嵌段共聚物受限于接枝混合刷板间的相行为

Self-assembly diblock copolymers confined between mixed brush-grafted surfaces

采用自洽场理论研究了AB两嵌段共聚物受限于交替接枝两种不同性质的聚合物刷平行板间的相行为.考虑了嵌段共聚物对称性、聚合物刷接枝周期、聚合物刷体积分数、平板间距以及AB嵌段间的相互作用参数对体系相形貌的影响,获得了四角柱状与六角柱状的交替相、四角柱状与八角柱状的交替相、平行的斜层状相以及弯层状相等结构;同时发现,接枝周期性混合刷有利于减少体系无序相的产生,并且较小周期的聚合物刷体系有利于六角柱状相的形成;在一定条件下,通过调节聚合物刷体积分数能够实现由水平层状到垂直层状的转变,这对纳米平板制造具有重要的意义;随着平板间距的减小,也获得了从水平层状到垂直层状的转变.本文所提出的调控共聚物结构的新方法以及获得的新颖结构,可对新型功能材料的设计提供一定的指导.

The confined environment plays a very important role in the phase separation of copolymers,which can change bulk phase behaviors of copolymers.The different confinement conditions can induce the formations of various interesting and novel morphologies,which can be used in a variety of nanotechnology applications such as high-density medium storage,nanolithography and photonic crystals.The grafting of polymers to confined surfaces is an efficient means for tailoring surface properties.In this work,we investigate the effect on architecture of the AB diblock copolymer confined between mixed brush-grafted surfaces by using self-consistent field theory.The brush contains two types of homopolymers.We study the effects of the fraction of A block,grafted period and the volume fraction of the polymer brush,the distance between two surfaces and the interaction strength between two blocks on the morphology.1） With the increase of the fraction of A block（fA）,the phase morphology changes from the A-block hexagonal cylinder to the parallel lamellae,to the curving lamellae,and then to the B-block hexagonal cylinder.The period of hexagonal cylinder and curving lamellae is equal to the grafted period of the polymer brush due to the influence of the polymer brush.2） The grafted period of polymer brush is a very important factor for the morphology of diblock copolymer.When fA= 0.3,we change the grafted period of the polymer brush.We obtain the phase transition from the hexagonal cylinder to the alternating phase of tetragonal and hexagonal cylinder,then to the alternating phase of tetragonal and octagonal cylinder.When f A=0.4,the structure changes from the hexagonal cylinder to the order phase of the waving lamellae and cylinder with the increase of the grafted period of the polymer brush.Compared with the single homopolymer brush system,the mixed brush enlarges the range of ordered phase and reduces the range of disordered phase.Block copolymers are prone to forming cylinder in mixed brush system and tending to form lamellae in single homopolymer brush system.3） When fA= 0.3,we obtain the phase transition from the hexagonal cylinder to the one-layered cylinder phase by increasing the volume fraction of the polymer brush.This transition is different from that of the single homopolymer brush system.Interestingly,when fA= 0.45,the structure of AB block copolymer changes from the parallel lamellae to the perpendicular lamellae with the increase of the volume fraction of the polymer brush.The entropic energy plays an important role in this transition process.Similarly,we also observe the phase transition from the parallel lamellae to the perpendicular lamellae by decrease the distance between two surfaces.4） We construct the phase diagram for a range of the fraction of A block and the interaction strength.The results provide an effective approach to obtaining the desired microstructures for fabricating nanomaterials.