The glass transition in confined liquids

Pissis, P.; Daoukaki-Diamanti, D.; Apekis, L.; Christodoulides, C.

doi:10.1088/0953-8984/6/21/008

Cited by 71 publications

(76 citation statements)

References 14 publications

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“…This concept is at the center of discussions concerning the glass transition and there is growing interest in relating it to measurable physical quantities [3]. Donth et al [4][5][6] estimated the length of cooperativity to be a few nm (~2-3 nm).…”

Section: Introductionmentioning

confidence: 99%

“…Investigations of the glass transition in confined liquids have been published recently [3,[7][8][9]. In all these papers, controlled porous glasses were used to investigate the influence of size effects on relaxation dynamics.…”

Section: Introductionmentioning

confidence: 99%

“…The results were conflicting. Both a decrease [3,7] and a small increase [8] in the dynamic glass transition temperature due to restriction was found. An increase in the glass transition temperature is in accordance with the theoretical prediction of Sappelt and J~ickle [1].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Dielectric spectroscopy and calorimetry in the glass transition region of semi-crystalline poly(ethylene terephthalate)

Dobbertin

Hensel

Schick

1996

Journal of Thermal Analysis

120

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Confinement of the glass-forming regions in the nanometer range influences the (x-relaxation which is associated with the glass transition. These effects were investigated for semicrystalline poly(ethylene terephthalate) by dielectric spectroscopy and differential scanning calorimetry. The. results are discussed within the concept of cooperative length, i.e. the characteristic length of the cooperative process of glass transition. Both experiments showed a dependence of the glass transition on the mean thickness of the amorphous layers. For the dielectric relaxation, the loss maximum was found to shift to higher temperatures with decreasing thickness of the amorphous layers, but no differences were observed in the curve shape for the differently crystallized samples. For the calorimetric measurements, in contrast, there was no correlation for the glass transition temperature, whereas the curve shape did correlate with the layer thickness of the mobile amorphous fraction. From the structure parameters, a characteristic length of approximately (2.5+1) nm was estimated for the unconfined glass relaxation (transition).

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dielectric spectroscopy and calorimetry in the glass transition region of semi-crystalline poly(ethylene terephthalate)

Dobbertin

Hensel

Schick

1996

Journal of Thermal Analysis

120

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“…If CRR's do exist and grow with decreasing temperature the dynamics should differ from the bulk behavior as soon as the size of the CRR's at a given temperature becomes comparable to the system size. Indeed, almost all experiments on glass formers confined to porous host material [6][7][8][9][10][11][12] and supported (or even free standing) films [13][14][15][16][17] do indeed show a relaxation dynamics that differs from the one in the bulk. However, so far it has not been possible to give a conclusive interpretation of experimental results, since, e.g., one sometimes finds that the dynamics in confined systems is faster than the one of the bulk, whereas in other systems it is slower (see, e.g., [8,10]).…”

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confidence: 99%

Cooperative motion and growing length scales in supercooled confined liquids

2002

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Abstract. -Using molecular dynamics simulations we investigate the relaxation dynamics of a supercooled liquid close to a rough as well as close to a smooth wall. For the former situation the relaxation times increase strongly with decreasing distance from the wall whereas in the second case they strongly decrease. We use this dependence to extract various dynamical length scales and show that they grow with decreasing temperature. By calculating the frequency dependent average susceptibility of such confined systems we show that the experimental interpretation of such data is very difficult.Motivation. -The details of the mechanism giving rise to the dramatic slowing down of the dynamics of glass-forming liquids upon supercooling are still unknown (see, e.g. [1]). Although the mode-coupling theory of the glass transition allows to rationalize many features of the relaxation dynamics of these systems [2], the answers to certain important questions (e.g. the relaxation dynamics at low temperatures) are still unknown. A further popular approach is the phenomenological concept of "cooperativity", introduced by Kauzmann [3], and Adam and Gibbs [4]. A typical example of this cooperativity is the so-called "cage-effect", i.e. the fact that in a dense liquid each particle is surrounded by neighboring particles which form a temporary cage. In order to allow the particle to change its position the cage has to open up. However, each of the particles of the cage is itself also caged and hence can move only if other particles make room. Therefore one can conclude that the particle motion is collective and there exist "cooperatively rearranging regions" (CRR's) within the liquid. The typical size of a CRR is postulated to grow with decreasing temperature, hence "rationalizing" the slowing down of the dynamics [4,5].Experimentally it is difficult to test the concept of the CRR's since usually one does not have direct access to the dynamics of single particles. Therefore many studies have focused on investigating systems in spatial confinement. If CRR's do exist and grow with decreasing temperature the dynamics should differ from the bulk behavior as soon as the size of the CRR's at a given temperature becomes comparable to the system size. Indeed, almost all experiments on glass formers confined to porous host material [6][7][8][9][10][11][12] and supported (or even free standing) films [13][14][15][16][17] do indeed show a relaxation dynamics that differs from the one in the bulk. However, so far it has not been possible to give a conclusive interpretation of

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“…It should be pointed out that the dynamics of glass-forming liquids in confined geometries has been widely studied in the last decade. Usually, the confinement is imposed by nano-pores of controlled dimensions [85,86] or trough the preparation of ultra-thin films [87].…”

Section: Relaxations In Semi-crystalline Polymersmentioning

confidence: 99%

Molecular dynamics in polymeric systems

2004

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It is well known that the properties of polymeric materials depend strongly upon their chemical structure. Other more specific factors that may be related to the chemical structure also determine the macroscopic behaviour of such materials, namely the relative position of the different segments of the polymeric chain, the molecular architecture (molecular weight distribution, branching, copolymer organisation, cross-linking extent, etc.), the crystalline environment and the pressure/temperature conditions. All these factors have a common impact in the material: they are strongly correlated to the mobility on the molecular level. That is why a huge amount of work has been devoted to the study of translational/rotational mobility that occurs within the polymeric chains. This review is intended to provide a brief survey on such kinds of mobilities, how they can be studied and what are their main characteristics. Examples on systems studied in our groups will be provided, obtained by dielectric and mechanical spectroscopies and differential scanning calorimetry. It will be mainly focused on molecular motions that occur in the solid phase (i.e., to temperatures up to the rubbery plateau). The dynamics in blends or copolymers will be avoided here, as they would deserve a special discussion in their own context. Special attention will be paid to the glass transition and the mobility that occurs below and above it. The dynamics that are observed in peculiar systems, such as semi-crystalline or liquid crystalline polymers, will be addressed.

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The glass transition in confined liquids

Cited by 71 publications

References 14 publications

Dielectric spectroscopy and calorimetry in the glass transition region of semi-crystalline poly(ethylene terephthalate)

Dielectric spectroscopy and calorimetry in the glass transition region of semi-crystalline poly(ethylene terephthalate)

Cooperative motion and growing length scales in supercooled confined liquids

Molecular dynamics in polymeric systems

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