Ken-ichiro Murata

Liquid–liquid transition without macroscopic phase separation in a water–glycerol mixture

The existence of more than two liquid states in a single-component substance and the ensuing liquid-liquid transitions (LLTs) has attracted considerable attention because of its counterintuitive nature and its importance in the fundamental understanding of the liquid state. Here we report direct experimental evidence for a genuine (isocompositional) LLT without macroscopic phase separation in an aqueous solution of glycerol. We show that liquid I transforms into liquid II by way of two types of kinetics: nucleation and growth, and spinodal decomposition. Although liquid II is metastable against crystallization, we could access both its static and dynamical properties experimentally. We find that liquids I and II differ in density, refractive index, structure, hydrogen bonding state, glass transition temperature and fragility, and that the transition between the two liquids is mainly driven by the local structuring of water rather than of glycerol, suggesting a link to a plausible LLT in pure water.

Broadband complex permittivity measurement techniques of materials with thin configuration at microwave frequencies

A test method to evaluate the complex permittivity of materials with thin configuration (thickness of 50–300μm) is presented. We evaluate the complex permittivity of materials with various mechanical and electrical characteristics (films, powders, and liquids) at frequencies from 100 MHz to 20 GHz and at temperatures from 293 to 353 K using an experimental method presented in this paper. We have developed a fixture having a circular parallel-plate capacitor which is suitable for the measurement of materials with thin configuration. Our method is based on theoretical consideration of wave propagation in the capacitor, which is associated with multiple reflections along the diameter of the sample. The consideration of time delay in the sample section makes it possible to evaluate the permittivity of high dielectric constant materials in the frequency range up to 20 GHz. In addition, some examples for the measurements show that the resolution with tanδ is as low as 0.001. Our method is powerful to understand...

Novel kinetic trapping in charged colloidal clusters due to self-induced surface charge organization

We study metastable clusters in a colloidal system with competing interactions. A short-ranged polymer-induced attraction drives clustering, while a weak, long-ranged electrostatic repulsion prevents extensive aggregation. We compare experimental yields of cluster structures expected from theory, which assumes simple addition of the competing isotropic interactions. For clusters of size

General nature of liquid–liquid transition in aqueous organic solutions

4\leq m\leq6

Microscopic identification of the order parameter governing liquid–liquid transition in a molecular liquid

, the yield is significantly less than that expected. We attribute this to an anisotropic self-organized surface charge distribution linked to the cluster symmetry: non-additivity of electrostatic repulsion and polymer-induced attraction. 7-membered clusters have a clear optimal yield of the expected pentagonal bipyramid structure as a function of strength of the attractive interaction.Colloidal clusters are an unusual state of matter where tunable interactions enable a sufficient reduction in their degrees of freedom that their energy landscapes can become tractable — they form a playground for statistical mechanics and promise unprecedented control of structure on the submicron lengthscale. We study colloidal clusters in a system where a short-ranged polymer-induced attraction drives clustering, while a weak, long-ranged electrostatic repulsion prevents extensive aggregation. We compare experimental yields of cluster structures with theory which assumes simple addition of competing isotropic interactions between the colloids. Here we show that for clusters of size 4 ≤ m ≤ 7, the yield of minimum energy clusters is much less than expected. We attribute this to an anisotropic self-organized surface charge distribution which leads to unexpected kinetic trapping. We introduce a model for the coupling between counterions and binding sites on the colloid surface with which we interpret our findings.

Thermodynamic origin of surface melting on ice crystals

The presence or absence of a liquid-liquid transition in water is one of the hot topics in liquid science, and while a liquid-liquid transition in water/glycerol mixtures is known, its generality in aqueous solutions has remained elusive. Here we reveal that 14 aqueous solutions of sugar and polyol molecules, which have an ability to form hydrogen bonding with water molecules, exhibit liquid-liquid transitions. We find evidence that both melting of ice and liquid-liquid transitions in all these aqueous solutions are controlled solely by water activity, which is related to the difference in the chemical potential between an aqueous solution and pure water at the same temperature and pressure. Our theory shows that water activity is determined by the degree of local tetrahedral ordering, indicating that both phenomena are driven by structural ordering towards ice-like local structures. This has a significant implication on our understanding of the low-temperature behaviour of water.

In situ Determination of Surface Tension-to-Shear Viscosity Ratio for Quasiliquid Layers on Ice Crystal Surfaces

Significance Liquid–liquid transition (LLT) in single-component liquids is one of the most mysterious phenomena in condensed matter. To understand this phase transition, it is essential to elucidate the order parameter governing it. We have succeeded in accessing the structural order parameter governing LLT by simultaneously measuring small- and wide-angle X-ray scattering during the process of LLT. We identify the order parameter to be the number density of locally favored structures, whose size is a few nanometers. This suggests that the order parameter is scalar and nonconserved. This finding sheds new light on the physical nature of this unconventional transition from one liquid to another. A liquid–liquid transition (LLT) in a single-component substance is an unconventional phase transition from one liquid to another. LLT has recently attracted considerable attention because of its fundamental importance in our understanding of the liquid state. To access the order parameter governing LLT from a microscopic viewpoint, here we follow the structural evolution during the LLT of an organic molecular liquid, triphenyl phosphite (TPP), by time-resolved small- and wide-angle X-ray scattering measurements. We find that locally favored clusters, whose characteristic size is a few nanometers, are spontaneously formed and their number density monotonically increases during LLT. This strongly suggests that the order parameter of LLT is the number density of locally favored structures and of nonconserved nature. We also show that the locally favored structures are distinct from the crystal structure and these two types of orderings compete with each other. Thus, our study not only experimentally identifies the structural order parameter governing LLT, but also may settle a long-standing debate on the nature of the transition in TPP, i.e., whether the transition is LLT or merely microcrystal formation.

Oscillations and accelerations of ice crystal growth rates in microgravity in presence of antifreeze glycoprotein impurity in supercooled water

Significance Phase transitions of ice are a major source of a diverse set of natural phenomena on Earth. In particular, quasi-liquid layers (QLLs) resulting from surface melting are recognized to be key players involved in various natural phenomena spanning from making snowballs to electrification of thunderclouds. With the aid of in situ observations with our advanced optical microscopy combined with two-beam interferometry, we elucidate a thermodynamic origin of the formation of QLLs and their unique wetting behavior (pseudo-partial wetting and wetting transitions) on ice surfaces. We show that QLLs are a metastable transient state formed through vapor growth and sublimation of ice that are absent at equilibrium. Since the pioneering prediction of surface melting by Michael Faraday, it has been widely accepted that thin water layers, called quasi-liquid layers (QLLs), homogeneously and completely wet ice surfaces. Contrary to this conventional wisdom, here we both theoretically and experimentally demonstrate that QLLs have more than two wetting states and that there is a first-order wetting transition between them. Furthermore, we find that QLLs are born not only under supersaturated conditions, as recently reported, but also at undersaturation, but QLLs are absent at equilibrium. This means that QLLs are a metastable transient state formed through vapor growth and sublimation of ice, casting a serious doubt on the conventional understanding presupposing the spontaneous formation of QLLs in ice–vapor equilibrium. We propose a simple but general physical model that consistently explains these aspects of surface melting and QLLs. Our model shows that a unique interfacial potential solely controls both the wetting and thermodynamic behavior of QLLs.

Impact of surface roughness on liquid-liquid transition

We have experimentally determined the surface tension-to-shear viscosity ratio (the so-called characteristic velocity) of quasiliquid layers (QLLs) on ice crystal surfaces from their wetting dynamics. Using an advanced optical microscope, whose resolution reaches the molecular level in the height direction, we directly observed the coalescent process of QLLs and followed the relaxation modes of their contact lines. The relaxation dynamics is known to be governed by the characteristic velocity, which allows us to access the physical properties of QLLs in a noninvasive way. Here we quantitatively demonstrate that QLLs, when completely wetting ices, have a thickness of 9±3  nm and an approximately 200 times lower characteristic velocity than bulk water, whereas QLLs, when partially wetting ices, have a velocity that is 20 times lower than the bulk. This indicates that ice crystal surfaces significantly affect the physical properties of QLLs localized near the surfaces at a nanometer scale.

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

The free growth of ice crystals in supercooled bulk water containing an impurity of glycoprotein, a bio-macromolecule that functions as ‘antifreeze’ in living organisms in a subzero environment, was observed under microgravity conditions on the International Space Station. We observed the acceleration and oscillation of the normal growth rates as a result of the interfacial adsorption of these protein molecules, which is a newly discovered impurity effect for crystal growth. As the convection caused by gravity may mitigate or modify this effect, secure observations of this effect were first made possible by continuous measurements of normal growth rates under long-term microgravity condition realized only in the spacecraft. Our findings will lead to a better understanding of a novel kinetic process for growth oscillation in relation to growth promotion due to the adsorption of protein molecules and will shed light on the role that crystal growth kinetics has in the onset of the mysterious antifreeze effect in living organisms, namely, how this protein may prevent fish freezing.