College of Material, Chemistry and Chemical Engineering, Hangzhou Normal University, No. 16 Xuelin Rd., Xiasha High-tech Zone, Hangzhou 310036, People's Republic of China.
J Chem Phys. 2013 Jun 28;138(24):244907. doi: 10.1063/1.4811471.
The competition between "dewetting" and "phase separation" behaviors in polymer blend films attracts significant attention in the last decade. The simultaneous phase separation and dewetting in PMMA∕SAN [poly(methyl methacrylate) and poly(styrene-ran-acrylonitrile)] blend ultrathin films upon solvent annealing have been observed for the first time in our previous work. In this work, film thickness and annealing solvent dependence of phase behaviors in this system has been investigated using atomic force microscopy and grazing incidence small-angle X-ray scattering (GISAXS). On one hand, both vertical phase separation and dewetting take place upon selective solvent vapor annealing, leading to the formation of droplet∕mimic-film structures with various sizes (depending on original film thickness). On the other hand, the whole blend film dewets the substrate and produces dispersed droplets on the silicon oxide upon common solvent annealing. GISAXS results demonstrate the phase separation in the big dewetted droplets resulted from the thicker film (39.8 nm). In contrast, no period structure is detected in small droplets from the thinner film (5.1 nm and 9.7 nm). This investigation indicates that dewetting and phase separation in PMMA∕SAN blend film upon solvent annealing depend crucially on the film thickness and the atmosphere during annealing.
在过去的十年中，聚合物共混膜中“去湿”和“相分离”行为的竞争引起了人们的极大关注。我们之前的工作首次观察到 PMMA/SAN（聚甲基丙烯酸甲酯和苯乙烯-丙烯腈共聚物）共混超薄膜在溶剂退火时同时发生相分离和去湿。在这项工作中，使用原子力显微镜和掠入射小角 X 射线散射（GISAXS）研究了该体系中相行为对膜厚和退火溶剂的依赖性。一方面，在选择溶剂蒸汽退火时，会发生垂直相分离和去湿，导致形成具有各种尺寸的液滴/模拟膜结构（取决于原始膜厚）。另一方面，在普通溶剂退火时，整个共混膜会在氧化硅上离析基底并产生分散的液滴。GISAXS 结果表明，较厚膜（39.8nm）中较大去湿液滴的相分离。相比之下，较薄膜（5.1nm 和 9.7nm）中的小液滴中未检测到周期结构。这项研究表明，溶剂退火时 PMMA/SAN 共混膜中的去湿和相分离取决于膜厚和退火时的气氛。
