Papers by Author: Seok Ho Yoon

Abstract: Electrorheological (ER) particles were obtained by the adsorption of multiwalled carbon nanotubes (MWCNT) on the surface of silk fibroin microspheres. The resulting spherical polymeric microspheres consist of a silk fibroin core and an MWCNT shell, which is electrically conducting. The silk fibroin microspheres were prepared by the phase separation of the silk fibroin and poly(ethylene oxide) (PEO) blend solution, and the MWCNT dispersion was prepared by ultrasonication with cetyltrimethylammonium bromide (CTAB) surfactant. The ER particles were prepared using a simple process involving the blending of the silk fibroin microsphere suspension and aqueous MWCNT dispersion. The morphology of the ER particles was examined by field emission scanning electron microscopy (FESEM) and their electrical conductivity measured by the four-probe method was 4.8×10-4 S/cm. The prepared composite microspheres suspended in silicone oil showed typical ER characteristics, including the formation of a chain-like structure under an applied electric field (1.9 kV/mm). This phenomenon can be explained by the interfacial polarizability of the MWCNTs adsorbed on the surface of the polymeric microspheres.

Abstract: A simple and mass producible method was developed to incorporate multiwalled carbon nanotubes (MWCNTs) into electrospun silk fibroin (Bombyx mori) nanofibers. The process consists of dispersing the acid-treated MWCNTs in an aqueous silk fibroin solution, and blending this solution with a water-soluble polymer, poly(ethylene oxide) (PEO), followed by electrospinning of the composite solution. The morphology and microstructure of the electrospun nanofibers were characterized using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The FESEM and TEM images show that the MWCNTs are embedded along the nanofibers. Aqueous-based electrospinning of silk/PEO/MWCNTs composites provides potentially useful options for the fabrication of biomaterial scaffolds, e.g. wound dressings, based on this unique fibrous protein.

Abstract: Surface-conductive microspheres consisting of poly(methyl methacrylate) (PMMA) (6.5 μm) core and carbon nanotubes (CNTs)-adsorbed shell were prepared using a simple process involving the blending of two colloidal solution; an aqueous CNT dispersion with surfactants and an aqueous PMMA microsphere colloid. These were adopted as the suspended particles for electrorheological (ER) fluids, in which the electrical conductivity originated primarily from the surface-coated conducting CNT layers. The CNT-adsorbed polymeric microspheres were monodisperse and spherical in shape. The CNT-PMMA composite suspensions in silicone oil showed the typical ER characteristics of forming a chain-like structure under an applied electric field. The CNT-PMMA composite microspheres exhibited a conductivity ranging from 5.2×10-4 to 6.3×10-5 S/cm, which is an acceptable conductivity range for ER fluids. This phenomenon can be explained by the interfacial polarizability of CNTs adsorbed on the surface of the polymeric microspheres.