Ice formation in atmospheric aereosols, consisting primarily of graphitic layers, occurs via heterogeneous nucleation mechanism. Despite many experimental and theoretical efforts, the formation of ice on a surface remains poorly understood. While experimental investigations are hampered by the limited spatial and temporal resolution, molecular simulations may provide an effective means for understanding such prevailing and important process. Employing forward flux sampling method and the coarse-grained water model (mW), we investigated heterogeneous ice nucleation on a graphitic surface. In particular, we explicitly computed the heterogeneous ice nucleation rates over a wide temperature range (220 K-240 K) independently of nucleation theory. Remarkably, the calculated heterogeneous ice nucleation rates were found to fit well according to the classical theory of heterogeneous nucleation, an extension of the classical nucleation theory for homogeneous nucleation. The fitting procedure further yields the estimate of the potency factor of graphene which measures the degree of reduction in the nucleation barrier. Interestingly, the estimated potency factor was further found to agree well with the simulation-determined volume ratio of the critical nuclei between the heterogeneous and homogeneous nucleation, which allows verifying one of the major assumptions employed by the classical theory of heterogeneous nucleation. The strong support to the quantitative power of the nucleation theory provides the numerical justification to the theory established more than 60 years ago, and allows better understanding ice nucleation in the presence of a heterogeneous nucleation center.

Ice nucleation on graphene surface supports the classical theory of heterogeneous nucleation

249th National Meeting (2015)

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