Effects of additives on the mechanical and thermal properties of epoxy-based nanocomposites produced using sonication

YoonKook Park,Chun-Hyung Cho 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.6

Epoxy nanocomposites were synthesized in the presence of hydroxyapatite with the aid of an ultrasonicator. In general, as the amount of hydroxyapatite increased from 0wt% to 10wt%, the mechanical properties of the hydroxyapatite-containing nanocomposite were enhanced. The mechanical properties of the nanocomposite were significantly enhanced by the simple addition of 10 wt% of hydroxyapatite. Specifically, the storage modulus of the 10 wt% hydroxyapatite-containing nanocompsote was 3.2GPa, which is 46% higher compared to that of the pristine epoxy nanocomposite. The glass transition temperature of hydroxyapatite-containing nanocomposites generally decreased by few degrees in Celsius. To investigate the effect of additives on the mechanical properties of the epoxy-based nanocomposite, nanocomposites were synthesized using both montmorillonite and tellurium dioxide instead of hydroxyapatite. Intrestingly, both additive-based nanocomposite materials resulted in an increase in the storage modulus while the glass transition temperature decreased. These results demonstrate that the addition of few wt% of all three additives (hydroxyapatite, montmorillonite, and tellurium dioxide) can enhance the mechanical properties of epoxy-based nanocomposites.

Effects of pH, salt type, and ionic strength on the second virial coefficients of aqueous bovine serum albumin solutions

YoonKook Park,최진규 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.1

The osmotic pressures of aqueous bovine serum albumin (BSA) solutions were measured at different pH (3.6, 4.6, 5.6, and 7.6) in combination with different concentrations (0.01M, 0.1M, 1M, and 3M) of salts (sodium, pottasium, and lithum) by using a Wescor colloid membrane osmometer. The osmotic second virial coefficients for BSA were determined from the experimental osmotic pressure. Predominant forces between protein molecules were measured at the various pH, ionic strength, and type of salt. These experimental data were utilized to determine the depth of square-well potential, which accounts for specific interactions between protein molecules at various conditions.

Measurement and correlation of vapor-liquid equilibria for a binary system containing 1-butyl-3-methylimidazolium tridecafluorohexylsulfonate and carbon dioxide

YoonKook Park,Soon Kang Hong 한국화학공학회 2016 Korean Journal of Chemical Engineering Vol.33 No.1

Using a high-pressure variable-volume view cell, the vapor-liquid equilibria of the binary system CO2 and 1-butyl-3-methylimidazolium tridecafluorohexylsulfonate ([BMIM][TDfO]) were determined. The CO2 mole fraction ranged from 0.104 to 0.952 over a temperature range of 298.2-323.2 K. Both the Peng-Robinson and Soave-Redlich- Kwong equations of state were applied with two different mixing rules to correlate with the experimentally obtained results. Increasing the alkyl chain length in perfluorinated sulfonate anion mother structure from methyl to hexyl markedly increased the CO2 solubility. To investigate the effect of the number of fluorine atoms in the anion on the phase behavior of imidazolium-based ionic liquid, these experimental results were then compared with those reported in previous experimental studies of 1-alkyl-3-methylimidazolium cations-including ionic liquid+CO2 binary system.

공학교육인증에서 교과목 학습성과와 프로그램 학습성과의 관계 - 실질적인 프로그램 학습성과 평가를 지향하며

박윤국(YoonKook Park) 한국공학교육학회 2010 공학교육연구 Vol.13 No.4

공학인증의 여러 인증 요건들 중의 하나인 프로그램 학습성과에 대한 평가와 분석등은 평가도구 개발이라는 관점에서만 보더라도 지속적인 연구가 필요한 분야이다. 본 연구에서는 본 프로그램 학습성과 평가체제에서 제시한 절차대로 졸업시험, 에세 이, 종합설계, 그리고 공인 영어점수를 평가도구로 활용한 프로그램 학습성과 평가결과와 교과목 학습성과를 이용한 프로그램 학습성과 결과를 비교하였다. 4가지 평가도구를 활용한 프로그램 학습성과 평가는 2010년 심화과정 졸업자 15명을 대상으로 하였고, 교과목 학습성과를 이용한 프로그램 학습성과는 2009년 1학기와 2학기에 개설하여 운영한 교과목을 이용하였다. 두가지 평가결과 모든 학습성과 평가에서 큰 차이를 보이지 않는 것으로 보아 교과목 학습성과를 이용한 프로그램 학습성과도 프로그램에서 활용할 수 있는 실질적인 프로그램 학습성과 평가방법 중 하나임을 알 수 있었다. It is strongly desirable to continuously study the program outcomes that are one of the requirements of engineering accreditation. In this paper, the results of program outcome evaluation obtained by using four tools - exit written exams, essay tests, capstone design, and an official English test - were compared to those of program outcome evaluation obtained by a course-embedded assessment method. The former evaluation was carried out for 15 students who graduated in February 2010 by using the four evaluation tools, while the latter was performed by using a course offered in the Spring and Fall semesters in 2009. Two evaluation results revealed no large difference in almost all 12 program outcomes, which indicates that course-embedded assessment would be one of the practical and effective program outcome evaluation tools.

Exploring the correlation between MoS₂ nanosheets and 3D graphene-based nanostructures for reversible lithium storage

Son, Yoonkook,Lee, Jung-Soo,Choi, Min,Son, Yeonguk,Park, Noejung,Ko, Minseong,Jang, Ji-Hyun,Park, Minjoon Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.459 No.-

<P><B>Abstract</B></P> <P>Graphene-based materials are an attractive lithium storage material for next-generation lithium-based batteries due to its high capacity, surface area and conductivity. However, one of the major problems for its broad application in batteries is a large irreversible capacity, and the poor cycle stability and low rate capability remain. Here, we report a MoS<SUB>2</SUB>-stabilized hierarchical three-dimensional graphene-based nanostructure, in which the MoS<SUB>2</SUB> layer acts as a stabilizer as well as an active material. We show that the presence of MoS<SUB>2</SUB> thin layer adjacent to the graphene surface can improve lithium storage capability by improving lithium ion diffusion property with fast Li-ion transport kinetic. On the basis of experimental and theoretical approaches, we ascribe the improved reversible lithium storage to the unusual reversible Li-MoS<SUB>2</SUB> redox reaction and charge distribution on the graphene and MoS<SUB>2</SUB> interlayers. These findings will provide a potential new direction in the design of electrode materials for advanced lithium storage technologies.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The development of MoS<SUB>2</SUB> nanosheet-assisted hierarchical 3D-graphene nanostructure. </LI> <LI> The study of mechanism for the improved Li ion transport capability on MoS<SUB>2</SUB> and graphene interlayer. </LI> <LI> The improvement of lithium-storage capability by Li ion diffusion with fast Li-ion transport kinetic. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>MoS<SUB>2</SUB> nanosheet-assisted hierarchical 3D graphene nanostructure was developed to improve Li adsorption property, in which MoS<SUB>2</SUB> layer went through the reversible Li redox reaction. We show that the presence of MoS<SUB>2</SUB> on 3D graphene surface can significantly improve lithium storage capability by improving Li ion diffusion property with fast Li-ion transport kinetic.</P> <P>[DISPLAY OMISSION]</P>

교과목 성취도에 근거한 학습성과의 평가 - 시험과 보고서를 위주로

박윤국(YoonKook Park) 한국공학교육학회 2006 공학교육연구 Vol.9 No.3

Although it has taken some time to apply the accreditation system in Korea , most programs have a very difficult time in assessing program outcomes , one of the most important standards in accreditation . The major purpose of this work is to suggest a method , so called course embedded assessment , by which to assess a course that includes several program outcomes . The course was evaluated based on student performance on each exam taken in the course as well as a report submitted by the students . The course embedded assessment provides not only an effective tool by which to assess course - set program outcomes , but also allow the instructor to follow up and / or modify the course material to be offered in next semester . 공학인증을 시행한 지 적지 않은 시간이 흘렀음에도 인증에 가장 중요한 요소들 중의 하나인 학습성 과의 평가에 대한 평가도구 개발은 대부분의 프로그램들이 가지는 어려움들 중의 하나이다. 본 연구에 서는 이의 한 방편으로 교과목과 학습성과의 연관성에 근거하여 해당 교과목이 어떤 학습성과를 성취할 수 있는지의 여부를 정한 후, 한 학기동안 해당 교과목을 수강한 학생들이 치룬 시험과 제출한 보고서를 근거로 하여 학습성과를 정량적으로 평가하는 방법을 보여준다. 또한 학기말에 해당 교과목 담당교수가 작성하여야 할 CQI보고서의 작성 예를 통하여 이에 대한 즉각적이고 효과적인 학습성과의 방법에 관하여 고찰하였다.

Hollow Silicon Nanostructures via the Kirkendall Effect

Son, Yoonkook,Son, Yeonguk,Choi, Min,Ko, Minseong,Chae, Sujong,Park, Noejung,Cho, Jaephil American Chemical Society 2015 NANO LETTERS Vol.15 No.10

<P>The Kirkendall effect is a simple, novel phenomenon that may be applied for the synthesis of hollow nanostructures with designed pore structures and chemical composition. We demonstrate the use of the Kirkendall effect for silicon (Si) and germanium (Ge) nanowires (NWs) and nanoparticles (NPs) via introduction of nanoscale surface layers of SiO<SUB>2</SUB> and GeO<SUB>2</SUB>, respectively. Depending on the reaction time, Si and Ge atoms gradually diffuse outward through the oxide layers, with pore formation in the nanostructural cores. Through the Kirkendall effect, NWs and NPs were transformed into nanotubes (NTs) and hollow NPs, respectively. The mechanism of the Kirkendall effect was studied via quantum molecular dynamics calculations. The hollow products demonstrated better electrochemical performance than their solid counterparts because the pores developed in the nanostructures resulted in lower external pressures during lithiation.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-10/acs.nanolett.5b02842/production/images/medium/nl-2015-02842p_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5b02842'>ACS Electronic Supporting Info</A></P>

Recent Advances in Lithium Sulfide Cathode Materials and Their Use in Lithium Sulfur Batteries

Son, Yoonkook,Lee, Jung-Soo,Son, Yeonguk,Jang, Ji-Hyun,Cho, Jaephil Wiley Blackwell (John Wiley Sons) 2015 Advanced energy materials Vol.5 No.16

Inverse giant magnetoresistance in CoFe/Tb multilayer with perpendicular magnetic anisotropy

Son, Yoonkook,Lee, Seungkyo,Lee, Kisu,Cho, B. K. American Institute of Physics 2011 JOURNAL OF APPLIED PHYSICS - Vol.109 No.7

Quantum Confinement and Its Related Effects on the Critical Size of GeO₂ Nanoparticles Anodes for Lithium Batteries

Son, Yoonkook,Park, Mihee,Son, Yeonguk,Lee, Jung-Soo,Jang, Ji-Hyun,Kim, Youngsik,Cho, Jaephil American Chemical Society 2014 NANO LETTERS Vol.14 No.2

<P>This work has been performed to determine the critical size of the GeO<SUB>2</SUB> nanoparticle for lithium battery anode applications and identify its quantum confinement and its related effects on the electrochemical performance. GeO<SUB>2</SUB> nanoparticles with different sizes of ∼2, ∼6, ∼10, and ∼35 nm were prepared by adjusting the reaction rate, controlling the reaction temperature and reactant concentration, and using different solvents. Among the different sizes of the GeO<SUB>2</SUB> nanoparticles, the ∼6 nm sized GeO<SUB>2</SUB> showed the best electrochemical performance. Unexpectedly smaller particles of the ∼2 nm sized GeO<SUB>2</SUB> showed the inferior electrochemical performances compared to those of the ∼6 nm sized one. This was due to the low electrical conductivity of the ∼2 nm sized GeO<SUB>2</SUB> caused by its quantum confinement effect, which is also related to the increase in the charge transfer resistance. Those characteristics of the smaller nanoparticles led to poor electrochemical performances, and their relationships were discussed.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2014/nalefd.2014.14.issue-2/nl404466v/production/images/medium/nl-2013-04466v_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl404466v'>ACS Electronic Supporting Info</A></P>