Comparison of two protic ionic liquid behaviors in the presence of an electric field using molecular dynamics

The effects of an external electric field on two ionic liquids (ILs) are investigated using molecular dynamics electrospray simulations of ethylammonium nitrate (EAN) and ethanolammonium nitrate (EOAN). In the absence of an external electric field, long alkyl chains were observed in EAN but not in EOAN. When the electric field was applied, the anions of both ILs formed a barrier along the applied field, but only in EAN did this barrier result in a static bilayer composed of two parallel layers of cations and anions. The primary hydrogen bonds (HBs) connecting the EAN cations and anions were formed between the ammonium and the nitrate groups. In contrast, they were formed between the ammonium as well as the hydroxyl groups and the nitrate groups in EOAN. The applied electric field was found effective in reducing the number of O₁-H_O⋯O type HBs but was less effective against the N-H_N⋯O type HBs. It was observed that the N-C₁-C_M backbone angles of EAN allowed for greater storage of the energy supplied by the electric field in the form of torsional degree of freedom compared to the N-C₁-C_M angles of EOAN. The combination of stronger HBs and higher energy storage in the N-C₁-C_M covalent angle in EAN results in a stronger resistance of ion emission from the bulk compared to EOAN.