Adhesion of polyelectrolyte multilayers: sealing and transfer of microchamber arrays

Polyelectrolyte multilayer (PEM) films with array of responsive microchambers are promising candidates for site-specific release of chemicals in small and precisely defined quantities on demand. It requires effective sealing of the microchambers toward a support to prevent leakage of a cargo. In this paper, we study the pressure-induced adhesion of poly(allylammonium)-poly(4-styrenesulfonate) (PAH-PSS) multilayers assembled on different templates toward the poly(4-styrenesulfonate)-poly(diallyldimethylammonium) multilayer. The tensile bond strength increases from 0.4 to 3.5 MPa upon the increase of PAH-PSS bilayers from 10 to 40, if assembled on a silicon template. Weaker tensile bond strength of 0.35 MPa between the PAH-PSS multilayer and a poly(methylmethacrylate) (PMMA) template results in adhesive break at this interface and allows mechanical removal of the template. The successful PEM transfer is demonstrated for templates of various geometrical patterns, while the tensile break of a multilayer film happens for the others.     

Combined frequency conversion and pulse compression in nonlinear tapered waveguides

We suggest an application of pump-degenerate four-wave mixing process in tapered waveguides for generation of ultrashort pulses with central frequency tunable over the material transparency range. Our method can produce strongly compressed frequency-converted pulses in presence of group-velocity mismatch and group-velocity dispersion. Additionally, the proposed technique does not require pulse phase synchronization and effectively operates for strongly chirped pump pulses, thus enabling the use of longer nonlinear media for high conversion efficiency.     

The isotope effect and phase separation in (La0.5Pr0.5)0.7Ca0.3MnO3 films: Optical data

A new approach to the study of phase separation in lanthanum manganites is proposed based on the combined investigation of their optical and magnetooptical characteristics providing information about the conducting and ferromagnetic regions, respectively. Effects of the ¹⁸O isotope substitution for ¹⁶O in the epitaxial films of (La_0.5Pr_0.5)_0.7Ca_0.3MnO₃ (grown on SrTiO₃ or LaAlO₃ substrates) upon the IR absorption spectra and the equatorial Kerr effect measured in the 1.5–3.8 eV range were studied. A giant drop in the temperature of maximum resistance of the film grown on SrTiO₃ and disappearance of the metal-insulator transition in the film on LaAlO₃, observed upon the isotope exchange, are accompanied by a decrease in the contribution of free charge carriers to the absorption spectra, by the appearance of bands due to localized states, and by a decrease in magnitude of the equatorial Kerr effects. Measurements of the Kerr effect and the temperature variation of the optical transmission show evidence of the presence of ferromagnetic metal regions in the ¹⁸O-isotope-substituted (La_0.5Pr_0.5)_0.7Ca_0.3MnO₃/LaAlO₃ film at low temperatures, with a general semiconductor character of the resistivity behavior in the entire temperature range studied. Changes observed in the absorption spectra are explained based on a model of the pseudo-Jahn-Teller polar centers and phase separation. The optical and magnetooptical data show evidence of a percolation nature of the giant isotope effect in manganites.     

Polyelectrolyte Multilayer Microspheres as Carriers for Bienzyme System: Preparation and Characterization

Summary: Polyelectrolyte multilayer microspheres were prepared by alternating adsorption of dextran sulfate and protamine on melamine formaldehyde cores followed by the partial decomposition of the core. Peroxidase and glucose oxidase were immobilized in the prepared microspheres. Retention of enzymatic activity of the peroxidase/glucose oxidase system incorporated into the microspheres was demonstrated. Applicability of the bienzyme system immobilized in the microspheres for kinetic glucose assay was shown.

SEM image of the polyelectrolyte multilayer microsphere.     

Effect of isovalent doping of manganite (La1?xPrx)0.7Ca0.3MnO3 films (0≤x≤1) on their optical, magnetooptical, and transport properties near the metal-insulator transition

The optical, magnetooptical, and electric properties of epitaxial (La_1−x Pr_x)_0.7Ca_0.3MnO₃ films (0≤x≤1) grown by MOCVD on LaAlO₃ and SrTiO₃ substrates were studied. It is shown that the decrease in the average cation radius resulting from isovalent substitution of the Pr for La ions brings about a lowering of the Curie temperature, the metal-insulator transition temperature, and the temperatures of the maxima in magnetotransmission (MT) and magnetoresistance (MR). These temperatures depend only weakly on the substrate type. Substitution of La by Pr does not change the shape of the spectral response of the transverse Kerr effect. For concentrations x≤0.50, the maximum values of the Kerr effect and of the MT vary insignificantly, which should be assigned to the existence of a singly connected ferromagnetic metallic region at low temperatures. In films with x=0.75, the presence of ferromagnetic metallic drops in an antiferromagnetic insulating matrix was revealed. The totality of the experimental data obtained suggest that nanoscopic magnetic and electronic nonuniformities exist both in films with a singly connected metallic region and in an x=1 film, which is an antiferromagnetic insulator. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 7, 2004, pp. 1203–1213. Original Russian Text Copyright ? 2004 by Sukhorukov, Loshkareva, Gan’shina, Kaul’, Gorbenko, Mostovshchikova, Telegin, Vinogradov, Rodin.     

Coordination Polymers of Scandium Sulfate. Crystal Structures of (H2Bipy)[Sc(H2O)(SO4)2]2 · 2H2O and (H2Bipy)[HSO4]2

Compounds with the general formula Cat_x[Sc(H₂O)_z(SO₄)_y] · nH₂O (Cat = NH₄, H₂Bipy (Bipy is 4,4′-bipyridine), and HEdp (Edp is ethylenedipyridine) are synthesized and identified by elemental analysis and IR spectral data. The X-ray diffraction analysis of (H₂Bipy)[Sc(H₂O)(SO₄)₂]₂ · 2H₂O shows that in the structure of this compound, the chains of ScO₆ octahedra and SO₄ tetrahedra are united to form ribbons due to the tridentate coordination of the sulfate ion. The ribbons form a framework, whose infinite cavities contain H₂Bipy²⁺ cations.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 8, 2005, pp. 576–582.Original Russian Text Copyright © 2005 by Petrosyants, Ilyukhin, Sukhorukov.     

Optical-absorption anomalies near magnetic phase transitions in copper oxide

The optical absorption coefficient in the region of a wide charge-transfer band in copper oxide CuO (ℏω=3.19 eV) exhibits sharp and anomalously large (up to 8% (!)) changes near two magnetic phase transition temperatures . It is shown that the wide fundamental absorption bands can be used for optical detection of magnetic phase transitions, the parameters of long-and short-range magnetic order, and the effects of a magnetic-impurity state. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 4, 251–255 (25 February 1996)