TANAKA LAB. Physics of Soft Condensed Matter The University of Tokyo Graduate School of Engineering Department of Applied Physics The University of Tokyo Institute of Industrial Science Department of Fundamental Engineering
Entrance > Research > Polymer, Liquid Crystal, Colloid, Membrane, Protein > Phase Separation Dynamics > Viscoelastic Phase Separation
Polymer, Liquid Crystal, Colloid, Membrane, ProteinLiquid, Glass, GelLight and Soft Matter
Phase Separation in a Normal Fluid MixtureViscoelastic Phase SeparationPhase Separation of Colloidal SuspensionsNumerical Simulations of Viscoelastic Phase SeparationMicro-Phase Separation in Diblock CopolymerInterplay between Wetting and Phase SeparationPhase Separation under External FieldsDynamic Control of the Smectic MembranesCritical Phenomena in Polymer SolutionsCoil-Globule Transition of a Single PolymerColloidal ‘Atom’Colloidal Gel NetworkElectrophoretic Separation of Charged ParticlesAggregation of Charged Colloidal SystemsSurface-Assisted Monodomain Formation of a Lyotropic Liquid CrystalShear-Induced Topological Transitions in a Membrane SystemSpontaneous Onion-Structure FormationSelf-Organization in Phase Separation of a Lyotropic Liquid CrystalTransparent Nematic Phase in a Liquid-Crystal-Based MicroemulsionColloidal Aggregation in a Nematic Liquid CrystalPhase Separation of a Mixture of an Isotropic Liquid and a Liquid CrystalSpontaneous Partitioning of Particles in a Membrane System

Viscoelastic Phase Separation

Viscoelastic Phase Separation Descriptions of phase separation in condensed matter have so far been classified into a solid model (model B) and a fluid model (model H). In the former the diffusion is the only transport process, while in the latter material can be transported by both diffusion and hydrodynamic flow. It has recently been found that in addition to these well-known models a new model of phase separation, the “viscoelastic model”, is required to describe the phase-separation behaviour of a dynamically asymmetric mixture, which is composed of fast and slow components. Such ‘dynamic asymmetry’ can be induced by either the large size difference or the difference in glass-transition temperature between the components of a mixture. The former often exists in so-called complex fluids, such as polymer solutions, micellar solutions, colloidal suspensions, emulsions and protein solutions. The latter, on the other hand, can exist in any mixture in principle. This new type of phase separation is called ‘viscoelastic phase separation’ since viscoelastic effects play a dominant role. Viscoelastic phase separation may be a ‘general’ model of phase separation, which includes solid and fluid models as special cases: for example, fluid phase separation described by model H, which is believed to be the usual case, can be viewed as a “special” (rather rare) case of viscoelastic phase separation. Here we review the experiments, theories and numerical simulations for viscoelastic phase separation. In dynamically asymmetric mixtures, phase separation generally leads to the formation of a long-lived “interaction network” (a transient gel) of slow-component molecules (or particles), if the attractive interactions between them are strong enough. Because of its long relaxation time, it cannot catch up with the deformation rate of the phase separation itself and as a result the stress is asymmetrically divided between the components. This leads to the transient formation of networklike or spongelike structures of a slow-component-rich phase and its volume shrinking. Domain shape is determined by the force-balance condition in this intermediate stage. However, the true late stage of this phase separation can be described by a fluid model. The process can be viewed as viscoelastic relaxation in pattern formation. We discuss the morphological and kinetic features of viscoelastic phase separation, focusing on the differences from those of usual phase separation. The significance of viscoelastic phase separation in pattern formation in Nature and its engineering applications are also pointed out.