Abstract
Summary: The phase separation kinetics of a poly(methyl methacrylate), PMMA, and poly(α‐methylstyrene‐co‐acrylonitrile), P__α__MSAN, blend exhibiting a LCST‐type phase diagram have been investigated as functions of temperature and demixing time for the near critical composition (P__α__MSAN/PMMA = 25:75) using a time‐resolved light scattering technique. We found that the scattering data in the early stage spinodal decomposition (SD) can be well described by the linearized Cahn–Hilliard theory. Spinodal temperature T~s~ ∼ 171 °C was determined from D~app~ versus T and q versus T based on the analysis of Cahn theory in the early stage SD, where D~app~ is the apparent diffusion coefficient and q~m~ is the scattering vector at the maximum scattering intensity. The value of T~s~ obtained from the analysis of light scattering data was in good agreement with the phase diagram obtained visually at the equilibrium condition. The LCST‐type phase diagram of this blend was also calculated using the Flory–Huggen theory. The estimated interaction parameter used for the calculation of the phase diagram was found to be composition and temperature dependent. The coarsening behavior of the blend at the late stage SD was also studied by analyzing the magnitudes of q~m~ and I~m~ at various demixing times and temperatures based on the nonlinear statistical theories. Both of q~m~ and I~m~ obtained at different times and temperatures can be superposed and reduced to the respective master curves by horizontal shifting when they are plotted against log (t/a~T~) at a given reference temperature, where a~T~ is the temperature‐dependent shift factor. The shape of the phase separation domain structures as a function of time during the SD was also considered. The scaling structure function F(x,t;T) = q~m~(t;T)^3^I(q,t;T) versus q/q~m~ was found to be time independent and falls onto a universal curve in the late stage SD as a result of the dynamical self‐similarity accompanying with the phase separation process.
Optical microscopy pictures for the structure development of spinodal decomposition for P__α__MSAN/PMMA = 25:75 blend at 180 °C for different demixing times.
imageOptical microscopy pictures for the structure development of spinodal decomposition for P__α__MSAN/PMMA = 25:75 blend at 180 °C for different demixing times.