Shear banding in biphasic liquid-liquid systems

In this Letter, we present the first systematic report of shear-induced banding in microconfined biphasic liquid-liquid systems, i.e., formation of alternating regions of high and low volume fraction of dispersed-phase droplets in a parallel plate flow cell. Such a flow-driven, gap-dependent phenomenon is only observed at low values of the viscosity ratio between the dispersed and the continuous phase, and in a given range of the applied shear rate. Based on rheological measurements, band formation is found to be associated with a viscosity decrease as compared to the homogeneous, structureless case, thus showing that system microstructure is somehow evolving towards reduced viscous dissipation under shear flow.     

Langmuir-Blodgett films of diazobenzene molecules

Langmuir-Blodgett (LB) films from diazobenzene Sudan III have been investigated using surface potential measurements as a function of number of layers and deposition pressures, with the surface potential data being related to molecular dipole moments obtained from theoretical electronic structure calculations. The surface potential increased with the number of layers for SIII LB films, and then tended to saturate. Results from density functional theory (DFT) and UV-vis spectroscopy indicated that the increase is due to addition of layers with oriented molecular dipoles, with the saturation tendency being attributed to a decrease in the amount of material deposited in each layer. The surface potential increased with the surface pressure used for deposition, probably owing to a higher contribution from the vertical component of the dipole moment as a closer molecular packing, which is associated with decreasing conformational entropy, was reached.     

Continuous nondestructive monitoring of <Emphasis Type="Italic">Bordetella pertussis</Emphasis> biofilms by Fourier transform infrared spectroscopy and other corroborative techniques

This work describes the application of several analytical techniques to characterize the development of Bordetella pertussis biofilms and to examine, in particular, the contribution of virulence factors in this development. Growth of surface-attached virulent and avirulent B. pertussis strains was monitored in continuous-flow chambers by techniques such as the crystal violet method, and nondestructive methodologies like fluorescence microscopy and Fourier transform (FT) IR spectroscopy. Additionally, B. pertussis virulent and avirulent strains expressing green fluorescent protein were grown adhered to the base of a glass chamber of 1-μm thickness. Three-dimensional images of mature biofilms, acquired by confocal laser scanning microscopy, were quantitatively analysed by means of the computer program COMSTAT. Our results indicate that only the virulent (Bvg⁺) phase of B. pertussis is able to attach to surfaces and develop a mature biofilm. In the virulent phase these bacteria are capable of producing a biofilm consisting of microcolonies of approximately 200 μm in diameter and 24 μm in depth. FTIR spectroscopy allowed us not only to follow the dynamics of biofilm growth through specific biomass and biofilm marker absorption bands, but also to monitor the maturation of the biofilm by means of the increase of the carbohydrate-to-protein ratio.     

Nanoscale conformational ordering in polyanilines investigated by SAXS and AFM

Understanding the adsorption mechanisms in nanostructured polymer films has become crucial for their use in technological applications, since film properties vary considerably with the experimental conditions utilized for film fabrication. In this paper, we employ small-angle X-ray scattering (SAXS) to investigate solutions of polyanilines and correlate the chain conformations with morphological features of the nanostructured films obtained with atomic force microscopy (AFM). It is shown that aggregates formed already in solution affect the film morphology; in particular, at early stages of adsorption film morphology appears entirely governed by the chain conformation in solution and adsorption of aggregates. We also use SAXS data for modeling poly(o-ethoxyaniline) (POEA) particle shape through an ab initio procedure based on simulated annealing using the dummy atom model (DAM), which is then compared to the morphological features of POEA films fabricated with distinct pHs and doping acids. Interestingly, when the derivative POEA is doped with p-toluene sulfonic acid (TSA), the resulting films exhibit a fibrillar morphology-seen with atomic force microscopy and transmission electron microscopy-that is consistent with the cylindrical shape inferred from the SAXS data. This is in contrast with the globular morphology observed for POEA films doped with other acids.     

Fabrication of phytic acid sensor based on mixed phytase-lipid Langmuir-Blodgett films

This paper reports the surface activity of phytase at the air-water interface, its interaction with lipid monolayers, and the construction of a new phytic acid biosensor on the basis of the Langmuir-Blodgett (LB) technique. Phytase was inserted in the subphase solution of dipalmitoylphosphatidylglycerol (DPPG) Langmuir monolayers, and its incorporation to the air-water interface was monitored with surface pressure measurements. Phytase was able to incorporate into DPPG monolayers even at high surface pressures, ca. 30 mN/m, under controlled ionic strength, pH, and temperature. Mixed Langmuir monolayers of phytase and DPPG were characterized by surface pressure-area and surface potential-area isotherms, and the presence of the enzyme provided an expansion in the monolayers (when compared to the pure lipid at the interface). The enzyme incorporation also led to significant changes in the equilibrium surface compressibility (in-plane elasticity), especially in liquid-expanded and liquid-condensed regions. The dynamic surface elasticity for phytase-containing interfaces was investigated using harmonic oscillation and axisymmetric drop shape analysis. The insertion of the enzyme at DPPG monolayers caused an increase in the dynamic surface elasticity at 30 mN m(-)(1), indicating a strong interaction between the enzyme and lipid molecules at a high-surface packing. Langmuir-Blodgett (LB) films containing 35 layers of mixed phytase-DPPG were characterized by ultraviolet-visible and fluorescence spectroscopy and crystal quartz microbalance nanogravimetry. The ability in detecting phytic acid was studied with voltammetric measurements.     

Er, Yb Doped Yttrium Based Nanosized Phosphors: Particle Size, “Host Lattice” and Doping Ion Concentration Effects on Upconversion Efficiency

The upconverter phosphors studied herein have different percentages of Er³⁺ and Yb³⁺ as doping ions in different Y³⁺ matrixes (Y₂O₃, Y₂O₂S), and were prepared from different precursors (polymeric resin, oxalate, basic carbonate) and method (combustion). Upconversion emission spectra were recorded at 298 K for all the doped samples in the visible region, for efficiency and Green/Red emission relative intensity comparisons. Therefore, an investigation of the influence of the doping ion concentration, particle size and host lattice on the upconversion process is provided in view of the UPT (Upconverting phosphor technology application). On the basis of the results, it was possible to evaluate the best combination for a specific assay, considering whether it is advantageous to have the greatest contribution from the green or red emissions, or from both in comparable intensities.