Thermal diffusivity of polymer films by the flash radiometry method

We have developed a flash radiometry technique for the determination of the thermal diffusivity of polymer films that consists of flashing a laser pulse on the front surface of the sample and monitoring the thermal radiation from the rear surface as a function of time using an infrared detector. This method is applicable to polymer films of thickness 14–250 μm in the wide temperature range between 150 and 500 K. We have performed measurements on four polymers, including polycarbonate, polyimide, polyvinylidene fluoride, and polyethylene terephthalate. The temperature dependence of the thermal conductivity of polycarbonate can be understood by considering the phonon mean free path, and the crystallinity and orientation dependence of the thermal conductivity of polyethylene terephthalate can be explained in terms of the two-phase model proposed by Choy and Young.     

Synthesis of new visible light active photocatalysts of Ba(In(1/3)Pb(1/3)M'(1/3))O3 (M' = Nb, Ta): a band gap engineering strategy based on electronegativity of a metal component

We have synthesized new, efficient, visible light active photocatalysts through the incorporation of highly electronegative non-transition metal Pb or Sn ions into the perovskite lattice of Ba(In(1/3)Pb(1/3)M'(1/3))O3 (M = Sn, Pb; M' = Nb, Ta). X-ray diffraction, X-ray absorption spectroscopic, and energy dispersive spectroscopic microprobe analyses reveal that tetravalent Pb or Sn ions exist in the B-site of the perovskite lattice, along with In and Nb/Ta ions. According to diffuse UV-vis spectroscopic analysis, the Pb-containing quaternary metal oxides Ba(In(1/3)Pb(1/3)M'(1/3))O3 possess a much narrower band gap (E(g) approximately 1.48-1.50 eV) when compared to the ternary oxides Ba(In(1/2)M'(1/2))O3 (E(g) approximately 2.97-3.30 eV) and the Sn-containing Ba(In(1/3)Sn(1/3)M'(1/3))O3 derivatives (E(g) approximately 2.85-3.00 eV). Such a variation of band gap energy upon the substitution is attributable to the broadening of the conduction band caused by the dissimilar electronegativities of the B-site cations. In contrast to the ternary or the Sn-substituted quaternary compounds showing photocatalytic activity under UV-vis irradiation, the Ba(In(1/3)Pb(1/3)M'(1/3))O3 compounds induce an efficient photodegradation of 4-chlorophenol under visible light irradiation (lambda > 420 nm). The present results highlight that the substitution of electronegative non-transition metal cations can provide a very powerful way of developing efficient visible light harvesting photocatalysts through tuning of the band structure of a semiconductive metal oxide.     

Thermomechanical trnasitions in polyphosphazenes

Unoriented and oriented samples of two phosphazene homopolymers with chemical structure [NPX₂]_n, where X = CF₃CH₂O and p-CH₃C₆H₄O, and three unfilled and filled alkoxy-type polyphosphazene copolymers, plus one filled aryloxy-type copolymer were examined with a Rheovibron viscoelastometer. Measurements were made from ?120°C to temperatures above the T(1) transition of the respective polymers. The effects of orientation and repeated temperature cycling through the T(1) transition temperatures were studied. The overall physical behavior of these polyphosphazenes was dominated by changes that occurred in the primary softening dispersion and the mesomorphic or T(1) transition region. The enthalpy of the T(1) transition and the T(1) temperature were investigated by differential scanning calorimetry (DSC) as a function of temperature cycling in the T(1) region; for instance, the change in enthalpy in the T(1) region is about an order of magnitude larger than it is at T_m for the unfilled polyphosphazene homopolymers. The T_g's of the polyphosophazenes were also determined. Density measurements were made on oriented and unoriented specimens by the flotation method. Although an increase in density (and crystallinity) was observed when specimens were cycled through the T(1) transition, no significant difference in density was found between oriented and unoriented materials. Some discussion of the molecular origin of the T(1) transition is included.     

Isomorphous substitution effects on the thermally induced interlayer reaction inN-hexylammonium layered aluminosilicates

It was found that the variation in the thermally evolved gases obtained by decomposition ofn-hexylammonium layered aluminosilicates is mainly due to the difference between octahedral and tetrahedral coordination of aluminium in the lattice and also to the contribution of the excess negative layer charges.ESCA, TG-DSC, GC and MS results indicate that the layer charge originated from the octahedral substitution induces only desintercalation ofn-hexylamine around 250–360°C, whereas that from the tetrahedral substitution induces the catalytic decomposition reaction involving the cleavage of C–N and C–C bonds at 350–450°C with the evolution of ammonia, ethylene, pentene and hexene.It is therefore concluded that the former reaction step is a simple desintercalation, but for the latter one a Brönsted acid catalytic mechanism is proposed.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

(Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics with simultaneous addition of CeO2 and La2O3

(Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (BNBT-6) with simultaneous addition of 0.5 mol% CeO₂ and 0.25, 0.5 and 0.75 mol% La₂O₃, respectively, was prepared by a conventional ceramic fabrication technique. An addition of 0.5 mol% CeO₂ together with 0.5 mol% La₂O₃ enhanced the piezoelectric and dielectric constant of BNBT-6 ceramics significantly. At room temperature, this composition exhibits a high piezoelectric constant (d₃₃=162×10^-12 C/N) and relatively low dielectric loss (cos=2.0%) at 1 kHz. X-ray diffraction pattern shows that the coexistence of tetragonal and rhombohedral phases in the BNBT-6 composition was not changed by adding CeO₂+La₂O₃, and they diffused into the BNBT lattice during sintering. SEM observation indicates that a small amount of CeO₂+La₂O₃ almost does not affect the microstructure. PACS 77.65.Bn; 77.84.Dy; 77.22.-d     

Controllable synthesis and optical properties of novel ZnO cone arrays via vapor transport at low temperature

Novel ZnO cone arrays with controllable morphologies have been synthesized on silicon (100) substrates by thermal evaporation of metal Zn powder at a low temperature of 570 degrees C without a metal catalyst. Clear structure evolutions were observed using scanning electron microscopy: well-aligned ZnO nanocones, double-cones with growing head cones attached by stem cones, and cones with straight hexagonal pillar were obtained as the distance between the source and the substrates was increased. X-ray diffraction shows that all cone arrays grow along the c-axis. Raman and photoluminescence spectra reveal that the optical properties of the buffer layer between the ZnO cone arrays and the silicon substrates are better than those of the ZnO cone arrays due to high concentration of Zn in the heads of the ZnO cone arrays and higher growth temperature of the buffer layer. The growth of ZnO arrays reveals that the cone arrays are synthesized through a self-catalyzed vapor-liquid-solid (VLS) process.     

Aripiprazole?Montmorillonite: A New Organic–Inorganic Nanohybrid Material for Biomedical Applications

Poor aqueous solubility and the unpleasant taste of aripiprazole (APZ) have been recurring problems, owing to its low bioavailability and low patient tolerance, respectively. Herein, we prepared a nanohybrid system that was based on a bentonite clay material, montmorillonite (MMT), which could both mask the taste and enhance the solubility of APZ (i.e., APZ‐MMT). To further improve the efficacy of this taste masking and drug solubility, APZ‐MMT was also coated with a cationic polymer, polyvinylacetal diethylamino acetate (AEA). In vitro dissolution tests at neutral pH showed that the amount of drug that was released from the AEA‐coated APZ‐MMT was greatly suppressed (<1 %) for the first 3 min, thus suggesting that AEA‐coated APZ‐MMT has strong potential for the taste masking of APZ. Notably, in simulated gastric juice at pH 1.2, the total percentage of APZ that was released within the first 2 h increased up to 95 % for AEA‐coated APZ‐MMT. Furthermore, this in vitro release profile was also similar to that of Abilify®, a commercially available medication. In vivo experiments by using Sprague–Dawley rats were also performed to compare the pharmacokinetics of AEA‐coated APZ‐MMT and Abilify®. AEA‐coated APZ‐MMT exhibited about 20 % higher systemic exposure of APZ and its metabolite, dehydro‐APZ, compared with Abilify®. Therefore, a new MMT‐based nanovehicle, which is coated with a cationic polymer, can act as a promising delivery system for both taste masking and for enhancing the bioavailability of APZ.