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Partially Oxidized Asphaltene as a Bitumen Viscosity Reducer
Choi, Seonung,Choi, Siyoung Q.,Kim, Jong-Duk,Nho, Nam-sun American Chemical Society 2017 ENERGY AND FUELS Vol.31 No.9
<P>Heavy oil/bitumen with asphaltene requires high energy consumption for transportation, because of its high viscosity. This often causes serious pipeline problems; therefore, it is necessary to reduce the viscosity to resolve these issues. In this paper, we propose a new simple method to reduce the viscosity of diluted bitumen using partially oxidized asphaltene without removing asphaltene. This partially oxidized asphaltene, modified by exposing asphaltene to ozone, has a strong affinity to nonoxidized asphaltene via pi-pi stacking, hydrogen bonding, and acid-base interaction. The added oxidized asphaltene thus facilitated the agglomeration of asphaltene, so that the hydrophilic part can be hidden, and a small amount (1250 ppm) decreased the viscosity of diluted bitumen by up to 45%. We investigated the change in rheological properties of the diluted bitumen for various oxidized fractions of asphaltene and for various fractions of oxidized asphaltene to asphaltene. We showed that the decreased shear viscosity is likely to originate with the increased particle size of the asphaltene, that is, not the change in interactions between the asphaltene particles, but rather from their nonuniform distribution in size.</P>
Choi, Joonhyeong,Kim, Wansun,Kim, Donguk,Kim, Seonha,Chae, Junsu,Choi, Siyoung Q.,Kim, Felix Sunjoo,Kim, Taek-Soo,Kim, Bumjoon J. American Chemical Society 2019 Chemistry of materials Vol.31 No.9
<P>Mechanical properties of conducting polymers are an essential consideration in the design of flexible and stretchable electronics, but the guidelines for the material design having both high mechanical and electrical properties remain limited. Here we provide an important guideline for the design of mechanically robust, electroactive polymer thin films in terms of the molecular weight of the polymers. These studies based on a highly efficient, representative n-type conjugated polymer (P(NDI2OD-T2)) revealed a marked enhancement in mechanical properties across a narrow molecular weight range, highlighting the existence of a critical molecular weight that can be exploited to engineer films that balance processability and mechanical and electronic properties. We found the thin films formed from high molecular weight polymers (i.e., number-average molecular weight (<I>M</I><SUB>n</SUB>) ∼ 163 kg mol<SUP>-1</SUP>) to exhibit superior mechanical compliance and robustness, with a 114-fold enhanced strain at fracture and a 2820-fold enhanced toughness, as compared to those of low molecular weight polymer films (<I>M</I><SUB>n</SUB> = 15 kg mol<SUP>-1</SUP>). In particular, we observed a jump in the mechanical properties between the <I>M</I><SUB>n</SUB> = 48 and 103 kg mol<SUP><B>-</B>1</SUP>, yielding a 26-fold enhanced strain at fracture and a 160-fold enhanced toughness. The significant improvement of tensile properties indicates the presence of a critical molecular weight at which entangled polymer networks start to form, as supported by the analysis of the thermal and crystalline properties, specific viscosity, and microstructure. Our work provides useful guidelines for the design of conjugated polymers with recommendations for the best combinations of mechanical robustness and electrical performance for flexible and stretchable electronics.</P> [FIG OMISSION]</BR>
Influence of Molecular Coherence on Surface Viscosity
Choi, Siyoung Q.,Kim, Kyuhan,Fellows, Colin M.,Cao, Kathleen D.,Lin, Binhua,Lee, Ka Yee C.,Squires, Todd M.,Zasadzinski, Joseph A. American Chemical Society 2014 Langmuir Vol.30 No.29
<P/><P>Adding small fractions of cholesterol decreases the interfacial viscosity of dipalmitoylphosphatidylcholine (DPPC) monolayers by an order of magnitude per wt %. Grazing incidence X-ray diffraction shows that cholesterol at these small fractions does not mix ideally with DPPC but rather induces nanophase separated structures of an ordered, primarily DPPC phase bordered by a line-active, disordered, mixed DPPC-cholesterol phase. We propose that the free area in the classic Cohen and Turnbull model of viscosity is inversely proportional to the number of molecules in the coherence area, or product of the two coherence lengths. Cholesterol significantly reduces the coherence area of the crystals as well as the interfacial viscosity. Using this free area collapses the surface viscosity data for all surface pressures and cholesterol fractions to a universal logarithmic relation. The extent of molecular coherence appears to be a fundamental factor in determining surface viscosity in ordered monolayers.</P>
Siyoung Choi,Hyunsung Park,Taewon Hwang IEEE 2014 IEEE Transactions on Vehicular Technology VT Vol.63 No.1
<P>In this paper, the optimal beamforming and power allocation strategy for the secondary transmitter based on the sensing result on the state of the primary user in a multiantenna cognitive radio (CR) network is proposed. Unlike the existing sensing-based spectrum sharing, where the secondary transmitter employs a single antenna and adjusts only its transmit power, in the proposed scheme, the secondary transmitter employs multiple transmit antennas and adjusts the beamforming vector as well as the transmit power. An iterative algorithm that can efficiently obtain the optimal beamforming vector and power allocation is developed. Simulation results show that the proposed scheme achieves a significant rate gain over the existing sensing-based spectrum sharing schemes.</P>
유량-유달부하량 관계식을 이용한 용전천 및 단장천의 수질특성 평가
최시영 ( Siyoung Choi ),이남주 ( Namjoo Lee ),임수빈 ( Soobin Yim ) 한국수처리학회 2021 한국수처리학회지 Vol.29 No.6
This study was conducted to identify the runoff characteristics of Yongjeon and Danjang streams, tributaries of Nakdong river basin, through analyzing the flow rate-delivery pollution loading curves and the correlation of water quality factors. The flow rate-delivery pollutant concentration curve analysis exhibited that the water concentration of pollutants increased as the flow rate increased, but it was difficult to derive a correlation formula that could accurately predict changes in water concentration. In the flow rate-delivery pollution loading equation analysis for Yongjeon stream, the flow coefficient of TOC and T-N items were found to have 1.396 and 1.304, respectively, and the flow coefficient of T-P showed a high correlation of 1.606 and the determination coefficient (R<sup>2</sup>) of the relational expression was mostly 0.93 or higher. In the case of Danjang stream, TOC, T-N, and T-P items showed flow coefficient values of 1.347, 1.232, and 1.301, respectively, and the determination coefficient (R<sup>2</sup>) of the relational expression was higher than 0.95. These results suggest that Yongjeon and Danjang streams are watersheds with runoff characteristics that increase the organic and nutrient loadings as the flow rate increases. In Yongjeon stream, the flow rate (Q) correlated turbidity with high positive (+) and relatively high positive (+) correlation with TOC, T-N and NO<sub>3</sub>-N items (p<0.01). For Danjang stream, the flow rate (Q) revealed a relatively high positive (+) correlation with turbidity, TOC and T-P items (p<0.01), and negative (-) correlation with EC (p<0.01).