环形对称两嵌段共聚物在薄膜中自组装行为的计算机模拟

Computer Simulation of Self-assembly Behavior of Cyclic Symmetric Diblock Copolymers in Thin Film

采用Monte Carlo模拟方法考察了AB环形对称两嵌段共聚物受限在薄膜中的自组装行为。模拟结果表明,AB环形对称两嵌段共聚物在薄膜中自组装形成的层状结构的取向依赖于薄膜表面的选择性或膜厚。当薄膜表面无选择性或具有强选择性时,体系中层状结构的取向分别为垂直和平行于薄膜表面;当薄膜表面选择性较弱时,随着膜厚的增加层状结构的取向会发生由垂直向平行于薄膜表面的转变。这些模拟结果与文献报道中线形体系十分一致。然而值得注意的是,当薄膜表面的选择性适中时,环形体系中形成了一种在线形体系中未被观察到的具有波浪形层状结构的新颖有序结构。通过对该结构相互作用焓密度与链构象的分析发现,该结构是一种稳定态结构。此外,通过对比相同参数下环形体系与线形体系的层状结构发现,环形体系层状结构的特征尺寸明显小于线形体系。上述模拟结果表明相对于与其分子量相同的线形嵌段共聚物,环形嵌段共聚物由于其特殊的几何结构能够形成新颖的或具有更小特征尺寸的微相分离结构,而控制特征尺寸,尤其是获得尽可能小的特征尺寸,对于制备具有更小纳米结构和更高集成度的微电子器件具有重要意义。

The self-assembly behaviors of AB cyclic symmetric diblock copolymers confined in thin films were investigated by Monte Carlo simulation.The simulation results show that the orientation of the lamellar structure formed by AB cyclic symmetric diblock copolymers in the films depends on the selectivity of the film surface or the film thickness.When the film surface is neutral or has strong selectivity,the orientation of the lamellar is vertical or parallel to the film surface,respectively;When the film surface selectivity is weak,the orientation of the lamellar structure changes from vertical to parallel to the film surface with the increase of the film thickness.These simulation results are in good agreement with the linear systems reported in the literature.However,it is worth noting that when the selectivity of the film surface is moderate,a novel ordered structure with wavy-like structure,not observed in the linear system,is formed in the cyclic copolymer system.By analyzing the interaction enthalpy density and the chain conformation of the structure,it is found that the structure is a stable structure.In addition,by comparing the lamellar structures of the cyclic system and the linear system under the same parameters,it is found that the characteristic size of the lamellar structure of the cyclic system is significantly smaller than that of the linear system.The simulation results above show that compared with linear block copo-lymers with the same molecular weight,cyclic block copolymers can form novel or smaller characteristic size microphase separation structures due to their special geometric structure.Controlling the characteristic size,especially obtaining the smaller characteristic size,is of great significance for the preparation of microelectronic devices with smaller nanostructures and higher integration.