Exploring the discrepancies between experiment, theory, and simulation for the homogeneous gas-to-liquid nucleation of 1-pentanol

Abstract

Using an efficient Monte Carlo approach known as Aggregation-Volume-bias Monte Carlo with self-adaptive Umbrella Sampling and Histogram Reweighting (AVUS-HR), we obtained the nucleation free energy profile of 1-pentanol at various temperatures from 220 to 360 K. From these profiles, differences between the free energy barrier heights obtained from our simulations and those predicted by the classical nucleation theory (CNT) were calculated. Our results strongly support that the logarithm of the nucleation rate ratio between simulation (or experiment) and CNT increases almost linearly with the inverse temperature. Among the various factors that contribute to the discrepancy between simulation and CNT nucleation rates, the nonzero surface free energy of the monomer included in the CNT makes the largest contribution. On the molecular level, the simulations indicate that a gas-phase cluster of 1-pentanol molecules is relatively compact and can contain multiple hydrogen bonded aggregates of various sizes and that this aggregate size distribution depends strongly on temperature and also on the overall size of the cluster system.

Isothermal Nucleation Rates of n-Propanol, n-Butanol, and n-Pentanol in Supersonic Nozzles: Critical Cluster Sizes and the Role of Coagulation

“…This is particularly true for molecules that readily form hydrogen-bonded aggregates in the gas phase, like the n-alcohols, that are not compact spherical objects. Recent work by Nellas et al 33 illustrates clearly that the change in free energy between cluster sizes, δΔG(n), for n-pentanol is not a linear function of n 2/3 − (n − 1) 2/3 , as predicted by CNT once n < ∼15, and that the deviations from the expected behavior become more severe as the temperature decreases to the range of those used in the current experiments. Furthermore, Girshick 34 showed that the free energies of the smallest clusters can affect both the height of the free energy barrier and its location.…”

Excess equimolar radius of liquid drops

“…Other umbrella sampling based methods [50,51], which will not be discussed here in detail, are confronted with similar difficulties, in particular regarding the relation between the surface tension and the surface excess free energy.…”

Surface tension data of n-propane, n-octane and n-dodecane from nucleation simulations

“…This model is one of the most accurate models currently available, predicting saturated liquid densities and critical constants for n-alkanes within experimental error (Errington and Panagiotopoulos, 1999). As previously done (Nellas et al, 2010), we employed here an energy-based Stillinger-type cluster criterion (Stillinger, 1963) for these chain molecules. Here, a cluster is defined as a group of molecules of which every molecule has at least one neighbour with an interaction energy of less than U cl = −3.59×10 −21 J.…”

“…Here, a cluster is defined as a group of molecules of which every molecule has at least one neighbour with an interaction energy of less than U cl = −3.59×10 −21 J. This value is greater than the energy involved in methyl-methyl interactions (∼ 1.38 × 10 −21 J), but negligible compared to that of hydrogen bonding interactions (∼ 2.76 × 10 −20 J) (Nellas et al, 2010).…”

“…The steady improvement of computing power has paved the way for continuous advancement of smart algorithms and their implementations in the natural sciences, including the development of nucleation simulations to predict nucleation rates and thermophysical properties (Padilla and Toxvaerd, 1991;Laaksonen et al, 1995;Panagiotopoulos, 1995Panagiotopoulos, , 1996Smit et al, 1995;Errington and Panagiotopoulos, 1999;Anwar et al, 2013;Diemand et al, 2013). Using these advanced computer techniques such as aggregation-volume-bias Monte Carlo (AVBMC) with umbrella sampling (US) (Chen et al, , 2008Nellas et al, 2010) and by invoking Equation (2), we can calculate the temperature-dependent values of any desired compound without resorting to experimental procedures. Previously, Kemper and Hale have demonstrated that the excess surface entropy , and by extension the surface tension, of water can be calculated from the simulated free energy profiles of small water clusters.…”