共查询到20条相似文献,搜索用时 109 毫秒
1.
L. Andreozzi M. Faetti M. Salmerón Sanchez J. L. Gómez Ribelles 《The European physical journal. E, Soft matter》2008,27(1):87-97
The aim of this work is to explore the consequences on the kinetics of structural relaxation of considering a glass-forming
system to consist of a series of small but macroscopic relaxing regions that evolve independently from each other towards
equilibrium in the glassy state. The result of this assumption is a thermorheologically complex model. In this approach each
relaxing zone has been assumed to follow the Scherer-Hodge model for structural relaxation (with the small modification of
taking a linear dependence of configurational heat capacity with temperature). The model thus developed contains four fitting
parameters. A least-squares search routine has been used to find the set of model parameters that fit simultaneously four
DSC thermograms in PVAc after different thermal histories. The computersimulated curves are compared with those obtained with
Scherer-Hodge model and the model proposed by Gómez and Monleón. The evolution of the relaxation times during cooling or heating
scans and also during isothermal annealing below the glass transition has been analysed. It has been shown that the relaxation
times distribution narrows in the glassy state with respect to equilibrium. Isothermal annealing causes this distribution
to broaden during the process to finally attain in equilibrium the shape defined at temperatures above T
g
. 相似文献
2.
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
3.
J.F. Willart V. Caron R. Lefort F. Danède D. Prévost M. Descamps 《Solid State Communications》2004,132(10):693-696
In this paper, we report the possibility to reach pure glassy amorphous lactose by ball milling of crystalline α lactose under a dry nitrogen atmosphere. This route to the glassy state is found to be free of mutarotation towards the anomer β while this mutarotation is unavoidable using the usual thermal route, i.e. the quench of the liquid. This result definitely makes the ‘local quench melting’ hypothesis unsuitable to account for amorphization by ball milling. 相似文献
4.
D. C. Lin A. Sharif 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(4):483-491
We study the intermittent behavior of the energy decay and the linear magnetic response
of a glassy system during isothermal aging after a deep thermal quench,
using the Edward-Anderson spin glass model as a paradigmatic example.
The large intermittent changes in the two observables
occur in a correlated fashion and through irreversible bursts,
`quakes', which punctuate reversible and equilibrium-like fluctuations of zero average.
The temporal distribution of the quakes is
a Poisson distribution with an average growing logarithmically on time,
indicating that the quakes are triggered by record sized fluctuations.
As the drift of an aging system is to a good approximation subordinated to the quakes,
simple analytical expressions [Sibani et al. Phys Rev B 74, 224407 (2006)]
are available for the time and age dependence of the average response and average energy.
These expressions are shown to capture the time dependencies of the EA simulation results.
Finally, we argue that whenever the changes of the linear response function and of its
conjugate autocorrelation function follow from the same intermittent events
a fluctuation-dissipation-like relation can arise between the two in off-equilibrium aging. 相似文献
5.
6.
NMR velocimetry has been used to observe the steady-shear rheological behaviour of a concentrated suspension of hard-sphere
like 370 nm diameter PMMA core-shell latex particles at the volume fraction Φ = 0.46, the liquid core of the spheres rendering
possible NMR observation of the particles themselves. Rheological measurements in a cone-and-plate geometry indicate that
when aged (i.e. left at rest for two weeks), the material exhibits yield stress behaviour at very low shear rates. For shear rates greater
than 1 s - 1 a transition to liquid-like behaviour was observed, leading to a rejuvenated fluid state which exhibits shear-thinning behaviour
over a wide range of shear rates. A similar yield stress behaviour was reflected in NMR velocimetry measurements in a Couette
geometry, where the solid-to liquid transition could be clearly observed. Under steady-state flow, the fluid state inside
the radius at which yield stress was observed, exhibited shear-thinning behaviour with a power law exponent n slowly approaching
unity with increasing shear rate. This behaviour has some similarities with a model of Derec et al. in which aging and rejuvenation effects compete. Substantial wall slip was observed both at the inner and at the outer wall,
an effect which disappeared as the shear rate was increased. No radial particle migration from the high-shear region at the
inner wall was observed. 相似文献
7.
N. Clarke 《The European physical journal. E, Soft matter》2001,4(3):327-336
We study the early stages of phase separation in a mixture of a polydisperse and a monodisperse polymer within the Cahn-Hilliard
framework. We model the polydisperse component using a finite, but arbitrarily large, number of components, and show that
the number of components required for convergent behaviour to be achieved is computationally undemanding. We study the growth
rate of fluctuations following a quench into the two-phase region of the phase diagram. The q-dependence of the growth rate is shown to be commensurate with the behaviour of a monodisperse-monodisperse mixture, with
the major difference being an effective mobility that is dependent on the quench depth. We also study the deviation of the
time dependence of the scattering function from single exponential behaviour.
Received 29 June 2000 and Received in final form 20 November 2000 相似文献
8.
The relaxations of conductivity have been studied in the glassy regime of a strongly disordered two-dimensional electron system in Si after a temporary change of carrier density during the waiting time tw. Two types of response have been observed: (a) monotonic, where relaxations exhibit aging, i.e., dependence on history, determined by tw and temperature; (b) nonmonotonic, where a memory of the sample history is lost. The conditions that separate the two regimes also have been determined. 相似文献
9.
P.G. de Gennes 《The European physical journal. E, Soft matter》2002,7(1):31-34
When a glassy polymer film is formed by evaporation, the region near the free surface is polymer rich and becomes glassy first,
as noticed long ago by Scriven et al. We discuss the thickness of this “crust” and the time interval where it is present --before freezing of the whole film. We
argue that the crust is under mechanical tension, and should form some cracks. This may be the source of the roughness observed
on the final, dry films, when the solvent vapor pressure is high (and leads to thin crusts).
Received 13 November 2001 相似文献
10.
Recently we have used a cellular automata model which describes the dynamics of a multi-connected network to reproduce the refractory behavior and aging effects obtained in immunization experiments performed with mice when subjected to multiple perturbations. In this paper we investigate the similarities between the aging dynamics observed in this multi-connected network and the one observed in glassy systems, by using the usual tools applied to analyze the latter. An interesting feature we show here, is that the model reproduces the biological aspects observed in the experiments during the long transient time it takes to reach the stationary state. Depending on the initial conditions, and without any perturbation, the system may reach one of a family of long-period attractors. The perturbations may drive the system from its natural attractor to other attractors of the same family. We discuss the different roles played by the small random perturbations ("noise") and by the large periodic perturbations ("immunizations").Received: 7 May 2003, Published online: 23 July 2003PACS:
87.18.Hf Spatiotemporal pattern formation in cellular populations -
87.10.+e General theory and mathematical aspects -
61.43.Fs GlassesD.A. Stariolo: Research Associate of the Abdus Salam International Center for Theoretical Physics, Strada Costiera 11, Trieste, Italy 相似文献
11.
Gomathi Natarajan David C. Cameron 《Applied Physics A: Materials Science & Processing》2009,95(3):621-627
In this paper we report on the influence of film thickness on the electrical and gas-sensing properties of tin oxide thin
films grown by atomic layer deposition (ALD) technique. The nature of the carrier and post-flow gases used in ALD was found to have a dramatic influence on the electrical conductance of the deposited films. Up to a film
thickness of 50 nm the sheet conductance of the films increased with the thickness, and above 50 nm the sheet conductance
was not significantly influenced by the film thickness. This effect was attributed to oxygen depletion at the film surface.
When the depth of oxygen depletion (d
dep) was greater than or equal to the film thickness (t), the sheet conductance was thickness dependant. On the other hand, when d
dep≤t, the sheet conductance was independent of the film thickness but depended on the depth of the oxygen depletion. This proposed
explanation was verified by subjecting the films to different lengths of post-annealing in an oxygen depleted atmosphere.
Gas-sensing functionality of the films with various thicknesses was examined. It was observed that the film thickness had
a significant influence on the gas-sensing property of the films. When the thickness was greater than 40 nm, the sensitivity
of the films to ethanol was found to follow the widely reported trend, i.e., the sensitivity decreases when the film thickness
increases. Below the film thickness of 40 nm the sensitivity decreases as film thickness decreases, and we propose a model
to explain this observation based on the increase in resistance due to multiple grain boundaries. 相似文献
12.
We report detailed studies of the non-equilibrium magnetic behavior of antiferromagnetic Co3O4 nanoparticles. The temperature and field dependence of magnetization, wait time dependence of magnetic relaxation (aging), memory effects, and temperature dependence of specific heat have been investigated to understand the magnetic behavior of these particles. We find that the system shows some features that are characteristic of nanoparticle magnetism such as bifurcation of field-cooled (FC) and zero-field-cooled (ZFC) susceptibilities and a slow relaxation of magnetization. However, strangely, the temperature at which the ZFC magnetization peaks coincides with the bifurcation temperature and does not shift on application of magnetic fields up to 1 kOe, unlike most other nanoparticle systems. Aging effects in these particles are negligible in both FC and ZFC protocols, and memory effects are present only in the FC protocol. We show that Co3O4 nanoparticles constitute a unique antiferromagnetic system which enters into a blocked state above the average Néel temperature. 相似文献
13.
Sharp JS Vader D Forrest JA Smith MI Khomenko M Dalnoki-Veress K 《The European physical journal. E, Soft matter》2006,19(4):423-432
Optical microscopy and atomic force microscopy were used to study a novel roughness-induced wrinkling instability in thin-film
bilayers of poly(ethylene oxide) (PEO) and polystyrene (PS). The observed wrinkling morphology is manifested as a periodic
undulation at the surface of the samples and occurs when the bilayers are heated above the melting temperature of the semi
crystalline PEO (Tm = 63
) layer. During the wrinkling of the glassy PS capping layers the system selects a characteristic wavelength that has the
largest amplitude growth rate. This initial wavelength is shown to increase monotonically with increasing thickness of the
PEO layer. We also show that for a given PEO film thickness, the wavelength can be varied independently by changing the thickness
of the PS capping layers. A model based upon a simple linear stability analysis was developed to analyse the data collected
for the PS and PEO film thickness dependences of the fastest growing wavelength in the system. The predictions of this theory
are that the strain induced in the PS layer caused by changes in the area of the PEO/PS interface during the melting of the
PEO are sufficient to drive the wrinkling instability. A consideration of the mechanical response of the PEO and PS layers
to the deformations caused by wrinkling then allows us to use this simple theory to predict the fastest growing wavelength
in the system. 相似文献
14.
A. N. Raegen M. V. Massa J. A. Forrest K. Dalnoki-Veress 《The European physical journal. E, Soft matter》2008,27(4):375-377
We have used nulling ellipsometry to measure the glass transition temperature, T
g , of thin films of polystyrene in ambient, dry nitrogen, and vacuum environments. For all environments, the measured T
g values decrease with decreasing film thickness in a way that is quantitatively similar to previously reported studies in
ambient conditions. These results provide strong reinforcement of previous conclusions that such reduced T
g values are an intrinsic property of the confined material. Furthermore, the results are in contrast to recent reports which
suggest that the T
g reductions measured by many researchers are the results of artifacts (i.e. degradation of the polymer due to annealing in ambient conditions, or moisture content). 相似文献
15.
F. Thalmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(1):65-73
The mean field approach of glassy dynamics successfully describes systems which are out-of-equilibrium in their low temperature
phase. In some cases an aging behaviour is found, with no stationary regime ever reached. In the presence of dissipative forces
however, the dynamics is indeed stationary, but still out-of-equilibrium, as inferred by a significant violation of the fluctuation
dissipation theorem. The mean field dynamics of a particle in a random but short-range correlated environment, offers the
opportunity of observing both the aging and driven stationary regimes. Using a geometrical approach previously introduced
by the author, we study here the relation between these two situations, in the pure relaxational limit, i.e. the zero temperature case. In the stationary regime, the velocity (v)-force (F) characteristics is a power law v∼F
4, while the characteristic times scale like powers of v, in agreement with an early proposal by Horner. The cross-over between the aging, linear-response regime and the non-linear
stationary regime is smooth, and we propose a parametrization of the correlation functions valid in both cases, by means of
an “effective time”. We conclude that aging and non-linear response are dual manifestations of a single out-of-equilibrium
state, which might be a generic situation.
Received 7 May 2000 and Received in final form 22 August 2000 相似文献
16.
We present a new set of electrical field effect measurements on granular aluminium insulating thin films. We have explored how the conductance relaxations induced by gate voltage changes depend on the age of the system, namely the time elapsed since its quench at low temperature. A clear age dependence of the relaxations is seen, qualitatively similar to ageing effects seen in other well studied glassy systems such as spin glasses or polymers. We explain how our results differ from the previous ones obtained with different protocols in indium oxide and granular aluminium thin films. Our experimental findings bring new information on the dynamics of the system and put new constraints on the theoretical models that may explain slow conductance relaxations in disordered insulators. 相似文献
17.
Tatsunori Sakano Hiroki Fukuoka Yoshihiro Yata Toshiharu Saiki Minoru Obara 《Applied Physics A: Materials Science & Processing》2008,93(3):697-703
We employed epi-GaN substrates for ZnO film growth, and studied the deposition and post-annealing effects. ZnO films were
grown by pulsed laser deposition (PLD) method. The as-grown films were annealed for one hour under atmospheric pressure air.
ZnO morphologies after annealing were investigated and the post-annealed ZnO films grown at T
g
=700oC have very smooth surfaces and the rms with roughness is about 0.5 nm. Finally, ZnO post-annealed buffer layer was inserted
between ZnO epilayer and GaN/sapphire substrates. It is confirmed by AFM that growth temperature of 700oC helps the films grow in step-flow growth mode. It is observed by cathode luminescence spectrum that the ZnO film grown at
700oC has very low visible luminescence, indicating the decrease of the deep level defects. It is also revealed by Hall measurements
that carrier concentration is decreased by increasing the growth temperatures. It is suggested that low temperature buffer
layer growth and post-annealing technique can be used to fabricate ZnO hetero-epitaxy. 相似文献
18.
We have studied the effect of physical ageing in thin supported glassy polystyrene films by using ellipsometry to detect overshooting
in the expansivity-temperature curve upon heating of aged samples. Films with thickness 10-200 nm have been aged at 70°
C and 80°
C (below the bulk glass transition temperature). We observe clear relaxation peaks in the expansivity-temperature curve for
films thicker than 18 nm but not for the 10 nm film. The intensity of the relaxation peak is inversely proportional to the
film thickness, while the temperatures characteristic to the relaxation peak are almost independent of the film thickness.
These observations are successfully interpreted by the idea that the surface layer of the order of 10 nm has liquid-like thermal
properties.
Received 28 October 2002 / Published online: 1 April 2003
RID="a"
ID="a"Present address: Yokohama Research Center, Mitsubishi Chemical Corporation, 1000 Kamoshida-chou, Aoba-ku, Yokohama 227-8502, Japan; e-mail:
kawana@rc.m-kagaku.co.jp 相似文献
19.
Surface quasi-elastic light scattering has been applied to a spread film of a block copolymer of polystyrene and polydimethyl
siloxane. The influence of surface concentration (surface pressure) at a fixed surface wave number has been explored. The
capillary wave frequency and damping showed a similar dependence on the surface concentration as values obtained earlier,
but due to a more appropriate analysis of the correlation functions, surface visco-elastic moduli obtained were distinctly
different. By correlating the values obtained with the variations in solvated polystyrene layer thickness from neutron reflectometry,
the maximum in dilational modulus was shown to occur at the same nominal surface concentration where the layer begins to stretch
and take on brush-like behaviour. This same surface concentration is where the relaxation time of the spread film also has
a maximum value, the relaxation time being calculated using the standard linear model of visco-elasticity, which was found
to fit the frequency dependence of the surface tension and dilational moduli at the resonant nominal surface concentration
of 3.1 mg m-2.
Received 21 August 2001 and Received in final form 11 January 2002 相似文献
20.
J.J. Zanna H.T. Nguyen J.P. Parneix G. Ruffié M. Mauzac 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):345-351
Dielectric response, from 1 Hz to 10 MHz, of liquid crystalline side chain elastomers has been compared to the one of analogous
uncrosslinked materials. Results are discussed in terms of mobility of the mesogens. Two different systems have been investigated:
smectic A elastomers allow to determine the influence of crosslinking on the relaxation (i.e. the reorientation of the whole mesogen around the chain), a S
C
* elastomer shows the drastic influence of the polymer network on the Goldstone mode.
Received 12 October 1998 相似文献