Fabrication and utilization of SiC based ceramic microreactors and microrobots with 3D printing methods of polysilazane resin

Abstract

Microfluidics consists of small-size flow channels for dealing with fluids, with an under 1000 μm of channel dimension and the small volume of working fluids. Microfluidics which deals with a small amount of volume and dimension has many advantages toward conventional approaches related to various fields including chemistry, biochemistry, material science, and analytical techniques. Many advantages of microfluidics come from fast heat and mass transport phenomena owing to the small dimension of the fluidic channels and short diffusion length and come from the optimized operation condition and uniform residence time of the chemical species inside of the microfluidic channels and reactors. Therefore, microfluidics has become increasingly attractive in many fields, since its advent approximately three decades ago. In particular, microfluidic system integration and process diversification have greatly enhanced the system performance for continuous-flow chemistry. Despite the advantage of microfluidics, there are several limitations of its application to academic and industrial fields. One of the commonplace limitations to apply microfluidics to the real world is the fabrication of the microfluidic system. Fabricating the microreactor with specific design and functionality has strongly been dependent on molding and lithographic approaches with photoresists and polydimethylsiloxane (PDMS). However, these routes need complex steps and skillful hands, and difficult yet to realize the sophisticated design of microfluidic devices. Therefore, 3D-printing techniques as an additive manufacturing technology draw much attention due to its relatively facile way of fabricating monolithic bodies several micrometers to centimeters in size. However, most of the 3D printing techniques utilize organic polymer and due to its low chemical and thermal resistance, 3D printing of microreactor still hardly meets the demand of the microreactor-related field. In Chapter 2, I demonstrated the 3D-printing of polyvinylsilazane (PVSZ), inorganic polymer, microreactor with high printing resolution which has high chemical resistance for versatile microreactor fabrication. With a chemical modification of PVSZ with acrylate group-containing reagent, the modified PVSZ (mPVSZ) can be 3D-printed by UV light with optimized photoinitiators. The 3D-printed PVSZ structures have high solvent resistance toward various organic solvents and basic solution which are known to damage 3D printable polymers. By 3D-printing PVSZ, a custom-designed microreactor with high dimensional has been proposed. In chapter 3, I demonstrate the fabrication of fully dense 3D-printed SiCN non-oxide ceramic monoliths with various shapes and structures via pyrolysis of the 3D-printed structures (henceforth, “green body”) derived from a photocurable preceramic composite resin containing 10 wt.% of silica nanoparticle filler as a ceramic precursor. A working proof-of-concept microreactor for the production of hydrogen by an ammonia cracking process demonstrated excellent heat tolerance and chemical resistance against long exposure to corrosive conditions. In chapter 4, to extend the 3D-printed SiCN ceramics toward further applications, a two-photon laser lithography technique with a higher spatial resolution has been adopted to mPVSZ 3D printing. By using two-photon laser lithography, SiCN ceramic structures can be fabricated with 4-micrometer resolution and the high-resolution SiCN structures have been utilized for microrobot application. The SiCN ceramic has biocompatibility and similar physical strength to human bone tissue. Also, magnetic nanoparticles can be immobilized on the surface of the SiCN ceramic by utilizing the surface modifiable feature. Therefore, the ceramic microrobot which can be remote-controlled by the external magnetic field has been fabricated for cell-delivering applications. These proposed 3D-printed PVSZ inorganic polymer and SiCN ceramic microreactor/microstructure systems are expected to be the breakthrough platforms for versatile chemical processes and applications.