| 摘要: | 本研究探討表面接枝不同鏈段長度的羧酸氧化鋯奈米粒子於不同分子量聚甲基丙烯酸酯薄膜(PMMA)中的分散、聚集及偏析行為，依據碳鏈長短，所使用的羧酸有甲基丙烯酸(Methacrylic acid, MA)、丁酸(Butyric acid, BA)、亞麻油酸(Linoleic aicd, LOA)三種接枝鏈。同時也改變聚甲基丙烯酸酯分子量，進而探討這三種接枝鏈段影響氧化鋯奈米粒子在聚甲基丙烯酸酯聚集行為之熱力學機制。 接枝相異鏈段的氧化鋯粒子與均聚物甲基丙烯酸酯之間有不同的相容性，其中接枝鏈段為甲基丙烯酸和丁酸與甲基丙烯酸酯的相容性較佳，相對的，接枝鏈段為亞麻油酸的氧化鋯粒子其相容性最差，因為亞麻油酸的接枝鏈段與均聚物甲基丙烯酸酯之間不相互容，使得氧化鋯粒子彼此聚集成團聚物，此三種相容性差異造成MA-ZrO2 及BA-ZrO2在PMMA高分子中以團聚物的形式分散及LOA-ZrO2 在PMMA高分子中呈現團聚物聚集的形式。 藉由熱回火處理，接枝不同鏈段種類的氧化鋯粒子會聚集成不同尺寸的團聚物，團聚物的種類上有線狀、圓盤狀以及趨近於球狀等結構。然而相容性最差的LOA-ZrO2 不僅會聚集成大尺寸的圓盤狀團聚物，在熱回火過程還會形成奈米尺度的內連結圓盤狀聚集結構，同時也形成微米尺度的非潤濕結構，此時LOA-ZrO2會偏析至薄膜高低起伏的邊緣處聚集，降低PMMA鏈段的伸展熵，這是接枝亞麻油酸鏈段的氧化鋯粒子較為特殊的現象。 不同羧酸氧化鋯奈米粒子混摻聚甲基丙烯酸酯製備出的複合材料經過熱回火處理有不同表面形態，LOA-ZrO2混摻PMMA製備出的奈米複合材料會產生非潤濕結構，相對的，MA-ZrO2或BA-ZrO2製備出的奈米複合材料則會均勻潤濕在矽基板上。 In this work, I investigated organic-inorganic thin films of poly (methyl methacrylate) (PMMA) homopolymers of three molecular weights (MWs, Mn =17, 45 and 105 kg/mol) hybridized with zirconia nanoparticles (ZrO2 NPs). Prior to mixing with PMMA, the ZrO2 NPs were surface-modified by grafting a layer of various carboxylic acids (methacrylic acid, butyric acid and linoleic acid). For brevity, the surface-modified ZrO2 NPs were designated as MA-ZrO2, BA-ZrO2 and LOA-ZrO2. In the following context, I systematically studied the dispersion, aggregation and segregation behaviors of surface-modified ZrO2 NPs within the PMMA thin films. The dispersion, aggregation and segregation behaviors of carboxylic acid-grafted ZrO2 NPs within PMMA homopolymers depend on the enthalpic effect. According to the solubility parameters, I proposed that the MA or BA dispersants are miscible with PMMA whereas LOA is immiscible with PMMA. The former cases revealed the dispersion of small MA- and BA-ZrO2 clusters within PMMA homopolymers whereas the latter case was found to form large aggregates. The formation of the large aggregates is ascribed to reducing the unfavorable contacts between LOA-ZrO2 NPs and PMMA chains. Additionally, the ZrO2 NPs with surface grafted by a layer of LOA were found to preferentially segregate to the boundaries of cracks within the LOA-ZrO2/PMMA films. As a result, the conformational entropy loss associated with stretching of PMMA chains could be minimized. Moreover, LOA has the lowest surface energy. It is likely that LOA-ZrO2 nanoparticles preferentially aggregate to the free surface of poly (methyl methacrylate) thin films when thermal-annealing were implemented at a high temperature far above the glass transition temperature of PMMA. As a result, the thermal-annealed LOA-ZrO2/PMMA thin films revealed a morphology of dewetting. By contrast, the thin films of MA-ZrO2/PMMA and those of BA-ZrO2/PMMA still revealed homogeneous in thickness (i.e., fully wetting) on substrates. |
