Polyester-supported Chitosan-Poly(vinylidene fluoride)-Inorganic-Oxide-Nanoparticles Composites with Improved Flame Retardancy and Thermal Stability

Polyester(PET) was pre-activated by atmospheric air plasma and coated by various inorganic oxide nanoparticles(MOx) such as titanium dioxide(TiO2), zinc oxide(ZnO), and silicon oxide(SiO2), using poly(vinylidene fluoride)(PVDF) and chitosan(CT) as binders. The resulting PET-PVDF-MOx-CT composites were thermally compressed and then characterized by scanning electron microscopy, Fourier infrared spectroscopy, thermal gravimetric analysis, and flame retardancy(FR) ability tests. PET modifications resulted in more thermally stable and less harmful composites with weaker hazardous gas release. This was explained in terms of structure compaction that blocks pyrolysis gas emissions.CT incorporation was found to reduce the material susceptibility to oxidation. This judicious procedure also allowed improving flame retardancy ability, by lengthening the combustion delay and slowing the flame propagation. Chitosan also turned out to contribute to a possible synergy with the other polymers present in the synthesized materials. These results provide valuable data that allow understanding the FR phenomena and envisaging low-cost high FR materials from biodegradable raw materials.     

Enantioselective Crystallization of Chiral Inorganic Crystals of ϵ-Zn(OH)2 with Amino Acids

Many inorganic materials can form crystals, but little is known about their enantioselective crystallization. Herein, we report on the enantioselective crystallization of ϵ-Zn(OH)₂ (Wulfingite) chiral crystals by using amino acids. Crystals of ϵ-Zn(OH)₂ were crystallized from supersaturated sodium hydroxide and zinc nitrate aqueous solutions in the presence of l - or d -arginine. All of the chiral measurements, such as selective chiral adsorption by circular dichroism (CD), chiral chromatography, and polarimetry measurements, clearly show chiral discrimination during the crystallization of ϵ-Zn(OH)₂. In addition, a new method has been developed for identifying chirality in crystals by using electron paramagnetic resonance (EPR). Although the values of chiral induction of the ϵ-Zn(OH)₂ crystals obtained are somewhat low, these values are still significant because they demonstrate that enantioselectivity during the crystallization of chiral inorganic crystals with chiral additives can be achieved. The method can be applied to many chiral inorganic systems. Understanding and controlling the crystallization of chiral inorganic crystals is important for gaining knowledge on the interaction of chiral molecules with inorganic surfaces. This knowledge can lead to an understanding of basic scientific questions such as the evolution of homochirality in biomolecules and the development of chiral inorganic crystals for a variety of purposes such as asymmetric catalysis and optical applications.     

Cycloaddition of sulfonyl azides and cyanogen azide to enamines. Quantum-chemical calculations concerning the spontaneous rearrangement of the adduct into ring-contracted amidines

Enamines derived from cyclic ketones react with arenesulfonyl azides and cyanogen azide, mainly via ring contraction, with formation of the corresponding amidines. The mechanism of this efficient rearrangement, which has not been investigated experimentally, was determined with the aid of quantum-chemical calculations. In the transition state, from the intermediate 5-amino-v-triazolines, the loss of dinitrogen and a cyclic rearrangement occurred in one-step in a quite synchronous manner with a very low transition state energy.     

On the stability of Langmuir films of pyramidic mesogens

Abstract

Pyramidic mesogens forming thermotropic liquid crystal bulk phases were spread in an air-water interface. Pressure surface measurements and polarizing microscopy on the Langmuir films were used to characterize the various states of these pyramidic-like molecules. For two compounds bearing short lateral aliphatic chains, the surface pressure isotherms exhibit a large plateau region corresponding to a metastable monolayer in which the molecules may adopt an ‘edge-on’ arrangement. The coexistence of multilayered, anisotropic, slowly growing domains with the monolayer in the plateau region has been observed at long time scale. The film area relaxation kinetics at constant surface pressure show the existence of two nucleation mechanisms for the formation of these domains.     

Assigning Possible Ion Exchange Sites in Cerium(IV) Antimonates

Empirical formulae, based upon thermo-analytical investigations, have been assigned for different cerium(IV) antimonate samples prepared under varying conditions of precipitation. Equilibria and apparent Na⁺-capacity measurements at different pH values were carried out to throw more light on their sorption behavior. From the general curve shape analysis of the capacity-pH curves, the possible ion exchange site acidity and site group concentration were characterized. The samples showed almost bifunctional cation exchange behavior. The results obtained are discussed in detail referring to some conclusions.     

The mechanism of aromatic nitration by tetranitromethane

Aromatic nitrations by tetranitromethane are shown to be photo-chemically initiated and are believed to proceed via trinitromethyl nitrite.     

The classical KAM theorem for Hamiltonian systems via rational approximations

In this paper, we give a new proof of the classical KAM theorem on the persistence of an invariant quasi-periodic torus, whose frequency vector satisfies the Bruno-Rüssmann condition, in real-analytic non-degenerate Hamiltonian systems close to integrable. The proof, which uses rational approximations instead of small divisors estimates, is an adaptation to the Hamiltonian setting of the method we introduced in [4] for perturbations of constant vector fields on the torus.     

Proton spin conversion of coupled methyl groups in lithium acetate studied by inelastic neutron scattering

The temperature dependence of the tunneling spectrum of methyl groups in lithium acetate dihydrate has been studied in the temperature range between 1.2 and 8.0 K by inelastic neutron scattering. The results unambiguously prove that it is to a first order approximation correct to describe the tunneling motions by a model of coupled CH₃ pairs which are isolated from each other. However, from the fact that the tunneling frequencies shift to higher values with decreasing spin temperature, we conclude that coupling effects are important not only between nearest neighbour CH₃ groups. Quantitatively we can describe the observations by a model of coupled pairs with a fixed value for the interaction potentialW ₃ and a variable single particle potentialV ₃ which depends linearly on the concentration of the spin symmetry species.     

Preparative manipulation of gold nanoparticles by reversible binding to a polymeric solid support

A preparative scheme is presented for controlled modification of gold nanoparticles (NPs) by using reversible binding to a polymeric solid support through boronic acid chemistry. Octanethiol-capped Au NPs were bound to a boronic acid functionalized resin by custom-synthesized bifunctional linker molecules. The NPs were chemically released from the resin to the solution, with one (or a few) linker molecules embedded in their capping layer. This was confirmed by rebinding the linker-derivatized NPs to a boronic resin, exploiting the reversibility of the boronic acid/diol chemistry. The same scheme was employed to demonstrate a new method for affinity separation of NPs by means of a solid-phase reaction. The use of boronic acid provides versatility and chemical reversibility, while the polymeric solid support affords the separation and preparative aspects. The method presented here may be useful in various facets of NP handling, manipulation, and separation.