| 研究生: |
陳偉豪 Chen, Wei-Hao |
|---|---|
| 論文名稱: |
聚四甲基一戊烯在對二甲苯溶液中結晶行為之研究 The crystallization behavior of isotactic poly(4-methyl-pentene-1) in the p-xylene solution |
| 指導教授: |
阮至正
Ruan, Jr-Jeng |
| 學位類別: |
碩士 Master |
| 系所名稱: |
工學院 - 材料科學及工程學系 Department of Materials Science and Engineering |
| 論文出版年: | 2010 |
| 畢業學年度: | 98 |
| 語文別: | 中文 |
| 論文頁數: | 89 |
| 中文關鍵詞: | 介穩相 、相圖 、固相-固相相變化 |
| 外文關鍵詞: | mesophase, phase stability, Solid-solid transitions |
| 相關次數: | 點閱:60 下載:1 |
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聚四甲基一戊烯在熔融態(bulk state)中,僅能形成一密度略低於非晶態的晶相Form I。然而在對二甲苯溶液中,可以觀察到多種結晶相(如Form III 與 Form II晶相)的成長,以及結晶成長前中間相形成的網路(prior formation of mesophase network)。面對如此豐富的結晶路徑與聚集行為,此研究以X-ray繞射與電子顯微鏡的觀察,逐一探討不同熱歷程下的結晶成長機制,以確認各晶相可以穩定存在的溫度範圍,並推論於聚四甲基一戊烯/對二甲苯溶液系統之相穩定曲線圖(phase stability diagram)。
在0.04%的稀薄P4MP/對二甲苯溶液中,由溶解溫度165℃降溫至65℃至75℃之間,可觀察到Form I晶相在中間相網路中的成長。而降溫至55℃至45℃之間,則觀察到Form III晶相方形單晶的成長,並伴隨著中間相網路的消失。經由自成核(self-seeding)的實驗發現,在有Form I晶核存在下,於55℃亦可發現Form I晶相的成長,但在45℃依然僅有Form III晶相。因此可以推論在55℃至45℃之間,Form III晶相較為穩定。而Form III方形單晶的成長,顯示出經歷一獨立的成核與結晶成長(independent nucleation and growth)過程,使得結晶形態呈現出分子鏈段排列的對稱性。這個實驗觀察證實,中間相網路僅選擇性的幫助Form I晶相成長,而非所有的晶相。而Form I晶相的成長,則是因中間相的存在而有較低的動力學障礙。因此Form I晶相有可能是一較不穩定,卻成長較快速的晶相。
若在165℃降溫至20℃的過程,能夠避開Form I與Form III晶相的成長,則在20℃的持溫可發現Form II晶相的成長。因此推論,在45℃以下較穩定的晶相是Form II晶相。但受限於過冷度(析出趨勢),僅在20℃左右可以有足夠的成長趨勢來發展(需較Form III晶相更快發展出來)。由於這些晶相不會彼此轉變,因此較困難確認其相對的熱力學穩定性,但依據這些實驗觀察,依然可推論出一相穩定曲線圖。
在熔融態與對二甲苯溶液中,於升溫過程可以有截然不同的相變化路徑。溶液中形成的Form III及Form II晶相均在升溫過程,分別在85℃及65℃左右溶解成中間相。而等溫及時的廣角X-ray實驗指出,在沒有對二甲苯溶劑存在下,普遍以固-固相轉變機制(solid-solid transition)直接轉變為Form I晶相。但這樣的固-固相轉變,不僅進行分子鏈在晶相中的位移,亦牽涉分子鏈構形的改變。這樣的實驗結果指出,未參與結晶之分子鏈段於溶液中的狀態,可以對相變化路徑有相當的影響。
The crystallization behavior of poly(4-methylene-1-pentene) (P4MP) in the dilute p-xylene solution was studied via X-ray diffraction and transmission electron microscopy (TEM) in this research. The presence of mesophase was found in the bulk and solution state, and considered as a critical factor for the quick growth of Form I phase. The development of mesophase in the solution is in a form of network, revealing the growth feature of diffusion-controlled process.
The Form I crystal, the only crystalline phase found in the bulk, was recognized to develop within the mesophase network in the 0.04% p-xylene solution in the temperature range from 60℃ to 75℃, or during the quench process by liquid nitrogen. Around 55℃ to 45℃, the Form III square single crystals were able to grow via homogeneous nucleation process, and lead to the dissolution of mesophase network. To further study the stability of Form III in the p-xylene solution, a self-seeding experiment was designed. It was found that, with the presence of Form I nuclei, the square single crystal of Form I can isothermally grow at 55℃, but at 45℃, still only the development of Form I crystals. The revealed crystal growth kinetics suggests that the Form III crystalline form is more stable than the Form I below 55℃.
Indicated by the in-situ x-ray experiment, as the surrounding solvent of p-xylene was completely evaporated, a solid-solid transition from Form III to Form I phase takes place at 60℃. Nevertheless in the dilute p-xylene solution, the grown Form III single crystals dissolved into mesophase above 85℃. Obviously the environmental solvent, p-xylene, stabilized the mesophase, replacing the kinetically-favored transformation pathway to Form I in the bulk state.
At the temperature around 25℃, the Form II crystals grew while the development of Form III and Form I crystals can be avoided during cooling process. The Form II crystals also dissolved into mesophase network above 60℃ in the p-xylene solution, but without the presence of solvent, still transformed to Form I phase via solid-solid transition. This research thus clarifies the growth conditions of three crystalline forms, and mesophase network in the dilute p-xylene solution. Since these crystalline forms do not transform into each other with changing temperatures, it is difficult to completely assure their metastability according to the presence or growth kinetics of these crystals. However, a phase stability diagram has been derived according to obtained results, which provides satisfactory understanding to the observed growth routes and morphologies of crystals developed in the p-xylene solution. However, more investigations for the stability issue are needed and currently underway.
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