Hyung-Seok Jang

Self-Assembly of Silver Nanowire Ring Structures Driven by the Compressive Force of a Liquid Droplet

In a nanowire dispersed in liquid droplets, the interplay between the surface tension of the liquid and the elasticity of the nanowire determines the final morphology of the bent or buckled nanowire. Here, we investigate the fabrication of a silver nanowire ring generated as the nanowire encapsulated inside of fine droplets. We used a hybrid aerodynamic and electrostatic atomization method to ensure the generation of droplets with scalable size in the necessary regime for ring formation. We analytically calculate the compressive force of the droplet driven by surface tension as the key mechanism for the self-assembly of ring structures. Thus, for potential large-scale manufacturing, the droplet size provides a convenient parameter to control the realization of ring structures from nanowires.

Shaping characteristics in alginate hydrogel encapsulation via a two-fluid spraying method

Recently, an alginate hydrogel containing amphiphilic liposomes was suggested for application to an antifouling coating. In this study, we investigate the shaping characteristics of the alginate hydrogel by a spraying method for application to the coating. Sodium alginate droplets from the spraying nozzle are known to be differently shaped by several external forces during the encapsulation process when such a droplet impacts onto the surfaces of liquid containing calcium ions. We adopted a two-fluid spraying method for fast alginate droplets with a scalable size suitable for mass production. Various shapes, such as mushroom, petal, sphere, and thin-sheet alginate hydrogel shapes containing liposomes, were obtained via this experimental approach. Supported by a theoretical analysis, we determined regimes for the various shapes depending on the droplet size and the concentration of the sodium alginate solution. Alginate hydrogel of different shapes based on the regimes will be used for the coating throughout a different post-processing.

Biomimetic, Flexible, and Self-Healable Printed Silver Electrode by Spontaneous Self-Layering Phenomenon of a Gelatin Scaffold

Organic-inorganic hybrid layer-by-layer (LBL) composite structures can not only increase the strength and ductility of materials but also well disperse nanomaterials for better-conducting pathways. Here, we discovered the self-assembly process of an organic and silver (Ag) LBL hybrid structure having excellent sustainability during the long-term bending cycle. During the assembly process, the organic and Ag hybrid structure can be self-assembled into a layered structure. Unlike other conventional LBL fabrication processes, we applied the hydrogel scaffold of a biological polymer, which can spontaneously phase separate into an LBL structure in a water/alcohol solvent system. This new hydrogel-based Ag LBL patterns can successfully be printed on a flexible polyimide film without nozzle-clogging problem. Although these Ag LBL patterns cracked during the bending cycle, carbonized organic compounds between the Ag layers help to self-heal within few minutes at a low temperature (<80 °C). On the basis of our new hydrogel-based Ag ink, we could fabricate a fully printed reliable microscale flexible heater. We expect that our self-layering phenomenon can expand to the broad research field of flexible electronics in the near future.

Synthesis and integration of 2D Iron Phosphate sheets for energy storage devices

This work presents the synthesis, assembly, and integration of two-dimensional (2D) phosphate sheets Lithium-ion energy storage devices. Three achievements have been accomplished in this work: (1) synthesis and assembly of 2D, poly-crystalline phosphate sheets greater than 50μm² in area, and (2) 3× improved capacitance of an Iron-Phosphate-Polypyrrole battery/supercapacitor (3.6 mF/cm²) over bare Polypyrrole (PPY) films, and (3) 20× improved capacitance of an FePO<inf>4</inf>-Carbon Nanotube (CNT) battery/supercapacitor (20.8 mF/cm²) over bare CNT-based electrodes.