Effects of Hydration and Temperature on the Microstructure and Transport Properties of Nafion Polyelectrolyte Membrane: A Molecular Dynamics Simulation

Abstract

To investigate the effects of temperature and hydration on the microstructure of polymer electrolyte membrane and the transport of water molecules and hydronium ions, molecular dynamics simulations are performed on Nafion 117 for a series of water contents at different temperatures. The interactions among the sulfonate groups, hydronium ions, and water molecules are studied according to the analysis of radial distribution functions and coordination numbers. The sizes and connectivity of water clusters are also discussed, and it is found that the hydration level plays a key role in the phase separation of the membrane. However, the effect of the temperature is slight. When the water content increases from 3.5 to 16, the size of water clusters in the membrane increases, and the clusters connect to each other to form continuous channels for diffusion of water molecules and hydronium ions. The diffusion coefficients are estimated by studying the mean square displacements. The results show that the diffusion of water molecules and hydronium ions are both enhanced by the increase of the temperature and hydration level. Furthermore, the diffusion coefficient of water molecules is always much larger than that of hydronium ions. However, the ratio of the diffusion coefficient of water molecules to that of hydronium ions decreases with the increase of water content.

Computational Modeling of Hydrated Polyamine-Based Anion Exchange Membranes via Molecular Dynamics Simulation

“…Different studies 64,68,69 proved that both OH − and H 2 O diffusion become faster as temperature increases, due to a reduction of the activation energy associated with ion hopping. Water content plays an important role, and in particular the nanophase segregation between hydrophobic and hydrophilic regions.…”

Current Trends and Changes in Use of Membrane Molecular Dynamics Simulations within Academia and the Pharmaceutical Industry

“…Focus on synthetic membranes has also become more represented in current trends in pharmaceutical product design. Due to the nature of detection and sensitivity, membrane embedded proteins are one of the most useful tools in diagnostic chips for medical labs ranging from simple fluid analysis to phlebotomy [ 155 , 156 ]. In almost all of the chips, it is both beneficial and necessary to embed the proteins within lipid bilayer systems attached to Silicon, Ni, Cu, Ag, and Au platforms [ 157 ].…”

Measurement of Water Uptake and States in Nafion Membranes Using Humidity-Controlled Terahertz Time-Domain Spectroscopy

“…In particular, water within these hydrophilic domains can exist in 3 states: bound water (strongly hydrogen bonded and predominantly bound to the hydrophilic sulfonate groups), , bulk water (weakly hydrogen bonded, exhibiting co-operative reorganization of hydrogen bonds), , and free water (not hydrogen bonded). Due to the importance of hydration in terms of the performance of PFSAs, prevailing methods have been used for characterizing hydration such as small-angle X-ray scattering spectroscopy, − neutron scattering and imaging, − nuclear magnetic resonance, − microwave dielectric relaxation spectroscopy, , Fourier transform infrared (FTIR) spectroscopy, − dynamic vapor sorption (DVS), , differential scanning calorimetry (DSC), − and Raman spectroscopy. − These techniques have been used to study different aspects of membrane hydration such as structure, − ,,,− diffusion, ,,,,,, and proton conduction. ,,− ,− Terahertz time-domain spectroscopy (THz-TDS) is a rapid, noninvasive, and contactless technique, which has previously shown sensitivity to water − and in particular water uptake (WU) and water states in PFSAs. , The terahertz frequency region is of interest as it contains information on the reorientation dynamics of water, with contributions from bulk water relaxation at ∼18 GHz…”

“…Due to the importance of hydration in terms of the performance of PFSAs, prevailing methods have been used for characterizing hydration such as small-angle X-ray scattering spectroscopy, 15 − 17 neutron scattering and imaging, 18 − 22 nuclear magnetic resonance, 23 − 26 microwave dielectric relaxation spectroscopy, 10 , 27 Fourier transform infrared (FTIR) spectroscopy, 28 − 32 dynamic vapor sorption (DVS), 33 , 34 differential scanning calorimetry (DSC), 35 − 42 and Raman spectroscopy. 43 − 46 These techniques have been used to study different aspects of membrane hydration such as structure, 15 − 17 , 22 , 30 , 47 − 50 diffusion, 23 , 24 , 33 , 34 , 43 , 49 , 50 and proton conduction. 15 , 25 , 27 − 29 , 36 − 38 Terahertz time-domain spectroscopy (THz-TDS) is a rapid, noninvasive, and contactless technique, which has previously shown sensitivity to water 51 − 53 and in particular water uptake (WU) and water states in PFSAs.…”