成膜溶剂与氟化嵌段共聚物膜的表面富集行为

利用接触角、XPS、SFG、AFM等技术研究了环己酮、甲苯和三氟甲苯为成膜溶剂所得聚甲基丙烯酸甲酯-b-聚（甲基丙烯酸-2-全氟辛基乙酯）（PMMA—b—PFMA）嵌段共聚物膜的表面结构与性能．发现浇铸成膜时成膜溶剂对聚合物氟化组分向表面富集程度的影响相对较小，而旋涂成膜时溶剂的影响很大．不管以何种形式成膜，三氟甲苯溶剂最有利于氟化组分向表面富集，甲苯次之，环己酮最差．这一现象与溶剂的挥发速度无关．聚合物在溶液中的聚集结构、气／液界面结构是造成成膜方式对聚合物表面结构与性能产生巨大影响的主要原因．当聚合物在溶液中形成以PFMA为核、PMMA为冠的胶束结构时，在溶液固化过程中氟化组分向表面富集需要较长的时间，这时由于成膜方法直接影响溶液的固化速度，造成其对氟化组分向表面富集的程度影响很大．当聚合物在溶液中以单分子或松散聚集体存在，在溶液固化过程中氟化组分向表面富集的速度很快，这时成膜方法对氟化组分向表面富集的程度影响很小．以上结果无论对理论研究还是应用研究都具有重要意义．

Effect of solvents on surface segregation behavior of fluorinated block copolymer films

The surface structure and properties of poly（methyl methacrylate）-b-poly （2-perfluorooctylethyl methacrylate） （PMMA-b-PFMA） films, prepared by their cyclohexanone, toluene and benzotrifluoride solutions, were investigated using contact angle measurement, X-ray photoelectron spectroscopy （XPS）, sum frequency generation （SFG） vibrational spectroscopy, atomic force microscopy（AFM）, and so on. The highest surface enrichment of fluorinated moieties was found when the film was prepared by benzotrifluoride solution. However, the film prepared by cyclohexanone solution exhibited the lowest surface segregation regardless of film-formation methods. The reason was mainly attributed to molecular aggregation structure of the copolymer in the solution and interracial structure at the air/liquid, which affects formation of surface structure during film formation. When the copolymers in solution formed micelles composed of a PMMA corona and a PFMA core, the segregation rate of the fluorinated moieties was not high enough, the macromolecules were then ＇frozen＇ into a specific structure as the solvent evaporated, in which parts of the fluorinated moieties were buried in the bulk. Therefore, the extent of fluorine enrichment at the polymer surface was affected greatly by film formation methods. When more free chains are in solution due to the presence of loose and unstable aggregates, faster chain exchange should accordingly occur, with more facile segregation of the perfluoroalkyl side chains on the surface. Thus the extent of fluorine enrichment at the copolymer surface was less affected by film formation methods.