Andruzzi Luisa, Hexemer Alexander, Li Xuefa, Ober Christopher K, Kramer Edward J, Galli Giancarlo, Chiellini Emo, Fischer Daniel A
Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA.
Langmuir. 2004 Nov 23;20(24):10498-506. doi: 10.1021/la049264f.
Surface-grafted styrene-based homopolymer and diblock copolymer brushes bearing semifluorinated alkyl side groups were synthesized by nitroxide-mediated controlled radical polymerization on planar silicon oxide surfaces. The polymer brushes were characterized by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS), and time-dependent water contact angle measurements. Angle-resolved XPS studies and water contact angle measurements showed that, in the case of the diblock copolymer brushes, the second block to be added was always exposed at the polymer-air interface regardless of its surface energy. Values of z*/Rg were estimated based on the radius of gyration, Rg, of the grafted homopolymer or block copolymer chains for the grafted brushes and thickness of the brush, z*. The fact that z*/Rg > 1 suggests that all these brushes are stretched. These results support the idea that after grafting the first block onto the surface the nitroxide-end capped polymer chains were able to polymerize the second block in a "living" fashion and the stretched brush so formed was dense enough that the outermost block in all cases completely covers the surface. NEXAFS analysis showed a relationship between the surface orientation of the fluorinated side chains and brush thickness with thicker brushes having more oriented side chains. Time-dependent water contact angle measurements revealed that the orientation of the side chains of the brush improved the surface stability toward reconstruction upon prolonged exposure to water.
通过氮氧自由基介导的可控自由基聚合反应，在平面氧化硅表面合成了带有半氟化烷基侧基的表面接枝苯乙烯基均聚物和二嵌段共聚物刷。通过X射线光电子能谱（XPS）、近边X射线吸收精细结构（NEXAFS）和随时间变化的水接触角测量对聚合物刷进行了表征。角分辨XPS研究和水接触角测量表明，对于二嵌段共聚物刷，无论其表面能如何，后添加的第二个嵌段总是暴露在聚合物-空气界面处。基于接枝刷的接枝均聚物或嵌段共聚物链的回转半径Rg和刷的厚度z*，估算了z*/Rg的值。z*/Rg > 1这一事实表明所有这些刷都是伸展的。这些结果支持了这样一种观点，即在将第一个嵌段接枝到表面后，氮氧端封聚合物链能够以“活性”方式聚合第二个嵌段，如此形成的伸展刷足够致密，以至于在所有情况下最外层的嵌段完全覆盖了表面。NEXAFS分析表明氟化侧链的表面取向与刷的厚度之间存在关系，较厚的刷具有更多取向的侧链。随时间变化的水接触角测量表明，刷的侧链取向提高了表面在长时间暴露于水时对重构的稳定性。
