Unconventional ice nucleation pathway induced by irregular silver iodide surfaces

In nature, water freezes predominantly in a heterogeneous manner. Silver iodide (AgI) serves as one of the most universal and efficient ice nucleating agents. Despite the acknowledged influence of factors like low lattice mismatch and surface dipole fields on the rapid freezing of water on AgI surfaces, one commonly neglects the impact of irregular surfaces on nucleation mechanisms. Using molecular dynamics simulations, we explore heterogeneous ice nucleation on irregular AgI surfaces. Unlike the prevailing view, our study reveals an unconventional nucleation pathway where water molecules align themselves with spatially inhomogeneous dipole field near irregular AgI surfaces. This alignment is triggered by a deviation in orientation between the water molecular dipole and the spatial dipole field generated by AgI substrates, leading to the crystallisation of distinct metastable ice phases. These findings promote our understanding of ice nucleation on AgI surfaces, highlighting the role of surface roughness in the molecular-level phase transitions.