ナノ リュウシ ノ ジコ シュウセキ カ オ リヨウ シタ ポリマー ビリュウシ カイメン ノ μ コウゾウ ノ セイミツ セイギョ

博士（学術）熊本大

Preparation of High Refractive Index Composite Films Based on Titanium Oxide Nanoparticles Hybridized Hydrophilic Polymers

Optical materials with high refractive index (n) have been rapidly improved because of urgent demands imposed by the development of advanced photonic and electronic devices such as solar cells, light emitting diodes (LED and Organic LED), optical lenses and filters, anti-reflection films, and optical adhesives. One successful method to obtain high refractive index materials is the blending of metal oxide nanoparticles such as TiO2 and ZrO2 with high n values of 2.1–2.7 into conventional polymers. However, these nanoparticles have a tendency to agglomerate by themselves in a conventional polymer matrix, due to the strong attractive forces between them. Therefore, there is a limitation in the blending amount of inorganic nanoparticles. In this paper, various hydrophilic polymers such as poly(N-hydroxyl acrylamide) (pHEAAm), poly(vinyl alcohol), poly(ethylene glycol), and poly(acrylic acid) were examined for preparation of high refractive index film based on titanium oxide nanoparticle (TiNP) dispersed polymer composite. The hydrogen bonding sites in these hydrophilic polymers would improve the dispersibility of inorganic nanoparticles in the polymer matrix. As a result, pHEAAm exhibited higher compatibility with titanium oxide nanoparticles (TiNPs) than other water-soluble polymers. Transparent hybrid films were prepared by mixing pHEAAm with TiNPs and drop casting the mixture onto a glass plate. The refractive indices of the films were in good agreement with calculated values. The compatibility of TiNPs with pHEAAm was dependent on the surface characteristics of TiNPs. TiNPs with the highest observed compatibility could be hybridized with pHEAAm at concentrations of up to 90 wt%, and the refractive index of the corresponding film reached 1.90. The high compatibility of TiNPs with pHEAAm may be related to the hydrophilicity and amide and hydroxyl moieties of pHEAAm, which cause hydrogen bond formation on the TiO2 surface. The obtained thin film was slightly yellow due to the color of the original TiNP dispersion; however, the transmittance of the film was higher than 80% in the wavelength range from 480 to 900 nm

Fabrication of Hollow Silica Microspheres with Orderly Hemispherical Protrusions and Capability for Heat-Induced Controlled Cracking

Hollow silica microspheres with orderly protrusions on their outer and inner surfaces were fabricated in three simple steps: (1) suspension polymerization of a polymerizable monomer containing silica nanoparticles to obtain polymeric microspheres with a layered shell of silica particles; (2) sol–gel reaction of tetraethoxysilane (TEOS) on the surface of the microspheres to connect the silica nanoparticles; (3) removal of polymer core by calcination. The shell composed of silica-connected silica nanoparticles remained spherical even after calcination, and the characteristic surface morphology with protrusions were obtained on both inner and outer surfaces. Measurements of the mechanical strength revealed that the compression modulus of the hollow microspheres increased with increasing thickness of the silica layer, which could be controlled by changing the concentration of TEOS in the sol–gel reaction. Rapid heating of the hollow silica microspheres with the thin silica-connected layer led to silica shell cracking, and the cracks were mostly observed in the connecting layer between the silica nanoparticles. The stress was probably concentrated in the connecting layer because of its lower thickness than the nanoparticles. Such characteristic of the hollow microspheres is useful for a capsule with capability for heat-induced controlled cracking caused by internal pressure changes

Chiral H ‐aggregation‐induced large stokes shift with CPL generation assisted by α‐helical poly(L‐lysine) substructure

Fluorescent materials with large Stokes shifts have significant potential for use in optical applications. Typically, a synthetic design strategy is utilized for this purpose. In this study, we demonstrated a novel method by binding a chiral template to a nonchiral fluorescent agent without chemical modification. Specifically, α‐helical poly(L‐lysine) was employed as the chiral template, which interacted with a disulfonic fluorescent dye, such as NK2751. The dye caused excimer luminescence by inducing the formation of a chirally H ‐aggregated dimer only when poly(L‐lysine) was in an α‐helical shape. The result was a Stokes shift of 230 nm. Similar effects were not observed when the chiral template was in a random coil condition and the Stokes shift was less than 40 nm. These findings imply that H ‐aggregated dimerization, which often results in quenching, permits the electronic transitions necessary for fluorescence events by the formation of the chirally twisted state. In addition, we introduce for the first time the generation of circularly polarized luminescence using the chirality induction phenomena in a dye supported by poly(L‐lysine)

Sequential chiral induction between organic and inorganic supramolecular helical assemblies for the in situ formation of chiral carbon dots

Self-organised helical bilayers of dicationic gemini surfactants confined in helical silica nanospace were transformed in situ to carbon dots (CDots) via pyrolysis