Papers by Author: Jae Rock Lee

Abstract: In this work, the thermal and mechanical interfacial properties of diglycidylether of bisphenol A (DGEBA)/polyurethane modified epoxy (UME-305) blends were investigated. 4,4’-Diaminodiphenyl methane (DDM) was used as a curing agent, and the content of UME-305 in the mixture was 0, 20, 40, 60, 80, and 100 wt%. The cure behaviors of DGEBA/UME-305 blends were studied by DSC. The mechanical interfacial properties were confirmed by critical stress intensity factor (KIC) at 77K and 298K. As a result, the exothermic peaks in DSC results were shifted to higher temperature region as increasing the UME-305 content in the blends. The KIC was also enhanced with increasing the UME-305 content and showing a maximum value at 60 wt.% UME-305.

Abstract: The environmental-compatible epoxy resins/clay nanocomposites were prepared by using epoxidized castor oil (ECO) and two ion-exchanged clays. The glass transition temperature (Tg) and mechanical interfacial properties of ECO/clay nanocomposites were investigated. As a result, the nanocomposites showed higher Tg than that of neat ECO. The mechanical interfacial properties of both the nanocomposites were significantly increased on increasing the clay content.

Abstract: In this work, effects of the oxygen plasma on surface characteristics of carbon fibers were investigated in impact strengths of the carbon fibers-reinforced composites. The surface properties of the carbon fibers were determined by acid-base values, FT-IR, and X-ray photoelectron spectroscopy (XPS). Also, the mechanical properties of the composites were studied in impact strength measurements. As experimental results, the O1S/C1S ratio of the carbon fiber surfaces treated by oxygen plasma was increased compared to that of untreated ones, possibly due to development of oxygen-containing functional groups. The mechanical properties of the composites, including impact strength had been improved in the oxygen plasma on fibers. These results indicate that the oxygen plasma can lead to an increase in the adhesion between fibers and matrix in a composite system.

Abstract: In this work, the polymeric electrolyte composites (PECs) based on poly(ethylene oxide) (PEO), ethylene carbonate (EC) as a plasticizer, and lithium montmorillonite (Li-MMT) clay were fabricated, and investigated for understanding the effects of Li-MMT/EC in the polymer matrix on the ionic conductivity. For a lithium battery application, the native sodium cations in MMT were exchanged for lithium cations. As a result, the lithium ion was intercalated into the layer of the MMT clay, and thus PEO entered the galleries of MMT clay. The ionic conductivity was enhanced with increasing MMT contents due to the immobile MMT clay serving as the anion species and the decreased crystallinity of PEO.