Figure 1

Film thickness $\left(\mathrm{\AA }\right)$ vs undercooling (Kelvin) for various monovalent electrolyte $\left(\mathrm{NaCl}\right)$ concentrations at an ice grain boundary with a solid/film surface charge density $q_s$ of (a) $0.01\mathrm{C}{\mathrm{m}}^{-2}$, (b) $0.001\mathrm{C}{\mathrm{m}}^{-2}$, and (c) $0.0001\mathrm{C}{\mathrm{m}}^{-2}$. In (a)–(c), $N_i=6\times {10}^{-5}$ (solid line), $6\times {10}^{-4}$ (long dashed line), $6\times {10}^{-3}$ (medium dashed line), $1.8\times {10}^{-2}$ (small dashed line), and 6 (dotted line) $\mu \mathrm{M}{\mathrm{m}}^{-2}$. At the lower dopant levels where the Debye length is long, we observe an abrupt or discontinuous onset of grain boundary melting. The transition moves to higher temperatures as the surface charge density and dopant levels decrease, thereby showing the expected behavior for melting driven solely by dispersion forces. Note, for example in (a), that at $T_m-T=0.01\mathrm{K}$, the film thickness is not a monotonically increasing function of ion concentration. Indeed, the film thickness decreases with increasing concentration until a threshold level is surpassed. Hence, there is a transition from melting dominated by dispersion and ionic force interactions to that dominated by the more commonly considered colligative effects. In (b) and (c), we see that for low surface-charge densities, the Coulomb interaction is weak, resulting in a much less pronounced plateau, or complete absence thereof, except for the lowest dopant concentrations.Reuse & Permissions