Morphology control in symmetric polymer blends using two-step phase separation

Abstract

This paper studied through modeling and computer simulation the two-step thermal-induced phase separation phenomenon in a symmetric polymer blend via spinodal decomposition. The two-step phase separation phenomenon involves the two-step process where the initial quench is allowed to phase separate for a certain period of time before the second quench takes place into the unstable region. The second quench occurs at the transition between the early and intermediate stages of spinodal decomposition, which is the time frame when functional polymeric materials with predefined material properties are fabricated. The one-dimensional model consisted of the Cahn–Hilliard theory for spinodal decomposition, and incorporated the Flory–Huggins–deGennes free energy equation, the slow mode mobility theory and reptation model for polymer diffusion. The numerical results replicated frequently reported experimental observations published in the literature. This includes the observation that secondary phase separation occurs only if the second quench is sufficiently deep. Furthermore, the numerical results indicate that a dimensionless diffusion coefficient may be used as a parameter to control the formation and evolution of the phase-separated regions during spinodal decomposition as a means to tailor-make functional polymeric materials with predefined material properties.