Instability and Soft Patterning Laboratory, Department of Chemical Engineering, Indian Institute of Technology Kharagpur, West Bengal, Pin 721302, India.
Department of Polymer Engineering and Akron Functional Materials Centre (AFMC), University of Akron, Akron, Ohio 44325, USA.
Soft Matter. 2017 Jul 21;13(27):4709-4719. doi: 10.1039/c7sm00799j. Epub 2017 Jun 14.
Substrate pattern guided self-organization of ultrathin and confined polymeric films on a topographically patterned substrate is a useful approach for obtaining ordered meso and nano structures over large areas, particularly if the ordering is achieved during film preparation itself, eliminating any post-processing such as thermal or solvent vapor annealing. By casting a dilute solution of two immiscible polymers, polystyrene (PS) and polymethylmethacrylate (PMMA), from a common solvent (toluene) on a topographically patterned substrate with a grating geometry, we show the formation of self-organized meso patterns with various degrees of ordering. The morphology depends on both the concentration of the dispensed solution (C) and the blend composition (R). Depending on the extent of dewetting during spin coating, the final morphologies can be classified into three distinct categories. At a very low C the solution dewets fully, resulting in isolated polymer droplets aligned along substrate grooves (Type 1). Type 2 structures comprising isolated threads with aligned phase separated domains along each substrate groove are observed at intermediate C. A continuous film (Type 3) is obtained above a critical concentration (C*) that depends on R. While the extent of ordering of the domains gradually diminishes with an increase in film thickness for Type 3 patterns, the size of the domains remains much smaller than that on a flat substrate, resulting in significant downsizing of the features due to the lateral confinement imposed on the phase separation process by the topographic patterns. Finally, we show that some of these structures exhibit excellent broadband anti-reflection (AR) properties.
在具有形貌图案的基底上，通过基底图形引导的超薄受限聚合物薄膜的自组织是获得大面积有序介观和纳米结构的有用方法，特别是如果在薄膜制备过程中本身就能实现有序排列，避免任何后处理，如热退火或溶剂蒸汽退火。通过从甲苯等共同溶剂浇铸两种不混溶的聚合物聚苯乙烯（PS）和聚甲基丙烯酸甲酯（PMMA）的稀溶液，在具有光栅几何形状的具有形貌图案的基底上，我们展示了具有不同有序度的自组织介观图案的形成。形态取决于分配溶液的浓度（C）和共混物组成（R）。根据旋涂过程中的去湿程度，最终形态可以分为三类。在非常低的 C 下，溶液完全去湿，导致聚合物液滴沿着基底沟槽排列（类型 1）。在中间 C 下观察到包含沿着每个基底沟槽排列的分离相的孤立纤维的类型 2 结构。在依赖于 R 的临界浓度（C*）之上获得连续薄膜（类型 3）。虽然对于类型 3 图案，随着膜厚度的增加，畴的有序度逐渐减小，但畴的尺寸仍然比在平坦基底上小得多，由于形貌图案对相分离过程施加的横向限制，特征尺寸显著缩小，从而导致显著的尺寸缩小。最后，我们表明这些结构中的一些具有优异的宽带抗反射（AR）性能。
