Dynamics of Materials at the Nanoscale: Small‐Molecule Liquids and Polymer Films

McKenna, Gregory B.

doi:10.1002/9780470600160.ch5

Cited by 7 publications

(3 citation statements)

References 143 publications

(130 reference statements)

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“…The behavior of polymers in sub-μm thick films can be drastically different from that in bulk membrane format (several tens of μm thick). Polymer chains experience confinement within films when the film thickness approaches the radius of gyration of free polymer chains. − The polymer chain entrapment as well as complex interfacial interactions (among water, polymer, and substrate) impacts the rheology − and diffusion coefficient of both water and polymer chains − in hydrated thin films. These can make the water-mediated ion conduction very difficult in thin films of ion conducting polymer (ionomer), − critical for energy technologies.…”

Section: Introductionmentioning

confidence: 99%

“…In this work, we leveraged a fluorescent photoacid probe, HPTS that fluorescently responded to local hydration environment when incorporated within sub-μm thick (∼20–470 nm thick) films of Nafion (EW ∼ 1100, IEC = 0.909 mequiv/g), 3M PFSA (EW ∼ 825, IEC = 1.21 mequiv/g), and 3M PFIA (EW ∼ 620, IEC = 1.61 mequiv/g) exposed to air with certain relative humidity (RH). Fluorescent dyes have been found effective to reveal the glass transition, ,,,, water sorption and diffusivity, ,, aging ,, or structural relaxation, polymer–substrate interaction, , proton conduction, and mechanical behavior ,, within confined systems. Many critical parameters of proton conduction environment, such as the extent of proton conduction, , proton transport dynamics, ,,, and water orientational relaxation dynamics have been investigated by incorporating photoacid probes within polymeric, ,,,,, reverse micelle, ,,,, and biological , systems.…”

Section: Introductionmentioning

confidence: 99%

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Fluorocarbon-Based Ionomers with Single Acid and Multiacid Side Chains at Nanothin Interfaces

Farzin

Yandrasits²,

Dishari

2019

J. Phys. Chem. C

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Unraveling ion conduction limitations in nanothin ionomer films is crucial for designing efficient ionomer−catalyst interfaces and improving redox efficiency in electrochemical devices. This work took a multifaceted approach to understand local proton conduction environments in sub-μm thick films of three fluorocarbon-based ionomers, Nafion, 3M PFSA and 3M PFIA with IEC ∼ 0.91, 1.21, and 1.61 mequiv/g, respectively. After incorporating fluorescent photoacid probe pyranine (HPTS) into films, the extent of proton conduction (I d /I p ), local proton concentration, pH, and ionic domain size (d id ) were predicted by monitoring the ratio of fluorescence intensity of deprotonated (I d ) to that of the protonated (I p ) state of HPTS. I d /I p decreased with film thickness and followed the trend: 3M PFIA > 3M PFSA > Nafion. A higher water uptake did not necessarily lead to higher I d /I p indicating that other factors than water uptake control proton conduction under confinement. Size of the ionic domains (d id ), measured independently using in-plane reflection small-angle X-ray scattering and fluorescence spectroscopy, followed the same trend as I d /I p . As the RH and film thickness decreased, d id became smaller. The close match of d id obtained from both techniques supported the reliability of information confered by fluorescence spectroscopy about key controlling parameters of the local proton conduction environment. The highest I d /I p of 3M PFIA films was attributed to its flexible, multiacidic side chain that helped to form larger ionic domains with better phase segregation. Conversely, smaller, extremely acidic and poorly phase segregated ionic domains with highly confined water molecules led to lower I d /I p in Nafion films, despite high water uptake.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Fluorocarbon-Based Ionomers with Single Acid and Multiacid Side Chains at Nanothin Interfaces

Farzin

Yandrasits²,

Dishari

2019

J. Phys. Chem. C

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“…The mobility and thermal dynamic properties of polymers when confined at nanometer length scales differ greatly from properties in the bulk. − By using fluorophores to label a single layer within a multilayer polystyrene (PS) film, Ellison and Torkelson performed the first direct measurement of glass transition temperature ( T g ) gradients in substrate-supported PS films. Paeng and Ediger et al measured the molecular mobility in free-standing polystyrene films dispersed with fluorescent probe by an optical photobleaching technique.…”

Section: Introductionmentioning

confidence: 99%

Confinement-Induced Deviation of Chain Mobility and Glass Transition Temperature for Polystyrene/Au Nanoparticles

Zhu

Wang

et al. 2013

Macromolecules

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The mobility and glass transition temperature (T g ) for polymers under nanoscale confinement differ substantially from the bulk. Whereas many studies have focused on the one-dimensional confinement, it has great significance to extend studies to higher geometries. Here, we systematically investigate the mobility by dipolar-filter sequence in solid-state NMR and T g by DSC for thiolated polystyrene (PS-SH) on gold nanoparticles. The increase in T g and signal suppression in NMR spectra clearly indicate that the surface confinement dominates molecular mobility as well as T g . The molecular weight of PS-SH and nanoparticles size show significant influence on the immobilization and T g . Our results can be fitted with a core−two shell model; the inner shell is under strong constraints while the outer shell with less confinement. This work is essential to better understand the confinement effect and also provides a step toward the ultimate desire to tailor the properties of nanomaterials.

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The Glass Transition and Structural Recovery Using Flash DSC

Simon

Koh

2016

Fast Scanning Calorimetry

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Dynamics of Materials at the Nanoscale: Small‐Molecule Liquids and Polymer Films

Cited by 7 publications

References 143 publications

Fluorocarbon-Based Ionomers with Single Acid and Multiacid Side Chains at Nanothin Interfaces

Fluorocarbon-Based Ionomers with Single Acid and Multiacid Side Chains at Nanothin Interfaces

Confinement-Induced Deviation of Chain Mobility and Glass Transition Temperature for Polystyrene/Au Nanoparticles

The Glass Transition and Structural Recovery Using Flash DSC

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