Paik Marvin Y, Bosworth Joan K, Smilges Detlef-M, Schwartz Evan L, Andre Xavier, Ober Christopher K
Department of Materials Science and Engineering, Cornell University, Ithaca, NY, 14850.
Macromolecules. 2010 Nov 5;43(9):4253-4260. doi: 10.1021/ma902646t.
The real time changes occurring within films of cylinder-forming poly(α-methylstyrene-block-4-hydroxystyrene) (PαMS-b-PHOST) were monitored as they were swollen in tetrahydrofuran (THF) and acetone solvent vapors. In situ information was obtained by combining grazing incidence small angle X-ray scattering (GISAXS) with film thickness monitoring of the solvent vapor swollen films. We show that for self assembly to occur, the polymer thin film must surpass a swollen thickness ratio of 212% of its original thickness when swollen in THF vapors and a ratio of 268% for acetone vapor annealing. As the polymer becomes plasticized by solvent vapor uptake, the polymer chains must become sufficiently mobile to self assemble, or reorganize, at room temperature. Using vapors of a solvent selective to one of the blocks, in our case PHOST-selective acetone, an order-order transition occured driven by the shift in volume fraction. The BCC spherical phase assumed in the highly swollen state can be quenched by rapid drying. Upon treatment with vapor of a non-selective solvent, THF, the film maintained the cylindrical morphology suggested by its dry-state volume fraction. In situ studies indicate that self-assembly occurs spontaneously upon attaining the threshold swelling ratios.
监测了圆柱形聚（α-甲基苯乙烯-嵌段-4-羟基苯乙烯）（PαMS-b-PHOST）薄膜在四氢呋喃（THF）和丙酮溶剂蒸汽中溶胀时的实时变化。通过将掠入射小角X射线散射（GISAXS）与溶剂蒸汽溶胀薄膜的膜厚监测相结合，获得了原位信息。我们表明，为了发生自组装，聚合物薄膜在THF蒸汽中溶胀时，其溶胀厚度必须超过原始厚度的212%，在丙酮蒸汽退火时该比例为268%。随着聚合物因吸收溶剂蒸汽而增塑，聚合物链必须变得足够可移动，以便在室温下进行自组装或重新组织。使用对其中一个嵌段具有选择性的溶剂蒸汽，在我们的例子中是对PHOST具有选择性的丙酮，由体积分数的变化驱动发生了有序-有序转变。高度溶胀状态下呈现的体心立方球形相可以通过快速干燥来猝灭。用非选择性溶剂THF的蒸汽处理后，薄膜保持了由其干燥状态体积分数所暗示的圆柱形形态。原位研究表明，达到阈值溶胀比后自组装会自发发生。
