Tae-Ho Yoon

Novel inorganic polymer derived microreactors for organic microchemistry applications

Microreactors fabricated with optically transparent inorganic polymers from two types of precursors using a UV-microimprinting process demonstrated reliable solvent resistance and capability for performing three model organic synthetic reactions, which were compared with batch systems and glass based microreactors.

Adhesion force measurement between the stamp and the resin in ultraviolet nanoimprint lithography—an investigative approach

In the ultraviolet nanoimprint lithography (UV-NIL) process, the surface interaction between the mold and the resist is essential along with molecularly clean separation of the mold from the surface of the cured resist for repeated use of the mold. In our present study, various mold-resin combinations have been examined by a tensile strength method to determine the adhesion force between a mold with a relief pattern and a photocurable resin. The adhesion force of polymer molds of the fluorine-containing polymers perfluoropolyether dimethacrylate (PFPE) and polydimethylsiloxane (PDMS) were compared to those of hard molds such as Si and quartz against several commercial UV-NIL resins. Eventually, PFPE with higher molecular weight-AMONIL-was found to be an excellent UV-NIL mold-resin combination with the lowest adhesion force per unit area (20 kPa). In particular, the 36-fold repeated imprinting with a high molecular weight PFPE mold showed only a slight increase of adhesion force by 36 kPa with molecularly clean release from the AMONIL resin, whereas a surface-modified PDMS mold revealed highly increased adhesion from an initial 20 kPa to 120 kPa after repeated use.

Novel Micro/Nanofluidics Fabricated by Imprint Molding of Inorganic Polymers

We have successfully fabricated the polysilazane glass derived microfluidics with high optical transparency, biocompatibility thermal stability and chemical inertness via simple fabrication process. And also a hydrophilic nanofluidic system was fabricated with newly synthesized organic-inorganic material with excellent patternability. The preliminary study for photochemical reactions with the microfluidics, the separation of biomolecules with nanofluidics, it was claimed the obvious niche between conventional devices using glass and PDMS materials, thus it holds tremendous potential in the field of micro reaction technology as well as biosensor and bioreactors

Encapsulation of cell into monodispersed hydrogels on microfluidic device

In here, we present the microfluidic approach to produce monodispersed microbeads that will contain viable cells. The utilization of microfludics is helpful to synthesize monodispersed alginate hydrogels and in situ encapsulate cell into the generating hydrogels in microfludic device. First, the condition of formation of hydrogels in multiphase flows including oil, CaCl2, and alginate was optimized. Based on the preliminary survey, microfludic device could easily manipulate the size of alginate beads having narrow size distribution. The microfluidic method manipulates the size of hydrogel microbeads from 30 to 200um with a variation less than 2%. For the proof of concept of cell entrapment, the live yeast expressing green fluorescence protein is successfully encapsulated in microfluidic device.

Characterization and Fabrication of Nano-Sized Patterns and Microfluidic Channels Derived from Polyvinylsilazane via Soft Lithographic Technique

Interests on the fabrication of microfluidic devices have increased in the fields of micro total analysis system (μ-TAS) and MEMS (Microelectromechanical systems) due to their chemical inertness and high thermal stability. The thermal characterization of the SiCN preceramic polymer, polyvinylsilazane, showed that the cured polymer has ceramic properties at heat treatment temperature of 600 oC or above. In the characterization of the mechanical properties, the characteristic values of the elastic modulus and hardness notably increased for the heat-treated SiCN. The present study describes the preparation of nano-sized patterns and microfluidic channels using a soft lithographic technique. The study shows that the fabrication of microchannels using the cured inorganic polymers holds tremendous potential in the field of microfluidics, where materials with high optical transparency, thermal stability and chemical inertness are in demand as niche between conventional microfluidics using glass and polymeric materials.

Fabrication of SiC-based Ceramic Microstructures from Preceramic Polymers with Sacrificial Templates and Softlithography Techniques

Silicon derived polymers containing nitrogen, carbon and boron have been considered as precursors for various non-oxide ceramics such as SiC, SiCN and SiBCN (Madou, 2002, Nguyen & Wereley, 2002, Liew et al., 2003). These ceramics can be easily shaped using various forming processes and then crosslinked by exposure to heat or UV radiation to form an infusible solid. The consolidated preceramic polymers are finally pyrolyzed at high temperatures to transform into the dense ceramic phases. These materials can be used for high temperature applications in areas such as structural composites (Kim et al., 1996), electronic devices (Xia & Whitesides, 1998) and catalytic chemical reactions (Xia et al., 1999). Table 1 shows some selected important preceramic polymers that have been studied in various aspects. In particular, silicon carbide (SiC) is a typical non-oxide ceramic that has attracted the most interest on account of its unique physical and chemical properties such as high thermal conductivity, excellent thermal stability, superior stability towards oxidation compared with carbon, high mechanical strength and chemical inertness. Commercially available polysilazane (VL-20, KiON Corp. USA) and two types of polycarbosilanes, Polymethylsilane (PMS) and Allyhydridopolycarbosilane (Starfire System, USA) are readily used as preceramic polymers for SiCN and SiC ceramics, respectively.

Durable hydrophilic microchannels with controlled morphology by the direct molding method.

We present a laminated hydrophilic microchannel fabricated by a direct micromolding and facile bonding technique with a hydrophilic organic-inorganic hybrid (HP) resin, which is built into two supporting parallel polydimethylsiloxane (PDMS) substrates. This approach allows one to shape the cross-section of the hydrophilic channel into a regular rectangular or geometrically complicated mouth-throat structure. Spontaneous self-wetting flow of water occurs when water is introduced to the HP microchannel with rectangular cross-section without the aid of mechanical pumping or electric field. The capillary flow velocity can be controlled by varying the channel size. The channel surface behaves like a glass surface in terms of zeta potential for pH larger than 3, and the electro-osmotic flow (EOF) velocity can be as high as 4.7 × 10(-4) cm(2)/V·sec at pH 9.0. The capillary electrophoresis (CE) module made of the HP resin for amino acid or DNA separation is demonstrated to yield a higher resolution in a shorter retention time with repeatability and long-lasting durable performance with antifouling property, when compared with PDMS CE.

Preparation and Applications of Ceramic Composite Phases from Inorganic Polymers

Silicon-based polymers containing nitrogen, carbon and boron have been considered as precursors for various non-oxide ceramics such as silicon carbide (SiC), SiCN and SiBCN.[1] These ceramics can be easily shaped using various forming processes and then cross-linked by exposure to heat or radiation to form an infusible solid. The consolidated preceramic polymers are finally pyrolyzed at high temperature to transform into the dense ceramic phases. These materials can be used for high temperature applications in areas such as electronic devices and structural composites.[2] Table 4.1 shows some selected important preceramic polymers that have been studied in various aspects. The polymers such as polysilanes, polycarbosilanes, polysilanzane, polysiloxanes are good candidates for ceramic phases due to their high ceramic yields on account of the combination of cross-linking and pyrolysis. Commercially available polysilazane (VL-20, KiON Corp., USA) and two types of polycarbosilane (Starfire System, USA and Nippon Carbon Co., Ltd., Japan) are readily used as preceramic polymers for SiCN and SiC ceramics, respectively.

Novel Inorganic Polymer Derived Microfluidic Devices: Materials, Fabrication, Microchemical Performance

We introduce the successful fabrication of inorganic polymer derived microchannels with organic solvent resistance and optical transparency, via economic micro-molding process by using two types of source materials: commercial polyvinylsilazane (HTT1800 Kion Corp.), or allylhydropolycarbosilane (SMP-10, Starfire Co.). And we demonstrated the reliable microchemical performance in various organic solvents such as THF, DMF and acetonitrile at elevated temperatures. Knovenagel and Diels-Alder reactions were successfully run by pressured-driven flow in 2 cm and 16 cm long channel, respectively. It is proven that the developed inorganic polymer-based microchannels were obviously performed as a niche material-based microfluidic device between plastic and glass based device. In addition, we present the fabrication and characterization of ceramic microreactors composed of inverted beaded silicon carbide (SiC) monoliths with interconnected pores as catalyst supports, integrated within high-density alumina housings obtained via an optimized gel-casting procedure. These tailored macroporous SiC monoliths deposited Ru as a catalyst was run for the decomposition of ammonia with at temperatures between 450 and 1000 °C, which demonstrated a high temperature fuel cell reformer.Copyright