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A simulated annealing method is used to investigate the self-assembled morphologies of symmetric ABA triblock copolymer brushes, formed by one end of the A-blocks tethered onto a planar surface, immersed in a solvent selective for the middle B-blocks. The morphological dependences of the brushes on polymer grafting density and block lengths are investigated systematically. Phase diagrams for systems with different grafting densities are constructed. The simulation results show that the grafted amphiphilic triblock copolymers can self-assemble to form a variety of complicated morphologies which can be classified in terms of the number of A-rich layers in the morphology. In particular, the formation of the structures with one A-rich layer or called 'folded' brush structures is consistent with the speculation from the experimental studies of ABA triblock copolymer brushes. More detailed structures depend on the grafting density and the lengths of the blocks. Furthermore, at a high grafting density, the effects of the lengths of blocks and the interaction energies between different species in the system on the conformation of chains are investigated to illustrate the formation mechanisms of self-assembled morphologies of the amphiphilic triblock copolymer brushes. [ABSTRACT FROM AUTHOR]

The phase behavior of gradient copolymers is studied theoretically using random phase approximation (RPA) and self-consistent field theory (SCFT), focusing on the effects of monomer sequence distribution, or compositional polydispersity, of the polymer chains. The stability of the disordered phase is examined using RPA analysis, whereas the ordered phases of the system are studied using SCFT calculations. It is discovered that the critical domain spacing increases and the disorder-order transition temperature moves to higher values with the increase of the compositional polydispersity. SCFT results reveal that, depending on the value of the degree of segregation, structural change due to the different chain-to-chain monomer sequence distribution is controlled by two different mechanisms. [ABSTRACT FROM AUTHOR]

The basic idea of fast off-lattice Monte Carlo (FOMC) simulations is to use "soft" repulsive potentials that allow particle overlapping in continuum Monte Carlo (MC) simulations. For multichain systems, this gives much faster chain relaxation and better sampling of the configurational space than conventional molecular simulations using "hard" excluded-volume interactions that prevent particle overlapping. Such coarse-grained models are particularly suitable for the study of equilibrium properties of soft materials. Since soft potentials are commonly used in polymer field theories, it is another advantage of FOMC simulations that using the same Hamiltonian in both FOMC simulations and the theories enables quantitative comparisons between them without any parameter fitting to unambiguously reveal the consequences of approximations in the theories. Moreover, FOMC simulations can be performed with various chain models and in any statistical ensemble, and all the advanced off-lattice MC techniques proposed to date can be implemented to further improve the sampling efficiency. We have performed canonical-ensemble FOMC simulations with an isotropic soft pair potential for three systems: we first used (small-molecule) soft spheres to demonstrate the improved sampling of FOMC simulations over conventional molecular simulations; we then used single-chain simulations to show that the effects of excluded-volume interactions can be well captured by the soft repulsive potential; finally, for compressible homopolymer melts, we compared FOMC results with those under the random-phase approximation to demonstrate that FOMC simulations can be used to unambiguously and quantitatively reveal the fluctuation/correlation effects in the system. In addition, we examined in detail in our single-chain simulations the spatial discretization scheme used in all previous FOMC simulations.

Self-assembled morphologies of grafted Y-shaped ABC triblock copolymers are investigated using a simulated annealing method. The block copolymers are composed of two incompatible arms (A and B) and a short stem (C), with the C-stems grafted onto a flat surface. A rich array of novel morphologies is discovered. The formation of these morphologies is controlled by polymer grafting density, the incompatibility between the A-B-blocks, as well as the quality and selectivity of the solvents. In particular, it is observed that solvent selectivity drives lateral and/or perpendicular microphase separation. A phase diagram for systems with low grafting density is constructed. It is predicted that multiple morphological transitions, such as these from mixed or core-shell micelles to internally segregated micelles, to hamburger-like micelles, to segmented wormlike micelles, to connected micelles, and to split micelles, can be induced by varying either the incompatibility between the two arms or the quality of the solvents. These results are consistent with previous experiments and theories.

We report a simulated annealing study of the morphology of asymmetric diblock copolymer thin films confined between two homogeneous and identical surfaces. We have focused on copolymers that form a gyroidal morphology in the bulk. The morphological dependence of the confined films on the film thickness and the surface-polymer interaction has been systematically investigated. From the simulations it is found that much richer morphologies can form for the gyroid-forming asymmetric diblock copolymer thin films, in contrast to the lamella-forming symmetric and cylinder-forming asymmetric diblock copolymer films. Multiple morphological transitions induced by changing the film thickness and polymer-surface interactions are observed.

The simulated annealing method was applied to study the self-assembling process of diblock copolymers in selective solvents for one block. The simulation results illustrated that the morphologies of the copolymer aggregates strongly depend on the interactions between the core-forming blocks and the solvents and on the length of the corona-forming blocks. Multiple morphological transitions were observed in one system. The transition sequence (disordered state-spherical micelles-short rodlike micelles-long rodlike micelles-onionlike aggregates) was observed for copolymers with increasing core-solvent interaction. Similar transitions were observed with the decrease of the length of the corona-forming blocks. The mechanisms of these transitions are investigated. The simulation results are compared with experiments and other simulations.