17:15 〜 18:45
[MIS18-P05] キラルな氷III/水界面に生成する同素不混和水のスピノーダル様キラル秩序形成
キーワード：水、同素不混和水、キラリティ、氷III、キラル液晶、スピノーダル液ー液相分離
[Introduction] Water is the most abundant liquid on earth. The mysterious properties of water, unlike those of standard liquids, are known to play crucial roles in various phenomena in nature, from global climate to biological functions. The key to understanding this mysterious property is considered to be the diversity of water’s liquid structures, which are endowed with hydrogen bonding networks. Thus, the experimental confirmation of the structural diversity of water is significant for various research fields. Chirality, which is the lack of mirror symmetry, is known to be a structural feature that plays an important role not only in biomolecular functions but also in homochirality on the Earth. It is natural that the diversity of structures in liquid water raises the question whether liquid water is capable of the formation of chiral structures. Recently, nonlinear spectroscopy has revealed that chiral supermolecular structures are formed by interaction with chiral biological molecules such as double-helix DNA, peptides, and b-sheet proteins. 1 However, the experimental findings on the chirality of water have been limited to the microscopic. molecular scale chirality of water molecules interacting with chiral biological molecules. It is still unclear whether liquid water can form a chiral structure without any interactions with foreign molecules.
On the other hand, we have recently discovered that unknown waters, which separate from the surrounding bulk water, appear macroscopically at the interfaces between water and ices by conventional in-situ optical microscopic observations.2-4 We named the unknown waters as “homoimmiscible water”. The in-situ observations implied the existence of diversity in the liquid structure of the homoimmiscible water such as low-density, high-density3, and liquid crystal-like homoimmiscible waters4. The diversity in the structures of the homoimmiscible waters provokes the question whether the homoimmiscible water can form chiral structures.
Here, we discovered, by in-situ microscopic observations, that the homoimmiscible water at the interface between water and ice III, which has chirality in its crystal structure, exhibits macroscopic chiral order in its bicontinuous morphology formed through spinodal phase separation-like dynamics without any interactions with foreign molecules.
[Experimental] A single crystal of ice III was obtained by pressurizing ultrapure water to approximately 284 MPa using a dynamic anvil cell with sapphire anvils at -20oC.3,5 The dynamic sapphire anvil cell can electrically regulate the applied pressure by driving piezo actuators placed between metal fixtures supporting anvils using a square wave from a function generator. The ice III crystal was grown by applying pressure using the dynamic anvil cell. The non-equilibrium water/ice III interface was observed by differential interference contrast microscopy in-situ.
[Results and Discussion] In-situ observations revealed that a layer of the homoimmiscible water appears at the water/ice III interface while showing a bicontinuous pattern (Fig. 1). The time evolution of the characteristic length of the bicontinuous pattern was proportional to the exponentiation of time, t. The exponent changed discontinuously from approximately 0.75 to 0.31 with time. This change is similar with the change predicted by model H, which describes spinodal liquid-liquid phase separation.6 We also found that the fast Fourier transformation of the bicontinuous pattern formed through the spinodal-like dynamics showed vortex-like anisotropic profiles. This profile indicates that the ordering of the spinodal-like waves changes continuously in the radial direction, suggesting chiral ordering. This chiral ordering is possibly due to the chirality of the ice III crystal as substrate. In addition, the laser interferometer measurement indicated that the thickness of the homoimmiscible water is at least about 100 nm. The appearance of the chiral order at a distance more than 100 nm from the ice III crystal interface suggests that the homoimmiscible water has elastic anisotropy. Our observations imply that the homoimmiscible water is transiently a state that simultaneously exhibits fluidity, elastic anisotropy and chirality, namely, chiral liquid crystal.7
[1] Yan et al., Acc. Chem. Res. 2023, 56, 12, 1494. [2] Niinomi et al., J. Phys. Chem. Lett. 2020, 11, 6779. [3] Niinomi et al., J. Phys. Chem. Lett. 2022, 13, 4251.[4] Niinomi et al., Sci. Rep. 2023, 13, 16227. [5] Evans et al., Rev. Sci. Instrum. 2007,78, 073904. [6] Hohenberg et al., Rev. Mod. Phys. 1977, 49, 435. [7] Niinomi et al., J. Phys. Chem. Lett. 2024, 15, 659.
On the other hand, we have recently discovered that unknown waters, which separate from the surrounding bulk water, appear macroscopically at the interfaces between water and ices by conventional in-situ optical microscopic observations.2-4 We named the unknown waters as “homoimmiscible water”. The in-situ observations implied the existence of diversity in the liquid structure of the homoimmiscible water such as low-density, high-density3, and liquid crystal-like homoimmiscible waters4. The diversity in the structures of the homoimmiscible waters provokes the question whether the homoimmiscible water can form chiral structures.
Here, we discovered, by in-situ microscopic observations, that the homoimmiscible water at the interface between water and ice III, which has chirality in its crystal structure, exhibits macroscopic chiral order in its bicontinuous morphology formed through spinodal phase separation-like dynamics without any interactions with foreign molecules.
[Experimental] A single crystal of ice III was obtained by pressurizing ultrapure water to approximately 284 MPa using a dynamic anvil cell with sapphire anvils at -20oC.3,5 The dynamic sapphire anvil cell can electrically regulate the applied pressure by driving piezo actuators placed between metal fixtures supporting anvils using a square wave from a function generator. The ice III crystal was grown by applying pressure using the dynamic anvil cell. The non-equilibrium water/ice III interface was observed by differential interference contrast microscopy in-situ.
[Results and Discussion] In-situ observations revealed that a layer of the homoimmiscible water appears at the water/ice III interface while showing a bicontinuous pattern (Fig. 1). The time evolution of the characteristic length of the bicontinuous pattern was proportional to the exponentiation of time, t. The exponent changed discontinuously from approximately 0.75 to 0.31 with time. This change is similar with the change predicted by model H, which describes spinodal liquid-liquid phase separation.6 We also found that the fast Fourier transformation of the bicontinuous pattern formed through the spinodal-like dynamics showed vortex-like anisotropic profiles. This profile indicates that the ordering of the spinodal-like waves changes continuously in the radial direction, suggesting chiral ordering. This chiral ordering is possibly due to the chirality of the ice III crystal as substrate. In addition, the laser interferometer measurement indicated that the thickness of the homoimmiscible water is at least about 100 nm. The appearance of the chiral order at a distance more than 100 nm from the ice III crystal interface suggests that the homoimmiscible water has elastic anisotropy. Our observations imply that the homoimmiscible water is transiently a state that simultaneously exhibits fluidity, elastic anisotropy and chirality, namely, chiral liquid crystal.7
[1] Yan et al., Acc. Chem. Res. 2023, 56, 12, 1494. [2] Niinomi et al., J. Phys. Chem. Lett. 2020, 11, 6779. [3] Niinomi et al., J. Phys. Chem. Lett. 2022, 13, 4251.[4] Niinomi et al., Sci. Rep. 2023, 13, 16227. [5] Evans et al., Rev. Sci. Instrum. 2007,78, 073904. [6] Hohenberg et al., Rev. Mod. Phys. 1977, 49, 435. [7] Niinomi et al., J. Phys. Chem. Lett. 2024, 15, 659.