Heterogeneous nucleation of ice is important for the formation of ice in the atmosphere, but there is not yet a molecular level understanding of this process. Some organic compounds are good ice nucleating agents. It is not known, however, which characteristics of these organic surfaces promote the nucleation of ice. In experiment, alcohol monolayer induces ice nucleation up to -1 °C. It has been hypothesized that alcohol monolayers promote ice nucleation by templating the ice-order through the –OH. It has also been proposed that match between the ice lattice and the 2D crystalline structure of alcohol monolayer is the key physical factor that facilitates the heterogeneous nucleation. In this study, we use molecular dynamic simulations to investigate the mechanism of heterogeneous nucleation of ice induced by alcohol monolayers. In simulation, alcohol monolayer promotes heterogeneous crystallization of water. We find that heterogeneous nucleation of ice is very sensitive to the spacing of –OH: either larger or smaller separation between the –OH disables the ice nucleating ability of the monolayer. We also show that –OH connects directly to ice after crystallization and there is no disordered liquid layer between the monolayer and ice. Moreover, diffraction patterns from simulations demonstrate that the hydroxyl structure changes due to the coupling with water after ice crystallization, the same as observed in experiment. All the results imply that the mechanism might be water templated by the monolayer. We also find that the fluctuation of –OH in the direction normal to the hydroxyl plane depresses heterogeneous ice crystallization, while fluctuation in the plane does not reduce the heterogeneous nucleation. Our simulations are first to show heterogeneous nucleation of ice on alcohol monolayers and the first step to investigate the mechanism of heterogeneous nucleation induced by soft organic interfaces.

Heterogeneous nucleation of ice on alcohol monolayers

250th National Meeting (2015)

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