Phase Behavior Of The Polymer System Under Soft Confinement

Block copolymers are a typical class of soft material that can self-assemble into periodical ordered morphologies. The confined environment plays a very important role in the phase separation of copolymers, which can change bulk phase behavior of copolymers. The different confinement conditions can induce the formation of various interesting and novel morphologies, which can be used in a variety of nanotechnology applications such as high-density media storage, nanolithography and photonic crystals. The grafting of polymers to confined surfaces is an efficient means for tailoring surface properties. In this paper, we investigate the phase behavior of diblock copolymer and the blend of AB diblock copolymer and star homopolymer in different confined environment.Firstiy, we investigate the effect on architecture of the AB diblock copolymers confined between mixed brush-grafted surfaces by using self-consistent field theory. The brush contains two types of homopolymer. We study the effect 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 increasing 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 morphologies of diblock copolymers. 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 fA = 0.4 , the structure changes from the hexagonal cylinder to the order phase of the waving lamellae and cylinder with the increasing of the grafted period of the polymer brush. Comparing to the single homopolymer brush system, the mixed brush enlarge the range of ordered phase and decrease the range of disordered phase. Block copolymers are prone to form cylinder in mixed brush system and tend 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 of the volume fraction of the polymer brush. This transition is different from the single homopolymer brush system. Interestingly, When fA = 0.45 , the structure of AB block copolymers changes from the parallel lamellae to the perpendicular lamellae with the increasing 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 decreasing the distance between two surfaces. (4)We construct the phase diagram for a range of the fraction of A block and the interaction strength.Secondly, we study the phase behavior of the blend of AB diblock copolymer and star homopolymer confined in soft cylindrical pore. We discuss the effects of the volume fraction of the star homopolymer and the volume fraction of the polymer brush on the morphology.The star homopolymer have the interact with the B block. For symmetric block copolymer,the phase of block copolymer changes from the lamellae to the micelle with the increasing of the fraction of the star homopolymer and the fraction of the polymer brush. When fA = 0.7 ,the phase of block copolymer show the cylinder structure. The number of cylinder layers will decrease with the increasing of the fraction of the star homopolymer. When fA = 0.6 , in addition to the micelle, there are also many interesting and novel structures with the increasing of the fraction of the star homopolymer and the fraction of the polymer brush. At the same time, we constract the ternary phase diagram about the ?H , ?AB, ?AB.The results provide some effective approachs to obtain the desired microstructures for fabricating nanomaterials.