Intermolecular momentum transfer in poly(perfluorosulfonic acid) membrane hydrated by aqueous solution of methanol: A molecular dynamics simulation study

Abstract

Intermolecular momentum transfer in methanol-water mixture solvated poly(perfluoro-sulfonic acid) membrane is studied in terms of center of mass velocity cross-correlation functions between molecular mass centers in their first coordination shells based on molecular dynamics simulations. Moreover, the center of mass velocity cross-correlation functions are also decomposed into longitudinal and transversal contributions. The fastest momentum transfer is observed between hydronium cation and water molecule due to the strong hydrogen bond interaction. The center of mass velocity cross-correlation functions reach peak value in about 36 fs, corresponding to a single collision with a neighboring molecule. For the momentum transfer between the water molecule and methanol molecule, the peaking time is 70 fs or about twice of that between hydronium cation and water molecule. Oscillation of the center of mass velocity cross-correlation functions between hydronium cation and water molecule is also observed due to the cage effect in their equilibrium positions.

Field-Induced Transport in Sulfonated Poly(styrene-co-divinylbenzene) Membranes

“…The investigation of transport and equilibrium phenomena in ion-exchange membranes have been studied in a number of papers, − and additionally, some mathematical models have been proposed to explain the macroscopic characteristics of such processes (e.g., proton transport and membrane conductivity). − However, in spite of such significant amount of work, nanoscale details about the molecular structure of ion-exchange membranes and the proton transport mechanism remain essentially unknown. Although theoretical studies based on molecular dynamics (MD) simulations are expected to be important not only for the elucidation of details about the protons transport across membranes but also for the design of good performance conducting membranes, the number of reported investigations is relatively scarce. − Goddard and co-workers used atomistic MD simulations to predict the nanostructure of hydrated Nafion 117, a polyelectrolyte consisting of nonpolar tetrafluoroethylene and polar perfluorosulfonic vinyl ether segments used in polymer electrolyte membrane fuel cells, with a focus on investigating the effect of the polar and nonpolar monomeric sequence on the nanophase-segregated morphology and the water/hydronium transport . More recently, the effects of electric field in transport dynamics inside hydrated Nafion membranes were investigated by different authors. − In addition, Allahyarov and Taylor used MD simulations to investigate the effect of stretching induced structure on the proton conductivity of Nafion-like polymer electrolyte membranes.…”

“…Although theoretical studies based on molecular dynamics (MD) simulations are expected to be important not only for the elucidation of details about the protons transport across membranes but also for the design of good performance conducting membranes, the number of reported investigations is relatively scarce. − Goddard and co-workers used atomistic MD simulations to predict the nanostructure of hydrated Nafion 117, a polyelectrolyte consisting of nonpolar tetrafluoroethylene and polar perfluorosulfonic vinyl ether segments used in polymer electrolyte membrane fuel cells, with a focus on investigating the effect of the polar and nonpolar monomeric sequence on the nanophase-segregated morphology and the water/hydronium transport . More recently, the effects of electric field in transport dynamics inside hydrated Nafion membranes were investigated by different authors. − In addition, Allahyarov and Taylor used MD simulations to investigate the effect of stretching induced structure on the proton conductivity of Nafion-like polymer electrolyte membranes. Results showed that uniaxial stretching causes the hydrophilic regions to become elongated in the stretching direction, enhancing the conductivity along such direction.…”

Weak Anion Binding to Poly(N-isopropylacrylamide) Detected by Electrophoretic NMR

“…Hence, the effective charge should represent well (contribution from counterion binding should be small at our lowest concentrations, where the Debye length of 3 nm is larger than Bjerrum length, 0.7 nm) the actual charge of the ion-decorated chain. Yet, the tacit assumption here is that the ion–polymer interaction is strong enough to provide full momentum transfer − from the ion acted upon by the electric field to the polymer. This was clearly the case for cations binding to poly­(ethylene oxide) (PEO) in methanol .…”

“…Yet (i) N is much lower for Cl – than that for the other anions and (ii) with one extra anion per hundred monomers there is indeed no mechanism that would yield a saturation behavior. Hence, we must invoke that, in contrast to cations associated in methanol with PEO, , the actual attractive interaction between anions and PNIPAM is so weak that the momentum transfer from ion to polymer is only partial. − If so, the actual number of ions can be high enough to render ion–ion repulsion as a mechanism limiting the number of anions associated with a PNIPAM chain (for example, with 20 ions per chain, the anion–anion distance approaches 1 nm). Thus, N being lower for Cl – becomes the consequence of the attractive short-range forces between Cl – and PNIPAM being weaker than that for the other chaotropic anions (leading to smaller momentum transfer).…”

Atomistic simulations of the structure of highly crosslinked sulfonated poly(styrene-co-divinylbenzene) ion exchange resins

“…Within this context, some atomistic computer simulation studies have been reported to stablish relationships between the structure and transport phenomena in ion-exchange membranes. [20][21][22][23][24][25][26][27][28] However, such studies were essentially focused on the controlled diffusion of small molecules (e.g. protons and water) across the membranes rather than on structural aspects for the application of the material in catalysis.…”