Ji Sun Park

Enhanced Thermal Conductivity of Epoxy/Three-Dimensional Carbon Hybrid Filler Composites for Effective Heat Dissipation

Graphitic carbon nanomaterials (CNMs) are recognized as next-generation heat dissipating materials (HDMs) for efficient thermal conduction within a polymer composite. Commercially used carbon-based HDMs, including carbon blacks, carbon nanotubes (CNTs), and graphites, are limited by low thermal conductivity under 50% filler content. Two-dimensional graphenes show high thermal conductivity in their major (xy) planes; however, they still exhibit low thermal conductivity in the z direction, i.e., perpendicular to the major plane, because of the difficulty in obtaining a proper vertical alignment. Here, we introduce a straightforward strategy to improve the thermal conductivity of graphene-based HDMs in both the xy- and z-directions and report the results of our investigation of the thermal conductivity behavior of the epoxy composites. Our newly designed graphene-based HDMs were observed to adopt directly anchored and ohmic-contact morphologies between graphene nanoplatelets (GNP) and CNTs via bimetallic nanoparticle decoration on the GNP surface and subsequent carbon vapor deposition (CVD), and their epoxy composites showed an approximately two-fold enhancement of both in- and through-plane thermal conductivities compared to those of bare GNPs.

Liquid-phase exfoliation of expanded graphites into graphene nanoplatelets using amphiphilic organic molecules

Graphenes with a two-dimensional lattice of carbons have been widely employed in diverse applications owing to their excellent electrical, thermal, mechanical, and gas-barrier properties. However, the frequently-used reduced graphene oxide (rGO), which is synthesized from natural graphites by strong oxidation and subsequent reduction via highly toxic components, exhibits imperfect characteristics because of remaining defect sites on its basal planes. Therefore, in this work, we present a convenient way to prepare graphene nanoplatelets (GNPs) with minimized defect sites on their basal planes employing liquid-phase exfoliation of edge-functionalized expanded graphites (EGs) with amphiphilic organic molecules. Exfoliated GNPs revealed approximately sub-7-nm-thickness and showed stable dispersibility in an organic media during 9 months. Furthermore, spray-coated GNP films presented homogeneously stacked morphologies without noticeable agglomerations.

Patterned transparent electrode with a continuous distribution of silver nanowires produced by an etching-free patterning method

The outstanding electrical, optical, and mechanical properties of silver nanowire transparent electrodes are attractive for use in many optoelectronic devices, and the recent developments related to these electrodes have led to their commercialization. To more fully utilize the advantages of this technology, developing new process technologies in addition to performance improvements is important. In this report, we propose a novel ultra-simple patterning technology to generate a silver nanowire transparent layer and a unique patterned structure with continuously distributed silver nanowires without any etched areas. The patterning is conducted by exposure to ultraviolet light and rinsing. The exposed and unexposed regions of the resulting layer have dramatically different electrical conductivities, which produces an electrical pathway without using any etching or lift-off processes. The unique patterned structure produced by this etching-free method creates hardly any optical difference between the two regions and results in excellent visibility of the patterned transparent electrode layer.