Hideyuki Nakanishi

Reaction‐driven self‐organization of nanocrystals offers a promising route to functional patterns, yet the kinetic principles governing this process remain poorly understood. Here, we investigate how CsPbBr ₃ perovskite quantum dots (PQDs) migrate and spontaneously organize under patterned‐light‐induced photopolymerization. Using a custom‐built digital micromirror device‐based light projection system combined with in situ confocal microscopy, we directly correlate the applied light field with nanocrystal transport. We show that PQD migration is driven by the time‐dependent generation of a monomer‐conversion difference between high‐ and low‐light‐intensity regions, but that the final pattern is not determined by this driving force alone. Under weak irradiation, redistribution of other mobile species relaxes the conversion difference, whereas under strong irradiation, rapid polymerization is inferred to reduce PQD mobility through viscosity buildup and solidification. Intermittent and periodic irradiation reveal that nanocrystal self‐organization is governed by a competition between buildup of the driving force and loss of mobility during solidification. These results establish a kinetic design principle for reaction‐driven nanocrystal patterning and show that photopolymerization can serve as a programmable reaction‐diffusion field for directing colloidal transport and self‐organization.

Electrochemically exfoliated borophene–graphene hybrids (EEBGs), produced via electrochemical methods, offer multifunctionality including antimicrobial effects, improved supercapacitor performance, and efficient HER electrocatalysis.

Perovskite quantum dots (PQDs) are inherently unstable under environmental conditions, making it difficult to form patterns using conventional techniques. Herein, a unique approach is reported for patterning PQDs by the nonuniform photopolymerization of the liquid monomer. The demonstrated approach employs a PQD‐dispersed photocurable liquid, which is illuminated with the patterned light formed using a digital micromirror device (DMD). As the monomers are photopolymerized, the PQDs in the solution are patterned by diffusion (migration), and eventually, their pattern is imprinted on the film after photopolymerization. The migration process of the PQDs is in situ observed using an inverted‐type confocal microscope, and the patterning principle is examined by fine‐tuning the spatial distribution of the light intensity using the DMD. These findings will promote the generation of clear nanocrystal patterns with high contrasts and narrow line widths on films.

Precipitation of oppositely charged entities is a common phenomenon in nature and laboratories. Precipitation and crystallization of oppositely charged ions are well-studied and understood processes in chemistry. However, much less is known about the precipitation properties of oppositely charged nanoparticles. Recently, it was demonstrated that oppositely charged gold nanoparticles (AuNPs), also called nanoions, decorated with positively or negatively charged thiol groups precipitate only at the point of electroneutrality of the sample (i.e., the charges on the particles are balanced). Here we demonstrate that the precipitation of oppositely AuNPs can occur not only at the point of electroneutrality. The width of the precipitation window depends on the size and concentration of the nanoparticles. This behavior can be explained by the aggregation of partially stabilized clusters reaching the critical size for their sedimentation in the gravitational field.

All-inorganic cesium lead halide perovskite quantum dots (QDs) have several potential applications, owing to their unique optical and electronic properties. However, patterning perovskite QDs using conventional methods is difficult because of the ionic nature of QDs. Here, we demonstrate a unique approach, in which perovskite QDs are patterned in polymer films through the photocuring of monomers under patterned light illumination. The pattern illumination creates the transient polymer concentration difference, which drives the QDs to form patterns; hence controlling polymerization kinetics is essential for the generation of the QD pattern. For the patterning mechanism, a light projection system equipped with a digital micromirror device (DMD) is developed; thus, light intensity, an important factor to determine polymerization kinetics, is precisely controlled per position on the photocurable solution, resulting in the understanding of the mechanism and the formation of distinct QD patterns. The demonstrated approach assisted by the DMD-equipped projection system can form desired perovskite QD patterns solely by patterned light illumination, paving the way for the development of patterning methods for perovskite QDs and other nanocrystals.

One of the main purposes of smart and multifunctional coatings is to have the versatility to be applied in a wide range of applications. However, the functions of smart materials are often highly limited. In particular, the stimuli-responsive lateral expansion of coatings based on 2D materials has not been reported before. This manuscript describes small two-dimensional graphene oxide (GO) flakes (e.g., thin sheets with a thickness of a few nanometers and much larger lateral dimensions) that act as elementary agents for the formation of smart and multifunctional coatings. The coating can be self-assembled from the GO flakes and disassembled flexibly when required. The coating is stimuli-responsive: upon localized contact with water, it expands and forms wrinkling patterns throughout its whole surface. Evaporating the water allows the wrinkles to disappear; hence, the process is reversible. This stimuli-responsiveness can be controlled to be reduced or completely switched off by temperature or pressure. These features are fundamentally due to the reversible intermolecular interactions among the flakes and favorable packing structure of the coating. The smart coating is shown to be useful for patterned fluidic systems of the desired shapes and the development of channels between fluidic reservoirs via the shortest path. Importantly, these results showed that a simple collection of uniquely 2D elementary agents with small nanoscale thickness can self-assemble into macroscopic materials that perform interactive and multifunctional operations.

Patterning nanocrystals in polymer films is essential for the widespread use of nanocrystals in various fields from optics to electronics; therefore, the development of patterning methods for nanocrystals is an important task. Here, we report a unique approach for patterning silver nanowires (AgNWs) using a thermodynamic driving force induced by transient concentration gradients in reaction mixtures. The procedure starts with the preparation of a photocurable monomer solution containing homogeneously dispersed AgNWs. Ultraviolet illumination through a straight-line mask reduces the polymerization rate of monomers in the masked area, decreasing the polymer concentration in comparison with that in the unmasked area. Such transient polymer concentration gradients yield imbalances in the chemical potentials of AgNWs, inducing the migration of AgNWs to form a straight-line pattern of AgNWs. The pattern of AgNWs was visualized via photoluminescence imaging under a laser scanning confocal microscope and compared with the light patterns applied to the mixture. These observations revealed that the magnitude of the AgNW migration is enhanced as the transient concentration gradient increases by thickening the mask to decrease the intensity of light passing through the mask. The structural features of the AgNW pattern were reproduced using numerical simulations based on a set of reaction–diffusion equations, which suggested the key role of the polymerization kinetics characterized by the Trommsdorff–Norrish effect. Moreover, as the AgNW pattern becomes clearer, the electrical resistance along the patterns decreases and more complex patterns can be produced, indicating the potential of the method. Overall, the present patterning method constitutes a simple approach that only requires illumination through a mask to generate the AgNW pattern, which renders it a promising alternative for patterning nanocrystals in polymer films.