聚苯乙烯/銀之複合材料之製備

Abstract

本論文根據過硫酸銨具有還原銀離子以及起始高分子聚合反應的特性，設計一銀/聚苯乙烯複合材料之原位合成系統，並探討其反應機制。 在聚苯乙烯乳膠懸浮液中，加入硝酸銀/過硫酸銨可使得銀離子於聚苯乙烯微球表面還原，形成奈米銀顆粒；同時銀離子可於水相中被還原成次微米級的不完整樹枝狀結構。吾人經由XRD及TEM暗視野像可鑑定其為銀之晶體結構，並在此二步合成系統中，解釋聚苯乙烯表面官能基以及過硫酸銨兩種物種與銀離子還原反應的關係。 在苯乙烯懸浮液中，硝酸銀/過硫酸銨首先進行氧化還原反應產生自由基，並起始苯乙烯之聚合反應；同時過硫酸銨亦氧化苯乙烯產生副產物苯甲醛，此副產物可在FTIR圖譜上觀察到。在苯乙烯耗盡後，剩餘的過硫酸銨可還原銀離子產生聚苯乙烯上的奈米銀顆粒以及水相中之次微米級棒狀銀結構，此為一原位合成系統。吾人經由XRD及TEM繞射圖譜鑑定銀晶體，而此一銀的還原反應同樣由聚苯乙烯上的表面官能基幫助之。 最後吾人以GPC鑑定生成的聚苯乙烯之分子量，以及TGA/DTA鑑定複合材料中各成份之比例。

Based on the two capabilities of reducing silver ion and initiating polymerization possessed by APS, we design an in-situ silver/polystyrene composite synthesis method, and, and we further investigate the reaction mechanism of this system. When we add silver nitrate/APS into the polystyrene latex dispersions, silver ions were reduced by APS, forming nanoparticles on the polystyrene microspheres’ surfaces and submicron-sized incomplete dendrites in water phase. Through XRD and TEM dark images we can determine their crystal structures. What’s more, in this two-step synthesis system, we explain the relation between silver ion reduction and two reducing agents, APS and functional groups on the PS microspheres. In the styrene dispersion, silver nitrate/APS first generate free radicals through redox-initiation, and initiate the polymerization of styrene. At the same time, it is possible that APS oxidizes styrene to form a byproduct, benzaldehyde, and we do observe it in FTIR spectrum. After styrene monomer’s depletion, remaining APS is able to reduce silver ions thus forming silver nanoparticles on PS surfaces and submicron-sized rods in water phase. This is an in-situ synthesis system. We can determine silver’s crystal structure by XRD and TEM diffraction patterns. The functional groups on the PS surfaces also help to trigger the silver ion reduction. Finally we use GPC to determine the molecular weight of PS, and TGA/DTA to analyze the composition of the composite.