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Commercially available eye-drops scarcely penetrate the eye because of the cornea, which is located at the surface of the eye and function of barrier to keep out foreign matter. To enhance the pene...

The conversion curve of solid-state polymerization in polydiacetylene (PDA) nanofibers (NFs) was so different from that of PDA nanocrystals (NCs). PDA NFs clearly showed the longer induction period...

The third-order nonlinear optical (NLO) susceptibility for morphologically controlled polydiacetylene (PDA) nanocrystals (NCs) and PDA nanofibers (NFs) have been determined for the first time by the experimental combination of transient pump-probe spectroscopy and spectroscopic ellipsometry. The figure of the merit of PDA NFs was much superior to PDA NCs and/or PDA bulk crystals, and the excitonic relaxation time was of order of sub-pico second. Namely, this is the first case to reveal the morphological effect on NLO response. PDA NFs having the long effective π-conjugation length are one of the most promising organic third-order NLO nanomaterials toward the photonic device application

Methods for the control of molecular deposition and orientation are critical for the development of organic electronic devices. Here, we show the fabrication of ribbons of the optical material polydiacetylene (PDA) using a controlled evaporative self-assembly method. The ability to form these ribbons is highly dependent on both the side groups on the PDA as well as the solvent used in the preparation. Arrays of ribbons of one type of PDA, poly[1,6-di(N-carbazolyl)-2,4-hexadiyne], with widths on the order of 1-2 urn and lengths of 100s of micrometers, could be successfully obtained with good orientation.

[6,6]-Phenyl-C61-butyric acid methyl esters (PCBM) have emerged in recent years as important building blocks for photovoltaic devices. However, the potential of PCBM itself as a photocatalyst has not been reviewed. Here, we demonstrate PCBM nanoparticles (NPs) fabricated by the reprecipitation method as suitable photocatalysts for an effective visible-light-driven photocatalytic degradation for organic dyes. An enhanced catalytic performance of PCBM can be achieved by a simple annealing process. The present PCBM NPs outperform the state-of-the-art P25 TiO2 and therefore highlights its potential as promising small molecule organic semiconductor photocatalysts with high photocatalytic activity and good long-term stability.

We have successfully fabricated insoluble polymer-metal complex [{Cu2(µ-Br)2(PPh3)2}(µ-bpy)]n (bpy = 4, 4′-bipyridine) nanocrystals by developing already-established heterogeneous reaction process,...

Polystyrene (PS) microspheres embedding perylene fluorophores have been fabricated by the two kinds of encapsulation method; (A) seed polymerization of styrene using perylene nanocrystals as a seed, and (B) emulsion polymerization of perylene-styrene solution. In both methods, the PS microspheres formed were ca. 200 nm in size, roughly larger than bare perylene nanocrystals. Interestingly, the fluorescence peak positions in both the PS microspheres were located between those of solution and nanocrystal states. These facts suggest that the dispersion state of perylene fluorophores in PS microspheres would be changed to be intermediate between solution and nanocrystal states during the polymerization process.

Pure nanodrugs (PNDs) is a newly designed drug materials, which is a carrier-free drug nanoparticles fabricated by the reprecipitation method. In the present study, the cytotoxicity of PNDs consisting of SN-38 dimer and podophyllotoxin dimer with size in the range 30–50 nm was evaluated in human cancer HepG2, KPL-4, and MCF-7 cells. It was observed that the cytotoxicities of PNDs were changed depending on the type of cells. In addition, PNDs coated with polysorbate 80 showed higher activity than free PNDs, which suggests that the surface state of PNDs was the one of the important factors to affect cytotoxicity.

We have successfully fabricated insoluble copper(I) complex [Cu(μ-I)dppet]2 nanocrystals by developing the heterogeneous reaction process between rod-like nanocrystals of dppet ligand prepared in advance and added acetonitrile solution of copper(I) halide. During this reaction process, the shape of dppet ligand nanocrystals was dramatically changed from rod-like to spherical. Probably, the complexation reaction and subsequent nanocrystallization would proceed on or near swollen surface of dppet nanocrystals in acetonitrile droplet as restricted reaction field.

Phase transformation of solvated C60 microcrystals (MCs) was directly observed for the first time by use of thermal treatment to induce the phase transformation. C60 MCs were changed from bundle rod-shape to disc-shape, accompanied with the change of crystal structure from P63 symmetry to fcc symmetry. This kind of phase transformation included three steps in solvent medium: exchange of incorporated solvent, decomposition of old crystals, and formation of new crystals. It is not likely a kind of crystal-to-crystal phase transition assisted by incorporation of dispersing solvents but can be demonstrated as a decomposition–recrystallization process. The mechanism has been also tested by the thermal-induced phase transformation of C60 MCs from bundle shape to bipyramid shape.

The electric field-induced orientation of rubrene single crystals was observed in a nonpolar solvent. Rubrene single microcrystals responded to an AC electric field beyond a crystal-size dependent threshold. The longitudinal axis, i.e. , b -axis, of rubrene single crystals on a SiO 2 /Si substrate was aligned almost parallel to the direction of the applied electric field. Field-effect transistors with these orientated crystals exhibited low variability of the carrier mobility.

We studied the relationship between the surface morphology and optical property of 9,10-bis(4-(N-carbazolyl)phenyl)anthracene (BCPA) nanocrystals having a small nanoparticle on their surface using ...

Nanocrystals of seven p-phenylenediacrylates, i.e., dimethyl (1a), didecyl (1b), diundecyl (1c), ditetradecyl (1d), dipentadecyl (1e), dioctadecyl (1f), and dicholesteroyl (1g) derivatives, and 2,5-distyrylpyrazine (2) were fabricated by the re-precipitation method and their photochemical reaction behaviors were investigated in comparison to those of bulk crystals. The bulk crystals of 1a−1c and 2 were found to be photoreactive, whereas those of 1d−1g were less photoreactive. In contrast, all of the nanocrystals of 1a−1g and 2 showed high photoreactivity. Nanocrystals of 1a and 2 were demonstrated to have the same packing as the corresponding polymerizable bulk crystals, and they gave the corresponding polymers by photoirradiation. The polymer crystal structures in their nanocrystals were confirmed to be the same as those in bulk crystals by X-ray and electron diffraction analyses. Their single-crystal-to-single-crystal transformation was established by their nanocrystallization. On the other hand, other ...

Anomalous polyimide (PI) nanoparticles with controllable morphology, i.e., porous hollow structures, hollow structures, or bowl-like structures, were fabricated by blending a second polymer with poly(amic acid) (PAA, the precursor of PI) through the reprecipitation method and subsequent imidization. The phase separation between PAA and the porogen induced the formation of various hollow PI nanoparticles. The hollow morphology was mainly affected by the compatibility/interaction between PAA and the porogen. Hollow PI nanoparticles with superficial pores (ca. 30 nm), smooth surface, or holes in their surfaces can be obtained by selecting a suitable porogen, respectively.

We have investigated that photoreactivities of a series of diynediammonium dienecarboxylates in the crystalline state. In the case of 4,4′-butadiynedibenzylammonium disorbate, almost all diene moieties were polymerized during photoirradiation for 8 h. On the other hand, the conversion of diyne moieties was still low. Crystal structure of the monomer crystal indicates that the alignment of diene moieties is very similar to those of topochemically polymerizable crystals of diene derivatives. Even though the translation distance of diyne moieties is also suitable for the polymerization, the tilt angle is different from the ideal angle. It is the reason why the conversion of diyne moieties was low. By X-ray single-crystal structure analysis of the polymer crystal, we confirmed that the polymerization proceeded via topochemical reaction mechanism indeed. On the other hand, photodimerization of diene moieties in the crystals of 2,4-hexadiyne-1,6-diammonium (E,E)-muconate occurred because of the face-to-face ali...

Novel porous polyimides (PIs) having diameters of several hundred nanometers have been fabricated successfully from precursor poly(amic acid) (PAA) derivatives with poly(acrylic acid) (PAS) as the porogen, using a reprecipitation method and subsequent imidization. The superficial high porosity with deep pores was introduced when using a more compatible combination of PAA and the porogen, i.e., PI (BPDA-PDA) and PAS rather than PI (10FEDA-4FMPD and PAS); the pore sizes ranged from 20 to 100 nm. The resulting porous PI nanoparticles had thermally stabilities (determined from their 5% weight loss temperatures at 400 °C) similar to those of corresponding PI nanoparticles lacking porous structures. Microphase separation within the PAA nanoparticles after reprecipitation induced the porous surface structure, the properties of which were influenced by the molecular weight of PAS and the chemical structure of PAA. These unique porous PI nanoparticles have great potential for application as low-k materials in next-generation technologies.

The preparation and size control for mono-dispersed fullerene C 60 fine particles was successfully achieved during the high temperature and high pressure fluid (HTPL) crystallization process, in which acetone was used as the HTPL solvent and pure water or the mixture of acetone and water as the cooling solvent. The prepared fullerene C 60 particles had spherical shape and narrow size distribution with the average size ranging from 44 nm to 110 nm depending on the various experimental conditions, such as fluid temperature, solvent flow rate, system pressure and the ratio of acetone and water in cooling solvent. The products were characterized by using X-ray powder diffraction (XRD), scan electron microscopy (SEM), dynamic light scattering technique (DLS) and UV–VIS spectrum, respectively. And the size effect of such fullerene C 60 nanocrystals was confirmed.

Relationship between the size of Polyimide fine particles and some conditions in the reprecipitation method was investagatge. As a result, polyimide ultrafine particles with ca. 50 nm in size have been successfully fabricated through the “two-steps imidization”, i.e. chemical imidization followed by thermal imidization of poly(amic acid) (PAA) precursor ultrafine particles prepared under an optimum reprecipitation condition.

Monodispersed DAST nanocrystals have almost been successfully fabricated by means of the inverse reprecipitation method. By employing AC electric field, high electric field of above ca. 1.0 kVcm -1 could be applied to polar DAST nanocrystals dispersed in decahydronaphthalene, so as to avoid electrophoresis of nanocrystals under DC electric field. The response of DAST nanocrystal dispersion to applied AC electric field was analyzed phenomenologically by fitting Langevin function, which provided a large permanent dipole moment of DAST nanocrystal. In addition, we have succeeded in in situ observation of AC electric-field-induced orientational motion of DAST crystals by using an optical microscope. The present DAST nanocrystal dispersion system will be expected as an optical device like display monitor.

Core–dual-shell-type hybridized nanoparticles (NPs) having Au-core/dye-doped silica inner shell/Au outer shell are successfully fabricated by developing a biphasic process that is a kind of so-called “one-pot” method. The resulting hybridized NPs exhibit evidently about 20-fold enhancement of fluorescence intensity, increase in fluorescence quantum yield, and decrease in fluorescence lifetime. These effects depend on the metal nanostructure being optimized, compared with the reference hybridized NPs with neither a Au-core nor a Au outer shell, due to the gap-mode effect induced by localized surface plasmon resonance in the core–dual-shell-type MIM-like nanostructure. More detailed elucidation concerning the enhancement mechanism will provide the possibility of photonic device application, for example as a high-performance point light source, nanolaser, or sensor for bioimaging in the visible region in the near future.

We have succeeded, for the first time, in fabrication of diarylethene (DAE), 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene, nanocrystals using two nanocrystallization processes base...

The specific methodological features in the emulsion and the reprecipitation methods to fabricate organic nanocrystals were examined using perylene. The size-control of perylene nanocrystals was accomplished for the first time using the emulsion method, which has not been achieved so far by the reprecipitation method. The standard deviation of size distribution of nanocrystals in the emulsion method became smaller than that in the reprecipitation method. Although the residual good solvent may influence the nanocrystal growth process in the reprecipitation method, no such influence was detected in the emulsion method.

We report a novel method of producing monodispersed polycyclic aromatic hydrocarbon nanocrystals as a result of crystal growth in a stabilizer-free oil-in-water emulsion. The emulsion was prepared by dispersing a hot organic solvent including target molecules into an aqueous medium at the same temperature as the solvent, and nucleation and crystal growth were then induced in the emulsion by decreasing the temperature. The emulsifier of the organic solvents was easily removed from the dispersion medium, and we were able to obtain π-conjugated organic nanocrystals such as tetracene, C60 fullerene, and anthracene at high dispersion concentrations.

Gold nanoparticles were densely deposited on the surface of C60 microcrystals having a variety of unique shapes. C60 microcrystals were prepared by a conventional liquid–liquid reprecipitation method. The shapes of C60 microcrystals, such as bipyramid, belt, disc, and rod, were achieved by carefully adjusting the solvent species in the liquid–liquid reprecipitation process. Gold nanoparticles were directly deposited on C60 microcrystals without adding any conventional reducing agent but only heating HAuCl4 in C60 microcrystals ethanol dispersion containing CS2. Scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, powder X-ray diffraction, absorption spectroscopy, and X-ray photoelectron spectroscopy studies were conducted to characterize the gold–C60 heterostructure. The gold–C60 heterostructure showed charge transfer behaviour where gold was an electron donor and C60 was an electron acceptor. C60 microcrystals-supported gold nanoparticles also showed catalytic activity in reduction of p-nitrophenol at room temperature. A facile reduction mechanism was suggested for gold deposition on the surface of C60 microcrystals.

Butadiyne nanocrystals in water are usually polymerized by UV or gamma-ray irradiation to give polydiacetylene (PDA) nanocrystals. In this study, we confirmed that solid-state polymerization of 1,6-di(N-carbazolyl)-2,4-hexadiyne (DCHD) and 5,7-dodecadiyn-1,12-diyl bis[N-(butoxycarbonyl-methyl)carbamate] (4BCMU) could be stimulated by water-soluble radical initiators. The radical initiators used were potassium peroxodisulfate, three kinds of azo-type compounds and a redox initiator. In all cases, the solid-state polymerization was confirmed by color change into blue indicating that PDA modified by the radical residues at the end was formed. However, nanocrystal cohesion occurred especially when the concentration of the initiators was high or the dispersion was kept for a long time. In order to improve the dispersion stability, two kinds of surfactants, i.e., sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium chloride (DTMAC), were added to the DCHD nanocrystal aqueous dispersion. As a result, when anionic SDS was added, the solid-state polymerization of nanocrystals proceeded without coagulation and quantitative conversion was confirmed for all initiators. Cationic DTMAC has no effect on dispersion stabilization. PDA nanocrystal surfaces in water are negatively charged in nature and electric interaction of nanocrystals with the cations results in decrease of surface charge and aggregation of nanocrystals.

Polystyrene microgels (PSMG) were prepared by soap-free emulsion co polymerization of styrene and divinylbenzene (DVB), and then dispersed in tetrahydrofuran (THF). The apparent diffusion constant Dapp and the intrinsic viscosity [η] for PSMG were determined in THF. Dapp was measured with dynamic light scattering technique, and the hydrodynamic radius Rh of PSMG swollen in THF was estimated using the Stokes-Einstein relation. The slope of plots of Dapp vs. concentration of PSMG changed from positive to negative with decreasing DVB content. This result was interpreted by a core-shell type network structure of swollen PSMG. Formation of the network structure is also supported by the difference in reactivity ratio between styrene and DVB. The swelling ratio of PSMG, which was calculated from the ratio of Rh and the diameter of dried PSMG, showed maximum at intermediate DVB content, while [η] showed minimum around the similar DVB content. This behavior was ascribed to the aggregation of PSMG. The dispersion mechanism could be qualitatively explained by considering both steric and topological repulsive forces, to which the network structure of the core-shell type may contribute.

We present a colloidal crystal wire composed of thousands of connected microspheres that is fabricated by a simple dewetting process utilizing a drain phenomenon, and we directly observe the light propagation within the wire by near-field scanning optical microscopy. The optical properties of propagation light suggest that the propagation mechanism was attributed mainly to nanojet-induced mode coupling for the straight propagation component and partly to whispering-gallery mode coupling within the colloidal crystal wire.

Polyimide particles were fabricated through the two-steps imidization of poly(amic acid) particles prepared by using reprecipitation method. PAA and PI nanoparticles were all spherical, and the changes of particle size, its distribution, and morphology were not observed before and after the imidization. The preparation of PI nanoparticles size-controlled between ca. 20-500 nm was also achieved by changing the experimental conditions, temperature of the poor solvent, the composition of two kind of poor solvent, and PAA-NMP solution concentration.

The cover illustrates trans-4-[4-(dimethylamino)]stilbazolium p-toluenesulfonate (DAST) nanocrystals as white rectangular parallelepipeds anisotropically oriented by an applied magnetic field. As reported by Kaneko and co-workers on p. 160, the oriented DAST nanocrystals dispersed in lauryl acrylate monomer can be easily fixed by UV curing in a magnetic field. The inset displays a picture of the cured DAST dispersions with a quarter for scale.

Monodispersed quinacridone nanocrystals were fabricated by a high-temperature and high-pressure liquid crystallization method, which proved to be an advanced technique for fabricating nanocrystals of pigment compound. The aqueous dispersion liquid of quinacridone nanocrystals was very stable. The nanocrystats had a spherical shape with an average size of 60 nm when water was used as the high-temperature and high-pressure liquid at 260 degrees C and cooling solvent. The crystal structure of the nanocrystals could be controlled by varying the experimental conditions.

The high-temperature and high-pressure liquid (HTPL) crystallization method was proved to be effective to fabricate nanocrystals of quinacridone and its dimethyl derivative. The quinacridone nanocrystals were spherical shape and monodispersed with the average size of around 50 nm, respectively. It was found that quinacridone nanocrystal in different crystal form could be obtained by changing experimental conditions in HTPL method.

We have presented a simple technique for the fabrication of nanocrystals of organic molecules and polymers and have shown that it is possible, using the liquid-phase technique, to fabricate organic nanocrystals ranging in size from 10 nm to 1 μm by manipulating the preparative conditions. In particular, nanocrystals of poly(4-BCMU) ranging from 20 nm to 350 nm were prepared by controlling the preparation conditions. The main advantages of the liquid-phase technique are the practicality and suitability of the technique for a wide range of materials. The fabrication of organic nanocrystals, though at a very early stage, seems a promising approach for producing low-dimensional organic materials and, like inorganic nanocrystals, another important objective for future study would be to incorporate organic nanocrystals into a variety of inorganic and organic media. It is hoped that extensive work will be done on organic nanocrystals to evaluate their potential for electronics and photonics.

Many reports discuss the unique electronic, optical and magnetic properties of fullerene molecules. Such properties originate in their special molecular structure, which is spherical and highly symmetric. Not only fullerene molecules, several interesting papers describe bulk fullerene crystals formed by simple crystal growth from solutions, and which contain solvent molecules. However, only a few studies have been made on the synthesis of uniform fullerene fine crystals with a size in nano/micrometer scale. The preparation of fullerene nano/microcrystals with a uniform size and shape would permit the control of their specific electronic energy levels and the totally new properties. Thus, we have attempted this research, using reprecipitation method developed in our laboratory. By changing simply experimental conditions such as the selection of solvents, we have obtained various unexpected and unique shapes of C60 nano/microcrystals and with surprisingly monodispersed size.

We have successfully fabricated doped Cu-TCNQ nanocrystals, using the reprecipitation method involving a chemical reduction process, which took the composition ratio of Cu:TCNQ = 1.3:1 and contained both TCNQ anion and dianion. Interestingly, the doped nanocrystals exhibited a new strong absorption in NIR region, clearly dependent on the content of the TCNQ dianion.

The cyclic transformations in shape and crystal structure of C60 microcrystals in dispersion are experimentally demonstrated by changing the dispersion solvent medium, and keeping the dispersion under ultrasonication. The shape of C60 microcrystals was changed from as-grown rod-shape to hexagonal disc-shape, then to belt-shape, and again back to rod-shape. The transformation processes were investigated by means of TEM, XRD and FT-IR measurements. As a results, the present transformation is regarded to be a crystal-to-crystal phase transition induced by the exchange of the dispersion medium, which is finally ascribed to weak intermolecular interactions between C60s inside the crystal.

Two negatively charged nanoparticles (SDS-coated SWCNT and polydiacetylene nanocrystals) were sequentially adsorbed onto the same water-hexane interface. The absorbed film can be transferred onto a solid substrate. Repeating the adsorption and transfer process enables assembly of the two nanoparticles in a layer-by-layer growth fashion up to three bi-layers.

We have clarified nanocrystallization process of diarylethene in the reprecipitation method using a derivative, cis-1,2-cyano-1,2-bis(2,4,5,-trimethyl-3-thienyl)ethene (CMTE) as a typical example of diarylethene. The crystal growth was investigated by the time-dependence measurement of crystal size with dynamic light scattering (DLS). Nanocrystallization process could be explained by the cluster-model.

Fullerene (C60) nanoparticles were assembled in two-dimension using a liquid–liquid interface. C60 nanoparticles dispersed in ethyl lactate/water solution were added to a glass vessel. Then, hexane was added to the dispersion solution to create the liquid–liquid interface. C60 nanocrystals were assembled at the interface, when ethanol was added to the water dispersion–hexane solution. The assembled film was transferred onto a solid substrate and the film morphology was observed by a scanning electron microscope (SEM) and atomic force microscope (AFM).