掌性嵌段共聚物與其寡聚物混摻系統的相行為研究

Phase Behaviors of Chiral Block Copolymer and Oligomer Blends

余呂宏(Yu, Luhong)

指導教授 ： 何榮銘

國立清華大學/工學院/化學工程學系/碩士(2013年)

摘要

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.

關鍵字

掌性 ； 嵌段共聚物 ； 混摻 ； 螺旋24面體結構 ； 螺旋奈米陣列

並列摘要

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.

並列關鍵字

chiral ； block copolymer ； blends ； double gyroid ； helix

參考文獻

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