Synthesis of a three-dimensional graphene structure and its nanocomposite based on a microfluidic droplet system

Abstract

Graphene has demonstrated its extraordinary physical and chemical properties including excellent carrier mobility, high electrical and thermal conductivity, superb mechanical strength, and typical photolumi-nescence due to its unique two dimensional (2D) sp2-bonded carbon network structure. Thanks to these char-acteristics, not only graphene but also its derivatives such as graphene oxide (GO) and reduced graphene ox-ide (rGO) have found their diverse applications in the fields of nanoelectronics, nanosensors, and nanocom-posites. Recently, three-dimensional (3D) graphene also attracts huge attention because of its enhanced spe-cific surface area and high compression/aggregation resistance. In this thesis, the combination effect of the 3D structure and the intrinsic excellent properties of graphene has been investigated to be applied for a glu-cose biosensor and a polymer composite with core-shell structure. In Chapter 2, 3D graphene microballs (3D GMs) were synthesized by using a microfluidic droplet gen-erator and thermal evaporation-induced capillary compression phenomenon. To investigate the effect of the GO concentration and the droplet size on the morphology of the 3D GM, different concentration of a GO solution and flow rate of an oil phase were employed. As the concentration of a GO solution increased, the degree of the crumpling phenomenon became intensified, showing gradually dense GO assembly. However, the diameter of the 3D GM was not significantly augmented in proportion to the GO concentration. These results imply that high concentration of a GO solution is required if more densely packed morphology of the 3D GMs is desired. To control the size of the GM, the flow rate of an oil phase was changed while the flow rate and the concentration of an aqueous GO solution were fixed at 1.0 L/min and 10 mg/mL, respectively. As the flow rate of an oil phase increased to reduce the diameter of droplets, the diameter of the GM was gradually reduced, while the...