evolution as well as bond strength relative to experimental data. The hybrid protection system and nano-modified concrete mixtures produced good quality concrete-steel interface with adequate bond strength, without need for heating operations before casting and during curing under freezing temperatures down to -20℃.