Influence of Chain Stiffness on Thermal and Mechanical Properties of Polymer Thin Films

Torres, J.; Wang, Chengqing; Coughlin, E. Bryan; Bishop, John; Register, Richard A.; Riggleman, Robert A.; Stafford, Christopher M.; Vogt, Bryan D.

doi:10.1021/ma201482b

Cited by 83 publications

(94 citation statements)

References 58 publications

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“…In this context, stiff polynorbornenes that contain a bicylic ring exhibit excellent performance in membranes for butanol–water separations . Similar polynorbornenes are not significantly impacted by confinement with no statistical decrease in T g or elastic modulus down to 10 nm, so one might expect that the aging of these polymers might be thickness independent to enable the use of ultrathin membranes for efficient separations.…”

Section: Introductionmentioning

confidence: 99%

Thickness dependence of structural relaxation in spin‐cast polynorbornene films with high glass transition temperatures (>613 K)

Lewis

Vogt

2017

J Polym Sci B Polym Phys

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The isothermal structural relaxation (densification) of a family of glassy polynorbornene films with high glass transition temperatures (T g > 613 K) is assessed via spectroscopic ellipsometry. Three polymers were examined: poly(butylnorbornene) (BuNB), poly(hydroxyhexafluoroisopropyl norbornene) (HFANB), and their random copolymer, BuNB-r-HFANB. The effective aging rate, b(T), of thick ($1.2 lm) spun cast films of BuNB-r-HFANB is approximately 10 23 over a wide temperature window (0.49 < T/T g < 0.68). At higher temperatures, these polymers undergo reactions that more dramatically decrease the film thickness, which prohibits erasing the process history by annealing above T g . The aging rate for thick BuNB-r-HFANB films is independent of the casting solvent, which infers that rapid aging is not associated with residual solvent. b (at 373 K) decreases for films thinner than $500 nm. However, the isothermal structural relaxation of thin films of BuNB-r-HFANB exhibits nonmonotonic temporal evolution in thickness for films thinner than 115 nm film. The thickness after 18 h of aging at 373 K can be greater than the initial thickness. The rapid aging of these polynorbornene films is attributed to the unusual rapid local dynamics of this class of polymers and demonstrates the potential for unexpected structural relaxations in membranes and thin films of high-T g polymers that could impact their performance.

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Section: Introductionmentioning

confidence: 99%

Thickness dependence of structural relaxation in spin‐cast polynorbornene films with high glass transition temperatures (>613 K)

Lewis

Vogt

2017

J Polym Sci B Polym Phys

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“…T g depression observed in thin films relative to the bulk is mainly attributed to the free‐surface‐induced enhancement of segmental mobility and shift of chain relaxation . Previous experiments and molecular simulations have consistently demonstrated that the free‐surface effects on thin film T g are influenced by factors relevant to polymer chain relaxation and dynamics, such as film thickness, chain rigidity, cohesive interactions, and others . Among these factors, the role of molecular weight (MW) effects on T g ‐confinement behavior has been studied experimentally, and has also led to theoretical models such as de Gennes' sliding motion mechanism and the delayed glassification model …”

Section: Introductionmentioning

confidence: 99%

Molecular Weight Effects on the Glass Transition and Confinement Behavior of Polymer Thin Films

Xia

Hsu

Keten

2015

Macromol. Rapid Commun.

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Nanoscale polymer thin films exhibit strong confinement effects on Tg arising from free surfaces. However, the coupled influence of molecular weight (MW) and surface effects on Tg is not well understood for low MW film systems below the entanglement length. Utilizing atomistically informed coarse-grained molecular dynamics simulations for poly(methyl methacrylate) (PMMA), it is demonstrated that the decrease in free-standing film Tg with respect to bulk is more significant for low MW compared to high MW systems. Investigation of the local interfacial properties reveals that the increase in the local free volume near the free surface is greater for low MW, explaining the MW dependence of Tg -confinement behaviors. These findings corroborate recent experiments on low MW films, and highlight the relationship between nanoconfinement phenomena and local free volume effects arising from free surfaces.

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“…Moreover, this value depends on several aspects such as the thermal history of the sample, the technique/method followed and the thermal rate used for the measurement [41]. For example, recent experiments [42,43] and simulation [44] studies have demonstrated a pronounced thickness-dependent confinement effect on Tg, together with a strong dependence on the solvent and on the substrate used [45]. These effects are totally disregarded if a technique like DSC is employed.…”

Section: Introductionmentioning

confidence: 99%

Predicting thermal stability of organic solar cells through an easy and fast capacitance measurement

Tessarolo

Guerrero

Gedefaw

et al. 2015

Solar Energy Materials and Solar Cells

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Degradation of Organic Photovoltaic (OPV) devices is currently a topic under intense research as it is one of the main limitations towards the commercialization of this technology. Morphological changes at both active layer and interfaces with the outer contacts are believed to determine main key issues to be overcome. In-line techniques are essential to rule out any effect arising during sample fabrication.Unfortunately, the number of physical techniques able to provide morphological information on complete and operational devices is certainly limited. In this work, we study the thermal degradation of bulk heterojunction (BHJ) solar cells composed by different donor polymers with techniques developed to provide in-situ information on operational devices. Capacitance measurement as a function of temperature monitors the electrical integrity of the active layer and provides the threshold temperature (T MAX ) at which the whole device becomes thermally unstable. We found a direct correlation between the threshold temperature T MAX , obtained by capacitance-temperature measurements on complete OPV devices, and the power conversion efficiency decay measured at 85°C. Devices show to be thermal stable when the temperature of the thermal stress is below the T MAX , while above the T MAX evident changes in the active layer or at the active layer/electrode interface are also detected by confocal fluorescence microscopy. The capacitance method gives precious guidelines to predict the thermal stability of BHJ solar cells using accelerated and easy tests.

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Influence of Chain Stiffness on Thermal and Mechanical Properties of Polymer Thin Films

Cited by 83 publications

References 58 publications

Thickness dependence of structural relaxation in spin‐cast polynorbornene films with high glass transition temperatures (>613 K)

Thickness dependence of structural relaxation in spin‐cast polynorbornene films with high glass transition temperatures (>613 K)

Molecular Weight Effects on the Glass Transition and Confinement Behavior of Polymer Thin Films

Predicting thermal stability of organic solar cells through an easy and fast capacitance measurement

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