Effects of vapor‐phase‐formaldehyde treatments on thermal conductivity and diffusivity of ramie fibers in the range of low temperature

To understand the influence to thermal conductivity by bridging in the polymer fibers, the thermal conductivity, and thermal diffusivity of ramie fiber and those bridged by formaldehyde (HCHO) using vapor‐phase method (VP‐HCHO treatment) were investigated in the lower temperature range. The thermal conductivities of ramie fiber with and without VP‐HCHO treatments decreased with decreasing temperature. Thermal diffusivities of ramie fiber with and without VP‐HCHO treatments were almost constant in the temperature range of 250–50 K, and increased by decreasing temperature below 50 K. Thermal conductivity and thermal diffusivity of ramie fiber decreased by VP‐HCHO treatment. The crystallinities and orientation angles of ramie fibers with and without VP‐HCHO treatment were measured using solid state NMR and X‐ray diffraction. These were almost independent of VP‐HCHO treatment. Although tensile modulus decreased slightly by VP‐HCHO treatment, the decrease could not explain the decrease in thermal conductivity and diffusivity with decreasing sound velocity. The decrease of the thermal diffusivity and thermal conductivity by VP‐HCHO treatment suggested the possibility of the reduction of the mean free path of phonon by HCHO in VP‐HCHO treated ramie fiber. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2754–2766, 2005     

Sterically stabilized polypyrrole–palladium nanocomposite particles synthesized by aqueous chemical oxidative dispersion polymerization

Aqueous chemical oxidative dispersion polymerizations of pyrrole using PdCl₂ oxidant were conducted using water-soluble polymeric colloidal stabilizers in order to synthesize polypyrrole–palladium (PPy–Pd) nanocomposite particles in one step. PPy–Pd nanocomposite particles with number average diameters of approximately 30 nm were successfully obtained as colloidally stable aqueous dispersions, which were stable at least for 7 months, using poly(4-lithium styrene sulfonic acid) colloidal stabilizer. The resulting nanocomposite particles were extensively characterized with respect to particle size, size distribution, colloidal stability, nanomorphology, surface/bulk chemical compositions, and conductivity. X-ray photoelectron spectroscopy indicated the existence of poly(styrene sulfonic acid) colloidal stabilizer on the surface of the nanocomposite particles. Transmission electron microscopy studies confirmed that nanometer-sized Pd nanoparticles were distributed in the PPy matrix.     

Colloidal crystallization of poly(n-butyl acrylate) spheres in deionized aqueous suspension and the melting during dryness

Colloidal crystallization of poly(n-butyl acrylate) spheres (ammonium persulfate-poly(n-butyl acrylate) (APS-PBA), 320?±?50 nm in diameter) was studied in deionized aqueous suspension. Coexistence of the crystal and distorted crystal structures was observed by the reflection spectroscopy. The critical concentrations of melting were ca. 0.01 and 0.03 in volume fraction in the presence of ion-exchange resins and in their absence, respectively. Crystal structures melted away during dryness by fusion of each spheres on the substrates, i.e., cover glass, watch glass, and Petri glass dish. Thickness profiles of the dried film changed sharply from the broad ring to the round hill as sphere concentration increased. The sharpness parameter S was evaluated from the ratio of the film size (diameter) against the full width at half maximum in the thickness profiles of the ring and/or the round hill. The S values decreased sharply from 30 to 1.2 as initial volume fraction of the spheres increased from 0.0005 to 0.1. The S values were significantly low compared with those of typical colloidal spheres, which supports the aggregate and/or fusion of the spheres resulting in their low convectional flow during dryness. The round hill profile at the high sphere concentration also supports that the fusion takes place easier during dryness. Microscopic observation of the dried film supports the formation of the homogeneous fused structures. It was clarified that colloidal crystallization of APS-PBA spheres takes place by the extended electrical double layers around the spheres like typical colloidal crystals of hard spheres. However, APS-PBA spheres are not so stable by the fusion especially at the high sphere concentrations and on the substrates.     

Discrimination of ionic pollutants except condensation nuclei of acid fog using an ultrasonic humidifier.

Fog droplets in the atmosphere are first produced by the activation of cloud condensation nuclei (CCN), which are originally some ionic compound. Subsequently, the nuclei grow by vapor diffusion. Fog droplets are polluted through the activation process and successive diffusion growth and residence (post activation). We cannot distinguish the effects of the two pollution processes of natural fog water samples. We found that fog droplets can be produced artificially without CCN using an ultrasonic humidifier. Because the artificial fog droplets are not polluted by CCN, the movement of the fog droplets in natural air will take up some pollutants in the air. Consequently, the two pollution processes of fog (the activation of CCN and the post activation process) can be discriminated using data from field experiments. This sampling analytical method is extremely important for further research regarding fog, clouds and environmental chemistry.     

Synthesis of macrocyclic bis(phenylbenzoxazole) derivatives via tandem claisen rearrangement and their fluorescence behavior

Novel macrocyclic bis(phenylbenzoxazole) derivatives were easily synthesized from macrocyclic isobutenyl bis(amide‐ether)s by tandem Claisen rearrangement and subsequent intramolecular cyclization of the amide‐phenol intermediates. The position of substitution of the oligoethylene glycol moiety on the phenylamido groups of the macrocycles did not have a large effect on the yields of the bis(benzoxazole)s for the meta and para derivatives. The fluorescence quantum yields of most of the macrocyclic bis(benzoxa‐zole)s were lower than those of the corresponding nonmacrocyclic bis(benzoxazole) model compounds. The quantum yields of the para‐substituted macrocyclic bis(benzoxazole)s were clearly lower than those of the model compounds and decreased with increasing length of the oligoethylene chain.     

Enhanced photoluminescence of InGaAs quantum dots induced by nanoprobe indentation

We have found in the nanoprobe-photoluminescnece (PL) measurement that the PL from InGaAs quantum dots was enhanced remarkably by small elastic indentation of the nanoprobe onto the sample surface. In order to clarify the mechanism of the PL enhancement, the nanoprobe-induced strain distribution and the energy-band profiles in the bulk GaAs have been calculated on the bases of linear continuum elastic theory and six-band strain Hamiltonian. It was found that the nm-scale strain modulation by the nanoprobe indentation results in the confinement potential for light holes 50–70 nm beneath the nanoprobe, revealing that the hole accumulation into the minimum causes the PL enhancement.     

Preparation and characterization of redox cellulose Langmuir–Blodgett films containing a ferrocene derivative

The 3‐ferrocenoylpropanoyl group, one of the redox species, was introduced at C‐2 and/or C‐3 positions of 6‐O‐(4‐stearyloxytrityl)cellulose. The spreading behavior of the cellulose derivatives on the water surface and the properties of Langmuir–Blodgett (LB) films were investigated. The surface pressure–area isotherm of the cellulose monolayer was changed by the subphase temperature. Uniform monolayers of 6‐O‐(4‐stearyloxytrityl)cellulose 3‐ferrocene propionate (STCFc) could be deposited successively onto several substrates by the horizontal lifting method at 10 mN m^?1, and this produced X‐type LB films. The successive uniform depositions of STCFc were confirmed by ultraviolet–visible absorption spectra. X‐ray diffraction measurements indicated that the thickness of the STCFc molecules in the LB films was 1.99 nm. Fourier transform infrared spectroscopy measurements supported the idea that hydrocarbon chains in the LB films were highly ordered (trans‐zigzag) and oriented considerably perpendicular to the surface of the substrate. Moreover, the C?O group of the ferrocenoyl groups was perpendicular to the surface of the substrate, and the ferrocene group was occupied in the water phase. Cyclic voltammograms for the STCFc monolayer on a gold electrode exhibited surface waves. The interfacial electron‐transfer process between the redox site incorporated into the cellulose LB monolayer and the electrode surface was fast enough at a scanning rate lower than 100 mV s^?1. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5023–5031, 2005