Modeling on swelling behavior of a confined polymer network

Li, Xuemei; Shen, Zhou; He, Tianbai; Weßling, Matthias

doi:10.1002/polb.21495

Cited by 13 publications

(11 citation statements)

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“…19 The primary difference between the original theory and the modified version is the relationship of the thickness swelling ratio with the polymer volume fraction. The classic Flory- Rehner theory assumes isotropic expansion of the film whereas the modified theory only considers swelling along the thickness direction with lateral expansion restricted by the rigid substrate.…”

Section: à ámentioning

confidence: 99%

Swelling of ultrathin crosslinked polyamide water desalination membranes

Chan

Young

Lee

et al. 2012

J Polym Sci B Polym Phys

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ABSTRACT:We study the water swelling behavior of semiaromatic crosslinked polyamide (PA) ultrathin films to characterize the network properties of the polymer. Specifically, we use Xray reflectivity to measure film thickness increase and polymer density decrease of the PA films due to swelling. With the aid of a modified Flory-Rehner theory used to describe the constrained swelling behavior of polymer networks, we are able to extract the Flory interaction parameter and the monomer units between crosslinks by performing the swelling experiments at different levels of hydration.

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Section: à ámentioning

confidence: 99%

Swelling of ultrathin crosslinked polyamide water desalination membranes

Chan

Young

Lee

et al. 2012

J Polym Sci B Polym Phys

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“…In fact, there has been only minimal research into swelling of constrained polymers in general with notable exceptions of gels and elastomers, for which Flory-Rehner theory 25,26 is commonly employed to develop models. [27][28][29] However, it is debatable that these models, at least in their current form, are applicable to semi-crystalline perfluorinated membranes due to these membranes' much different mechanical and uptake properties and relationships, which stem from their different intrinsic morphology in comparison to gels and elastomers that contain significant amounts of water and deform much easier and without internal crystallite structures. Therefore, the water uptake of compressed/constrained ionomers warrants further investigation, both theoretically and experimentally.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Effects of Compression and Constraints on Water Uptake of Fuel-Cell Membranes

Kusoglu

Kienitz

Weber

2011

J. Electrochem. Soc.

118

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Accurate characterization of polymer-electrolyte fuel cells (PEFCs) requires understanding the impact of mechanical and electrochemical loads on cell components. An essential aspect of this relationship is the effect of compression on the polymer membrane's water-uptake behavior and transport properties. However, there is limited information on the impact of physical constraints on membrane properties. In this paper, we investigate both theoretically and experimentally how the water uptake of Nafion membrane changes under external compression loads. The swelling of a compressed membrane is modeled by modifying the swelling pressure in the polymer backbone which relies on the changes in the microscopic volume of the polymer. The model successfully predicts the water content of the compressed membrane measured through in-situ swelling-compression tests and neutron imaging. The results show that external mechanical loads could reduce the water content and conductivity of the membrane, especially at lower temperatures, higher humidities, and in liquid water. The modeling framework and experimental data provide valuable insight for the swelling and conductivity of constrained and compressed membranes, which are of interest in electrochemical devices such as batteries and fuel cells. † Current Address: W.L. Gore and Associates, 201 Airport Road, Elkton, MD USA ‡ Corresponding author. E-mail address: azweber@lbl.gov Tel: (510) 486-6308. * ECS Member. IntroductionIonomer membranes used in polymer-electrolyte-fuel-cell (PEFC) applications are always subjected to mechanical constraints to some extent due to cell design and clamping loads to reduce contact resistances and seal cells using compression seals. Furthermore, swelling of the membranes due to water uptake results in compressive stresses during cell operation. [1][2][3] Compression in the cell is known to influence membrane stresses, [2][3][4][5][6] transport in gas-diffusion layers (GDL), [7][8][9] and cell resistance. 10 However, the effect of the constraints and mechanical loads on the membrane's water-uptake behavior is yet to be determined due to the difficulty of such measurement. Moreover, due to the lack of the experimental data on the swelling behavior of constrained membranes, mathematical models on water uptake cannot be fully validated. In this work, we aim to investigate how the constraints on the membrane affect its water-uptake behavior and other water-dependent transport properties such as conductivity.In a PEFC, the extent to which the membrane is deformed depends on a number of factors including, but not limited to, geometry of the cell (e.g. land/channel ratio), thickness and stiffness of the cell components (e.g. bipolar plates, gas-diffusion layers (GDLs)), and operating conditions (e.g., humidity). Thus, stresses and pressures in the membrane are not uniform; they depend on location, time, and component material properties. In addition, the membrane itself is subjected to a combination of constraints and mechanical loads: (i) interfacial con...

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“…According to the constrained swelling model, the swelling of the SPEEK in the SPEEK-PES layer is largely compressed due to the non-swollen PES. Therefore, the pore size of the NF membrane is then determined to a large extent by the channel size in the SPEEK-PES entangled layer [29].…”

Section: Hypothesis For Instability Of Speek Nf Membranementioning

confidence: 99%

“…According to Flory's swelling theory, high osmotic pressure drives water through the polymer chains into the SPEEK dense skin layer as well as deep into the SPEEK-PES entangled layer [28]. The swelling of SPEEK polymer results in a channel-like network which forms the actual passages for water molecules and the ions [12,29]. The swelling of SPEEK at the top skin layer is free in comparison to that in the SPEEK-PES layer, therefore, corresponding to a higher swelling degree.…”

Section: Hypothesis For Instability Of Speek Nf Membranementioning

confidence: 99%