在高分子產業中，因為溶劑被廣泛應用於合成、純化和加工製成當中，因此研究溶劑和高分子之間的作用力及其對於高分子結構上的影響是重要的主題。由於雙嵌段共聚物中不同化學性質的鏈段間會因為其互不相容的特性而有微相分離的發生，經由分離強度(χN)和體積分率(f)的調控，進而形成繁雜的奈米尺度結構。添加均聚物亦或是選擇性溶劑也是一種簡潔的方法來調控這些相分離結構，在一些特殊情況下，這甚至可以製造出在純均聚物中不易出現的特殊結構。
在本實驗中，我們利用由聚乙二醇和聚丁二烯組成的團聯式高分子poly(ethylene oxide)-block-poly(butadiene) (簡稱PEO-b-PB)來做為共聚物的來源，和十二烷基苯(dodecyl benzene, 簡稱DB)作為選擇性溶於PB鏈段的溶劑摻混，形成球核是PEO，而PB/DB包覆在外圍殼層的球型微胞所形成的PEO-b-PB/DB微相分離摻混物，並藉由小角度X光散射實驗(SAXS)來系統性地探討其微相分離的型態並建構相圖。在此實驗中發現了部分的新現象，除了在非常低的PEO體積分率下會出現面心立方(FCC)的晶格排列，發現在緊密堆積球(CPS)相中的主要結構是六方最密堆積(HCP)的晶體結構。在HCP相中展現了疊積缺層(stacking fault)的程度變化與溫度相關，在此，疊積缺層的熱力學驅動概論是藉由晶格在相對較低的溫度下，堆疊成HCP和FCC相之間的自由能差異會隨著減少。在高溫下會發現結構從CPS相轉變為體心立方(BCC)的堆疊結構，這是因為升高溫度削弱了晶格位勢(lattice potential)並增強了晶格熵(lattice entropy)的效應。最後，我們確認了在六角柱狀(Hex)相和球狀結構的邊界附近出現了Frank-Kasper (FK) σ相。總體來說，雙嵌段共聚物與選擇性溶劑的混摻物隨著選擇性溶劑的組成增加，呈現了HEXFK σ HCP  FCC 無序微胞(disordered micelle,簡稱DM)相的溶致相轉換(lyotropic phase transition)的發生。
此研究揭示了一種簡單達到由雙嵌段共聚物所形成的多樣的球狀圖譜，特別是很少被觀測到的由HCP相成為微胞主要的緊密堆結構，因此突顯了柔軟的嵌段共聚物微胞與堅硬的膠體粒子之間的差異。此外，我們確認了HCP相中的疊積缺層是源自於熱力學上的因素，這與硬球膠體中來自動力學特性的疊積缺層成為對比。因此，嵌段共聚物混摻物可以做為接下來研究柔軟膠體有序堆排的複雜機制的模型。

Solvent has been widely utilized in polymer industry for synthesis, purification, and processing, so the interaction between solvent and polymer and the effect of such an interaction on the structure of the polymer have been the important subjects of research. Due to the immiscibility of the chemically distinct block chains, block copolymer can produce diverse nanoscale morphology via the microphase separation governed by the segregation strength (χN) and the constituent volume fraction (f). The addition of homopolymer or selective solvent also offers a facile approach for tuning the microphase-separated structure of block copolymers. In some instances, this method can even create the unusual structures not easily formed in the neat copolymer.
In this study, we used poly(ethylene oxide)-block-poly(butadiene) (PEO-b-PB) as the parent copolymer and blended it with dodecyl benzene (DB) which acted as a PB-selective solvent to form the microphase-separated PEO-b-PB/DB mixture in which spherical micelles composed of PEO core and the corona containing PB/DB mixture formed. The microphase-separated morphology of the mixtures was systematically studied by small angle X-ray scattering (SAXS) to establish their phase diagrams. A number of new phenomena were disclosed in this study. It was found that close-packed sphere (CPS) phase dominated the phase window, where hexagonal close-packed (HCP) lattice was the predominant CPS structure except at very low PEO composition where face-centered cubic (FCC) lattice emerged. The HCP phase exhibited temperature-dependent variation of the degree of stacking fault. In this case, the introduction of stacking fault was thermodynamically driven by the decrease of the free energy difference between HCP and FCC packing under the condition of relatively low temperature. The CPS phase was found to transform into body-centered cubic (BCC) packing at the elevated temperature, which was attributed to the weakening of the lattice potential and the strengthening of the lattice entropy effect upon increasing temperature. Finally, we have identified the noncanonical Frank-Kasper (FK) σ phase in the vicinity of the boundary between hexagonally packed cylinder (Hex) phase and sphere phase. Generally speaking the diblock copolymer/selective solvent mixture exhibited the lyotropic phase transition sequence of HexFK σ HCP  FCC  disordered micelle phase with the increase of selective solvent composition.
The present study revealed a simple approach to access a rich spectrum of spherical phase of block copolymer, in particular that the rarely observed HCP phase became the dominant close-packed structure of the micelles, thereby highlighting the difference between soft block copolymer micelle and hard colloidal particle. Moreover, in contrast to the kinetic nature of the stacking fault in hard colloids, here we identified the thermodynamically originated stacking fault in the HCP phase. The block copolymer mixture can hence serve as a model system for further study of the complex mechanism underlying the ordered packing of soft colloids.

Abstract---------------------------------------------------------I
中文摘要----------------------------------------------------------III
Contents---------------------------------------------------------V
Figure contents--------------------------------------------------VII
Table contents---------------------------------------------------XII
Chapter 1 Introduction-------------------------------------------1
1.1 Phase behavior of diblock copolymer--------------------------1
1.1.1 Phase behavior of diblock copolymer in neat block copolymer-1
1.1.2 Phase behavior of diblock copolymer in block copolymer/homopolymer blends-------------------------------------5
1.1.3 Phase behavior of diblock copolymer in block copolymer/selective solvent blends-------------------------------8
1.2 Lattice structures of block copolymer in sphere phase--------14
1.2.1 Body-centered cubic (BCC) lattice--------------------------14
1.2.2 Close-packed sphere (CPS) lattices-------------------------18
1.2.3 Frank Kasper (FK) phase------------------------------------22
1.3 Research motivation------------------------------------------26
Chapter 2 Experimental section-----------------------------------29
2.1 Materials----------------------------------------------------29
2.2 Small angle X-ray scattering (SAXS) measurement--------------32
2.3 Lattice identification for SAXS profile----------------------33
2.3.1 FK σ phase-------------------------------------------------33
2.3.2 CPS phase with stacking fault------------------------------35
Chapter 3 Result & Discussion------------------------------------38
3.1 Mixtures of a compositionally asymmetric PEO-b-PB and DB-----38
3.2 Mixtures of a compositionally symmetric PEO-b-PB and DB------53
3.3 Discussion---------------------------------------------------65
3.3.1 Effects of the molecular weight and composition of the neat diblock on the HEX-Sphere phase boundary-------------------------68
3.3.2 The emergence of FK σ phase and the temperature-dependent structural order of σ phase--------------------------------------70
3.3.3 The thermodynamic origin of the temperature-dependent degree of stacking fault in HCP phase-----------------------------------76
3.3.4 The stability of the high-temperature BCC phase------------84
Chapter 4 Conclusions--------------------------------------------86
Chapter 5 Reference----------------------------------------------89

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