| As a new interdisciplinary, microfluidics have attracted the interests from many scientists of different backgrounds, which have been applied successfully in diverse areas such as biology, chemistry, and materials. However, there are still some problems to be solved about microfluidics, such as insufficient stability of materials, complicated and fabrication methods of low reproducity, difficulty in designing the surface wetting property of microchannel. To overcome those problems, three kinds of novel microreactors were fabricated by combining “preceramic polymers” and “superamphiphobic silicon nanowires(Si NWs)” with microfluidics, including whole ceramic-like microreactor, pressure-tolerant microreactor, and membrane-fee dual channel microreactor. The microreactors were then utilized for chemical synthesis under high temperature high pressure, flash chemistry and gas-liquid biphasic reaction.Two types of whole ceramic-like microreactors were fabricated from preceramic polymers, polysilsesquioxane(POSS) and polyvinylsilazane(PVSZ) by scaffold method and were utilized for high temperature or/and high pressure chemical synthesis. A ceramic-like transparent phase can be achieved by treating POSS and PVSZ at 300 °C and 500 °C respectively. The polymers combined such good processability and solvent resistance as ceramics, and were suitable to fabricate microreactors. POSS microreactor was fabricated by embedding perfluoroalkoxy(PFA) tube template in POSS to obtain PFA/POSS composite, followed by removing PFA tube and heating at 300°C for 1 h. PVSZ microreactor was fabricated by embedding polystyrene(PS) film template in PVSZ and firing at 500°C for 2 h to decompose PS template. The obtained whole ceramic-like microfluidic devices revealed excellent chemical and thermal stabilities in various solvents. They demonstrated unique chemical performance under high temperature or/and high pressure conditions such as Michaelis-Arbuzov rearrangement(150~170°C), Wolff-Kishner reduction(200°C), synthesis of super-paramagnetic Fe3O4 nanoparticles(320°C) and Claisen rearrangement(250°C and 450 psi). These economic ceramic-like microreactors fabricated by a facile non-lithographic method displayed excellent utility under challenging conditions that is superior to other plastic microreactors and comparable to glass and metal microreactors of high cost.Conventionally polymer microreactor was fabricated through sequential solidification-bonding method. Herein, pressure-tolerant polymer microfluidic reactors with excellent bonding strength were fabricated by simultaneous solidification-bonding(SSB) method, which prevented the long-lasting bonding difficulties in polymer microfluidics devices. A viscous and reactive matrix polymer was cast onto the glass substrate with pre-patterned wax as the sacrificial template. Elaborate interfacial chemistry between the matrix polymer and the functionalized glass surface was designed to achieve simultaneous solidification and chemical bonding under UV or/and mild thermal condition(<200°C with no pressure). Highly pressure-tolerant microchannels were obtained by complete removal of the liquid wax template at 80°C. The versatility was demonstrated by fabricating microreactors from various polymers with different interfacial chemistry, including PVSZ, fluoropolymer, Su8 photoresist, polyethyleneglycol diemethacrylate, NOA 81 adhesive and Duralco 4525 resin, which were all stable at 1000 psi with the highest burst pressure of 2000 psi(PVSZ microeactor). In particular, the burst pressure of fluoropolymer glass microreactor was two orders of magnitude higher than that of the microchannel made by conventional method. This user-friendly method with no use of sophisticated facilities allows fabrication of polymer based microreactors under mild conditions, leading to high success-yield, excellent bonding strength, and various channel design with no conformal contact difficulty. This method is also able to fabricate microchannel with built-in micromixers, hydrophilic-hydrophobic Janus microreactor, and microreactor on the curved surface. Finally, the polymer-glass microfluidic device was used for synthesis of a natural product of Tryptanthrin by flash chemistry under high pressure induced condition(synthetic yield: 90%, flow rate: 10.5 m L/min, reaction time: 14 ms). The transparent microfluidic device can be used as a useful platform for miniaturizing spectroscopic tools for chemical analysis study under high pressure conditions.Cone-shaped Si NWs superamphiphobic surface were fabricated by silver assisted chemical etching of Si, nanoparticle decoration of silicon nanowire surface, and fluorination treatment(the contact angles of water, DMSO, hexadecane were 164o, 155o, 120o respectively). The superamphiphobic Si NWs surface with excellent thermal, chemical and mechanical stability is able to be fabricated in large scale with predesigned pattern by employing AZ1512 positive photoresist as protecting layer during the etching step. The superamphiphobic Si NWs surface exhibited unique gas manipulation capability. They could float on the surface of water or oil, and capture gas under water to form under-water gas pattern. By bonding PDMS microchannel with superamphiphobic Si NWs pattern via PVSZ adhesive, membrane-free dual channel microreactor can be fabricated. This novel microreactor can treat or manipulate both liquids(including water and oil) and gas under dynamic conditions. Oxidative heck biphasic gas-liquid reaction was performed in this novel reactor with the conversion of 79% at the retention time of 5 min, in which gas was flowing through the gaps between Si NWs, and liquid was flowing in the PDMS channel, so direct gas-liquid contact was formed. Comparing with PDMS membrane dual channel reactor, it is not necessary for gas to transport through a membrane, which can improve the conversion of the reaction. The superamphiphobic Si NWs embedded microreactor can be a novel platform to perform membrane-free gas-liquid synthesis with high gas-liquid contact area and low gas diffusion barrier. |
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