Interfacial free energy of the structure II cyclopentane hydrate in cyclopentane liquid from the capillary wave fluctuation method

TL;DR

This study measures the interfacial free energy of structure II cyclopentane hydrate in liquid using the capillary wave fluctuation method, confirming the simulation approach's accuracy through comparison with experimental data.

Contribution

The paper demonstrates a novel application of the capillary wave fluctuation method to determine interfacial free energy in molecular hydrate systems, aligning simulation results with experimental estimates.

Findings

Interfacial stiffness range: 35-55×10^{-3} J/m^2

Average interfacial stiffness: 45(5)×10^{-3} J/m^2

Agreement with experimental estimates of 47(5)×10^{-3} J/m^2

Abstract

The interfacial stiffness of structure II cyclopentane hydrate in cyclopentane liquid has been measured by the Capillary Wave Fluctuation (CWF) method for an equilibrated system with temperature of T=280K and pressure of P~20bar, close to the upper (L$_w$-Hyd-Vap-L$_{HC}$) Quadruple-point, on the boundary of the hydrate stable region. The hydrate-II/cyclopentane interfacial stiffness results fall broadly in the range $\Gamma_{ho}$=(35-55)$\times 10^{-3}$J/m$^2$, with an average over all simulations giving $\Gamma_{ho}$=45(5)$\times 10^{-3}$J/m$^2$. Earlier work of the author has determined the cubic harmonic expansion of the natural crystalline oscillations in structure II hydrate. Using this work, the stiffness value translates directly into an orientation-averaged interface free energy of $\gamma_{ho}$=45(5)$\times 10^{-3}$J/m$^2$. The latter is in excellent agreement with the experimentally based estimates of $\gamma_{ho}$=47(5)$\times 10^{-3}$J/m$^2$ from particle-particle adhesion force measurements of Aman et. al. (Langmuir, 29(8):2676-2682, 2013) This provides further evidence for the feasibility and robustness of the simulation approach to measure interfacial free energies in molecular systems.