Self-assembly of AB diblock copolymers under confinement into topographically patterned surfaces.
Self-assembly of AB diblock copolymers under confinement into topographically patterned surfaces.
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DOI：
10.1021/jp9033613
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发表时间：
2009-10
期刊：
影响因子：
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通讯作者：
Guang Yang;P. Tang;Yuliang Yang;J. Cabral
中科院分区：
文献类型：
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作者：
Guang Yang;P. Tang;Yuliang Yang;J. Cabral
受最近纳米压印共聚物图案化实验的启发，我们利用自洽场理论（SCFT）研究了具有块状层状结构、限制在平坦底面和方波顶面之间的对称AB二嵌段共聚物的微相分离和形态。采用高效、高阶精确的伪谱方法，借助“掩蔽”技术，将任意形状的受限域嵌入到更大的矩形计算单元中，对不规则形状域中的SCFT方程进行数值求解。我们的模拟表明，分别出现在相对强和弱表面场中的倒T型和梯形结构遵循我们的地形图案表面。对于中性壁，当下部部分的厚度与本体嵌段共聚物的片晶周期相当时，本研究中的地形图案表面导致平行片晶，并且当上部截面的宽度和高度都等于片晶本体周期时，完全平行的片晶是有利的。此外，普遍的结构是上部的平行薄片与下部的垂直薄片相结合。当壁排斥其中一种块体物质时，与中性壁的情况相比，会在较宽的膜厚度范围内出现平行片层。然而，据我们所知，一些新结构，例如方形和部分方形结构以及倒T形和梯形结构，在平行表面限制下以前尚未报道过。一般来说，可以通过选择适当的空间限制程度来获得所需的结构，其特征是薄膜厚度与体重复周期之比的变化以及块-基底相互作用。此外，我们表明下部截面的限制宽度（或方波的周期）在微观结构的形成中起着至关重要的作用。这些发现为通过地形图案表面和表面场设计涉及对称二嵌段共聚物的新颖微结构提供了指导，与纳米压印相关。
Motivated by recent experiments of copolymer patterning by nanoimprinting, we investigate microphase separation and morphology for symmetric AB diblock copolymers with lamellar structure in bulk, confined between a flat bottom surface and a square-wave top surface by using the self-consistent field theory (SCFT). The efficient and high-order accurate pseudospectral method is adopted to numerically solve the SCFT equations in irregularly shaped domains with the help of the "masking" technique by embedding the confined domains of arbitrary shape within a larger rectangular computational cell. Our simulations reveal that the inverted T-style and trapezoid structures occurring in the relatively strong and weak surface fields, respectively, are following our topographically patterned surface. For neutral walls, when the thickness of the lower section is commensurate with the lamellae period of bulk block copolymers, the topographically patterned surface in this work leads to parallel lamellae, and completely parallel lamellae are favored when both the width and height of the upper section are equal to the lamellae bulk period. Furthermore, the prevalent structures are the parallel lamellae in the upper section combined with the perpendicular lamellae in the lower section. When the walls repel one of the block species, parallel lamellae occur in a wide range of film thicknesses compared to the case of neutral walls. To our knowledge, some new structures, however, such as square and partial square structures and reversed-T and trapezoid structures, have not been reported before under parallel surface confinement. In general, the required structures can be obtained by choosing the proper degree of spatial confinement, characterized by variations of the ratio of film thicknesses to bulk repeat period, and the block-substrate interactions. Moreover, we show that the confinement width of the lower section (or the period of the square wave) plays a critical role in microstructure formation. These findings provide a guide to designing novel microstructures involving symmetric diblock copolymers via topographically patterned surfaces and surface fields, relevant to nanoimprinting.