Zhang Xiaohua, Berry Brian C, Yager Kevin G, Kim Sangcheol, Jones Ronald L, Satija Sushil, Pickel Deanna L, Douglas Jack F, Karim Alamgir
Polymers Division, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland 20899, USA.
ACS Nano. 2008 Nov 25;2(11):2331-41. doi: 10.1021/nn800643x.
We investigate the effect of the ordering temperature (T) and film thickness (h(f)) on the surface morphology of flow-coated block copolymer (BCP) films of asymmetric poly(styrene-block-methyl methacrylate). Morphology transitions observed on the ordered film surface by atomic force microscopy (AFM) are associated with a perpendicular to a parallel cylinder BCP microphase orientation transition with respect to the substrate with increasing h(f). "Hybrid" surface patterns for intermediate h(f) between these limiting morphologies are correspondingly interpreted by a coexistence of these two BCP microphase orientations so that two "transitional" h(f) exist for each T. This explanation of our surface patterns is supported by both neutron reflectivity and rotational SANS measurements. The transitional h(f) values as a function of T define upper and lower surface morphology transition lines, h(fu) (T) and h(fl) (T), respectively, and a surface morphology diagram that should be useful in materials fabrication. Surprisingly, the BCP film surface morphology depends on the method of film formation (flow-coated versus spun-cast films) so that nonequilibrium effects are evidently operative. This morphological variability is attributed primarily to the trapping of residual solvent (toluene) within the film (quantified by neutron reflectivity) due to film vitrification while drying. This effect has significant implications for controlling film structure in nanomanufacturing applications based on BCP templates.
我们研究了有序温度（T）和薄膜厚度（h(f)）对非对称聚（苯乙烯-嵌段-甲基丙烯酸甲酯）流延共聚物（BCP）薄膜表面形貌的影响。通过原子力显微镜（AFM）在有序薄膜表面观察到的形貌转变与随着h(f)增加，BCP微相相对于基底从垂直圆柱取向转变为平行圆柱取向有关。对于这些极限形貌之间的中间h(f)，“混合”表面图案相应地由这两种BCP微相取向的共存来解释，因此对于每个T存在两个“过渡”h(f)。中子反射率和旋转小角中子散射测量都支持我们对表面图案的这种解释。作为T的函数的过渡h(f)值分别定义了上表面形貌转变线h(fu)(T)和下表面形貌转变线h(fl)(T)，以及一个在材料制造中应该有用的表面形貌图。令人惊讶的是，BCP薄膜表面形貌取决于成膜方法（流延薄膜与旋涂膜），因此非平衡效应显然起作用。这种形貌变化主要归因于干燥过程中薄膜玻璃化导致薄膜内残留溶剂（甲苯）的截留（通过中子反射率量化）。这种效应对于基于BCP模板的纳米制造应用中控制薄膜结构具有重要意义。
