Citric-acid-coated magnetite nanoparticles for biological applications

Water-based magnetic fluids, generally intended for biomedical applications, often have various coating molecules that make them stable and compatible with biological liquids. Magnetic fluids containing iron oxide particles have been prepared by a co-precipitation method, using citric acid as stabilizer. The magnetic particles of the magnetic fluids were obtained by chemical precipitation from ferric ( FeCl₃) and ferrous salts ( FeSO₄ or FeCl₂) in alkali medium (ammonia hydroxide). Citric acid was used to stabilize the magnetic-particle suspension. Physical tests were performed in order to determine various microstructural and rheological features. Transmission electron microscopy was the main investigation method for assessing the magnetic-particle size. The dimensional distribution of the magnetic-particle physical diameter was analyzed using the box-plot statistical method while infrared absorption spectra were used to study the colloidal particle structure. The magnetic-fluid density (picnometric method), viscosity (capillary method) and surface tension (stalagmometric method) were measured using standard methods.     

Asymmetric azomethine amines with azobenzene moieties – liquid crystalline and optical properties

ABSTRACT

Three asymmetric azomethine-azobenzene intermediates (M1-M3), having internal reactive amine functional group, and both n-butoxy and p-chloro, p-methyl, o-methyl terminal moieties, have been synthesised by reacting asymmetric substituted azobenzene diamines with 4-butoxybenzaldehyde. Their proposed chemical structures were confirmed by FTIR and 2D-NMR spectroscopy. The mesomorphic behaviour was investigated by polarised optical microscopy (POM), differential scanning calorimetry (DSC) and room temperature powder X-ray diffraction techniques. Characteristic textures of smectic A and nematic phases have been observed for samples M1 and M2, while only unsolved texture was revealed for sample M3 at room temperature, showing sharp reflections in the medium-wide angle region. From X-ray diffraction measurements, a layered ordered structure of all compounds was established by analyzing successive scattering vectors ratios (q_i/q₁). The dependence of thermal behaviour on molecular parameters like: interdigitation parameter γ, dipole moment, molecular polarisability, halogen radius, was commented. The UV-Vis spectral investigations of the intermediates, performed in six solvents, revealed that the absorption bands were influenced by the substituent nature.     

Polyelectrolyte complexes. II. Specific aspects of the formation of polycation/dye/polyanion complexes

We report on the formation of the polycation/dye/polyanion (PC/D/PA) complexes by the interaction between nonstoichiometric polycation/dye (PC/D) complexes with polyanions. Polycations differed in their content of the (N,N‐dimethyl‐2‐hydroxypropylene ammonium chloride) units in the main chain. Poly(sodium acrylate) (NaPA), poly(sodium 2‐acrylamido‐2‐methylpropane sulfonate) (NaPAMPS) and poly(sodium styrenesulfonate) (NaPSS) were used as polyanions. Crystal Ponceau 6R (CP6R) and Ponceau 4R (P4R) with two or three sulfonic groups were used as anionic dyes. The interaction between nonstoichiometric PC/D complexes and polyanions was followed by UV‐VIS spectroscopy, viscometry, and conductometry measurements. Formation of PC/D/PA complexes takes place mainly by the electrostatic interaction between the polyanion and the free positive charges of the nonstoichiometric PC/D complex. The stoichiometry and the stability of the tricomponent complexes depended on the polycation structure, the structure and molecular weight of polyanion, the dye structure, and the P/D molar ratio. A high amount of the dye was excluded from the complex before the end point when a branched polycation was used. The higher the solubility of the dye the lower the stability of the PC/D/PA complexes. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 409–418, 1999     

Chemical modification of polysulfones by bisphenolic copper chelates

Chloro-terminated polysulfones with various molecular weights were chemically modified with bis(2,4-dihydroxybenzaldehyde)copper(II). The properties of modified polysulfones are compared with the unmodified ones, and an increase in glass transition temperatures, softening points and reduced viscosities of the former materials was observed. In addition, the chelate-modified polymers exhibited excellent thermal stability properties and semicrystalline patterns. Also, they provided transparent and flexible films. © 1998 John Wiley & Sons, Ltd.     

On the Electrical and Optical Properties of Some Poly(Azomethine Sulfone)s in Thin Films

Poly(azomethine sulfone)s were synthesized by reacting 4,4′-sulfonyl bis(4-chlorophenyl) with 2,2-bis(4-hydroxyphenyl)propane and azomethine bisphenol in different molar ratios. Thin films were deposited from solution onto glass substrates. Study of the temperature dependences of the electrical conductivity, σ, and Seebeck coefficient, S, were performed in the temperature range 300 K–500 K. Thermal activation energies of electrical conduction, E_a , calculated from these dependences, ranged between 1.50 eV and 1.85 eV. The values of E_a were smaller for polymers with extended conjugation systems. The possibility to use the polymers in thermistor technology is discussed. The aspect of the temperature dependences of σ and S shows that a model based on the energy band-gap representation can be successfully used for explaining the electronic transport mechanism in the higher temperature range. In the lower temperature range, the mechanism of the electrical conduction is discussed in terms of the Mott variable range hopping conduction. The values of some optical parameters (absorption coefficient, optical band gap, etc.) were determined from transmission spectra.     

Interactions of di- and trivalent anionic azo dyes with polycations of integral type

The spectral changes of Crystal Ponceau 6R and Ponceau 4R induced by the interaction with polycations having N,N-dimethyl-2-hydroxypropane-1,3-diylammonium chloride units in the main chain were followed. The stoichiometry of the polycation-dye complex related to the dye structure was elaborated by UV-VIS spectrophotometry and viscosimetric measurements. Formation of a tricomponent complex between the polycation/dye complex and poly(sodium acrylate) was also revealed.     

Structural characteristics of some high density polyethylene/EPDM blends

Blends of ethylene propylene diene terpolymer rubber (EPDM) with high density polyethylene were obtained by melt mixing. Mechanical properties of the composites, tensile strength, hardness, resilience, elongation at break, 100% modulus and tear strength were determined. Differential scanning calorimetry and wide angle x-ray diffraction were employed to study melting behavior and crystalline structure. The surface properties were analyzed using contact angle determinations. Also, compatibilization with PE-g-MA or dynamical vulcanization using phenolic resins was applied to obtain improved mechanical properties. It was found that the crystalline structure of HDPE was not changed during blending. The vulcanized composite presents a lower degree of crystallinity. Elongation at break and hardness were significantly increased for composites containing compatibilizing agent. The morphology of EPDM composites was studied by atomic force microscopy.     

Silver nanoparticles obtained with a glucose modified siloxane surfactant

Journal of Nanoparticle Research - Silver nanoparticles were obtained in aqueous medium, at room temperature, by redox reactions, with or without glucose, in the presence of a glucose-containing...