(272e) Molecular Dynamics Simulations of Diffusion and Clustering Along Critical Isotherms of Medium-Chain n-Alkanes
Understanding the transport properties of n-alkanes and other molecular fluids in the critical region is important for a number of industrial and natural systems. It is well-established that the Fickian diffusion coefficient vanishes at the critical point in binary fluids. However, there are strongly conflicting results for the behavior of the self diffusion coefficient Ds near the critical point in single-component systems. Further, there is no molecular-scale understanding of the behavior of Ds in single-component molecular fluids in the critical regime. Thus, we perform extensive molecular dynamics simulations of single-component fluids composed of medium-chain n-alkanes (n-pentane, n-decane and n-dodecane) using anisotropic united-atom potentials. For each system, we quantify the self-diffusion coefficient, cluster sizes and lifetimes along critical isotherms. We show that Ds decreases and the average size of molecular clusters increases as a function of density along critical isotherms, but Ds remains finite at the critical point. This work confirms that the self-diffusion coefficient is finite at the critical point in single-component molecular fluids.