Copolymerization of methyl vinyl ketone with styrene in the presence of cobalt(II) nitrate

Copolymerization of methyl vinyl ketone (MVK) with styrene was carried out at 50°C in the presence of cobalt(II) nitrate. The resulting monomer reactivity ratios decreased with an increasing concentration of the cobalt salt. This finding suggests that the metal salt participates in the propagation step of the copolymerization. Absolute copolymerization parameters were determined by assuming a three-component system as free MVK (M₁), MVK complexed with cobalt(II) nitrate (M₂), and styrene (M₃): k₁₁/k₁₂ = 0.184, k₁₁/k₁₃ = 0.235, k₂₂/k₂₁ = 7.18 × 10⁻², k₂₂/k₂₃ = 6.79 × 10⁻⁴, k₃₃/k₃₁ = 0.380, and k₃₃/k₃₂ = 2.77 × 10⁻³, and Q₂ = 19.65 and e₂ = 2.83. The complexed MVK monomer is more reactive to the polymer radical with the terminal styrene unit than the free MVK. Very small values for the monomer reactivity ratios, k₂₂/k₂₃ and k₃₃/k₃₂, show the marked alternating tendency for the copolymerization of the complexed monomer with styrene. In practice, however, alternating copolymer could not be obtained because of the poor solubility of cobalt(II) nitrate.     

Dependence of sonochemical luminescence on various sound fields

To understand the effect of the sound field on sonochemical luminescence, the exact sound pressure must be determined in each field. In this study it was determined by the Shlieren method, which measures the sound pressure without mixing the sound fields. We compared the efficiency of the sonochemical luminescence in three different ways: changing the diameter of the transducer, combining two transducers to obtain crossed propagating directions and surrounding the sound field by a glass cylinder. In the last case cylinders with various sizes were studied. We found that (i) at the same sound pressure, the larger transducer induces stronger luminescence per unit volume, (ii) driving two transducers produces stronger luminescence than the sum of each transducer and (iii) a glass cylinder surrounding the sound field induces stronger luminescence.     

Relation between the thermal behavior of polyacrylonitrile and polymerization factors

In order to clarify the mechanism to produce the large dispersion of the exothermic peak temperature (T_pk) of polyacrylonitrile, a systematic and quantitative study was made by means of the differential thermal analysis and the viscosity measurment. General tendency between T_pk and the polymerization methods was reconfirmed. Under a controlled condition (i.e., aqueous solution system), presence of N,N-dimethyl formamide or isopropyl alcohol produced a lower T_pk of resulting polymer, while presence of activator produced a higher T_pk. Thus, the large dispersion of T_pk (250–300°C) can be explained inclusively in terms of a single reaction factor, i.e., chain transfer mechanism. Particularly in the above third case it was shown that owing to strong and rapid chain transfer to activator, some kind of secondary reaction (caused by propagating chain end radical), probably chain branching which deteriorates the higher thermal quantity of molecule, is restrained effectively. Furthermore, some specific behaviors (i.e., cooperativeness and dynamic character, etc.) were observed in this reaction of PAN in solid amorphous phase.     

Harmonic waves in three-dimensional elastic composites

For a periodic elastic composite which consists of a matrix and fibers with finite dimensions (i.e. a three-dimensional problem), here are given estimates for eigenfrequencies and eigenfunctions. Calculations are based on a new quotient which has been proposed by Nemat-Nasser. The periodic character of the eigenfrequencies is pointed out, and illustrative examples are given.     

Structure and thermochromic solid-state phase transition of poly (3-alkylthiophene)

In order to clarify the structural changes that occur in the thermochromic phase transition of poly (3-dodecylthiophene) [P3DT] and poly (3-hexylthiophene) [P3HT], the temperature dependence of x-ray diffraction and Fourier transform infrared spectra was measured. (1) Orthogonal unit-cell parameters were determined at room temperature: a=25.83 Å, b=7.75 Å, c (fiber axis)=7.77 Å for P3DT and a=16.63 Å, b=7.75 Å, and c=7.77 Å for P3HT. A large variation of the a-axis length between P3DT and P3HT indicates the extended trans conformation for the alkyl side chains which are oriented along the lateral a-axis direction. (2) The interplanar spacing, intensity, and integral width of the x-ray (h00) and (00l) reflections were found to change drastically in the transition region. (3) Polarized infrared measurements at high temperature revealed a marked increase of the gauche band intensity for the alkyl side group modes followed by a decrease in the band intensity of the thiophene ring modes. (4) The layer reflections of the x-ray fiber diagram become diffuse at high temperatures, indicating that the transition occurs in a liquidcrystalline manner with the orientation of the main chain axes preserved but with almost no axial correlation between the neighboring main chains. These results provide experimental support for the structural model proposed earlier: as the temperature increases, the trans-type side chains begin to disorder by introduction of gauche bonds. This disordering disrupts the regularity of the main chain conformation and decreases the effective length of the polythiophene conjugated system.     

A trial of the gauge theory for the stress-function space

Following Golebiewska-Lasota and Edelen, a gauge structure existing in the field of the stress and the stress function is demonstrated, on the basis of an electromagnetic analogy given elsewhere. The four-tensors and four-vectors are used to state the set of fundamental equations, and the gauge condition and the gauge transformations are given in a similar way to electromagnetic theory.     

Direct deposition of gold nanoparticles onto polymer beads and glucose oxidation with H2O2

Gold nanoparticles (Au NPs) were deposited directly from aqueous solution of diethylenediaminegold(III) complex onto polymer beads commercially available, such as poly(methyl methacrylate) (PMMA), polystyrene (PS), and polyaniline (PANI) without surface modification. The dropwise addition of NaBH4 to reduce Au(III) was found to be very effective to obtain small Au0 NPs with a narrow size distribution except for PANI. The catalytic performance of Au NPs deposited on polymer beads for H2O2 decomposition and glucose oxidation with H2O2 were more significantly affected by the kinds of polymer supports than by the size of Au NPs. The equimolar oxidation of glucose with H2O2 could be operated by controlling the decomposition rate of H2O2 over Au/PMMA.     

Characterization of chitosan nanofiber fabric by electrospray deposition: electrokinetic and adsorption behavior

Cationic biopolymer nanofiber fabrics were prepared from a chitosan/poly(ethylene oxide) blend solution by electrospray deposition. Their electrokinetic properties and DNA adsorption behavior were analyzed as a function of pH. The zeta potential was determined from streaming potential/streaming current measurements. The adsorption of DNA onto the fabrics was investigated by spectrophotoscopy. The adsorption behavior of DNA correlated well with the electrokinetic properties of the fabrics. This revealed that the electrokinetic approach was a useful option for characterization of novel nanofiber assemblies made by the electrostatic spray process. In addition, these results provided fundamental information about chitosan nanofiber fabrics for both biomedical and analytical applications.     

Platonic hexahedron composed of six organic faces with an inscribed Au cluster

The structures of nanomaterials determine their individual properties and the suprastructures they can form. Introducing anisotropic shapes and/or interaction sites to isotropic nanoparticles has been proposed to extend the functionality and possible suprastructure motifs. Because of symmetric anisotropy, Platonic solids with regular polygon faces are one of the most promising nanoscale structures. Introduction of Platonic solid anisotropy to isotropic nanomaterials would expand the functionality and range of possible suprastructure motifs. Here, we demonstrate a novel strategy to obtain nano-Platonic solids through the face coordination of square porphyrins on an inscribed Au sphere with adequate size. The face coordination of the multidentate porphyrin derivatives, with four acetylthio groups facing the same direction, on the Au cluster encased the Au cluster in a Platonic hexahedron with six porphyrin faces. Transmission electron microscopy, mass spectrometry, elemental analysis, and scanning tunnelling microscopy were used to confirm the formation of the nano-Platonic hexahedron.     

Effect of collision and velocity model of lattice Boltzmann model on three-dimensional turbulent flow simulation

Various collision and velocity models of the lattice Boltzmann model (LBM) were compared to determine their effects on the efficiency of a three-dimensional homogeneous isotropic decaying turbulent flow simulation. We determined that a decrease in the number of velocities, in particular, 13-velocities, which can be used in the quasi-equilibrium lattice Boltzmann and in the multiple-relaxation time models (MRT), could considerably decrease the computational effort. However, decreasing the number of velocities deteriorates the stability and the accuracy of the results. By comparing the collision models, we also determined that the stability of the entropic lattice Boltzmann model (ELBM), and 19- and 27- velocity MRT is much higher than in other models. However, the numerical viscosity introduced by the ELBM underestimates the enstrophy, and the computational effort increases because of the calculation overhead required to solve the additional equations if special care is not given to the calculation.