PHASE-TRANSITIONS IN DIBLOCK COPOLYMERS - THEORY AND MONTE-CARLO SIMULATIONS

The ordering phenomena of symmetric diblock copolymers at the micropha se separation transition (MST) are studied both by Monte Carlo simulat ions 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 tempe rature 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 obser ved in the simulations. The RPA is able to explain this elongation of the chains. Additionally, the influence of vacancies on the location o f the MST and the static properties of the chains are analyzed by theo ry and simulations. The vacancies are found to make the melt compatibl e and to lower the critical temperature.