Sunday Daniel F, Thelen Jacob L, Zhou Chun, Ren Jiaxing, Nealey Paul F, Kline R Joseph
Materials Science and Engineering Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899, United States.
Institute for Molecular Engineering, University of Chicago, 5801 S Ellis Ave, Chicago, Illinois 60637, United States.
ACS Nano. 2021 Jun 22;15(6):9577-9587. doi: 10.1021/acsnano.0c09907. Epub 2021 May 20.
Interactions between polymers and surfaces can be used to influence properties including mechanical performance in nanocomposites, the glass transition temperature, and the orientation of thin film block copolymers (BCPs). In this work we investigate how specific interactions between the substrate and BCPs with varying substrate affinity impact the interfacial width between polymer components. The interface width is generally assumed to be a function of the BCP properties and independent of the surface affinity or substrate proximity. Using resonant soft X-ray reflectivity the optical constants of the film can be controlled by changing the incident energy, thereby varying the depth sensitivity of the measurement. Resonant soft X-ray reflectivity measurements were conducted on films of polystyrene--poly(2-vinylpyridine) (PS--P2VP) and PS--poly(methyl methacrylate) (PS--PMMA), where the thickness of the film was varied from half the periodicity () of the BCP to 5.5 . The results of this measurement on the PS--P2VP films show a significant expansion of the interface width immediately adjacent to the surface. This is likely caused by the strong adsorption of P2VP to the substrate, which constrains the mobility of the junction points, preventing them from reaching their equilibrium distribution and expanding the observed interface width. The interface width decays toward equilibrium moving away from the substrate, with the decay rate being a function of film thickness below a critical limit. The PMMA block appears to be more mobile, and the BCP interfaces near the substrate match their equilibrium value.
聚合物与表面之间的相互作用可用于影响多种性能，包括纳米复合材料的机械性能、玻璃化转变温度以及薄膜嵌段共聚物（BCP）的取向。在这项工作中，我们研究了具有不同底物亲和力的底物与BCP之间的特定相互作用如何影响聚合物组分之间的界面宽度。通常认为界面宽度是BCP性质的函数，与表面亲和力或底物距离无关。利用共振软X射线反射率，通过改变入射能量可以控制薄膜的光学常数，从而改变测量的深度灵敏度。对聚苯乙烯-聚（2-乙烯基吡啶）（PS-P2VP）和聚苯乙烯-聚（甲基丙烯酸甲酯）（PS-PMMA）薄膜进行了共振软X射线反射率测量，其中薄膜厚度从BCP的半周期（）变化到5.5 。对PS-P2VP薄膜的测量结果表明，紧邻表面的界面宽度显著扩大。这可能是由于P2VP对底物的强烈吸附，限制了连接点的迁移率，阻止它们达到平衡分布并扩大了观察到的界面宽度。远离底物时，界面宽度向平衡衰减，衰减速率是低于临界极限的薄膜厚度的函数。PMMA嵌段似乎更具流动性，靠近底物的BCP界面与它们的平衡值匹配。
