Is the molecular surface of polystyrene really glassy?

Meyers, Gregory F.; DeKoven, Benjamin M.; Seitz, Jerry T.

doi:10.1021/la00045a042

Cited by 232 publications

(183 citation statements)

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“…The behavior of thin glassy films has often been interpreted in terms of a two-population model, in which there is a glassy, immobile layer near the center of the film and a liquid-like mobile layer near the free surfaces [1,[24][25][26]. This interpretation is supported by observations of probe molecules embedded in films [27,28].…”

Section: {S} {Smentioning

confidence: 99%

Disconnecting structure and dynamics in glassy thin films

Sussman

Schoenholz

Cubuk

et al. 2017

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

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Nanometrically thin glassy films depart strikingly from the behavior of their bulk counterparts. We investigate whether the dynamical differences between bulk and thin film glasses can be understood by differences in local microscopic structure. We employ machine-learning methods that have previously identified strong correlations between local structure and particle rearrangement dynamics in bulk systems. We show that these methods completely fail to detect key aspects of thin-film glassy dynamics. Furthermore, we show that no combination of local structural features drawn from a very general set of two-and multi-point functions is able to distinguish between particles at the center of film and those in intermediate layers where the dynamics are strongly perturbed.Confinement of glassy materials to nanometric length scales leads to striking changes to their microscopic dynamics and consequently to their material properties [1]. Direct observations in both experiments and simulations find exponentially more particle rearrangements near the free surface of a film [2][3][4][5]. A key question is whether enhanced dynamics near a free surface (or suppressed dynamics near a substrate) are connected with structural changes. So far, all structural features studied decay too rapidly into the bulk [1] to explain the altered dynamics.Until recently, the study of bulk glassy systems has also been plagued by the inability to connect dynamical changes with structural ones. However, machine learning methods have proven remarkably successful in identifying a local structural quantity, termed "softness" and denoted S i for particle i, that is strongly correlated with particle rearrangements [6][7][8]. Softness is over an order of magnitude more predictive of rearrangements than measures such as the local potential energy or coordination number [9]. The average softness, S , is directly predictive of the relaxation time of a bulk supercooled liquid [7] or aging bulk glass [8], with higher values of S corresponding to shorter relaxation times at higher temperatures. In bulk systems, it is therefore now clear that dynamical slowing down near the glass transition is intimately associated with structural changes. Here we ask whether the enhancement of dynamics near the surface of free glassy films can similarly be understood.The answer is no. Not only does softness fail to predict the enhanced dynamics near the surface of free glassy films, we find that for a very general set of quantities that characterize the local structural environment surrounding a particle, there is no combination of these quantities that can distinguish between parts of the film with very different dynamics. The enhanced dynamics near a free glassy surface therefore appear to be fundamentally different from the enhanced dynamics that result from heating bulk glassy systems. Although we cannot rule out the possibility that structural quantities that we have not considered might tell a different story, our results suggest that near glassy free surfaces, relaxat...

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Section: {S} {Smentioning

confidence: 99%

Disconnecting structure and dynamics in glassy thin films

Sussman

Schoenholz

Cubuk

et al. 2017

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

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“…state at room temperature [2]. Some further studies have focused on the formation conditions for such structures.…”

Section: Introductionmentioning

confidence: 99%

Bundle structure formation on a polymer film at various temperatures and scanning velocities

Wang

Xiao

2002

Nanotechnology

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The structures formed by atomic force microscopic tip scanning on a 133 nm thick poly(tert-butyl acrylate) (PtBuA) film were examined at temperatures ranging from room temperature to 58• C with various scanning velocities from 1 to 20 µm s −1 . It was observed that bumps were created at low temperatures and high scanning velocities. As the temperature was increased and the scanning velocity was decreased, bundles were produced through aggregation of the bumps. The width of the bundles was about 100 nm. As the temperature was further increased to higher than the glassy-rubbery phase transition temperature, T g ∼ 50• C, of the PtBuA polymer, no bundle structures were formed at low scanning velocities. Our results clearly indicate that the formation of bumps and bundles occurs from the interplay of polymer peeling and relaxation. With polymer peeling taking place on soft polymer surfaces, slower relaxation favours the accumulation of polymer coil displacement and the formation of the bump and bundle structures, while fast relaxation results in the recovery of the polymer perturbation and no formation of surface structures.

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“…In the present study, we also showed how vibration cutting is further useful for the dissection of dried, fragile biological samples. On the other hand, simple cutting without probe oscillation is not suitable for the precise dissection of our samples, probably because it produces a sliding interaction between a probe of the AFM and the sample surface (Meyers et al, 1992;Leung and Goh, 1992), making it difficult to cut the sample smoothly for micro or nanometer-scale fabrication.…”

Section: Discussionmentioning

confidence: 99%

Development of a nano manipulator based on an atomic force microscope coupled with a haptic device: a novel manipulation tool for scanning electron microscopy

Iwata

Kawanishi

Aoyama

et al. 2009

Archives of Histology and Cytology

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since the operator can move the AFM probe freely at any position on the sample surface while feeling the interaction force between the probe and the sample surface. We tested two types of cutting methods: simple cutting and vibration cutting. Our results showed that vibration cutting with probe oscillation is very useful for the dissection of biological samples which were dried for SEM observation. Thus, cultivated HeLa cells were successfully microdissected by vibration cutting, and the dissection process could be observed in real time in the SEM. This AFM manipulation system is expected to serve as a powerful tool for dissecting various biological samples at the micro and nanometer-scale under SEM observation.

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Is the molecular surface of polystyrene really glassy?

Cited by 232 publications

References 0 publications

Disconnecting structure and dynamics in glassy thin films

Disconnecting structure and dynamics in glassy thin films

Bundle structure formation on a polymer film at various temperatures and scanning velocities

Development of a nano manipulator based on an atomic force microscope coupled with a haptic device: a novel manipulation tool for scanning electron microscopy

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