Tg depression and invariant segmental dynamics in polystyrene thin films

Boucher, Virginie M.; Cangialosi, Daniele; Yin, Huajie; Schönhals, Andreas; Alegría, Ángel; Colmenero, Juan

doi:10.1039/c2sm25419k

Cited by 180 publications

(195 citation statements)

References 32 publications

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“…However, a series of reports has cast doubt on this connection (10,11). For example, although the T g was found to decrease with confinement length scale, the segmental dynamics remain unchanged (10,11). In explaining these results, a confinement-induced phenomenon is often invoked (10,12,13).…”

Section: A1mentioning

confidence: 97%

“…For example, although the T g was found to decrease with confinement length scale, the segmental dynamics remain unchanged (10,11). In explaining these results, a confinement-induced phenomenon is often invoked (10,12,13). However, the physics underlying this decoupling remain incomplete and rich in unexplored phenomena.…”

Section: A1mentioning

confidence: 97%

“…On the other hand, a unique fluorescence multilayer technique has provided a direct correlation between the free surface T g and the change in T g with confinement for thin glassy polymer films (4, 21). It therefore seems appropriate to consider the notion that a decoupling between mobility and T g at the surfaces of glasses may exist, as has been reported for the average properties of thin films (10). Or in other words, that the relationship between a mobile surface layer and the suppression in T g with confinement is more complex than initially thought.…”

Section: A1mentioning

confidence: 99%

“…Therefore, a suppression in the T g of confined glasses would suggest an enhancement in molecular dynamics. However, a series of reports has cast doubt on this connection (10,11). For example, although the T g was found to decrease with confinement length scale, the segmental dynamics remain unchanged (10,11).…”

Section: A1mentioning

confidence: 99%

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Discrete mobility on the surface of glasses

Chowdhury

Priestley

2017

Proc. Natl. Acad. Sci. U.S.A.

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Section: A1mentioning

confidence: 97%

Section: A1mentioning

confidence: 97%

Section: A1mentioning

confidence: 99%

Section: A1mentioning

confidence: 99%

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Discrete mobility on the surface of glasses

Chowdhury

Priestley

2017

Proc. Natl. Acad. Sci. U.S.A.

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“…For the study of enthalpy recovery, the samples underwent a heating ramp to a temperature of 393 K, that is, above the films' T g (348 K on cooling at 20 K/min [30]), with a stabilization period of 1 min, to erase the materials previous thermal history. They were subsequently cooled down at 20 K/min to 233 K before stabilizing at the temperature used for structural recovery, T a .…”

mentioning

confidence: 99%

Reaching the ideal glass transition by aging polymer films

Boucher

Cangialosi

Alegría

et al. 2017

Phys. Chem. Chem. Phys.

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Searching for the ideal glass transition, we exploit the ability of glassy polymer films to explore low energy states in remarkably short time scales. We use 30 nm thick polystyrene (PS) films, which in the supercooled state basically display the bulk polymer equilibrium thermodynamics and dynamics. We show that in the glassy state, this system exhibits two mechanisms of equilibrium recovery. The faster one, active well below the kinetic glass transition temperature (Tg), allows massive enthalpy recovery. This implies that the 'fictive' temperature (T f ) reaches values as low as the predicted Kauzmann temperature (TK ) for PS. Once the thermodynamic state corresponding to T f = TK is reached, no further decrease of enthalpy is observed. This is interpreted as a signature of the ideal glass transition. PACS numbers: 64.70.pj, 65.60.+a.Glasses are a special class of materials characterized by the disordered structure of liquids and the mechanical properties of solids. The most common route to form a glass is by cooling a liquid through its melting temperature avoiding crystallization. In this case, before forming a glass, the supercooled state is explored, that is, a system in metastable equilibrium [1, 2]. A problem of extraordinary fundamental importance arises from the observation that the supercooled state exhibits second order thermodynamic properties typical of a liquid, in particular, larger than those of the crystal. Given the difference between the supercooled and crystal specific heats, Kauzmann noticed that there will be a temperature (T K ) at which the entropy of the supercooled liquid and that of the crystal would be equal [3]. Gibbs and Di Marzio [4] subsequently theorized that a second order thermodynamic transition to an ideal glass would occur. This transition would avoid that the paradoxical scenario of a disordered glass with entropy smaller than that of the crystal is realized. Investigating the intriguing scenario of a liquid with the entropy of a crystal is prevented by the occurrence of the so-called kinetic glass transition [5] transforming the supercooled liquid into a glass. Once formed, non-equilibrium glasses evolve towards the metastable equilibrium of the supercooled liquid by decreasing their energy, a well-known phenomenon addressed as physical aging or structural recovery [6].Motivated by the search for the second order thermodynamic transition (the ideal glass transition), different routes to low energy glassy states have been recently explored. One of them is the investigation of fossil glassy amber naturally aged for millions of years [7], showing fictive temperature (T f ) − i.e. the temperature corresponding to the intercept of the extrapolated glass and * Second.Author@institution.edu † http://www.Second.institution.edu/˜Charlie.Author equilibrium lines for a given glass (see Figure 1) − significantly lower than T g , the glass transition temperature. Another route, much faster, is the preparation of vapor deposited glasses which, when obtained in appropriate experimenta...

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Physical Aging of Polymers

Cangialosi

2018

Encyclopedia of Polymer Science and Technology

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This article provides an overview of the most important aspects of physical aging of polymers. First, we briefly introduce basic concepts of the glass transition, that is, the way a nonequilibrium glass is formed. Subsequently, after presenting the way physical aging can be monitored, we describe the main well‐established signatures of physical aging, that is, its nonexponential and nonlinear nature. The next part of the article is dedicated to recent advancements in the physical aging of bulk polymers. In this context, recent experimental activity is discussed, where the existence of multiple mechanisms for equilibrium recovery is presented. In addition, important aspects of physical aging in polymers altered by geometrical confinement are scrutinized in light of the past 20 years efforts aiming to understand glass dynamics in such conditions. It is shown how confined polymers weakly interacting with the confining medium exhibit accelerated physical aging. Importantly, such acceleration was found to be decoupled from the molecular mobility of the glass. Finally, we briefly discuss how recent advancements in physical aging of polymers in bulk and under geometrical confinement should foster experimental efforts to unveil important basic aspects of the glass transition, such as the existence of the so‐called “ideal glass.”

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Tg depression and invariant segmental dynamics in polystyrene thin films

Cited by 180 publications

References 32 publications

Discrete mobility on the surface of glasses

Discrete mobility on the surface of glasses

Reaching the ideal glass transition by aging polymer films

Physical Aging of Polymers

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