Asymmetric block copolymer melts near the microphase separation transition: a Monte Carlo simulation

A three-dimensional lattice model of a diblock copolymer melt with composition f= 3/4 is studied by Monte Carlo methods, extending our previous work for the symmetric case (f=1/2). The polymers are represented as self-avoiding walks, at a volume fraction O= 0.8 of occupied sites, and chain lengths N =24, 32, and 40 are used. Different monomers at nearest-neighbor sites repel each other with an energy k B Te. Due to the use of a finite lattice size L=32, the microphase separation transition to the heragonal phase can only be located rather roughly (e c N=11±1), but accurate data are obtained in the disordered phase at temperatures above the transition temperature