高等学校化学学报 ›› 2014, Vol. 35 ›› Issue (8): 1799-1809.doi: 10.7503/cjcu20140330

• 高分子化学 • 上一篇    下一篇

对称柔性-半刚性-柔性三嵌段共聚物自组装行为

杨光1(), 王传明1, 唐萍2, 顾松园1   

  1. 1. 上海石油化工研究院, 中国石油化工有限公司, 上海 201208
    2. 聚合物分子工程国家重点实验室, 复旦大学高分子科学系, 上海 200433
  • 收稿日期:2014-04-08 出版日期:2014-08-10 发布日期:2019-08-01
  • 作者简介:联系人简介: 杨 光, 女, 博士, 工程师, 主要从事高分子凝聚态物理研究. E-mail: yangg.sshy@sinopec.com
  • 基金资助:
    国家自然科学基金(批准号: 21304109, 91127033)资助

Self-assembling Behavior of Symmetric Coil-semiflexible-coil Triblock Copolymers

YANG Guang1,*(), WANG Chuanming1, TANG Ping2, GU Songyuan1   

  1. 1. Shanghai Research Institute of Petrochemical Technology, China Petroleum & Chemical Corporation, Shanghai 201208, China
    2. Key Laboratory of Molecular Engineering of Polymer, and Department of Macromolecular Science, Fudan University, Shanghai 200433, China
  • Received:2014-04-08 Online:2014-08-10 Published:2019-08-01
  • Contact: YANG Guang E-mail:yangg.sshy@sinopec.com
  • Supported by:
    Supported by the National Natural Science Foundation of China(Nos.21304109, 91127033)

摘要:

基于蠕虫状链模型和高斯链模型的自洽场理论研究了对称柔性-半刚性-柔性三嵌段共聚物在二维空间中的相行为. 在设定的计算参数下得到了多种该体系的热力学平衡态相结构, 包括各向同性Isotropic相、 各向异性Nematic相、 层状Smectic-C相、 四角柱状相、 斜交型冰球状相、 断层型冰球状相和稻粒状结构. 与刚-柔两嵌段共聚物相比, 对称柔性-半刚性-柔性三嵌段共聚物更容易形成Smectic-C相. 在柱状相结构中, 在柔性嵌段的牵伸作用下半刚性嵌段在液晶相区中相互穿插, 从而形成菱形和长方形液晶相区. 当取向相互作用较强时, 半刚性嵌段沿长方形液晶相区的短边方向出现2次折叠. 为进一步探索高分子折叠现象产生的原因以及液晶成核机理奠定了理论基础.

关键词: 对称柔性-半刚性-柔性三嵌段共聚物, 自洽场理论, 蠕虫状链模型, 自组装, 链折叠, 液晶成核机理

Abstract:

The self-assembly of symmetric coil-semiflexible-coil triblock copolymers in 2D space was investigated using self-consistent field theory(SCFT). The semiflexible block and the coil block of the copolymers were described as wormlike chain model, and Gaussian chain model, respectively. A highly accurate and efficient operator splitting pseudospectral algorithm combined with SPHEREPACK software package was employed to solve modified diffusion equations for the propagators of wormlike chains. The anisotropic interactions favoring the parallel alignment between semiflexible segments was described by Maier-Saupe orientational interactions μN, and the enthalpic interactions between coil and semiflexible segments were described by isotro-pic Flory-Huggins interactions χN. By increasing χN and volume fraction of the coil blocks, a phase diagram including isotropic, nematic, smectic-C, tetragonal cylinders, oblique pucks, broken lamella pucks and rice-shaped phase for symmetric coil-semiflexible-coil triblock copolymers was built. At relatively low coil fractions and strong interactions, semctic-C phases were readily formed because the strong chain-stretching energy, which came from the highly ordered orientation of semiflexible blocks, dominates the system free energy. In the meanwhile, the stretch from two coil sides to the bridged semiflexble block results in a higher chain-stretching energy. Therefore, more smectic-C phases formed than that in biblock copolymers. The tetragonal cylinders exhibiting weak segregation were obtained in the region of coil fractions from 0.5 to 0.6. With the increase of coil fractions and orientational interactions, hexagonal packed pucks were found. In the rhombus and rectangle liquid crystal domain, the coil-semiflexible block junctions were observed at opposite sides, therefore a cross-link conformation of the semiflexible blocks was produced. More interestingly, the semiflexible chain folds twice along the short side of the rectangle liquid crystal domain of the oblique pucks at coil fraction 0.6 and broken lamella pucks at coil fraction 0.7. Chain folding behavior increases the interfaces between coils and semiflexible blocks allowing for the coils with larger fractions to gain conformational entropy. When the coil fraction is 0.8, chain folding behavior decreases and the semiflexible blocks orient along the long side of the rectangle liquid crystal domain, forming rice-shaped phase. These simulation results are of paramount importance in rationalizing chain folding phenomena and understanding the nucleation mechanism of liquid crystals.

Key words: Symmetric coil-semiflexible-coil triblock copolymer, Self-consistent field theory(SCFT), Wormlike chain model, Self-assembly, Chain folding, Nucleation mechanism of liquid crystal

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