Effect of temperature on structure and water transport of hydrated sulfonated poly(ether ether ketone): A molecular dynamics simulation approach

Abstract

The effects of temperature on hydrated sulfonated poly(ether ether ketone) are studied using molecular dynamics. Three different temperature conditions (298 K.15 K, 323.15 K, and 353.15 K) with two different water contents (10 wt. % and 20 wt. %) are simulated. Analyzing the pair correlation functions, it is found that there is limited temperature effect on the distribution and solvation of the sulfonate groups. The structure factor analysis shows that the temperature dependence of the nanophase-segregated morphology is not significant in the simulated temperature range. On the contrary, the structure factors S q ð Þ at $30 Å (q ¼ $0.2 Å À1 ) and $13 Å (q ¼ $0.5 Å À1 ) clearly increase with water content, indicating that the development of water channels is mostly affected by the water content. Within such water phase in the nanophase-segregated structure, the internal structure of water phase becomes more developed with decreasing temperature and increasing water content. By analyzing the mean square displacement of the water molecules, it is also found that self-diffusion of water is enhanced with the increasing temperature. From the observation that the activation energies calculated from such temperature dependency are very similar (E a ¼ 25.7 kJ=mol and E a ¼ 24.9 kJ=mol for 10 wt. % and 20 wt. %, respectively), it is inferred that the extent of the structural change in the water phase as a function of temperature is very similar between the 10 wt. % water content and the 20 wt. % water content. Compared to the bulk water (13.2 kJ=mol) and the water in Nafion (16.7-18.9 kJ=mol), it is confirmed that more nanophase-segregation enhances water transport through the membrane.

Molecular dynamics simulation analysis of hydration effects on microstructure and transport dynamics in sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) fuel cell membranes

“…The calculated bulk densities and dimension (size) of amorphous simulation cells for hydrated and non-hydrated SPPO membranes are collected in Table 1. It can be seen that an increase in membrane hydration level results in an increase in bulk density, the same trend as reported by Brunello et al [28,38] in the MD simulations of hydrated SPEEK membranes and Lins et al [30] in the MD simulation for hydrated phenylated sulfonated poly(ether ether ketone ketone) (Ph-SPEEKK) membranes. Kruczek Considering that SPPO membranes swell and increase in volume upon hydration, predicted bulk densities provided in Table 1 for water solvated SPPO membranes seem to be satisfactory.…”

“…DREIDING force field was employed for SPPO chains [37], which is a generic force field based on simple hybridization rules and can be easily applied for parameterization of new combination of various atoms, as previously applied in the MD studies of proton exchange polymeric membranes [20,24,28,29,34,38]. Partial atomic charges of polymeric chains were assigned using charge equilibration (QEq) method developed by Rappe and Goddard [39].…”

Experimental investigation and molecular dynamics simulation of acid-doped polybenzimidazole as a new membrane for air-breathing microbial fuel cells

“…The potential parameters for Nafion and PBI were adopted from DREIDING force field [25], as successfully used in previous studies of hydrated PEMs [26][27][28][29]. Charge equilibration (QEq) method [30] was employed to assign partial atomic charges for Nafion and PBI.…”

Morphological and transport characteristics of swollen chitosan‐based proton exchange membranes studied by molecular modeling

“…The interaction parameters for polymeric chains of chitosan were taken from DREIDING force filed reported by Mayo et al . This force field has been employed successfully in earlier MD simulations of PEMs , and also in our previous studies of alternative membranes . The charge equilibration method described by Rappe and Goddard was adopted to calculate partial atomic charges of chitosan chains.…”