Using a combinatorial screening method based on the self-consistent-field theory for polymers, we study the bulk morphology and the phase behavior of π-shaped ABC block copolymers, in which A is the backbone and B and C are the two grafts. By systematically varying the positions of the graft points, the π-shaped block copolymer can change from a star block copolymer to a linear ABC block copolymer. Thus, the corresponding order−order phase transition due to the architecture variation can be investigated. At two given compositions, we find seven different morphologies (“three-color” lamellar phase, “three-color” hexagonal honeycomb phase, lamellae with beads inside, dodecagon−hexagon−tetragon, hexagon−hexagon, lamellae with alternating beads, and octagon−octagon−tetragon). The hexagon−hexagon morphology has not been reported previously for linear and star triblock copolymers in the bulk state. The phase diagram of the π-shaped ABC block copolymer with symmetric interactions among the three species is constructed. When the volume fractions of block B and block C are equal, the triangle phase diagram shows reflection symmetry. When the shorter block is fixed at the backbone end and the other block moves to the other end along the backbone, the resulting morphology reaches to the same as that of a linear triblock copolymer rapidly. These results may help the design of the microstructures of complex block copolymers.

Introduction.Phase separation in polymer blends can occur due to the immiscibility between blend components, resulting in a variety of structures, which are important to many applications ranging from biomedical (e.g., gas separating membrane) to microelectronic device fabrication (e.g., lithography). 1,2 It is known that, after a blend is quenched into a metastable or unstable state, phase separation may proceed either by nucleation and growth (NG) or by spinodal decomposition (SD). The time evolution of SD phase separation can be divided into three stages, namely, the early, intermediate, and late stages. In the early stage, the behavior is well described by Cahn's linearized theory. 3,4 In the intermediate and the late stages, time evolution of phase separating domains is traditionally characterized by the power law q*(t) ∼ t -n , where q*(t) and n are the peak wavenumber and the power exponent characterizing the time evolution. After Lifshitz and Slyozov 5 obtained a scaling exponent n ) 1 / 3 considering diffusion effects and Siggia 6 proposed tube hydrodynamic instability with n ) 1 for the bulk system, various theories and simulations [7][8][9][10][11][12][13][14][15][16][17][18][19][20] and many experiments (especially scattering experiments) [21][22][23][24][25][26][27][28][29][30] have been focused on the power law describing the phase separation of polymer

By using a combinatorial screening method based on the self-consistent field theory (SCFT) for polymers, we have investigated the morphology of H-shaped ABC block copolymers (A2BC2) and compared them with those of the linear ABC block copolymers. By changing the ratios of the volume fractions of two A arms and two C arms, one can obtain block copolymers with different architectures ranging from linear block copolymer to H-shaped block copolymer. By systematically varying the volume fractions of block A, B, and C, the triangle phase diagrams of the H-shaped ABC block copolymer with equal interactions among the three species are constructed. In this study, we find four different morphologies (lamellar phase (LAM), hexagonal lattice phase (HEX), core-shell hexagonal lattice phase (CSH), and two interpenetrating tetragonal lattice (TET2)). Furthermore, the order-order transitions driven by architectural change are discussed.

By using a combinatorial screening method based on the self-consistent field theory, we investigate the equilibrium morphologies of linear ABCBA and H-shaped (AB)(2)C(BA)(2) block copolymers in two dimensions. The triangle phase diagrams of both block copolymers are constructed by systematically varying the volume fractions of blocks A, B, and C. In this study, the interaction energies between species A, B, and C are set to be equal. Four different equilibrium morphologies are identified, i.e., the lamellar phase (LAM), the hexagonal lattice phase (HEX), the core-shell hexagonal lattice phase (CSH), and the two interpenetrating tetragonal lattice phase (TET2). For the linear ABCBA block copolymer, the reflection symmetry is observed in the phase diagram except for some special grid points, and most of grid points are occupied by LAM morphology. However, for the H-shaped (AB)(2)C(BA)(2) block copolymer, most of the grid points in the triangle phase diagram are occupied by CSH morphology, which is ascribed to the different chain architectures of the two block copolymers. These results may help in the design of block copolymers with different microstructures.

The phase behaviors of comblike block copolymer A(m+1)B(m)/homopolymer A mixtures are studied by using the random phase approximation method and real-space self-consistent field theory. From the spinodals of macrophase separation and microphase separation, we can find that the number of graft and the length of the homopolymer A have great effects on the phase behavior of the blend. For a given composition of comblike block copolymer, increasing the number of graft does not change the macrophase separation spinodal curve but decreases the microphase separation region. The addition of a small quantity of long-chain homopolymer A increases the microphase separation of comblike block copolymer/homopolymer A mixture. However, the addition of short-chain homopolymer A will decrease the phase separation region of comblike block copolymer/homopolymer A mixture. It is also found that the microstructure formed by diblock copolymer is easier to be swelled by homopolymer than that formed by comblike block copolymer. This can be attributed to the architecture difference between the comblike block copolymer and linear block copolymer.