Understanding the Confinement Effects and Dynamics of Methylimidazole in Nanoscale Silica Pores

Abstract

Although the confined behaviors of liquids, especially water, in the nanoscale pores of silica have been investigated using both experimental and theoretical methods, the reports about the structure and dynamics of 1-methylimidazole (MeIm) confined in the silica nanopores remain insufficient. In this work, the pore size-dependent structure and dynamics behaviors of the confined MeIm in such nanopores were investigated using molecular dynamics (MD) simulation and ultrafast infrared spectroscopy. MD results reveal the pore size-independent layering behaviors of MeIm density and charge density along the pore radius. The reorientational relaxation of the probe molecule (methyl thiocyanate, MeSCN) in confined and bulk MeIm from MD simulations agrees well with polarization selective pump-probe (PSPP) experiments. Particularly, MeSCN in confined MeIm in 2.8 nm pore presents more than two times slower reorientational relaxation than that in bulk MeIm. The reorientational relaxation and translation diffusion of MeIm near the pore surface is significantly slowed down because of the strong interaction between MeIm and the pore wall as well as geometry confinement effects. At last, the smaller pore gives rise to a stronger confinement on the reorientational and translational dynamics of MeIm. The information obtained in this work is expected to give a better understanding about the confined effects of nanopores on liquid behaviors.

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