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1.
R.M.C. de Almeida N. Lemke I.A. Campbell 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):513-518
We study random walks on the dilute hypercube using an exact enumeration Master equation technique, which is much more efficient
than Monte Carlo methods for this problem. For each dilution p the form of the relaxation of the memory function q(t) can be accurately parametrized by a stretched exponential over several orders of magnitude in q(t). As the critical dilution for percolation is approached, the time constant tends to diverge and the stretching exponent drops towards 1/3. As the same pattern of relaxation is observed in a wide class of glass formers, the fractal like morphology
of the giant cluster in the dilute hypercube appears to be a good representation of the coarse grained phase space in these
systems. For these glass formers the glass transition may be pictured as a percolation transition in phase space.
Received 16 June 2000 and Received in final form 13 October 2000 相似文献
2.
Sciortino F La Nave E Scala A Stanley HE Starr FW 《The European physical journal. E, Soft matter》2002,9(3):233-237
We present an overview of the recent studies on the properties of the potential energy surface for a simple model of water.
We emphasize the relations between PES properties and dynamics in supercooled states for the model and discuss possible future
application of the PES studies.
Received 13 March 2002 相似文献
3.
S. Moreno R.G. Rubio G. Luengo F. Ortega M.G. Prolongo 《The European physical journal. E, Soft matter》2001,4(2):173-182
The complex dielectric permittivity has been measured for three poly(ethylenglycol)-b-poly(propylenglycol)-b-poly(ethylenglycol)
copolymers with different content of poly(ethylenglycol) (15%, 33% and 80%), and increasing degree of crystallinity (0%, 10%
and 20%, respectively). Only the non-crystalline sample shows the normal mode relaxation together with the segmental (α-relaxation)
and the Johari-Goldstein (β-relaxation) modes. The crystalline samples show also polarization contributions due to the existence
of interfaces between the crystallites and the amorphous phase. The relaxation times of the (α and normal modes can be described
by a VFT equation with the same value of T0. There is a slowing-down of the segmental mode due to the presence of crystallites. The temperature dependence of the α and
β relaxations in the copolymers is very similar to that found in pure PPG, while there are significant differences in the
case of the normal mode of the non-crystalline sample. The size of the cooperatively rearranging regions CRR, and the width
of the glass transition region increase slightly with the degree of crystallinity. The temperature dependence of the size
of CRRs is compatible with the prediction of fluctuation theory. No systematic effect of the degree of crystallinity on the
β-relaxation has been found. Near T
g the β-relaxation time is close to the primitive time of the coupling model.
Received: 31 May 2000 相似文献
4.
After classifying amorphous materials according to their topology, we review a recently proposed theory of pressure amorphization
(PA) that arises from some degree of displacive disorder while retaining a crystalline topology. That theory is based on the
notion that one or more branches of the phonon spectrum become soft and flat with increasing pressure and is illustrated by
a simple model that possesses the range of features displayed by many of the materials which undergo PA with displacive disorder.
We report the results of Langevin simulations of the simple model which show how the probability of amorphization increases
with the number of unit cells in the system and support our theory. We comment on how to generalize the model for the study
of real systems.
Received 29 march 2002 相似文献
5.
V. Teboul 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(1):111-118
Finite size effects on dynamical heterogeneity are studied in liquid silica
with Molecular Dynamics simulations using the BKS potential model. When the
system size decreases relaxation times are found to increase in accordance
with previous results in finite-size simulations and confined liquids. It
has been suggested that this increase may be related to a modification of
the spatially heterogeneous dynamics in confined liquids. In agreement with
this hypothesis we observe a decrease of the spatially heterogeneous
dynamics when the size decreases. The spatially heterogeneous dynamics is
usually characterized by the dynamical aggregation of the most or the least
mobile atoms. However we find that the decrease of the dynamical aggregation
associated to the least mobile atoms is much more important than the
decrease associated to the most mobile atoms when the size decreases. This
result associated with a slowing down of the liquid is surprising as it is
expected that the dynamical aggregation of the least mobile atoms should
increase the slowing down of the liquid dynamics. The decrease of the
heterogeneous behaviour is also in contradiction with the increase of the
spatially heterogeneous dynamics observed in liquids confined inside
nanopores. However, an increase of the non-Gaussian parameter appears both
for the confinement inside nanopores and for the finite size simulations. As
the non-Gaussian parameter is usually associated with the heterogeneous
dynamics, the increase of the non-Gaussian parameter together with a
decrease of the spatially heterogeneous dynamics is also surprising. 相似文献
6.
W. Peng P.M. Goldbart 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):461-466
Certain density correlators, measurable via various experimental techniques, are studied in the context of the vulcanization transition. It is shown that these correlators
contain essential information about both the vulcanization transition and the emergent amorphous solid state. Contact is made
with various physical ingredients that have featured in experimental studies of amorphous colloidal and gel systems and in
theoretical studies of the glassy state.
Received 30 September 2000 相似文献
7.
8.
N. Geier M. Weiss M. Moske K. Samwer 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):37-40
The thermal expansion of non-crystalline Zr65Al7.5Cu17.5 Ni10 has been studied in the range of the glass transition and in the undercooled liquid using a dilatometric device. The measuring
technique used permits reliable experimental results up to 40 K above the glass transition temperature. The linear thermal
expansion coefficient obtained is almost constant in the glassy state with a value of . It discontinuously increases at the glass transition temperature yielding a value of in the undercooled liquid. The results are compared with specific heat measurements of the amorphous material in this temperature
range and are interpreted in the framework of a cluster model.
Received 5 March 1999 and received in final form 11 June 1999 相似文献
9.
S. Davatolhagh 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(3):291-295
The most puzzling aspect of the glass transition observed in
laboratory is the decoupling of the dynamics from the structure.
As an attempt to reconcile the dynamic and the static lengthscales
associated with the glass problem, we discuss the apparent
correlations between the static relaxation length, defined as that
lengthscale over which the potential energy fluctuation is
correlated, with the linear size of the dynamic heterogeneity. The
dynamic heterogeneous domains with long life-times, may therefore
be linked to the droplets of low potential energy, or the tightly
bound regions inside the liquid. 相似文献
10.
Slow dynamics of density fluctuations near the colloidal glass transition is discussed from a new viewpoint by numerically
solving a nonlinear stochastic diffusion equation for the density fluctuations recently proposed by one of the present authors
(MT). The effects of spatial heterogeneities on the dynamics of density fluctuations are then investigated in an equilibrium
system. The spatial heterogeneities are generated by the nonlinear density fluctuations, while in a nonequilibrium system
they are described by a nonlinear deterministic equation for the average number density. The dynamics of equilibrium density
fluctuations is thus shown to be quite different from that of nonequilibrium ones, leading to a logarithmic decay followed
by less distinct α- and β-relaxation processes.
Received 9 March 2002 and Received in final form 19 September 2002 相似文献
11.
It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both
by measuring the diffusion coefficient of tagged particles or by NMR studies. Recent experiments have also demonstrated that
the glass transition temperature of thin polymer films can be shifted as compared to the same polymer in the bulk. We propose
here first a thermodynamical model for van der Waals liquids, which accounts for experimental results regarding the bulk modulus
of polymer melts and the evolution of the density with temperature. This model allows us to describe the density fluctuations
in such van der Waals liquids. Then, by considering the thermally induced density fluctuations in the bulk, we propose that
the 3D glass transition is controlled by the percolation of small domains of slow dynamics, which allows to explain the heterogeneous
dynamics close to T
g. We show then that these domains percolate at a lower temperature in the quasi-2D case of thin suspended polymer films and
we calculate the corresponding glass transition temperature reduction, in quantitative agreement with experimental results
of Jones and co-workers. In the case of strongly adsorbed films, we show that the strong adsorption amounts to enhance the
slow domains percolation. This effect leads to 1) a broadening of the glass transition and 2) an increase of T
g in quantitative agreement with experimental results. For both strongly and weakly adsorbed films, the shift in T
g is given by a power law, the exponent being the inverse of that of the correlation length of 3D percolation.
Received 21 March 2000 and Received in final form 4 December 2000 相似文献
12.
Recent experiments have demonstrated that the dynamics in liquids close to the glass transition temperature is strongly heterogeneous.
The characteristic size of these heterogeneities has been measured to be a few nanometers at T
g. We extend here a recent model for describing the heterogeneous nature of the dynamics which allows both to derive this length
scale and the right orders of magnitude of the heterogeneities of the dynamics close to the glass transition. Our model allows
then to interpret quantitatively small probes diffusion experiments.
Received 29 March 2002 and Received in final form 11 November 2002
RID="a"
ID="a"e-mail: long@lps.u-psud.fr 相似文献
13.
E. Brézin C. De Dominicis 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):71-76
The field theory of a short range spin glass with Gaussian random interactions, is considered near the upper critical dimension
six. In the glassy phase, replica symmetry breaking is accompanied with massless Goldstone modes, generated by the breaking
of reparametrization invariance of a Parisi type solution. Twisted boundary conditions are thus imposed at two opposite ends
of the system in order to study the size dependence of the twist free energy. A loop-expansion is performed to first order
around a twisted background. It is found, as expected but it is non trivial, that the theory does renormalize around such
backgrounds, as well as for the bulk. However two main differences appear, in comparison with simple ferromagnetic transitions:
(i) the loop expansion yields a (negative) anomaly in the size dependence of the free energy, thereby lifting the lower critical
dimension to a value greater than two (ii) the free energy is lowered by twisting the boundary conditions. This situation
is common in spin glasses, reflecting the non-positivity of mode multiplicity in replica symmetry breaking, but its physical
meaning is still unclear.
Received 12 April 2002 / Received in final form 30 July 2002 Published online 19 November 2002 相似文献
14.
The T
g of organic liquids confined to nanoporous matrices and that of thin polymer films can decrease dramatically from the bulk
value. One possible explanation for this phenomenon is the development of hydrostatic tension during vitrification under confinement
that results in a concomitant increase in the free volume. Here we present experimental evidence and modeling results for
ortho-terphenyl (o-TP) confined in pores as small as 11.6 nm that indicate that, although there is an important hydrostatic
tension in the liquid in the pores, it does not develop until near the reduced T
g of the constrained material --well below the bulk T
g. Enthalpy recovery for the o-TP in the nanopores exhibits accelerated physical aging relative to the bulk, as well as a leveling
off of the fictive temperature at equilibrium values greater than the aging temperature. An adaptation of the structural recovery
model that incorporates vitrification under isochoric conditions is able to provide a quantitative explanation for the apparently
anomalous aging observed in nanopore confined liquids and in thin polymeric films. The results strongly support the existence
of an intrinsic size effect as the cause of the reduced T
g.
Received 3 September 2001 相似文献
15.
M. Sasaki V. Dupuis J.-P. Bouchaud E. Vincent 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):469-479
We study the deviations from perfect memory in negative temperature cycle spin glass experiments. It is known that the a.c.
susceptibility after the temperature is raised back to its initial value is superimposed to the reference isothermal curve
for large enough temperature jumps ΔT (perfect memory). For smaller ΔT, the deviation from this perfect memory has a striking non monotonous behavior: the `memory anomaly' is negative for small ΔT's, becomes positive for intermediate ΔT's, before vanishing for still larger ΔT's. We show that this interesting behavior can be reproduced by simple Random Energy trap models. We discuss an alternative
interpretation in terms of droplets and temperature chaos.
Received 23 May 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: sasaki@ipno.in2p3.fr 相似文献
16.
Parisi G 《The European physical journal. E, Soft matter》2002,9(3):213-218
In this paper I will describe some results that have been recently obtained in the study of random Euclidean matrices, i.e. matrices that are functions of random points in Euclidean space. In the case of translation invariant matrices one generically finds a phase transition between a phonon phase and a saddle phase. If we apply these considerations to the study of the Hessian of the Hamiltonian of the particles of a fluid, we find
that this phonon-saddle transition corresponds to the dynamical phase transition in glasses, that has been studied in the
framework of the mode coupling approximation. The boson peak observed in glasses at low temperature is a remanent of this
transition.
Received 4 May 2002 相似文献
17.
U. Schneider R. Brand P. Lunkenheimer A. Loidl 《The European physical journal. E, Soft matter》2000,1(1):67-73
The Nagel scaling and the modified scaling procedure proposed recently by Dendzik et al. have been applied to broadband dielectric data on two glass-forming liquids (glycerol and propylene carbonate) and three
plastic crystals (ortho-carborane, meta-carborane, and 1-cyano-adamantane). Our data extend the upper limit of the abscissa
range to considerably higher values than in previously published analyses. At the highest frequencies investigated, deviations
from a single master curve show up which are most pronounced in the Dendzik scaling plot. The loss curves of the plastic crystals
do not scale in the Nagel plot, but they fall onto a separate master curve in the Dendzik plot. In addition, we address the
question of a possible divergence of the static susceptibility near the Vogel-Fulcher temperature. For this purpose, the low-temperature
evolution of the high-frequency wing of the dielectric loss peaks is investigated in detail. No convincing proof for such
a divergence can be deduced from the present broadband data.
Received 14 June 1999 and Received in final form 4 October 1999 相似文献
18.
L. Bellon S. Ciliberto C. Laroche 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):223-231
A new kind of memory effect on low frequency dielectric measurements on plexiglass (PMMA) is described. These measurements
show that cooling and heating the sample at constant rate give an hysteretic dependence on temperature of the dielectric constant
ε. A temporary stop of cooling produces a downward relaxation of ε. Two main features are observed (i) when cooling is resumed
ε goes back to the values obtained without the cooling stop (i.e. the low temperature state is independent of the cooling history) (ii) upon reheating ε keeps the memory of all the cooling
stops (Advanced memory). The dependence of this effect on frequency and on the cooling rate is analyzed. The memory deletion is studied too. Finally
the results are compared with those of similar experiments done in spin glasses and with the famous experiments of Kovacs.
Received 24 September 2001 and Received in final form 20 November 2001 相似文献
19.
Ellison CJ Kim SD Hall DB Torkelson JM 《The European physical journal. E, Soft matter》2002,8(2):155-166
Fluorescence intensity measurements of chromophore-doped or -labeled polymers have been used for the first time to determine
the effects of decreasing film thickness on glass transition temperature, T
g, the relative strength of the glass transition, and the relative rate of physical aging below T
g in supported, ultrathin polymer films. The temperature dependence of fluorescence intensity measured in the glassy state
of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(isobutyl methacrylate) (PiBMA), and poly(2-vinylpyridine)
(P2VP) differs from that in the rubbery state with a transition at T
g. Positive deviations from bulk T
g are observed in ultrathin PiBMA and P2VP films on silica substrates while substantial negative deviations from bulk T
g are observed in ultrathin PS films on silica substrates. The relative difference in the temperature dependences of fluorescence
intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength
of the glass transition is reduced in thinner films. The temperature dependence of fluorescence intensity also provides useful
information on effects of processing history as well as on the degree of polymer-substrate interaction. In addition, when
used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of
physical aging in films as thin as 10 nm.
Received 21 August 2001 相似文献
20.
Grohens Y Hamon L Reiter G Soldera A Holl Y 《The European physical journal. E, Soft matter》2002,8(2):217-224
We have measured, the thickness dependence of the glass transition temperature T(g)( h), using ellipsometry at variable temperature, for poly(methyl-methacrylate) (PMMA) of various tacticity in confined geometry. We report that several factors significantly affect T(g)( h): i) polymer microstructure (stereoregularity of PMMA) related to local dynamics; ii) interfacial interactions; iii) conformation of the polymer chains. These results raise many fundamental questions on the origin of the thickness-dependent glass transition. Why and how do the interactions with the substrate significantly affect T(g)( h)? Does T(g)( h) depend on the modifications of conformational parameters of the chains (their entropy)? What is the correlation between local dynamics and T(g)( h) in thin films? The aim of this paper is to summarise these open questions, which should stimulate further investigations in the thin polymer film scientific community. 相似文献