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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...

It has been difficult to selectively modify the surface of molecular crystals by chemical reactions because they usually have no reaction points on their surfaces. In this paper, focusing on the unique nanocrystal surface of the polymer metal complex (PMC) [{Cu2(μ-Br)2(PPh3)2}(μ-bpy)]n having an exposed reactive terminal chain, we successfully modified the surface of PMC nanocrystals (NCs) through an alkylation reaction. Interestingly, after the alkylation reaction, the luminescence spectrum of PMC NCs blue-shifted, and the luminescence quantum yield increased. PMC NCs with a large specific surface area showed optically peculiar or characteristic properties compared with the corresponding bulk crystals. PMC NCs have high potential as a new class of luminescent materials due to their surface effect.

Layered type hybridized thin films, which were composed of oriented polydiacetylene (PDA) nanofibers (NFs) and silver (Ag) nanoparticles (NPs), have been fabricated successfully by means of the alternative processes of the layer-by-layer (LbL) method and the convective assembly method. The wavelength dispersion of third-order nonlinear optical (NLO) susceptibility, χ(3)(ω), and the corresponding figure of merit (FOM) have been evaluated correctly by the combined analysis with femtosecond pump–probe spectroscopy and spectroscopic ellipsometry. It has become apparent that both χ(3)(ω) and FOM were enhanced evidently in the layered type hybridized thin films under the optimized condition of a suitably adsorbed amount of Ag NPs, compared with random thin films of PDA NFs and/or oriented thin films of PDA NFs, because of the localized surface plasmon resonance (LSPR) effect from Ag NPs as well as the orientation effect of PDA NFs. This would provide a new design guide for organic NLO hybrid nanomaterials towar...

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.

Porous zirconia medium (PZrM) has been fabricated successfully using polystyrene microparticles (MPs) as templates. The emission spectra of rhodamine B (RhB) [optical amplifying medium] loaded inside PZrM [porous scatterers] were obtained at numerous excitation light intensities. The lasing thresholds (Ith) have been determined experimentally from the variations in the intensity of random laser oscillation peaks, which are suitably separated from the measured emission spectra. Ith is closely related to the pore sizes of PZrM and the added amount of PZrM powder, and it clearly provided the minimum against the pore size. This fact is explained reasonably by the simulation of scattering efficiency on the basis of the Mie scattering theory. Consequently, PZrM as a porous scatterer is superior to Zr MPs from the viewpoint of random laser oscillation.

We have successfully fabricated a series of polymer–metal complex [{Cu2(µ-Br)2(PPh3)2}(µ-PyX)]n nanocrystals (NCs) with different kinds of ligands. Interestingly, the luminescence spectrum of the NCs of [{Cu2(µ-Br)2(PPh3)2}(µ-PyX)]n were red-shifted, compared with those of their corresponding bulk crystals. IR spectra of [{Cu2(µ-Br)2(PPh3)2}(µ-Py2)]n, whose ligand had a phenyl linker between two pyridine rings, revealed that the conformation of the coordinated Py2 ligand in the NCs was different from that in the bulk crystal, but similar to that of the un-coordinated Py2 ligand. The results suggest that the rotational degree of freedom in the PyX ligands would affect the looseness of the crystal lattice in the polymer–metal complex NCs, thereby affecting their luminescence properties.

Conjugated polymers have recently emerged as a new class of photocatalysts. However, many conjugated polymer photocatalysts are not as effective as inorganic materials due to the limited electronic properties of their LUMO and HOMO and low long-term stability caused by the degradation of the conjugated backbone. In the present study, we have demonstrated, for the first time, the superior Visible (Vis) light-driven photocatalytic activity of conjugated polymer nanocrystals (NCs) of polydiacetylene (PDA) derivatives, namely, p-DCHD NCs for the photodegradation of Rhodamine B (RhB) compared with that of the state-of-the-art P25 TiO2 nanoparticles (NPs). In addition, we have revealed the morphological effects of p-DCHD NCs, long-term stability, and the photocatalytic degradation mechanisms. These results will open a new pathway for the further development and understanding of conjugated polymer photocatalysts toward various potential applications.

We have successfully visualized the surface terminal structure of polymer–metal complex [{Cu2(μ-Br)2(PPh3)2}(μ-bpy)]n nanocrystals (NCs) using Prussian blue (PB) nanoparticles (NPs). From TEM observation and analysis of the electron beam diffraction pattern, it was found that the (010) plane had grown well, and that the terminal ends of main chains would be located on the (010) plane of the present NCs as a dangling bond. Actually, PB NPs were selectively adsorbed on the (010) plane of [{Cu2(μ-Br)2(PPh3)2}(μ-bpy)]n NCs. This fact clearly means bipyridine ligands having a nitrogen-terminal located on the surface of the (010) plane would coordinate and bind to Fe ions in PB NPs, which would lead to a new class of polymer–metal complex NCs materials.

Carrier-free drug nanoparticles are a promising drug delivery system for cancer therapy; however, the fabrication of nanoparticles composed of small molecule drugs is challenging. In this study, we fabricated pure drug nanocrystals, with nearly 100% of 7-ethyl-10-hydroxycamptothecin (SN-38) molecules, by using the ultrasound-assisted reprecipitation method. The rod-like nanocrystals with ca. 150 nm in a long axis were obtained through the ultrasound-assisted reprecipitation method, and the nanofibers were obtained without irradiation. Furthermore, the SN-38 nanocrystals exhibited considerably higher cytostatic activity against cancer cells than irinotecan hydrochloride, which is a clinically used prodrug of SN-38. These results demonstrate the potential of the ultrasound-assisted precipitation method as a powerful process to fabricate nanoparticles assembled using only small molecule drugs.

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,...

Emission photon statistics, i.e., single-photon and multi-photon emissions, of isolated QDs is required for tailoring optoelectronic applications. In this article, we demonstrate that the emission photon statistics can be modified by the control of the spectral overlap of the QDs with the localized surface plasmon resonance (LSPR) of the metal nanoparticle (metal NP) and by the distance between the QD and the metal NP. Moreover, the contribution to the modification of the emission photon statistics, which is the excitation and emission enhancements and the quenching generated by the spectral overlap and the distance, is elucidated. By fabricating well-defined SiO2-coated AgNPs and AuNPs (metal/SiO2), the spectral overlap originated from the metal species of Ag and Au and the distance constituted by the thickness of the SiO2 shell are controlled. The probability of single-photon emission of single QD was increased by the enhancement of the excitation rate via adjusting the distance using Ag/SiO2 while the single-photon emission was converted to multi-photon emission by the effect of exciton quenching at a short distance and a small spectral overlap. By contrast, the probability of multi-photon emission was increased by enhancement of the multi-photon emission rate and the quenching via the spectral overlap using Au/SiO2. These results indicated the fundamental finding to control emission photon statistics in single QDs by controlling the spectral overlap and the distance, and understand the interaction of plasmonic nanostructures and single QD systems.

Organic nanocrystals are occupied in an intermediate state between single molecule and the corresponding molecular crystal in a bulk state, which are fabricated in common by using the reprecipitation method. The crystal size is in the range of several tens nanometer to sub-micrometer. In particular, linear optical properties such as excitonic absorption spectrum and fluorescence emission spectrum are evidently dependent on crystal size, owing to thermally soften nanocrystal lattice with increasing specific surface area. Core–shell-type hybridization between organic nanocrystals and novel metal nanoparticles is of too much interest in current material science. In this chapter, creation of polydiacetylene nanocrystal fibers hybridized with gold nanoparticles will be introduced in details toward nonlinear optics applications. Polydiacetylene is typically one-dimensional π-conjugated polymer, and one of the most promising organic nonlinear optical materials. It is expected that nonlinear optical properties would be enhanced because of peculiar optoelectronic interaction between exciton in polydiacetylene and localized surface plasmon resonance effect in gold nanoparticles.

Charge-transfer complex exhibits versatile characteristics such as optical properties, conductivity, and magnetism. The physicochemical properties can be controlled through molecular design combining various kinds of electron donors and acceptors. In particular, the degree of charge-transfer γ and the composition ratio of electron donor to acceptor are important factors to determine physicochemical properties. On the other hand, nanocrystallized charge-transfer complex would lead to unique properties, being different from both isolated molecule and bulk crystal. However, the reprecipitation method for common organic nanocrystals cannot be employed due to low solubility of charge-transfer complex in common organic solvents. Therefore, novel nanocrystallization method for charge-transfer complex should be developed. In this chapter, nanocrystallization involving doping process of charge-transfer complex, copper 7,7,8,8-tetracyanoquinodimethane (Cu-TCNQ), will be introduced in detail towards nanoelectronics application. Cu-TCNQ is typical Mott insulator and indicates a unique resistive switching behavior. It is expected that Cu-TCNQ nanocrystals with an excess amount of Cu, namely doped Cu-TCNQ nanocrystals, would show unique resistive switching behavior because of the degree of charge-transfer γ different from bulk crystal.

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.

Porous polyimide (PI) thin films have been fabricated successfully by using silica microparticles (MPs) with different particle sizes as a template, and the three dimensional porous structure has been observed clearly by mean of transmission electron microtomography. The measured values of dielectric constant (e) decreased remarkably by introducing a porous structure, compared with ordinary PI thin films. Especially, the porosity evidently increased (ca. 10%) by suitably employing silica MPs having different particle sizes, and then the value of e was further reduced. Bruggeman model could reproduce nearly the relationship between the value of e and porosity.

Aiming at a highly bright emitter, hybridized thin films consisting of organic dye TDBC J-aggregates (JA) and titanium oxide (TO) nanoparticles (NPs) have been fabricated successfully. The fluorescence intensity and the corresponding fluorescence quantum yield multiplied ca. 10 times and ca. twice, respectively. TO NPs have a high refractive index, and have no absorption loss like metal NPs. On the other hand, extinction (absorption) and fluorescence spectra are in general overlapped in organic dye JA, that is, so a small Stokes’ shift. Namely, the present phenomenon could be qualitatively explained by the simultaneously optical processes of both “excitation enhancement” induced directly by near-field effect from TO NPs and “emission enhancement” as a radiation of scattering field from TO NPs, which were polarized by the excitation energy from TDBC JA to TO NPs. In other words, the definite scattering peak in the extinction spectrum of TO NPs should be tuned efficiently with extinction (absorption) and fluorescence peak bands of TDBC JA.

We demonstrate high potential of polymer nanosheets as a soft scaffold for the growth of metal–organic framework films. Nanofilms of a Cu-based metal–organic framework (HKUST-1) were deposited by the layer-by-layer processing on polymer nanosheets fabricated by the Langmuir–Blodgett technique. The film growth proceeds in the (111) direction to yield a highly smooth surface.

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.

Organic nanocrystals are, for the definition, crystals of nanometer order of an organic compound. Organic nanocrystals are the nanomaterials that have been attracting attention in recent years because they show some interesting characteristics for basic science, and many applications using organic nanocrystals are expected as well.

Nano eye-drops are a new type of ophthalmic treatment with increased potency and reduced side effects. Compounds in conventional eye-drops barely penetrate into the eye because the cornea, located at the surface of eye, has a strong barrier function for preventing invasion of hydrophilic or large-sized materials from the outside. In this work, we describe the utility of nano eye-drops utilising brinzolamide, a commercially available glaucoma treatment drug, as a target compound. Fabrication of the nanoparticles of brinzolamide prodrug increases the eye penetration rate and results in high drug efficacy, compared with that of commercially available brinzolamide eye-drops formulated as micro-sized structures. In addition, the resulting nano eye-drops were not toxic to the corneal epithelium after repeated administration for 1 week. The nano eye-drops may have applications as a next-generation ophthalmic treatment.

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.

International audience; Controlling or switching the optical signal from a large collection of molecules with the minimum of photons represents an extremely attractive concept. Promising fundamental and practical applications may be derived from such a photon-saving principle. With this aim in mind, we have prepared fluorescent photochromic organic nanoparticles (NPs), showing bright red emission, complete ON–OFF contrast with full reversibility, and excellent fatigue resistance. Most interestingly, upon successive UV and visible light irradiation, the NPs exhibit a complete fluorescence quenching and recovery at very low photochromic conversion levels (

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 ...

We have fabricated well-defined nanostructures such as SiO2-coated Ag nanoparticles (NPs) connected with quantum dots (QDs) (Ag/SiO2-QDs) so as to control the fluorescence enhancement induced by localized surface plasmon resonance. Namely, the distance between Ag NP and QD should be noted as a controllable model to investigate the fluorescence enhancement effect. Actually, highly monodispersed Ag NP as a core was first coated with five thicknesses of SiO2 as a shell, and then QDs were specifically adsorbed onto the surface of the amino-functionalized SiO2-coated Ag NPs. As a result, the fluorescence intensity increased with the shell thickness as a result of excitation enhancement. On the other hand, the fluorescence intensity decreased when the shell thickness became thinner because of the induced quenching. Therefore, the distance between Ag NPs and QDs should be optimized to control and enhance the fluorescence intensity.

We have investigated silver nanoparticles (AgNPs)-accelerated photopolymerization of a diacetylene derivative, 1,6-di(N-carbazolyl)-2,4-hexadiyne (DCHD), which undergoes a phase transformation of the crystal structure from monomer to polymer during the photopolymerization. We have successfully fabricated nanocomposites of AgNPs and DCHD monomer nanocrystals by means of the modified reprecipitation method, and we monitored its photopolymerization process with Raman spectroscopy upon 532 nm excitation. Although the localized surface plasmon resonance (LSPR) wavelength of AgNPs in an aqueous dispersion was located around 400 nm, that of AgNPs in the present nanocomposites was shifted to longer wavelength region. The extinction of the nanocomposites at 532 nm became significant because of the red-shift and broadening of the LSPR, and, thus, surface plasmon-enhanced photoelectric fields on the AgNP surfaces could generate upon 532 nm excitation. As compared to the Raman spectra of bare DCHD monomer nanocrystal...

Photopolymerization of SU-8 was performed on gold films over microspheres (AuFOMs) that can provide plasmon-enhanced fields on their surfaces. Strong dependence of the photopolymerization reactivit...

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.

Organic crystals, such as phthalocyanine nanocrystal, were successfully hybridized with Pt nanoparticles using a nanohybridization technique. The presence of highly dispersed Pt nanoparticles on the surface of phthalocyanine was confirmed by the combination of transmission electron microscopy and three-dimensional electron tomography. Catalytic activities of hybridized samples with different degrees of dispersions were also examined as oxygen reduction reactivity (ORR) with a linear potential sweep method. It was found that oxygen reduction activity increased with increasing Pt dispersion, and reasonably high ORR was observed on Pt-dispersed phthalocyanine nanocrystal even at 2 wt% Pt loading.

Polydiacetylene (PDA) nanocrystals were successfully encapsulated by soap-free copolymerization of styrene monomer and hydrophilic styrene derivative. The resulting polystyrene-encapsulated PDA nanocrystals became almost uniform and spherical and could be arranged conveniently on a patterned substrate using the tapered cell method. These basic processes to fabricate ordered array structure on a substrate are very important toward photonic devices application made up of PDA nanocrystals in the near future. In addition, the formation mechanisms for encapsulation were discussed in detail.

Single-photon behavior in the emission from a single nanoparticle consisting of a single poly[2-methoxy-5-(2′-ethylhexyloxy)- p -phenylene vinylene] (MEH-PPV, molecular weight: 2,600,000 amu) chain has been investigated. Photon correlation measurements of a number of single nanoparticles revealed that the probability of single-photon emission from the single nanoparticles clearly increases, compared with that of single chains embedded in host polymer matrices, poly(methyl methacrylate) (PMMA) and polystyrene (PS). The result suggested that even a single MEH-PPV chain with high molecular weight, which does not exhibit single-photon emission in PMMA and PS, is forced to exhibit single-photon emission by adopting “compact” chain conformation like nanoparticle. Efficient exciton migration and exciton annihilation processes in the compact chain conformation most probably result in the efficient single-photon emission from the single nanoparticle. The present results indicate that multi-quantum systems consisting of a large number of chromophores, such as the MEH-PPV, can be made to behave as single-photon sources by appropriately controlling their size.

We report a fabrication of densely packed polydiacetylene nanocrystal film using a liquid–liquid interface. Polydiacetylene (pDCHD) nanocrystals was dispersed into water solution by reprecipitation method from a good solvent. Then, hexane was added to the water dispersion to create the liquid–liquid interface. pDCHD nanocrystals were assembled at the interface, when ethanol was added to the pDCHD water dispersion–hexane solution. The assembled film was transferred onto a solid substrate and the film morphology was observed by scanning electron microscope (SEM). With addition of 10 vol% of ethanol to 2.5 mM of pDCHD water dispersion–hexane solution, a densely packed pDCHD film is fabricated. Optical and electrical properties of the pDCHD film are discussed by UV–vis spectroscopy and current–voltage measurement.

In the core-shell type hybridized nanocrystals composed of silver (Ag)-core and polydiacetylene (PDA)-shell, the localized surface plasmon (LSP) from Ag-core disappeared during solid-state polymerization in the coreprecipitation method. From high-energy X-ray photoelectron spectroscopy measured with synchrotron radiation X-ray in SPring-8, it has become apparent that a Ag-core is composed of nano-sized conductive domains. Domain boundaries may cause the reduction of the conduction electron mean free path in a Ag-core, and may be responsible for LSP damping without changing the plasmon frequency. [DOI: 10.1380/ejssnt.2009.711]

Polyimide (PI) is a candidate material that is showing promise for use in a wide range of applications in several advanced technologies. In this study, we employed the reprecipitation method and subsequent imidization to prepare unique hollow PI nanoparticles (NPs) by blending a suitable polymer porogen with the PI precursor in the form of individual NPs. The hollow structures were induced through phase separation between the PI and the porogen, a process that was influenced by the compatibility between the two polymers. We then assembled multilayered films by depositing the hollow PI NPs electrophoretically onto a substrate. After spin-coating a solution of the PI precursor and then subjecting the system to thermal treatment, the individual PI NPs were bound to their adjacent neighbors, thereby improving the film strength to some extent. We obtained dense, uniformly packed films having controlled thicknesses in the range from 500 nm to 10 μm. This strategy provided films in which air voids existed betwee...

We have used the reprecipitation method and subsequent two-step imidization to fabricate highly porous polyimide (PI) nanoparticles possessing crater-like surface pores (depths, diameters: tens of nanometers) from poly(amic acid) (PAA) derivatives in the presence of poly(sodium-4-styrenesulfonate) (PSS) as a polyelectrolytic porogen. The porous structures arose presumably through segregative microphase separation of PAA and PSS (i.e. repulsion between PAA and PSS in the presence of a common solvent) and subsequent removal of PSS. The addition of this strong polyelectrolyte improved the degree of porosity of the resulting PI nanoparticles and allowed controllable release of the porogen. The resulting porous PI nanoparticles exhibited a high thermal stability (5% weight loss at temperature 450°C). This technique is suitable for the preparation of novel low-k materials and their surface-related applications. Copyright © 2008 John Wiley & Sons, Ltd.

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.

Two-dimensional ordered arrays of polystyrene microspheres (PSMSs) with a large-scale area were successfully fabricated on a lithographically patterned substrate using a so-called tapered cell. The repetition of the deposition procedure provided the subsequent second array on the first array as a template. Consequently, we succeeded in the fabrication of a Kagome structure on the hexagonally patterned substrate, and evidently observed through the corresponding fluorescence microscopy images that two types of fluorescent PSMSs were, respectively, separately arranged in the dimple and on the terrace. Namely, a potential application of the present method using a patterned substrate would be the step-by-step deposition of microspheres with different refractive indexes, and optoelectronic and magnetic properties.

The effects of microwave irradiation on the crystal sizes and morphology of diacetylene nanocrystals have been investigated carefully by controlling experimental conditions such as temperature and concentration in a reprecipitation/microwave-irradiation method. As a result, the fabrication condition of diacetylene nanowire crystals has been clarified. The formation mechanism of such nanowire crystals is also discussed.

We have studied the external-field-induced orientation of fibriform polydiacetylene nanocrystals in dispersions that we fabricated through reprecipitation followed by orientational fixation. The polymer employed was poly[1,6-di(N-carbazolyl)-2,4-hexadiyne] (polyDCHD). An AC electric field and a magnetic field were both effective agents for controlling the orientation of the nanocrystals in the dispersions; in contrast, we observed no orientational effect when applying a DC electric field. The application of the AC electric and magnetic fields led to different anisotropic orientations of the same dispersed nanocrystals. The degree of orientation depended on the AC frequency and the strength of the AC electric or magnetic field.

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.

Porous polyimide (PI) nanoparticles were fabricated using the reprecipitation method, with a second polymer as a porogen, and subsequent imidization. Poly(acrylic acid) was a suitable porogen for generating unprecedented PI nanoparticles having superficial nanopores, the sizes of which were in the range 20−70 nm. The porous morphology of the PI nanoparticles was affected mainly by the molecular weight and content of poly(acrylic acid). After thermal imidization, almost no poly(acrylic acid) remained inside the porous PI nanoparticles. Infrared spectroscopy and thermogravimetric analysis indicated that the porous nanoparticles consisted purely of PI and exhibited high thermal stability (5% weight loss temperature: 400 °C). The porous structure probably resulted from microphase separation of poly(amic acid) and poly(acrylic acid) during the reprecipitation process. This strategy provides a new means for improving the degree of porosity of PI nanoparticles, which have the potential for application as altern...