Determination of percolation threshold electroactivity and phase behavior study on conducting blends of thermotropic polyesters and polyaniline

The new thermotropic polyester/polyaniline (PIn/PAni) blends have been prepared by solution blend of synthesized liquid crystalline poly[4,4′‐bis (ω‐alkoxy) biphenylisophthalate]s having four and six methylene units in spacer (PI4 and PI6) with PAni doped with camphorsolfonic acid (CSA). The percolation threshold electroactivity of prepared blend films has been determined by cyclic voltammetry. The effect of the PAni concentration, solvent nature and polyester structure on the electroactivity of the blends has been investigated. The extremely low percolation threshold of prepared PIn/PAni‐CSA blends from dimethylformamide (DMF) and m‐cresol solution was 3% weight of PAni‐CSA. The amount of conducting polymer necessary to retard the formation of the liquid crystalline (LC) phase is up to 45% by weight. Phase behavior studies by differential scanning calorimetry and polarizing microscopy show that blends with 45% of conducting polymer are both liquid crystal and conductive. The morphology of the blends has been investigated by scanning electron microscopy. Copyright © 2004 John Wiley & Sons, Ltd.     

Non-covalent dendrimer-based liquid crystalline complexes: Synthesis and characterization

The synthesis and structural characterization of dendritic macromolecules based on 3,5-dihydroxybenzoic acid are described. The molecular structures and purity of all new compounds were confirmed by ¹H NMR, ¹³C NMR spectroscopy and elemental analysis. The dendritic non-covalent liquid crystalline complexes were prepared through the formation of hydrogen bonds between different generation of dendritic acids (proton donor) and stilbazole derivative containing bipyridyl units (proton acceptor). We found that, the hydrogen-bonded dendritic liquid crystals supramolecules (G1-2py, G2-2py and G3-2py) exhibits nematic and semectic phase. The polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) were used for investigation of the liquid crystalline properties of the hydrogen-bonded dendritic supramolecular complexes.     

Thermotropic polyesters. 1: Synthesis, characterization and thermal transition of poly[4,4-bis(ω-alkoxy)biphenyl isophthalate]

A new homologous series of thermotropic polyesters has been synthesized by polycondensation reaction between isophthaloyl chloride and mesogenic diols 4,4^′-bis(ω-hydroxyalkoxy)biphenyl in which the spacer length is varied from 3 to 6 methylene units. The thermal behavior of the polymers has been characterized using polarized light microscopy and differential scanning calorimetry (DSC). The odd members exhibit a smectic C (S_C) phase in a narrow temperature interval, while the even members form a smectic A (S_A) phase in a broader temperature range. All of the obtained compounds were characterized by conventional spectroscopic methods.     

Electrochemical capacitance study of cellulose-manganese dioxide nano-composite

In this study, cellulose-manganese dioxide nano-composites were synthesized and their electrochemical behavior studied as electrode in an electrochemical supercapacitor (ECS). The morphology of composites were investigated by scanning electron microscopy (SEM). Thermal gravimetric analysis (TGA) was used to determine the thermal stability and water content of the composites. The electrochemical capacitance of the composites is studied by cyclic voltammetry (CV) in Na₂SO₄ electrolyte (0.5 M) at room temperature. The results show that the capacitance of the composites are strongly affected by the nano-structure, structural continuity, thermal stability and surface/structural water of manganese dioxide. A high specific capacitance of 171 F/g was obtained for cellulose-manganese dioxide nano-composite which has higher structural continuity, lower water content and better thermal stability.     

Characterization of gelatin/cellulose acetate nanofibrous scaffolds: Prediction and optimization by response surface methodology and artificial neural networks

Gelatin/cellulose acetate electrospun nanofibers are a good candidates for simulation of extracellular matrix (ECM). Electrospinning of the blend is controlled by many parameters such as applied voltage, gap distance, solvent composition, polymer composition and solution concentration. The individual and interactive effects of these parameters on pH, electrical conductivity (EC) and viscosity of solutions, and diameter and quality of fibers were investigated. Response surface methodology (RSM) and artificial neural networks (ANNs) were considered to model and optimize the responses. EC, pH and viscosity of solutions were dependent on the solution parameters. The solvent composition and solution concentration had an influence on the fiber diameter and quality. The optimum conditions for fabricating qualified nanofibers with minimum diameter were 16.9 kV, 15.3 cm, 77.5 wt % of gelatin, 88.9 vol % of acetic acid and solution concentration of 20 wt %/vol %. Uniform beadless nanofibers with a diameter of 284 nm were attained at this optimum condition.     

Thermotropic polyesters. 2: Synthesis, characterization and thermal transitions of copolyesters containing 4,4′-bis (ω-alkyloxy) biphenyl isophthalate units

Thermotropic copolyesters containing an isophthalate unit and mesogenic 4, 4′-bis (ω-hydroxyalkyloxy) biphenyls (n = 3, 4, 6) with different numbers of methylene units have been synthesized by melt polymerization. The number-average molar mass (M_n) was estimated from end group analysis by ¹H NMR. The copolymer compositions were also obtained from ¹H NMR. The thermal behavior of the copolymers containing even-even (n = 4, 6) and odd-even (n = 3, 4) pairings has been investigated and is also compared with that of the analogous homopolymers. The copolymers exhibit reduced melting point and extending liquid crystalline range identified using polarizing microscopy and DSC. All of the obtained compounds were characterized by conventional spectroscopic methods.     

Fabrication of tapers with Gaussian refractive-index profile in azo polymers

We have fabricated a refractive-index-tapered waveguide by exposing an azo polymer film to a 532-nm wavelength laser beam focused to about 60-μm spot size at the film with no surface deformation. The converging ability of the taper (ability to increase intensity along the taper) was measured to be 5 db/cm while the loss was 0.39 db/cm. According to the data obtained, the power density increases along the taper while loss is nearly constant along the tapered and non-tapered segments.     

Physical stability of oil-in-water emulsions in the presence of gamma irradiated gum tragacanth

Gum tragacanth (GT) exuding from an Iranian Astragalus species was γ-irradiated at 0, 0.75, 1.5, 3, 5, 7, and 10?kGy and used to stabilize a model oil-in-water emulsion system. Stability and physicochemical properties of emulsion samples were investigated with respect to the effect of irradiation treatment on functional properties of gum tragacanth. Particle size distribution, interfacial tension, zeta potential, steady shear, and oscillatory rheological measurements were used to characterize and evaluate the emulsion samples and obtain more information about the possible stability mechanism. Emulsions were prepared by homogenizing 10% w/w sun flower oil with 90% w/w aqueous gum dispersions and stored quiescently at 25°C for 120 days. The results indicated that using 1.5?kGy irradiated GT was more effective in providing optimum values of apparent viscosity, number mean diameter, electrosteric repulsion, and structure strength for getting the maximum emulsion stability. GT significantly reduced the interfacial tension of the oil and water system, but no significant differences were observed among all irradiation treated and non-irradiated samples. This study revealed that GT acts as a bifunctional emulsifier and irradiation treatment has a great positive influence on its ability to reduce droplets’ collision frequency and stabilize the oil-in-water emulsion.     

Synthesis and characterization of liquid crystalline diethanolamine‐based dendrimers

Three generations of diethanolamine‐based dendrimers containing nitroazobenzene were synthesized. Firstly, G₁ was prepared by the diazotation of p‐nitroaniline, and then the obtained salts reacted with n‐phenyl‐2,2′‐iminodiethanol. The reaction of hydroxyl groups of diethanolamine of G₁ and G₂ with acryloyl chloride resulted in G_1.5 and G_2.5. Then, G₂ and G₃ were synthesized using Michael addition of amino group of diethanolamine and G_1.5 and G_2.5. The Williamson etherification and azo‐reaction were employed in the preparation of the mesogenic unit 4‐[4‐(6‐bromohexyloxy)phenylazo]nitrobenzene (N₆‐Br). Secondly, mesogen‐functionalized dendrimers were synthesized via the coupling of the hydroxyl group of G₁, G₂, G₃, and bromine from mesogenic units (N₆‐Br). The polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) were used for the investigation of the liquid crystalline properties of the mesogen‐functionalized dendrimers. The structures of obtained compounds were investigated using common spectroscopy methods and CHN analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

Dendrimer-based hydrogen-bonded liquid crystalline complexes: Synthesis and characterization

Three generations of dendritic polyester macromolecules based on 5-hydroxyisophthalic acid were synthesized by the divergent growth approach. The characterization of dendritic fragments was performed using a combination of ¹H NMR, ¹³C NMR spectroscopy and elemental analysis. The dendritic hydrogen-bonded supramolecular liquid crystalline complexes were prepared from different generation of dendritic acids and stilbazole derivative containing pyridyl units. The polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) were used for investigation of the liquid crystalline properties of the hydrogen-bonded dendritic supramolecular complexes.