Cahn-Hilliard mobility of fluid-fluid interfaces from molecular dynamics

PL Barclay and JR Lukes, PHYSICS OF FLUIDS, 31, 092107 (2019).

DOI: 10.1063/1.5116576

The Cahn-Hilliard equation is often used to model the temporospatial evolution of multiphase fluid systems including droplets, bubbles, aerosols, and liquid films. This equation requires knowledge of the fluid-fluid interfacial mobility gamma, a parameter that can be difficult to obtain experimentally. In this work, a method to obtain gamma from nonequilibrium molecular dynamics is presented. gamma is obtained for liquid-liquid and liquid-vapor interfaces by perturbing them from their equilibrium phase fraction spatial distributions, using molecular dynamics simulations to observe their relaxation toward equilibrium, and fitting the Cahn-Hilliard model to the transient molecular simulations at each time step. gamma is then compared to a different measure of interfacial mobility, the molecular interfacial mobility M. It is found that gamma is proportional to the product of M, the interface thickness, and the ratio of thermal energy to interfacial energy.

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