Jung Hyeun Kim

Application of content optimized ZnS-ZnO-CuS-CdS heterostructured photocatalyst for solar water splitting and organic dye decomposition

Heterostructured ZnS-ZnO-CuS-CdS photocatalyst was synthesized via a sequential fabrication approach (ZnS→thermal treatment (ZnS-ZnO)→CuS formation (ZnS-ZnO-CuS)→CdS addition (ZnS-ZnO-CuS-CdS)). Each component in this heterostructure has its own role for photocatalytic reaction. The oxide content controlled by thermal processing condition is a crucial factor for improving photocatalytic activity, and the CuS and CdS contents are controlled by their feedstocks. The effects of heterostructure composition on the solar water splitting and organic dye decomposition were investigated under 1 sun irradiation (100 mW/cm2, AM 1.5G filter). The content optimized ZnS-ZnO-CuS-CdS photocatalyst produces 2452.7 μmol g−1 h−1 hydrogen, and it decomposes methyl blue much faster than the other cases. Thus, heterostructured photocatalysts can benefit the use of electrons and holes for improved photocatalytic activity.

Effect of high molecular weight isocyanate contents on manufacturing polyurethane foams for improved sound absorption coefficient

Noises generated in automobile compartments can be controlled by utilizing sound absorption and insulation materials such as polyurethane foams. Polyurethane foams are synthesized by varying polymeric methylene diphenyl diisocyanate (MDI) content for exploring the effect of high functional isocyanate on cellular and acoustic properties. The use of polymeric MDI affects polyurethane matrix modulus and drainage flow rate of the foams, and it also has strong effects on cell structure and air flow resistance (AFR). The highest sound absorption coefficient is achieved at the optimum amount of the polymeric MDI. Therefore, the optimum amount of polymeric MDI content is recommended to achieve not only high sound absorption coefficient but also high transmission loss from the polyurethane foams.

Effects of composition and layer thickness of a butyl acrylate/acrylic acid copolymer on the adhesion properties

Acrylic pressure-sensitive adhesives are synthesized by solution copolymerization using n-butyl acrylate and acrylic acid (AA) in ethyl acetate anhydrous. The copolymer composition is controlled for good adhesive properties by varying AA content. The monomer conversion is measured by the gravimetric method and FTIR technique. The adhesive layer thickness is measured by scanning electron microscopy, and the adhesive properties are evaluated with loop tack, 180° peel, and holding time measurements. The peel force increases with increasing the AA content up to 3 wt% and decreases at the AA content higher than 3 wt%, but the tack force decreases with increasing the AA content. The holding time increases with increasing the AA content, and it shows a similar trend with the Tg of adhesives. The increase of layer thickness improves tack and peel forces, but it weakens the holding power. A tape thickness of about 20 μm shows well-balanced properties at 3 wt% AA content in the acrylic copolymer system.

Morphological, acoustical, and physical properties of free-rising polyurethane foams depending on the flow directions

Polyurethane foam is widely used for automobile compartments as sound absorption materials due to its excellent noise dissipation characteristics. This sound absorption property is strongly dependent on the cavity and pore structures of the foams, and the cell morphology can be modulated by controlling experimental parameters. Two types of gelling catalysts were demonstrated in fabrications of polyurethane foams to control the cell morphology. The cell morphology of the free-rising polyurethane foams was investigated using dibutyltin-dilaurate and triethylenediamnine gelling catalysts, and the cell structures were analyzed from the free-rising samples obtained in various sampling heights and flow directions. The finer cell morphology was obtained with the organotin type catalyst by the faster gelling reactivity, compared with the amine type catalyst. In addition, the spherical small cavities in the samples obtained from horizontal planes of the free-rising foams revealed higher sound absorption coefficient and physical toughness than the elliptical irregular cavities from vertical planes, due to the higher homogeneity of cavity distributions in the horizontal planes.

Fabrication of acrylic copolymer with aluminum nitride fillers and its physical and thermal properties

Heat dissipation during operations of electronic devices is a serious issue with device miniaturization and high power consumption. As one practical approach to reducing the device temperature, thermally conductive adhesives can be used between printed circuit board and heatsink materials. By incorporating the aluminum nitride (AlN) with acrylic copolymer matrix, thermal conductivity and adhesive properties are examined with different sizes and content of particulate fillers. Acrylic copolymer is synthesized using butyl acrylate and acrylic acid monomers via solution polymerization, and AlN particles are used as thermally conductive fillers. The overall monomer conversion reaches more than 96% after 140 min reaction time. Considering both adhesive properties and thermal conductivity of adhesives, it is desirable to apply 20 wt% nano-AlN filler to acrylic copolymer adhesives.