Nanoconfinement effects on the fragility of glass formation of a model freestanding polymer film

Marvin, Michael D.; Lang, Ryan J.; Simmons, David

doi:10.1039/c3sm53160k

Cited by 54 publications

(61 citation statements)

References 31 publications

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“…Experimentally, m is often found to vary in proportion to T g 34 . Figure 1f-h show a correlation between T g and m for all films, but this relation is not strictly proportional, expected from recent studies 19,35 .…”

Section: Resultsmentioning

confidence: 62%

Interfacial mobility scale determines the scale of collective motion and relaxation rate in polymer films

2014

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Thin polymer films are ubiquitous in manufacturing and medical applications, and there has been intense interest in how film thickness and substrate interactions influence film dynamics. It is appreciated that a polymer-air interfacial layer with enhanced mobility plays an important role in the observed changes and recent studies suggest that the length scale x of this interfacial layer is related to film relaxation. In the context of the Adam-Gibbs and random first-order transition models of glass formation, these results provide indirect evidence for a relation between x and the scale of collective molecular motion. Here we report direct evidence for a proportionality between x and the average length L of string-like particle displacements in simulations of polymer films supported on substrates with variable interaction strength and rigidity. This relation explicitly links x to the theoretical scale of cooperatively rearranging regions, offering a promising route to experimentally determine this scale of cooperative motion.

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Section: Resultsmentioning

confidence: 62%

Interfacial mobility scale determines the scale of collective motion and relaxation rate in polymer films

2014

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“…10,[23][24][25][42][43][44] The physical picture is that polymers with large degrees of cooperative motion should experience greater confinement effect due to the truncation of this intrinsic length scale. The cooperative string is a common indicator to describe the CRR size of Adam-Gibbs theory.…”

Section: Resultsmentioning

confidence: 99%

“…1,6,11 Apart from these interfacial effects, the concept of "cooperatively rearranging regions" (CRRs) which is embedded in the Adam-Gibbs (AG) theory 21,22 is often used to explain the origin of nanoconfinement effect. 10,[23][24][25] According to AdamGibbs theory, 21,22 there are CRRs in glass-forming liquids and the average size of such CRRs, ξ CRR , will grow with decreasing temperature, indicating an increase in relaxation time. Intuitively, the growth of ξ CRR should be truncated under the condition of confinement and it will lead to a reduced T g .…”

Section: Introductionmentioning

confidence: 99%

The glass transition of polymers with different side-chain stiffness confined in free-standing thin films

Xie

Huang

2015

The Journal of Chemical Physics

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The effect of confinement on the glass transition temperature Tg of polymeric glass formers with different side chain stiffness is investigated by coarse-grained molecular dynamics simulations. We find that polymer with stiffer side groups exhibits much more pronounced Tg variation in confinement compared to that with relatively flexible side groups, in good agreement with experiments. Our string analysis demonstrates that the polymer species dependence of dynamics can be described by an Adam-Gibbs like relation between the size of cooperatively rearranging regions and relaxation time. However, the primary effect of changing side-group stiffness is to alter the activation barrier for rearrangement, rather than string size. We clarify that free-surface perturbation is the primary factor in determining the magnitude of Tg variation for polymers in confinement: It is more significant for polymers having higher Tg and results in much more pronounced reduction of surface Tg and then the overall Tg of the polymers.

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“…One challenge in this area is that it is not clear how mean measures of relaxation in nanostructured polymers reflect gradients in local fragility. To address this problem, we have recently presented a theoretical development indicating that the mean fragility of a nanostructured polymer reflects a relaxation‐time‐weighted average of local fragilities

〈 m 〉 = {[\int τ_{α} (z, T) m (z, T) normald z / \int τ_{α} (z, T) normald z]}_{T = T_{normalg}}

…”

Section: Introductionmentioning

confidence: 99%

An Emerging Unified View of Dynamic Interphases in Polymers

Simmons

2015

Macro Chemistry & Physics

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The properties of nanostructured polymeric materials reflect the presence of a dynamic interphase in which polymer segmental dynamics, glass formation, mechanics, and transport properties are altered from their bulk states. Examples include nanoconfinement effects on polymer nanofilms, reinforcement effects in polymer nanocomposites and filled rubbers, formation of a rigid amorphous fraction in semicrystalline polymers, and observation of suppressed‐mobility domains around ionic aggregates in ionomers. Whereas many of these phenomena have been viewed as emerging from system‐specific mechanisms, here recent work is highlighted that contributes to an emerging unified understanding of the dynamic interphase in all of these systems. This view suggests that the size scales of dynamic interphases in polymers are generally determined by the scale of cooperative rearrangements intrinsic to relaxation dynamics in supercooled glass‐forming liquids. It also implicates alterations in local segmental rattling as playing a central role in the dynamic interphase, and it suggests that near‐interface modifications in dynamics exhibit a general dependence on the interfacial work of adhesion and the relative high‐frequency moduli of the interface‐adjacent domains.

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Nanoconfinement effects on the fragility of glass formation of a model freestanding polymer film

Cited by 54 publications

References 31 publications

Interfacial mobility scale determines the scale of collective motion and relaxation rate in polymer films

Interfacial mobility scale determines the scale of collective motion and relaxation rate in polymer films

The glass transition of polymers with different side-chain stiffness confined in free-standing thin films

An Emerging Unified View of Dynamic Interphases in Polymers

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