Published papers

We investigated the motion of spherical polystyrene/polypyrrole-coated polystyrene Janus particles placed at an air/saline interface and driven by a permanent magnetic field of ca. 0.5 T. For the sake of comparison, the motion of pure floating polystyrene particles was studied. Both kinds of the studied particles moved toward the magnet and stopped at the boundary of the near-surface well produced by the magnetic field. The Moses effect-driven motion of floating Janus particles was analyzed and investigated under different strengths of the magnetic field and salt concentrations. The study of the Janus particle displacement led to the development of a unified theoretical framework explaining the mechanism of the motion. This framework predicts that the motion of particles placed at an air-salt solution interface is not only dictated by magnetic energy but also intricately influenced by the interplay of factors, including the curvature of the interface caused by the static magnetic field, gravitational potential, and capillary forces. The orientation of the particles was observed. A qualitative explanation of the observed phenomena is suggested. The investigated process has potential for the self-assembly of particles placed at the liquid/air interface.

Development of organic energy storage requires enhancing performances of active materials. In particular, reaction potential and specific capacity of cathode-active materials have significant impact on energy density of organic lithium-ion battery. However, discovery of new compounds for active materials based on professional experience and intuition meets the limitation of huge search space of organic molecules. The performance predictors enable efficient discovery of new potential compounds. Although the predictors of potential, capacity, and energy density (models G1) are prepared in the previous work, these become older and have problems. In the present work, the updated models G2 have been constructed to improve the accuracy, usability, and generalizability. The models G2 are prepared by sparse modeling for small data combining machine learning and chemical insight on the training data set with adding new data. The updated models are validated using a new test data set and data-scientific methods. The improved predictors contribute to efficient exploration of new cathode-active materials to realize high-performance batteries.

Temperature monitoring is significant and fundamental in the fields of healthcare and medicine. In surgery, ultrasonic cutting devices are used for cutting, coagulation, and hemostasis. However, surgeons are concerned about the collateral thermal damages. For example, due to the limited space during endoscopic surgery, thermal damage is caused by touching the surrounding tissues of the targeted organ with the heated shaft of the ultrasonic cutting device. The present work exhibits thermoresponsive and reversible color-change coatings for temperature-distribution imaging. The phase-separated structures of the layered conjugated and matrix polymers enable both the tuned thermoresponsivity and large-scale coating. Layered polydiacetylene (PDA) with intercalated guests exhibits reversible and thermoresponsive gradual color changes from blue to red. A matrix polymer facilitates formation of the phase-separated layered PDA and large-scale coating. Spraying the precursor solution containing the diacetylene monomer, guest molecule, and matrix polymer provides the self-organized large-scale coatings on substrates. The temperature distribution on the shaft of an ultrasonic cutting device is monitored using the coatings. The phase-separated structure of thermoresponsive and matrix polymers can be applied to tunable temperature monitoring in a variety of fields.

Simple and environmentally friendly synthetic method of polypyrrole (PPy) microtubes were proposed. First, sucrose microfibers coated by PPy overlayer were synthesised by solvent-free vapor-phase coupling polymerization of pyrrole (Py) monomer using solid oxidant in the presence of sucrose microfibers with a diameter of approximately 4 μm without any liquid media. Next, selective extraction of sucrose core component from the sucrose-core/PPy-sheath microfibers using water resulted in the formation of PPy microtubes. The sheath thickness of PPy microtubes increased from 168 nm to 209 nm by controlling relative humidity during the polymerization from 10 to 40%. Furthermore, the sheath thickness increased from 73 nm to 207 nm with an increase of the polymerization time from 4 h to 24 h. The capacitance of PPy microtubes (157.0 F g−1) was approximately three times higher than that of the bulk PPy films (52.2 F g−1), thanks to good accessibility of ions in the electrolyte to the PPy surface due to their hollow structure. The PPy microtubes synthesized in this study are expected to be applied as electrodes for energy storage devices such as capacitors and lithium-ion secondary batteries and soft micropump.

Eye-catching metallic luster materials, especially those whose colors can be controlled by external stimuli, have many potential applications. Here, we present a silver luster material that changes color to gold upon UV irradiation. Diacetylene (DA) derivatives with stilbenes introduced via linkers at both ends (DS-DAn (n = 1-6)) exhibited significantly different metallic luster and color change behaviors depending on the linker carbon number (n). The results revealed that the stacked structure of platelet crystals consisting of DS-DA1 with the shortest linker carbon chain exhibited a silver luster and changed its appearance to gold upon UV irradiation; this was an exceptional property of this material. More importantly, we found a unique crystal structure formed by DS-DA1, where the two assembled states coexisted. Partial topochemical polymerization of DA within this unique crystal structure dramatically changed its color from silver to gold. The findings of this study not only contribute to the development of the basic science of DA polymerization but also facilitate the development of new applications of metallic luster materials due to their attractive features that are adaptable to photomask patterning and UV laser lithography.

Morphologies are important in chemistry and materials science. A wide variety of functional molecules and their assemblies are synthesized on the basis of molecular design. These morphologies, from molecular to nanometer scales, have been summarized in previous nice reviews. Here we focus on recent advances in morphology design and control of organic polymer materials from nanoscopic to macroscopic scales, which are larger than the molecular scale, for which general strategies are now being developed. This review summarizes crystal-controlled polymerization from a new perspective for the morphology design and control of organic polymer materials. Characteristic structures, surfaces, and morphologies of solid crystals are employed for morphology control of organic polymer materials. Morphology control contributes to the emergence and/or improvement of the properties.

Fluorine-free superhydrophobic surfaces have been required to meet environmental regulations in recent years. A new nanoarchitectonics is required to achieve superhydrophobicity without using perfluoroalkyl compounds. In the present work, surface-modified exfoliated nanosheets with polydispersed sizes were utilized to prepare coatings with high surface roughness and low surface energy. Fluorine-free superhydrophobic surfaces were obtained by spray coating of surface-modified exfoliated nanosheets based on transition-metal oxides. The water contact angle (ªw) 166.0 « 0.5° is the highest compared with that of the fluorine-free substrate-independent coatings in previous reports. The significant factors related to ªw were studied using machine learning combined with our chemical insight in the small data obtained in the present work. The resultant superhydrophobic coatings exhibited unique properties, such as sliding of water droplets, superoleophilic behavior, recyclability, and durability. The present design strategy can be applied to development of various functional coatings using exfoliated 2D materials with polydispersity.

Performances of functional polymers are enhanced by designing the structures in different hierarchies, such as monomers, polymers, secondary structures, and nanoscale morphologies. In the present work, an amorphous conjugated polymer network was designed and synthesized to obtain a metal-free electrocatalyst for hydrogen evolution reaction (HER) in an efficient manner. A prediction model for the catalytic performance, i.e. overpotential for HER, was constructed using machine learning on small data based on the literature. The straightforward linear prediction model assisted in the design of the network polymer containing quinone and heteroaromatic moieties. The simultaneous multiple reactions of benzoquinone (BQ) and benzoxazole (BO) formed the amorphous conjugated polymer network at 200 °C. After the morphology control, the BQ-BO polymer showed an overpotential of 230 mV for the electrochemical HER at 10 mA cm−2, which is one of the highest performances in the metal-free electrocatalysts synthesized at low temperatures. Moreover, we found that the amorphous conjugated polymer networks showed specific hydration behavior in aqueous media. The results indicate that designing an amorphous conjugated polymer network coupled with machine learning is a potential approach for the development of functional materials.

Nanospace has been used as a specific field for syntheses and assemblies of molecules, polymers, and materials. Free volume space among polymer chains is related to their properties, such as permeation of gas and small molecules. However, the void has not been used as a functional nanospace in previous works. The present work shows synthesis of guest conductive polymers in free volume space of conventional synthetic resins and rubbers as a new nanospace. Vapor of heteroaromatic monomer and oxidative agent is diffused into the soft dynamic nanospace among the polymer chains under ambient pressure at low temperature. The oxidative polymerization provides the conductive polymers, such as polypyrrole (PPy), in the free volume space of poly(methyl methacrylate) (PMMA), polypropylene (PP), silicone rubber (SR), and polyurethane rubber (PU). The ratio of the free volume decreases with the infiltration of the conductive polymers. The composites exhibit the improved mechanical and gas barrier properties. The rubbers containing PPy are used as mechanical-stress sensors with both the conductivity and flexibility. The free volume space of resins and rubbers can be used as a new dynamic nanospace for synthesis of functional polymer composites.