Rei Kurita

On the abundance and general nature of the liquid–liquid phase transition in molecular systems

Even a single-component liquid may have more than two kinds of isotropic liquid states. The transition between these different states is called a liquid?liquid transition (LLT). An LLT has been considered to be a rather rare phenomenon, in particular for molecular liquids. Very recently, however, we found an LLT in triphenyl phosphite, which may be the first experimental observation of an LLT for molecular liquids. Here we report convincing evidence of the second example of LLT for another molecular liquid, n-butanol. Despite large differences in the chemical structure and the molecular shape between triphenyl phosphite and n-butanol, the basic features of the transformation kinetics are strikingly similar. This suggests that an LLT may not be a rare phenomenon restricted to specific liquids, but may exist in various molecular liquids, which have a tendency to form long-lived locally favoured structures due to anisotropic interactions (e.g., hydrogen bonding).

Spatial distribution of lamella structure in PCL/PVB band spherulite investigated with microbeam small- and wide-angle X-ray scattering

The microbeam small- and wide-angle X-ray scattering (SAXS/WAXS) technique gives the novel information about micron-scale structural inhomogeneity of polymer crystal. By using this technique, we have studied structural inhomogeneity of lamella within the band spherulite of miscible polymer blend poly(e caprolactone) (PCL)/poly(vinyl butyral) (PVB) and the structure development of lamella during crystallization. It is known that PCL/PVB forms very large spherulites (∼several mm in radius) with highly regular band structure because of low frequency of nucleation and that PCL/PVB crystallized at 41 °C has at least two kinds of lamella structure (150 A, 180 A). With an X-ray microbeam initially fixed outside near the growth front of the band spherulite, we have observed the lamella formation at the local point and have found that the larger long period grows before the appearance of the shorter long period. We have also observed that the orientation of lamella with the larger long period is different from that of lamella with the shorter long period from SAXS experiment with an X-ray microbeam scanning the band spherulite along its radial direction. Further, the discontinuity in lamella twisting was observed from scanning microbeam WAXS. Based on the experimental results, we propose two possible spatial distribution models. The result of PCL/PVB crystallized at 35 °C was also discussed.

Microscopic structural evolution during the liquid-liquid transition in triphenyl phosphite

Recently the liquid?liquid transition (LLT) was found in a molecular liquid, triphenyl phosphite, which allows us to follow the kinetics of the transformation of one liquid to another. Here we investigate the microscopic structural change during the LLT by means of time-resolved synchrotron x-ray scattering measurements. We confirm that during spinodal-decomposition-type transformation a new peak corresponding to a particular intermolecular phosphor?phosphor distance emerges and grows with time. This indicates that short-range order develops in the liquid during LLT. We show that the short-range order does not represent the crystalline structure, but the locally favoured structure. We found that the temporal increase of the intensity of this peak, i.e., the fraction of locally favoured structures, is proportional to that of the heat released during the transformation. This means that the formation of locally favoured structures is the origin of the heat release. This is consistent with the proposal that the order parameter governing LLT is the number density of locally favoured structures. This yields a valuable insight into the nature of the ordering in the liquid?liquid transition.

Response of Soft Continuous Structures and Topological Defects to a Temperature Gradient

Thermophoresis, which is mass transport induced by a temperature gradient, has recently attracted considerable attention as a new way to transport materials. So far the study has been focused on the transport of discrete structures such as colloidal particles, proteins, and polymers in solutions. However, the response of soft continuous structures such as membranes and gels to a temperature gradient has been largely unexplored. Here we study the behavior of a lamellar phase made of stacked surfactant bilayer membranes under a temperature gradient. We find the migration of membranes towards a low-temperature region, causing the increase in the degree of membrane undulation fluctuations towards that direction. This is contrary to our intuition that the fluctuations are weaker at a lower temperature. We show that this can be explained by temperature-gradient-induced migration of membranes under the topological constraint coming from the connectivity of each membrane. We also reveal that the pattern of an edge dislocation array formed in a wedge-shaped cell can be controlled by a temperature gradient. These findings suggest that application of a temperature gradient provides a novel way to control the organization of soft continuous structures such as membranes, gels, and foams, in a manner essentially different from the other types of fields, and to manipulate topological defects.

Dynamic Nature of the Liquid‐Liquid Transition of Triphenyl Phosphite Studied by Simultaneous Measurements of Dielectric and Morphological Evolution

We performed broadband dielectric measurements for the process of liquid‐liquid transformation in triphenyl phosphite (TPP). According to our dielectric measurements, the static dielectric constant monotonically decreases and the distribution of the relaxation time becomes broader during the liquid‐liquid transformation from liquid I to II. The direct comparison with morphological evolution provides key information on the dynamical and structural evolution during LLT.

Kinetics and Control of Liquid‐Liquid Transition

Recently it was revealed that even a single‐component liquid can have more than two liquid states. The transition between these liquid states is called “liquid‐liquid transition”. This phenomenon has attracted a considerable attention because of its counter‐intuitive character and the fundamental importance for our understanding of the liquid state of matter. The connection between the liquid‐liquid transition and polyamorphism is also an interesting issue. In many cases, liquid‐liquid transitions exist in a region which is difficult to access experimentally. Because of this experimental difficulty, the physical nature and kinetics of the transition remains elusive. However, a recent finding of liquid‐liquid transition in molecular liquids opens up a possibility to study the kinetics in detail. Here we report the first detailed comparison between experiments and a phenomenological theory for the liquid‐liquid transition of a molecular liquid, triphenyl phosphite. Both nucleation‐growth‐type and spinodal‐d...

Fragility Control Using the Liquid‐Liquid Transition in Molecular Liquid

Liquids, whose viscosity obeys the Arrhenius law, are called “strong,” while “fragile” liquids have the super‐Arrhenius behavior. Here we report the first continuous control of the fragility of liquid of the same material over a wide range of fragility, using a continuous liquid‐liquid transition. Our study clearly demonstrates that the fragility is not a material specific quantity, but is controlled by the order parameter governing the liquid‐liquid transition, which may be the fraction of locally favored structures in the liquid.