Coarse-grained model of water diffusion and proton conductivity in hydrated polyelectrolyte membrane

Abstract

Using dissipative particle dynamics (DPD), we simulate nanoscale segregation, water diffusion, and proton conductivity in hydrated sulfonated polystyrene (sPS). We employ a novel model [Lee et al. J. Chem. Theory Comput. 11(9), 4395-4403 (2015)] that incorporates protonation/deprotonation equilibria into DPD simulations. The polymer and water are modeled by coarse-grained beads interacting via short-range soft repulsion and smeared charge electrostatic potentials. The proton is introduced as a separate charged bead that forms dissociable Morse bonds with the base beads representing water and sulfonate anions. Morse bond formation and breakup artificially mimics the Grotthuss mechanism of proton hopping between the bases. The DPD model is parameterized by matching the proton mobility in bulk water, dissociation constant of benzenesulfonic acid, and liquid-liquid equilibrium of water-ethylbenzene solutions. The DPD simulations semi-quantitatively predict nanoscale segregation in the hydrated sPS into hydrophobic and hydrophilic subphases, water self-diffusion, and proton mobility. As the hydration level increases, the hydrophilic subphase exhibits a percolation transition from isolated water clusters to a 3D network. The analysis of hydrophilic subphase connectivity and water diffusion demonstrates the importance of the dynamic percolation effect of formation and breakup of temporary junctions between water clusters. The proposed DPD model qualitatively predicts the ratio of proton to water self-diffusion and its dependence on the hydration level that is in reasonable agreement with experiments.

Theoretical analyses on water cluster structures in polymer electrolyte membrane by using dissipative particle dynamics simulations with fragment molecular orbital based effective parameters

“…60 Neimark et al modeled the proton dissociation and conductivity. [61][62][63] Ref. [64][65][66] utilized DPD as well.…”

DL_MESO_DPD: development and use of mesoscale modelling software

“…This model can represent proton-base bonds, allowing for formation of intermediate complexes and artificial mimicking of the Grotthuss diffusion mechanism. The modified version of dl meso dpd has subsequently been used to examine water diffusion and proton conductivity in membranes of hydrated polyelectrolytes and Nafion [18,128].…”

“…As such, it has been applied to a wide range of soft matter problems acting at the mesoscale, including e.g. loading and release of drugs in amphiphilic vesicles [16], self-assembly of liquid crystals [17] and protonation effects in polyelectrolyte membranes [18].…”

Multiscale simulations of polyzwitterions in aqueous bulk solutions and brush array configurations

“…[28][29][30][31][32][33] A definite advantage of DPD is that it correctly represents hydrodynamic interactions. The DPD method has been applied to a variety of problems involving polymers and copolymers, 32,34,35 nanocomposites, 34 water-oil interfaces, 36,37 brush arrays, 38,39 liquid/solid 40 and liquid/vacuum 41 interfaces, bilayers/membranes, 31,[42][43][44][45][46] and liquid flow in bulk 47 and microchannels. 48 The objective of the present study is to develop a multiscale molecular modeling and simulation methodology that can facilitate the design of polyzwitterionic brush arrays capable of repelling bacteria and other bio-fouling agents from solid surfaces in aqueous environments.…”

“…Parameterizing a DPD simulation so as to represent a specific chemical system is not a trivial undertaking. 30,[35][36][37][42][43][44][45][46][48][49][50] A usual practice is to tune the repulsive parameters of a ramp potential a ij for each interaction pair ij in a way that reproduces specific Flory-Huggins parameters χ ij , using the correlation proposed by Groot et al 30 to link χ ij with the repulsion parameters, a ij , of the DPD potential.…”