• Computers and Concrete
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• v.6 no.2
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• pp.133-153
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• 2009

Discrete element modeling (DEM) in concrete technology is concerned with design and use of models that constitute a schematization of reality with operational potentials. This paper discusses the material science principles governing the design of DEM systems and evaluates the consequences for their operational potentials. It surveys the two families in physical discrete element modeling in concrete technology, only touching upon probabilistic DEM concepts as alternatives. Many common DEM systems are based on random sequential addition (RSA) procedures; their operational potentials are limited to low configuration-sensitivity features of material structure, underlying material performance characteristics of low structure-sensitivity. The second family of DEM systems employs concurrent algorithms, involving particle interaction mechanisms. Static and dynamic solutions are realized to solve particle overlap. This second family offers a far more realistic schematization of reality as to particle configuration. The operational potentials of this family involve valid approaches to structure-sensitive mechanical or durability properties. Illustrative 2D examples of fresh cement particle packing and pore formation during maturation are elaborated to demonstrate this. Mainstream fields of present day and expected application of DEM are sketched. Violation of the scientific knowledge of to day underlying these operational potentials will give rise to unreliable solutions.

• Membrane Journal
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• v.11 no.1
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• pp.22-28
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• 2001

Various charged homogeneous membranes were fabricated by blending of ionic polymer with a non-ionic polymer with different ratios. In this study. sodium alginate, chitosan and poly(vinyl alcohol) were employed as anionic. cationic and non-ionic polymers, respectively. The permcation and separation behaviors of aquCOll::; salt solutions have been investigated through the charged membranes. As the content of ionic polymer increases in the membrane, the hydrophilicity of the membrane increases and pure water flux as well as solution flux increases correspondingly, indicating that the permeation performance through the membrane is cletemunecl mainly by its hydrophilicity-, Electrostatic interaction between the charged membrane and ionic solute molecules, that is. Donnan exclusion was observed to be attributed to salt rejection to a great deal of extent, and molecular sieve mechanism was effective [or the separation of the salt solution under a similar electrostatic circumstance of solutes.

• Proceedings of the Membrane Society of Korea Conference
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• 1997.10a
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• pp.39-45
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• 1997

Introduction : Polyimides are one of the most important classes of the high performance polymers due to their excellent electrical, thermal, and high-temperature mechanical properties. But their uses are limited because of their poor solubility. Most polyimide derivatives are processed in the form of polyamic acids, which are subsequently converted into the imide structures.Recently, it has been found that the soluble polyimides with large molecular weight sufficient to application. For enhancing processability, the majority of approaches have involved the following factors. As much as, the separation of the imide ring along the back-bone, that is to say, reducing the density of imide ring in the repeat structure. The introduction of bulky substituents along the back-bone, in order to enhance the free volume of main-chain. The incorporation of flexible or thermally stable linkages in the main-chain, reducing the packing force. The disruption of symmetry or recurrence regularity through copolymerization in order to reduce crystallnity.The objectives of this investigation are the synthesis and characterization of soluble polyimides as membrane materials by the single-step polymerization and the preparation of the asymmetric polyimide membrane by using phase inversion technique. In the present study, three series of polyimide derivatives are synthesized; H series is homopolyimides, A series is prepared from single dianhydride and two diamines, B series is yielded from two dianhydrides and a diamine. The dope solution was directly prepared from the PI solution via one step polymerization from monomers.

• Bulletin of the Korean Chemical Society
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• v.35 no.6
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• pp.1675-1680
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• 2014

A peroxopolyoxotungsten-based ionic hybrid was synthesized by anion-change of peroxopolyoxometalate (POM) $PW_4O{_{24}}^{3-}$ with dicationic long-chain alkyl imidazolium ionic liquids. The characterization was conducted by FT-IR, TGA, $^1H$-NMR and CHN Elemental analyses. Its catalytic performance was evaluated by the epoxidation of soybean oil with $H_2O_2$ under solvent-free condition, including testing of organic cations influence, catalytic reusability and reaction conditions. The catalyst was proved to be a highly efficient recyclable catalyst for epoxidation of various vegetable oils with $H_2O_2$, showing high $H_2O_2$ utilization efficiency, high catalytic activity, convenient recovery and good reuse ability.

• Bulletin of the Korean Chemical Society
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• v.34 no.12
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• pp.3762-3766
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• 2013

This article examines the modification of surface properties of ultrahigh-molecular-weight polyethylene (UHMWPE) with nanoscale ceramic particles to fabricate an improved composite with butadiene-nitrile rubber (BNR). Adhesion force data showed that ceramic zeolite particles on the surface of UHMWPE modulated the surface state of the polymer and increased its compatibility with BNR. Atomic force microscopy phase images showed that UHMWPE made up the microphase around the zeolite particles and formed the evolving layer with a complex interface. The complex interface resulted in improvements in the mechanical properties of the composite, especially its low-temperature resistance coefficients, thereby improving its performance in low-temperature applications.

• Journal of the Korean Chemical Society
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• v.62 no.1
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• pp.7-13
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• 2018

The potential of zinc fluorides with different molar ratios of Zn/F was applied as a solid catalyst in the simultaneous reaction of transesterification and esterification of crude palm oil (CPO) for biodiesel production. These materials were prepared by the fluorolytic sol-gel technique with different fluorine contents. The resulting samples were investigated using elemental analysis, XRD, FT-IR, TG/DTG, $N_2$ physisorption measurements and SEM. The results exhibited that the presence of fluorine strongly affected the catalytic activity in the biodiesel production. The catalysts with smaller fluorine contents (${\leq}1$) showed the best performance in all of the observed samples, yields from 92.94 to 89.95, 87.38 and 85.21% with increasing fluorine contents, respectively. The yield toward the formation of biodiesel depended on the phase and particle sizes of catalysts, but it was not influenced by surface area, pore size, and volume of the samples. The recovered catalyst showed a gradual decrease in activity over three cycles of same reactions.

• Carbon letters
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• v.28
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• pp.16-23
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• 2018

A novel, unique, and effective method for carbon nanotube (CNT) dispersion by the free arc stimulation is proposed. CNTs are introduced as an aerogel into the air space via the dispersion method and can be utilized as a solution by adding it to solvents. The volume of the original generated CNT aerogel with a high-volume expansion ratio displays a performance two orders of magnitudes better than that of raw CNTs, which is considered a powerful characterization of the dispersion effect. The CNT aerogel, which was observed by scanning electron microscopy also showed a satisfactory dispersion morphology. Its structure and properties were tested before and after dispersion by Raman spectroscopy and great consistency was observed, which proved that the CNTs were undamaged. This approach may greatly promote the large-scale application of CNTs.

• Journal of the Korean Ceramic Society
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• v.45 no.2
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• pp.132-137
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• 2008

The main purpose of this study is enhancing the filtering efficiency, performance and durability of filter by growing SiC whiskers on cordierite honeycomb substrate. The experiment was performed by Chemical Vapor Infiltration (CVI) in order to control pore morphology of substrate. Increasing the mechanical strength of porous substrate is one of important issues. The formation of "networking structure" in the pore of porous substrate increased mechanical strength. The high pressure gas injection to the specimen showed that a little of whiskers were separated from substrate but additional film coating enhanced the stability of whisker at high pressure gas injection. Particle trap test was performed. More nano-particle was trapped by whisker growth at the pore of substrate. Therefore it is expected that the porous cordierite which deposited the SiC whisker will be the promising material for the application as filter trapping the nano-particles.

• Journal of the Korean Ceramic Society
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• v.55 no.2
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• pp.126-134
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• 2018

Using aqueous solution free radical polymerization with glacial acrylic acid (GAA), maleic anhydride (MA) and sodium methallyl disulfonate (SMADS), a novel linear polycarboxylate dispersant was synthesized for ceramics. Dispersant linear structural characterization was done by FTIR, $^1H$ NMR, HPLC and GPC, and the ratio of monomers was determined using an orthogonal experiment. This research is focused on the effects of polymerization temperature, monomer mole ratios and dosage of initiator on ceramic slurry viscosity with linear polycarboxylate dispersant for ceramic dosage rate of 0.30% (based on dry slurry), all of which were investigated by single factor test. The best polymerization conditions for linear GAA-MA-SMADS are when n(AA) : n(MA) : n(SMADS) equals 3.0 : 1.0 : 0.5, the molecular weight of the polymer is 4600 daltons, the initiator sodium persulfate accounts for 7% of the total mass of polymerized monomers, the polymerization temperature is $90^{\circ}C$ and the reaction time is 2 h. The ceramic body slurry viscosity drops from $820mPa{\cdot}s$ to $46mPa{\cdot}s$ when the concentration of the polycarboxylate dispersant is 0.30%.

• 한국생물공학회:학술대회논문집
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• 2005.10a
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• pp.502-506
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• 2005

Three EGCG analogues were synthesized by the acceptor reaction of a glucansucrase from Leuconostoc mesenteroides B-1299CB with EGCG and sucrose. The transfer products was purified using Sephadex LG-20 column chromatography and high performance liquid chromatography (HPLC). EGCG-G1 and EGCG-G2 were novel compounds for the first time reported in this paper. EGCG glycosides showed similar or slower antioxidative effects according to their structures $(EGCG{\geq}EGCG-G1>EGCG-G1'>EGCG-G2)$. However, the water solubilities of the EGCG-G1, EGCG-G1' and EGCG-G2 were 52, 76 and 140 times higher than that of EGCG. Furthermore, they showed more browning resistance against UV irradiation than EGCG.