Tae Gun Kim

Highly flexible, stretchable, wearable, patternable and transparent heaters on complex 3D surfaces formed from supersonically sprayed silver nanowires

Here we demonstrate a scalable production process for a highly transparent, flexible, patternable, and wearable heater using a single-step supersonic kinetic spraying technique that deposits silver nanowires (AgNWs) on rollable substrates, facilitating a roll-to-roll process. AgNWs were suspended in an aqueous solution and supersonically sprayed onto a rolling substrate to produce a flexible heater film without use of any binders or additional post-process treatments. Because of the high-speed impact, the intersections of the nanowires were fused, thus creating a junction-free network of nanowires, which significantly reduced the contact and thus the sheet resistance. Cyclic temperature testing confirmed the thermal stability of the AgNW heater. A heater bent to a radius of less than 2 mm was tested for 600000 cycles; the heater exhibited little change in the sheet resistance. Moreover, it does not experience significant thermal expansion, which would manifest itself in buckling, and thus such heaters do not buckle during operation. AgNWs were sprayed onto a complex surface of a replica of Venus de Milo and Jejus Dol Hareubang statues, demonstrating the deposition capability onto a 3D surface. Defogging and defrosting tests showed potential applications of this heater in smart mirrors or windows. The highest heating temperature of 160 °C was achieved in a transparent fibrous film having 95% transparency and 15 Ω sq−1 sheet resistance at a supplied voltage of 8 V. Because the film fabrication method is rapid and scalable with the installation of multiple nozzles, the method is commercially viable.

Self-Cleaning Anticondensing Glass via Supersonic Spraying of Silver Nanowires, Silica, and Polystyrene Nanoparticles

We have sequentially deposited layers of silver nanowires (AgNWs), silicon dioxide (SiO2) nanoparticles, and polystyrene (PS) nanoparticles on uncoated glass by a rapid low-cost supersonic spraying method to create antifrosting, anticondensation, and self-cleaning glass. The conductive silver nanowire network embedded in the coating allows electrical heating of the glass surface. Supersonic spraying is a single-step coating technique that does not require vacuum. The fabricated multifunctional glass was characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), ultraviolet-visible spectroscopy, and transmission electron microscopy (TEM). The thermal insulation and antifrosting performance were demonstrated using infrared thermal imaging. The reliability of the electrical heating function was tested through extensive cycling. This transparent multifunctional coating holds great promise for use in various smart window designs.

Packing of metalized polymer nanofibers for aneurysm embolization

Aneurysmal subarachnoid hemorrhage (SAH) is the extravasation of blood into the subarachnoid space and is fatal in most cases. Platinum coils have been used to fill the hemorrhage site and prevent the extravasation of blood. Here we explored the use of Pt-coated polymer nanofibers (NF) to prevent blood extravasation and were able to achieve improved results in vitro. The polymer nanofibers were produced via electrospinning and were subsequently electroplated with Pt, resulting in metalized nanofibers. These nanofibers were installed within a microfluidic channel, and the resulting reduction in the permeability was evaluated using a fluid similar to blood. Based on the obtained results, these newly developed nanofibers are expected to decrease the operation cost for SAH, owing to their reduced size and low material cost. Furthermore, it is expected that these nanofibers will be used in a smaller amount during SAH operation while having the same preventive effect. This should reduce the operational risk associated with the multiple steps required to place the Pt coils at the SAH site. Finally, the underlying hydrodynamic mechanism responsible for the reduced permeability of the synthesized nanofibers is described.