非对称双嵌段共聚物薄膜在平板受限和溶剂蒸发下自组装行为的分子模拟研究

采用模拟退火和Monte Carlo方法研究体相形成柱状相的双嵌段共聚物薄膜在平板受限和溶剂蒸发条件下的自组装,特别关注柱状相形貌的取向.对于平板受限下的薄膜,研究了表面选择性、溶剂选择性和膨胀程度对柱状相取向的影响.对于溶剂蒸发的薄膜,研究了表面选择性和薄膜厚度对柱状相取向的影响,并讨论了柱状相取向的机理.结果表明,薄膜内存在中性溶剂时形成垂直柱形貌的表面选择性范围较小;存在亲长嵌段的溶剂时形成垂直柱形貌的表面选择性范围较大.溶剂蒸发后薄膜生成垂直柱形貌的参数范围较热退火下增大;柱状相取向取决于蒸发过程中体系由球状相演化为柱状相时的薄膜厚度与体相周期的匹配性.

Simulation of Asymmetric Diblock Copolymer Films Confined between Two Flat Walls and Upon Solvent Evaporation

Solvent evaporation has proven to be a remarkably successful tool for directing the self-assembled nanostructures of block copolymers,yet the mechanisms of how its control parameters affect the nanostructure and its principles governing the structural formation remain poorly understood.In this paper,the simulated annealing and Monte Carlo method are used to study the self-assembly of cylinder-forming diblock copolymer films confined between two flat walls and under solvent evaporation on a simple cubic lattice model.Specific attention is paid to the orientation control of cylinders in the films.For films confined between two identical homogeneous flat walls,the effects of surface preference,solvent selectivity and swelling ratio on the cylinder orientation are investigated.The surface preference window for the formation of perpendicular cylinders is wider with a solvent of stronger affinity for the majority block,especially when the swelling ratio is higher.Whereas a neutral solvent leads to the formation of perforated lamellae,making the surface preference window for the formation of perpendicular cylinders narrower.For films under solvent evaporation,the effects of surface preference and film thickness on the resulting morphology of films are also studied.The maximum surface preference that leads to the formation of perpendicular cylinders varies with film thickness cyclically.The surface preference window for the formation of perpendicular cylinders after solvent evaporation is wider than that after thermal annealing,indicating that perpendicular orientation is promoted by the solvent evaporation.To unravel the mechanism of perpendicular cylinders forming,film morphology at different stages during solvent evaporation is plotted and compared to those of the films swollen to the corresponding thicknesses.It is noted that cylinder orientation after solvent evaporation is the same as that in a swollen film with a swelling ratio at which the spheres in the film begin to merge into cylinders.The surface preference window for the formation of perpendicular cylinders in this swollen case is determined by the commensurability between the film thickness and the bulk period.