Depolarization field effect on the ferroelectric behavior of polymers

The effect of the depolarization field in crystallites on the ferroelectric behavior of polymers is discussed on the assumption that the crystallite is a prolate ellipsoid with its major axis directed along the electric field. The theory relates the polarization P and the electric field E in the crystallite to the overall values P and E for the polymer. The determination of the P -E hysteresis of a crystallite from the P-E hysteresis is given with examples for poly(vinylidene fluoride) (PVDF) and vinylidene fluoride (VDF)–trifluoroethylene (TrFE) copolymer. The ratio R = J/(P_s ? P), with J the switching current density and P_s the saturation polarization of polymer, is proved to be free from the depolarization field effect and the plot of logR against logarithmic time is shown to have merit for characterization of switching behavior. Examples of the curves are given for PVDF and VDF-TrFE copolymers. The temporal change of local electric field in the unreversed domains in the crystallite in the course of polarization reversal is predicted by the theory and this change is proved to be a significant mechanism of switching acceleration.     

Hydroalumination and Hydrogallation Reactions with Tri(ethynyl)silanes – Generation of Compounds with up to Three Coordinatively Unsaturated Aluminium Atoms

Hydroalumination or hydrogallation of tri(ethynyl)silanes, RSi(C≡C‐Ar)₃ ( 1a , R = Ph, Ar = Ph; 1b , R = Me, Ar = Ph; 1c , R = Me, Ar = C₆H₄Me), with the element hydrides H‐EtBu₂ (E = Al, Ga) in stoichiometric ratios of 1:1 to 1:3 at ambient temperature yielded the addition products (PhC≡C)₂(R)Si[(tBu₂E)C=C(H)Ph] ( 2 , R = Ph, E = Ga; 3a , R = Me, E = Al; 3b , R = Me, E = Ga), (PhC≡C)(Me)Si[(tBu₂E)C=C(H)Ph]₂ ( 4a , E = Al, 4b , E = Ga) and (Me)Si[(tBu₂Al)C=C(H)Ar]₃ ( 5 , Ar = Ph; 6 , Ar = C₆H₄Me). Compounds 2 – 4 show a relatively close interaction between the coordinatively unsaturated aluminium or gallium atoms and one of the C_α(≡C) atoms of unreacted alkyne substituents [245 (E = Al) and 266 pm (E = Ga)] that stabilises the kinetically favoured cis addition products with E and hydrogen on the same side of the resulting C=C double bonds. In the absence of these stabilising effects the compounds were found to isomerise to the thermodynamically favoured trans isomers.     

Development of a new software for the X-ray structural analysis of polymer crystals by utilizing the X-ray imaging plate system

A software and some useful tools have been developed for identifying individual x-ray reflectional peaks recorded with an x-ray imaging plate system. These techniques were applied to analyze the crystal structure of uniaxially oriented polymer samples. Characteristic features of the present method may be summarized as follows. (1) The indexing of the observed reflections and the determination of the unit cell parameters can be made easily on the display of the computer. (2) The integrated intensity of the individual component of the overlapped reflections can be evaluated quantitatively through the curve separation technique. The R_merge's for the equivalent reflections were 5–6%, indicating the exact evaluation of the integrated intensities. (3) The thus obtained reflectional data were successfully utilized for the extraction of the initial structural models by the direct method. The actual applications have been made for orthorhombic polyethylene, trigonal polyoxymethylene, and isotactic polybutene-1, giving the refined crystal structures including even the positions of hydrogen atoms in some cases. The reliability factors were 12, 5, and 15%, respectively, for these three polymer cyrstals. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1677–1700, 1997     

Density matrices for correlated Gaussians: Helium and dipositronium

Formulas are derived for the density matrices belonging to an n-particle wave function built on the basis of single-center explicitly correlated Gaussian basis functions. An explicit formula for the first-order density matrix, P(r₁, r′₁), is obtained for computing the probability distribution P(r₁, r₁). Other formulas are derived for matrix elements of the first-order density operator P on a basis of single-particle Gaussian orbitals so that natural orbitals (NOs) can be expressed in such a basis. The method is illustrated for the case of the ground state of the helium atom using the 16-term (geminal) wave function by Singer and Longstaff (E = −2.90233 au) and a set of even-tempered Gaussian orbitals. The resulting natural orbitals compare favorably with natural orbitals from Cl expansions. The method is also applied to our 20 term (trimal) wave function for the ground state of dipositronium (E = −0.51560 au). Analysis is made in this case for pair correlation functions of both the electron-electron and the positron-electron pairs; results include the radial distributions of these pairs and their relative angular momentum. © 1996 John Wiley & Sons, Inc.     

Theoretical calculation of the low laying electronic states of the molecular ion KH

Using an ab initio method the potential energy has been calculated for the 25 lowest molecular states of symmetries ²Σ⁺, ²Π, ²Δ for the molecular ion KH⁺. The calculation is based on nonempirical pseudopotentials and parameterized ℓ-dependent polarization potentials. Gaussian basis sets have been used for both atoms. The spectroscopic constants for 18 electronic sates have been calculated by fitting the calculated energy values to a polynomial in terms of the internuclear distance R. Through the canonical functions approach the eigenvalue E_v, the abscissas of the corresponding turning points (R_min and R_max) and the rotational constants B_v have been calculated up to 24 vibrational levels for the considered bound states. The comparison of the present results with those available in literature shows a very good agreement.     

EDX depth profiling by means of effective layers

A new approach is described for depth profiling in stratified multilayer samples by recording energy dependent characteristic x-ray EDX(E ₀ ) curves in a scanning electron microscope. An effective layer technique replaces the x-ray excitation function of the heterogeneous target by an equivalent function of a homogeneous sample. First results of thickness determination are shown and compared to direct measurements of film thickness monitoring (FTM) and atomic force microscopy (AFM).     

Cathodoluminescence Depth Profiling in SiO2:Ge Layers

 For investigation of the luminescent center profile cathodoluminescence measurements are used under variation of the primary electron energy E ₀ = 2…30 keV. Applying a constant incident power regime (E ₀·I ₀ = const), the depth profiles of luminescent centers are deduced from the range of the electron energy transfer profiles dE/dx. Thermally grown SiO₂ layers of thickness d = 500 nm have been implanted by Ge⁺-ions of energy 350 keV and doses (0.5–5)10¹⁶ ions/cm². Thus Ge profiles with a concentration maximum of (0.4 – 4) at% at the depth of d_m≅240 nm are expected. Afterwards the layers have been partially annealed up to T _a = 1100 °C for one hour in dry nitrogen. After thermal annealing, not only the typical violet luminescence (λ = 400 nm) of the Ge centers is strongly increased but also the luminescent center profiles are shifted from about 250 nm to 170 nm depth towards the surface. This process should be described by Ge diffusion processes, precipitation and finally Ge nanocluster formation. Additionally, a Ge surface layer is piled-up extending to a depth of roughly 25 nm.     

Theoretical calculation of the low laying electronic states of the molecular ion RbH+

Using an ab initio method, the potential energy has been calculated for the 29 lowest molecular states of symmetries ²Σ⁺, ²Π, ²Δ for the molecular ion RbH⁺. The calculation is based on nonempirical pseudopotentials and parameterized ?‐dependent polarization potentials. Gaussian basis sets have been used for both atoms. The spectroscopic constants for 18 electronic sates have been calculated by fitting the calculated energy values to a polynomial in terms of the internuclear distance R. Through the canonical functions approach the eigenvalue E_v, the abscissas of the corresponding turning points (R_min and R_max) and the rotational constants B_v have been calculated up to 24 vibrational levels for the considered bound states. The comparison of the present results with those available in literature shows a very good agreement. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Flow of polymer chains and segregation in a flow field with a hybrid simulation

Effects of a flow field (E) on segregation and flow of polymer chains are studied in two dimensions using a hybrid (discrete‐to‐continuum) simulation. The flow rate (j) of polymer chains is found to increase monotonically with E, a linear response in the low field regime followed by a slow approach to saturation in the high field regime. The effective chain permeability (ϕ_c = j/E) varies nonmonotonically on increasing the field E, with a maximum (ϕ_cm) at a characteristic value of the field (in the range 0.2 < E < 2); ϕ_cm depends on the chain length. Chain aggregates exhibit an anisotropic mass distribution due to the field with a molecular bridging at high fields. The longitudinal component of the radius of gyration (R_gx) exhibits a crossover from a random walk (RW) (R_gx ˜ L_c^1/2) at E = 0 to an elongated conformation (R_gx ˜L_c) at E ⪈ 0.2; the transverse component changes from R_gy ˜ L_c^1/2 to R_gy ˜ L_c^1/3. The width of the radial distribution function (ρ(r)) of the monomers increases while its peak varies nonmonotonically with E and is consistent with the observation of anisotropic mass distribution.     

Calorimetric and theoretical studies on the system of {(R)-(+)-limonene+(S)-(-)-limonene}

In order to reveal the origin of chiral discrimination, excess molar heat capacities (C_P ^E) of ((R)-(+)-limonene+(S)-(−)-limonene) were determined by using a differential scanning calorimeter at temperatures between T=293.15 and 303.15 K. All C_P ^E curves show S-shape. It was inferred that randomness appears in the (S)-(-)-limonene-rich region, and that non-randomness appears in the (R)-(+)-limonene-rich region. To clarify the differences in homochiral interactions and heterochiral interactions, molecular orbital calculations were carried out.     

Investigation on molecular interaction studies of binary mixture of DEHPA and petrofin at 298.15 K

The present article reports the values of density (ρ₁₂), molar volume (V₁₂), apparent molar volume (V_?), dielectric constant (?₁₂), molar polarisation (P₁₂) and molar refraction (R₁₂) of binary mixture of di-2-ethylhexyl phosphoric acid (DEHPA) and petrofin at various compositions. The excess properties such as V^E, ?^E, ΔnD, P^E and R^E have been calculated to throw light on the existence of interaction between the DEHPA and petrofin molecules in the binary mixture. The values of V^E and R^E were found to be positive while the values of ?^E, ΔnD and P^E were negative over the entire composition showing weak interaction between the two unlike molecules in the mixture. The Kirkwood-correlation factors (g) have been evaluated to know the nature of interaction prevailing in DEHPA and petrofin. These data provide useful information regarding interaction between self-associated protic DEHPA and non-associated petrofin which in turn helps the metallurgist to use DEHPA diluted with petrofin as effective solvent in extraction of metals.     

Optical spectroscopy of (C2H5NH3)2CdCl4:Cu2+ under pressure: Study of Cu2+ local structure from theoretical calculations

The variations experienced by the energy E_u(π) of the e_u(π)→b_1g (～x²–y²) charge‐transfer transition of (C₂H₅NH₃)₂CdCl₄:Cu²⁺ upon pressure in the 0‐ to 40‐kbar range have been measured at room temperature by means of a sapphire anvil cell. These data reveal that E_u(π) undergoes a red shift of 1400 cm^?1 on passing from ambient pressure to 40 kbars. To understand this puzzling result theoretical calculations of ?E_u(π)/?R_eq and ?E_u(π)/?R_ax have been performed where R_eq and R_ax mean the equatorial and axial Cu²⁺–Cl^? distances of the elongated CuCl₆^4? complex, respectively. All results indicate that ?E_u(π)/?R_eq and ?E_u(π)/?R_ax for R_eq=228 pm and R_ax=297 pm are indeed negative. Moreover ab initio complete active space self‐consistent field (CASSCF/CASPT2) and density functional calculations lead to ?E_u(π)/?R_ax values, which are about 10 times smaller than those of ?E_u(π)/?R_eq. From the ensemble of experimental and theoretical results, it is concluded that a pressure of 40 kbars gives rise to a decrement of ≈25 pm of the axial distance and at the same time to an increase of ≈7 pm of the equatorial one. It is stressed that the present study on a diluted Jahn–Teller impurity lies far beyond the current possibilities of X‐ray absorption structure techniques. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Synthesis,Crystal Structure and Magnetic Property of Copper(II) Complex with 4′-Cyanobenzyl-1-imidazol

A neutral mononuclear complex [Cu(cbIm)₄(NO₃)₂] (cbIm = 4'-cyanobenzyl-1-imidazol) was synthesized and characterized by x-ray crystallography. It crystallizes in the triclinic space group P-1 with a = 8.249(2), b = 8.735(2), c = 16.597(2) Å, f = 81.980(10), g = 88.540(10), n = 63.570(10)° and Z = 2. The final refinement of the structure leads to R and Rw of 0.0394 and 0.0991, respectively. The crystal structure of the complex indicates a distorted octahedral environment around the Cu(II) atom, coordinated by four imidazole N atoms of four cbIm and two O atoms of two nitrates. Magnetic measurements show that the complex exhibits Curie behavior.     

Palladium-catalyzed allylic substitution assisted by 1,3,2-diazaphospholidine derivatives of (<Emphasis Type="Italic">R,R</Emphasis>)-<Emphasis Type="Italic">N</Emphasis>-naphthyltartarimide

P,P-Bidentate diamidophosphite ligands containing the (3R,4R)-3,4-dioxy-1-(1-naphthyl)pyrrolidine-2,5-dione framework and 1,3,2-diazaphospholidine rings with the stereogenic P atoms were obtained. The use of these ligands provides up to 85% ee in Pd-catalyzed asymmetric amination of (E)-1,3-diphenylallyl acetate and up to 95% ee in its asymmetric alkylation with dimethyl malonate.     

New Insights on the Mechanism of Thermal Cleavage of Unsaturated Bicyclic Diaziridines: A DFT Study

A DFT calculations are carried out at UB3LYP/6‐311++G (3df, 2p) levels of theory to study electrocyclic thermal cleavage of four (R) derivatives of unsaturated bicyclic diaziridines, 1_X‐R , to produce corresponding (Z) and (E) azomethine imides ( 2_X‐Z , 2_X‐E , 3_X‐Z and 3_X‐E ), where X=H, Me, t‐Bu and Ph. Cleavage of 1_X‐R series to form the most stable 3_X‐Z product, (path 2) is found the favored procedure because of delocalized negative charge on five atoms and lower steric effect in related transition state. According to IRC calculations in paths 1 and 2, C⁶ N¹ bond is cleaved before the rate determinating step (transition state). The stability of unsaturated bicyclic diaziridines and their corresponding (Z) and (E) azomethine imides is in the following order in gas phase and chloroform, tetrahydrofuran, and acetone solvents: 3_X‐Z < 3_X‐E < 2_X‐Z < 2_X‐E < 1_X‐R < 1_X‐S .     

Structural study of oriented non-crystalline PET by CDF method

The two-dimensional wide angle X-ray scattering (WAXS) intensities of oriented non-crystalline polyethylene terephthalate (PET) films extended umaxially are collected by the symmetrical transmission method; he-sides,the overlapped non-crystalline peaks at WAXS intensity curves,I(K) obtained at different azimuthal angles are also separated by computer,resulting in two peaks caused by interchain atomic scattering in the reciprocal space,KA(K=0.122),KB(K=0.171),and the other two peaks from intracham atomic scattering,Kc(K=0.310) and KD(K=0.548); their cylindrical distribution functions (CDF),CDF(R,α) in the real space are further calcu lated from the intensity functions,IE(K) using sampled transforms,thereof arising in turn the peaks in the real space as,RA(R=0.658),RB(R=0.456),RC(R=0.253) and RD(R=0.152),corresponding to KA,KP,K,and KD The equivalent relationships and distribution characteristics of the above-mentioned corresponding peaks in the reciprocal and real space,as well as their sources of struc     

Synthesis and structural studies of (2 E ,3 E ,6 R ,9 E ,11 E )-6-isopropenyl-3,6,10-trimethyl-5,8-dioxa-4,9-diazadodeca-3,9-diene-2,11-dione dioxime, ligand and its Mono-, homo, and heterodinuclear copper(II)/nickel(II) complexes

This article describes the synthesis of a new (2E,3E,6R,9E,11E)-6-isopropenyl-3,6,10-trimethyl-5,8-dioxa-4,9-diazadodeca-3,9-diene-2,11-dione dioxime (H₂hmdm), and its mono-, homo, and heterodinuclear copper(II)/nickel(II) complexes. Elemental analyses, stoichiometric and spectroscopic data of the metal complexes indicated that the metal ions are coordinated to the oxime and imine nitrogen atoms (C=N). The Cu(H₂hmdm), molecule coordinates to the second copper(II) ion through the oximate oxygens to afford a binuclear structure doubly bridged by the oximate groups in the cis arrangement. In the dinuclear complexes, in which the first Cu^II ion was complexed with nitrogen atoms of the oxime and imine groups, the second Cu^II ion is ligated with the 1,10-phenanthroline nitrogen atoms. Ligand and its mononuclear copper(II), homo and heterodinuclear copper(II)–nickel(II) complexes of (H₂hmdm) were characterized by elemental analyses, magnetic moments, ¹H-n.m.r. and ¹³C-n.m.r., i.r., and mass spectral studies. The data support the proposed structure of H₂hmdm and its complexes.     

Reaction of 5-oxo-2-phenyl-4,4-bis(trifluoromethyl)-4,5-dihydro-1,3,2-benzodioxaphosphepine with chloral. The synthesis and spatial structure of 5-carbaphosphatrane containing a four-membered ring

Phosphorylation of 2-hydroxyphenyl 2,2,2-trifluoro-1-hydroxy-1-(trifluoromethyl)ethyl ketone with dichloro(phenyl)phosphine gave 5-oxo-2-phenyl-4,4-bis(trifluoromethyl)-4,5-di-hydro-1,3,2-benzodioxaphosphepine. Heating of the latter initiated an intramolecular interaction of the P atom with the carbonyl group. Hydrolysis of the intermediate product yielded 3-hydroxy-2-oxo-2-phenyl-3-[2,2,2-trifluoro-1-hydroxy-1-(trifluoromethyl)ethyl]-2,3-di-hydro-1,2λ⁵-benzo[d]oxaphosphole. The reaction was highly stereoselective (P_RC_S/P_SC_R). The reaction of the starting phosphepine with chloral proceeded highly stereoselectively (P_RC_SC_S/P_SC_RC_R) to give a 5-carbaphosphatrane derivative containing a four-membered ring, namely, 1-phenyl-3-trichloromethyl-10,10-bis(trifluoromethyl)-6,7-benzo-2,4,8,9-tetraoxa-1λ⁵-phosphatricyclo[3.3.2.0¹,⁵]decene. The trigonal bipyramid of the 5-carbaphosphatrane derivative is made up of the equatorial O atoms and the apical C atoms.     

“Short-bite” ligands in cluster synthesis

The short-bite ligands CH₂(PR ₂)₂ or CH(PR ₂)₃ (R = Me, Ph),RN(PX ₂)₂ (R=H, Me, Et;X = F, OR (R= Me, Et, i-Pr, Ph), Ph),RE(CH₂ ER₂)₂ (E = P, As;R = Me, Ph ), Ph₂ P(2-C₅H₄N) and related species are particularly versatile for the synthesis of di- and polynuclear complexes which frequently possess metal-metal bonds. In addition to homometallic products, these ligands often permit the directed synthesis of heterometallic complexes. Selected aspects of the chemistry of these complexes are also reviewed.