Structural Relaxations of Thin Polymer Films

Frieberg, Bradley; Glynos, Emmanouil; Green, Peter

doi:10.1103/physrevlett.108.268304

Cited by 63 publications

(94 citation statements)

References 32 publications

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“…6,19,20 However

T_{g}^{surf}

became gradually lower than

T_{g}^{bulk}

as M w arm became much larger than M e, the molecular weight between entanglements; this trend is consistent with the behavior of linear chain polymers. 6,19,20 Molecular dynamics simulations revealed that this behavior–

T_{g}^{surf} > T_{g}^{bulk}

-might be due to positional correlations of the star-shaped molecular at the free surface of the film. 20 In this letter we demonstrate using XPCS that the in contrast to the linear chain polymers, the free surface layer relaxations are slow compared to the bulk and this persists to temperatures T > T g + 50 K. Molecular dynamics simulations of supported thin polymer films indicate that the slow dynamics, and

T_{g}^{surf} > T_{g}^{bulk}

, would be due to a preferential localization of these molecules at the free surface.…”

supporting

confidence: 75%

“…

T_{g}^{surf} > T_{g}^{bulk}

. 6,19,20 However

T_{g}^{surf}

became gradually lower than

T_{g}^{bulk}

T_{g}^{surf} > T_{g}^{bulk}

-might be due to positional correlations of the star-shaped molecular at the free surface of the film.…”

supporting

confidence: 65%

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Free Surface Relaxations of Star-Shaped Polymer Films

et al. 2017

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The surface relaxation dynamics of supported star-shaped polymer thin films are shown to be slower than the bulk, persisting up to temperatures at least 50 degrees above the bulk glass transition temperature Tgbulk. This behavior, exhibited by star-shaped polystyrenes (SPSs) with functionality f = 8-arms and molecular weights per arm Marm < Me (Me is the entanglement molecular weight), is shown by molecular dynamics simulations to be associated with a preferential localization of these macromolecules at the free surface. This new phenomenon is in notable contrast to that of linear chain polymer thin film systems where the surface relaxations are enhanced in relation to the bulk; this enhancement persists only for a limited temperature range above the bulk Tgbulk. Evidence of the slow surface dynamics, compared to the bulk, for temperatures well above Tg and at length and time scales not associated with the glass transition has not previously been reported for polymers.

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“…6,19,20 However

T_{g}^{surf}

became gradually lower than

T_{g}^{bulk}

T_{g}^{surf} > T_{g}^{bulk}

T_{g}^{surf} > T_{g}^{bulk}

, would be due to a preferential localization of these molecules at the free surface.…”

supporting

confidence: 75%

“…

T_{g}^{surf} > T_{g}^{bulk}

. 6,19,20 However

T_{g}^{surf}

became gradually lower than

T_{g}^{bulk}

T_{g}^{surf} > T_{g}^{bulk}

-might be due to positional correlations of the star-shaped molecular at the free surface of the film.…”

supporting

confidence: 65%

Free Surface Relaxations of Star-Shaped Polymer Films

et al. 2017

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“…This is consistent with findings of previous experimental studies. 37,57 At this point, it is important to note that this effect is not due to the increased free volume caused by an increased number of free-ends into the system. If that would be true, then decreasing the length of the arms would further decrease T c iso , which is not consistent to our findings as presented above.…”

Section: Core Particlementioning

confidence: 96%

Structure and dynamical intra-molecular heterogeneity of star polymer melts above glass transition temperature

Chremos

Glynos

Green

2015

The Journal of Chemical Physics

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Structural and dynamical properties of star melts have been investigated with molecular dynamics simulations of a bead-spring model. Star polymers are known to be heterogeneous, but a systematic simulation study of their properties in melt conditions near the glass transition temperature was lacking. To probe their properties, we have expanded from linear to star polymers the applicability of Dobkowski's chain-length dependence correlation function [Z. Dobkowski, Eur. Polym. J. 18, 563 (1982)]. The density and the isokinetic temperature, based on the canonical definition of the laboratory glass-transition, can be described well by the correlation function and a subtle behavior manifests as the architecture becomes more complex. For linear polymer chains and low functionality star polymers, we find that an increase of the arm length would result in an increase of the density and the isokinetic temperature, but high functionality star polymers have the opposite behavior. The effect between low and high functionalities is more pronounced for short arm lengths. Complementary results such as the specific volume and number of neighbors in contact provide further insights on the subtle relation between structure and dynamics. The findings would be valuable to polymer, colloidal, and nanocomposites fields for the design of materials in absence of solution with the desired properties.

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“…Another element tuning aging rates of thin polymer films is the molecular architecture. The aging rate of star‐shaped PS thin films on silicon oxide is reduced compared with its linear counterpart, and physical aging is also suppressed with reducing the degree of polymerization per arm in thin films of star‐shaped PS 105…”

Section: Polymer Nanoparticles: Our Recent Contributionsmentioning

confidence: 99%

Confined glassy properties of polymer nanoparticles

Zhang

Guo

Priestley³

2013

J Polym Sci B Polym Phys

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For nearly the past two decades, significant effort has been devoted to pursuing an understanding of the glass transition temperature and associated dynamics of polymers confined to the nanoscale. Without question, we know more about the glassy properties of confined polymers today than we knew two decades ago or even a decade ago. Much of our understanding has been obtained via studies on thin polymer films, as they are facile to process and are of substantial technological importance. Nevertheless, studies on polymers confined to other geometries are becoming increasingly more important as we pursue questions difficult to address using thin films and as technology demands the use of confined polymers beyond thin films. In this feature article, we highlight the impact of nanoscale confinement on the glassy properties of polymer nanoparticles. Although the emphasis is placed on contributions from our work, a discussion of the related literature is also presented. Our aim is to elucidate commonalities or fundamental differences in the deviations of glassy properties from the bulk for polymers confined to different geometries. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 574-586 KEYWORDS: calorimetry; confinement; fragility; glass transition; nanoparticles; structural relaxation INTRODUCTION Central to the advancement of many technologies is the miniaturization of functional devices to the nanometer length scale. As polymers continue to play a prominent role in material solutions in meeting the challenges of reducing size, they are undoubtedly being utilized at length scales that are approaching the dimensions of the unperturbed macromolecule. Furthermore, with decreasing the confining dimension to the nanoscale an increasingly larger fraction of molecules are in direct contact with interfaces. Often, the average properties or the distribution in properties away from the interfaces of a confined polymer can be strongly perturbed from the bulk. It is the deviation in properties of confined polymers relative to the bulk that is commonly referred to as the confinement effect, and in the special case when the property of interest is the glass transition temperature (T g ), the T g -confinement effect.

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Structural Relaxations of Thin Polymer Films

Cited by 63 publications

References 32 publications

Free Surface Relaxations of Star-Shaped Polymer Films

Free Surface Relaxations of Star-Shaped Polymer Films

Structure and dynamical intra-molecular heterogeneity of star polymer melts above glass transition temperature

Confined glassy properties of polymer nanoparticles

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