Glass-like Arrest Research Articles

Interplay between percolation and glassiness in the random Lorentz gas

The random Lorentz gas (RLG) is a minimal model of transport in heterogeneous media that exhibits a continuous localization transition controlled by void space percolation. The RLG also provides a toy model of particle caging, which is known to be relevant for describing the discontinuous dynamical transition of glasses. In order to clarify the interplay between the seemingly incompatible percolation and caging descriptions of the RLG, we consider its exact mean-field solution in the infinite-dimensional d→∞ limit and perform numerics in d=2...20. We find that for sufficiently high d the mean-field caging transition precedes and prevents the percolation transition, which only happens on timescales diverging with d. We further show that activated processes related to rare cage escapes destroy the glass transition in finite dimensions, leading to a rich interplay between glassiness and percolation physics. This advance suggests that the RLG can be used as a toy model to develop a first-principle description of particle hopping in structural glasses.

Motility-limited aggregation of mammary epithelial cells into fractal-like clusters

Migratory cells transition between dispersed individuals and multicellular collectives during development, wound healing, and cancer. These transitions are associated with coordinated behaviors as well as arrested motility at high cell densities, but remain poorly understood at lower cell densities. Here, we show that dispersed mammary epithelial cells organize into arrested, fractal-like clusters at low density in reduced epidermal growth factor (EGF). These clusters exhibit a branched architecture with a fractal dimension of [Formula: see text], reminiscent of diffusion-limited aggregation of nonliving colloidal particles. First, cells display diminished motility in reduced EGF, which permits irreversible adhesion upon cell-cell contact. Subsequently, leader cells emerge that guide collectively migrating strands and connect clusters into space-filling networks. Thus, this living system exhibits gelation-like arrest at low cell densities, analogous to the glass-like arrest of epithelial monolayers at high cell densities. We quantitatively capture these behaviors with a jamming-like phase diagram based on local cell density and EGF. These individual to collective transitions represent an intriguing link between living and nonliving systems, with potential relevance for epithelial morphogenesis into branched architectures.

Decoupling Arrest Origins in Hydrogels of Cellulose Nanofibrils.

Colloidal gels with various architectures and different types of interactions provide a unique opportunity to shed light on the interplay between microscopic structures and mechanical properties of soft glassy materials. Here, we prepare acetylated cellulose nanofibrils with 2 degrees of substitution and make a structural and rheological characterization of their hydrogels. Two-step yielding processes are observed in the shear experiments, which allow us to deduce more precise knowledge regarding localized structural changes of the fibrils. We separate the viscoelastic response into two contributions: the establishment of cross-linked clusters on a fibril level and the arrested phase separation on a cluster level. We hypothesize that with the addition of salt, the hydrogels exhibit different arrested states that are identified as unable to access the thermodynamic equilibrium. Our results highlight that the coexistence of gelation and glass transitions are experimentally recognized in the hydrogels, with a global gelation driven by a local glasslike arrest during spinodal decomposition.

ChemInform Abstract: Broad 1St Order Phase Transitions: Phase Coexistence, Unusual Hysteresis and Glasslike ′Kinetic Arrest′

AbstractReview: 25 refs.

Complex ferromagnetic-antiferromagnetic phase transition and glass-like arrest of kinetics in Sm1−xBaxCrO3 (x = 0 and 0.1)

The dc magnetization studies of polycrystalline sample Sm1−xBaxCrO3 (x = 0 and 0.1) show the existence of a magnetic glass-like arrest of kinetics. There exist constant frozen fractions of antiferromagnetic state in this complex phase transition process, the frozen fractions are about 33% and 17%, respectively, in SmCrO3 and Sm0.9Ba0.1CrO3 at the cooling and warming rates of 1.5 K/min. The degree of ferromagnetic-antiferromagnetic (FM-AFM) phase transitions is closely corresponding to the kinetic behaviors and thermomagnetic irreversibility. The FM-AFM phase transition and the frozen AFM fractions jointly affect the kinetics of glassy behaviors. The magnetic phase transition and glassy state was gradually repressed with the increase of the applied magnetic field, this complex behavior could be tuned in a number of ways in a two parameter (T and H) phase space.

ChemInform Abstract: Phase‐Coexistence and Glass‐Like Behavior in Magnetic and Dielectric Solids with Long Range Order

AbstractReview: [57 refs.]

Formation of magnetic glass in calcium-doped YBaCo2O5.5cobaltites

The d.c. magnetization and magnetic relaxation studies of the calcium doped samples, Y0.95Ca0.05BaCo2O5.5 and YBa0.95Ca0.05Co2O5.5, show the existence of a magnetic glass like behaviour in the family of cobaltites for the first time. Our investigations reveal glass-like arrest of kinetics at low temperature which prevents the system from reaching its magnetic ground state. We show that the low temperature state of these calcium doped phases, which consists of coexisting antiferromagnetic and ferro (or ferri) magnetic phase fractions, can be tuned in a number of ways. Our observations establish that the low temperature state of this oxide is not in thermal equilibrium. The glassy state is formed with the assistance of an external magnetic field, which makes it distinctly different from the more well known metastable state, the spin glass state. The cooling field can tune the fractions of the coexisting phases, and the glass-like state formed at low temperature can also be devitrified by warming the sample. The role of Ca doping in the appearance of these phenomena is discussed in terms of phase separation, involving Co3+ disproportionation into Co4+ ferromagnetic clusters and Co2+ antiferromagnetic clusters.

Anomalous first-order transition inNd0.5Sr0.5MnO3: an interplay between kinetic arrest and thermodynamic transitions

A detailed investigation of the first-order antiferromagnetic insulator (AFI) to ferromagnetic metal (FMM)transition in Nd0.5Sr0.5MnO3 is carried out by resistivity and magnetization measurements. These studies reveal severalanomalous features of thermomagnetic irreversibility across the first-order transition. We show thatthese anomalous features cannot be explained in terms of the supercooling effect alone and theH–T diagram basedon isothermal M–H or R–H measurements alone does not reflect the true nature of the first-order transition in thiscompound. Our investigations reveal glass-like arrest of kinetics at low temperature which playsa dominant role in the anomalous thermomagnetic irreversibility observed in this system. Theinterplay between kinetic arrest and supercooling is investigated by following novel paths in theH–T space. It is shown that coexisting FMM and AFI phases can be tuned in a numberof ways at low temperature. These measurements also show that kinetic arresttemperature and supercooling temperature are anticorrelated, i.e. regions which arearrested at low temperature have higher supercooling temperature and vice versa.

Relating supercooling and glass-like arrest of kinetics for phase separated systems: DopedCeFe2and(La,Pr,Ca)MnO3

Coexisting ferromagnetic and antiferromagnetic phases over a range of temperature as well as magnetic field have been reported in many materials of current interest, showing disorder-broadened 1st order transitions. Anomalous history effects observed in magnetization and resistivity are being explained invoking the concepts of kinetic arrest akin to glass transitions. From magnetization measurements traversing novel paths in field-temperature space, we obtain the intriguing result that the regions of the sample which can be supercooled to lower temperatures undergo kinetic-arrest at higher temperatures, and vice versa. Our results are for two diverse systems viz. the inter-metallic doped CeFe$_2$ which has an antiferromagnetic ground state, and the oxide La-Pr-Ca-Mn-O which has a ferromagnetic ground state, indicating the possible universality of this effect of disorder on the widely encountered phenomenon of glass-like arrest of kinetics.

Glasslike Arrest in Spinodal Decomposition as a Route to Colloidal Gelation

Colloid-polymer mixtures can undergo spinodal decomposition into colloid-rich and colloid-poor regions. Gelation results when interconnected colloid-rich regions solidify. We show that this occurs when these regions undergo a glass transition, leading to dynamic arrest of the spinodal decomposition. The characteristic length scale of the gel decreases with increasing quench depth, and the nonergodicity parameter exhibits a pronounced dependence on scattering vector. Mode coupling theory gives a good description of the dynamics, provided we use the full static structure as input.

Clustering, glass transition and gelation in a reactive fluid

We study the dependence of the dynamics on the size of particle clusters that grow bystepwise aggregation in a two-component reactive mixture. The data reveal thecluster property involved in the glasslike arrest and its quantitative link with thestructural relaxation time. Specifically, we measured the number-average cluster sizexn—i.e., the average number of bonded monomers per molecule—and, independently, the characteristictime τ for decay of the photon correlation function, throughout the reaction. We find thatxn diverges as the system freezes at the glass transition,xn and τ being exponentially related. The comparison with the gel transition that occurs at thedivergence of the weight-average cluster size provides evidence that the two transitionsare associated to distinct properties of the same underlying clustering process.

Clustering and Cooperative Dynamics in a Reactive System

We study the dependence of the dynamics on the size of particle clusters that grow by stepwise aggregation in a reactive epoxy-amine mixture. The data reveal the cluster property involved in the glasslike arrest and its quantitative link with the structural relaxation time. We find that the number-average cluster size xn governs the formation of a glassy phase as distinct from a gel phase, and that xn correlates to the size of the "cooperatively rearranging regions" postulated by the Adam-Gibbs model for glass forming liquids. These results suggest that the step polymerization process generates clusters that behave much like dynamical heterogeneities observed in supercooled liquids.