| Summary: | 碩士 === 國立清華大學 === 化學工程學系 === 103 === This project finished the preparation of silver nanoparticles in CO2-expanded liquids (CXL), and then add poly(methyl methacrylate) to synthesize composite by using compressed fluid anti-solvent technique. The precipitate of composite was in compression molding for preparing the conductive film. When the metal precursor (silver isosteric, AgISt) was prepared by ion exchange method from isosteric acid and silver nitrite first, it dissolved in hexane before adding hydrogen and carbon dioxide. The silver nanoparticles were reduced with hydrogen in CXL from the precursor, and it can be the well-disperse solution of silver nanoparticles. After the reduction, change solvent from hexane to toluene by rotary evaporator. The toluene solution was mixed with poly(methyl methacrylate). In the next step, put the solution mixture containing silver nanoparticles and poly(methyl methacrylate) in a high pressure gauge, then the pressure of carbon dioxide was gradually increased to let the solute co-precipitation onto a substrate, and supercritical carbon dioxide as a drying medium to extract residual solvent. Finally, the isosteric acid was eliminated from the precipitate by compression molding to form conductive composite. The factors containing pressure, temperature and rate of pressure rise, influenced the conductivity and the dispersity of composite. Design of experiment was used to determine the best condition for the anti-solvent. From the experiment data, the optimal operating conditions was 2,000 psi, 40 oC and 75 psi/min in anti-solvent, and 6.90 MPa, 175 oC in compression molding. In conclusion, we could get the composite with conductivity of 2.83 x 10-1 S/cm and silver content of 12.75 vol%. The advantages are: (1) as silver nanoparticles being added in a base of polymer by compressed anti-solvent, it maintain the dispersity of nanoparticles; (2) it would get small particle size and distribution of silver nanpaticle by using CXL to reduce metal precursor; (3) supercritical carbon dioxide prevent destruction of the composite structure in the drying process; (4) the precipitate was in a lower temperature to eliminate the dispersing agent like isosteric acid, and it can be higher conductivity with lower silver content.
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