Speaker : Prof. Jongnam Park

Affiliation : Department of Energy and Chemical Engineering, UNIST

Title : Synthesis of Nanoparticles in the Continuous Process, and their Surface Engineering for Energy and Biological Applications

Date : March 16, 2016

Location : Science building 604

Time : 5 pm

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Abstract​

The idea to design the continuous process could be related to the development of new nanomaterials using microfluidic system. Firstly, we prepare the microfluidic device using MEMS technique and then investigate the kinetics of the synthetic reaction of nanomaterials in the microfluidic device. We’ve made great efforts to improve the reactor design to be available in high temperature and high pressure far from the normal condition. In the previous single-phase laminar flow, diffusion is the only means of mixing. As a result of the parabolic fluid-velocity profile, particles near the wall spend more time in the reactor than those in the center, resulting in broad residence time distributions (RTDs). We achieved the supercritical flow through the fabrication of high temp, and high pressure microfluidic reactor up to 450 °C, 200 bars by adopting the compression part. In the supercritical condition, the hexane solvent itself (liquid or supercritical) allows decreasing significantly the effect of RTD on the size distribution of the QDs because of its low viscosity, compared to squalane. Then, under its supercritical phase, high supersaturations can be obtained in hexane, providing high nucleation rate, which produce more nuclei and reduce the size distribution. Also, perfect mixing that cannot separate the liquid slug and gas zone brings material from the wall to the center of the channel, inducing the narrower size distributions. We also successfully extend the microfluidic work to the synthesis of other nanomaterials under high pressure.

For the energy application of nanomaterials such as batteries and solar cells, based on the surface engineering of nanomaterials, we modified the surface properties of nanomaterals. We designed new lidands such as PEG polymer, and single organic molecules with the functional group. We also developed the ligand exchange method to apply new nanomaterials synthesized using microfluidic system for homogeneous dispersion, showing long-term stability in various conditions and good processability.