Confined static microstructures and dynamics of glycerol molecules within sub-2-nm diameter carbon nanotubes: Molecular dynamics study

In this work, molecular dynamics (MD) simulations were performed to investigate the microstructural and dynamical properties of glycerol molecules confined within sub-2-nm diameter carbon nanotubes (CNTs). As the tube diameter increases, the arrangement of confined glycerol molecules transitions from a single-file chain to a single-layer ring, and then to a multi-layer structure. The average self-diffusion coefficient of glycerol molecules within CNTs is found to change from 0.021 × 10^–8 to 4.26 × 10^–8 m²/s. Notably, the relaxed single-file arrangement of glycerol molecules in (8, 8) CNT exhibits the highest self-diffusion (4.26 × 10^–8 m²/s), which is an order of magnitude greater than that observed in aquaglyceroporins. Based on the detailed hydrogen bond (HB) microstructure analysis, we found that the product of average number of HBs (〈n_HB〉) and the percentage of glycerol molecules with two HBs (f₂), and the 1 / average HB lifetime (〈τ_HB〉) can serve as indicators of the self-diffusion coefficients of confined glycerol molecules. A higher 〈n_HB〉 _* f₂ / 〈τ_HB〉 can result in a faster self-diffusion coefficient.