Effect of Gas Permeability and Solubility on Foam

We perform a study on the influence of gas permeability and solubility on the drainage and stability of foam stabilized with an anionic surfactant. Our study compares the foam stability for four pure gases and two gas mixtures while previous works only compared two pure gases. Drainage and foam-volume-decay rates are calculated from the experimental data and analysed. We find good agreement with existing theory as the foam stability is strongly influenced by the properties of the gas phase, in particular its solubility in the aqueous phase (measured by Henry’s solubility constant, kH) and permeability (measured by foam-film permeability coefficient, K). The foam volume decreases considerably with increasing K. Moreover, we observe that foams are more stable when a less soluble gas is added to a more soluble gas. Our analysis confirms theories linking drainage, stability, and coarsening rate. Finally, we introduce a new formulation for the foaming index that considers gas solubility and permeability.

Kinetic Treatment of the Reaction of Fructose and N-Bromosuccinimide in Cationic/Anionic/Nonionic Micelles

The kinetics of oxidation of fructose by N-bromosuccinimide in acidic medium in the absence and presence of cationic, anionic, and nonionic surfactants has been measured iodometrically under pseudo-first-order condition. The oxidation kinetics of fructose by N-bromosuccinimide shows a first-order dependence on N-bromosuccinimide, fractional order dependence on fructose, and negative fractional order dependence on sulfuric acid. The kinetics is treated using Berezin’s micellar model that was previously used for the catalysis and inhibition of the reaction. The determined stoichiometric ratio was 1 : 1 (fructose : N-bromosuccinimide). The variation of Hg(OAC)2 and succinimide (reaction product) has insignificant effect on reaction rate. Effects of surfactants, added acrylonitrile, added salts, and solvent composition variation have been studied. Activation parameters for the reaction have been evaluated from Arrhenius plot by studying the reaction at different temperatures. The rate law has been derived on the basis of obtained data. A plausible mechanism has been proposed from the results of kinetic studies, reaction stoichiometry, and product analysis.

Burst Diaphragms Based on Carbon Black/Silica Hybrid Filler Reinforced Nitrile Rubber Compounds

Nitrile rubber (NBR) based elastomer compounds containing different carbon black/silica composition ratios were prepared using laboratory-scale two roll mill. According the cure characterization results, addition of the reinforcing filler, either carbon black or silica, shortened the optimum cure time and also scorch time of samples compared to that of pure NBR gum where the optimum cure time and scorch time both decreased with increasing the silica content of hybrid filler. Analysis of mechanical properties showed that burst strength of carbon black-rich NBR compounds was higher compared to the samples containing silica. This is presumably due to the higher elongation at break observed in NBR/silica compounds revealing lower crosslink density. In fact, adsorption of curing agents onto the functional groups present at the silica surface would be responsible for the lower crosslink density. According to the Barlow’s formula, despite the higher tensile strength of NBR/silica compounds, higher elongation at break leads to the lower burst strength of NBR/silica/carbon black diaphragms.

Preparation and Properties of 3D Chitosan Microtubes

The preparation of 3D chitosan microtubes from polymer solutions in citric and lactic acids by the wet and dry molding methods is described. The mechanism of formation of the insoluble polymeric layer constructing the walls of these microtubes is characterized. The microtubes obtained from chitosan solutions in citric acid are found to have a fragile porous inner layer. For those obtained from chitosan solutions in lactic acid the morphology, elastic-deformation properties, physicomechanical properties, and biocompatibility were assessed. These samples have smooth outer and inner surfaces with no visible defects and high values of elongation at break. The strength of the microtubes obtained by the dry method is much higher than in the case of the wet one. A high adhesion and high proliferative activity of the epithelial-like MA-104 cellular culture on the surface of our microtubular substrates in model in vitro experiments were revealed. Prospects of using chitosan microtubes as vascular prostheses are suggested.

Electrical Conduction Mechanism in Solid Polymer Electrolytes: New Concepts to Arrhenius Equation

Solid polymer electrolytes based on chitosan NaCF3SO3 have been prepared by the solution cast technique. X-ray diffraction shows that the crystalline phase of the pure chitosan membrane has been partially disrupted. The fourier transform infrared (FTIR) results reveal the complexation between the chitosan polymer and the sodium triflate (NaTf) salt. The dielectric constant and DC conductivity follow the same trend with NaTf salt concentration. The increase in dielectric constant at different temperatures indicates an increase in DC conductivity. The ion conduction mechanism follows the Arrhenius behavior. The dependence of DC conductivity on both temperature and dielectric constant (σdc(T,ε′)=σ0e−Ea/KBT) is also demonstrated.

Thermal Conductivity of Gel-Grown Barium Oxalate at 326 and 335 K

Single crystals of barium oxalate have been grown by gel method using agar-agar gel as media of growth at ambient temperature. The grown crystal crystallizes under monoclinic structure. Thermal conductivity of gel-grown barium oxalate crystals as a function of temperature has been studied at 326 and 335 K by using divided bar method. The thermal conductivity of barium oxalate crystal at 326 K was found 3.685 W m−1 K−1 and 3.133 W m−1 K−1 at 335 K. The reduction of thermal conductivity with the rise in temperature may be due to reduction in mean free path of phonons in the solid.

An Elastin-Derived Self-Assembling Polypeptide

Elastin is an extracellular matrix protein responsible for the elastic properties of organs and tissues, the elastic properties being conferred to the protein by the presence of elastic fibers. In the perspective of producing tailor-made biomaterials of potential interest in nanotechnology and biotechnology fields, we report a study on an elastin-derived polypeptide. The choice of the polypeptide sequence encoded by exon 6 of Human Tropoelastin Gene is dictated by the peculiar sequence of the polypeptide. As a matter of fact, analogously to elastin, it is constituted of a hydrophobic region (GLGAFPAVTFPGALVPGG) and of a more hydrophilic region rich of lysine and alanine residues (VADAAAAYKAAKA). The role played by the two different regions in triggering the adoption of beta-turn and beta-sheet conformations is herein discussed and demonstrated to be crucial for the self-aggregation properties of the polypeptide.