Theory of microphase separation in block copolymer solutions

Microphase separation in semidilute solutions of block copolymers in nonselective good solvent is analyzed. The swelling due to the presence of solvent is taken into account. The solvent effects on the thermodynamics in the disordered region and in the ordered region in the weak segregation limit are discussed. It is found that the concentration of block copolymer at the microphase separation transition scales as N−0.62 in good solvents and as N−1/2 in Φ solvents. In the asymptotic semidilute regime in good solvents, the coexistence curve at the microphase separation transition is negligible, and the transition scales as (χ′AB φ1.61N)t ∼constant, where the constant is determined by the relative composition of the blocks in the block copolymer and χAB is proportional to the usual Flory interaction parameter.