Kyung Moon Choi

Alternating droplet generation and controlled dynamic droplet fusion in microfluidic device for CdS nanoparticle synthesis

A multifunctional and high-efficiency microfluidic device for droplet generation and fusion is presented. Through unique design of the micro-channels, the device is able to alternately generate droplets, generating droplet ratios ranging from 1 ratio 5 to 5 ratio 1, and fuse droplets, enabling precise chemical reactions in several picoliters on a single chip. The controlled fusion is managed by passive control based on the channel geometry and liquid phase flow. The synthesis of CdS nanoparticles utilizing each fused droplet as a microreactor for rapid and efficient mixing of reagents is demonstrated in this paper. Following alternating droplet generation, the channel geometry allows the exclusive fusion of alternate droplets with concomitant rapid mixing and produces supersaturated solution of Cd2+ and S2- ions to form CdS nanoparticles in each fused droplet. The spectroscopic properties of the CdS nanoparticles produced by this method are compared with CdS prepared by bulk mixing.

An internal doping method for the preparation of transparent hybrid xerogels containing nano-sized iron particles

Sol-gel copolymerization of iron tricarbonyl-2-(triisopropoxysilyl)-1,3-butadiene with 1,6-bistriethoxysilylhexane and 1,4-bistriethoxysilylbenzene followed by drying produced bridged polysilsesquioxane xerogels. These porous, transparent hybrid materials containing the iron metal precursor were irradiated (UV) and heated under vacuum resulting in the deposition of nano-sized iron particles doped in the xerogels. EDAX and electron diffraction techniques were used to characterize the iron phases. The TEM images of these doped xerogels provided additional information regarding the domain size of the iron phase.Using a combination of external doping of Cd2+ and S2− ions and internal doping of Fe°, mixed Fe/CdS phases were prepared within the porous bridged polysilsesquioxane xerogels. The resulting doped xerogels were found to have retained their porous morphology.

Microfluidic Approach for the Synthesis of Micro- or Nanosized Molecularly Imprinted Polymer Particles

Molecularly imprinted polymers (MIPs) have specific molecular recognition sites for chemical detection.High affinity receptors can increase the sensitivity of sensors/devices. The synthesis of micro- or nanosized MIPs particles is desirable to improve the sensitivity since MIPs particle sizes are inversely proportional to the affinity between receptors and template molecules. To synthesize nano- or microsized MIPs particles, we demonstrate here a novel microfluidic approach, which presents continuous and uniform MIPs particle generation.

Functional Polymers for Advanced Lithography

In nanotechnology, many scientists have been seeking for new functional polymers, which can replica nano-sized features to achieve improved performances of nano-devices. Soft lithography has been widely used in replica of small features as a low cost alternative to conventional UV photolithography. However, commercial silicon rubbers, PDMS polymers, which have been used in current soft lithography, show limitations, especially for nano-resolution soft lithography. These limitations have motivated us to develop a new version of PDMS polymers to overcome those limitations and thus to extend current technology in soft lithography to the advanced level. Since the resolution of soft lithography significantly relies on stamping performance, we designed a novel PDMS prepolymer, which has photocurable cross-linkers to enhance mechanical property to improve lithographic performance and also to create photocurable capability.