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71.
Toyoyuki Kitamura 《Physica A》2007,383(2):232-252
An established unified theory of the liquid-glass transition in one-component liquids is extended to multi-component liquids. The universal features such as the Kauzmann paradox, the Vogel-Tamman-Fulcher (VTF) law on the relaxation times and the transport coefficients, the jump of the specific heat at the glass transition temperature and the Boson peaks are elucidated. The Kauzmann entropy in a form of a Curie law with a negative sign comes from the mixing between the sound and the intra-band fluctuation entropies, where the critical temperature corresponds to the sound instability temperature at a reciprocal particle distance. The VTF law is constructed from the Einstein relation on entropy and probability so that the Kauzmann entropy is included as a normal form in exponent of the VTF law. The Kauzmann entropy explains the Kauzmann paradox and the jump of the specific heat so that the universal features of the glass transition are elucidated consistently. 相似文献
72.
Grimau M Laredo E Sánchez F López-Carrasquero F Báez ME Bello A 《The European physical journal. E, Soft matter》2004,15(4):383-393
A series of poly(
-n-alkyl
-L-aspartates) which are nanophase self-assembled comb-like polymers has been studied by dielectric spectroscopy in a broad frequency range ( 10-23×106 Hz), with n-alkyls side chains of various lengths, 10n18. In every member of the series the same relaxations were identified after the decomposition of the experimental isothermal trace in up to three peaks with relaxation times distributions. The strength, width and average relaxation time for all the relaxation modes were determined for each material. Besides the local low temperature, Arrhenius modes, two relaxation modes,
and
, present a cooperative character whose dynamics are not affected by the side chains melting. The
relaxation is a polyethylene-like glass transition of the amorphous side chains and its dynamics is strongly dependent on the n value due to the increasing restrictions imposed by the self-assembled confinement. The strength of the
relaxation mode increases as the lateral chains loose their 2D order. The restricted chopstick motion of the rigid rods is thought to be the origin of the
mode; this motion is hindered at temperatures where the cage size decreases as a result of the increasing disorder with temperature. 相似文献
73.
Head DA 《The European physical journal. E, Soft matter》2007,22(2):151-155
In an attempt to extend the range of model jamming transitions, we simulate systems of athermal particles which attract when
slightly overlapping. Following from recent work on purely repulsive systems, dynamics are neglected and relaxation performed
via a potential energy minimisation algorithm. Our central finding is of a transition to a low-density tensile solid which
is sharp in the limit of infinite system size. The critical density depends on the range of the attractive regime in the pair-potential.
Furthermore, solidity is shown to be related to the coordination number of the packing according to the approximate constraint-counting
scheme known as Maxwell counting, although more corrections need to be considered than with the repulsive-only case, as explained.
We finish by discussing how the numerical difficulties encountered in this work could be overcome in future studies. 相似文献
74.
Théneau C Salmerón Sánchez M Rodríguez Hernández JC Monleón Pradas M Saiter JM Gómez Ribelles JL 《The European physical journal. E, Soft matter》2007,24(1):69-77
The enthalpy relaxation of polymer-silica nanocomposites prepared by simultaneous polymerization of poly(2-hydroxyethyl methacrylate)
(PHEMA) and tetraethyloxysilane, TEOS, a silica precursor, is investigated. Both the glass transition temperature, Tg, and the temperature interval of the glass transition, ΔT
g , increase as the silica content in the sample does. Structural relaxation experiments show that the temperature interval
in which conformational motions take place broadens as the silica content in the hybrid increases. A phenomenological model
based on the evolution of the configurational entropy during the structural relaxation process, the SC model, has been used
for determining the temperature dependence of the relaxation times during the process. The results show an increase of the
fragility of the polymer as the silica content increases, a feature that can be related to the broadening of the distribution
of relaxation times characterized by the β parameter of the stretched exponential distribution. On another hand the silica
content increase produces a significant change of the relaxation times in the glassy state. 相似文献
75.
Prashanth Badrinarayanan 《Journal of Non》2007,353(26):2603-2612
A comparison of the values of the glass transition temperature (Tg) measured on cooling and the limiting fictive temperature measured on heating as a function of cooling rate is performed for a polystyrene sample using both capillary dilatometry and differential scanning calorimetry (DSC). The results from both techniques indicate that is systematically lower than Tg presumably due to the breadth of the relaxation on cooling. The Tool-Narayanaswamy-Moynihan (TNM) model is used to fit the experimental data from dilatometry and DSC in order to ascertain the origins of the higher value of Tg compared to . 相似文献
76.
R.J. Jiménez Riobóo K.-P. Bohn J.K. Krüger 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):643-651
High performance Brillouin spectroscopy (BS) has been used to study the elastic properties (static and dynamic) of the orientational
glassy state of Na(CN)xCl1-x samples ). The temperature behaviour of the elastic properties reveals a more complex scenario for the orientational glass transition
than generally believed. The shear elastic constant shows the well-known c
44
(
T
) anomaly, indicated by a minimum, found in other cyanide mixed crystals. The results obtained for the hypersonic attenuation
are in clear contradiction with the dynamic character of the c
44
(
T
)-minimum. The temperature behaviour of the longitudinal elastic constant c11 of very dilute Na(CN)xCl1-x samples shows two striking features: i) Similar to the anomalous temperature behaviour of c
44
(
T
), lowering the temperature c
11
(
T
) first decreases, goes through a minimum and then rises again. The minimum takes place at a temperature above the temperature,
, where c
44
(
T
) reaches its minimum value. ii) A kink-like anomaly of c
11
(
T
) is observed at lower temperatures. This second anomaly is similar to the classical one observed in canonical glasses at their
glass transition temperature .
Received 8 April 1999 and Received in final form 3 June 1999 相似文献
77.
Role of Viscosity Stratification and Insoluble Surfactant in Instability of Two-Layer Channel Flow 下载免费PDF全文
We study, for the case of the two layer plane Poiseuille flow, the effect of viscosity stratification and interracial surfactant on the flow instability. Considering a normal mode of the streamwise wave number α, both the linear and energy analyses are presented. The expressions of perturbation energy supplied at the interface are derived. The result demonstrates that the jumps of horizontal velocity and tangential stress of the perturbed flow across the interface could be induced by the presence of viscosity stratification and surfactant. This is expected to be responsible for the Yih and Marangoni instability. 相似文献
78.
B. AhlströmJ. Bergenholtz 《Fluid Phase Equilibria》2011,305(1):9-18
Gibbs ensemble Monte Carlo (GEMC) simulations have been done on polydisperse systems of particles interacting via the Asakura-Oosawa depletion potential. On restricting the range of the depletion attraction particles aggregate forming long-lived, unequilibrated structures and it becomes increasingly difficult to sample phase space. It is found that by simply equilibrating systems sequentially starting at longer ranges of attraction, the equilibrium fluid-fluid phase coexistence can be determined down to polymer-colloid size ratios approaching 10%. For such short ranges of the depletion interaction it becomes difficult to obtain reliable estimates of chemical potentials due to occasional particle insertions resulting in very low energies. The results show that full equilibrium is not reached at a polymer-colloid size ratio of 10% in spite of lengthy simulations due to persistent structures in the dense-fluid phase dominated by particles belonging to the larger size fraction. Free-volume theory with a polydisperse colloid component, modeled as a three-component mixture, is used for qualitative comparison with some of the results of the computer simulations. 相似文献
79.
S. Hui L.-H. Tang 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):77-84
RNA molecules form a sequence-specific self-pairing pattern at low
temperatures. We analyze this problem using a random pairing
energy model as well as a random sequence model that includes
a base stacking energy in favor of helix propagation.
The free energy cost for separating a chain into two equal halves
offers a quantitative measure of sequence specific pairing.
In the low temperature glass phase, this quantity
grows quadratically with the logarithm of the chain length, but
it switches to a linear behavior of entropic origin in the high
temperature molten phase. Transition between the two phases is
continuous, with characteristics that resemble those of a disordered
elastic manifold in two dimensions. For designed sequences, however,
a power-law distribution of pairing energies on a coarse-grained level
may be more appropriate. Extreme value statistics arguments then
predict a power-law growth of the free energy cost to break a chain,
in agreement with numerical simulations. Interestingly, the distribution
of pairing distances in the ground state secondary structure follows
a remarkable power-law with an exponent -4/3, independent
of the specific assumptions for the base pairing energies. 相似文献
80.
We locate the glass transition line of the charged-hard-sphere system in the density-temperature plane, using a mean-field hypernetted chain approximation within the replica-symmetry-breaking scenario [S. Franz and G. Parisi, Phys. Rev. Lett. 79 (1997) 2486. [11]]. Our results demonstrate a dominant role of the steric factor and explain the ineffectiveness of purely Coulombic interactions in driving phase transitions. 相似文献