Nucleation and growth in order-to-order transitions of a block copolymer

A poly(isoprene-b-ethyleneoxide) diblock undergoes multiple ordered state transitions: from a crystalline lamellar (L c ), to a hexagonal (Hex) mesophase, to a bicontinuous cubic phase (Gyroid) before disordering (Dis). We have studied the kinetics of the Hex-to-Gyroid, Hex-to-L c and L c -to-Gyroid transitions using synchrotron SAXS and rheology. The Hex-to-Gyroid transformation proceeds via a nucleation and growth mechanism with a small mismatch between the two phases, as anticipated by recent theoretical predictions (M. W. Matsen, Phys. Rev. Lett. , 80 (1998) 4470). We provide the first quantitative measure of the activation barrier involved in an order-to-order transition and show the importance of nucleation and growth in these transformations.