Molecular dynamics simulation of microscopic structure and hydrogen bond network of the pristine and phosphoric acid doped polybenzimidazole

The microscopic structure and hydrogen bonding characteristics of the pristine and phosphoric acid (PA) doped polybenzimidazoles (poly[2,2′-(meta-phenylene)-5,5′-benzimidazole] or m-PBI, and poly[2,2′-(para-phenylene)-5,5′-benzimidazole] or p-PBI) were studied by molecular dynamics simulations based on a united-atom force field model. In all the simulated systems, a benzimidazole group and an adjacent phenylene group are almost in coplanar configuration, while two adjacent benzimidazole groups are in twisted configuration. In pristine PBIs, the p-PBI is more ordered and stretched than the m-PBI. In PA doped PBIs, hydrogen bonding network is formed by donating phosphoric acid proton to imine nitrogen, phosphoric acid proton to phosphoric acid oxygen, and amine proton to phosphoric acid oxygen. In addition, the structural transport of proton is attributed to the formation of hydrogen bonding network in PA doped PBIs.