title: Fluctuations in symmetric diblock copolymers: testing theories old and new.
abstract: Computer simulations are used to study composition fluctuations in disordered diblock copolymer melts over a range of values of the chain length N, and test several theories for the structure factor S(q). Specifically, we test the random-phase approximation (RPA), which is based on a self-consistent field treatment of fluctuations, the Fredrickson-Helfand theory, which was designed to describe fluctuations near the order-disorder transition, and the relatively new renormalized one-loop (ROL) theory. The results confirm claims that the RPA is exact in the limit N→∞ and that the ROL theory yields the dominant corrections to the RPA within a systematic expansion in powers of N(-1/2), and show that the ROL theory is much more accurate than either older theory.
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Qin
authors.forename: David C
authors.initials: DC
authors.lastname: Morse