Single-walled carbon nanotube-mediated physical gelation of binary polymer blends: An efficient route to versatile porous carbon electrode materials

Kim, Yukyung,Kim, Saerona,Noh, Seonmyeong,Kim, Semin,Park, Geunsu,Le, Thanh-Hai,Han, Hyunwoo,Kim, Yoong Ahm,Yoon, Hyeonseok Elsevier 2018 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.353 No.-

<P><B>Abstract</B></P> <P>A non-covalent approach to prepare nanotube-containing gels was developed based on the physical gelation of two polymers, polyvinyl alcohol (PVA) and polyacrylonitrile (PAN), with different microphase behaviors in water/dimethyl sulfoxide (DMSO) mixture. Single-walled carbon nanotubes (SWNTs) were incorporated into the binary-polymer/binary-solvent system to alter the physical gelation behavior and, in turn, to achieve unique physicochemical characteristics of the resulting gels. SWNTs were wrapped with PVA, which extended the binary polymer system to a ternary polymer system consisting of PVA bound to SWNTs, free PVA, and PAN. It was observed that the SWNT/PVA/PAN ensembles gelled with appropriate amounts of water in DMSO and the gelation behavior was reversible. The amounts of water and SWNT were determined to be key parameters affecting the formation of the gels. The SWNT/PVA/PAN gels were successfully converted to carbonaceous gels via heat treatment in an inert atmosphere, which can be extended to several applications such as electrode materials. The macroporous carbonaceous gels were further functionalized via manganese deposition followed by potassium hydroxide activation, which yielded excellent cell performance in a neutral electrolyte with the energy density of 9.6–24.8 Wh kg<SUP>−1</SUP> and power density of 8.0–0.1 kW kg<SUP>−1</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effect of co-nonsolvents on the microstructure of the gel was demonstrated. </LI> <LI> The SWNT-mediated physical gelation of binary polymer blends were reported. </LI> <LI> Physically cross-linked gels were converted to versatile electrode materials. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Tunable Electrical-Sensing Performance of Random-Alternating Layered Graphene/Polyaniline Nanoarchitectures

Kim, Min-Sik,Kim, Saerona,Kong, Hye Jeong,Kwon, Oh Seok,Yoon, Hyeonseok American Chemical Society 2016 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.120 No.32

<P>Nanostructured materials feature-a high surface-to volume ratio and small dimensions, which are highly beneficial for sensor applications. In this work, graphite was physically exfoliated by a conducting polymer polyaniline (PANI), which resulted in the formation of random-alternating layered graphene/PANI (G-PANI) nanoarchitectures. Resistometric sensors were assembled using a G-PANI nanoarchitecture film as the transducer electrode to examine the characteristics of the: G-PANI nanoarchitectures in sensor applications. The sensing performance of the electrode depended on the type of dopant employed, and more importantly, the unique geometrical composition of the nanoarchitecture gave rise to anisotropic electrical properties. A series or parallel connection-like configuration of intercalated PANI nanolayers was formed when a voltage was: applied perpendicular,or parallel to the stacked graphene plane. Compared with the parallel connection-like configuration, the series connection-like configuration yielded a far better sensing performance, particularly in terms of sensitivity. For the series connection-like configuration, electrochemical impedance spectroscopy analysis confirmed that the nanoarchitecture film was comprised of numerous resistance circuit elements arranged in a chain.</P>

Controlled Radical Polymerization by Alkali Metal Lewis-Base Hydrogen Atom Transfer Catalyst

Saerona Kim,Gyu Leem 한국고분자학회 2022 한국고분자학회 학술대회 연구논문 초록집 Vol.47 No.1

Size Effect of Conducting Polymer Nanoparticles on Electrode Performance

Saerona Kim,Hyeonseok Yoon 한국고분자학회 2016 한국고분자학회 학술대회 연구논문 초록집 Vol.41 No.2

Single-Walled Carbon Nanotube-in-Binary-Polymer Nanofiber Structures and Their Use as Carbon Precursors for Electrochemical Applications

Kim, Yukyung,Le, Thanh-Hai,Kim, Saerona,Park, Geunsu,Yang, Kap Seung,Yoon, Hyeonseok American Chemical Society 2018 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.122 No.8

<P>Hierarchical structuring of materials in the nanometer regime provides opportunities to achieve extraordinary characteristics of the resulting products. Here, we report unique one-dimensional hierarchical nanostructures consisting of single-walled carbon nanotubes (SWNTs), polyvinyl alcohol (PVA), and polyacrylonitrile (PAN). First, SWNT-in-binary-polymer nanofiber (SbPNF) structures were obtained through the incorporation of PVA-wrapped SWNTs into PAN, followed by the electrospinning of the SWNT/PVA/PAN solution. Importantly, the SbPNFs exhibited an aligned SWNT-in-nanofiber structure and enhanced ordering of the polymer chains. The SbPNFs were successfully converted to carbonized products [SWNT-in-carbon nanofibers (SbCNFs)] with enhanced crystallinity and tunable electrochemical properties. Compared to those of the control samples (no SWNT), the charge-transfer resistance and the surface area of the SbCNFs were two orders of magnitude lower and 11–20% higher, respectively, which resulted in better electrochemical properties. The major factors determining the properties of the SbCNFs included the SWNT content and PVA/PAN microphase behavior. Furthermore, the removal of the PVA phase from the SbPNFs provided another opportunity to control the textural properties of the carbonized products. It was found that meso- and macropores were more developed in the carbonized products (SCNFs). The specific capacitance of the SCNFs increased to a maximum of 577 F g<SUP>–1</SUP>, which was 3.7 times higher than that of the SbCNFs. The SCNF with the best properties was successfully applied to electrochemical capacitors as the electrode material. It is believed that further optimization of the hierarchical nanostructures will impart attractive properties for various applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2018/jpccck.2018.122.issue-8/acs.jpcc.7b12145/production/images/medium/jp-2017-12145m_0013.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp7b12145'>ACS Electronic Supporting Info</A></P>

Cost Stickiness and Financial Analysts’ Information Environment : An Evidence from the Korean Market

Saerona Kim(김새로나),Dong-Hoon Yang(양동훈),Jun Hyeok Choi(최준혁) 한국국제회계학회 2021 국제회계연구 Vol.- No.99

[연구목적] 본 연구에서는 원가하방경직적인 기업에 대한 재무분석가의 예측정확성과 커버리지 감소(Weiss 2010)가 재무분석가의 예측 정보환경에 기인한 것인지 살펴보았다. [연구방법] 본 연구는 Weiss(2010)의 기업 단위 원가하방경직성과 Barron et al.(1998)의 재무분석가의 공적 및 사적정보 정확성 그리고 공적 또는 사적정보 의존도(consensus) 변수를 이용하였다. [연구결과] 첫째, 원가하방경직성이 커질수록 재무분석가의 공적정보와 사적정보가 모두 감소하는 것으로 나타났다. 또한 공적정보와 사적정보 중에서는 사적정보가 더 크게 감소하였다. 두번째로, 원가하방경직적인 기업에서 재무분석가의 사적정보에 대한 의존도가 높아지면 재무분석가의 이익예측오차가 감소하였다. 마지막으로, 원가하방경직적인 기업에 대해 재무분석가는 차기에서 사적정보 활용도를 증가시키는 것으로 나타났다. [연구의 시사점] 원가하방경직성이 공적정보나 사적정보로 구성된 재무분석가의 정보환경에 미치는 영향에 관한 연구는 아직까지 드문 편이라는 면에서 본 연구는 선행연구에 대해 추가적인 기여점이 있다고 보여진다. 본 연구는 원가하방경직성이 재무분석가의 정보중개 활동에 미치는 영향을 보여주었고, 특히 원가하방경직성이 높은 환경에서 사적 정보가 재무분석가의 분석에서 가지는 중요성이 크다는 것을 보였다는 면에서 원가하방경직성에 대한 이해의 폭을 넓히는 데 기여할 수 있으리라 여겨진다. [Purpose] This study investigates whether the decline in the forecast accuracy and coverage for sticky firms (Weiss 2010) is due to the analysts’ information environment such as the decrease in reliance on private information. [Methodology] We used Weiss (2010)’s firm-level cost stickiness and Barron et al. (1998)’s precision of analysts’ public and private information, and the consensus, the degree to which analysts rely on public or private information. [Findings] First, we found that sticky cost behavior decreases both public and private information. Besides, sticky cost behavior decreases private information to a more significant extent than public information. Second, we found that forecast errors are reduced for the sticky firms when analysts increase their reliance on private information. Finally, sticky cost behavior increases analysts’ reliance on private information in the next period. [Implications] We believe that our study contributes to the literature because not many studies have investigated the influence of asymmetric cost structure on the analysts’ information set, private and public information. We believe that this study contributes to the understanding of cost stickiness in that we showed the sticky cost’s impact on the information intermediation activities of individual analysts, especially we confirmed that analysts’ private information plays an important role in improving the accuracy of analysts’ earnings forecast for firms with cost stickiness.

Bicyclic Nitroxyl Mediated Biopolymer Degradation Under Mild Conditions

Saerona Kim,Hyeong Cheol Kang,Shuya Li,Kicheon Yoo,Jae Joon Lee,Gyu Leem 한국고분자학회 2022 한국고분자학회 학술대회 연구논문 초록집 Vol.47 No.1

이익투명성이 재무분석가의 정보환경에 미치는 영향: 이익 예측정확성 및 정보활용도를 중심으로

김새로나 ( Saerona Kim ),유혜영 ( Hae Young Ryu ) 한국회계학회 2018 회계저널 Vol.27 No.1

본 연구는 기업의 이익투명성이 재무분석가의 정보환경에 미치는 영향에 대해 살펴보았다. 구체적으로, 기업의 이익투명성 수준에 따라 재무분석가의 이익 예측정확성 및 정보활용도가 차별적으로 나타나는지 분석하고자 하였다. 2000년부터 2013년까지 코스피 및 코스닥 시장에 상장된 12월 결산법인 중 금융업을 제외한 기업들을 대상으로 검증한 결과, 이익투명성이 낮은 기업일수록 재무분석가의 이익예측오차가 커지는 것으로 나타났다. 이는 이익정보가 기업의 경제적 가치를 보다 잘 설명하지 못할수록 이익정보를 활용한 전문가의 이익예측 정확도가 낮아짐을 의미한다. 한편, 낮은 이익투명성에 따른 재무분석가 예측오차 증가는 대규모기업집단 소속 기업의 경우, 줄어드는 것으로 나타났다. 해당 결과는 대규모기업집단에 소속된 기업의 경우, 경영활동에 대한 적극적 감시 및 감독이 이루어지기 때문에 불투명한 이익정보에 의한 재무분석가 이익예측오차가 보다 줄어듦을 의미한다. 아울러, 낮은 이익투명성은 재무분석가의 전체정보정밀성에 부(-)의 영향을 미치는 것으로 나타났다. 추가분석을 통해 해당 관계의 원인에 대해 살펴본 결과, 이익투명성이 낮을수록 재무분석가의 사적정보 정밀성이 감소하여 전체정보 정밀성이 낮아지는 것을 확인하였다. 본 연구는 재무분석가의 이익예측정확성에 미치는 요인으로 기업의 이익투명성을 고려하여, 이익투명성의 수준에 따른 정보비대칭 변화를 실증적으로 규명하였다는데 그 의의가 있다. This study examines how earnings transparency affect on analysts’ information environment. Specifically, we investigate whether earnings transparency is associated with earnings forecast accuracy and the precision of analysts’ information sets. Prior studies indicate that earnings attributes are important considerations to analysts. One attribute is earnings transparency; Barth et al.(2013) define earnings transparency as the extent to which earnings reveals an entity's underlying economics. Following Barth et al.(2013), we measure earnings transparency as the extent to which earnings and change in earnings co-vary contemporaneously with returns. Our results show that lower earnings transparency is significantly related to greater forecast error. The extent of forecast error is reduced when a firm is affiliated with a large business group. We further examine whether lower transparency causes the analyst information set to be more unreliable. Additional analysis reveals that low earnings transparency leads to decreased precision of private information, thus lowers the total precision of analysts’ information sets. Our study contributes to understand how the accuracy of analysts’ earnings forecasts is affected by earnings attributes. In addition, our results show that the relation between earnings transparency and earnings forecast accuracy is affected by business group affiliation. Overall, our evidence suggests that earnings transparency plays an important role in information environments.

염료감응형 광전기화학전지기반 광촉매를 이용한 리그닌 분해

김새로나(Saerona Kim),강형철(Hyeong Cheol Kang),이재준(Jae-Joon Lee),임규(Gyu Leem) 한국고분자학회 2021 고분자 과학과 기술 Vol.32 No.1

Multi-agent 주행시뮬레이션을 이용한 공격성향 위험운전 이벤트 검지기법 개발

김윤종(KIM, Yunjong),오철(OH, Cheol),최병호(CHOE, Byongho),최새로나(CHOI, Saerona),김기용(KIM, Kiyong) 대한교통학회 2018 大韓交通學會誌 Vol.- No.-

공격운전은 밀착주행과 급감속과 같은 행위로 상대 운전자를 위협하는 고의적인 행동으로 교통사고 발생 가능성이 높은 위험운전이벤트이다. 본 연구에서는 Multi-agent 주행 시뮬레이션 실험을 통해 공격운전 가해자와 피해자의 상호작용을 차량거동형태를 분석하였다. 운전자의 고의적인 공격의지 검지를 위해 주행패턴을 효과적으로 상대 평가할 수 있는 지표(Erratic Driving Index, EDI)를 도출하였다. 기존의 상용차의 디지털운행기록계 자료를 활용한 위험운전 검지기법과 본 연구에서 도출한 EDI를 연계한 공격운전 검지 방법론을 새롭게 개발하였고 활용성을 평가하였다. 공격운전을 억제하고 운전자의 안전운전을 유도하는 운전자 행태 관리를 위해 본 연구의 결과물이 효과적으로 사용될 것으로 기대된다. Intentional aggressive driving (IAD) is defined as a hazardous driving event that the aggressive driver intentionally threatens neighbor drivers with abrupt longitudinal and lateral maneuvering. This study developed a methodology for detecting IAD events based on the analysis of interactions between aggressive driver and normal driver. Three major aggressive events including rear-close following, side-close driving, and sudden deceleration were analyzed to develop the algorithm. Then, driving simulation experiments were conducted using a multi-agent driving simulator to obtain data to be used for the development of the detection algorithm. In order to detect the driver’s intention to attack, a relative evaluation index (Erratic Driving Index, EDI) reflecting the driving pattern was derived. The derived IAD event detection algorithm utilizes both the existing absolute detection method and the relative detection method. It is expected that the proposed methodology can be effectively used for detecting IAD events in support of in-vehicle data recorder technology in practice.