Hajime Tanaka

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

We develop a new simulation method of colloidal suspensions, which we call a "fluid particle dynamics" (FPD) method. This FPD method, which treats a colloid as a fluid particle, removes the difficulties stemming from a solid-fluid boundary condition in the treatment of hydrodynamic interactions between the particles. The importance of interparticle hydrodynamic interactions in the aggregation process of colloidal particles is demonstrated as an example. This method can be applied to a wide range

Two types of isotropic disordered nonergodic states exist in colloidal suspensions: glasses and gels. The difference between the two is that the nonergodicity, or elasticity, of gel stems from the existence of a percolated network, while that of glass stems from caging effects. Despite this clear difference in the origin of nonergodicity, it is not straightforward to distinguish the two states in a clear manner. Taking a Laponite suspension as an explicit example, we propose a general phase diag

We present a general view of a liquid-liquid phase transition, based on a simple physical picture that there is "cooperative medium-range bond ordering" for any liquids. Contrary to the common belief, we argue that liquid is not homogeneous and in any liquid there exist locally favored structures, which are frustrated with normal-liquid structures. The cooperative excitation of locally favored structures leads to a gas-liquid-like critical point of bond ordering. This picture naturally leads to

We demonstrate here the possibility that strong dynamic asymmetry between two components of a fluid mixture generally leads to unusual phase separation (``viscoelastic phase separation''), which does not belong to the conventional classification of phase separation. In addition to polymer solutions, a mixture, one of whose components is close to its glass transition, transiently exhibits a morphology peculiar to viscoelastic phase separation, namely, a spongelike continuous pattern of the minori

Here we demonstrate the first evidence that phase separation in polymer solutions could be essentially different from that in binary liquid systems. This difference is likely to originate from the strong asymmetry in molecular dynamics between the two separated phases. When the rheological time of the polymer-rich phase is slower than the deformation time, the stress field can be strongly coupled with the concentration diffusion and the coarsening dynamics is dominated by the viscoelastic effect

We propose a simple two-state model of water to explain the unusual thermodynamic and dynamic behavior of liquid water. Our model is based on a physical picture that there exist two competing orderings in water, namely, density ordering and bond ordering. Short-range bond ordering leads to the formation of a rather stable locally favored structure (in a ground state) in a sea of disordered normal-liquid structures (in an excited state). Its fraction increases with decreasing temperature, obeying

Contrary to the conventional wisdom that there is only one unique liquid state for any material, recent evidence suggests that there can be more than two liquid states even for a single-component substance. The transition between these liquid states is called a liquid-liquid phase transition. We report the detailed experimental investigation on the kinetics of the continuous spinodal-decomposition-type transformation of one liquid into another for triphenyl phosphite. From the analysis of the li

We found both nucleation-growth-type and spinodal-decomposition-type transformation from one liquid state to another in a "molecular liquid," triphenyl phosphite (TPP). Binodal and spinodal temperatures of this transition at ambient pressure were determined by the characteristics of morphological evolution, domain-growth kinetics, and rheological evolution. Furthermore, a distinct thermal signature of the glass transition of a second liquid was also detected in addition to that of an ordinary li

There is a possibility that the phase separation process is coupled with other ordering processes such as crystallization. New types of phase separation behavior during the crystallization process in polymer blends with phase diagram are presented probably for the first time. Two different types of nonequilibrium phenomena take place simultaneously and new structures and new dynamics of pattern formation are observed as the result of the competition between these two phenomena.

Here we propose a simple physical model that may universally describe glass-transition phenomena from the strong to the fragile limit. Our model is based on the idea that there always exist two competing orderings in any liquids, (i) density ordering leading to crystallization and (ii) bond ordering favoring a local symmetry that is usually not consistent with the crystallographic symmetry. The former tries to maximize local density, while the latter tries to maximize the quality of bonds with n