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Shen, Tian-Zi,Hong, Seung-Ho,Guo, Jin-Kun,Song, Jang-Kun Elsevier 2016 Carbon Vol.105 No.-
<P>Electro-optical switching of graphene oxide (GO) liquid crystals is of great interest owing to its potential applications. However, a GO dispersion undergoes vinylogous carboxylic acidic reaction with time, accompanied by a decrease in pH, which deteriorates the electro-optical performance of a GO cell. We find that the vinylogous carboxylic reaction is hindered in high concentration GO dispersions, and also demonstrate that the deteriorating electro-optical performance can be recovered either by re-cleaning or by ionic neutralization treatment. The electro-optical performance is systematically analyzed in terms of the acidity of the neutralizing solvent, GO dispersion, and supernatant liquid. The best performance is obtained in a GO dispersion with a pH-7 supernatant liquid after neutralization by weakly alkaline water. The neutralization process decreases the bulk conductivity, and also improves the surface conductivity on GO. Approximately 56% of newly generated H+ ions reside near the GO surface, and the rest diffuse away into the bulk solvent. These findings may provide better understanding for the electro-optical switching phenomenon and its applicability. (C) 2016 Elsevier Ltd. All rights reserved.</P>
A Kinetic Study of Thermal Degradations of Chitosan/Polycaprolactam Blends
Liao, Shen-Kun,Hung, Chi-Chih,Lim, Ming-Fung The Polymer Society of Korea 2004 Macromolecular Research Vol.12 No.5
We have used FT-IR spectra to explain the effects of hydrogen bonding between chitosan and polycaprolactam (PA6). A dynamic mechanical analysis study suggested that the optimum chitosan and PA6 miscibility under the conditions of this experiment were obtained at a blending ratio of 40:60. We studied the thermal degradation of chitosan blended with PA6 (chitosan/PA6) by thermogravimetric analysis and kinetic analysis (by the Ozawa method). Dry chitosan and PA6 exhibited a single stage of thermal degradation and chitosan/PA6 blends having> 20 wt% PA6 exhibited at least two stages of degradation. In chitosan/PA6 blends, chitosan underwent the first stage of thermal degradation; the second stage proceeded at a temperature lower than that of PA6, because the decomposition product of chitosan accelerated the degradation of PA6. The activation energies of the blends were between 130 and 165 kJ/mol, which are also lower than that of PA6.
Kun Fang,Xu Ye,Yawen Huang,Guanjun Chang,Junxiao Yang,Yueqin Shen 한국고분자학회 2015 Macromolecular Research Vol.23 No.6
Three original conjugated polymers were devised and synthesized via the alternating conjugated polymerization of the electron-donating monomer of the modified benzo[1,2-b:4,5-b']dithiophene (BDT) and electronaccepting monomers of perylene diimide (PDI), dithienyl-perylene diimide (DTPDI) and dithienocoronene diimide (DTCDI), respectively. The synthesized conjugated polymers presented excellent thermal stability (Td >400 oC) as well as broad absorption in visible region and narrow gap of energy level (1.80 to 2.01 eV). Moreover, P(BDT-DTCDI) exhibited strong fluorescence properties ( =736 nm with excitation at 680 nm). According to the theoretical calculations, P(BDT-PDI) and P(BDT-DTPDI) displayed significant polymer backbone torsion (41.44o and 39.64o), and P(BDT-DTCDI) had highly coplanar backbone with negligible angle between BDT and DTCDI. The results indicated that P(BDT-DTCDI) had potential applications in the fields of organic thin-film transistors (OTFTs) and fluorescence materials, and P(BDT-PDI) and P(BDT-DTPDI) could be used as a stable n-type semiconductor for polymer solar cells.
Application of Horizontal Wells to Reduce Water Production during Gel Treatment
Shen, Guang Xi,Lee, Ji Ho,Lee, Kun Sang Trans Tech Publications, Ltd. 2013 Advanced materials research Vol.807 No.-
<P>It is well known that gel treatment has outstanding potential to delay water breakthrough and reduce water production. However, it causes the decrease of oil production by permeability reduction, even though it is not as much as reduction of water production. For this reason, to improve oil production with substantial reduction of water production, performances of gel treatments through the combination of horizontal and/or vertical wells were assessed and compared. An extensive numerical simulation was executed for four different well configurations under gel treatment associated with waterflood to accomplish the purpose of this study. Performances were compared according to cumulative oil recovery and water-oil ratio at the production well for different systems. Though all of well configurations considered in this study effectively decreased the water production compared with waterflood, applications of horizontal wells led to much higher oil recovery than vertical well because of improved sweep efficiency. Based on these results, the potential of horizontal wells was examined through different scenarios in combinations of injection and production wells. Furthermore, various well lengths of injectors or producers were assessed for horizontal wells. Because cross-flow between layers dominates performance of gel treatment, effects of vertical permeability were also investigated in application of gel treatment with horizontal well. Longer wells and higher cross-flow results in better performance. This study represents that effectiveness of horizontal wells for gel treatment even for reservoirs having dominant cross-flow.</P>
Electro-optical switching of graphene oxide liquid crystals with an extremely large Kerr coefficient
Shen, Tian-Zi,Hong, Seung-Ho,Song, Jang-Kun Nature Publishing Group, a division of Macmillan P 2014 NATURE MATERIALS Vol.13 No.4
The sensitive response of the nematic graphene oxide (GO) phase to external stimuli makes this phase attractive for extending the applicability of GO and reduced GO to solution processes and electro-optic devices. However, contrary to expectations, the alignment of nematic GO has been difficult to control through the application of electric fields or surface treatments. Here, we show that when interflake interactions are sufficiently weak, both the degree of microscopic ordering and the direction of macroscopic alignment of GO liquid crystals (LCs) can be readily controlled by applying low electric fields. We also show that the large polarizability anisotropy of GO and Onsager excluded-volume effect cooperatively give rise to Kerr coefficients that are about three orders of magnitude larger than the maximum value obtained so far in molecular LCs. The extremely large Kerr coefficient allowed us to fabricate electro-optic devices with macroscopic electrodes, as well as well-aligned, defect-free GO over wide areas.
Nutritional Effects and Antimicrobial Activity of Kefir (Grains)
Shen, Ying,Kim, Dong-Hyeon,Chon, Jung-Whan,Kim, Hyunsook,Song, Kwang-Young,Seo, Kun-Ho Korean Society of Dairy Science and Biotechnology 2018 Journal of Dairy Science and Biotechnology (JMSB) Vol.36 No.1
Kefir exhibits antimicrobial activity in vitro against gram-positive and gram negative bacteria, as well as some fungi. The ability of LAB to inhibit the growth of closely related bacteria is well known. This inhibition of pathogenic and spoilage microbes may be due to the production of organic acids, hydrogen peroxide, acetaldehyde, diacetyl, carbon dioxide, or bacteriocins. Lactobacilli are the major contributors to acid production and, hence, a determining factor in the flavor development in kefir. Lactic acid, proteolytic activity, and acetaldehyde are the essential flavor compounds in kefir. Both acid and bacteriocins contribute to the antimicrobial activity of kefir and kefir grains. Kefir is rich in proteins, calcium, vitamin $B_{12}$, niacin, and folic acid. Many studies have investigated the benefits of consuming kefir and have shown that it is a natural probiotic, which when consumed regularly, can help relieve intestinal disorders, promote bowel movement, reduce flatulence, and improve the overall health of the digestive system. Tibetan kefir, which is different from traditional kefir, is produced in China. It has been reported to exhibit antimicrobial activity that is nearly identical to that of traditional kefir. Kefir production is considered a rapidly growing food industry in China.