Interface Parallel Ionic Conformation Enhances the Nanoflow of Ionic Liquids Confined in the Silica Nanochannel

JY Qin and YL Wang and F Huo and HY He, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH, 62, 15648-15655 (2023).

DOI: 10.1021/acs.iecr.3c02117

Understanding the confined structure and flow behavior is significant for the design and application of ionic liquids (ILs) in the field of chemical engineering. Herein, the molecular mechanism of interfacial structure and flow behavior of ILs confined in crystalline silica (c-SiO2) and graphene-covered crystalline silica (g@c-SiO2) nano- channels are investigated via molecular dynamics simulation. The number density and angle distribution of ILs reveal that the cations at the c-SiO2 interface display a vertical conformation, while those at the g@c-SiO2 interface display a parallel conformation. Meanwhile, the anions are randomly distributed on these two substrates. Interestingly, the vertical distribution of cations in the c-SiO2 substrate mainly presents three morphological structures, which will hinder the ion diffusion compared to the parallel ionic conformation. Furthermore, the nanoflow of ILs driven by external pressure shows a parabolic form in the nanochannel of c-SiO2, but the plug flows in the nanochannel of g@c-SiO2. The joint analysis of the mean square displacement, self- diffusion coefficient, flow velocity, and flow rate demonstrates that the parallel conformation of the cation can significantly facilitate the nanoflow process of confined ILs. These quantitative results are meaningful for understanding the molecular mechanism of nanoflow and lay the foundation for the rational design of IL-based devices and other chemical engineering processes.

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