Discrete mobility on the surface of glasses

Chowdhury, Mithun; Priestley, Rodney D.

doi:10.1073/pnas.1704886114

Cited by 17 publications

(28 citation statements)

References 25 publications

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“…This enabled us to detect the 17 O sites. Figure S10 shows that the 17 O signal of the PTA-OH sample is mostly correlated with OH protons signals, whereas for the thermally treated sample, it is clear that the two different 17 O sites are connected with the 1 H signal of OH and aromatics, in agreement with the expected shifts. At the same time, the 15 N CP-MAS and the 15 N-1 H CP-MAS HETCOR of the thermally treated membranes reveal a distribution of new signals in the range of 380 to 390 ppm that are attributed to the nitrogen atoms labeled N 4 and N 5 (Fig.…”

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confidence: 68%

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Polytriazole membranes with ultrathin tunable selective layer for crude oil fractionation

Chişcă

Musteata

Zhang

et al. 2022

Science

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The design of materials and their manufacture into membranes that can handle industrial conditions and separate complex nonaqueous mixtures are challenging. We report a versatile strategy to fabricate polytriazole membranes with 10-nanometer-thin selective layers containing subnanometer channels for the separation of hydrocarbons. The process involves the use of the classical nonsolvent-induced phase separation method and thermal cross-linking. The membrane selectivity can be tuned to the lower end of the typical nanofiltration range (200 to 1000 gram mole −1 ). The polytriazole membrane can enrich up to 80 to 95% of the hydrocarbon content with less than 10 carbon atoms (140 gram mole −1 ). These membranes preferentially separate paraffin over aromatic components, making them suitable for integration in hybrid distillation systems for crude oil fractionation.

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confidence: 68%

“…We distinguished two sets of oxygen coordinations (labeled O 1 and O 2 ) for the thermally treated sample demonstrated by 17 O DNP spectra, which offers very high sensitivity, without using isotopically enhanced samples (Fig. 1C and fig.…”

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confidence: 99%

Polytriazole membranes with ultrathin tunable selective layer for crude oil fractionation

Chişcă

Musteata

Zhang

et al. 2022

Science

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“…54 Although these studies have reached a consensus that more heterogeneous dynamics emerge both with decreasing temperature or as interfaces are approached, a full picture that includes focused experimental measurements has yet to emerge. 43 One specific challenge is translating realistic experimental conditions, such as surface energies, mechanical properties, etc., of the substrate−polymer pairs, into useful parameters that may serve as input to theories/models. To leverage the findings of these important theoretical works, an experimental investigation that systematically studies interfacial effects on both T g and D in a convenient polymer system is strongly desired.…”

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confidence: 99%

Glass Transition and Self-Diffusion of Unentangled Polymer Melts Nanoconfined by Different Interfaces

et al. 2018

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In nanoconfined thin films, numerous studies have revealed the thickness dependencies of different thermophysical properties, including the glass transition temperature (T g) and self-diffusion coefficient (D). While quantitative relationships between these properties are well-known for bulk polymers, analogous relationships for nanoconfined polymers are still not clear. Herein, T g−D relationships are studied under nanoconfinement using spectroscopic ellipsometry for measuring T g and fluorescence recovery after photobleaching for measuring D. Poly(isobutyl methacrylate) (PiBMA) was selected as a model unentangled polymer, and it was nanoconfined to 14–300 nm thick films. Multilayered geometries incorporating PiBMA were constructed to systematically study the influence of free surfaces (i.e., polymer surfaces exposed directly to air, also called uncapped) and surfaces that were in contact with a secondary polymer (also called capped). This multilayer approach additionally allowed investigation of both relatively weak and strong interactions between the polymer and substrate, depending on the existence of hydrogen bonding. The T g–D relationship observed in nanoconfined thin films deviated from that in the bulk state (e.g., as described by Williams–Landel–Ferry and Stokes–Einstein, or similar relationships). A model was employed that considered the effects of molecular friction between the different confining interfaces and PiBMA, and it successfully described the deviation from bulk behavior.

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“…This can be as large as 70 K and visible for thickenesses of ∼100 nm for freestanding polystyrene (PS) films. , Beside this observation, a number of studies, where τ is measured by techniques probing the linear response, show the presence of a dominant component with bulk-like dynamics. − To explain these results, two main hypotheses have been formulated. On one side, it has been argued that in nanoscale confinement T g and molecular dynamics are decoupled. ,,− Beside, the role of free surface to speed dynamics, which has been shown in several studies, − has been invoked to explain T g suppression in confinement …”

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confidence: 99%

Glass Transition and Molecular Dynamics in Polystyrene Nanospheres by Fast Scanning Calorimetry

2017

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We employ fast scanning calorimetry (FSC) to characterize the glass transition of polystyrene (PS) nanospheres. We observe suppression of the glass transition temperature (T g) in comparison to bulk PS, both in terms of limiting fictive temperature (T f) and temperature range of vitrification. At the same time, the polymer molecular mobility is found to be independent of the nanospheres diameter and bulk-like. Importantly, apart from the fact that this result has been obtained on the same samples and experiments and at comparable time scales, in all cases, a perturbation of the entropy is induced. Hence, to understand these results, the conceptual difference between vitrification kinetics and molecular mobility is highlighted. The main consequence of the outcome of the present study is that arguments beyond those based on the modification of the molecular mobility must be accounted for to explain T g suppression in polymer glasses subjected to nanoscale confinement.

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Discrete mobility on the surface of glasses

Cited by 17 publications

References 25 publications

Polytriazole membranes with ultrathin tunable selective layer for crude oil fractionation

Polytriazole membranes with ultrathin tunable selective layer for crude oil fractionation

Glass Transition and Self-Diffusion of Unentangled Polymer Melts Nanoconfined by Different Interfaces

Glass Transition and Molecular Dynamics in Polystyrene Nanospheres by Fast Scanning Calorimetry

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