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- 저자 : Yumin Cheng (검색결과 4 건)
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Yumin Cheng,Huibo Zhang,Shuangkun Zhang,Weiwei Liu,Jing Wang,Run Cheng,SeungKon Ryu,Riguang Jin 한국탄소학회 2013 Carbon Letters Vol.14 No.1
Polyacrylonitrile (PAN) copolymers of different molecular weights were synthesized by a suspension polymerization and precipitation polymerization method. The rheology behaviors of the synthesized PAN copolymers were investigated in relation to their molecular weight, solid content and melting temperature. The influence of "historical effects" on the spinning solution of PAN was studied by analyzing the laws of viscosity considering the diversification time and temperature. The viscosity disciplines of each spinning solution conformed well to the rheological universal laws in a comparison of the suspension polymerization product with that of precipitation polymerization. Viscosity changes in the swelling process of dissolution were gentler in the suspension polymerization product; a small amount of water will quickly debase the solution viscosity, and high-speed mixing can greatly shorten the time required by the spinning solution to reach the final viscosity.
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High Char-Yield in AN-AM Copolymer by Acidic Hydrolysis of Homopolyacrylonitrile
Run Cheng,You Zhou,Jing Wang,Yumin Cheng,Seungkon Ryu,Riguang Jin 한국탄소학회 2013 Carbon Letters Vol.14 No.1
Acrylonitrile (AN)-acrylamide (AM) copolymers were prepared by nitric acidic hydrolysis of homopolyacrylonitrile. The acrylamino group increased as a function of hydrolysis time, while crystallinity decreased. Differential scanning calorimetry and a thermal gravimetric analysis indicated that the acylamino introduced by acidic hydrolysis effectively enhanced the cyclization reaction at low temperature due to the change of the cyclization reaction mechanism. Char-yield of AN-AM copolymers also gradually increased with increasing hydrolysis time. The maximum char-yield was 49.48% when hydrolized at 23°C in 65% nitric acid solution for 18 h, which was 30% higher than that of non-acidic hydrolysis of homopolyacrylonitrile. Simulation of the practical process also showed an increase of char yields, where the char yields were 55.43% and 62.60% for homopolyacrylonitrile and copolyacrylonitrile, respectively, with a hydrolysis time of 13 h.
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Chen, Li,Liew, K.M.,Cheng, Yumin Techno-Press 2010 Interaction and multiscale mechanics Vol.3 No.3
The complex variable reproducing kernel particle method (CVRKPM) and the FEM are coupled in this paper to analyze the two-dimensional potential problems. The coupled method not only conveniently imposes the essential boundary conditions, but also exploits the advantages of the individual methods while avoiding their disadvantages, resulting in improved computational efficiency. A hybrid approximation function is applied to combine the CVRKPM with the FEM. Formulations of the coupled method are presented in detail. Three numerical examples of the two-dimensional potential problems are presented to demonstrate the effectiveness of the new method.
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Shi, Shengbin,Wang, Hang,Chen, Peng,Uddin, Mohammad Afsar,Wang, Yuxi,Tang, Yumin,Guo, Han,Cheng, Xing,Zhang, Shiming,Woo, Han Young,Guo, Xugang The Royal Society of Chemistry 2018 Polymer chemistry Vol.9 No.28
<P>Due to their high-lying lowest unoccupied molecular orbitals (LUMOs), π-conjugated polymers based on benzothiadiazole and its derivatives typically are p-type. We report here the successful development of two narrow bandgap, ambipolar donor-acceptor copolymers, PDCNBT2T and PDCNBSe2T, which are based on new cyano-substituted strong electron acceptors, 4,7-dibromo-5,6-dicyano-2,1,3-benzothiadiazole (DCNBT) and 4,7-dibromo-5,6-dicyano-2,1,3-benzoselenadiazole (DCNBSe), respectively. Compared to their polymer analogues with fluorine substituents, the LUMO was lowered by a big margin of <I>ca.</I> 0.6 eV and the bandgap was reduced by 0.2-0.3 eV for the cyano-substituted polymers. Therefore, the cyano-substituted benzothiadiazole polymers showed very low-lying LUMO levels of <I>ca.</I> 4.3 eV. Benefiting from their narrow bandgaps of 1.1-1.2 eV and appropriately positioned LUMO levels, both polymers exhibit well balanced ambipolar transport characteristics in organic thin-film transistors, which differ from the p-type dominating transport properties of their fluorinated polymer analogues. A balanced hole/electron mobility of 0.59/0.47 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> was achieved for polymer PDCNBT2T, and a reduced hole/electron mobility of 0.018/0.014 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> was observed for the benzoselenadiazole-based PDCNBSe2T due to its lower crystallinity. These results show that the electron mobility can be enhanced by approximately two orders <I>versus</I> the electron mobility of the previously reported 4,7-di(thiophen-2-yl)-5,6-dicyano-2,1,3-benzothiadiazole-based polymer. This improvement was achieved by using the new acceptor units without additional electron-rich thiophene flanks, which allow a higher degree of freedom in selecting the donor co-unit and more effective tuning of energy levels of frontier molecular orbitals.</P>
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