Synthesis of polyynes in a submerged electric arc in organic solvents

The products formed by the electric arc between graphite electrodes submerged in organic solvents like acetonitrile, n-hexane and methanol consist of a series of polyynes having the general chemical structure: H(CC)_mH (with m an integer 1,2,3,…m). The polyynes were separated through liquid chromatography (HPLC) and identified through their characteristic electronic absorption spectra recorded by a diode-array detector. When acetonitrile was arced at −40 °C, the entire polyynes series to m=9 (chain with 18 carbon atoms) were produced. Instead, at room temperature the entire polyynes series to m=8 (chain with 16 carbon atoms) were obtained. Similar results were obtained by arcing graphite electrodes in n-hexane and in methanol. The purest polyynes mixture is obtained in methanol while in n-hexane and in acetonitrile by-products are formed together with the polyynes series. In particular, in acetonitrile, a series of monocyanopolyynes was detected together with the normal polyynes series.The polyynes are formed by the vaporization of the elemental carbon from the graphite electrodes and dissolved in the solvent where the electrodes are submerged. The demonstration that the polyynes series H(CC)_mH is hydrogen-capped is based on several experimental data from electronic and FT-IR spectroscopy as well as their reactivity with a specific reagent for terminal acetylenes. Some chemical properties of the polyynes solutions (hydrogenation, oxidation) are also treated and discussed.     

MALDI-TOF MS characterization of polystyrene synthesized by ATRP

In this work, we investigated the peculiar peaks found in the MALDI-TOF mass spectra of polystyrenes (PS) with a bromine end prepared by atom transfer radical polymerization when silver trifluoroacetate (AgTFA) and THF were used as cationization agent and solvent, respectively, in the MALDI sample preparation. In the MALDI mass spectrum, PS with a terminal bromine was not detected but the species with a terminal double bond (U series), and −22 m/z (T series) and +18 m/z (W series) peaks relative to U series appeared as major peaks. While the U species was reported as a result of the elimination reaction of HBr, but the origin and the structure of the other species have not been elucidated. We found that the −22 m/z peak of U_n is in fact T_n-2, which is the adduct of THF and the anion of the Ag salt, TFA⁻ (+186 m/z) to U_n-2. The +18 m/z peak was confirmed to be the species with a terminal OH. All these reactions were catalyzed by Ag salt and the T and W series were not found at all when NaTFA was used as a cationization agent.     

Compatibility and neutron scattering studies of mixtures of polystyrene with poly(2,6-dimethyl 1,4-phenylene oxide) and its brominated derivatives

Several narrowly disperse polystyrenes (PS) were mixed with three series of random copolymers of 2,6-dimethyl phenylene oxide (also known as xylenyl ether (XE)) and 3-bromo-2,6-dimethyl phenylene oxide (BrXE), each series having a fixed chain length. The critical BrXE comonomer concentration necessary to induce phase separation, x_c′ was characterized for each blend series by a number of techniques. x_c was extrapolated to a value of about 0.5 at infinite chain lengths of each polymer of the blend. This finding supports the negative heat of mixing of PS with PXE reported by other workers. Small-angle neutron scattering studies were carried out using small amounts of perdeuteropolystyrene in several matrices for which single phase behaviour had been shown to exist. The radius of gyration R₂ and the second virial coefficient A₂ were greatest in the pure PXE matrix reflecting the goodness of this material as a ‘solvent’ for PS. In matrices containing $\text{50\%}\text{PS}\text{50\%}$ copolymer, A₂ extrapolated to zero at x_c ≥ 1 which was consistent with the phase behaviour of this series of blends.     

Synthesis of exfoliated poly(styrene-co-acrylonitrile) copolymer/silicate nanocomposite by emulsion polymerization; monomer composition effect on morphology

Two types of SAN/silicate nanocomposites were prepared to set up the relationship between the composition of monomers and the resultant morphology of the composites using a pristine sodium montmorillonite (Na-MMT). SAN I series were synthesized with acrylonitrile in initial stage and a mixture of styrene and acrylonitrile in increment stage. SAN II series were prepared with the mixture of styrene and acrylonitrile throughout polymerization. SAN I series showed exfoliated states but SAN II series exhibited intercalated states because SAN I series consisted of hydrophilic AN initially. The chemical affinity between monomer and silicate had a strong influence on the morphology of SAN/silicate nanocomposites. The exfoliated SAN I series had enhanced moduli and glass transition temperatures, T_g, compared to the intercalated SAN II series and pure SAN.     

Chemo-Enzymatic Synthesis and Antimicrobial Evaluation of Alkyloxy Propanol Amine-Based Cationic Ether Lipids

The present study involved the synthesis and antimicrobial evaluation of alkyloxy propanol amine-based cationic lipids N,N-dimethyl-1-octadecylamino-3-alkyloxy-2-propanol (series A, 7a–e) and N-methyl-N,N-di-(2-hydroxy-3-alkyloxy-2 propyl) octadecylamine (series B, 9a–e) and their acetylated derivatives (8a–e and 10a–e). A simple three-step chemo-enzymatic approach was employed for the synthesis of 7a–e and 9a–e in 71–80 and 67–88 % yields, respectively. The first step involved the synthesis of a series of glycidyl ethers from a series of alcohols (C₄, C₈, C₁₀, C₁₂, C₁₄) which were opened in the second step with octadecylamine to obtain 1-octadecylamino-3-alkyloxy-2 propanol (5a–e) and N,N-di-(2-hydroxy-3-alkyloxypropyl) octadecylamine (6a–e). In the third step, alkyloxy propanolamines (5a–e, 6a–e) were quaternized using methyl iodide to yield quaternized ammonium salts. The quaternized ammonium salts were enzymatically acetylated using Candida antarctica lipase-B based immobilized enzyme Novozym 435 to obtain their acetylated derivatives. The quaternized salts as well as their acetylated derivatives were evaluated for antibacterial and antifungal properties. The title compounds were found to possess moderate to good antibacterial activities against all the studied bacterial strains namely, Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Klebsiella aerogenes compared to streptomycin and cetyl trimethyl ammonium bromide (CTAB). The title compounds exhibited relatively good antifungal activities against Candida albicans and no significant activities against other fungal strains namely, Saccharomyces cerevisiae, Rhizopus oryzae and Aspergillus niger when compared to amphotericin B and CTAB.     

Aliphatic acid esters of (2-hydroxypropyl) cellulose—Effect of side chain length on properties of cholesteric liquid crystals

A series of aliphatic acid esters of (2-hydroxypropyl) cellulose (C_nPC) were synthesized via the esterification of aliphatic acid chloride and (2-hydroxypropyl) cellulose (HPC). The liquid crystalline (LC) phases and transitions were investigated using differential scanning calorimetry, wide-angle X-ray diffraction (WAXD), and polarized light microscope (PLM) techniques. This series of C_nPC polymers exhibited characteristic features of cholesteric LC phases between their glass transition and isotropization temperatures. The cholesteric LC characteristics were studied utilizing an ultraviolet/visible/near infrared spectrometer in a reflection mode. It was confirmed that, with an increase in the number of methylene units in the side chains of this series of C_nPC polymers, there was an increase, on the scale of nanometers, in the layer spacing values for the cholesteric LC phases measured by WAXD. This periodic layer spacing represents the thickness of the neighboring twisted layers in a helical structure. Based on a unique significant red shift of the maximum reflection peak for the LC phases in this series of C_nPCs, it is evident that the pitch distance in the helical structure also increases with an increase in the length of methylene units in the side chains.     

Structural characterization of poly(ε-caprolactone)-grafted cellulose acetate and butyrate by solid-state C NMR, dynamic mechanical, and dielectric relaxation analyses

Investigations were made into the molecular dynamics and intercomponent mixing state in solid films of two series of cellulosic graft copolymers, cellulose acetate-g-poly(ε-caprolactone) (CA-g-PCL) and cellulose butyrate-g-PCL (CB-g-PCL), both series being prepared over a wide range of compositions with CAs or CBs of acyl DS ≈ 2.1, 2.5, and 2.95. It was shown by T_1ρ^H measurements in solid-state ¹³C NMR spectroscopy that all the copolymer samples, except ones using CA of DS = 2.98, formed an amorphous monophase in which the trunk and graft components were mixed homogeneously at least in a scale of a few nanometers. However, those copolymer samples gave, more or less, a response of dynamic heterogeneity, when examined under mechanical oscillation. Through dielectric relaxation measurements, a clear comparison was made between the CA-g-PCL and CB-g-PCL series, regarding the cooperativeness in segmental motions of the trunk and graft chains, directly associated with the extent of the dynamic heterogeneity. The cooperativeness was generally higher in the CB-based copolymer series, probably due to working of the butyryl substituent as an internal compatibilizer.     

The structural properties of B–O codoped diamond films

Using Raman spectroscopy and positron annihilation technology (PAT), we investigate the structural properties of the codoped samples by implanting boron and oxygen ions into the intrinsic diamond films (called BO series) and by implanting oxygen ions into the diamond films doped with small amounts of boron in chemical vapor deposition (called CVDBO series). It is found that after 1000 °C annealing, the full width at half maximum (FWHM) value of diamond peak in Raman spectrum reduces, the amount of diamond increases above 99.6% and the stress changes from compression to tension. More important, the FWHM value in CVDBO series decreases by 1.6 cm^{? 1} after 1000 °C annealing, which is larger than that in the BO series with a decrease of 0.2 cm^{? 1}, showing that the annealing prefers to more significantly reduce the defect concentration in CVDBO series. Also, the PAT measurements indicate that the S_n value of CVDBO series is smaller than that of BO series after 800 °C annealing, suggesting that CVDBO series has lower defect concentrations. It is revealed that the co-doping that implanting oxygen ions into the low concentration B-doped diamond films can give a better restoration of the damaged diamond lattice by oxygen ion implantation after high temperature annealing. The intrinsic mechanism is also discussed.     

Self-assembly of amphiphilic liquid crystal block copolymers containing a cholesteryl mesogen: Effects of block ratio and solvent

We report on the self-assembly, in water and in bulk, of amphiphilic liquid crystal block copolymers consisting of a cholesterol-based smectic LC polymer block (PAChol) and poly(ethylene glycol) (PEG) block. Two series of block copolymers, PEG₄₅-b-PAChol and PEG₁₁₄-b-PAChol (45 and 114 are the degree of polymerization of PEG blocks) with different hydrophilic/hydrophobic weight ratios were synthesized and characterized in detail. Depending on the diblock composition, smectic polymer vesicles and/or nanofibers were formed by adding water into a dilute solution of copolymers in dioxane. If THF is used instead of dioxane as solvent, solid spherical aggregates were obtained upon water addition for PEG₄₅-b-PAChol series, while macroscopic precipitation occurred for PEG₁₁₄-b-PAChol series. The mesomorphic and microphase segregation structures of the block copolymers in bulk were studied by X-ray scattering, DSC and POM. The interdigital smectic A (SmA_d) phase with a lamellar period of 4.25 nm was detected in all block copolymers. For PEG₁₁₄-b-PAChol₅ (PEG/PAChol weight ratio = 66/34) and PEG₁₁₄-b-PAChol₁₂ (45/55), lamellar type of microphase segregation was observed.     

Enhancement of oxygen/pressure sensing performance of Eu3+-doped YSZ phosphors via Bi3+ sensitization

The effects of the incorporation of a Bi³⁺ sensitizer on the phosphorescence properties and oxygen partial pressure sensitivity of the Eu³⁺ doped yttria stabilized zirconia (YSZ) phosphors were studied using a lifetime-based optical measurement system. Two series of YSZ: Eu phosphors were investigated in this work: Eu_0.01Bi_xY_0.07-xZr_0.92O_1.96 substitutional series and Eu_0.01Bi_xY_0.07Zr_0.92-xO_1.96-0.5x additive series. The phosphorescence intensity of the additive-series phosphors was enhanced by 47% excited at 405 nm with a Bi³⁺ concentration of 2 mol% due to the energy transfer between Bi³⁺ and Eu³⁺. In contrast, the phosphorescence intensity of the substitutional-series phosphors decreased as the Bi³⁺ concentration increased. The phosphorescence lifetimes for both series phosphors were highly sensitive to oxygen partial pressure at elevated temperatures. With increasing Bi³⁺ concentration, the oxygen sensitivities of both series were enhanced initially, which was related to the increment of concentration dependent non-radiative decay via cross-relaxation between Bi³⁺ and Eu³⁺. With 1 mol% Bi³⁺ doping, the oxygen sensitivity was enhanced by 28% and 12% for substitutional-series and additive-series phosphors, respectively. As the Bi³⁺ concentration further increased, the oxygen sensitivities of both series declined, which was attributed to the energy transfer between Bi³⁺, the formation of Bi³⁺ aggregates as well as the increase of the Eu³⁺ site symmetry. The results of this study not only provided valuable references for phosphor thermometry, but also offered new ideas for developing high-temperature non-contact pressure sensors.     

Electrical and light-emitting properties from (111)-oriented homoepitaxial diamond p–i–n junctions

We have succeeded in fabricating a (111)-oriented diamond p–i–n junction with high crystalline quality intrinsic layer and with low series resistance. The series resistance of this diamond p–i–n junction was improved by decreasing the resistivity and specific contact resistance of n-type layer, which is allowed to inject higher current while maintaining lower junction temperature. Current density–voltage characteristics showed a rectification ratio of 10⁶ at ± 15 V at room temperature. A clear ultraviolet emission at around 235 nm due to free exciton recombination was observed at a forward current, while the broad visible light emission from deep levels was significantly suppressed. Moreover, stronger excitonic emission by two orders of magnitude than that of (001)-oriented diamond p–i–n junctions with high series resistance was realized.     

Effect of Pyridine on the Mesophase of Teraryl Liquid Crystals: A New Series of Nematic Liquid Crystals Named 2-(4-Alkoxybiphen-4′-yl)-5-methylpyridines

A new series of teraryl 2-(4-alkoxybiphen-4′-yl)-5-methylpyridines (nO-PPPyMe, n = 3–8) nematic liquid crystal compounds, bearing a biphenylene core and a picoline terminus, were synthesized using a short two-step reaction, and overall yields between 34% and 38% were obtained. Spectral analysis results were in accordance with the expected structures. The thermotropic behavior of the teraryl liquid crystal compounds was investigated through polarized optical microscopy and differential scanning calorimetry. All compounds exhibited a solely enantiotropic nematic phase at the medium–high temperature range of 162.4–234.2 °C. Furthermore, the results for the nO-PPPyMe series were analyzed relative to three other compound series, mO-PPPyCN (m = 2–8), iO-PPQMe (i = 3–8) and xO-PPyPMe (x = 1–10). Consequently, the effect of pyridine on the mesophase of teraryl liquid crystals was demonstrated.     

Influence of block composition on structural,thermal and mechanical properties of novel aliphatic polyester based triblock copolymers

A series of ABA type triblock copolymers [Poly(lactide)-block-poly(hexamethylene 2,3-O-isopropylidene tartarate)-block-poly(lactide)] PLA-b-PHIT-b-PLA based on renewable monomers l-tartaric acid and l-lactide have been synthesized and the effect of the PLA chain length on the properties of the triblock copolymers has been systematically investigated. The block nature of the copolymers was established by differential scanning calorimetry (DSC) which showed two glass transition temperatures (T_g) corresponding to PHIT and PLA blocks. Solution cast films of these triblock copolymers turned out to be brittle in nature and to overcome this, ε-caprolactone was copolymerized with l-lactide to generate a separate series of triblock copolymers [PLA-ran-PCL]-b-PHIT-b-[PLA-ran-PCL]. Our study systematically demonstrates that the PLA-to-PCL ratio in the outer block composition influences the mechanical properties via a delayed post-yield stress drop phenomenon. The study further elaborates the time-synchronized strain-field analysis of the novel triblocks to be a convincing approach for the characterization of micro-deformation modes.     

Wool wax acids: A review

Wool wax acids consist predominantly of alkanoic,α-hydroxy andω-hydroxy acids. Each group contains normal, iso, and anteiso series of various chain length. Practically all the acids are saturated. The average weight-percent of the various series is based on recently published results.     

The effect of ion-polymer binding on ionic diffusion in dicarbazole-based conducting polymers

An electrochemical polymerization and characterization is reported on a series of eight dicarbazole-type conducting polymers with different attached functional groups. The influence of the electronic character of the subgroup on the ionic conductivity properties of the polymers was examined. Impedance spectroscopy measurements were used to set the ionic chemical diffusion coefficients, D, in the polymer matrix at a variety of doping levels, for each of the polydicarbazoles. We relate D dependency with potential to morphological and electronic processes in the polymer occurring during oxidation. By combination of cyclic voltammetry and impedance spectroscopy for part of the series we reveal that the diffusion of ions in the matrix is easier in polymers were the functional group is highly electron-attracting.     

Control of the growth of the diffusional boundary layer on a rotating axisymmetric electrode of arbitrary shape in an ostwaldian fluid

Using a suitable coordinate transformation, an analysis is first described for the prediction of the velocity distribution in a laminar boundary layer flow near a rotating axisymmetric electrode of arbitrary shape in an Ostwaldian fluid, by expressing the governing conservation equations in a series representation universal with respect to electrode contour parameters, patterned by Blasius procedure.Using the first leading term of the series, we define the profiles of the electrodes which fulfil the diffusional limiting density flux j_x = j₀$\text{x}$^p, in which j₀ is an independent coordinate coefficient, p is a numerical power-factor and $\text{x}$, is measured along the direction of the longitudinal component of the flow. The relation between the permitted values of p with the behaviour coefficient of the fluid is described. The particular case of the uniformly accessible electrode (p = 0) is discussed.     

Extrinsic behavior in La0.67Ca0.33MnO3–BaTiO3 composites

A manganite matrix based nano-composite series, (1 ? x)La_0.67Ca_0.33MnO₃(LCMO)–(x)BaTiO₃(BTO), has been prepared by the pyrophoric method. Influence of BTO phase on structural and magneto-transport properties of LCP phase has been studied using structural and transport investigations. The series exhibits a conduction threshold at x_m ～ 0.30. Overall pattern of temperature dependence of resistivity for this series has been fitted with a percolation model. Almost 200% improvement has been observed by the formation of composite when compared to the parent sample.