Libuše Brožová

Reduction of silver nitrate by polyaniline nanotubes to produce silver-polyaniline composites

Polyaniline (PANI) nanotubes were prepared by oxidation of aniline in 0.4 M acetic acid. They were subsequently used as a reductant of silver nitrate in 1 M nitric acid, water or 1 M ammonium hydroxide at various molar ratios of silver nitrate to PANI. The resulting PANI-silver composites contained silver nanoparticles of 40–60 nm size along with macroscopic silver flakes. Under these experimental conditions, silver was always produced outside the PANI nanotubes. Changes in the molecular structure of PANI were analyzed by FTIR spectroscopy. Silver content in the composites was determined as a residue by thermogravimetric analysis, and confirmed by density measurements. The highest conductivity of a composite, 68.5 S cm−1, was obtained at the nitrate to PANI molar ratio of 0.67 in water. Also, the best reaction yield was obtained in water. Reductions performed in an acidic medium gave products with conductivity of 10−4–10−2 S cm−1, whereas the reaction in alkaline solution yielded non-conducting products.

Antibacterial nanofiber materials activated by light

Electrospun polymeric nanofiber materials doped with 5,10,15,20-tetraphenylporphyrin (TPP) photosensitizer were prepared from four different polymers and were characterized with microscopic methods, steady-state, and time-resolved fluorescence and absorption spectroscopy. The polymers used included polyurethane Larithane™ (PUR), polystyrene (PS), polycaprolactone (PCL), and polyamide 6 (PA6). The antibacterial activity of all nanofiber materials against E. coli was activated by visible light and it was dependent on oxygen permeability/diffusion coefficients and the diameter of the polymeric nanofibers. This activity is based on oxidation ability of singlet oxygen O₂(¹Δ(g)) that is generated upon irradiation. All tested nanofiber materials exhibited prolonged antibacterial properties, even in the dark after long-duration irradiation. The post-irradiation effect was explained by the photogeneration of H₂O₂, which provided the material with long-lasting antibacterial properties.

Increasing selectivity of a heterogeneous ion-exchange membrane

AbstractSelectivity, permselectivity, and conductivity are the main ion-exchange membrane parameters. While permselectivity determines how well the membrane separates cations from anions, the selectivity determines how well the membrane transports uni- and multivalent ions. On the other hand, conductivity determines how fast the ions are transported through the membrane. All these parameters depend on many other factors, especially on the membrane structure. It is difficult to develop highly selective (permselective) and highly conductive heterogeneous ion-exchange membranes. Reason for this is porosity: while the conductivity increases with increasing porosity, the selectivity and permselectivity decreases. This work was focused on increasing the selectivity and, at the same time, the conductivity of heterogeneous ion-exchange membranes. It was found that most of the techniques of modification of homogeneous membranes cannot be used with modification heterogeneous ion-exchange membranes. It appears that ...

Map of gas and vapor permeability in polymer blends

Abstract A novel method for measuring local permeabilities of gas or vapor in polymers was proposed and developed. The method utilizes a thin reactive layer of potassium prepared on one side of the examined polymer film. Molecules of an appropriate gas (oxygen, water vapor) diffusing through the film corrode the reactive layer to various extent at various places, proportionally to the amount of the gas passed. A “permeation map” is created which can be visualized with optical microscopy. Compatibilized polystyrene/polypropylene blend was examined with this method. The permeability map pattern obtained was in accord with the morphology of that system. The lateral resolution attained was approximately 2 μm.