Ice-Melting Dynamics: The Role of Protons and Interfacial Geometry

The surface of ice plays a significant role in melting. To better understand the role of the surface, we studied the melting of ice using infrared imaging and pH-sensitive dyes. Ice was allowed to melt in baths of water of varying depths. When the ice melted in a high level of room-temperature water, equal to the height of the ice, the conventional melting pattern appeared. When the ice melted in a chamber with a lower water level, the melting pattern was unexpected. Seconds after the ice was placed in the water, localized regions of low-temperature water appeared around the perimeter of the ice. These regions grew radially outward and seemed to originate as streams coming from inside the ice. Those streams contained high concentrations of protons, as indicated by the color change of a pH-sensitive dye initially placed in the water surrounding the ice. This observation, together with the temperature distribution and ice-shape changes during melting implied that the streams may be propelled by protons from inside the ice. In contrast to conventional melting, which progresses from the outer surface inward, the stream-melting pattern implies a melting process originating inside the ice.