Charged colloidal particles form a variety of association structures in their dispersions due to electrostatic interactions acting between them. The microgravity environment, where the sedimentation effect is negligible, is ideal for studying the structure formation of colloidal particles with high specific gravity. In this paper, we report a recent space experiment on the association (clustering) of charged colloidal particles under microgravity conditions in the International Space Station (JAXA Colloidal Clusters Formation Project). The average association number and the regularity of the clusters under microgravity were larger than those on the ground. Based on the findings obtained through the space experiments and ground-based investigations during the preparation of the experiment, we were also able to fabricate a two-dimensional diamond lattice structure in which tetrahedral colloidal aggregates are regularly arranged in a series on a two-dimensional substrate.

  We have found that lysozyme crystallization is promoted by gap-mode surface plasmon resonance of gold nanoparticles (AuNPs). Crystallization experiments were performed by dropping a metastable lysozyme solution in a supersaturated state in which spontaneous nucleation does not occur onto substrates prepared by dropping a 40 nm diameter AuNPs colloidal solution onto a glass substrate and subsequent drying. These substrates were capable of inducing gap-mode surface plasmon resonance. Crystals were deposited on the prepared substrates in numbers that increased with light irradiation, whereas none were deposited on control substrates. A crystallization mechanism involving lysozyme adsorption on AuNPs was proposed. The results showed that the number of lysozyme molecules adsorbed on the AuNPs corresponded well to the number of deposited crystals.

  External fields such as electric and magnetic fields are nowadays known to impact crystal growth process and the resulting polymorphs. However, the impact of chiral external fields such as circularly polarized light (CPL) on chiral crystallization has been overlooked because of the intrinsically weak chiral light-matter interaction between CPL and chiral matters. Here, the author demonstrates that large crystal enantiomeric excess which cannot be attained by the irradiation of CPL in chiral crystallization can be induced by superchiral near-field co-created by electric and magnetic fields of near-fields of localized surface plasmon resonance and Mie resonance of metal and dielectric nanostructures, respectively. This demonstration opens a new avenue for the control of chiral crystallization by chiral external fields.

  We introduce the crystallization technique using ultrashort pulse lasers. In this crystallization technique, cavitation bubbles generated by laser irradiation in the solution can be one of the triggers for crystallization. Laser-induced cavitation bubbles and subsequent crystallization were studied, discussing the optimization of laser conditions, such as pulse duration and pulse energy, depending on the compound. We have demonstrated the crystallization control of polymorphs by considering the laser condition. These findings suggest that ultrashort-pulse laser-induced crystallization has the possibility to offer promising applications for a variety of compounds.

  We developed the hydrothermal-optical-microscopy cell system of the flow type and the Mach–Zehnder interferometry combined with differential interference contrast microscopy (MZI-DIM) for the evaluation of surface morphology, and then verified the utility of these apparatuses by the comparison with the laser confocal microscopy combined with differential interference contrast microscopy (LCM-DIM). Furthermore, we investigated the dissolution of calcite under hydrothermal conditions at the step level. Consequently, the hydrothermal-optical-microscopy cell system enabled to confirm the equilibrium even under hydrothermal conditions, and precisely measure the solubility. The MZI-DIM also provided the evaluation of the normal dissolution rate given by the retreat of macrosteps inside/outside pits. We, directly, revealed that the dissolution of calcite crystals at 8 MPa, 150 °C was, kinetically, governed by the appearance of etch pits by LCM-DIM. Thus, we suggested the fruitful methods to in-situ observe step dynamics under hydrothermal conditions at the nanometer level.