Phase transitions in diblock copolymers: Theory and Monte Carlo simulations

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Abstract
The ordering phenomena of symmetric diblock copolymers at the microphase separation transition (MST) are studied both by Monte Carlo simulations using the cooperative-motion algorithm for dense polymer systems in three dimensions and analytically by the random-phase approximation (RPA) applying the Edwards Hamiltonian approach. The transition temperature is found from an analysis of the specific heat of the copolymer melt. Besides a phase separation into a definite lamellar structure, a stretching of the chains and an ordering effect at the MST are observed in the simulations. The RPA is able to explain this elongation of the chains. Additionally, the influence of vacancies on the location of the MST and the static properties of the chains are analyzed by theory and simulations. The vacancies are found to make the melt compatible and to lower the critical temperature.