Characteristic length of glass transition from calorimetry in different confinements

Hempel, E; Vieweg, S.; Huwe, A.; Otto, Katharina A.; Schick, Christoph; Donth, E.

doi:10.1051/jp4:2000714

Cited by 12 publications

(7 citation statements)

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“…The tetrahedral hydrogenbonded network structure of bulk water will, for instance, break up and this is, as mentioned above, expected to increase the fragility of the supercooled water and affect the glass transition temperature. Experiments have shown that the relevant length scale for the glass transition is typically a few nanometers for small molecular systems [19]. However, in the case of water this length scale is likely to be shorter since molecular dynamics simulations have shown that the influence of confinement and/or surface interactions on the structural and dynamical properties of water does not exceed a few molecular diameters from the surfaces [20].…”

Section: ͑1͒mentioning

confidence: 99%

Dynamics of water in strawberry and red onion as studied by dielectric spectroscopy

et al. 2005

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We have investigated the microscopic dynamics of strawberry and red onion by means of broadband dielectric spectroscopy. In contrast to most of the previous experiments on carbohydrate-rich biological materials, which have mainly considered the more global dynamics of the "biological matrix," we are here focusing on the microscopic dynamics of mainly the associated water. The results for both strawberry and red onion show that the imaginary part of the permittivity contains one conductivity term and a clear dielectric loss peak, which was found to be similar to the strongest relaxation process of water in carbohydrate solutions. The temperature dependence of the relaxation process was analyzed for different water content. The relaxation process slows down, and its temperature dependence becomes more non-Arrhenius, with decreasing water content. The reason for this is most likely that, on average, the water molecules interact more strongly with carbohydrates and other biological materials at low water content, and the dynamical properties of this biological matrix changes substantially with increasing temperature (from an almost rigid matrix where the water is basically unable to perform long-range diffusion due to confinement effects, to a dynamic matrix with no static confinement effects), which also changes (i.e., reduces) the activation energy of the relaxation process with increasing temperature (i.e., causes a non-Arrhenius temperature dependence). This further changes the conductivity from mainly polarization effects at low temperatures, due to hindered ionic motions, to long-range diffusivity at T>250 K . Thus, around this temperature ions in the carbohydrate solution no longer get stuck in confined cavities, since the motion of the biological matrix "opens up" the cavities and the ions are then able to perform long-range migration.

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Section: ͑1͒mentioning

confidence: 99%

Dynamics of water in strawberry and red onion as studied by dielectric spectroscopy

et al. 2005

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“…One large class of experiments are done on molecular liquids (such as salol, glycol, ortho-terphenyl) confined to porous material such as Vycor glass, sol-gel glass and zeolithes with pore sizes ranging from several hundred to only a few nanometer. Typical experimental methods are differential scanning calorimetry (DSC) [21,22,23], dielectric spectroscopy [24,25,26,27,28,29], neutron scattering [30,31], solvation dynamics [32,33,34] and many more.…”

Section: Introductionmentioning

confidence: 99%

The Relaxation Dynamics of a Supercooled Liquid Confined by Rough Walls

2004

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We present the results of molecular dynamics computer simulations of a binary Lennard-Jones liquid confined between two parallel rough walls. These walls are realized by frozen amorphous configurations of the same liquid and therefore the structural properties of the confined fluid are identical to the ones of the bulk system. Hence this setup allows us to study how the relaxation dynamics is affected by the pure effect of confinement, i.e. if structural changes are completely avoided. We find that the local relaxation dynamics is a strong function of z, the distance of the particles from the wall, and that close to the surface the typical relaxation times are orders of magnitude larger than the ones in the bulk. Because of the cooperative nature of the particle dynamics, the slow dynamics also affects the dynamics of the particles for large values of z. Using various empirical laws, we are able to parameterize accurately the z−dependence of the generalized incoherent intermediate scattering function Fs(q, z, t) and also the spatial dependence of structural relaxation times. These laws allow us to determine various dynamical length scales and we find that their temperature dependence is compatible with an Arrhenius law. Furthermore, we find that at low temperatures time and space dependent correlation function fulfill a generalized factorization property similar to the one predicted by mode-coupling theory for bulk systems. For thin films and/or at sufficiently low temperatures, we find that the relaxation dynamics is influenced by the two walls in a strongly non-linear way in that the slowing down is much stronger than the one expected from the presence of only one confining wall. Finally we study the average dynamics of all liquid particles and find that the data can be described very well by a superposition of two relaxation processes that have clearly separated time scales. Since this is in contrast with the result of our analysis of the local dynamics, we argue that a correct interpretation of experimental data can be rather difficult.

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“…339 Thus, most probably it was not the geometrical confinement which was responsible for the unusual behaviour of the graphitic micropores with respect to CCl 4 . Hempel et al 346 report that the glass transition temperature of confined glasses was also lower than in the bulk systems. Manias et al 345 have even observed a suppression of the glass transition in polymers confined in 2 nm slit-pores.…”

Section: Phase Transitionsmentioning

confidence: 99%

6 Recent developments in calorimetry

Randzio

2002

Annu. Rep. Prog. Chem., Sect. C: Phys. Chem.

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Characteristic length of glass transition from calorimetry in different confinements

Cited by 12 publications

References 0 publications

Dynamics of water in strawberry and red onion as studied by dielectric spectroscopy

Dynamics of water in strawberry and red onion as studied by dielectric spectroscopy

The Relaxation Dynamics of a Supercooled Liquid Confined by Rough Walls

6 Recent developments in calorimetry

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