Search results for "ALLOYS"
showing 10 items of 1689 documents
Second harmonic generation in self-assembled alternating multilayers of hemicyanine containing polymers and polyvinylamine
1995
Abstract Assembly of noncentrosymmetric multilayers is a facile technique for preparing noncentrosymmetric films avoiding electrical poling procedures and problems from subsequent relaxation of the induced orientational order. A maximum Xzzz of 13 × 10−9 esu was achieved for the assembly of up to six layers. Current problems are the long-term hydrolysation of the hemicyanine nonlinear optical chromophores and the reduction of polar orientation with increasing layer thickness.
Composites of ethylene-vinyl acetate copolymers with modified magnesium hydroxide-thermo-oxidative ageing
2014
Flame retardant composites must perform their protective roles permanently, also under conditions of intermittent or long-term exposure to sunlight, moisture or increased temperature. The aim of our work was characterization of the thermo-oxidative ageing (90 °C) and the changes in flammability of ethylene-vinyl acetate copolymer composites with 40 and 60 wt.% of magnesium hydroxide. The neat polymer and its composites were investigated for their thermal (DSC) and structural (FTIR) characteristics as well as their density, melt flow index, tensile properties and combustibility during ageing test. As FTIR results identified the different carbonyl groups in copolymer were created, the highest…
Composite films of natural clay nanotubes with cellulose and chitosan
2014
Composite films based on cellulose, chitosan and halloysite clay nanotubes were prepared using a solution casting method, which allowed for a uniform distribution of nanotubes within the material and provided control over the morphology of the composite. The mechanical performance of these bio nanocomposites is influenced by humidity and the nanotubes showed a plasticisation effect on the polymeric matrix. The composites of chitosan and halloysite nanotubes (HNTs), with modified hydrophobic inner lumens, resulted in a technique for controlled and sustainable surface cleaning. Lignocellulose wood microfibres modified with HNTs were also produced by a layer-by-layer assembly. The obtained ma…
Mixed polymeric monolayers and Langmuir-Blodgett multilayers with functional low molecular weight guest compounds
2008
Abstract Mixed monolayers and Langmuir-Blodgett multilayers of functional low molecular weight guest compounds, especially nonlinear optical (NLO) dyes, within the matrix of an amphotropic spacer polymer have been prepared. The polymer matrix enabled the transfer of guest compounds not capable of self-organizing at the air-water interface by themselves. The structure of the LB multilayers and the transfer process were studied by small angle X-ray scattering and UV-visible spectroscopy. Good NLO coefficients were found in the mixed films.
Colloidal stability and self-assembling behavior of nanoclays
2020
Abstract Currently, nanoclays are attracting the attention of a wide part of the scientific community, due to some of their most peculiar features that make them good candidates for applications in different fields. In light of this, some strategies can be pursued in order to obtain stable colloidal dispersions of nanoclays with the aim to improve their features and to expand their use. Hence, this chapter presents an overview on the structural and morphological characteristics, the physico-chemical properties and the main approaches that are taken into account for the preparation of homogeneous suspensions of Halloysite, Imogolite and Laponite in both aqueous and apolar solvent media. In p…
Supramolecular isomerism in spin crossover networks with aurophilic interactions
2004
Assembly of FeII, 3-cyanopyridine and [Au(CN)2]– affords, in one-pot reaction, three coordination polymers that represent a genuine example of supramolecular isomerism with strong influence in the spin crossover regime of the FeII ions. Real Cabezos, Jose Antonio, Jose.A.Real@uv.es
Efficient photovoltaic and electroluminescent perovskite devices.
2015
Planar diode structures employing hybrid organic–inorganic methylammonium lead iodide perovskites lead to multifunctional devices exhibiting both a high photovoltaic efficiency and good electroluminescence. The electroluminescence strongly improves at higher current density applied using a pulsed driving method.
Thermo- and light responsive micellation of azobenzene containing block copolymers
2010
In this communication, the synthesis and characterization of thermo- and light responsive block copolymers is reported. PEO-b-PNIPAM polymers with azobenzene moieties were prepared and analyzed by turbidimetry, fluorescence, NMR and DLS measurements. A temperature controlled reversible formation as well as a light induced disruption and reformation of micellar structures in water was found.
Superexchange pathways in oxovanadium(IV) phosphates
1992
Abstract Oxovanadium(IV) phosphates show a diversity of magnetic behaviours that cannot be deduced from their respective structural features only. In part, this is due to the involvement of phosphate bridges in the spin transfer between V(IV) centres, and 31P solid state nuclear magnetic resonance becomes a key tool in determining the exchange mechanisms. The magnetic properties of a wide set of vanadium(IV) containing derivatives can be explained by realizing that a good overlap of the magnetic orbits may be achieved through paths involving phosphorus d orbitals.
P-chirogenic organocatalysts: application to the aza-Morita–Baylis–Hillman (aza-MBH) reaction of ketimines
2013
The P-chirogenic organocatalysts were found to promote the enantioselective aza-Morita-Baylis-Hillman reaction of ketimines derived from acyclic α-keto esters. In the P-chirogenic organocatalyzed aza-MBH reactions, α,α-disubstituted α-amino acid derivatives were obtained in high yields with high enantioselectivities (up to 97% ee).