Kinetics of metastable states in block copolymer melts

A theory is presented to describe the nucleation and subsequent growth of weakly inhomogeneous lamellar phases from a supercooled disordered phase. Detailed calculations are performed for the case of near-symmetric diblock copolymer melts, although the results have relevance for other physical systems in the Brazovskii ‘‘universality class.’’ Nucleation phenomena in such systems are particularly interesting because the bulk phase transitions have a very weak, fluctuation-induced first order character. We find unusually small nucleation barriers and critically slowed growth kinetics. For a diblock copolymer melt with degree of polymerization N and undercooling δ∝(Tt−T)/Tt≪1, the barrier is of order ΔF*/kBT∼N−1/3δ−2. Our estimate for the completion time of the nucleation and growth processes is θc ∼N1/12 δ−3/4 τd exp(ΔF*/4kBT), where τd is the copolymer terminal relaxation time.