Kinetics of phase separation in poly(ε-caprolactone)/poly(ethylene glycol) blends

The poly(E-caprolactone)/poly(ethylene glycol) (PCL/PEG) blends reveal a miscibility window of upper critical solution temperature (UCST) character. The kinetics of liquid-liquid phase separation (LLPS) for the blends of PCL/PEG is investigated by time-resolved small angle light scattering (TRSALS). The time evolution of scattering profile is analyzed by linear Cahn-Hilliard theory for early stage of spinodal decomposition (SD). The evolution of the maximum intensity I-m(t) and the corresponding wavenumber q(m)(t) obey the power-law scheme (I-m(t) similar to t(beta) and q(m)(t) similar to t(-alpha)). A relation of beta = 3 alpha in late stage is obtained almost the same scaling exponents with beta congruent to 1 and alpha congruent to 1/3 for various quenching depths. The alpha congruent to 1/3 implied that a coarsening mechanism at the late stage of phase separation may proceed with Ostwald ripening or Brownian coalescence process. Besides, the intermediate and late stages of SD can be scaled into a universal from represented well by Furukawa's structure factor. The percolation to cluster transition is accompanied with a similar to 0.13 -> 1/3 from intermediate to late stage of SD for the off-critical mixture of PCL/PEG (4/6) blend. In this study, the experimental result demonstrates that the crystallization is a viable mechanism to lock phase-separated structure of the blends. The competition between phase separation and crystallization has been Suggested to determine the final morphology.