Convergence Materials & Application Lab

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  Convergence Materials and Devices Lab

  • Professor : Kim, Byoung Suhk Professor
  • Phone : 063.270 2352
  • E-mail : kbsuhk@jbnu.ac.kr
  • Laboratory : technical Building 2, room 112

We aimed at fabricating different composites through various materials for hybrid supercapacitor application. With the intention of simplifying experiment methods, decreasing the cost of the supercapacitors, as well as minimizing the destruction of the environment, the carbon materials (e.g. carbon fiber papers, carbon nanofibers, biomass-derived carbon), conducting polymer (polyaniline), and metal oxides (NiCo2O4) were employed to make electrodes for supercapacitors through facile techniques, such as electrospinning, heat treatment, in-situ polymerization, and hydrothermal method.

light-emitting diodes, and solar cells. Flexibility of a transparent device has been required in accordance with miniaturization and mobilization, optically transparent, high conductivity, and be able to withstand high levels of bending without significant decrease in the electrical performance. In this work, the flexible and transparent conductive nylon nanofiber reinforced cellulose acetate films were prepared by a facile method, including vacuum filtration and mold transferring techniques. The flexible nylon nanofiber-reinforced cellulose acetate thin films were used as a substrate for spin coating of conductive coating using PANi, PEDOT: PSS, Silver Nanowire functionalized noble metals.

We introduce a facile way to improve the performance of NiCo2O4 electrode by introducing a Ni seed layer. The seed layer deposited on Ni foam electrode (NiCo2O4/Ni@NF) shows the higher electrochemical performances, such as superior specific capacity of 1142 C g-1 at a current density of 1 A g-1 with higher cyclic stability of ~96 % even after 5000 cycles at a higher current density of 5 A g-1. These values are higher than that of the electrode (NiCo2O4@NF) without seed layer, which shows the specific capacity of 305 C g-1@1A g-1 and cyclic stability of 84%@1A g-1. The enhanced performance of the NiCo2O4/Ni@NF electrode may be attributed to low interface resistance, fast redox reversible reaction, and improved surface active sites. The asymmetric supercapacitor device is fabricated using the NiCo2O4/Ni@NF electrode as a positive and reduced graphene oxide (rGO)-Fe2O3 nanograin as a negative electrode, and delivers an areal capacitance of 446 mF cm-2 with retention of 82 % after 10000 cycles. The fabricated asymmetric solid state device shows a maximum energy density of 124.3 Wh cm-2 (at a power density of 3.58 kW cm-2) and power density of 14.88 kW cm-2 (at energy density of 31.41 Wh cm-2).

Aerogel is a highly porous, ultralow weight and low denser material derived from gel, which the liquid component of the gel has been substituted with a gas is allows the liquid to be slowly desiccated off without causing the solid matrix in the gel to breakdown from capillary action. Aerogel does not have a chosen material with set chemical formula, but the term is used to collection of all the material with a certain geometric structure. Aerogels can be made up of variety of materials like silica, transition metal oxides, carbon materials (graphene, CNT, etc.), and polymers with tunable 3D hierarchical porous morphology and high surface area for wide range of applications such as solar cells, optical applications and energy storage devices (electrode materials for fuel cells, supercapacitors and batteries).

In our laboratory, particular attention has been given to non-enzymatic biosensor. Biological analytes such as oxalic acid and glucose have been successfully recognized by this procedure. Nanomaterials such as gold nanoparticle along with polypyrrole and rGO have been fabricated with simple approach. And, in present time continuous effort is being put in order to develop a novel material of some better significance. The biosensor has a wide range of application. Not only does it have its importance in medical field, but in various other areas such as environment and food industries it plays a significant role. Biosensor is a very interesting research field and tremendous effort and progress can be seen in the past decade. In addition, the roles of various nanoparticles as an electrocatalyst are also intensively investigated. We have researched on the role nickel phosphate nanoparticle response towards alcohol oxidation. We are continuously working on this particular area and exploring more.

New precursors, poly(acrylonitrile-co-crotonic acid) (poly(AN-CA)) and poly(acrylonitrile-co-itaconic acid-co-crotonic acid) (poly(AN-IA-CA)) copolymers, for the preparation of carbon fibers, were explored in this study. The effects of comonomers with acidic groups, such as crotonic acid (CA) and/or itaconic acid (IA), on the stabilization of nanofibrous polyacrylonitrile (PAN) copolymers were studied. The extent of stabilization, evaluated by Fourier transform infrared spectroscopy, revealed that the CA comonomer could retard/control the stabilization rate of PAN, in contrast to the IA comonomer, which accelerated the stabilization process. Moreover, the synthesized PAN copolymers containing CA possessed higher Mv than those of the IA copolymers and also showed outstanding dimension stability of nanofibers during the stabilization, which may be a useful property for improving the dimensional stability of polymer composites during manufacturing.

Shape memory materials: as one kind of smart materials, SMPs play a crucial role, especially for biomedical devices and robotics. In this study, we introduced a new form of SMP, Sylgard-coated PCL nanofiber filaments. Coating of PCL nanofiber filaments with Sylgard has greatly improved the thermomechanical properties of the as-spun PCL nanofiber filament. Annealing of the Sylgard-coated filaments has a significant role in increasing the crystalline levels of PCL, which resulted in the improvement of the toughness and elongation at break. Data analyzed and discussed in this study give insights for broadening the applications of the Sylgard-coated PCL nanofiber filaments such as aerospace industry, biomedical devices, and smart textiles. pH sensors: Development of an eco-friendly, reversible, and universal pH sensor based on electrospun cellulosenanofiber functionalized with a natural pigment is described in this study. A natural pigment from redcabbage has been extracted and incorporated onto the electrospun non-woven cellulose fibers by meansof adsorption and chemical cross-linking techniques. The results revealed that the developed biocom-posite is a universal pH sensor which is capable of detecting pH values in the range of 1–14 by indicatingthe unique color code against each pH. It was also found that the pH sensing was stable at different tem-peratures and at prolonged time. Moreover, the colors were reversible and the pH sensor was recyclable.Present study opens up new possibilities for using the developed universal pH sensor as a health monitor.

It has well known that a well-defined cage-like polyhedral oligosilsesquioxane (POSS) molecule contains a polyhedral silicon–oxygen nanostructured skeleton with intermittent siloxane chains (general formula: (SiO3/2)n), which was first reported in 1946 and was primarily used for electrical insulation at high temperature. This class of well-defined, highly symmetric molecules usually features a nanoscopic size, approximately 1.5 nm in diameter when the vertex (R = isobutyl, cyclohexyl, cyclopentyl, etc.) groups are included. We have studied a series of amphiphilic poly(ethylene glycol) (PEG)-POSS and poly(vinyl alcohol) (PVA)-POSS hybrids incorporating POSS macromers onto chain-ends or polymer backbone as pendent groups, respectively. The resultant PEG-POSS and PVA-POSS hybrids are amphiphilic and show unique microstructural features having two separate crystalline components, that is, the dual system of semicrystalline polymers (PEG or PVA crystalline phases) and POSS crystalline phases, as confirmed by WAXD and DSC analysis. It show various potential applications, such as associative thickening, drug delivery carriers, surface active materials, functional nanofibers, thermoset additives, Li-ion conductor, etc.

We have studied that swelling of filled polyelectrolyte multilayer microcapsules was indeed pH-controlled. The capsules swollen in high pH solution have much larger size than those immersed in low and neutral-pH solutions. This indicates the softening of the multilayer shells, which is likely due to a decrease in charge density of polycations. The capsules swollen at low pH are of the same size as those immersed in neutral-pH solution, indicating the same number of ionic cross-links and the same value of Young’s modulus. By using a combination of atomic force and confocal microscopy, we explore the deformation properties of multilayer microcapsules filled with a solution of strong polyelectrolyte. Encapsulation of polyelectrolyte was performed by regulation of the multilayer shell permeability in water-acetone solutions. The “filled” capsules prepared by this method were found to be stiffer than “hollow” ones, which reflects the contribution of the excess osmotic pressure to the capsule stiffness. The force-deformation curves contain three distinct regimes of reversible, partially reversible, and irreversible deformations depending on the degree of compression. The analysis of the shape of compressed capsules and of the inner polyelectrolyte special distribution allowed one to relate the deformation regimes to the permeability of the multilayer shells for water and inner polyelectrolyte at different stage of compression.