1,646 research outputs found
A toy model mimicking cage effect, structural fluctuations and kinetic constraints in supercooled liquids
The cage effect is widely accepted as the basic microscopic mechanism
underlying the physics of supercooled liquids in contrast with usual liquids
which are governed by molecular interactions only. In this work we implement a
new toy model coined to reproduce the cage effect with variants including
structural fluctuations and kinetic constraints. We use this new model to
investigate which glass-transition features are directly due to the cage effect
and which are due to more complex mechanisms.Comment: 5 pages, 4 figure
Self-organization of supercooled liquids confined inside nano-porous materials
Large scale molecular dynamics simulations are used to investigate the
structural and dynamical modifications of supercooled water when confined
inside an hydrophilic nanopore. We then investigate the evolution of the
auto-organization of the most and the least mobile molecules (dynamical
heterogeneity and string-like cooperative motions) when supercooled water is
confined. Our calculations use the recent TIP5P intermolecular potential for
water. We observe a strong slowing down of the dynamical properties when the
liquid is confined, although the liquid structure is found to remain unchanged
when corrected from the pore geometry. We then study cooperative motions inside
supercooled confined water in comparison with bulk water. We observe strong
modifications of the cooperative motions when the liquid is confined. We
observe that dynamical heterogeneities and the associated correlation lengths
are strongly increased as well as string-like motions in the confined liquid.
This result, which is in opposition with the expected limitation of the
correlation length by the confinement procedure, may explain (or be explained
by) the slowing down of the dynamics. However the comparison of the dynamical
heterogeneities at constant diffusion coefficient shows that the slowing down
of the dynamics is not sufficient to explain the increase of the correlation
lengths.Comment: 17 pages, 8 figures, 1 tabl
Heterogeneities in the Glassy State
We study heterogeneities in a binary Lennard-Jones system below the glass
transition using molecular dynamics simulations. We identify mobile and
immobile particles and measure their distribution of vibrational amplitudes.
For temperatures near the glass transition the distribution of vibrational
amplitudes obeys scaling and compares reasonably well with a mean field theory
for the amorphous solid state. To investigate correlations among the immobile
and mobile particles we identify clusters and analyze their size and shape. For
a fixed number of immobile particles we observe that the immobile particles
cluster more strongly together as the temperature is increased which allows the
particles to block each other more effectively, and to therefore stay immobile.
For the mobile particles, on the other hand, the clustering is most pronounced
at small temperatures, indicating that mobility at low temperatures can only be
sustained in cooperative motion.Comment: 9 pages, 15 figure
Three-body interaction-induced light scattering in krypton gas: A computer simulation of the spectral line shapes
he two-, three- and four-body effective collision induced scattering spectral line shapes are calculated for dense gaseous krypton using the pairwise additivity (PA) approximation and different polarizability models. These spectra and several interaction induced spectra calculated at various densities are compared with the experimental measurements of Barocchi et al. [1988, Europhys. Lett., 5, 607]. The potential effect on the spectrum is found to be weak. The results obtained with the Meinander et al. [1986, J. chem. Phys., 84, 3005] empirical polarizability model and molecular dynamics fit well the experimental two- and three-body spectral shapes. The irreducible contribution to the spectral shape is evaluated using the dipole induced dipole irreducible polarizability [buckingham, A. D., and Hands, I. D., 1991, Chem. Phys. Lett., 185, 544]. This contribution is found to be relatively weak for the anisotropic spectra in the frequency and density range studied, explaining the good agreement between the pairwise approximation calculations and the experimental data. The spectra radiated by the quasi-molecules Kr2, Kr3, and Kr4 (the total spectrum within the PA approximation) are also simulated
Controlled molecular motions in azobenzene containing materials
International audienc
Coopérativité de mouvements moléculaires dans l‟eau confinée à l‟intérieur de nano-pores hydrophiles
Date du colloque : 06/2008</p
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