Three-dimensional numerical simulations of viscoelastic phase separation: Morphological characteristics

We have studied the characteristic features of viscoelastic phase separation in three dimensions by using numerical simulations, focusing on the morphological development. The Langevintype equations of a two-fluid model, which includes both bulk and shear viscoelastic stresses, are solved numerically. The origin of phase inversion is discussed on the basis of a simple consideration on the symmetry of the "effective" phase diagram, and the importance of the bulk stress on this phenomenon is addressed. The roles of bulk and shear stresses are clarified by comparing simulation results for cases with and without each stress. We analyzed the temporal change in the structure factor and found that the structure factors cannot be scaled, and thus, the dynamical scaling law does not hold at all for viscoelastic phase separation. We also studied the geometrical characteristics such as the mean and Gaussian curvatures and the Euler characteristic of the interface, to characterize the topological features of viscoelastic phase separation. The results also unambiguously indicated the absence of the selfsimilarity, which is the central concept of the late-stage pattern evolution in conventional phase separation. The topological change accompanied by phase inversion was successfully characterized by the curvature of domain interface and the Euler charactristic. Our study indicated the advantage of the real-space analysis over the q (wavenumber)-space one in the topological characterization.