Surface segregation of fluorinated moieties on random copolymer films controlled by random-coil conformation of polymer chains in solution.
Surface segregation of fluorinated moieties on random copolymer films controlled by random-coil conformation of polymer chains in solution.
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DOI：
10.1021/la803409c
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发表时间：
2009-01
期刊：
影响因子：
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通讯作者：
Dongwu Xue;Xinping Wang;H. Ni;Wei Zhang;G. Xue
中科院分区：
文献类型：
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作者：
Dongwu Xue;Xinping Wang;H. Ni;Wei Zhang;G. Xue
通过接触角测量、X射线光电子能谱、和频振动光谱和表面张力测量，研究了由甲基丙烯酸丁酯和甲基丙烯酸十二氟庚酯（DFHMA）组成的无规共聚物的溶液性质、成膜方法和固体表面结构之间的关系。基于热力学考虑，结果表明溶液/空气界面处的无规共聚物链构象极大地影响了所得薄膜的表面结构，从而决定了通过各种成膜技术获得的薄膜上氟化部分的表面偏析。当共聚物溶液中的氟化单体含量较低时，熵力主导界面结构，全氟烷基无法迁移到溶液/空气界面，从而埋藏在无规螺旋链构象中。当使用该共聚物溶液通过旋涂制备薄膜时，溶液中的共聚物链可能由于离心力而延伸，从而削弱了聚合物链的熵效应。因此，这导致氟化部分在薄膜表面上分离。对于通过流延制备的薄膜，与溶液中的类似，全氟烷基不能在薄膜表面偏析，因此被埋在无规卷曲链中。当共聚物含有高含量的DFHMA时，全氟烷基在溶液/空气界面的迁移受到焓力的控制，并且无论成膜技术如何，全氟烷基都会在薄膜表面偏析。本工作的目的是加深对聚合物薄膜表面化学结构形成机制的理解，同时证明成膜方法可在实践中用于促进薄膜表面氟化部分的分离。
The relationship between solution properties, film-forming methods, and the solid surface structures of random copolymers composed of butyl methacrylate and dodecafluorheptyl methylacrylate (DFHMA) was investigated by contact angle measurements, X-ray photoelectron spectroscopy, sum frequency generation vibrational spectroscopy, and surface tension measurements. The results, based on thermodynamic considerations, demonstrated that the random copolymer chain conformation at the solution/air interface greatly affected the surface structure of the resulting film, thereby determining the surface segregation of fluorinated moieties on films obtained by various film-forming techniques. When the fluorinated monomer content of the copolymer solution was low, entropic forces dominated the interfacial structure, with the perfluoroalkyl groups unable to migrate to the solution/air interface and thus becoming buried in a random-coil chain conformation. When employing this copolymer solution for film preparation by spin-coating, the copolymer chains in solution were likely extended due to centrifugal forces, thereby weakening the entropy effect of the polymer chains. Consequently, this resulted in the segregation of the fluorinated moieties on the film surface. For the films prepared by casting, the perfluoroalkyl groups were, similar to those in solution, incapable of segregating at the film surface and were thus buried in the random-coil chains. When the copolymers contained a high content of DFHMA, the migration of perfluoroalkyl groups at the solution/air interface was controlled by enthalpic forces, and the perfluoroalkyl groups segregated at the surface of the film regardless of the film-forming technique. The aim of the present work was to obtain an enhanced understanding of the formation mechanism of the chemical structure on the surface of the polymer film, while demonstrating that film-forming methods may be used in practice to promote the segregation of fluorinated moieties on film surfaces.