Molecular dynamics simulation of diffusion and structure of n-alkane/n-alkanol mixtures at infinite dilution

Infinite dilute diffusion coefficients (D12) of normal alkanes (C1 to C14) in 1-octanol (C8-OH), as well as primary alkanols (C1-OH to C14-OH) in n-octane (C8) have been studied using molecular dynamics simulation in the temperature range from 298 to 374 K and at atmosphere pressure. Simulated D12 values for short-chain solute molecules show a good agreement with the experimental ones taken from literature, while for the long-chain solute molecules the overestimation is large. Besides, the structures of solute molecules in above fluid mixtures are investigated by calculating radial distribution functions, radius of gyration, end-to-end distance, and root mean square fluctuation of atomic positions. These results confirm long-chain n-alkanes and n-alkanols molecules are curved and curled up, which we call it flexibility. Moreover, flexibilities for solute molecules (5 ≤ n ≤ 9) are symmetric but for much long-chain solute molecules like n-tetradecane (C14) and 1-tetradecanol (C14-OH) are asymmetric. We believe that strong chain-chain interactions are existed between different long-chain molecules, and it will result in the solute and solvent molecules are intertwisted. The serious overestimation of simulated D12 for long-chain solute molecules can be reasonably explained by the intertwist effect.