The structural basis of transitions between highly ordered smectic phases in semifluorinated alkanes

The semifluorinated alkanes F(CF₂)₁₀(CH₂)₉H and F(CF₂)₁₀(CH₂)₁₁H both undergo a reversible transition between tilted smectic phases above room temperature as demonstrated previously for F(CF₂)₁₀(CH₂)₁₀H. The transformation on cooling is achieved in two stages: an increase in molecular tilt relative to the layer normal, followed by a change in the molecular interdigitation within each layer. The extent of complete transformation is sensitive to temperature and time, due to strains occasioned by the accompanying volume change, and because the second stage requires significant molecular translations. Characterization of the transformation is possible by transmitted light microscopy, supplemented by X-ray diffraction.     

Comparative study on different carbon nanotube materials in terms of transparent conductive coatings

We compared conductive transparent carbon nanotube coatings on glass substrates made of differently produced single-wall (SWNT), double-wall, and multiwall carbon nanotubes. The airbrushing approach and the vacuum filtration method were utilized for the fabrication of carbon nanotube films. The optoelectronic performance of the carbon nanotube film was found to strongly depend on many effects including the ratio of metallic-to-semiconducting tubes, dispersion, length, diameter, chirality, wall number, structural defects, and the properties of substrates. The electronic transportability and optical properties of the SWNT network can be significantly altered by chemical doping with thionyl chloride. Hall effect measurements revealed that all of these thin carbon nanotube films are of p-type probably due to the acid reflux-based purification and atmospheric impurities. The competition between variable-range hoping and fluctuation-assisted tunneling in the functionized carbon nanotube system could lead to a crossover behavior in the temperature dependence of the network resistance.     

Ternary Phase Equilibria for a Nitrocellulose/Solvent/Non-Solvent System

Phase diagrams for the system nitrocellulose/tetrahydrofuran/ethanol have been mapped out at room temperature, for two different degrees of substitution of the polymer (2·32 and 2·72). The phases formed by particular compositions were identified by using polarized light microscopy. There is a range of compositions which separate into an isotropic phase and a liquid-crystalline phase; the concentrations involved are qualitatively in agreement with Flory's theory of phase separation in a solution of rigid rod-like molecules. Our plotted room temperature sections of the phase diagrams obey the Gibbs phase rule at all points. We report evidence for the formation of a crystallosolvate of nitrocellulose (degree of substitution 2·72) and ethanol. The crystallosolvate formation only appears to be kinetically possible if there is initially also sufficient tetrahydrofuran present to dissolve the polymer.     

CO2 enhanced carbon nanotube synthesis from pyrolysis of hydrocarbons

We report on the role of CO(2) in improving carbon nanotube yield and crystallinity from catalytic chemical vapor deposition of hydrocarbons.     

Liquid crystalline order in mucus

Mucus plays an exceptionally wide range of important biological roles. It operates as a protective, exchange, and transport medium in the digestive, respiratory, and reproductive systems of humans and other vertebrates. Mucus is a polymer hydrogel. It is secreted as discrete packages (secretory granules) by specialized secretory cells. Mucus hydrogel is stored in a condensed state inside the secretory granules. Depending upon the architecture of their constituent macromolecules and on the composition of the solvent, polymer gels can form liquid crystalline microstructures, with orientational order being exhibited over optically resolvable distances. Individual mucin molecules consist of alternating rigid segments (heavily glycosylated; hydrophilic) and flexible segments (nonglycosylated; hydrophobic). Polymer molecules consisting of rigid units linked by flexible spacers are frequently associated with liquid crystalline behavior, which again raises the possibility that mucus could form anisotropic fluid phases. Suggestions that mucins may be self-associating in dilute solution have previously been challenged on the basis of sedimentation-equilibrium studies performed on mucus in which potential sites of association were competitively blocked with inhibitors. However, the formation of stable liquid crystalline phases does not depend on the existence of inter- or intramolecular associations; these phases can form on the basis of steric considerations alone.     

EFFECTS OF HEMATOPORPHYRIN DERIVATIVE ON THE CELLULAR ENERGY METABOLISM IN THE ABSENCE AND PRESENCE OF LIGHT

Effects of Photofrin II on energy metabolism and metabolic viability were studied in a mammalian transformed cell line (BHK-21) in dark and after photo-irradiation with visible light. Cells were allowed to accumulate Photofrin by incubating for 4 h in buffer containing Photofrin (5-60 micrograms/ml). The results show that Photofrin significantly affects the cellular energy metabolism even in the absence of light; activity of cytochrome c oxidase is decreased and glucose utilization and lactate production (glycolysis) are increased. Irradiation with light resulted in a significant decrease in the activity of cytochrome c oxidase, glycolysis, ATP content, energy charge, ratios of adenine nucleotides like ATP/ADP, ATP/AMP and cell viability (dye exclusion test). Presence of inhibitors of energy metabolism, potassium cyanide (respiration) and 2-deoxyglucose (glycolysis), further enhanced the cytotoxic effects induced by hematoporphyrin derivative and light.     

Effect of heat treatment on thermal and mechanical stability of NaOH-doped xanthan gum-based hydrogels

Journal of Solid State Electrochemistry - Xanthan gum (XG)-based hydrogels containing sodium hydroxide (NaOH) salt were synthesized with the use of distilled water (DW) at room temperature and...     

The structural basis of transitions between highly ordered smectic phases in semifluorinated alkanes

The semifluorinated alkanes F(CF₂)₁₀(CH₂)₉H and F(CF₂)₁₀(CH₂)₁₁H both undergo a reversible transition between tilted smectic phases above room temperature as demonstrated previously for F(CF₂)₁₀(CH₂)₁₀H. The transformation on cooling is achieved in two stages: an increase in molecular tilt relative to the layer normal, followed by a change in the molecular interdigitation within each layer. The extent of complete transformation is sensitive to temperature and time, due to strains occasioned by the accompanying volume change, and because the second stage requires significant molecular translations. Characterization of the transformation is possible by transmitted light microscopy, supplemented by X-ray diffraction.     

Evaluation of a Renewable Resource-based Carbon-Iron Oxide Nanocomposite for Removal of Arsenic from Contaminated Water

High arsenic concentration in groundwater is found in many countries, including Bangladesh, India, Vietnam, Thailand and United States. In these countries, the arsenic concentrations have reached dangerous levels for human consumption, especially where the main source of drinking water is from groundwater. Many techniques have been developed for arsenic removal, one being the use of iron oxide or magnetite nanoparticles for heavy metal removal. In this study, a novel tannin-based carbon-iron oxide composite has been developed by us for arsenic removal and results show that a concentration of 100 ppb As in water could be brought down to <10 ppb with the maximum capacity of the arsenic removal calculated to be 1.5 mg As/g Fe in the nanocomposite. The characterization of the nanocomposite and the advantages of using this renewable resource-based nanocomposite are also discussed.