Yong-Mun Choi

Enhancement of the crosslink density, glass transition temperature, and strength of epoxy resin by using functionalized graphene oxide co-curing agents

We synthesized diamine-functionalized graphene oxide, DDS–GO and HMDA–GO, by introducing 4,4′-diaminodiphenyl sulfone (DDS) or hexamethylenediamine (HMDA) into the carboxylic acid groups on graphene oxide (GO) via amide bonds. The introduction of diamines was confirmed by analytical methods such as FT-IR, TG-DTA, XPS, AFM, and optical microscopy. Then, we applied DDS–GO and HMDA–GO as co-curing agents for epoxy (EP) nanocomposites that were prepared by mixing bisphenol-A type EP and DDS curing agent (ca. 21 wt%). Interestingly, when 1.0 wt% of DDS–GO was added to the EP/DDS mixture, the crosslink density (CD) increased from 0.028 to 0.069 mol cm−3. Due to the higher CD, both the glass transition temperature and tensile strength of the EP/DDS/DDS–GO nanocomposite effectively improved from 160.7 °C to 183.4 °C and from 87.4 MPa to 110.3 MPa, respectively.

Defect healing of reduced graphene oxide via intramolecular cross-dehydrogenative coupling

A chemical defect healing of reduced graphene oxide (RGO) was carried out via intramolecular cross-dehydrogenative coupling (ICDC) with FeCl3 at room temperature. The Raman intensity ratio of the G-band to the D-band, the IG/ID ratio, of the RGO was increased from 0.77 to 1.64 after the ICDC reaction. From XPS measurements, the AC=C/AC-C ratio, where the peak intensities from the C=C and C-C bonds are abbreviated as AC=C and AC-C, of the RGO was increased from 2.88 to 3.79. These results demonstrate that the relative amount of sp(2)-hybridized carbon atoms is increased by the ICDC reaction. It is of great interest that after the ICDC reaction the electrical conductivity of the RGO was improved to 71 S cm(-1), which is 14 times higher than that of as-prepared RGO (5 S cm(-1)).

Chemical method for improving both the electrical conductivity and mechanical properties of carbon nanotube yarn via intramolecular cross-dehydrogenative coupling.

Chemical post-treatment of the carbon nanotube fiber (CNTF) was carried out via intramolecular cross-dehydrogenative coupling (ICDC) with FeCl3 at room temperature. The Raman intensity ratio of the G band to the D band (IG/ID ratio) of CNT fiber increased from 2.3 to 4.6 after ICDC reaction. From the XPS measurements, the AC═C/AC-C ratio of the CNT fiber increased from 3.6 to 4.8. It is of keen interest that both the electrical conductivity and tensile strength of CNT yarn improved to 3.5 × 10(3) S/cm and 420 MPa, which is 180 and 200% higher than that of neat CNT yarn.

Preparation of porous carbon materials by using coagulated polyamic acid precursor

Abstract

Liquid Crystallinity of p-Aramid/Multi-walled Carbon Nanotube Composites

A systematic study regarding the liquid crystallinity of p-Aramid and MWCNTs composite at various p-Aramid and MWCNTs concentrations in sulphuric acid was investigated and optimized by solution viscosity measurement and opalescence observation. We observed a merged liquid crystalline phase consisting of both p-Aramid and MWCNTs, and we believe this is the first study to report this combined liquid crystalline phase in one suspension. In addition to providing fundamental insights, we envision this study could be useful to those developing a strong, light, and high-performance polymeric composite fibers.

Advances in liquid crystalline nano-carbon materials: preparation of nano-carbon based lyotropic liquid crystal and their fabrication of nano-carbon fibers with liquid crystalline spinning

This review presents current progress in the preparation methods of liquid crystalline nanocarbon materials and the liquid crystalline spinning method for producing nano-carbon fibers. In particular, we focus on the fabrication of liquid crystalline carbon nanotubes by spinning from superacids, and the continuous production of macroscopic fiber from liquid crystalline graphene oxide.