“Freezing” of NaClO₃ Metastable Crystalline State by Optical Trapping in Unsaturated Microdroplet

We reversibly controlled phase conversion between a microdroplet of a NaClO₃ unsaturated aqueous solution and a metastable single crystal, which is usually a short-lived phase in spontaneous crystallization, simply by irradiating a tightly focused visible continuous-wave (CW) laser to the microdroplet. The laser irradiation allowed the metastable crystal to generate and stably grow without a polymorphic transformation. This successful metastable phase control is attributed to the combination of the advantage of optical trapping-induced nucleation that nucleation takes place from unsaturated mother solution and the advantage of microdroplet method, which suppresses additional nucleation leading to the transformation. In situ observation shows the crystal dissolves when the laser irradiation is stopped, whereas the laser irradiation stabilizes the crystal even if the size of the crystal becomes larger than that of focal spot. These observations indicate that a change in the relative magnitudes of chemical potentials between solution/crystalline phases. This change is possibly promoted via crystal growth by trapping of crystalline clusters in optical potential well formed on a crystal surfaces originating from “light propagation” through the crystal. Our results shed a light not only on polymorph control but also on a method to prepare a longer-lived achiral precursor for analysis on achiral–chiral transition by “freezing” a kinetic pathway of chiral crystallizatio

In Situ Live Observation of Nucleation and Dissolution of Sodium Chlorate Nanoparticles by Transmission Electron Microscopy

The formation of crystals from solution requires the initial self-assembly of units of matter into stable periodic structures reaching a critical size. The early stages of this process , called nucleation, are very difficult to visualize. Here we describe a novel method that allows real time observation of the dynamics of nucleation and dissolution of sodium chlorate clusters in an ionic liquid solution using in situ transmission electron microscopy. Using ionic liquids as solvent circumvents the problem of evaporation and charging, while the nucleation frequency was reduced by using saturated solutions. We observe simultaneous formation and dissolution of prenucleation clusters, suggesting that high-density fluctuations leading to solid cluster formation exist even under equilibrium conditions. In situ electron diffraction patterns reveal the simultaneous formation of crystalline nuclei of two polymorphic structures, the stable cubic phase and the metastable monoclinic phase, during the earliest stages of nucleation. These results demonstrate that molecules in solution can form clusters of different polymorphic phases independently of their respective solubility

Plasmonic Heating-Assisted Laser-Induced Crystallization from a NaClO₃ Unsaturated Mother Solution

We provide a novel laser-induced crystallization mechanism which explains crystallization induced by visible laser trapping of silver nanoparticles (AgNPs) at the air/unsaturated mother solution interface from the focal spot [Niinomi et al.<i>CrystEngComm</i> <b>2016</b>, <i>18</i>, 7441–7448]. Simultaneous in situ microscopic observation of Raman scattering and polarized-light image revealed that the optical trapping of nanoparticles that exhibit surface-enhanced Raman scattering (SERS) triggers the crystallization, showing the excitation of localized surface plasmon resonance (LSPR) significantly promotes the crystallization. Numerical analysis of temperature distribution based on the combination of finite-difference time-domain electromagnetic and finite-difference heat transfer calculations shows that temperature reaches 390 °C at the focal spot because of plasmonic heating, the energy dissipation of the plasmon-enhanced electromagnetic field as heat. A conceivable mechanism of the crystallization is local increment of supersaturation caused by local solvent evaporation via the Plasmonic heating. This plasmonic heating assisted laser-induced nucleation process has the possibility to provide not only a novel approach for spatiotemporal control of crystallization but also a novel nucleation field based on nonlinear light–matter interaction originating from the plasmon-enhanced electromagnetic near field through heterogeneous nucleation on the surface of plasmonic particles

Chiral Spinodal-like Ordering of Homoimmiscible Water at Interface between Water and Chiral Ice III

Diversity in structures of water endowed by a hydrogen-bonding network plays crucial roles in wide varieties of phenomena in nature. Chiral ordering of water molecules is an intriguing phenomenon from the viewpoint of bimolecular functions. However, experimental reports on chiral ordering have been limited to the water molecules interacting with biomolecules on the molecular scale. It remains unclear whether pure liquid water forms long-range chiral ordering without any interaction with biomolecules. Here, we show that chiral anisotropy can be observed in the macro/mesoscopic network pattern of an unknown water layer formed via spinodal phase separation-like dynamics at the interface between water and ice III with a chiral crystal structure. We named this unknown water homoimmiscible water. Our observations infer that the unknown water is a chiral liquid crystal. This possibility opens new avenues for a wide variety of research fields such as liquid polymorphism, biology, earth and planetary science, and so forth from the perspective of chirality

In Situ Observation of Chiral Symmetry Breaking in NaClO₃ Chiral Crystallization Realized by Thermoplasmonic Micro-Stirring

We have found that large chiral symmetry breaking in chiral crystallization can be achieved by irradiating a several milliwatts focused laser to a plasmonic nanolattice immersed in a stagnant NaClO₃ saturated aqueous solution. Several hundreds of chiral crystals with the same handedness showed up in the solution after the laser irradiation in contrast to spontaneous crystallization. In situ microscopic observation for the early stage of the crystallization in the vicinity of the focal spot revealed that microbubble generation followed by large supersaturation increase, in which supersaturation reaches 360%, promotes several numbers of crystal nucleation in the vicinity of the bubble as “mother” crystal. The generation of the microbubble induced Marangoni convection, the velocity of which reaches several hundreds of micrometers per second, crushing the first appearing chiral crystal into pieces by microfluidic shear. Namely, secondary nucleation caused by microfluidic shear amplified the number of “daughter” crystals with the same handedness. This spatiotemporally controllable micromixing experiment realized by laser irradiation gives us not only a novel route bridging a light and chiral symmetry breaking but also the novel method to observe the early stage dynamics of the secondary nucleation, which was hard to observe by conventional observation technique, in real time

Emergence and Amplification of Chirality via Achiral–Chiral Polymorphic Transformation in Sodium Chlorate Solution Growth

Chiral symmetry breaking during the chiral crystallization from a sodium chlorate (NaClO₃) aqueous solution is an intriguing phenomenon because it provides insights into the prebiotic process of biohomochirality. However, a mechanism of the emergence and amplification of chirality remains controversial, especially for crystallization from highly supersaturated solution, and one of the hypotheses proposed before is a transition toward the homochiral state during the early stages of crystallization. In this contribution, we directly examined the early stage of crystallization by in situ polarized-light microscopy. The observation revealed that achiral crystals, which appear prior to the formation of chiral crystals, transform to the chiral crystal through two kinds of polymorphic transformations: (1) martensitic transformation (MT) and (2) solution-mediated phase transition (SMPT). The SMPT is remarkably facilitated by contact with a chiral crystal. Notably, the resulting enantiomorph through contact-facilitated SMPT is strongly directed by the contacting enantiomorph. In contrast, the MT yields two enantiomorphs in equal probability. The emergence and amplification of chirality has generally been considered to be a result of direct nucleation of a chiral crystal and its fragmentation. In contrast, our observations provide a possibility that the MT and contact-facilitated SMPT play a role for the emergence and amplification of chirality, respectively

Chiral Spinodal-like Ordering of Homoimmiscible Water at Interface between Water and Chiral Ice III

Diversity in structures of water endowed by a hydrogen-bonding network plays crucial roles in wide varieties of phenomena in nature. Chiral ordering of water molecules is an intriguing phenomenon from the viewpoint of bimolecular functions. However, experimental reports on chiral ordering have been limited to the water molecules interacting with biomolecules on the molecular scale. It remains unclear whether pure liquid water forms long-range chiral ordering without any interaction with biomolecules. Here, we show that chiral anisotropy can be observed in the macro/mesoscopic network pattern of an unknown water layer formed via spinodal phase separation-like dynamics at the interface between water and ice III with a chiral crystal structure. We named this unknown water homoimmiscible water. Our observations infer that the unknown water is a chiral liquid crystal. This possibility opens new avenues for a wide variety of research fields such as liquid polymorphism, biology, earth and planetary science, and so forth from the perspective of chirality

In Situ Observation of Chiral Symmetry Breaking in NaClO₃ Chiral Crystallization Realized by Thermoplasmonic Micro-Stirring

We have found that large chiral symmetry breaking in chiral crystallization can be achieved by irradiating a several milliwatts focused laser to a plasmonic nanolattice immersed in a stagnant NaClO₃ saturated aqueous solution. Several hundreds of chiral crystals with the same handedness showed up in the solution after the laser irradiation in contrast to spontaneous crystallization. In situ microscopic observation for the early stage of the crystallization in the vicinity of the focal spot revealed that microbubble generation followed by large supersaturation increase, in which supersaturation reaches 360%, promotes several numbers of crystal nucleation in the vicinity of the bubble as “mother” crystal. The generation of the microbubble induced Marangoni convection, the velocity of which reaches several hundreds of micrometers per second, crushing the first appearing chiral crystal into pieces by microfluidic shear. Namely, secondary nucleation caused by microfluidic shear amplified the number of “daughter” crystals with the same handedness. This spatiotemporally controllable micromixing experiment realized by laser irradiation gives us not only a novel route bridging a light and chiral symmetry breaking but also the novel method to observe the early stage dynamics of the secondary nucleation, which was hard to observe by conventional observation technique, in real time

In Situ Observation of Chiral Symmetry Breaking in NaClO₃ Chiral Crystallization Realized by Thermoplasmonic Micro-Stirring

We have found that large chiral symmetry breaking in chiral crystallization can be achieved by irradiating a several milliwatts focused laser to a plasmonic nanolattice immersed in a stagnant NaClO₃ saturated aqueous solution. Several hundreds of chiral crystals with the same handedness showed up in the solution after the laser irradiation in contrast to spontaneous crystallization. In situ microscopic observation for the early stage of the crystallization in the vicinity of the focal spot revealed that microbubble generation followed by large supersaturation increase, in which supersaturation reaches 360%, promotes several numbers of crystal nucleation in the vicinity of the bubble as “mother” crystal. The generation of the microbubble induced Marangoni convection, the velocity of which reaches several hundreds of micrometers per second, crushing the first appearing chiral crystal into pieces by microfluidic shear. Namely, secondary nucleation caused by microfluidic shear amplified the number of “daughter” crystals with the same handedness. This spatiotemporally controllable micromixing experiment realized by laser irradiation gives us not only a novel route bridging a light and chiral symmetry breaking but also the novel method to observe the early stage dynamics of the secondary nucleation, which was hard to observe by conventional observation technique, in real time

In Situ Observation of Chiral Symmetry Breaking in NaClO₃ Chiral Crystallization Realized by Thermoplasmonic Micro-Stirring

We have found that large chiral symmetry breaking in chiral crystallization can be achieved by irradiating a several milliwatts focused laser to a plasmonic nanolattice immersed in a stagnant NaClO₃ saturated aqueous solution. Several hundreds of chiral crystals with the same handedness showed up in the solution after the laser irradiation in contrast to spontaneous crystallization. In situ microscopic observation for the early stage of the crystallization in the vicinity of the focal spot revealed that microbubble generation followed by large supersaturation increase, in which supersaturation reaches 360%, promotes several numbers of crystal nucleation in the vicinity of the bubble as “mother” crystal. The generation of the microbubble induced Marangoni convection, the velocity of which reaches several hundreds of micrometers per second, crushing the first appearing chiral crystal into pieces by microfluidic shear. Namely, secondary nucleation caused by microfluidic shear amplified the number of “daughter” crystals with the same handedness. This spatiotemporally controllable micromixing experiment realized by laser irradiation gives us not only a novel route bridging a light and chiral symmetry breaking but also the novel method to observe the early stage dynamics of the secondary nucleation, which was hard to observe by conventional observation technique, in real time