Morphological Evolution of Gyroid-Forming Block Copolymer Thin Films with Varying Solvent Evaporation Rate
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- 作者：Yi-Hsiu Wu ; Ting-Ya Lo ; Ming-Shiuan She ; Rong-Ming Ho
- 刊名：ACS Applied Materials & Interfaces
- 出版年：2015
- 出版时间：August 5, 2015
- 年：2015
- 卷：7
- 期：30
- 页码：16536-16547
- 全文大小：935K
- ISSN：1944-8252
文摘
In this study, we aim to examine the morphological evolution of block copolymer (BCP) nanostructured thin films through solvent evaporation at different rates for solvent swollen polystyrene-block-poly(l-lactide) (PS鈥揚LLA). Interesting phase transitions from disorder to perpendicular cylinder and then gyroid can be found while using a partially selective solvent for PS to swell PS鈥揚LLA thin film followed by solvent evaporation. During the transitions, gyroid-forming BCP thin film with characteristic crystallographic planes of (111)G, (110)G, and (211)G parallel to air surface can be observed, and will gradually transform into coexisting (110)G and (211)G planes, and finally transforms to (211)G plane due to the preferential segregation of constituted block to the surface (i.e., the thermodynamic origin for self-assembly) that affects the relative amount of each component at the air surface. With the decrease on the evaporation rate, the disorder phase will transform to parallel cylinder and then directly to (211)G without transition to perpendicular cylinder phase. Most importantly, the morphological evolution of PS鈥揚LLA thin films is strongly dependent upon the solvent removal rate only in the initial stage of the evaporation process due to the anisotropy of cylinder structure. Once the morphology is transformed back to the isotropic gyroid structure after long evaporation, the morphological evolution will only relate to the variation of the surface composition. Similar phase transitions at the substrate can also be obtained by controlling the ratio of PLLA鈥揙H to PS鈥揙H homopolymers to functionalize the substrate. As a result, the fabrication of well-defined nanostructured thin films with controlled orientation can be achieved by simple swelling and deswelling with controlled evaporation rate.