Geometrical properties and interface dynamics: Time evolution of spinodal interface in a binary polymer mixture at the critical composition

The time-evolution of a three-dimensional (3D), bicontinuous interface of a phase-separated polymer mixture in the late stage spinodal decomposition ( SD) process has been studied by laser scanning confocal microscopy (LSCM) a nd time-resolved light scattering. The time evolution of the interface betw een two coexisting phases developed via SD ("spinodal interface") was quant itatively captured in 3D by using LSCM. On the basis of the differential ge ometry, probability densities of the local curvatures, i.e., the mean and G aussian curvatures, of the spinodal interface have bees experimentally eval uated. We found that a large portion of the interface formed in. the late s tage SD consists of a saddle-shaped surface, i.e., a hyperbolic surface. Th e probability densities were used to predict the dynamics of the spinodal i nterface. Two basic mechanisms are found to be important for the system to reduce interface area during the late stage SD. In addition, the probabilit y densities of the curvatures at various times were successfully scaled by a time-dependent characteristic wavenumber, i.e., interface area per unit v olume. This clearly proves that the time evolution of the spinodal interfac e, which characterizes the local structure of the system, is dynamically se lf-similar.