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Surfaces of ice act as sites of various chemical reactions of atmospheric acidic gases, which cause serious environmental issues, such as the catalytic ozone depletion by hydrogen chloride (HCl) ga...

Surface melting of ice crystals proceeds below the melting point (0 °C) and forms thin liquid water layers, called quasi-liquid layers (QLLs), which govern a wide variety of phenomena in nature. Hence, many studies have been performed so far; however, the lowest temperature above which QLLs exist on ice crystal surfaces varied from −90 to −1 °C. To reveal the cause of such significant variations, here we show, by laser confocal microscopy combined with Michelson interferometry, the behavior of QLLs on polycrystalline ice thin films that include a large amount of grain boundaries and defects. We found that the QLLs can exist stably on the polycrystalline ice thin films even at −16.2 °C (the lowest temperature adopted in this study), although the QLLs on ice single crystals disappear at temperature lower than −2.4 ± 0.5 °C. These results emphasize the importance of grain boundaries and defects for the presence of QLLs. In addition, we also found that critical water vapor pressure above which the QLLs can gr...

Surfaces of ice have attracted considerable attention as “reaction sites” where atmospheric gases cause various chemical reactions in nature. Hence, revealing the uptake mechanism of atmospheric gases on/in ice remains an experimental challenge. Here we show the direct observation of ice crystal surfaces by advanced optical microscopy in the presence of hydrogen chloride (HCl) gas, which triggers a series of chemical reactions that cause ozone depletion. We found that the HCl gas induced the appearance of droplets of HCl solution on ice crystal surfaces. Under supersaturated water vapor pressure, the HCl droplets were quickly embedded in the ice crystals during the growth of the ice. In contrast, under undersaturated conditions, the embedded HCl droplets reappeared on the ice crystal surfaces during the evaporation of the ice. We estimated that the mole fraction of HCl incorporated into the ice as the HCl droplets (0.19% at −15 °C) was ten times larger than the solubility of HCl gas in an ice crystal (0.0...

We measured the velocity Vstep of isolated elementary spiral steps and the distance Leq between adjacent equivalent spiral steps on ice basal faces by advanced optical microscopy. We determined the step kinetic coefficient β from Vstep measured under various supersaturations. We performed similar experiments under various temperatures T, and determined the temperature dependence of β of ice basal faces, for the first time, in the temperature range of −26.0 to −2.7 °C. When −6.2 ≤ T ≤ −2.7 °C, the value of β decreased significantly with decreasing T. In contrast, when −15.0 ≤ T ≤ −6.2 °C, the value of β increased with decreasing T, and had the maximum at T ≈ −15 °C. When −26.0 ≤ T ≤ −15.0 °C, the value of β decreased monotonically with decreasing T. Such complicated temperature dependence of β strongly implies the existence of unknown phenomena in the temperature range examined. To obtain a clue to the complicated behavior of β, we also measured dependence of Leq on surface supersaturation Δμsurf. When −13...

Ice is one of the most abundant materials on the earth's surface, and its growth governs various natural phenomena. Hence, the molecular-level understanding of ice crystal surfaces is crucially important. However, it is generally acknowledged that the molecular-level observation of ice crystal surfaces by ordinary microscopy techniques, such as atomic force microscopy and scanning electron microscopy, is very difficult at temperatures near the melting point (0 °C). To overcome such difficulties, we have developed laser confocal microscopy combined with differential interference contrast microscopy (LCM-DIM). We proved that LCM-DIM can visualize individual elementary steps (0.37 nm in thickness) on a basal face by observing two-dimensional nucleation growth. Then we found by LCM-DIM that spiral steps on a basal face exhibit a double-spiral pattern, which can be expected from ice's crystallographic structure. In addition, we revealed that temperature dependence of growth kinetics of elementary spiral steps on a basal face exhibits complicated behaviors, which show the presence of unknown phenomena in the growth kinetics. Furthermore, we proved that surface diffusion of water admolecules on a basal face plays a crucially important role in the lateral growth of elementary steps when the distance between adjacent spiral steps is smaller than 15 µm. These findings will provide a clue for unlocking growth kinetics of ice crystals. In addition, through the use of LCM-DIM much progress has been made in studies on the surface melting of ice and the interaction between ice and atmospheric gasses.

In this experimental course, attendees will learn how to obtain useful information about growth processes of crystals using ordinary optical microscopes, which are usually available in laboratories. We will demonstrate how thicknesses of crystals can be estimated from interference colors. We will also show in-situ observations of spiral steps and strain distributions by differential interference contrast microscopy and polarizing microscopy, respectively.

Surface melting of ice crystals forms quasi-liquid layers (QLLs) on ice surfaces, and affects a wide variety of natural phenomena. Since QLLs enhance various chemical reactions in ice clouds, the formation of QLLs by atmospheric gases has been studied intensively. However, such studies were performed using spectroscopy techniques, which have low spatial resolution. Here we show the first direct visualization of QLLs on ice basal faces in the presence of hydrogen chloride (HCl) gas (model atmospheric gas) by advanced optical microscopy, which can visualize individual 0.37 nm-thick elementary steps on ice crystal surfaces. We found that the HCl gas induced the appearances of QLLs with a droplet shape in the temperature range from −15.0 to −1.5 °C, where no QLL appears in the absence of HCl gas. This result indicates that HCl gas adsorbed on ice crystal surfaces probably changed the surface structure of ice crystals and then induced the subsequent melting of ice surfaces. We also observed the movement, shape...

The surfaces of ice crystals near the melting point are covered with thin liquid water layers, called quasi-liquid layers (QLLs), which play crucial roles in various chemical reactions in nature. So far, there have been many spectroscopic studies of such chemical reactions on ice surfaces, however, revealing the effects of atmospheric gases on ice surfaces remains an experimental challenge. In this study, we chose HNO3 as a model atmospheric gas, and directly observed the ice basal faces by advanced optical microscopy under partial pressure of HNO3 (~10&minus, 4 Pa), relevant to those found in the atmosphere. We found that droplets (HNO3-QLLs) appeared on ice surfaces at temperatures ranging from &minus, 0.9 to &minus, 0.2 &deg, C with an increase in temperature, and that they disappeared at temperatures ranging from &minus, 0.6 to &minus, 1.3 &deg, C with decreasing temperature. We also found that the size of the HNO3-QLLs decreased immediately after we started reducing the temperature. From the changes in size and the liquid&ndash, solid phase diagram of the HNO3-H2O binary system, we concluded that the HNO3-QLLs did not consist of pure water, but rather aqueous HNO3 solutions, and that the temperature and HNO3 concentration of the HNO3-QLLs also coincided with those along a liquidus line.

The spiral growth of crystals, mediated by their screw dislocations, is a general crystal-growth mechanism observed over a large variety of crystalline solids. Despite its general nature, direct observations of the spiral growth of ice have been rarely reported so far. Here, with the aid of advanced optical microscopy, we succeed in making in situ observations of the perfect spiral growth during the vapor growth of ice. We find that the spiral steps observed are well described by the classical Burton--Cabrera--Frank theory, taking into account surface diffusion of water admolecules between adjacent steps. This is distinct from the dominant growth mode that we have assigned as spiral in our recent studies, which accompanies fluctuations of the adjacent step interval. We also successfully capture the birth of a screw dislocation and the ensuing spiral growth, originating in the lattice mismatch arising from the coalescence of single ice crystals. Furthermore, we demonstrate that the nucleation of quasi-liquid layers (QLLs) takes place at the spiral center immediately after the birth of the dislocation, which suggests a link between screw dislocations and the generation of QLLs near the ice melting point.

Liquid-liquid transition (LLT) in single-component liquids is one of the most mysterious phenomena in condensed matter. So far this problem has attracted attention mainly from the purely scientific viewpoint. Here we report the first experimental study on an impact of surface nano-structuring on LLT by using a surface treatment called rubbing, which is the key technology for the production of liquid crystal displays. We find that such a rubbing treatment has a significant impact on the kinetics of liquid-liquid transition (LLT) of an isotropic molecular liquid, triphenyl phosphite. For a liquid confined between rubbed surfaces, surface-induced barrier-less formation of the liquid II phase is observed even in a metastable state, where there should be a barrier for nucleation of the liquid II phase in bulk. Thus, surface rubbing of substrates not only changes the ordering behavior, but also accelerates the kinetics significantly. This spatio-temporal pattern modulation of LLT can be explained by a wedge filling transition and the resulting drastic reduction of the nucleation barrier. However, this effect completely disappears in the unstable (spinodal) regime, indicating the absence of the activation barrier even for bulk LLT. This confirms the presence of nucleation-growth-type and spinodal-decomposition-type LLT, supporting that LLT is truly a first-order transition with criticality. Our finding also opens up a new way to control the kinetics of LLT of a liquid confined in a solid cell by structuring its surface on a mesoscopic lengthscale, which may contribute to making LLT useful for micro-fluidics and other industrial applications., Comment: 14 pages, 5 figures in the main text; 2 pages, 2 figures in Supplementary Materials

The existence of more than two liquid states in a single-component substance and the ensuing liquid-liquid transitions (LLTs) has attracted considerable attention because of its counterintuitive nature and its importance in the fundamental understanding of the liquid state. Here we report direct experimental evidence for a genuine (isocompositional) LLT without macroscopic phase separation in an aqueous solution of glycerol. We show that liquid I transforms into liquid II by way of two types of kinetics: nucleation and growth, and spinodal decomposition. Although liquid II is metastable against crystallization, we could access both its static and dynamical properties experimentally. We find that liquids I and II differ in density, refractive index, structure, hydrogen bonding state, glass transition temperature and fragility, and that the transition between the two liquids is mainly driven by the local structuring of water rather than of glycerol, suggesting a link to a plausible LLT in pure water.

Matter in its liquid state is convenient for processing and controlling chemical reactions, owing to its fluidity. Recently much evidence has been accumulated for the existence of a liquid–liquid transition (LLT) in single-component liquids. Here, we report that we can control, by the LLT of a molecular liquid, triphenyl phosphite (TPP), the fluidity and miscibility of its mixture with another molecular liquid. For a mixture of TPP with toluene or aniline, we find that both liquid I and II mix well and liquid II remains in a ‘liquid’ state, in contrast to pure TPP, where liquid II is a non-ergodic amorphous state. This is the first example of a ‘true’ LLT in a molecular liquid. Furthermore, we find demixing induced by the LLT for a mixture of TPP with diethyl ether or ethanol. These findings will open a new phase of research towards various applications of the LLT. Recent work has provided evidence for the existence of a liquid–liquid transition (LLT) in some single-component fluids. It is now shown that the LLT can be used to control the fluidity and miscibility of triphenyl phosphite with another molecular liquid, demonstrating the possibility of the first definite application for exploiting this phenomenon.