Polymerization-induced phase separation .2. Morphological analysis

A model composed of the nonlinear Cahn-Hilliard and Floly-Huggins theories for spinodal decomposition (SD) and a second-order rate equation for polymerization for the self-condensation of a trifunctional monomer is used to study the polymerization-induced phase separation (PIPS) phenomena. The numerical results are consistent with experimental observations. These observations include the formation and evolution of a droplet-type morphology. In addition, the time evolution of the maximum value of the structure factor S(k(m),t) exhibits an exponential growth during the early stage but saturates during the intermediate stage of SD. Moreover, the dominant dimensionless wavenumber k(m)* decreases during the intermediate stage. The numerical results, however, also indicate that k(m)* increases during the early stage, which has not yet been observed experimentally. Furthermore, the morphological analysis is also consistent with experimental observations. The droplet size and shape distributions indicate that the average droplet size and shape prevail during the PIPS phenomena, and statistical analysis of the Voronoi polygons indicates that the droplets are randomly positioned within the matrix. Lastly, the characteristic time t, average dimensionless equivalent droplet diameter [d*], and droplet number density N-d depend on the magnitudes of a scaled diffusion coefficient D for phase separation and a scaled rate constant K-1 for polymerization. Consistent with experimental observations, tau and [d*] decrease while N-d increases as K-1 increases. Similarly, as D increases, tau and [d*] decrease while N-d increases. The parameters K-1 and D have no effect on the average shape factor.