Structurally isomeric monomers Directed copolymerization of polybenzimidazoles and their properties

Three different series of pyridine based polybenzimidazole (PyPBI) random copolymers consisting of meta-para pyridine linkages were synthesized from various stoichiometric mixtures of meta (2,4; 2,6 and 3,5) and para (2, 5) structure pyridine dicarboxylic acids (PDA) with 3, 3’, 4, 4’- tetra-aminobiphenyl (TAB) by solution polycondensation in polyphosphoric acid (PPA). The influences of the structural isomers of PDA on the PyPBI copolymerization and properties were elucidated by characterizing the resulting copolymers. The solubility of PDA monomers in PPA and the overall monomer concentration in the polymerization were found to be the deciding factors. The higher molecular weight PyPBI were obtained for higher para content copolymers due to the low solubility of para PDA in PPA. The introduction of para structure had enhanced the conjugation along the polymer chain. NMR study showed that the reactivity ratio of para PDA was not identical for all the three sets of PyPBI copolymers, it varied upon the positions of the dicarboxylic acids in the pyridine ring of meta PDAs (structural isomeric effect) with which 2,5 PDA is forming the copolymer. Introduction of para structure and meta PDAs structural isomers affected the thermal stability, flexibility and the photophysical properties of the PyPBI copolymers.     

Investigation of electrical and optical properties of polyvinyl acetate doped with some polymers

Polyglycerol (PG) and polytriethanolamine(PTEA) have been prepared. The electrical resistivity (ρ) and the optical absorption of polyvinylacetate (PVAc) doped with polyglycerol (PG), polyaniline (PA), and polytriethanolamine (PTEA) have been studied. It was found that the conduction was mainly ionic in the temperature range from 20 to 120°C. The resistivity decreased with the increase of the dopant cocentration. The optical absorption spectra were determined in the wavelength range 400–2500 nm. The analysis of the absorption spectra showed that the intensity of the bands is remarkably affected by the dopant concentration. The optical energy gap of pure PVAc and the samples containing different dopants were estimated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1558–1563, 2002     

Hydrodynamic properties of aqueous dextran solutions

The hydrodynamic performance of aqueous dextran solutions, including the rheological and thixotropic properties, were investigated. Three kinds of dextrans with different molecular weights were employed to examine the effects of the molecular weight, concentration, temperature, and so forth on the hydrodynamic properties of aqueous dextran solutions. The results showed that an aqueous solution of a dextran with a high molecular weight of 5.223 × 10⁵ at a high concentration of 30 wt % had pseudoplastic properties, in contrast to the conclusions of other researchers finding that aqueous dextran solutions were Newtonian liquids. The viscosity of the aqueous dextran solutions decreased with temperature, and the activation energy was calculated to be 16,849.2 J/mol with a 10 wt % dextran (weight‐average molecular weight = 5.223 × 10⁵) solution. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Noble metals on the nanoscale: optical and photothermal properties and some applications in imaging, sensing, biology, and medicine

Noble metal nanostructures attract much interest because of their unique properties, including large optical field enhancements resulting in the strong scattering and absorption of light. The enhancement in the optical and photothermal properties of noble metal nanoparticles arises from resonant oscillation of their free electrons in the presence of light, also known as localized surface plasmon resonance (LSPR). The plasmon resonance can either radiate light (Mie scattering), a process that finds great utility in optical and imaging fields, or be rapidly converted to heat (absorption); the latter mechanism of dissipation has opened up applications in several new areas. The ability to integrate metal nanoparticles into biological systems has had greatest impact in biology and biomedicine. In this Account, we discuss the plasmonic properties of gold and silver nanostructures and present examples of how they are being utilized for biodiagnostics, biophysical studies, and medical therapy. For instance, taking advantage of the strong LSPR scattering of gold nanoparticles conjugated with specific targeting molecules allows the molecule-specific imaging and diagnosis of diseases such as cancer. We emphasize in particular how the unique tunability of the plasmon resonance properties of metal nanoparticles through variation of their size, shape, composition, and medium allows chemists to design nanostructures geared for specific bio-applications. We discuss some interesting nanostructure geometries, including nanorods, nanoshells, and nanoparticle pairs, that exhibit dramatically enhanced and tunable plasmon resonances, making them highly suitable for bio-applications. Tuning the nanostructure shape (e.g., nanoprisms, nanorods, or nanoshells) is another means of enhancing the sensitivity of the LSPR to the nanoparticle environment and, thereby, designing effective biosensing agents. Metal nanoparticle pairs or assemblies display distance-dependent plasmon resonances as a result of field coupling. A universal scaling model, relating the plasmon resonance frequency to the interparticle distance in terms of the particle size, becomes potentially useful for measuring nanoscale distances (and their changes) in biological systems. The strong plasmon absorption and photothermal conversion of gold nanoparticles has been exploited in cancer therapy through the selective localized photothermal heating of cancer cells. For nanorods or nanoshells, the LSPR can be tuned to the near-infrared region, making it possible to perform in vivo imaging and therapy. The examples of the applications of noble metal nanostructures provided herein can be readily generalized to other areas of biology and medicine because plasmonic nanomaterials exhibit great range, versatility, and systematic tunability of their optical attributes.     

Effects of the aliphatic/aromatic structure on the miscibility,thermal, optical,and rheological properties of some polyimide blends

Two binary polyimide (PI) blends having a common monomer (diamine or dianhydride) were prepared. The first system was composed of PIs obtained from an alicyclic and flexible dianhydride, namely 5‐(2,5‐dioxotetrahydrofurfuryl)‐3‐methyl‐3‐cyclohexene‐1,2‐dicarboxylic acid anhydride (DOCDA) and two aromatic diamines: 4,4′‐oxydianiline (ODA) and p‐phenylenediamine, respectively. In the second system, ODA was combined with DOCDA and (hexafluoroisopropyldiene)diphthalic dianhydride (6FDA). Films of the resulted blends were transparent, suggesting their homogeneity. According to differential scanning calorimetry data, the existence of a single T_g intermediate to those of the pure PIs confirmed the miscibility of blends. Incorporation of aliphatic and asymmetric DOCDA moieties, hexafluoropropyldiene groups and ether linkages in the molecular structure of PIs reduced the charge transfer interactions and significantly increased transparency and optical gap energy, especially for the poly(DOCDA‐ODA)/poly(6FDA‐ODA) blend. These interactions are also reflected in viscosity dependence on shear rate, indicating that they are slightly stronger when the aromatic 6FDA component prevails. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Catalysts for the preparation of polybenzimidazoles

The single-stage preparation of poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole] (PBI), from 3,3′,4,4′-tetraaminobiphenyl (TAB) with isophthalic acid (IPA) in the presence of a catalyst, was explored and developed. The effects of a variety of catalysts on the polymerization of TAB with IPA and/or diphenyl isophthalate were screened and evaluated. Many organo phosphorus and silicon compounds catalyzed the PBI condensation reactions, increased the molecular weight, and improved the quality of PBI polymers. Fiber and reverse osmosis membrane properties of PBI prepared from TAB and IPA were comparable to those for commercial standard PBI prepared from TAB and diphenyl isophthalate. © 1994 John Wiley & Sons, Inc.     

Effect of mixed rare-earth ions on the structural and optical properties of some borate glasses

In order to study some effects of mixed ions of rare-earth (Sm and/or Dy) on the properties of a glass system, the formula 80% B₂O₃+ 18% Na₂O + (2-x)% Sm₂O₃ + (x) % Dy₂O₃; x = 0, 0.4, 1.6 and 2 mol. % has been prepared via the well-known melt quenching method. The presence of some structural groups such as BO₃, BO₄, as well as N₄ factor have been scrutinized via FTIR spectra. Absorbance of the prepared solid glass system has been performed by a spectrophotometer in wavelengths between 190 and 1100 nm. Using traditional techniques and standard formulas, the density (ρ_emp and ρ_exp), bond density (n_B), molar volume (V_m), Fermi energy (E_F), refractive index (n), optical bandgap (E_g) have been determined, then the impact of mixed rare-earth oxides (Dy and/or Sm) on the structural and optical properties have been scrutinized. The density, optical bandgap, IR intensity and the refractive index of glass samples shows nonlinear trend, which can be ascribed to the mixed effect of rare-earth cations. However Sm and Dy have been doped with the same percent in the glass system separated and mixed, the effect of Sm ions is obvious than Dy ions.     

Hydrodynamic and micellar properties of sodium alkyl benzene sulphonates

This paper provides hydrodynamic data and micellar properties of some sodium alkyl benzene sulphonates. The free energy of micellisation. as deduced from experimental data, is compared with that calculated from the structural parameters and shows that these sulphonates form spherical and ellipsiodal micelles in aqueous medium. The ease of micellisation and micelle size increases as one goes from sodium decyl to sodium hexadecyl benzene sulphonates. The solubilisation data of n-octane and ethyl benzene in aqueous sodium alkyl benzene sulphonate solutions above the cmc indicates that aliphatic hydrocarbons when solubilised reside within the micellar core whereas aromatic hydrocarbons reside in the micellar core as well as in the annular space between hydrodynamic shear surface and surface of the micellar core,     

Dilatometric properties of some butyropalmitins,butyrostearins, and acetopalmitins

1. Six aceto- and butyroglycerides, including di-and triglycerides, were prepared and purified, and a number of their physical properties were determined.
2. Melting and transition points for each of the glycerides were determined by experiments with small portions of the samples in capillary tubes; the “thrust-in” technique was employed to detect some polymorphic transitions occurring in intervals as short as one second.
3. Using the data on melting and transition points, dilatometric data were obtained, insofar as possible, for the various crystalline modifications of the compounds as well as for the liquid state. From the dilatometric data calculations were made for expansibilities in the liquid and various solid states, and melting dilations for several solid states. In one instance the volume change on phase transition, without melting, was calculated.
4. From X-ray diffraction patterns the long and short crystal spacings for the highest melting forms of several of the glycerides were determined. On the basis of the short spacings, polymorphic designations commonly used for fats and oils were assigned. The long spacings obtained indicated a triple chain length structure for some of the compounds and as yet an undetermined structure for the other compounds.

     

Insights into the optical,magnetic and dielectric properties of some novel polysulfone/NiFe2O4 composite materials

Novel polysulfone (PSU)/NiFe₂O₄ nanocomposites with good magneto‐dielectric properties were prepared in a simple and cost‐effective manner. Nickel ferrite nanoparticles exhibit a cubic spinel phase without any impurity phases according to X‐ray diffraction characterization. Transmission electron microscopy images of the nanoparticles showed a tetragonal particle shape with average particle size of 17–30 nm. The thermal stability of PSU proved to remain unaffected by nanoparticle concentration in the composite material. The emission spectra of the PSU/NiFe₂O₄ nanocomposites present a broad emission band located at 370 nm due to free exciton recombination. The composites exhibit hysteresis loops of a ferrimagnetic nature and good dielectric properties. Coercivity value measured at room temperature is 20.64 and 24.98 Oe and the squareness (M_r/M_s) is 0.290 and 0.225 for both polymer composite samples (4 and 24 vol% Ni ferrite). The formalism of the dielectric loss has been used to estimate the dipolar relaxations expressed by γ‐ and β‐relaxation processes. The presence of Ni ferrite nanoparticles in the PSU matrix increases the activation energy of secondary relaxations, which means a reduction of the molecular mobility in the nanocomposites as compared to PSU. © 2018 Society of Chemical Industry     

Mechanical,optical, and electrical properties of cellulosic semiconductor nanocomposites

Photoluminescent cellulose fibers were prepared by impregnation of bleached bagasse pulp with the different cadmium and zinc sulfides nanostructures, namely, CdS, ZnS, CdS/ZnS, ZnS/CdS (Core/shell nanostructures), CdS/ZnS/CdS and ZnS/CdS/ZnS multilayered nanostructures. The prepared cellulosic nanocomposites were characterized regarding strength properties (tensile strength, tensile energy absorption, and burst resistance), optical properties (fluorescence emission), thermal stability, and dielectric properties. The strength properties of paper sheets nanocomposites impregnated with different nanoparticles solutions were noticeably decreased in spite of the very low loading of the fibers with the semiconductor nanoparticles. The decrease in tensile index, tensile energy absorption, and burst index of paper sheets nanocomposites are found to be ranged from 12–27, 13–36, and 11–38 %, respectively. The different paper sheets nanocomposites showed fluorescence emission different from the as prepared polyethyleneimine‐stabilized nanoparticles. Thermogravimetric analysis results showed that: the semiconductor nanoparticles did not affect the onset degradation temperature of cellulosic fibers but it caused faster termination of the main degradation step. The dielectric loss and the dc‐conductivity of cellulosic fibers increased as a result of impregnating the fibers. The nature of the nanoparticles and the properties of the interphases strongly influenced the dielectric properties of the cellulosic/semiconductors nanocomposites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Hydrodynamic properties of coal in turbulent fluidized beds

Hydrodynamic properties in turbulent fluidized beds of three different sizes of coal (d _p = 0.507, 0.987, 1.147 mm) have been determined from the pressure fluctuations in a 0.1 m-ID × 3.0 m high Plexiglas column. The transition velocity from the slugging to turbulent flow regimes can be determined from the statistical analysis of pressure fluctuations such as mean amplitude, standard deviation and skewness, the pressure wave velocity, and the bed expansion with gas velocity. The bed expansion in the slugging and turbulent flow regimes cannot be estimated from the two-phase theory. The voids rise velocity and the bed expansion ratio (H/H _mf ) in the turbulent flow regime have been correlated with the relevant dimensionless and operating parameters The ransition velocity to the turbulent flow regime has been determined based on the slug breakdown caused by the inertial force of an upflowing maximum stable slug which overcomes the gravitational force induced by solid refluxing as:      

The synthesis,spectroscopic properties and crystal structures of some rhodanine merocyanine dyes for optical recording with a blue diode laser

Six rhodanine merocyanine dyes were synthesized via both a conventional solvent method and a microwave method using rhodanine, 2-methylthio quaternary salts and 1H-indole-3-carbaldehyde as starting materials. The products were identified using UV–Vis, IR, MS, ¹H NMR and elemental analysis. The UV–Vis absorption spectra of the dyes in chloroform, DMSO, water, acetone, ethanol and methanol were investigated. The structures of two dyes (5a and 5b) were characterized and analyzed by X-ray diffraction as well. Crystallographic data revealed that dye 5a belonged to tetragonal, I4 (1)/a space group, while dye 5b belonged to monoclinic, P-1 space group. In the case of both dyes, intermolecular associations occurred by π–π stacking and intermolecular hydrogen bonds, which contributed to stabilize the crystal structure.     

The synthesis, spectroscopic properties and crystal structures of some rhodanine merocyanine dyes for optical recording with a blue diode laser

Six rhodanine merocyanine dyes were synthesized via both a conventional solvent method and a microwave method using rhodanine, 2-methylthio quaternary salts and 1H-indole-3-carbaldehyde as starting materials. The products were identified using UV-Vis, IR, MS, ¹H NMR and elemental analysis. The UV-Vis absorption spectra of the dyes in chloroform, DMSO, water, acetone, ethanol and methanol were investigated. The structures of two dyes (5a and 5b) were characterized and analyzed by X-ray diffraction as well. Crystallographic data revealed that dye 5a belonged to tetragonal, I4 (1)/a space group, while dye 5b belonged to monoclinic, P-1 space group. In the case of both dyes, intermolecular associations occurred by π-π stacking and intermolecular hydrogen bonds, which contributed to stabilize the crystal structure.     

Synthesis and characterization of thermally stable polymers (polybenzimidazoles)

In this study, an alternative synthesis of polybenzimidazoles was performed with aromatic hydroxamoyl chloride. In contrast to the literature, polybenzimidazoles were obtained through the reaction of hydroxamoyl chlorides with 3,3′‐diaminobenzidine or 1,2,4,5‐tetraaminobenzene. The characterization of the polymers was performed with Fourier transform infrared, ¹H‐NMR, elemental analysis, LC mass spectrometry, and differential thermogravimetry/thermogravimetric analysis. Finally, the adhesion, corrosion resistance, and conducting properties of the synthesized polymers were examined. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Structural, optical and bioactive properties of calcium borosilicate glasses

Glass of composition 40SiO₂–20B₂O₃–30CaO–10M₂O₃ (M = Al, Cr, Y and La) were prepared by the splat quenching technique to investigate the effect of M₂O₃ on their bioactivity, structural and optical properties. Y₂O₃ and Cr₂O₃ containing glasses formed a crystalline hydroxyapatite (HA) layer after dipping in simulating body fluid (SBF) for 25 days. On the other hand, HA layer could not form in Al₂O₃ and La₂O₃ glasses. However, during soaking in SBF solution, these glasses exhibit higher dissolution rate, lower density and increased optical band gap as compared to unsoaked glasses. Their oxygen molar volume was also higher than for Y₂O₃ and Cr₂O₃ glasses. The change in composition affects the cross-link formation in the glass matrix and finally its durability and bioactivity in SBF. The results show that M₂O₃ plays an important role in controlling chemical durability and bioactivity of the glasses.     

Morphological, optical, and barrier properties of PP/MMT nanocomposites

In this work, nanocomposites of polypropylene (PP) and organically modified montmorillonite (MMT) were evaluated concerning optical, mechanical, and barrier properties. The nanocomposites were prepared by melt compounding using a twin-screw extruder. The PP/MMT films were evaluated by measurements of oxygen and water vapor permeability, and to verify its efficiency as a barrier to ultraviolet radiation (by UV–Vis spectroscopy). MMT has demonstrated a high ability to improve the gas barrier properties of the PP. Furthermore, MMT showed optical efficiency acting as a UV absorber, and presented higher absorptions at wavelengths between 215 and 254 nm. These results suggest that these nanocomposite materials have great potential for applications such as films with superior properties for food packing.     

Structural,magnetic, and optical properties of nano-sized Ni0.85Se

Nanocrystalline Ni_0.85Se was synthesized by a hydrothermal method. X-ray diffraction analysis by Rietveld method indicated that Ni_0.85Se has a NiAs-type hexagonal structure. Narrow crystallite size distribution with an average area-weighted size of 〈ɛ_F〉 = 8.5 nm is obtained by Warren-Averbach method. Structural analysis revealed deformed Se atoms octahedron with the shortest distance between Se atoms in adjacent planes 〈Se–Se〉_adj smaller than between nearest neighbors in layer plane 〈Se–Se〉_nea, and a rather short interatomic distance between the transition metal atoms 〈Ni–Ni〉. The optical property of Ni_0.85Se was studied by UV-spectroscopy. Magnetic measurement shows a ferromagnetic phase transition for Ni_0.85Se below 14 K.