14:00 〜 14:15
[MIS17-02] 水中の氷III結晶表面に見られた新しい水
キーワード：水、高圧氷、液体不混和、界面、顕微鏡その場観察
Ice is an abundant material on the Earth, and its surface plays a crucial role in controlling and catalyzing key chemical reactions governing the environment on the Earth. It is well-known that a wide variety of chemical reactions are governed by the structure and dynamics of interfacial layers on ice surfaces. The nature of the interface between water vapor and ice Ih has been actively debated in the context of a quasi-liquid layer as predicted by Michael Faraday in 1842. These active debates have highlighted the fact that ice surfaces are rich, not only in undiscovered phenomena governing key but obscure chemical processes but also in their underlying physics important for materials science. It is indisputable, therefore, that the elucidation of surface phenomena on ice is highly desirable for a broad range of scientific fields.
However, other interfaces between liquid water and ice that are abundant on the Earth and on icy extraterrestrial bodies remain relatively underexplored, despite having an importance comparable with that of the water vapor-ice interface. Here, we investigated the interface between water and high pressure ice III growing/melting in water by in-situ optical microscopic observation. We show that a macroscopic thin layer of “unknown” liquid, separated from bulk water by a clear interface, forms on the water/ice III interface.
Ice III was crystallized from ultrapure water by attaining high pressure condition (~248 MPa) using a symmetric-type sapphire anvil cell (SEED; Syntek Co. Ltd, Yokohama) in a low-temperature room kept at –20oC (Figure 1B). Growth and melting of the ice III crystal in the cell were controlled by compression and decompression of anvil cell, respectively. The dynamics of crystallization/melting of water in the cell was observed in situ by using a polarized-light microscope in the low-temperature room. The microscopic images were recorded in situ by using a CCD camera.
Figure 1 shows the time-lapse micrographs of the faceted ice III crystal grown/melted in compressed water. The surface morphology of one of the faceted crystal face fluctuated in a wave-like manner during the crystal growth, suggesting fluidity of the surface (Figure 1 A ii). On the other hand, slight depressurization caused the formation of numerous partially wetting liquid droplets on the crystal surface (Figure 1 A i). The contrast difference between the wave-like liquid film and droplets on the crystal surface suggests that the wave-like liquid thin layer is thin layer with concave holes. These observation shows that an unknown liquid distinguishable from surrounding bulk water by a clear interface existed on the interface between bulk water and ice III crystal. Moreover, we found that the liquid thin layer exhibited bicontinuous pattern when the compression was stopped (Figure 1B). Bicontinous pattern can be often seen in spinodal-type liquid-liquid phase separation (LLPS) of two kinds of immiscible liquid in two component system, suggesting the unknown liquid is immiscible with water. This immiscibility should originate from the difference of density and liquid structure because of one-component system.
So far, the hypothesis that there exists the liquid-liquid critical point (LLCP) in which water separates into two kinds of liquid –high density liquid (HDL) and low density liquid (LDL)- via LLPS under a low-temperature and high pressure condition has been considered to explain the abnormal thermodynamic properties of water. However, direct observation and confirmation of the LLPS of water has never been achieved because the hypothesized LLCP lies on an experimentally inaccessible condition due to the limit of supercooling. Our observation of the separation of two kinds of immiscible liquid water at water-ice III interface may have implications for the long-standing mystery of abnormal properties in water governing the environment on the Earth.
However, other interfaces between liquid water and ice that are abundant on the Earth and on icy extraterrestrial bodies remain relatively underexplored, despite having an importance comparable with that of the water vapor-ice interface. Here, we investigated the interface between water and high pressure ice III growing/melting in water by in-situ optical microscopic observation. We show that a macroscopic thin layer of “unknown” liquid, separated from bulk water by a clear interface, forms on the water/ice III interface.
Ice III was crystallized from ultrapure water by attaining high pressure condition (~248 MPa) using a symmetric-type sapphire anvil cell (SEED; Syntek Co. Ltd, Yokohama) in a low-temperature room kept at –20oC (Figure 1B). Growth and melting of the ice III crystal in the cell were controlled by compression and decompression of anvil cell, respectively. The dynamics of crystallization/melting of water in the cell was observed in situ by using a polarized-light microscope in the low-temperature room. The microscopic images were recorded in situ by using a CCD camera.
Figure 1 shows the time-lapse micrographs of the faceted ice III crystal grown/melted in compressed water. The surface morphology of one of the faceted crystal face fluctuated in a wave-like manner during the crystal growth, suggesting fluidity of the surface (Figure 1 A ii). On the other hand, slight depressurization caused the formation of numerous partially wetting liquid droplets on the crystal surface (Figure 1 A i). The contrast difference between the wave-like liquid film and droplets on the crystal surface suggests that the wave-like liquid thin layer is thin layer with concave holes. These observation shows that an unknown liquid distinguishable from surrounding bulk water by a clear interface existed on the interface between bulk water and ice III crystal. Moreover, we found that the liquid thin layer exhibited bicontinuous pattern when the compression was stopped (Figure 1B). Bicontinous pattern can be often seen in spinodal-type liquid-liquid phase separation (LLPS) of two kinds of immiscible liquid in two component system, suggesting the unknown liquid is immiscible with water. This immiscibility should originate from the difference of density and liquid structure because of one-component system.
So far, the hypothesis that there exists the liquid-liquid critical point (LLCP) in which water separates into two kinds of liquid –high density liquid (HDL) and low density liquid (LDL)- via LLPS under a low-temperature and high pressure condition has been considered to explain the abnormal thermodynamic properties of water. However, direct observation and confirmation of the LLPS of water has never been achieved because the hypothesized LLCP lies on an experimentally inaccessible condition due to the limit of supercooling. Our observation of the separation of two kinds of immiscible liquid water at water-ice III interface may have implications for the long-standing mystery of abnormal properties in water governing the environment on the Earth.