Time-Resolved Small-Angle X-ray Scattering Study of the Kinetics of Disorder-Order Transition in a Triblock Copolymer in a Selective Solvent for the Middle Block

The kinetics of the disorder-order transition (ODT) in a triblock of polystyrene (PS) and poly(ethylene-co-butylene) (PEB), in mineral oil, a selective solvent for the middle PEB block, was followed by time-resolved SAXS using both temperature ramp and rapid temperature quench techniques. Data analysis, using the Percus-Yevick interacting hard-sphere model plus Gaussians for the Bragg peaks in the ordered body-centered-cubic (bcc) state, shows that the core radius R_c, the hard-sphere volume fraction φ, and their interaction radius R_hs, increased with decreasing temperature in the disordered state. At the ODT, φ reaches a maximum and R_c and φ change on ordering. The kinetics exhibits two stages corresponding to temperature equilibration and supercooling of the micellar fluid followed by nucleation and growth of the ordered state. The induction time for the onset of the second stage shows a minimum around the glass transition of the polystyrene cores.