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Here we employ molecular dynamics simulation to study structures, dynamics, and hydrogen bonds of the imidazolium-based ionic liquid mixture, which consists of equimolar [Emim][BF₄] and [Bmim][BF₄]. Our simulation results demonstrate that the imidazolium rings of both different cations almost show identical structures with [BF₄]⁻ anions regardless of the alkyl chain length. Meanwhile, both kinds of cations almost display the same association/dissociation dynamics with anions. By comparison, the order of diffusion speed is [Emim]⁺ > [Bmim]⁺ > [BF₄]⁻ while that of rotation speed is [BF₄]⁻ > [Emim]⁺ > [Bmim]⁺ in the ionic liquid mixture. By analyzing the average numbers of hydrogen bonds (HBs) and the relevant HB dynamics between cations and anions, we find that [Bmim]⁺ cations have more and stronger HBs with anions than [Emim]⁺ cations, which should be partly responsible for slower diffusion …