Spinodal decomposition in binary blend of poly(methyl methacrylate)/ poly(α-methyl styrene-co-acrylonitrile): Analysis of early and late stage demixing

The phase separation kinetics of a poly(methyl methacrylate), PMMA, and poly(α-methylstyrene-co-acrylonitrile), PαMSAN. blend exhibiting a LCST-type phase diagram have been investigated as functions of temperature and demixing time for the near critical composition (PαMSAN/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 Tand q_m² 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)³I(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.