Self-assembly Of Complex Block Copolymers In Bulk And Under Confinements

Block copolymers have attracted a lot of attentions due to their ability to self-assemble into10-100nm rich nanoscale ordered morphologies. This property make them candidates for wide potential applications including lithographic templates for nanowires, photonic crystals, and high density magnetic storage media. As the simplest model of block copolymers, diblock copolymer has been extensively studied both by experiment and by theories. The classical mesophases formed by diblock copolymers include lamellae, cylinders, spheres, gyroid, Fddd, O70and perforated lamellae, etc. If only those morphologies can be formed, the application of diblock copolymer will be dramatically restricted. Therefore how to obtain more microstructures is essential for the understanding of self-assembly as well as increasing the application of diblock copolymer.There are two methods to obtain more ordered structures:one is adding another block into AB diblock to increase the architectural complexity of block copolymer, and the other is introducing geometric confinement. SCFT and TDGL were used to investigate the phase beheavior of block copolymer. Many interesting morphologies are fabricated by using those two methods. The main results are list as follows:1. The phase behavior of ABC star triblock copolymers was examined. There are five independent parameters which can affect the phase behavior of ABC triblock copolymer. The interaction parameters were fixed to reduce the calculation time. One3D and ten2D microstructures were obtained. By comparing the free energy of a number of candidate ordered phases, the central part of the triangular phase diagram for ABC triblock copolymers with equal A/B, B/C, and C/A interactions is determined. Among those morphologies, there is a hierarchical lamellar morphology. An angle, which is used to characterize the shifting magnitude between neighbor B/C conformed layers, varies from0to180degrees. A series of configurations including22.5°,45°,67.5°,90°, etc. was obtained by using some initional condition. Our results show that the180°morphology with larger shift has lower entropic energy and higher internal energy. In general, the morphology with the largest shift of180-degree is stable compared with those with smaller shift as the entropic energy dominates the internal energy. However, the relative stability can be tuned by the interactions among the three components as well as their relative compositions.2. The phase behaviors of multiblock terpolymers A(BC)nB (or A(BC)n) and A(BC),,BA’are investigated by further increasing the complexity of the architecture. A(BC)2B can self-assemble into hierarchical lamellar phases of perpendicular or parallel lamellae within lamellae. Our conclusion that the perpendicular phase is stable only in the case of χBC N> ΧABN>> χACN is consistent with experimental observations by Bates’s group. In addition, our results suggest that the existence of the perpendicular phase is generic in both types of terpolymers:A(BC)nB and A(BC)n, with different values of n, even for the special case of A(BC)n, that is, an ABC linear terpolymer. In linear A(BC)nBA’ multiblock terpolymers, the relative stability among the lamellae-in-lamellae structures with different BC internal layers is tuned by the volume fraction of the two long tails. A larger A volume fraction favors the formation of structures with fewer BC thin layers. When the volume fraction of A is increased further, a hierarchical cylinder phase can be formed because of the effect of the spontaneous curvature and vice versa. The separation between B and C significantly reduces the phase regime of the cylinder, especially for the case of small A volume fraction.3. Some interesting morphologies can also be observed under geometrical confinement. We focus on the self-assembly of ABC star triblock copolymers under the cylindrical confinement. Specifically, the investigation focuses on the confined self-assembly of a triblock copolymer which forms hierarchical lamellae in bulk. Generically, the hierarchical lamellae can be parallel or perpendicular to the pore surfaces. Concentric rings of A and B/C lamellae are formed in the parallel case. The B/C layers further phase separate to B/C domains. The number of B/C domains is controlled by the pore size. In the perpendicular case, the B/C layers are arranged alternatively along the pore axis. The stability of these observed structures is analyzed by calculating their free energy.4. Not only the noval morphologies can be formed under geometrical confinements, but also the long-range ordered structures can be obtained by the direction of the confinement. Long range order hexagonal patterns morphologies (Lx/L0=25) were observed by the self-assembly of hexagonal cylinder-forming diblock copolymer under the hexagonal-shape cylindrical confinement. The elvolution of dynamics was investigate by using the cell-dynamic simulation of the time-dependent Ginzburg-Landau theory. Our results show that there are two step in the ordering process, the first step is the formatin of semi-order morphologies after the elvolution of large defect. The second step is the formation of order morphologies by adjusting the stretching or compressing of polymer chian.