Enhanced dielectric properties and energy storage density of interface controlled ferroelectric BCZT-epoxy nanocomposites

Polymer nanocomposites with ferroelectric fillers are promising materials for modern power electronics that include energy storage devices. Ferroelectric filler, Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) nanopowder, was synthesized by sol-gel method. X-ray diffraction (XRD) studies confirmed the phase purity and the particle size distribution was determined by transmission electron microscopy (TEM). Extended aromatic ligand in the form of naphthyl phosphate (NPh) was chosen for surface passivation of BCZT nanoparticles. Surface functionalization was validated by thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy using slurry technique. The dielectric constant of surface-passivated BCZT nanopowder was ~155, whereas pristine BCZT nanopowder dielectric constant could not be assessed due to high innate surface conductivity. Furthermore, BCZT–epoxy nanocomposite films were prepared and analyzed by differential scanning calorimetry (DSC), dielectric spectroscopy, dielectric breakdown strength (DBS), and scanning electron microscopy (SEM). Owning to stronger polymer–particle interface, dielectric measurements of 5 vol.% NPh surface functionalized BCZT–epoxy nanocomposites indicated improved DBS and glass transition temperature (T_g), reduced dielectric loss, and enhanced energy storage density compared to untreated BCZT–epoxy composites and pure epoxy. The energy storage density of 30 vol.% NPh surface functionalized BCZT–epoxy nanocomposite of 20 μm film thickness was almost three times that of pure epoxy polymer of identical film thickness.     

Selective separation of strontium by multitopic ion‐pair receptor: A DFT exploration

Selective extraction of a radionuclide in the presence of other interfering ions is one of the vital steps in the back‐end‐of‐the‐nuclear fuel cycle. The presence of interfering cations (such as Ca²⁺) in the radioactive waste and involvement of multiple separation steps are known to be bottlenecks in the efficient Sr²⁺ extraction. Here, using free energy corrected density functional theory, we have proposed a two‐step Sr²⁺ extraction methodology in nitrate media in the presence of interfering Ca²⁺ ion using a multitopic ion‐pair receptor, which was earlier reported to be strongly selective for K⁺ (Kim et al. J. Am. Chem. Soc. 2012, 134 , 1782–1792). To depict the correct free energy trend in the proposed extraction processes, the most probable binding mode of the metal (Sr²⁺, Ca²⁺, and K⁺) nitrates in the host are identified. In excellent agreement with the previously reported experiment, Crown/Pyrrole (C/P) binding is noted to be the most preferable mode for KNO₃, where K⁺ and occupied the Crown (C) and Pyrrole (P) site, respectively. However, the divalent metal ions (Ca²⁺ and Sr²⁺) are noted to marginally prefer Crown/Crown‐Pyrrole (C/CP) mode, in which metal reside at the C site while two nitrates occupy the P site and also simultaneously bind at the outer sphere of C site to coordinate with the metal via monodentate motif. Based on the free energy of extraction, we predict that the selective separation of chemically alike Ca²⁺/Sr²⁺ pair is indeed achievable using this receptor. We propose that once [Sr(NO₃)₂] is extracted in organic media, the receptor's high affinity toward K⁺ in nitrate media can be used to back strip Sr²⁺ to the aqueous phase.     

Low‐Energy Electron‐Induced Transformations in Organolead Halide Perovskite

Methylammonium lead iodide perovskite (MAPbI₃), a prototype material for potentially high‐efficient and low‐cost organic–inorganic hybrid perovskite solar cells, has been investigated intensively in recent years. A study of low‐energy electron‐induced transformations in MAPbI₃ is presented, performed by combining controlled electron‐impact irradiation with X‐ray photoelectron spectroscopy and scanning electron microscopy. Changes were observed in both the elemental composition and the morphology of irradiated MAPbI₃ thin films as a function of the electron fluence for incident energies from 4.5 to 60 eV. The results show that low‐energy electrons can affect structural and chemical properties of MAPbI₃. It is proposed that the transformations are triggered by the interactions with the organic part of the material (methylammonium), resulting in the MAPbI₃ decomposition and aggregation of the hydrocarbon layer.     

Process monitoring of polymers by in-line ATR-IR, NIR and Raman spectroscopy and ultrasonic measurements

The aim of the present work is to show that spectroscopic and ultrasonic methods are powerful in situ methods for monitoring polymerization processes and for the determination of the composition of polymer blends and additives during extrusion. Quantitative analysis carried out with chemometric methods can determine the composition of multicomponent polymer mixtures and predict real world samples in real-time during extrusion. Examples are the modification of hyperbranched poly(urea-urethane)s, the polymerization of MMA, the real-time determination of flame retardants in PA, and the determination of the composition of the blend PE/PS. To cite this article: D. Fischer et al., C. R. Chimie 9 (2006).     

Translocation of copper within the cavity of cryptands: reversible fluorescence signaling

The movement of a copper ion inside the cavity of cryptands having two distinct metal binding sites at each end is linked to a fluorescence ON-OFF process in a reversible manner, providing a new way of fluorescence switching.     

Predicting the redox properties of uranyl complexes using electronic structure calculations

A plethora of chemical reactions is redox driven processes. The conversion of toxic and highly soluble U(VI) complexes to nontoxic and insoluble U(IV) form are carried out through proton coupled electron transfer by iron containing cytochromes and mineral surfaces such as machinawite. This redox process takes place through the formation of U(V) species which is unstable and immediately undergo the disproportionation reaction. Thus, theoretical methods are extremely useful to understand the reduction process of U(VI) to U(V) species. We here have carried out the structures and reduction properties of several U(VI) to U(V) complexes using a variety of electronic structure methods. Due to the lack of experimental ionization energies for uranyl (UO₂(V)‐UO₂(VI)) couple, we have benchmarked the current and popularly used density functionals and cost effective ab initio methods against the experimental electron detachment energies of [UO₂F₄]^1‐/2‐ and [UO₂Cl₄]^1‐/2‐. We find that electron detachment energy of U(VI) predicted by RI‐MP2 level on the BP86 geometries correlate nicely with the experimental and CCSD(T) data. Based on our benchmark studies, we have predicted the structures and electron detachment energies of U(V) to U(VI) species for a series of uranium complexes at the RI‐MP2//BP86 level which are experimentally inaccessible till date. We find that the redox active molecular orbital is ligand centered for the oxidation of U(VI) species, where it is metal centered (primarily f‐orbital) for the oxidation of U(V) species. Finally, we have also calculated the detachment energies of a known uranyl [UO₂]¹⁺ complex whose X‐ray crystal structures of both oxidation states are available. The large bulky nature of the ligand stabilizing the uncommon U(V) species which cannot be routinely studied by present day CCSD(T) methods as the system size are more than 20–30 atoms. The success of our efficient computational strategy can be experimentally verified in the near future for the complex as the structures are stable in gas phase which can undergo oxidation.     

Effect of three-body forces on the lattice dynamics of noble metals

A simple method to generate an effective electron-ion interaction pseudopotential from the energy wave number characteristic obtained by first principles calculations has been suggested. This effective potential has been used, in third order perturbation, to study the effect of three-body forces on the lattice dynamics of noble metals. It is found that three-body forces, in these metals, do play an important role. The inclusion of such three-body forces appreciably improves the agreement between the experimental and theoretical phonon dispersion curves.     

Caprin-1 Promotes Cellular Uptake of Nucleic Acids with Backbone and Sequence Discrimination

The cellular delivery of oligonucleotides has been a major obstacle in the development of therapeutic antisense agents. PNAs (Peptide Nucleic Acid) are unique in providing a modular peptidic backbone that is amenable to structural and charge modulation. While cationic PNAs have been shown to be taken up by cells more efficiently than neutral PNAs, the generality of uptake across different nucleobase sequences has never been tested. Herein, we quantified the relative uptake of PNAs across a library of 10 000 sequences for two different PNA backbones (cationic and neutral) and identified sequences with high uptake and low uptake. We used the high uptake sequence as a bait for target identification, leading to the discovery that a protein, caprin-1, binds to PNA with backbone and sequence discrimination. We further showed that purified caprin-1 added to cell cultures enhanced the cellular uptake of PNA as well as DNA and RNA.