arXiv subjects

Rei Kurita

Publications and source records attributed to Rei Kurita.

At least 19 recordsLinked to original sources

arXiv2026

Bond-number-controlled durability of cohesive granular materials under repeated vibration

Cohesive granular materials derive their mechanical stability not only from the strength of individual interparticle bonds but also from the number of bonds forming the load-bearing network. However, these two effects are difficult to separate experimentally because conventional control parameters, such as liquid content, generally alter both simultaneously. Here, we use a mixed granular system composed of cohesive and noncohesive grains to control the cohesive bond number while keeping the bond strength approximately unchanged. We investigate the failure lifetime under repeated vibration and find that the number of cycles to failure, $N_f$, depends strongly on the mixing ratio $α$. In a mean-field picture of random mixing, the fraction of cohesive contacts scales as $α^2$, and $N_f$ increases approximately exponentially with $α^2$. By contrast, although the lifetime tends to decrease with increasing vibration intensity $G$, its dependence on $G$ is comparatively weak over the present experimental range. Remarkably, although the Young's modulus is nearly independent of $α$ above the rigidity threshold, the lifetime continues to increase strongly with $α$. This demonstrates that mechanical rigidity and durability against repeated perturbations exhibit distinct dependences on the cohesive network. These results identify bond number as a key control parameter for the durability of cohesive granular materials.

cond-mat.soft↗

arXiv2026

Fluid-structure coupling governs a dynamic transition in foam scraping

Foam scraping exhibits a dynamic transition between a slip state, in which the foam moves beneath a plate, and a scraping state, in which the foam is expelled from the confined region. Although this transition has been associated with the propagation of local T1 rearrangements, the physical parameter controlling their propagation remains unclear. Here, we investigate the dependence of the critical scraping velocity on the liquid fraction, bulk viscosity, and surfactant system. For all examined conditions, the critical capillary number follows $\mathrm{Ca}_c\proptoϕ^{-1}$, apart from a solution-dependent prefactor. We propose a local fluid--structure-coupling model in which viscous work transmitted through the Plateau-border network competes with the effective energetic cost required for one T1 event to trigger the next. The observed scaling implies an effective energetic cost governed by the Laplace pressure and is consistent with a small local compressive component of the bubble deformation. These results identify local coupling between interstitial flow and bubble deformation as a mechanism controlling the macroscopic slip--scraping transition.

cond-mat.soft↗

arXiv2026

Geometric control of powder jet dynamics and energy dissipation

Applying an impulsive force to a powder layer shaped with a concave surface generates a sharp powder jet. This phenomenon has been proposed as a method for evaluating the flowability of powders from small amount of samples. In this study, we systematically varied the radius of the initial concave shape as a controllable parameter and quantitatively examined the resulting jet dynamics, focusing on ejection velocity and maximum height. Our high-speed observations revealed that increasing the concave radius led to broader jets with significantly reduced velocity and maximum height. These dynamic quantities followed a scaling relation with drop height, while the scaling coefficient decreased with the concave radius, indicating that the surface geometry directly governs the extent of energy dissipation. Furthermore, a minimal mechanical model incorporating the sliding distance and velocity squared type dissipation of the powder flow reproduces the observed linear dependence of the jet height on the concave radius. These findings establish powder jets as a sensitive probe of dissipation in dynamic powder flow and provide a quantitative framework for comparing powder specific interactions such as humidity, particle size and particle shape.

cond-mat.soft↗

arXiv2026

Liquid-state structural asymmetry governs species-selective crystallization in multicomponent systems

Multicomponent crystals are often assumed to form nearly random solid solutions when thermodynamically stable. However, crystal growth proceeds from structurally heterogeneous liquids, raising the possibility that the liquid state may influence which species are incorporated into the growing crystal. Here we demonstrate that liquid-state structural asymmetry can induce species-selective crystallization in multicomponent systems. Using molecular dynamics simulations of a multivalent rocksalt-type model (AgPbBiTe$_3$), we find that cations with higher valence readily form locally crystal-compatible coordination environments in the liquid and are efficiently incorporated into the growing lattice, whereas lower-valence cations exhibit more disordered liquid coordination and attach less efficiently at the crystal-liquid interface. This asymmetry leads to species-selective incorporation and slower crystal growth. Depth-resolved photoelectron spectroscopy measurements on AgPbBiTe$_3$ further reveal enhanced Ag concentration near grain-boundary and surface regions, consistent with the selective incorporation predicted by the simulations. These results demonstrate that structural compatibility between liquid-state structure and the target crystal motif governs selective incorporation during crystallization, providing a general kinetic mechanism by which compositional heterogeneity can emerge during growth of multicomponent crystals.

cond-mat.soft↗

arXiv2026

Curing-induced filler aggregation in epoxy-amine systems

Hypothesis: The macroscopic properties of polymer composites are governed by the dispersion and aggregation states of filler particles within a crosslinking matrix. Although curing transforms a liquid precursor into a solid network, its influence on filler aggregation remains insufficiently understood. We hypothesize that curing induces effective attractive interactions between filler particles, leading to aggregation even in non-Brownian systems. Experiment: Fluorescent polystyrene beads were homogeneously dispersed in a bisphenol F epoxy resin. Curing was initiated by adding trimethylhexamethylenediamine, and the evolution of the three-dimensional particle configurations was quantitatively examined using confocal laser fluorescence microscopy before and after completion of curing. Findings: Aggregation was enhanced during curing despite the absence of conventional attractive forces. The aggregation increment cannot be described solely by filler volume fraction but is governed by the mean interparticle gap $H$. Data collapse onto a linear scaling with the reduced gap parameter, identifying a geometric control parameter for curing-induced aggregation. This scaling demonstrates that curing dynamically generates an effective interaction whose spatial range scales with particle size, consistent with previously predicted rigidity-percolation-induced attractions. These findings establish a geometric criterion for predicting final dispersion states in curing polymer composites.

cond-mat.soft↗

arXiv2026

Hidden Structural Control of Solvent Transport under Soft Jamming

Transport in soft jammed materials is often described as fluid motion through a fixed structure, leading naturally to capillary based descriptions. This picture appears particularly appropriate in strongly jammed systems, where structural rearrangements are suppressed and little visible motion is observed. Here we investigate solvent transport in foam and show that this intuition fails to capture key aspects of the transport process. By directly observing both liquid penetration and bubble motion under controlled boundary conditions, we demonstrate that solvent transport is strongly influenced by the mechanical response of the foam structure, even though the intrinsic imbibition relative to the foam matrix remains purely capillary-driven. In closed systems, the jammed structure resists penetration and leads to a pronounced slowdown that cannot be accounted for by purely capillary descriptions. In contrast, in open systems, collective bubble motion accompanies solvent invasion, resulting in an apparent acceleration of transport. These results indicate that the lack of structural motion does not guarantee a purely capillary description of transport. Our findings reveal a boundary controlled coupling between flow and structure, and highlight the need to reconsider transport processes in soft jammed systems, including foams, dense colloids, and biological tissues.

cond-mat.soft↗

arXiv2025

Cooperative Ion Conduction Enabled by Site Percolation in Random Substitutional Crystals

Efficient and safe energy storage technologies are essential for realizing a sustainable and electrified society. Among the key challenges, the design of superionic conductors for all-solid-state batteries often faces a fundamental trade-off between stability and ionic conductivity. Random substitutional crystals, where atomic species are randomly distributed throughout a crystal lattice, present a promising route to overcome this trade-off. Although the importance of cooperative motion in ion conduction has been pointed out, there is a lack of understanding of the relationship between mesoscale structural organization and macroscopic conductivity, limiting the rational design of optimal compositions. Here, we systematically investigate the ionic conductivity of rock salt random substitutional ionic crystals Li$_x$Pb$_{1-2x}$Bi$_x$Te as a function of Li concentration $x$ using molecular dynamics simulations. We find that ionic conductivity increases sharply once the $x$ exceeds a critical threshold, without disrupting the underlying crystal structure. Strikingly, this threshold aligns with the site-percolation threshold predicted by percolation theory. Our findings establish ion percolation as a universal design principle that reconciles the trade-off between conductivity and stability, offering a simple and broadly applicable strategy for the development of robust, high-performance solid electrolytes.

cond-mat.mtrl-sci↗

arXiv2025

Critical-like phenomenon in scraping of jamming systems

In jamming systems like colloids, emulsions, foams, and biological tissues, significant deformation is essential for processes such as material scraping or wound self-healing. To adequately spread a foam or cream over a surface, external force must be applied to artificially scrape it. The scraping of foam using a rigid plate has been observed to exhibit complex behavior distinct from that of simple liquids. In this study, we quantitatively analyzed the transition between partial and slender scraping regimes by examining changes in internal structure and partial spreading lengths. Our findings reveal that the sequential propagation of bubble rearrangement in the foam's internal structure leads to the partial scraping. Moreover, the scraping length in the partial scraping regime shows divergence near the transition point, characterized by a critical exponent of approximately 0.61. These results imply that foam scraping is governed by directional percolation theory, supported by the agreement between the experimentally observed critical exponent and theoretical predictions. This research significantly advances the understanding of macroscopic kinetics and rheological behavior in jamming systems, including foams, colloids, emulsions, and biological tissues.

cond-mat.soft↗

arXiv2024

Effective osmotic pressure of foams in short-term dynamics

Foams exhibit absorptive properties and are widely used for cleaning contaminants, oil recovery, and selective mineral extraction via froth flotation. Although foam absorption has historically been linked to equilibrium osmotic pressure, empirical observations show that drainage occurs at levels much lower than theoretical predictions. In this study, we investigate the effective osmotic pressure in foams. The experimental findings indicate that effective osmotic pressure is primarily influenced by short-term dynamics and is governed by the yield stress rather than equilibrium osmotic pressure. Gravity-induced flow drives bubble movement downward, subjecting the lower bubbles to increased pressure. Once the pressure exerted by the solution exceeds the yield stress, internal bubble rearrangement occurs, and drainage is promoted by the relaxation of inter-bubble repulsive forces. In contrast, below the yield stress, these repulsive forces suppress drainage. While foams have traditionally been modeled as immobile porous media, the reality involves kinematic coupling between the solution and the bubbles, which establishes yield stress as the key factor in determining effective osmotic pressure. This framework is also relevant to the dynamics of soft jammed systems, such as blood flow in vessels, emulsions, and biological tissues, offering significant advancements in the understanding of soft jammed system behavior.

cond-mat.soft↗

arXiv2024

Spontaneous formation of Frenkel defects in high-entropy-alloys-type compound

High-entropy alloys (HEAs) are attracting attention due to their exceptional properties, such as enhanced mechanical toughness, superconducting robustness, and thermoelectric performance. Numerous HEAs have been developed for diverse applications, ranging from self-healing in fusion reactors to addressing environmental concerns with thermoelectric materials. Understanding atomic diffusion within HEA crystals is crucial for these applications. Here, this study investigates diffusion mechanisms in PbTe-based HEAs, focusing on the role of indium (In). Molecular dynamics simulations reveal that In inclusion prompts spontaneous Frenkel defect formation, notably enhancing diffusion not only of In$^+$ but also other cations. Frenkel defect formation, closely linked to alloy properties, is predominantly influenced by charge rather than cation size. This insight not only enhances comprehension of HEA diffusion mechanisms but also develops HEAs with properties such as self-healing from damage and high ion permeability, advancing the field of material science.

cond-mat.mtrl-sci↗

arXiv2023

Initial perturbations dependence of non-equilibrium continuous and discontinuous pattern transition

A phase separation in a spatially heterogeneous environment is closely related to intracellular science and material science. For the phase separation, initial heterogeneous perturbations play an important role in pattern formations. In this study, a pattern transition from a lamellar pattern to a columnar pattern is investigated in the presence of a slit pattern as the initial perturbations. Here it is found that the transition behavior depends on the initial slit width. When the initial slit width is close to the width of the columnar pattern at the steady state, the pattern transition is the second-order-like (continuous) transition. Meanwhile, the pattern transition becomes the first-order-like (discontinuous) transition if the width of the initial slit is much larger than that at the steady state. Then those transition behaviors can be explained by the dynamical path during the pattern formation. This finding will advance understanding of the initial perturbation dependence of nonequilibrium phenomena.

cond-mat.stat-mech↗

arXiv2023

Spreading of foam on a substrate

Foam is an industrially important form of matter, commonly deployed to clean objects and even our own skin, thanks to its ability to absorb oil and particles into its interior. To clean a large area, a foam is spread over a substrate, but the optimum conditions and mechanism have been unclear. Here, we study how a foam is spread by a rigid plate on a substrate as a function of spreading velocity, gap height, confinement length, amount of foam and wettability of the substrate. Three distinguishable spreading patterns were found: homogeneous spreading, non-spreading, and slender spreading. It is also found that the dynamics and the mechanism of the spreading can be explained by coupling among dewetting, anchoring, shear stress, viscous stress and yield stress. It is a unique feature of foams, which is not observed in simple liquids and then these findings are also critical for understanding the mechanical response of other soft jamming systems such as cells and emulsions.

cond-mat.soft↗

arXiv2023

Gel-like granular materials with high durability and high deformability

Building materials such as concretes and mortar are formed by solidifying granular slabs. Such materials are often fractured by giant forces such as during earthquakes, leading to the collapse of structures and potentially casualties. One avenue of enquiry to prevent cracking would be to realize a material that can maintain a stable shape without being solidified. Here, we focus on sand grains coated with silicone oil, experimentally investigating the Young's modulus of a granular slab where ordinary grains and the coated grains are mixed in a mixing ratio $α$. It is found that the Young's modulus increases rapidly at $α\ge 0.6$. We use numerical simulation to show that this sudden increase in the Young's modulus is caused by a rigidity percolation transition. Furthermore, we are able to show that granular slabs containing coated sand have outstanding deformability without collapsing under large external stress. We believe this may lead to the development of granular materials that are rigid under usual pressures but deformable under more extreme conditions, such as during seismic activity.

cond-mat.soft↗

arXiv2022

Selective 3-dimensional patterning during phase separation of a continuously laminated layer

Control over the physical properties of materials is ubiquitously required in many fields. One means by which this can be achieved is controlling the internal structure of multi-component materials with an eye to enhancing mechanical properties. Here, we focus on self-organized pattern formation in phase separating materials, where microscopic patterns with a smooth, continuous connection may be realized. We propose a feasible method to control pattern formation using phase separation combined with continuous ``lamination'' of material, when material is continuously and homogeneously layered on top of a base. We find that a random droplet pattern, a lamellar pattern, and a cylindrical pattern are formed depending on the lamination rate $V$. We clarify the dynamics of pattern formation, focusing on the mechanism. This study may lead to the creation of new functional materials through artificial pattern control.

cond-mat.soft↗

arXiv2022

Glassy atomic vibrations and blurry electronic structures created by local structural disorders in high-entropy metal telluride superconductors

The motivation of this work is our recent observation of the robustness of superconductivity in a High-entropy (HE) superconductor Ag0.2In0.2Sn0.2Pb0.2Bi0.2Te (CsCl-type) to external pressure. The superconducting transition temperature (Tc) of Ag0.2In0.2Sn0.2Pb0.2Bi0.2Te is almost constant with pressure, described as robustness of superconductivity to pressure, whereas the PbTe with zero configurational entropy of mixing exhibits a clear decrease in Tc with pressure. Here, we investigated the atomic displacement parameters (Uiso), the atomic-vibration characteristics, and the electronic states of metal tellurides (MTe) with various configurational entropy of mixing (DSmix) at the M site. The Uiso for the M site is clearly increased by M-site alloying with DSmix > 1.1R, which is the evidence of local disorder introduced by the increase in DSmix via the solution of three or more M elements. The revealed vibrational density of states (DOS) shows a remarkable broadening with DSmix > 1.1R, which indicates glassy characteristics of atomic vibration in HE MTe with a NaCl-type structure (low-pressure phase). On the electronic states of the CsCl-type (high-pressure) phases, where the robustness of Tc is observed, blurry electronic band structure appears with increasing DSmix, which indicates the evolution of blurry (glassy) electronic states in HE MTe with the CsCl-type structure. The estimated electronic DOS at Fermi energy cannot explain the changes in Tc for HE MTe when assuming conventional electron-phonon superconductivity, but the conventional explanation seems to work for PbTe. Therefore, the pairing mechanisms in MTe with DSmix > 1.1R are affected by glassy phonon and/or blurry electronic states in MTe, and the robustness of superconductivity would be originating from unique electron-phonon coupling.

cond-mat.supr-con↗

arXiv2012

Measuring every particle's size from three-dimensional imaging experiments

Often experimentalists study colloidal suspensions that are nominally monodisperse. In reality these samples have a polydispersity of 4-10%. At the level of an individual particle, the consequences of this polydispersity are unknown as it is difficult to measure an individual particle size from microscopy. We propose a general method to estimate individual particle radii within a moderately concentrated colloidal suspension observed with confocal microscopy. We confirm the validity of our method by numerical simulations of four major systems: random close packing, colloidal gels, nominally monodisperse dense samples, and nominally binary dense samples. We then apply our method to experimental data, and demonstrate the utility of this method with results from four case studies. In the first, we demonstrate that we can recover the full particle size distribution {\it in situ}. In the second, we show that accounting for particle size leads to more accurate structural information in a random close packed sample. In the third, we show that crystal nucleation occurs in locally monodisperse regions. In the fourth, we show that particle mobility in a dense sample is correlated to the local volume fraction.

cond-mat.soft↗

arXiv2011

Incompressibility of polydisperse random close packed colloidal particles

We use confocal microscopy to study a random close packed sample of colloidal particles. We introduce an algorithm to estimate the size of each particle. Taking into account their sizes, we compute the compressibility of the sample as a function of wave vector $q$, and find that this compressibility vanishes linearly as $q \rightarrow 0$. The particle sizes must be considered to calculate the compressibility properly. These results also suggest that the experimental packing is hyperuniform.

cond-mat.soft↗

arXiv2010

The glass transition of two-dimensional binary soft disk mixtures with large size ratios

We simulate binary soft disk systems in two dimensions, and investigate how the dynamics slow as the area fraction is increased toward the glass transition. The "fragility" quantifies how sensitively the relaxation time scale depends on the area fraction, and the fragility strongly depends on the composition of the mixture. We confirm prior results for mixtures of particles with similar sizes, where the ability to form small crystalline regions correlates with fragility. However, for mixtures with particle size ratios above 1.4, we find that the fragility is not correlated with structural ordering, but rather with the spatial distribution of large particles. The large particles have slower motion than the small particles, and act as confining "walls" which slow the motion of nearby small particles. The rearrangement of these confining structures governs the lifetime of dynamical heterogeneity, that is, how long local regions exhibit anomalously fast or slow behavior. The strength of the confinement effect is correlated with the fragility and also influences the aging behavior of glassy systems.

cond-mat.soft↗