Junho Jang

Physical barrier effect of geopolymeric waste form on diffusivity of cesium and strontium

The present study investigates the physical barrier effect of geopolymeric waste form on leaching behavior of cesium and strontium. Fly ash-based geopolymers and slag-blended geopolymers were used as solidification agents. The leaching behavior of cesium and strontium from geopolymers was evaluated in accordance with ANSI/ANS-16.1. The diffusivity of cesium and strontium in a fly ash-based geopolymer was lower than that in Portland cement by a factor of 10(3) and 10(4), respectively, showing significantly improved immobilization performance. The leaching resistance of fly ash-based geopolymer was relatively constant regardless of the type of fly ash. The diffusivity of water-soluble cesium and strontium ions were highly correlated with the critical pore diameter of the binder. The critical pore diameter of the fly ash-based geopolymer was remarkably smaller than those of Portland cement and slag-blended geopolymer; consequently, its ability physically to retard the diffusion of nuclides (physical barrier effect) was superior.

Quantum Dot/Siloxane Composite Film Exceptionally Stable against Oxidation under Heat and Moisture

We report on the fabrication of a siloxane-encapsulated quantum dot (QD) film (QD-silox film), which exhibits stable emission intensity for over 1 month even at elevated temperature and humidity. QD-silox films are solidified via free radical addition reaction between oligosiloxane resin and ligand molecules on QDs. We prepare the QD-oligosiloxane resin by sol-gel condensation reaction of silane precursors with QDs blended in the precursor solution, forgoing ligand-exchange of QDs. The resulting QD-oligosiloxane resin remains optically clear after 40 days of storage, in contrast to other QD-containing resins which turn turbid and ultimately form sediments. QDs also disperse uniformly in the QD-silox film, whose photoluminescence (PL) quantum yield (QY) remains nearly unaltered under harsh conditions; for example, 85 °C/5% relative humidity (RH), 85 °C/85% RH, strongly acidic, and strongly basic environments for 40 days. The QD-silox film appears to remain equally emissive even after being immersed into boiling water (100 °C). Interestingly, the PL QY of the QD-silox film noticeably increases when the film is exposed to a moist environment, which opens a new, facile avenue to curing dimmed QD-containing films. Given its excellent stability, we envision that the QD-silox film is best suited in display applications, particularly as a PL-type down-conversion layer.

Flexible Hard Coating: Glass‐Like Wear Resistant, Yet Plastic‐Like Compliant, Transparent Protective Coating for Foldable Displays

A flexible hard coating for foldable displays is realized by the highly cross-linked siloxane hybrid using structure-property relationships in organic-inorganic hybridization. Glass-like wear resistance, plastic-like flexibility, and highly elastic resilience are demonstrated together with outstanding optical transparency. It provides a framework for the application of siloxane hybrids in protective hard coatings with high scratch resistance and flexibility for foldable displays.

Flexible Transparent Conductive Films with High Performance and Reliability Using Hybrid Structures of Continuous Metal Nanofiber Networks for Flexible Optoelectronics

We report an Ag nanofiber-embedded glass-fabric reinforced hybrimer (AgNF-GFRHybrimer) composite film as a reliable and high-performance flexible transparent conducting film. The continuous AgNF network provides superior optoelectronic properties of the composite film by minimizing transmission loss and junction resistance. In addition, the excellent thermal/chemical stability and mechanical durability of the GFRHybrimer matrix provides enhanced mechanical durability and reliability of the final AgNF-GFRHybrimer composite film. To demonstrate the availability of our AgNF-GFRHybrimer composite as a transparent conducting film, we fabricated a flexible organic light-emitting diode (OLED) device on the AgNF-GFRHybrimer film; the OLED showed stable operation during a flexing.

Transparent, thermally stable methyl siloxane hybrid materials using sol-gel synthesized vinyl-methyl oligosiloxane resin

Vinyl-methyl oligosiloxane resin was synthesized by a hydrolytic sol-gel reaction of vinyltriethoxysilane and dimethyldiethoxysilane. Hydrochloric acid was added as a catalyst to promote the hydrolysis of silane monomers to form a highly condensed siloxane resin (Condensation degree = 95 %). The vinyl-methyl oligosiloxane and hydrogen-methyl oligosiloxane resin was then cured by a thermal hydrosilylation reaction with a minimal platinum catalyst content (3 ppm). The increased cross-linking density improved the thermal decomposition temperature and lowered the weight loss at a high temperature. The fabricated methyl-siloxane hybrid material (hybrimer) shows superior thermal stability (decomposition temperature >530 °C), good long-term thermal resistance (300 °C, 20 h) and transparency (92 % at 450 nm, 83 % at 350 nm) in the visible and ultraviolet ranges. Based on these characteristics, the methyl-siloxane hybrimer can be applied to various applications, including thermally stable optical materials.Graphical Abstract