Dipole moments of styrene/4-vinylpyridine copolymers—II: Relation to microstructure

Mean-square dipole moment values of styrene/4-vinylpyridine (S4VP) copolymers determined at 25–60°C in 1,4-dioxane solutions were related to the microstructure of the chains. Data on the synthesis and dipole moments of S4VP copolymers were used to calculate the distribution of triad fractions and effective dipole moments of styrene, S-centred, and 4-vinylpyridine, V-centred, fractions in the copolymer chains. The relative magnitudes of the effective dipole moment values calculated for each type of triad reflect the effect of dipole–dipole interactions on these values.     

微扰理论的应用研究(I)——水-正丁醇二元体系热力学计算

本文对流体分子中的色散能和排斥能采用Lennard-Jones位能函数和Barker-Henderson微扰理论进行计算;偶极定向能采用空间取向平均和微扰理论处理,并用Monte Carlo分子模拟数据进行了验证;还考虑了诱导偶极能.在此基础上,计算了H_2O-nC_4H_9HO二元体系液相组分活度系数,结果满意.     

微扰理论的应用研究(I)——水-正丁醇二元体系热力学计算

本文对流体分子中的色散能和排斥能采用Lennard-Jones位能函数和Barker-Henderson微扰理论进行计算;偶极定向能采用空间取向平均和微扰理论处理,并用Monte Carlo分子模拟数据进行了验证;还考虑了诱导偶极能.在此基础上,计算了H_2O-nC_4H_9HO二元体系液相组分活度系数,结果满意.     

The synthesis,electrochemical and theoretical nonlinear optical properties of push–pull chromophores for photorefractive composites

Four chromophores, of different dipole moment and polarizable anisotropy and which comprised conjugation bridges of both benzene and polyene with strong electron-donor and electron-acceptor groups, were characterized using ¹H NMR, FT-IR, UV–vis, and electrochemical analyses. The electric dipole moment (μ), polarizability (α) and the first hyperpolarizability (β) values of the chromophores were examined using computational methods. The contribution of orientational birefringence to total birefringence was estimated from the calculated molecular parameters of the chromophores; these parameters are important factors for predicting photorefractive efficiency.     

Electronic Structure and Ground State Properties of PMMA Polymer: I. Step-By-Step Formation and Stereo-Regularity of the Polymeric Chain—AM1-MO Treatment

ABSTRACT

The equilibrium ground state geometric parameters of benzoyl peroxide (as free radical initiator), methylmethacrylate monomer (as a reference molecule), benzoyl-MMA radical (I), phenyl-MMA radical (II) and the three polymeric chain of PMMA (syndiotactic, isotactic, and atactic) are investigated theoretically using AMI-MO method. The stability of phenyl, benzoyl-MMA radicals, and the conformational properties of isotactic, syndiotactic, and atactic structures of PMMA polymers are discussed. The initiation and propagation steps of polymerization are investigated theoretically. The calculated geometric parameters are analyzed in terms of heat of formation, total energy, dipole moment, net charge, ionization potential, electron affinity, energy gap, and charge density maps (Total, HOMO, and LUMO).     

Relative Dipole Moments of Excited Singlet and Triplet States in Molecules

The availability of experimental values of molecular dipole moments in electronically excited states suggests the desirability of establishing some general principles. Three such principles are proposed, as a means of explaining the observed values of the dipole moment in corresponding singlet and triplet states, where the relevant molecular orbitals are very similar. The general conclusion is that we shall usually expect μ_GS - μ_T to be larger than μ_GS - μ_S, where μ_GS, μ_T, μ_S are the dipole moments in the ground state, the excited triplet and singlet states respectively. The principles are illustrated by specific reference to NF, CO, BeO, formaldehyde, methylene and azulene. Some difficulties arise with larger molecules, and also when configuration interaction plays an unusually important rǒle.     

Solution behavior of Na sulfonated polystyrene: Dipole moment determinations

Solution behavior of Na sulfonated polystyrene (NaSPS) ionomers with different percentages of sulfonate was studied by viscosity and dipole moment measurements. Two solvents of different character were chosen, i.e. dioxane (? = 2.22) and dimethyl formamide (DMF, ? = 36) and their mixtures. The reduced viscosity as a function of concentration in polar solvents reflects the ‘polyelectrolyte’ behaviour of the ionomers. Mean-squared dipole moment (<μ²>/x) values were calculated over a temperature range of 20–100°C, in dioxane and in a mixture of 4% DMF in dioxane. The results confirm the ‘polyelectrolyte’ behavior of ionomers by the addition of a small amount of polar cosolvent. The effect of increasing temperature on <μ²>/x in the DMF-dioxane mixture is attributed to the formation of a coordination complex.     

Impedance,dielectric and modulus analyses of compounds LiMnVO4 and LiCuVO4

Abstract

A comparative study is carried out between the non-humidity sensitive Li vanadates, LiMnVO₄ and LiCuVO₄, from 25 to 500°C at frequencies from 42 Hz to 1 MHz. The mobile ion hopping rate of LiMnVO₄ is found to be higher than that of LiCuVO₄ due to the lower LiMnVO₄ bulk and grain boundary activation energy values. Dielectric constant values from 25 to 500°C at frequencies from 42 Hz to 1 MHz revealed the presence of all types of polarisation. At the plots of LiCuVO₄ tan?δ (dielectric loss) versus frequency, tan?δ displays a peak at a frequency that shifts to higher values with temperature. At 400°C, the maximum losses appear at 1 kHz and at 500°C at 10 kHz. The modulus master curves of LiCuVO₄ and LiMnVO₄ suggested the presence of conduction processes with the same activation energy at different frequencies.     

A theoretical study of the tautomerism kinetics of 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one in the gas phase: NBO population and NICS analysis

The tautomerization reactions of the 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one studied by means of M06-2x and CBS-QB3 theoretical methods. The measured energy profiles are complemented with kinetic rate coefficients calculations using transition state theory (TST). In line with the optimized tautomers geometries using the CBS-QB3 method, the natural bond orbital (NBO) analysis reveals that the stabilization energies of non-bonding LP(e)_S8 to the σ*_N2–C3 antibonding orbitals increase from tautomers 1 to 2. Furthermore, the delocalization energies of LP(e)_S8→σ*_N2–C3 could explain the increase of LP(e)_S8 non-bonding orbitals occupancies in the tautomers 1 and 2 (2?>?1). The increase of LP(e)_S8→σ*_N2–C3 delocalizations could fairly explicate the kinetics of tautomeric pathways 1 and 2 (k_2?>?k₁). Moreover, the HOMO–LUMO energy gap is increased parallel with the decreasing of activation energy barriers. NBO results also show that the kinetics of these processes controlled using LP→σ* resonance energies. Furthermore, nucleus-independent chemical shift (NICS) indices show the calculated reaction and energy barriers are involved by changes in aromaticity characters as well as electron transfer from LP(e)_S8 to σ*_N2–C3 orbitals, thus these reactions are controlled from both thermodynamic and kinetic viewpoints by the changes aromaticity characters.     

Inhibition Effects of a Synthesized Novel 4-Aminoantipyrine Derivative on the Corrosion of Mild Steel in Hydrochloric Acid Solution together with Quantum Chemical Studies

1,5-Dimethyl-4-((2-methylbenzylidene)amino)-2-phenyl-1H-pyrazol-3(2H)-one (DMPO) was synthesized to be evaluated as a corrosion inhibitor. The corrosion inhibitory effects of DMPO on mild steel in 1.0 M HCl were investigated using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, open circuit potential (OCP) and electrochemical frequency modulation (EFM). The results showed that DMPO inhibited mild steel corrosion in acid solution and indicated that the inhibition efficiency increased with increasing inhibitor concentration. Changes in the impedance parameters suggested an adsorption of DMPO onto the mild steel surface, leading to the formation of protective films. The novel synthesized corrosion inhibitor was characterized using UV-Vis, FT-IR and NMR spectral analyses. Electronic properties such as highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy (EHOMO and ELUMO, respectively) and dipole moment (μ) were calculated and discussed. The results showed that the corrosion inhibition efficiency increased with an increase in the EHOMO values but with a decrease in the ELUMO value.     

Dipole moments of styrene/4-vinylpyridine copolymers—I: Relation to the fraction of polar component

Mean-square dipole moments for styrene/4-vinylpyridine (S4VP) random copolymers were determined at five different temperatures, 25–60°C, in 1,4-dioxane solution. The dipole moment behaviour was examined with respect to the increase in mole fraction of the polar monomer, 4-vinylpyridine (4VP), in the copolymer. The behaviour observed was different from the general behaviour of similar copolymers. The temperature coefficient of the dipole moment ratio was found to be zero, within experimental error, in the temperature interval 25–60°C.     

Surface morphology and Flory-Huggins interaction strength in UCST blend system comprising poly(4-methyl styrene) and isotactic polystyrene

The surface morphology and polymer-polymer interaction parameter (χ₁₂) of UCST blend systems comprising isotactic polystyrene and poly(4-methyl styrene) (P4MS) were investigated using atomic-force microscopy (AFM) and differential scanning calorimetry (DSC). From the measured glass transition temperature and the specific heat increments (ΔC_p) at T_g, it was found that the P4MS dissolved more easily in the iPS rich-phase than did the iPS in the P4MS rich-phase. AFM result also supported that the compatibility increased more in the regions of P4MS-rich compositions than in the regions of PS-rich compositions of the PS/P4MS blends. From the measured T_g’s and apparent weight fractions of iPS and P4MS dissolved in each phase, the values of the Flory-Huggins interaction parameter (χ₁₂) were determined to be 0.0163-0.0232 depending on the composition. These results indicate that the χ₁₂ is quite dependend on the apparent volume fraction of the polymers dissolved in each phase. The values of χ₁₂ calculated from this work (method based on T_g’s of phases) were lower than those estimated using an earlier method based on the UCST or clarity temperatures. All values of χ₁₂ are greater than the values of interaction parameter at the critical point (χ₁₂)_c. This fact indicates that the iPS/P4MS blend are immiscible for all blend compositions. The surface of the phase-separated blend system was mostly covered with the P4MS rich-phase owing to its lower surface free energy in comparison with that of the neat iPS. The mechanism of surface phase separation for the P4MS blends with aPS or iPS is governed by two factors: (1) difference in the solubility of the two polymers in the solvent and (2) surface free energy.     

Performance improvement on the cold flow properties of crude oil with high asphaltene by adjusting the polarity of the third monomer in polymers

Asphaltenes and waxes are the primary factors affecting the cold flow properties of crude oil. In this paper, based on the binary polymer of acrylate-maleic anhydride (PM₂₂-MA), different third polar groups of acrylamide, N-(hydroxymethyl) acrylamide, N-phenylacrylamide (NPA), and styrene (SM) were introduced to synthesize a series of ternary pour point depressants (PPDs) to explore the effect of asphaltene on the cold flow properties of Xijiang (XJ) crude oil. Thereinto, PM₂₂-MA-NPA containing amide group and benzene ring exhibited the best depressive effect, which decreased pour point by 14°C at 1500 ppm. The mechanism of interaction of the polar groups in PPDs with asphaltene was studied. The polar groups could form stronger hydrogen bonds with asphaltene, delaying the asphaltene macromolecule bonding, allowing the synergistic effect of PPDs and asphaltene to be better utilized to improve the cold flow properties of crude oil. Furthermore, the dipole moment magnitude and electron cloud density were calculated with Gaussian. It was found that the polar group with a dipole moment magnitude of 3.2244 debye and an electron cloud density ranging from −1.6364 to 1.9944 eV was the most suitable third polar monomer for the PPDs of XJ crude oil.     

Enantioanalysis of S-deprenyl using enantioselective, potentiometric membrane electrodes based on C60 derivatives

Enantioselective, potentiometric membrane electrodes based on (1,2-methanofullerene C₆₀)-61-carboxylic acid, diethyl (1,2-methanofullerene C₆₀)-61-61-dicarboxylate and tert-butyl (1,2-methanofullerene C₆₀)-61-carboxylic acid were proposed for the enantioanalysis of S-deprenyl in pharmaceutical compounds. Molecular modeling calculations were performed to prove the reliability of the proposed electrodes. The different characteristics involved in this analysis were explained, namely (i) the stability of each molecule using total energy, hardness and dipole moment, and (ii) the explanation of the mechanism of interaction using intermolecular forces (moderate hydrogen bond interactions), atomic charges and electrostatic potential. Electronic structures as well as molecular interaction have been investigated using Hartree-Fock theory, 3-21G(*) basis set. Stability and feasibility of all the generated structures were supported by their respective energy minima and fundamental frequencies.     

Luminescence investigations of novel orange‐red fluorapatite KLaSr3(PO4)3F: Sm3+ phosphors with high thermal stability

Single‐phase KLaSr₃(PO₄)₃F: Sm³⁺ phosphors with fluorapatite structure were prepared via high‐temperature solid‐state method in air atmosphere for the first time. The X‐ray diffraction, scanning electron microscope, diffuse reflectance spectra, photoluminescence spectra, and temperature‐dependent emission spectra, as well as lifetimes were measured to characterize the as‐prepared phosphors. Phase results indicated that KLaSr₃(PO₄)₃F: Sm³⁺ belongs to hexagonal system with a space group of P‐6. Photoluminescence measurements showed the emission spectrum was composed of four sharp peaks at about 564, 602 (the strongest one), 646, and 702 nm, corresponding to the ⁴G_5/2‐⁶H_J (J=5/2, 7/2, 9/2, and 11/2) transitions of Sm³⁺ ions. The optimum doping concentration of Sm³⁺ ions was turned out to be 0.03 (mol), and the mechanism of energy transfer among Sm³⁺ ions was considered to be dipole‐dipole interaction by using Dexter's theory. In addition, the critical distance R_c for energy transfer among Sm³⁺ ions were calculated to be 9.97 Å according to Blasse concentration quenching method. The selected KLa_0.97Sr(PO₄)₃F: 0.03Sm³⁺ exhibited high thermal stability with an activation energy of 0.163 eV. Besides, the Commission International de l'Eclairage chromaticity coordinate of the phosphor were located in the orange‐reddish light region.     

Polar silicones: structure-dielectric properties relationship

A series of polar silicones was synthesized in order to compare their dielectric properties. Different substituents with high dipole moment (epoxy, pyridyl, aldehyde, cyano-, nitroazobenzene) were attached by hydrosilylation to a poly(dimethyl-methylhydro)siloxane. Thiol-ene addition on a dimethyl-methylvinyl siloxane copolymer with similar composition was also used for chemical modifications with chloro- or carboxy- derivatives. This approach allowed comparison of properties with emphasis on dielectric behavior measured in liquid state, as a preliminary step in design and preparation of materials suitable for dielectric elastomers. Although a relatively low content of polar groups was used (8%), permittivity values of 5.4 and even 7.4 were achieved (at 10 kHz), either due to the large dipole moment or to the presence of important amounts of moisture. The water sorption capacity of the polar silicones was investigated by dynamic vapor sorption, while structural parameters of model molecules were calculated, in order to correlate the dielectric properties with the polarity/hydrophilicity of the substituents to the silicone chain. A combined effect of the calculated dipole moment, molar polarizability, molar volume, and the measured water sorption capacity on dielectric permittivity was observed.     

Interaction of hydrogen sulfide with the pristine and B&N-doped beryllium oxide nanotube: DFT study

ABSTRACT

In this study, hydrogen sulfide interaction with pristine, B-, N-, and B&N atom-doped beryllium oxide nanotube (BeONTs) is investigated by the density functional theory (DFT) method. At the first step, we considered different configuration models for the adsorption of H₂S on the surface of nanotube and then we selected 12 stable models for this study. The structures of all selected models are optimized and the quantum properties, thermodynamic parameters, natural bond orbitals (NBO), reduced density gradient (RDG), molecular electrostatic potential (MEP), and atom in molecule (AIM) parameters are calculated at the cam–B3LYP level of theory with 6–31G (d) base set. The obtained E_ads for the exterior surface of nanotube is exothermic and is in the range –3.15 to –28.34?Kcal mol^–1, and that for the interior surface is endothermic and is in the range 19.17 to 27.17?kcal mol^–1. The gap energy for pure, B-doped, N-doped, and B&N-doped BeONTs is 10.11, 10.03 (α spin), 10.13 (α spin), and 9.35?eV, respectively. The results of thermodynamic parameters, such as ΔG and ΔH values for the adsorption of H₂S, on the surface of B-doped BeONTs are more negative than other models and favorable in thermodynamic approach. The NBO, MEP, NMR, and HOMO–LUMO results confirm that the electron charge transfer occurs from H₂S molecule toward BeONTs, as a result the bonding type of H₂S?…?BeONTs is weak ionic.