嵌段共聚物的微相分離可產生多種長程有序的奈米結構，影響奈米結構的重要參數包含Flory-Huggins interaction parameter (χ)、聚合度(N)以及體積分率(fA)，其中，χN的乘積稱為分離強度。根據χN與體積分率作圖建立而成的相圖除了包含有序結構區域外，還存在著無序狀態的區域，伴隨著分離強度χN的下降，共聚物會從有序狀態轉化到無序狀態，此相變程序稱為『有序-無序轉化』(order-disorder transition, 簡稱ODT)。

根據隨溫度變化所進行的相轉化方向，嵌段共聚物的ODT可以分為高臨界有序化(upper critical ordering transition, UCOT)與極其罕見的低臨界有序化(lower critical ordering transition, LCOT)。呈現UCOT的系統可經由升溫將有序狀態轉變成無序狀態，即ODT發生在升溫的程序。反之，LCOT系統之ODT發生於降溫程序，該現象與均聚物摻合體之LCST現象類似，乃是由於共聚物中鏈段之熱膨脹係數明顯差異所致。大多數的嵌段共聚物系統呈現UCOT的行為，但在極其少數的系統可觀察到LCOT的現象。本論文特別針對極其罕見的LCOT嵌段共聚物系統進行系統性的研究，在本研究中，我們將依序揭露該系統所具有之特性，實驗上所使用的雙嵌段共聚物是poly(ethylene oxide)-block-poly(4-vinyl pyridine) (PEO-b-P4VP)。

本論文的第一部分揭露PEO-b-P4VP形成之層狀奈米結構之界面發生異常緻密化(densification)的特殊現象，與此同時，界面密度分佈偏離傳統的雙曲正切函數(hyperbolic tangent function)，整體的電子密度分佈可用三相模型描述。本論文的第二部分將具有LCOT行為的PEO-b-P4VP摻混P4VP均聚物，並探討均聚物在P4VP微相中的溶解行為，結果顯示傳統UCOT系統的濕刷型溶解條件仍可適用於LCOT摻合體。我們進一步發現，摻混均聚物P4VP會導致表面自由能降低，進而誘導共聚物鏈段連結點(junction point)之間的距離過度膨潤。本論文的第三部分揭露PEO-b-P4VP/P4VP均聚物摻合體的層板-圓柱結構相轉化現象，有別於UCOT系統中的有序-有序之相轉化，該系統之層板到圓柱結構的轉化是在冷卻過程發生，此為該摻合系統之LCOT行為提供了更進一步確切的證據。

在LCOT系統中，自由體積與熱膨脹效應對於自由能扮演著舉足輕重的地位，我們認為本論文之實驗結果皆是LCOT系統中才會有的獨特現象。

Block copolymers constitute a fascinating class of soft material whose great feature lies in their capability of self-assembling into a broad spectrum of long-range ordered nanostructures. The theories of AB diblock copolymer have been well developed for predicting the thermodynamic stabilities of various mesophases and the spinodal lines. Melt incompressibility is a typical assumption made in the calculation of the phase diagram, and the Flory-Huggins interaction parameter χ was assumed to decrease with increasing temperature. In this case, the segregation strength decreases with increasing temperature, such that the order-disorder transition (ODT) occurs on heating. The diblock copolymer is said to display the “upper critical ordering transition” (UCOT) behavior.

For the diblock copolymers in which the constituent blocks possess significantly different thermal expansion coefficients, there is an additional entropic component in free energy arising from the reduction of entropy of the more expansive component when it is mixed with the less expansive one. Such an effect creates a stronger repulsive force between the constituent blocks at higher temperature; leading to a larger segregation strength. In this case, the ODT may occur upon cooling, and the system is said to display “lower critical ordering transition” (LCOT) behavior.

Most diblock copolymer systems exhibit the UCOT behavior, while LCOT was rarely observed. This thesis is dedicated to the studies of the special features associated with diblock copolymer systems displaying LCOT behavior. The diblock copolymer investigated was poly(ethylene oxide)-block-poly(4-vinylpyridine) (PEO-b-P4VP). Three special features of the diblock system were disclosed here, namely, (1) interfacial densification where a local zone in the microdomain interface displayed the highest density, causing a deviation of the interfacial density profile from the classical hyperbolic tangent function; (2) peculiar homopolymer solubilization behavior in the wet-brush blend of PEO-b-4VP with P4VP homopolymer, where the incorporation of homopolymer reduced the surface free energy and in turn led to an excessive swelling of the junction point separation; (3) order-order transition from lamellar morphology to cylinder structure on cooling, which was in opposite direction to the OOT displayed by UCOT system. All these phenomena were unique to LCOT systems, in particular that the constraint of the free volume of the more expansive EO segments imposed by the mixing with the 4VP segments in the interface played an important role underlying the phenomena observed.

Abstract I
中文摘要 III
Table of Contents V
List of Tables VIII
List of Figures IX

Chapter 1. Introduction 1
1-1. Background of Research 1
1-1-1. Phase Behavior of Diblock Copolymer 1
1-1-2. Theories of Microphase Separation in Block Copolymer 4
1-1-3. Phase Behavior of the Blends of Block Copolymer and the Corresponding Homopolymer 11
1-1-4. Lower Critical Ordering Transition of Block Copolymer 16
1-2. Objective of Research and Overview of Thesis 25
1-3. References and Notes 29

Chapter 2. Interface Densification in Microphase-separated Diblock Copolymer Displaying Lower Critical Ordering Transition 32
2-1. Introduction 32
2-2. Experimental Section 36
2-2-1. Materials 36
2-2-2. Sample Preparation 37
2-2-3. Small Angle X-ray Scattering (SAXS) Measurement 37
2-2-4. PVT Measurement 38
2-3. Results and Discussion 39
2-4. Conclusions 56
2-5. References and Notes 57

Chapter 3. Homopolymer Solubilization in the Blends of Diblock Copolymer and the Corresponding Homopolymer Displaying Lower Critical Ordering Transition Behavior 59
3-1. Introduction 59
3-2. Experimental Section 62
3-2-1. Materials 62
3-2-2. Sample Preparation 63
3-2-3. Small Angle X-ray Scattering (SAXS) Measurement 65
3-3. Results and Discussion 66
3-3-1. LCOT Phase Behavior of EO4VP01/H4VP01 Blends 66
3-3-2. Composition Dependence of Domain Spacing and Junction Point Separation 70
3-3-3. Homopolymer Solubilization Behavior Deduced from the Comparison with Hashimoto’s Model 76
3-3-4. Thermodynamic Reasoning for the Perturbation of Surface Free Energy 80
3-4. Conclusions 82
3-5. References and Notes 83

Chapter 4. LAM-HEX Transition of Diblock Copolymer/Homopolymer Blend Displaying Lower Critical Ordering Transition 86
4-1. Introduction 86
4-2. Experimental Section 89
4-2-1. Materials 89
4-2-2. Sample Preparation 90
4-2-3. Small Angle X-ray Scattering (SAXS) Measurement 91
4-3. Results and Discussion 92
4-3-1. Phase Behavior of EO4VP02 and EO4VP02/H4VP01 Blends 92
4-3-2. Effect of Blend Composition on TOOT 102
4-4. Conclusions 106
4-5. References and Notes 107

Chapter 5. Overall Summery 109

List of Publications 112

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