Monte Carlo phase diagram for diblock copolymer melts.
A partial phase diagram is constructed for diblock copolymer melts using lattice-based Monte Carlo simulations. This is done by locating the order-disorder transition (ODT) with the aid of a recently proposed order parameter and identifying the ordered phase over a wide range of copolymer compositions (0.2<or=f<or=0.8). Consistent with experiments, the disordered phase is found to exhibit direct first-order transitions to each of the ordered morphologies. This includes the spontaneous formation of a perforated-lamellar phase, which presumably forms in place of the gyroid morphology due to finite-size and/or nonequilibrium effects. Also included in our study is a detailed examination of disordered cylinder-forming (f=0.3) diblock copolymers, revealing a substantial degree of pretransitional chain stretching and short-range order that set in well before the ODT, as observed previously in analogous studies on lamellar-forming (f=0.5) molecules.
Matsen
M W
MW
Department of Physics, University of Reading, Whiteknights, Reading RG6 6AF, United Kingdom. m.w.matsen@reading.ac.uk
Griffiths
G H
GH
Wickham
R A
RA
Vassiliev
O N
ON