Metal ion-driven synthesis of polyaniline composite doped with metallic nanocrystals at the boundary of two immiscible liquids

In this work, silver and gold–polyaniline composite materials were chemically synthesized at the nitrobenzene/water interface. Aniline (monomer) was dissolved in nitrobenzene and the oxidizing agent (either silver (I) or gold (III)) was dissolved in water. Metals, which were formed during the reaction were in nano- and microcrystalline forms and were partially embedded in the polymer. The forms of gold and silver crystallites found in the synthesized composites differed significantly. The rate of growth of the PANI-Ag and -Au composites and their morphologies depended on concentration of the reagents in both phases. The average size of the gold crystals was smaller compared to silver and was in the range of 20–25 nm. The obtained composite materials were characterized by cyclic voltammetry, scanning electron microscopy, and Raman spectroscopy. The pernigraniline species of polyaniline dominated in the entire volume of the PANI-Au composite and in parts of the PANI-Ag material located at the aqueous solution side, while partially oxidized emeraldine was the main component of PANI-Ag at the organic phase side.     

Polymer coatings for improved protein crystal growth

The ability to grow quality protein crystals is necessary to analyze protein structure by X-ray diffraction and related techniques. As such it plays a key role in enzymology, structure-based drug design, molecular biology, and other biomedical areas. It is also required for macromolecule purification by crystallization. Protein crystal growth (PCG) may be negatively influenced by various factors related to nonspecific adsorption and adherence at growth chamber surfaces. Such factors include nucleation and growth of flawed crystals at chamber walls, or wall growth blockage of optical monitoring paths. Surface localized poly(ethylene glycol) (PEG) and other neutral, hydrophilic polymers are known to significantly reduce nonspecific adsorption of biological macromolecules and particles. Preliminary studies, involving various PCG methods (temperature induction, vapor diffusion), apparatii (test tubes, cuvettes, and specialized PCG hardware), growth chamber materials (glass, polystyrene, polysulfone), chamber volumes (0.1–10 ml) and protein samples (lysozyme, thaumatin, insulin) indicate the potential of PEG coatings to significantly reduce problems related to adsorption in PCG. The results, which match the ability of such coatings to reduce protein adsorption as evaluated by both ellipsometry and enzyme linked immunoassay, are discussed in relation to colloidal stabilization theory and properties of PEG coated surfaces.     

Thermo-Reversible Cellulose Micro Phase-Separation in Mixtures of Methyltributylphosphonium Acetate and γ-Valerolactone or DMSO

We have identified cellulose solvents, comprised of binary mixtures of molecular solvents and ionic liquids that rapidly dissolve cellulose to high concentration and show upper-critical solution temperature (UCST)-like thermodynamic behaviour - upon cooling and micro phase-separation to roughly spherical microparticle particle-gel mixtures. This is a result of an entropy-dominant process, controllable by changing temperature, with an overall exothermic regeneration step. However, the initial dissolution of cellulose in this system, from the majority cellulose I allomorph upon increasing temperature, is also exothermic. The mixtures essentially act as ‘thermo-switchable’ gels. Upon initial dissolution and cooling, micro-scaled spherical particles are formed, the formation onset and size of which are dependent on the presence of traces of water. Wide-angle X-ray scattering (WAXS) and ¹³C cross-polarisation magic-angle spinning (CP-MAS) NMR spectroscopy have identified that the cellulose micro phase-separates with no remaining cellulose I allomorph and eventually forms a proportion of the cellulose II allomorph after water washing and drying. The rheological properties of these solutions demonstrate the possibility of a new type of cellulose processing, whereby morphology can be influenced by changing temperature.     

Asymptotic distribution of the eigenvalues of the bending-torsion vibration model with fully nondissipative boundary feedback

Asymptotic and spectral results on the initial boundary-value problem for the coupled bending-torsion vibration model (which is important in such areas of engineering sciences as bridge and tall building designs, aerospace and oil pipes modeling, etc.) are presented. The model is given by a system of two hyperbolic partial differential equations equipped with a three-parameter family of non-self-adjoint (linear feedback type) boundary conditions modeling the actions of self-straining actuators. The system is rewritten in the form of the first-order evolution equation in a Hilbert space of a four-component Cauchy data. It is shown that the dynamics generator is a matrix differential operator with compact resolvent, whose discrete spectrum splits asymptotically into two disjoint subsets called the α-branch and the β-branch, respectively. Precise spectral asymptotics for the eigenvalues from each branch as the number of an eigenvalue tends to ∞ have been derived. It is also shown that the leading asymptotical term of the α-branch eigenvalue depends only on the torsion control parameter, while of the β-branch eigenvalue depends on two bending control parameters.     

Clay-fulleropyrrolidine nanocomposites

In this work, we describe the insertion of a water-soluble bisadduct fulleropyrrolidine derivative into the interlayer space of three layered smectite clays. The composites were characterized by a combination of powder X-ray diffraction, transmission electron microscopy, X-ray photoemission and FTIR spectroscopies, and laser flash photolysis measurements. The experiments, complemented by computer simulations, give insight into the formation process, structural details, and properties of the fullerene/clay nanocomposites. The reported composite materials constitute a new hybrid system, where C(60) differs from its crystals or its solutions, and open new perspectives for the design and construction of novel C(60)-based organic/clay hybrid materials.     

Exact controllability of damped coupled Euler-Bernoulli and Timoshenko beam model

^** Email: marianna.shubov{at}euclid.unh.edu The zero controllability problem for the system of two coupledhyperbolic equations which governs the vibrations of the coupledEuler–Bernoulli and Timoshenko beam model is studied inthe paper. The system is considered on a finite interval witha two-parameter family of physically meaningful boundary conditionscontaining damping terms. The controls are introduced as separableforcing terms g_i(x)f_i(t), i = 1, 2, on the right-hand sidesof both equations. The force profile functions g_i(x), i = 1,2, are assumed to be given. To construct the controls f_i(t),i = 1, 2, which bring a given initial state of the system tozero on the specific time interval [0, T], the spectral decompositionmethod has been applied. The approach, used in the present paper,is based on the results obtained in the recent works by theauthor and the collaborators. In these works, the detailed asymptoticand spectral analyses of the non-self-adjoint operators generatingthe dynamics of the coupled beam have been carried out. It hasbeen shown that for each set of the boundary parameters, theaforementioned operator is Riesz spectral, i.e. its generalizedeigenvectors form a Riesz basis in the energy space. Explicitasymptotic formulas for the two-branch spectrum have also beenderived. Based on these spectral results, the control problemhas been reduced to the corresponding moment problem. To solvethis moment problem, the asymptotical representation of thespectrum and the Riesz basis property of the generalized eigenvectorshave been used. The necessary and/or sufficient conditions forthe exact controllability are proven in the paper and the explicitformulas for the control laws are given. The case of the approximatecontrollability is discussed in the paper as well.     

Aronszajn null and Gaussian null sets coincide

We prove that in every separable Banach space the σ ideals of Aronszajn null sets, Gaussian null sets and cube null sets coincide. Research supported by the Hungarian National Foundation for Scientific Research Grant No. T019476 and FKFP Grant 0189/1997.     

Visible spectra of heavy ions with an open 4f shell

We present visible to near-infrared spectra of highly charged Yb (the atomic number 70) and W (74) obtained with a compact electron beam ion trap. By observing the dependence on the electron beam energy, the charge state that should be assigned to the observed lines is determined. For In-like Yb²¹⁺ and W²⁵⁺ and Sn-like W²⁴⁺, the experimental spectra are compared with theoretical calculations done by the CI+all-order method. In each spectrum, the most prominent line is identified as the magnetic dipole transition from the first excited fine structure level to the ground level in the ground electronic configuration, 4f³ for In-like ions and 4f⁴ for Sn-like ions.