Free Surface-Induced Glass-Transition Temperature Suppression of Simulated Polymer Chains

Wu, Chaofu

doi:10.1021/acs.jpcc.9b01253

Cited by 18 publications

(13 citation statements)

References 54 publications

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“…These observations are consistent with previous experimental and simulation reports of high mobility in the surface layer of metallic glasses near the T g,v , ,, which is similar to the picture of a liquid surface that persists below the T g,v that has been extensively developed for molecular and polymeric glasses. ,,− Our results expand upon this picture by adding metallic glasses to the materials exhibiting these phenomena, directly measuring the surface layer thickness, and demonstrating spatial heterogeneity. We also introduce the idea of and measure T g,s , the temperature at which the surface falls out of equilibrium and becomes glassy.…”

Section: Resultssupporting

confidence: 92%

Fast Surface Dynamics on a Metallic Glass Nanowire

et al. 2021

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The dynamics near the surface of glasses can be much faster than in the bulk. We studied the surface dynamics of a Pt-based metallic glass using electron correlation microscopy with sub-nanometer resolution. Our studies show an ∼20 K suppression of the glass transition temperature at the surface. The enhancement in surface dynamics is suppressed by coating the metallic glass with a thin layer of amorphous carbon. Parallel molecular dynamics simulations on Ni 80 P 20 show a similar temperature suppression of the surface glass transition temperature and that the enhanced surface dynamics are arrested by a capping layer that chemically binds to the glass surface. Mobility in the near-surface region occurs via atomic caging and hopping, with a strong correlation between slow dynamics and high cage-breaking barriers and stringlike cooperative motion. Surface and bulk dynamics collapse together as a function of temperature rescaled by their respective glass transition temperatures.

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Section: Resultssupporting

confidence: 92%

Fast Surface Dynamics on a Metallic Glass Nanowire

et al. 2021

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“…In the present work, three different methods via the computation of volumetric, energetic properties, and conformational transition of torsion angles (the characterization of conformational transition was exhibited in SI) were used to determine precisely the T g of silicone copolymer. These methods were applied in earlier studies to compute T g , and the simulated results were found to be consistent with the experimental results. , It was expected that the introduction of epoxy groups restricts the mobility of polymer segments and reduces the free volume in the rubber region . The assumption was validated by the results shown in Figure (a).…”

Section: Results and Discussionsupporting

confidence: 59%

“…These methods were applied in earlier studies to compute T g , and the simulated results were found to be consistent with the experimental results. 26,43 It was expected that the introduction of epoxy groups restricts the mobility of polymer segments and reduces the free volume in the rubber region. 50 The assumption was validated by the results shown in Figure 2(a).…”

Section: Preparation Of Epoxy-methyl-ethyl-vinyl Silicone Elastomer (...mentioning

confidence: 76%

“…One of the most commonly used SRs, polydimethylsiloxane (PDMS), exhibits excellent bulk properties , and has a very low T g (approximately equal to −124 °C). − However, its crystallization temperature is relatively high at −73 °C , and its temperature of the mesocrystalline phase transition is even higher at −10 °C to approximately −20 °C , which is close to the cold winter temperature in the northern hemisphere. This indicates that PDMS is fragile below such temperatures, which seriously limits its application in the extremely low-temperature environment.…”

Section: Introductionmentioning

confidence: 99%

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Exploiting Synergistic Experimental and Computational Approaches to Design and Fabricate High-Performance Elastomer

Hou

Xinyi

et al. 2020

Macromolecules

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Silicone elastomers (SRs) are of great scientific and technological importance due to their resistance to low temperatures. However, the glass transition temperature (T g) of existing SRs is not low enough to satisfy its utilization in the extremely low-temperature environment. Meanwhile, crystallization often occurs at the low-temperature, making it difficult for SRs to maintain their original properties in the extremely low-temperature environment. Here, by combining molecular dynamics (MD) simulation and experiment, a novel low-temperature resistance and crystalline-free SR (Epoxidized-Methyl-Ethyl-Vinyl Silicone Elastomer, also referred to E-MEVQ) is fabricated by random copolymerization of three different siloxane repeat units (dimethyl-siloxane, diethyl-siloxane and methyl-epoxy-siloxane). We showed that the T g of E-MEVQ computed from MD simulations using three different methods (specific volume, nonbond potential energy and conformational transition versus temperature) agrees well with that of the as-synthesized E-MEVQ determined by Differential Scanning Calorimetry. The T g is approximately −130 °C, much lower than that of Polydimethylsiloxane (PDMS), and the E-MEVQ is in the amorphous state without any crystallization. This novel silicone elastomer is expected to be widely applied in the field of smart devices, sensors, and medical equipment under extreme situations. Our work also provides a promising framework for designing and fabricating high-performance elastomeric polymer materials via simulation and experiment.

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“…Confinement of polymer chain mobility is well investigated by other authors. Often, the glass transition temperature is determined experimentally as a function of the distance to the substrate. − Also, molecular dynamics simulations support the experimental observations. ,− Depending on the polymer and the measurement technique, the substrate influences polymer chain mobility up to a distance of 5 to 10 nm to the substrate. As the diffusion coefficient is a measure of polymer chain mobility, this contradicts the observations of Buss et al and Vogt et al that the diffusion is slowed down in a range of even up to 40 nm (Buss et al) or 150 nm (Vogt et al) from the substrate due to confinement of polymer chains.…”

Section: Introductionmentioning

confidence: 97%

Drying Kinetics from Micrometer- to Nanometer-Scale Polymer Films: A Study on Solvent Diffusion, Polymer Relaxation, and Substrate Interaction Effects

2021

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The drying behavior of two different polymers [polyvinyl pyrrolidone (PVP) and polyisobutylene (PIB)] with different glass transition temperatures are investigated and compared as a function of film thickness from micrometer (∼3 μm) to nanometer scale (∼10 nm). The focus of this study is to distinguish between solvent diffusion, polymer relaxation, and substrate confinement of polymer chain mobility toward the interface as the dominating mechanism of drying kinetics. Relaxation kinetics becomes more dominant when the film thickness is reduced, which is shown experimentally for the first time for nanometer-scale film thicknesses. Identical drying curves regardless of the film thickness of PVP/methanol indicate the limitation of solvent transport by relaxation kinetics. The viscoelastic relaxation behavior of the polymer/solvent film is modeled by a Maxwell element. The results are in accordance with the experimental drying curves and allow for the determination of the characteristic relaxation time. Relaxation limitation becomes relevant at high diffusion Deborah numbers when the relaxation timewhich is a function of the deployed material and the polymer/solvent compositionis higher than the characteristic diffusion time in the film. The latter is a function of the polymer/solvent composition and the thickness of the film. Drying curves of PIB/toluene films show additional effect in a substrate-near region of about 5 nm in which polymer chain mobility is confined, resulting in decelerated solvent diffusion. Although this effect near the substrate interface is expected to be present regardless of the film thickness, it becomes more dominant when the substrate-near region represents a significant fraction of the total film thickness. The key to the derived methodology for characterization of the polymer/solvent drying process is to vary dry film thickness from micrometers to a few nanometers which allows us to determine the dominating mechanism of drying kinetics.

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Free Surface-Induced Glass-Transition Temperature Suppression of Simulated Polymer Chains

Cited by 18 publications

References 54 publications

Fast Surface Dynamics on a Metallic Glass Nanowire

Fast Surface Dynamics on a Metallic Glass Nanowire

Exploiting Synergistic Experimental and Computational Approaches to Design and Fabricate High-Performance Elastomer

Drying Kinetics from Micrometer- to Nanometer-Scale Polymer Films: A Study on Solvent Diffusion, Polymer Relaxation, and Substrate Interaction Effects

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