Interfacial Characteristics of Ice-Supporting Substrates via Molecular Dynamics Simulations

Ice accumulation on aircraft surfaces poses significant safety and performance risks, necessitating the development of coatings to prevent ice adhesion. The present work focuses on characterizing the interfacial properties of ice on various substrates through molecular descriptors. We follow the hypothesis that has been previously proposed in several experimental works according to which a disordered, quasi-liquid layer (QLL) of water at the substrate/ice interface is developed, which in turn acts as a self-lubricant reducing material's ice adhesion strength. To put this idea into the test, we conducted extensive molecular dynamics (MD) simulations on ice supported by different types of substrates, such as graphite, boron nitride, and a cross-linked epoxy polymer. Our findings reveal that the ice structure becomes disordered near the interface for all substrates, with a more pronounced effect in the polymer substrate. The formation of QLL at the interface was quantified using metrics such as local density, Q₆ order parameter, and hydrogen bonding. The polymer substrate showed a thicker QLL compared to the two flat surfaces, as this was verified by both the significant differences in the local water density profiles and the distribution of the employed order parameter. The latter ones were directly correlated to the development of hydrogen bonds between the interfacial water molecules and the polymer substrate's polar atoms, which was found to induce a more intense disruption of ice's crystal structure. Moreover, our analysis revealed that the polymer's oxygen atoms contribute more to hydrogen bonding with the water molecules than the nitrogen atoms, with hydroxyl oxygens (-OH) contributing more compared to the epoxy ones (-O-). The analysis related to the dynamics of the interfacial water molecules revealed a substantial reduction in mobility on the epoxy, exceeding the slowdown observed on boron nitride, with graphite demonstrating the least reduction in dynamic behavior among the substrates studied.