Study of the nonlinear phase-separation behavior of a polystyrene/poly (vinyl methyl ether) blend using small-angle light scattering

摘要

The thermally induced phase-separation behavior of a polystyrene/poly(vinyl methyl ether) (PS/PVME) blend was studied mainly using time-resolved small-angle light scattering, as a function of temperature and heating rate. Under a non-isothermal field, the dependence of the critical temperature on heating rate deviated obviously from linearity, even at very low heating rates. Such a nonlinear dependence was consistent with the deviation from linearity of the temperature dependence of the isothermal phase-separation behavior in a wider temperature range from 100 to 140°C. It was also found that a Williams-Landel-Ferry (WLF)-like equation could be employed to describe the temperature dependence of the apparent diffusion coefficient (D_(app)) and the relaxation time (t) of normalized scattering intensity at the early stage of spinodal decomposition (SD), as well as r of phase behavior at the late stage of SD for the PS/PVME blend. The equilibrium phase-separation temperature could hardly be established through the conventional linear extrapolation of heating rate or D_(app) to zero at the early stage of SD. The successful use of the WLF-like function for PS/PVME blends extends the applicability of the time-temperature superposition principle for describing the phase-separation behavior of binary polymer mixtures over a relatively large temperature range.