Completely non-polar solvation as a probe of mechanical relaxation in glass-forming liquids

AbstractWe have measured the time resolved phosphorescence of different probe molecules in glassforming solvents under the condition of geometrical confinement in porous glasses. This solvation dynamics technique probes the local dielectric relaxation in the case of a dipolar chromophore in polar liquids. In the absence of dipolar interactions, the observed Stokes shifts reflect the local density or mechanical responses. Therefore, both orientational and translational modes of molecular motions can be measured for liquids imbibed in porous silica glasses. The effect of confinement on the relaxations of supercooled liquids is strongly dependent on the surface chemistry and can be rationalized on the basis of the cooperativity concept. As in the bulk case, we find that the relaxations in nano-confined liquids display heterogeneous dynamics. The density relaxation turns out to be more sensitive to the thermal history relative to the orientational features of molecular motion. By selectively positioning the chromophores at the liquid/solid interface, we observe also that the structural relaxation of the liquid in the immediate vicinity of the glass surface is slowed down but not entirely blocked.

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New experimental features and revisiting the α and β mechanical relaxation in glasses and glass-forming liquids

Journal of Molecular Structure ◽

10.1016/s0022-2860(98)00869-2 ◽

1999 ◽

Vol 479 (2-3) ◽

pp. 183-194 ◽

Cited By ~ 32

Author(s):

J Perez ◽

J.Y Cavaille ◽

L David

Keyword(s):

Mechanical Relaxation ◽

Glass Forming

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Relaxation Dynamics of Glass-Forming Liquids Studied by Ultrasonic Spectroscopy: Stretched Response of Supercooled Ethylbenzene

MRS Proceedings ◽

10.1557/proc-754-cc5.4 ◽

2002 ◽

Vol 754 ◽

Author(s):

M. Cutroni ◽

A. Mandanici

Keyword(s):

Supercooled Liquids ◽

Mechanical Relaxation ◽

Relaxation Dynamics ◽

Arrhenius Law ◽

Ultrasonic Spectroscopy ◽

Fixed Frequency ◽

Acoustic Attenuation ◽

Glass Forming ◽

Typical Time ◽

Observed Behaviour

ABSTRACTGlass forming liquids exhibit their strong or fragile behaviour as a function of temperature, featuring a smaller or greater deviation from a simple Arrhenius law. The size of such deviation on a typical time scale of 10-6 s characterizes the ‘kinetic fragility’ F1/2 of a given material. Ultrasonic experiments in the MHz region are then suitable to show how the relaxational properties are influenced by the ‘fragile’ character of the liquid investigated. On this basis, measurements of acoustic attenuation at fixed frequency (15 MHz) have been performed on glass forming liquid ethylbenzene in the temperature range 100 K-300 K and compared with previous results on simple supercooled liquids derived from benzene. To prevent crystallization each temperature point below 190 K was reached by cooling the sample directly from 300 K and using also different cooling rates. Measurements have given evidence of a mechanical relaxation process: below the melting temperature the acoustic attenuation exhibits a peak and correspondingly the sound velocity increases from liquid-like to solid-like values. A stretched response function is required to reproduce the observed behaviour. The values of the Kohlrausch-Williams-Watts stretching parameter βkww which describe the experimental data are very low, if compared to those obtained for other glass-forming liquids.

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Electron Microscopy of Silicon Nitride-Based Ceramics

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100088944 ◽

1991 ◽

Vol 49 ◽

pp. 926-927

Author(s):

Gareth Thomas

Keyword(s):

Electron Microscopy ◽

High Temperature ◽

Silicon Nitride ◽

World Wide ◽

Sintering Temperature ◽

Liquid Phase Sintering ◽

High Temperature Strength ◽

Sintering Additives ◽

Glass Forming ◽

Dense Product

Silicon nitride and silicon nitride based-ceramics are now well known for their potential as hightemperature structural materials, e.g. in engines. However, as is the case for many ceramics, in order to produce a dense product, sintering additives are utilized which allow liquid-phase sintering to occur; but upon cooling from the sintering temperature residual intergranular phases are formed which can be deleterious to high-temperature strength and oxidation resistance, especially if these phases are nonviscous glasses. Many oxide sintering additives have been utilized in processing attempts world-wide to produce dense creep resistant components using Si3N4 but the problem of controlling intergranular phases requires an understanding of the glass forming and subsequent glass-crystalline transformations that can occur at the grain boundaries.

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The effect of an aluminum heat-sink layer on the laser-induced amorphization of SiOx/TeGeSn/SiOx phase-change recording films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100154846 ◽

1989 ◽

Vol 47 ◽

pp. 574-575

Author(s):

Matthew R. Libera ◽

Martin Chen

Keyword(s):

Thin Film ◽

Phase Change ◽

Heat Sink ◽

Multilayer Film ◽

Glassy Phase ◽

Film Structure ◽

Glass Forming ◽

Active Storage ◽

Dielectric Layers ◽

Amorphous States

Phase-change erasable optical storage is based on the ability to switch a micron-sized region of a thin film between the crystalline and amorphous states using a diffraction-limited laser as a heat source. A bit of information can be represented as an amorphous spot on a crystalline background, and the two states can be optically identified by their different reflectivities. In a typical multilayer thin-film structure the active (storage) layer is sandwiched between one or more dielectric layers. The dielectric layers provide physical containment and act as a heat sink. A viable phase-change medium must be able to quench to the glassy phase after melting, and this requires proper tailoring of the thermal properties of the multilayer film. The present research studies one particular multilayer structure and shows the effect of an additional aluminum layer on the glass-forming ability.

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