Search results for "Supercooling"
showing 10 items of 127 documents
Simulation of Models for the Glass Transition: Is There Progress?
2002
The glass transition of supercooled fluids is a particular challenge for computer simulation, because the (longest) relaxation times increase by about 15 decades upon approaching the transition temperature T g. Brute-force molecular dynamics simulations, as presented here for molten SiO2 and coarse-grained bead-spring models of polymer chains, can yield very useful insight about the first few decades of this slowing down. Hence this allows to access the temperature range around T c of the so-called mode coupling theory, whereas the dynamics around the experimental glass transition is completely out of reach. While methods such as “parallel tempering” improve the situation somewhat, a method…
Modeling non-linear dielectric susceptibilities of supercooled molecular liquids
2021
Advances in high-precision dielectric spectroscopy have enabled access to non-linear susceptibilities of polar molecular liquids. The observed non-monotonic behavior has been claimed to provide strong support for theories of dynamic arrest based on the thermodynamic amorphous order. Here, we approach this question from the perspective of dynamic facilitation, an alternative view focusing on emergent kinetic constraints underlying the dynamic arrest of a liquid approaching its glass transition. We derive explicit expressions for the frequency-dependent higher-order dielectric susceptibilities exhibiting a non-monotonic shape, the height of which increases as temperature is lowered. We demons…
Slow Dielectric Relaxation of Supercooled Liqutos Investigated by Nonresonant Spectral Hole Burning
1996
ABSTRACTWhen supercooled propylene carbonate and glycerol are subjected to a large-amplitude, low-frequency electric field, a spectral hole develops in their dielectric relaxation that is significantly narrower than their bulk response. This observation of nonresonant spectral hole burning establishes that the non-Debye response is due to a distribution of relaxation times. Refilling of the spectral hole occurs abruptly, indicative of a single recovery rate that corresponds to the peak in the distribution. The general shape of the spectral hole is preserved during recovery, indicating negligible interaction between the degrees of freedom that responded to the field. All relevant features in…
Crystallization kinetics of polydisperse hard-sphere-like microgel colloids: Ripening dominated crystal growth above melting.
2009
Highly cross-linked polystyrene microgel colloids dispersed in an index and density matching solvent provide a system with hard-sphere-like interactions, where gravity effects are effectively minimized. They are a suitable target for time-resolved observations of solidification in purely repulsive systems. We have investigated the crystallization kinetics at increasing undercooling using time resolved light scattering. Crystallization starts always with the formation of compressed, structurally heterogeneous precursor domains. In the coexistence region the precursors, after being converted into true crystallites, start growing fast by assimilating particles from the melt. The resulting poly…
Wave-Vector Dependence of the Dynamics in Supercooled Metallic Liquids
2020
Physical review letters 125(5), 055701 (2020). doi:10.1103/PhysRevLett.125.055701
Isotope effects on the dynamics of a supercooled van der Waals liquid
2000
Deuteron magnetic resonance was used to study three differently isotope-labeled species of the fragile glass-forming liquid ortho-terphenyl. The calorimetric glass transition of the isotope deuterated only at the central phenyl ring is significantly lower than that of the perdeuterated one. It is shown that while the ortho-terphenyl molecule is not as rigid as previously often assumed, its overall reorientation geometry is independent of deuteration. The characteristic jump angles are found to increase with temperature, thus resolving an apparent discrepancy previously noted when comparing typical jump sizes from NMR with other data.
Structural fluctuations in glass-forming liquids: Mössbauer spectroscopy on iron in glycerol.
1991
M\"ossbauer absorption spectra of $^{57}\mathrm{Fe}^{2+}$ dissolved in a glycerol-water mixture have been measured over a wide temperature range (80--275 K). In the supercooled liquid state the shapes of the spectra depend strongly on temperature. The M\"ossbauer spectra can be fit with jump diffusion with a Cole-Davidson distribution of fluctuation times. The results are in agreement with those obtained from dielectric and ultrasonic volume relaxations, proving that the \ensuremath{\alpha} relaxation of viscous liquids is responsible for the line broadening of the spectra. From the temperature dependence of the integrated area of the M\"ossbauer spectrum a second dynamic process is inferre…
Crystallization kinetics of poly(ethylene oxide) from its melt and from mixtures with tetrahydronaphthalene and oligo(ethylene oxide-block-dimethylsi…
2004
The crystallization of poly(ethylene oxide) (PEO) from the pure state and from its mixtures with oligo(dimethyl siloxane-b-ethylene oxide) (COP) and tetrahy- dronaphthalene (THN) was investigated. The crystallization kinetics was studied iso- thermally and nonisothermally with an automated device that monitored the light passing through the corresponding liquids as functions of time and/or temperature. The rate was strongly influenced by the concentration of COP in the mixture. A substantial decrease in the induction time (the time required for the onset of crystallization) and a considerable shift in the crystallization temperature (the transition from a liquid state to a solid state) to h…
Dynamics of sorbitol and maltitol over a wide time-temperature range
1999
The relaxation behaviour of two molecular glass-forming systems, namely sorbitol and maltitol, are investigated in the large temperature range relevant to the glass-transition. These data are obtained by combining three techniques, i.e. low-frequency mechanical spectroscopy, medium and high frequency dielectric spectroscopy, and viscosity measurements. This procedure allows to determine the relaxation map of these polyols on a wide time range [10-9-107 s]. Two different relaxation processes can be observed. The principal α-relaxation process exhibits a complex behaviour, comprising a non-Arrhenius temperature dependence above T g (supercooled liquid state), and an Arrhenius behaviour below …
On the nature of slow β-relaxation in supercooled liquids
2000
We propose a model for reorientational motions of molecules associated with secondary beta-relaxation in supercooled liquids. The secondary relaxation is attributed to relaxation within a given local minimum, while the primary relaxation is attributed to transitions between distinct free-energy minima. We find that (i) at the temperature where the peak frequency of the extrapolated beta-relaxation intersects the alpha-relaxation, the actual and the extrapolated spectra differ in their time constants by approximately one decade; (ii) there is no clear division between the imaginary part of the dielectric susceptibility for the alpha- and the beta-relaxation for temperatures larger than 1.1 T…