MO Method Research Articles

GEOMETRY AND MESOMORPHIC PROPERTIES OF NEW SCHIFF BASES CONTAINING THIAZOLE RING

New liquid-crystalline azomethines – 2-(4-alkoxybenzylideneamino)-4-(3-nitrophenylamino)thiazoles – displaying nematic mesomorphism at 42 137°C have been synthesized. The structure of these compounds was studied by the MNDO LCAO MO method. A correlation was found between the geometric parameters and liquid crystal properties. Authors: M. M. Murza, Z. Kh. Kuvatov, and M. G. Safarov. English Translation in Chemistry of Heterocyclic Compounds , 1999, 35 (9), pp 1097-1103 http://link.springer.com/article/10.1007/BF02251804

Theoretical studies of the structures and local aromaticity of conjugated polycyclic hydrocarbons using three aromatic indices

The structures and local aromaticity of some conjugated polycyclic hydrocarbons (from the butadienoid, acene, and phenylene series) are studied using ab initio MO and density functional methods. The aromaticities of the molecules are estimated using three indices: the nucleus-independent chemical shift (NICS), the harmonic oscillator model of aromaticity (HOMA), and the index of deviation from aromaticity (IDA). Assessment of the relationships between the structures and the aromatic indices shows that the IDA values correspond best to the characteristics of the conjugated polycyclic hydrocarbon structures.

Nonisothermal Crystallization Behavior of Polypropylene-C60 Nanocomposites

The nonisothermal crystallization behavior of polypropylene (PP) and PP-fullerene (C60) nanocomposites was studied by differential scanning calorimetry (DSC). The kinetic models based on the Jeziorny, Ozawa, and Mo methods were used to analyze the nonisothermal crystallization process. The onset crystallization temperature (Tc), half-time for the crystallization (t1/2), kinetic parameter (F(T)) by the Mo method and activation energy (ΔE) estimated by the Kissinger method showed that C60 accelerates the crystallization of PP, implying a nucleating role of C60. Furthermore, due to the reduced viscosity of PP by adding 5% C60, the parameters of crystallization kinetics for the PP-5%C60 nanocomposites changed remarkably relative to that of neat PP and when lower contents of C60 were added to PP.

Non-isothermal crystallization kinetics and morphology of wollastonite-filled β-isotactic polypropylene composites

To obtain wollastonite-filled β-iPP composites, the wollastonite with β-nucleating surface (β-wollastonite) was prepared through chemical reaction between wollastonite with α-nucleating surface (α-wollastonite) and pimelic acid. The formation of calcium pimelate on the surface of wollastonite was proved using Fourier transform infrared spectrometry and scanning electron microscopy. The crystallization behavior, melting characteristics, non-isothermal crystallization kinetics, and crystalline morphologies of α- and β-wollastonite-filled iPP composites were studied by differential scanning calorimetry and polarizing optical microscopy. It is found that the crystallization peak temperatures of β-wollastonite-filled iPP composites were higher than that of α-wollastonite-filled iPP composites, which indicated that wollastonite with β-nucleating surface has stronger heterogeneous nucleation than that of wollastonite with α-nucleating surface. Although the crystallization temperatures of iPP and iPP composites decreased with increasing cooling rates, α-wollastonite-filled iPP composites mainly crystallized in α-spherulite and β-wollastonite-filled iPP composites formed β-spherulite. In addition, the spherulite size of β-wollastonite-filled iPP composites was smaller than that of α-wollastonite-filled iPP composites. Jeziorny and Mo methods were applicable to study the non-isothermal crystallization kinetics of wollastonite-filled iPP composites. The activation energy (∆E) and the nucleation efficiency (EN) of non-isothermal crystallization were calculated by Kissinger method and the equation proposed by Fillon, respectively. The β-wollastonite-filled iPP composites exhibited higher crystallization rate, activation energy, and EN than that of α-wollastonite-filled iPP composites.

An Efficient Local Molecular Dynamics Polymerization Simulation Combined with an Ab Initio MO Method.

A new local ab initio molecular dynamics method, namely elongation molecular dynamics (ELG-MD) is proposed for highly efficient simulations of aperiodic polymer systems. ELG-MD combines the elongation method (ELG) with the Gear predictor corrector (GPC) algorithm of molecular dynamics simulation. In this method, the local gradients acting on the atom’s nucleus in the active region are calculated by the ELG method while the equations of the nucleus’s motion are solved by the GPC algorithm. In this work, the first application of this ELG-MD method is described to investigate the stable conformation of polyglycine with surrounding water molecules. The water effects on the structure of polyglycine are examined. The ELG-MD simulations show that the formation of the polyglycine helix is strongly induced by the hydrogen bonds observed in two types of H-bond rings.

Parameters characterizing the kinetics of the nonisothermal crystallization of thermoplastic starch/poly(lactic acid) composites as determined by differential scanning calorimetry

AbstractTo guide the use of thermoplastic starch (TPS)/poly(lactic acid) (PLA) composites, the nonisothermal crystallization kinetics of pure PLA and TPS/PLA composites were investigated with differential scanning calorimetry (DSC) at three different cooling rates. The results indicate that the TPS/PLA composites showed different crystallizations because of their different contents and different cooling rates. TPS, as a nucleating agent, improved the crystallinity of the PLA and constrained the mobility of the PLA chains. Three theoretical models, namely, the Avrami, Ozawa, and Mo models, were used to describe the process of nonisothermal crystallization. The Avrami analysis modified by Jeziorny and the Mo method was successful in describing the nonisothermal crystallization process of the pure PLA and the TPS/PLA composites. However, the Ozawa analysis could not give an adequate description. Kinetic parameters such as the Avrami exponent, kinetic crystallization rate constant, relative degree of crystallinity, and crystallization enthalpy, among others, were determined at various scanning rates. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Benchmarking of London Dispersion-Accounting Density Functional Theory Methods on Very Large Molecular Complexes.

A new test set (S12L) containing 12 supramolecular noncovalently bound complexes is presented and used to evaluate seven different methods to account for dispersion in DFT (DFT-D3, DFT-D2, DFT-NL, XDM, dDsC, TS-vdW, M06-L) at different basis set levels against experimental, back-corrected reference energies. This allows conclusions about the performance of each method in an explorative research setting on "real-life" problems. Most DFT methods show satisfactory performance but, due to the largeness of the complexes, almost always require an explicit correction for the nonadditive Axilrod-Teller-Muto three-body dispersion interaction to get accurate results. The necessity of using a method capable of accounting for dispersion is clearly demonstrated in that the two-body dispersion contributions are on the order of 20-150% of the total interaction energy. MP2 and some variants thereof are shown to be insufficient for this while a few tested D3-corrected semiempirical MO methods perform reasonably well. Overall, we suggest the use of this benchmark set as a "sanity check" against overfitting to too small molecular cases.

Non-Isothermal Crystallization of Poly(vinylidene Fluoride)/Multiwalled Carbon Nanotube Composites

Poly(vinylidene fluoride)/multiwalled carbon nanotube (PVDF/MWCNT) composites were prepared by the method of solution blending. The non-isothermal crystallization of PVDF and its composites was investigated by differential scanning calorimetry (DSC). The results showed that the crystallization peaks shifted to lower temperature and the exothermic trace became wider when cooling rate increased for PVDF and its composites. The MWCNTs caused an increase in crystallization temperature and initial crystallization temperature. In addition, the Jeziorny and Mo methods were used to analyze the non-isothermal crystallization kinetics. The results showed that the crystallization rate rose with an increase in cooling rate, however, the MWCNTs decreased the crystallization rates of PVDF.

Non-isothermal crystallization kinetics of polypropylene/MAP-POSS nanocomposites

Non-isothermal crystallization kinetics of polypropylene (PP)/methylacryloypropy polyhedral oligomeric silsesquioxanes (MAP-POSS) nanocomposites (PP/MAP-POSS) were investigated by DSC at various cooling rates. Jeziorny and Mo method were used to study the non-isothermal crystallization kinetics. The results show that the Jeziorny and Mo method are all successful in describing the non-isothermal crystallization kinetics of PP/MAP-POSS nanocomposites. The MAP-POSS can act a role of heterogeneous nucleation and increase the crystallization rate constant Z c and decrease crystallization half time t 1/2, and the spherulite crystal size decreases, the inter-spherulitic action or crosslinking structure each other appear at the appropriate content. The DSC peak temperature T p increase about 5 °C, t 1/2 reduce 0.21 min at 6 % content of MAP-POSS and heating rate of 10 °C/min. The MAP-POSS can also increase the mechanical property of PP/MAP-POSS nanocomposites, the tensile strength and impact strength increase from 12.97 to 19.93 MPa and from 33.2 to 52.6 kJ/m2, respectively, at 4 % content of MAP-POSS. But the spherulitic crystal becomes larger and boundaries become clearer again; the macrophase separation will occur and mechanical properties decrease when more and more MAP-POSS was added. The nanocomposite has the best mechanical property at 4 % content of MAP-POSS.

Ab initio MO Theory – An Important Tool in Foldamer Research: Prediction of Helices in Oligomers of ω‐Amino Acids

AbstractThe enormous developments of computer technologies allow the broad employment of ab initio MO theory in foldamer research. In this review, we demonstrate the efficiency and reliability of ab initio MO methods for the description of the helix formation in oligomers of ω‐amino acids on the basis of representative examples. Thus, ab initio MO theory successfully accompanies foldamer research by confirmation and interpretation of experimental results and stimulation of future experiments. The high predictive power of the methods opens the way to novel structure classes with special properties. Nowadays, ab initio MO theory has become an inherent part in the arsenal of methods applied in foldamer research.

Influence of Rare-earth Coupling Agent on Non-isothermal Crystallization Behaviour of Wood Flour/Polypropylene Composites

The influence of a rare-earth coupling agent (RE) on the non-isothermal crystallization behaviour of PP was studied by differential scanning calorimetry. Experimental results showed that use of RE caused a decrease in the crystallization temperature, melting temperature and crystallinity of PP in WF/RE/PP compared with those in WF/PP. The Avrami, Ozawa and Mo methods were used to describe the crystallization process. The Avrami and Ozawa methods neglected the secondary crystallization and followed primary crystallization. The Mo approach could successfully describe the overall crystallization process. The relation of the half times of crystallization ( t1/2) of the three samples, t1/2(WF/PP) < t1/2(WF/RE/PP) <t1/2 (PP) and the F( T)(WF/PP)< F( T)(WF/RE/PP) <F( T)(PP), suggested that the crystallization rate of WF/RE/PP was slower than that of WF/PP The activation energy was calculated by using the Kissinger method and the results indicated that the incorporation of RE resulted in a compatible effect, which led to a reduction in the crystallization rate and an increase in activation energy compared with WF/PP.

Influence of nanofiller dimensionality on the crystallization behavior of HDPE/carbon nanocomposites

AbstractThe isothermal and nonisothermal crystallization behavior of high density polyethylene (HDPE) containing various zero, one, and two dimensional (0‐D, 1‐D, and 2‐D) carbon nanofillers were investigated by means of differential scanning calorimetry. For a given temperature, the isothermal crystallization incubation time of HDPE became longer with the addition of lower dimensional carbon nanofillers, and the isothermal crystallization rate got slower. The values of Avrami and Tobin exponents indicated that the isothermal crystallization of HDPE followed two‐dimensional crystal growth in the presence of 2‐D and 1‐D carbon nanofillers, while exhibited three‐dimensional heterogeneous crystal growth in the presence of 0‐D carbon nanofillers. Contrary to the isothermal study, the nonisothermal crystallization of HDPE was accelerated in the presence of lower dimensional nanofillers. The nonisothermal crystallization data were finally analyzed using Ozawa and Mo methods. It was observed that only Mo approach could successfully describe the nonisothermal crystallization process of HDPE and HDPE/carbon nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Reaction Pathways and Dynamics Effects for Ionizations of Vinyl Diazonium Ions

Abstract The denitrogenation reactions of fifteen differently substituted vinyl diazonium (ethenediazonium) ions were examined by MO method at MP2/6-31G*. The parent vinyl diazonium ion (1, CH2=CH–N2+) was shown to initially give the H-bridged cation via the anti-H migration transition state (TS) or the syn-H migration TS. The relative barrier for the two TSs is very small, being 1.0 kcal mol−1 favoring the anti-H migration TS in free energy. The primary open cation is located on a very shallow minimum, and is 4.4 kcal mol−1 less stable than the bridged cation in free energy. The reactions of Me- and Ph-substituted vinyl diazonium ions showed characteristic features depending on the substituent. Molecular dynamics simulations for the reactions of 1 revealed that trajectories from the reactant state mostly gave the bridged cation as expected from the MO result, but there were trajectories that directly led to the open cation without H-participation, a clear manifestation of a dynamics effect. A dynamics effect on the relative population of the bridged versus the open cation is also presented.

Nonisothermal crystallization and morphology of poly(butylene succinate)/layered double hydroxide nanocomposites

Biodegradable poly(butylene succinate) (PBS) and layered double hydroxide (LDH) nanocomposites were prepared via melt blending in a twin-screw extruder. The morphology and dispersion of LDH nanoparticles within PBS matrix were characterized by transmission electron microscopy (TEM), which showed that LDH nanoparticles were found to be well distributed at the nanometer level. The nonisothermal crystallization behavior of nanocomposites was extensively studied using differential scanning calorimetry (DSC) technique at various cooling rates. The crystallization rate of PBS was accelerated by the addition of LDH due to its heterogeneous nucleation effect; however, the crystallization mechanism and crystal structure of PBS remained almost unchanged. In kinetics analysis of nonisothermal crystallization, the Ozawa approach failed to describe the crystallization behavior of PBS/LDH nanocomposites, whereas both the modified Avrami model and the Mo method well represented the crystallization behavior of nanocomposites. The effective activation energy was estimated as a function of the relative degree of crystallinity using the isoconversional analysis. The subsequent melting behavior of PBS and PBS/LDH nanocomposites was observed to be dependent on the cooling rate. The POM showed that the small and less perfect crystals were formed in nanocomposites.

Study on the nonisothermal crystallization kinetics of ternary-monomer solid-phase graft copolymer of polypropylene

In order to discover how the grafted side chains affect the crystallization of the graft copolymers, the ternary-monomer solid-phase graft copolymers of polypropylene (PP; PPSM) were synthesized by solid-phase grafting of maleic anhydride, styrene and butyl acrylate onto PP. The Jeziorny and Mo methods were used to investigate the nonisothermal crystallization kinetics and polarizing microscope was used to study the crystalline morphology of PPSM. Results show that the grafted side chains not only promoted the heteronucleation of PP and reduced the size of spherulites but also hindered the growth of crystals resulting in the formation of imperfect crystallization region in PP. Due to the hindrance of the grafted side chains on the crystallization, the nonisothermal crystallization energy (ΔE) of PPSM calculated by the Kissinger equation is evidently higher than that of PP.

Non-isothermal crystallization kinetics of β-nucleated isotactic polypropylene

Isotactic polypropylenes (iPP) samples were incorporated with two β-nucleating agents (NT-A and NT-C), respectively, and their non-isothermal crystallization and subsequent melt behaviors were investigated by means of differential scanning calorimeter. Jeziorny, Ozawa, and Mo methods were used to analyze non-isothermal crystallization kinetics of pure iPP and β-nucleated iPP samples. The activation energies (ΔE) of non-isothermal crystallization were calculated by Kissinger method. And the nucleation activities were calculated according to the Dobreva method. It is found that the crystallization temperature decreases and the crystallization rate increases with increasing cooling rate. The crystallization temperature and crystallization rate of nucleated iPP are higher than those of pure iPP. The order of ΔE is NT-A/iPP > pure iPP > NT-C/iPP. NT-C is more efficient than NT-A as a β-nucleating agent. But the non-isothermal crystallization kinetics of α- and β-phases cannot be determined separately. The present results should be considered with caution.

Non-Isothermal Crystallization of Poly(Vinylidenefluoride)/Hollow Glass Microspheres Composites

The Poly(vinylidene fluoride)/Hollow glass microspheres(PVDF/HGMs) composites were prepared by the method of solution blending. The non-isothermal crystallization of the PVDF and its composites were investigated with a differential scanning calorimeter (DSC). The results showed that the crystallization peaks shifted to a lower temperature and became wider with an increasing cooling rate. The HGMs caused to increase in crystallization temperature and initial crystallization temperature. In addition, the Jeziorny and the Mo methods were used to analyze the non-isothermal crystallization kinetics. The results showed that the crystallization rate rose with the cooling rate rising, however, the HGMs decreased the crystallization rates of the PVDF.

Non-isothermal crystallization kinetics of peroxide-crosslinked polyethylene: Effect of solid state mechanochemical milling

The influence of solid state mechanochemical milling process on the non-isothermal crystallization of peroxide-crosslinked-low-density polyethylene (peroxide-XLPE) was investigated via differential scanning calorimetry (DSC) at different cooling rates. Peroxide-XLPE was partially decrosslinked during mechanochemical milling process. The Avrami method modified by Jeziorny, the Ozawa method and the Mo method were applied to describe the non-isothermal crystallization process of peroxide-XLPE, decrosslinked XLPE (de-XLPE) and pure LDPE successfully. The results revealed that the decrosslinking effect could accelerate the crystallization process of XLPE due to the higher chain mobility after mechanochemical milling, which was confirmed by the values of half crystallization time (t1/2), crystallization rate exponent Zc, parameter K(T) and F(T).

Influence of Sn interaction on the structural evolution of Au clusters: A first principles study

Here we report the structural and electronic properties of AunSn (n=2–13) clusters by using pseudo-potential and LCAO–MO method. A comparison between the structures of Aun and AunSn clusters reveals that while Aun clusters favor planar isomers up to n=13, AunSn clusters follow a different trend; 3D structure for n=3 and 4, quasi planar in the size range n=5–11, and again 3D isomers from n=12 onwards. Enhanced contribution of Au p-orbital and significant charge transfer from Sn to the gold atoms is attributed for such interesting growth pattern of AunSn clusters.

Theoretical Study on the Phase Transition and the H/D Isotope Effect of Squaric Acid

We investigated the phase transition and the isotope effect in squaric acid (H2C4O4, abbreviated H2SQ), a hydrogen-bonded dielectric material. Using first-principles calculation, we found that Jahn-Teller distortion of the unit structure (C4H4O4) was the major driving force for the phase transition in the H2SQ crystal. In order to elucidate the isotope effect on the phase transition in deuterated squaric acid (D2SQ), we employed the multi-component molecular orbital (MC_MO) method, which directly takes into account the quantum effects of protons and deuterons. Using this model, we successfully predicted the difference between the phase transition temperature of H2SQ and that of D2SQ to be 192K, which is in reasonable agreement with the experimental value of 145 K. We found that the isotope effect in the H2SQ/D2SQ system was based more on shrinking distribution of the deuteron wave rather than that of the proton wave. When the MC_MO method was coupled with adequate cluster models, first-principles calculations were effective to determining the origin of the phase transition and the H/D isotope effect in hydrogen-bonded dielectric materials.