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Melting is analyzed dynamically as a problem of localization at a liquid-solid interface. A Lindermann-like criterion of melting is derived in terms of particular vibrational amplitudes, which turn out to equal a universal quotient (about one-tenth) of the molecular spacing, at the interface.

A study was carried out to explain how the molecular motions of a glass-forming solvent distort the protein's boundary and slave some of the protein's conformational motions by using the advanced Random First-Order transition theory of glass-forming liquids. The experimental measurements of slaving of myoglobin motions indicate that a major fraction of functionally important motions have shown to have significant entropic barriers.

A theory of reactive transport in the presence of environmental fluctuations that restart a transfer attempt, such as, for instance, during charge transfer through an intermediate state on a fluctuating bridge is formulated. Thus, a design principle of a controllable molecular scale device is proposed.

Apart from not having crystallized, supercooled liquids can be considered as being properly equilibrated and thus can be described by a few thermodynamic control variables. In contrast, glasses and other amorphous solids can be arbitrarily far away from equilibrium and require a description of the history of the conditions under which they formed. In this paper we describe how the locality of interactions intrinsic to finite-dimensional systems affects the stability of amorphous solids far off equilibrium. Our analysis encompasses both structural glasses formed by cooling and colloidal assemblies formed by compression. A diagram outlining regions of marginal stability can be adduced which bears some resemblance to the quasi-equilibrium replica meanfield theory phase diagram of hard sphere glasses in high dimensions but is distinct from that construct in that the diagram describes not true phase transitions but kinetic transitions that depend on the preparation protocol. The diagram exhibits two distinct sectors. One sector corresponds to amorphous states with relatively open structures, the other to high density, more closely packed ones. The former transform rapidly owing to there being motions with no free energy barriers; these motions are string-like locally. In the dense region, amorphous systems age via compact activated reconfigurations. The two regimes correspond, in equilibrium, to the collisional or uniform liquid and the so-called landscape regime, respectively. These are separated by a spinodal line of dynamical crossovers. Owing to the rigidity of the surrounding matrix in the landscape, high-density part of the diagram, a sufficiently rapid pressure quench adds compressive energy which also leads to an instability toward string-like motions with near vanishing barriers. Conversely, a dilute collection of rigid particles, such as a colloidal suspension leads, when compressed, to a spatially heterogeneous structure with percolated mechanically stable regions. This jamming corresponds to the onset of activation when the spinodal line is traversed from the low density side. We argue that a stable glass made of sufficiently rigid particles can also be viewed as exhibiting sporadic and localized buckling instabilities that result in local jammed structures. The lines of instability we discuss resemble the Gardner transition of meanfield systems but, in contrast, do not result in true criticality owing to being short-circuited by activated events. The locally marginally stable modes of motion in amorphous solids correspond to secondary relaxation processes in structural glasses. Their relevance to the low temperature anomalies in glasses is also discussed. [ABSTRACT FROM AUTHOR]

Weexplore several potential issues that have been raised overthe years regarding the “entropic droplet” scenarioof activated transport in liquids, due to Wolynes and co-workers,with the aim of clarifying the status of various approximations ofthe random first-order transition theory (RFOT) of the structuralglass transition. In doing so, we estimate the mismatch penalty betweenalternative aperiodic structures, above the glass transition; thepenalty is equal to the typical magnitude of free energy fluctuationsin the liquid. The resulting expressions for the activation barrierand the cooperativity length contain exclusively bulk, static properties;in their simplest form they contain only the bulk modulus and theconfigurational entropy per unit volume. The expressions are universalin that they do not depend explicitly on the molecular detail. Thepredicted values for the barrier and cooperativity length and, inparticular, the temperature dependence of the barrier are in satisfactoryagreement with observation. We thus confirm that the entropic dropletpicture is indeed not only internally consistent but is also fullyconstructive, consistent with the apparent success of its many quantitativepredictions. A simple view of a glassy liquid as a locally metastable,degenerate pattern of frozen-in stress emerges in the present description.Finally, we derive testable relationships between the bulk modulusand several characteristics of glassy liquids and peculiarities inlow-temperature glasses. [ABSTRACT FROM AUTHOR]

We propose a novel type of spectraldiffusion experiment that enablesone to decouple spatial characteristics of the environmental fluctuations,such as their concentration, from the interaction with the chromophore.Traditional hole broadening experiments do not allow for such decouplingin the common case when the chromophore–environment interactionis scale invariant. Here we propose to simultaneously follow the spectraltrails of a small number of nearby chromophorestwo or morewhichthereby sense a highly overlapping set of the fluctuations. To thisend, we estimate the combined probability distribution for the frequenciesof a set of chromophores contained within the samesample. The present setup introduces a new length scale, i.e., theinterchromophore distance, which breaks the aforementioned scale invarianceand enables one to determine independently the concentration of theenvironmental fluctuations and their coupling to the chromophores,by monitoring the time after which spectral diffusion of distinctchromophores becomes uncorrelated. We illustrate these results withstructural excitations in low temperature glasses. [ABSTRACT FROM AUTHOR]

We show that the crossover temperature to activated transportinglass-forming liquids can be predicted using their finite-frequencyelastic constants and the fusion entropy. The latter quantities determinethe size of the vibrational motions of chemically rigid molecularunits in the liquid as a function of temperature. Using the notionthat, at the crossover, the “Lindemann ratio” of thisvibrational displacement to the corresponding lattice spacing is nearlysystem-independent, one can estimate the crossover temperature. Fornine specific substances, the resulting predictions are consistentwith experimental estimates of the dynamical crossover temperatureand also with the predictions of the random first order transition(RFOT) theory for the onset of barrierless transport owing to fractalcorrelated rearrangements that occur at a critical configurationalentropy. In particular, the fragility index is found to inverselycorrelate with the ratio of the crossover and glass transition temperatures.This prediction agrees with most observations except for boron oxideB2O3, which deviates from the common trend.This exception is argued to result from additional local orderingwith lowering temperature in B2O3. Finally,we show that taking into account the temperature dependence of theelastic constants is crucial for accurate estimates of the crossovertemperature. [ABSTRACT FROM AUTHOR]

Melting is analyzed dynamically as a problem of localization at a liquid−solid interface. A Lindemann-like criterion of melting is derived in terms of particular vibrational amplitudes, which turn out to equal a universal quotient (about one-tenth) of the molecular spacing, at the interface. The near universality of the Lindemann ratio apparently arises owing to strongly overdamped dynamics near melting, and despite the anharmonic interactions being system-specific. A similar criterion is derived for structural displacements in the bulk of the solid, in particular the premelted layer; the criterion is no longer strictly universal, but still depends only on the harmonic properties of the solid. We further compute the dependence of the magnitude of the elemental molecular translations, in deeply supercooled fluids, on the temperature and the high frequency elastic constants. We show explicitly that the surface tension between distinct liquid states, near the glass transition of a supercooled liquid, is nearly evenly split between entropic and energetic contributions. [ABSTRACT FROM AUTHOR]