Recently, block copolymers comprising chiral entities, denoted as chiral block copolymers (BCP*s), have been designed in our laboratory, and a helical phase (denoted H* to distinguish its P622 symmetry from that of the normal hexagonally packed cylinder phase, denoted H with P6/mmm symmetry) was discovered in the self-assembly of poly(styrene)-b-poly(L-lactide) (PS-PLLA) BCPs*. The H* phase was found to be a long-lived metastable phase at which the H* phase will transform to thermodynamically stable phases such as double gyroid (DG) phase through order-order transition after long-time thermal annealing.
Here, we suggest a facile method to fabricate DG phase with long-range ordering for the PS-PLLA from blending. Unlike the conventional way for blending of BCP with homopolymer, the PS-PLLA blends are prepared by using styrene oligomer (SO) to fine-tune the morphologies of the blends. The DG-forming composition window can be enlarged by blending H*-forming PS-PLLA with styrene oligomers, and also the phase transformation from the H* to DG can be expedited due to the increase of chain mobility. Consequently, by taking advantage of degradable character of the PLLA, nanoporous gyroid SiO2 can be fabricated by using hydrolyzed PS-PLLA as a template for sol-gel reaction followed by removal of the PS matrix. This may provide a facile way to prepare large-scale, well-ordered nanoporous gyroid inorganic materials for practical applications in optics, optoelectronics and metamaterials.
To satisfy the requirements for practical applications, we aim to carry out oscillatory shear method for the induced orientation of self-assembled PS-PLLA nanostructures. With the control of rheology in BCP melt, large-scale oriented BCP nanostructures can be achieved at which oscillatory shear is one of the most widely used methods. In this study, combined SAXS experiments and rheological measurements are carried out to examine the induced orientation of DG-forming PS-PLLA. An interesting phase transition from DG phase to disorder continuous phase can be found after large amplitude oscillatory shear (LAOS) at the temperature above an order-disorder-like transition temperature. Most interestingly, the disorder continuous phase will gradually transform to well-defined DG phase with the [111] direction along the shear direction. We speculate that the long-range ordering of DG phase is achieved by nucleation and growth resulting from the shear stress relaxation at temperature below the order-disorder-like transition temperature.
Moreover, in contrast to the PS-rich polylactide-containing BCPs*, we aim to systematically examine the phase behavior of PLLA-rich polylactide-containing BCPs*. Similar to the blends of BCP/styrene oligomer, the blends composition can be fine-tuned using racemic lactide (LA) oligomer to enrich the phase behavior of self-assembled polylatide-containing BCPs* with polylactide-rich blends. Unlike the blends of PS-PLLA/styrene oligomers, addition of LA will lead to phase transition from lamellae to cylinder only when r value ( r=Mnh,LA/Mnb,PLLA) is smaller than 0.2. While r value is between 0.2 to one, the introduced LA oligomer will be localized in the central area of the PLLA microdomain so that there is no phase transformation due to the unchanged of interfacial mean curvature. We speculate that the discrepancy in the phase behaviors of PS-rich and PLLA-rich blends is attributed to the incompatibility of PLLA and LA.

Recently, block copolymers comprising chiral entities, denoted as chiral block copolymers (BCP*s), have been designed in our laboratory, and a helical phase (denoted H* to distinguish its P622 symmetry from that of the normal hexagonally packed cylinder phase, denoted H with P6/mmm symmetry) was discovered in the self-assembly of poly(styrene)-b-poly(L-lactide) (PS-PLLA) BCPs*. The H* phase was found to be a long-lived metastable phase at which the H* phase will transform to thermodynamically stable phases such as double gyroid (DG) phase through order-order transition after long-time thermal annealing.
Here, we suggest a facile method to fabricate DG phase with long-range ordering for the PS-PLLA from blending. Unlike the conventional way for blending of BCP with homopolymer, the PS-PLLA blends are prepared by using styrene oligomer (SO) to fine-tune the morphologies of the blends. The DG-forming composition window can be enlarged by blending H*-forming PS-PLLA with styrene oligomers, and also the phase transformation from the H* to DG can be expedited due to the increase of chain mobility. Consequently, by taking advantage of degradable character of the PLLA, nanoporous gyroid SiO2 can be fabricated by using hydrolyzed PS-PLLA as a template for sol-gel reaction followed by removal of the PS matrix. This may provide a facile way to prepare large-scale, well-ordered nanoporous gyroid inorganic materials for practical applications in optics, optoelectronics and metamaterials.
To satisfy the requirements for practical applications, we aim to carry out oscillatory shear method for the induced orientation of self-assembled PS-PLLA nanostructures. With the control of rheology in BCP melt, large-scale oriented BCP nanostructures can be achieved at which oscillatory shear is one of the most widely used methods. In this study, combined SAXS experiments and rheological measurements are carried out to examine the induced orientation of DG-forming PS-PLLA. An interesting phase transition from DG phase to disorder continuous phase can be found after large amplitude oscillatory shear (LAOS) at the temperature above an order-disorder-like transition temperature. Most interestingly, the disorder continuous phase will gradually transform to well-defined DG phase with the [111] direction along the shear direction. We speculate that the long-range ordering of DG phase is achieved by nucleation and growth resulting from the shear stress relaxation at temperature below the order-disorder-like transition temperature.
Moreover, in contrast to the PS-rich polylactide-containing BCPs*, we aim to systematically examine the phase behavior of PLLA-rich polylactide-containing BCPs*. Similar to the blends of BCP/styrene oligomer, the blends composition can be fine-tuned using racemic lactide (LA) oligomer to enrich the phase behavior of self-assembled polylatide-containing BCPs* with polylactide-rich blends. Unlike the blends of PS-PLLA/styrene oligomers, addition of LA will lead to phase transition from lamellae to cylinder only when r value ( r=Mnh,LA/Mnb,PLLA) is smaller than 0.2. While r value is between 0.2 to one, the introduced LA oligomer will be localized in the central area of the PLLA microdomain so that there is no phase transformation due to the unchanged of interfacial mean curvature. We speculate that the discrepancy in the phase behaviors of PS-rich and PLLA-rich blends is attributed to the incompatibility of PLLA and LA.

Chapter 1 Introduction 1
1.1 Self-assembly of Chiral Block Copolymers 1
1.2 Helical Structures from Self-assembly 4
1.2.1 Metastability of helical phase (H*) 5
1.2.2 Helical phase to double gyroid in chiral block copolymers 6
1.3 Phase Behavior of BCP and Homopolymer Blends 10
1.3.1 Dry brush in BCP/homopolymer blends 14
1.3.2 Wet brush in BCP/homopolymer blends 15
1.3.3 Continuous network morphologies in AB/A blends 17
1.3.4 Scaling behavior of D with χ or χeff 22
1.4 Templating from Block Copolymers 25
1.5 Large Amplitude Oscillatory Shear 28
1.5.1 LAOS applicating for lamellar and cylinder phase 29
1.5.2 LAOS applicating for BCC spheres and DG phase 32
1.5.3 Shear orientation for a DG diblock copolymer 35
1.5.4 Shear instability of a DG diblock copolymer 38
Chapter 2 Objectives 41
Chapter 3 Materials and Experimental Methods 43
3.1 Synthesis of Chiral Block Copolymer 43
3.1.1 Double-headed initiator (DHI) 43
3.1.2 Hydroxyl-terminated polystyrene (PS-OH) 44
3.1.3 Copolymerization of PS-PLLA 45
3.1.4 Nuclear magnetic resonance spectroscopy (NMR) 47
3.1.5 Gel permeation chromatography (GPC) 47
3.2 Nanostructure Characterization 48
3.2.1 Small angle X-ray scattering (SAXS) 48
3.2.2 Transmission electron microscopy (TEM) 48
3.2.3 Field-emission scanning electron microscopy (FESEM) 49
3.2.4 Thermogravimetric analysis (TGA) 49
3.3 Blending Methods 50
3.4 Hydrolysis for PS Templates 50
3.5 Sol-gel Reaction for Preparing SiO2 Nanoporous Templates 51
3.6 Rheology-SAXS Measurement 51
Chapter 4 Results and Discussion 53
4.1 Microphase Separation of PS-PLLA 53
4.2 Phase Behavior of PS-PLLA and Styrene Homopolymer or Oligomer Blends 57
4.2.1 Phase behavior in dry brush region 57
4.2.2 Phase transition from lamellae to helix in wet brush region 60
4.2.3 Phase behavior in wet brush region 62
4.2.4 Phase transfer from helix to DG with styrene oligomer (SO) 65
4.2.5 Effect of r on gyroid-forming in PS-PLLA/SO blends 67
4.3 Nanoporous Polymers 71
4.4 Shear Induced Orientation for DG 75
4.4.1 Thermal properties and behaviors of PS-PLLA 75
4.4.2 Transition temperature from DG to disorder continuous phase 77
4.4.3 Oscillatory shear for induced orientation 83
4.4.4 Large amplitude oscillatory shear (LAOS) for DG 85
4.5 Phase Diagram of PLLA-rich Polylactide-containing BCPs* and LAO Blends 94
4.5.1 Microphase separation of PLLA-rich PS-PLLA BCPs* 94
4.5.2 Difference between BCP/LLAO and BCP/LAO Blends 95
Chapter 5 Conclusion 103
Chapter 6 References 106

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