Ultra-fast coarsening dynamics in late-stage spinodal decomposition of critical binary polymer mixtures

This work aimed to elucidate the ultra-fast dynamics of late-stage spinodal decomposition in critical polymer mixtures using a home-built time-resolved small-angle light scattering (SALS) apparatus. A crossover from the interfacial-tension-driven linear dynamics $R\propto t$ to the ultra-fast dynamics $R\propto t^3$ was observed when the domain size $R$ exceeded the capillary length. According to our hydrodynamic model for late-stage spinodal decomposition, the ultra-fast dynamics is considered induced by the accelerating gravity-driven Stokes flow. At the same time, the acceleration is caused by the interfacial-tension-driven coarsening, which enlarges the size of the falling phase and increases the terminal velocity of the Stokes flow. Although the percolating phase-separating structure grows self-similarly on the xy-plane (normal vector parallel to gravity), we consider that the fluid tubes will elongate along the z-axis, resulting in the failure of the dynamical scaling hypothesis in the 3D space. Finally, SALS data also revealed that the gravitational effects should appear as long as there is a density difference between the phase-separating phases. Apart from a transition from one dynamics to another, it is the competition between the interfacial-tension-driven Poiseuille flow and the gravity-driven Stokes flow that determines the predominant mode of the coarsening dynamics in the late-stage spinodal decomposition process.