FePd melt-spun ribbons and nanowires: Fabrication and magneto-structural properties

Fe-30%Pd alloys in ribbon and nanowire geometry have been prepared. Ribbon samples were produced by the melt-spinning technique in the Ar environment. FePd nanowires, having about 35 nm in diameter, 105 nm inter-nanowires distance and around 4 μm in length, were synthesized into nanoporous anodic alumina membranes as templates. Energy dispersive X-ray microanalysis of ribbons shows an average atomic composition of Fe (73.2%) and Pd (26.8%). The X-ray diffraction at RT analysis was performed on both surfaces, free and wheel side, of the melt-spun ribbon. It shows the coexistence of two phases: fct and bct FePd, but with differences between both surfaces consisting the existence of Fe oxides (Fe₂O₃ and Fe₃O₄) and a textured 200 reflection in the free side. Heating and cooling thermomagnetic curves exhibit a reversible behaviour from RT to 720 K, but around 770 K a clear irreversible transformation takes place.     

Azophenol-based liquid-crystalline elastomers for light-driven actuators

Para-substituted azophenols exhibit a fast thermal cis-to-trans isomerization rate in ethanol, which can be transferred to the solid state by obtaining liquid-crystalline elastomeric systems. The absence of protic solvent is compensated by the establishment of hydrogen bonding between azophenol monomers that are close to each other. Opto-mechanical experiments reveal that azophenol-containing liquid single-crystal elastomers are valuable materials for light-controlled actuators exhibiting relaxation times of 1 s at room temperature.     

Liquid crystalline dendrimers containing photoactive cinnamate units

Cinnamate‐containing dendrimers have been prepared by peripheral functionalization of the amine groups of a poly(propyleneimine) dendrimer with 4‐methoxycinnamate‐ or 4‐(N,N‐dimethylamino)cinnamate‐derived units and/or 4‐cyanobiphenyl units in different proportions. The synthesis, full characterization in solution, thermal properties and optical properties of the novel monomers, homodendrimers and codendrimers are reported. The composition of the molecular structure of the codendrimers has been elucidated by matrix assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS). These liquid crystalline dendrimers display lamellar SmA mesophases. The codendrimers have been tailored in such a way that the photoactive units and the liquid crystal units absorb in different regions in order to allow better control over the processes induced by light. Linearly polarized UV light irradiation studies performed on thin films of the cinnamate codendrimers show that they are photoresponsive. A photoinduced anisotropy is generated with increasing exposure time, but in‐plane amplification of anisotropy by thermal annealing in the mesophase was not observed. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

A Bifunctional Amorphous Polymer Exhibiting Equal Linear and Circular Photoinduced Birefringences

The large and reversible photoinduced linear and circular birefringences in azo‐compounds are at the basis of the interest in these materials, which are potentially useful for several applications. Since the onset of the linear and circular anisotropies relies on orientational processes, which typically occur on the molecular and supramolecular length scale, respectively, a circular birefringence at least one order of magnitude lower than the linear one is usually observed. Here, the synthesis and characterization of an amorphous polymer with a dimeric repeating unit containing a cyanoazobenzene and a cyanobiphenyl moiety are reported, in which identical optical linear and circular birefringences are induced for proper light dose and ellipticity. A pump‐probe technique and an analytical method based on the Stokes–Mueller formalism are used to investigate the photoinduced effects and to evaluate the anisotropies. The peculiar photoresponse of the polymer makes it a good candidate for applications in smart functional devices.

     

SmCP-networked films obtained by in situ photopolymerization of neat reactive banana-shaped liquid crystals

The synthesis and characterization of reactive banana-shaped compounds have been carried out, and their ability to be photopolymerized in their SmCP mesophase has been assessed. The presence of a SmCP liquid crystalline phase in these compounds has been confirmed by X-ray studies. The polymerization of these molecules has been demonstrated by calorimetric techniques as well as by the preparation and characterization of SmCP-ordered free films that are mechanically stable at room temperature. Furthermore, polymerized films exhibit second harmonic generation activity at room temperature in the absence of an electric field.     

Curie temperature in Fe(Ni)Nb based mechanically alloyed materials

Summary A conventional thermogravimeter has been adapted with a small magnet to detect the Curie temperature, T_C. The measurements were performed in several Fe(Ni)NbB alloys developed in a nanocrystalline form by mechanical alloying. The B addition favors a slight diminution (10-20°C), and the Ni addition the existence of three transitions related with bccFe, fcc(Fe-Ni) abd fccNi-rich environments. Furthermore, complementary analysis were performed by means of differential thermal analysis, scanning electron microscopy with energy dispersive X-ray microanalysis and by induced coupled plasma. Small contamination was found. A mass increase (about 1 mass%) was detected by thermogravimetry related to oxidation. Analysis allows us to state the inhomogeneity of the alloys obtained after 80 h of milling.     

On Proper and Exterior Sequentiality

In this article a sequential theory in the category of spaces and proper maps is described and developed. As a natural extension a sequential theory for exterior spaces and maps is obtained.     

Nanomaterial-based electrochemical sensors for detection of glucose and insulin

Journal of Solid State Electrochemistry - Electrochemical sensors for the detection of specific biomolecules have attracted a lot of interest over the recent years due to their high sensitivity,...