Kinetics of BCC-FCC Transition in SI Diblock Copolymer Micelles in a Selective Solvent

Synchrotron based time-resolved small angle x-ray scattering (SAXS), was used to study the kinetics of ordering transition (OOT) in a 0.15(w/v) solution of a polystyrene-polyisoprene diblock (SI 15-15, Mw = 30K) copolymer in $n$-tetradecane, a selective solvent for the Isoprene block. This solution of spherical micelles is known to exhibit both FCC and BCC phases. From a temperature ramp experiment the OOT was identified at about 77C C and an ODT above 100 C. Several temperature jump experiments were performed over the temperature range of 50-110C. A disordered micellar solution at 110 C rapidly quenched to 50 C shows that a BCC phase appears very quickly following the temperature drop, which slowly transforms to the FCC phase at constant temperature. Two- dimensional SAXS patterns reveal the presence of grains. When the sample is melted for a short time the grains reappear producing almost the same scattering pattern as before the melting transition. Detailed analysis of the time evolution of the intensities of the Bragg peaks to follow the kinetics of the growth of the FCC phase will be presented.