Shingo Urata

Rate constants estimation for the reaction of hydrofluorocarbons and hydrofluoroethers with OH radicals

Abstract The rate constants for the hydrogen abstraction reaction of hydrofluoroethers (HFEs) and hydrofluorocarbons (HFCs) with OH radicals ( k OH ) at 298 K were estimated by using new empirical estimation method consisting of two steps. Firstly we calculated the bond dissociation enthalpies (BDEs) of the C–H bond by using the artificial neural network (ANN) technique from molecular formula. Next, k OH were evaluated by using the estimated BDEs and a modified Heicklen’s empirical equation. Consequently, the combination of these two empirical methods could estimate the k OH of HFEs and HFCs within the 0.56–1.8 times of experimental data as average deviation.

Prediction of vapor-liquid equilibrium for binary systems containing HFEs by using artificial neural network

Abstract A method using artificial neural network (ANN) was applied to estimate the vapor–liquid equilibrium (VLE) for the binary systems containing hydrofluoroethers (HFEs) and polar compounds. Our new estimation method is composed of three steps. In the first step, the sign of logarithm of activity coefficient ( γ ) is estimated for each binary system using ANN, because it had been found that the binary systems containing HFEs show different thermodynamic behaviors depending on the sign for ln( γ ). In the second step, two sets of relation between liquid mole fraction and ln( γ ) are constructed: one held for the case of positive sign and the other held for that of negative sign. In the third step, vapor–liquid composition and equilibrium temperature are calculated using the estimated activity coefficient. In order to construct this new method, the isobaric VLE data of 18 binary systems including HFEs was used. As a result, our new method could estimate VLE with reasonable accuracy.

Magnitude and orientation dependence of intermolecular interaction between perfluoroalkanes: High level ab initio calculations of CF4 and C2F6 dimers

Intermolecular interaction energies of eight orientation CF4 dimers and seven orientation C2F6 dimers were calculated with electron correlation correction by the second-order Moller–Plesset perturbation (MP2) method. The D3d CF4 dimer and C2h C2F6 dimer have the largest binding energies. Electron correlation correction increases the attraction considerably, while the effects of electron correlation beyond MP2 are small. Electrostatic and induction energies are not large in all cases. This indicates that dispersion interaction is mainly responsible for the attraction. The calculated binding energy of the CF4 dimer (0.69 kcal/mol) is about 60% larger than that of the CH4 dimer (0.44 kcal/mol), while the binding energy of the C2F6 dimer (1.02 kcal/mol) is close to that of the C2H6 dimer (0.90 kcal/mol). The intermolecular separations (C⋯C distance) in the CF4 and CH4 dimers at the potential minima are close (4.0 and 3.8 A, respectively), while the separation in the C2F6 dimer (4.8 A) is appreciably larger th...

Intermolecular interaction between the pendant chain of perfluorinated ionomer and water

The intermolecular interaction energies between a water molecule and four models of pendant chains for perfluorinated ionomers, such as CF3OCF2CF2SO3H, CF3OCF2CF2SO3−, CF3CF2CF2COOH, CF3CF2CF2COO−, were analyzed by using a molecular orbital calculation. In order to investigate a variety of configurations, five hundred random configurations that water and monomer contact at their van der Waals surfaces were generated for each system. We employed an empirical correction method for dispersion energy defined by the equation Edisp = −fd(R)C6R−6, so as to reduce the computational costs. The C6 coefficients of this equation were optimized to reproduce the energies obtained at the MP2/aug-cc-pVDZ level of calculations, and then overall intermolecular interaction energies (Eint = EHF + Edisp) were evaluated as a summation of Edisp and intermolecular interaction energy at the HF/aug-cc-pVDZ level (EHF). From these analyses, we obtained the following conclusions. (1) The ether oxygen in the pendant chain cannot bind with water strongly due to fluorination. (2) De-protonations of sulfonic and carboxylic acids extend the region where water molecules sufficiently bind with pendant chains, and this effect would cause rich water absorption when these pendant chains form membranes. Therefore, the degree of proton disassociation would be one of the key factors for the water sorption ratio and membrane morphology. (3) The binding energy of the optimized configuration for CF3CF2CF2COO− + H2O is about 2.5 kcal mol−1 larger than that for the CF3OCF2CF2SO3− + H2O system because of the larger electron negativities of the oxygen atoms on deprotonated carboxylic acid compared with those on the sulfonic acid.

Magnitude and orientation dependence of intermolecular interaction of perfluoropropane dimer studied by high-level ab initio calculations: Comparison with propane dimer

Intermolecular interaction energies of 12 orientations of C(3)F(8) dimers were calculated with electron correlation correction by the second-order Møller-Plesset perturbation method. The antiparallel C(2h) dimer has the largest interaction energy (-1.45 kcal/mol). Electron correlation correction increases the attraction considerably. Electrostatic energy is not large. Dispersion is mainly responsible for the attraction. Orientation dependence of the interaction energy of the C(3)F(8) dimer is substantially smaller than that of the C(3)H(8) dimer. The calculated interaction energy of the C(3)F(8) dimer at the potential minimum is 78% of that of the C(3)H(8) dimer (-1.85 kcal/mol), whereas the interaction energies of the CF(4) and C(2)F(6) dimers are larger than those of the CH(4) and C(2)H(6) dimers. The intermolecular separation in the C(3)F(8) dimer at the potential minimum is substantially larger than that in the C(3)H(8) dimer. The larger intermolecular separation due to the steric repulsion between fluorine atoms is the cause of the smaller interaction energy of the C(3)F(8) dimer at the potential minimum. The calculated intermolecular interaction energy potentials of the C(3)F(8) dimers using an all atom model OPLS-AA (OPLS all atom model) force field and a united atom model force field were compared with the ab initio calculations. Although the two force fields well reproduces the experimental vapor and liquid properties of perfluoroalkenes, the comparison shows that the united atom model underestimates the potential depth and orientation dependence of the interaction energy. The potentials obtained by the OPLS-AA force field are close to those obtained by the ab initio calculations.

Analysis of the intermolecular interaction between CH3OCH3, CF3OCH3, CF3OCF3, and CH4: High level ab initio calculations

The intermolecular interaction energies of the CH3OCH3CH4, CF3OCH3CH4, and CF3OCF3CH4 systems were calculated by ab initio molecular orbital method with the electron correlation correction at the second order Møller–Plesset perturbation (MP2) method. The interaction energies of 10 orientations of complexes were calculated for each system. The largest interaction energies calculated for the three systems are −1.06, −0.70, and −0.80 kcal/mol, respectively. The inclusion of electron correlation increases the attraction significantly. It gains the attraction −1.47, −1.19, and −1.27 kcal/mol, respectively. The dispersion interaction is found to be the major source of the attraction in these systems. In the CH3OCH3CH4 system, the electrostatic interaction (−0.34 kcal/mol) increases the attraction substantially, while the electrostatic energies in the other systems are not large. Fluorine substitution of the ether decreases the electrostatic interaction, and therefore, decreases the attraction. In addition the orientation dependence of the interaction energy is decreased by the substitution.

A study on the plasticity of soda-lime silica glass via molecular dynamics simulations

Molecular dynamics (MD) simulations were applied to construct a plasticity model, which enables one to simulate deformations of soda-lime silica glass (SLSG) by using continuum methods. To model the plasticity, stress induced by uniaxial and a variety of biaxial deformations was measured by MD simulations. We found that the surfaces of yield and maximum stresses, which are evaluated from the equivalent stress-strain curves, are reasonably represented by the Mohr-Coulomb ellipsoid. Comparing a finite element model using the constructed plasticity model to a large scale atomistic model on a nanoindentation simulation of SLSG reveals that the empirical method is accurate enough to evaluate the SLSG mechanical responses. Furthermore, the effect of ion-exchange on the SLSG plasticity was examined by using MD simulations. As a result, it was demonstrated that the effects of the initial compressive stress on the yield and maximum stresses are anisotropic contrary to our expectations.

A Multiscale Molecular Dynamics and Coupling with Nonlinear Finite Element Method

In this work, we have developed a multiscale coupling method between the multiscale micromorphic molecular dynamics (MMMD) and the nonlinear finite element method. The multiscale micromorphic molecular dynamics (MMMD) is a three-scale non-equilibrium molecular dynamics that span from microscale to mesoscale and to macroscale. A multiscale computational algorithm is formulated to couple the continuum scale equations of motion in terms of finite element method (FEM) with the coarse scale molecular dynamics of MMMD. To validate the computational formulation, we apply the multiscale coupling method to simulate nano-indentation of silicon crystals.

Simulation of Ductile Fracture in Amorphous and Polycrystalline Materials by Multiscale Cohesive Zone Model

A multiscale cohesive zone model (MCZM) that combines finite element method with atomistic modeling is applied to simulate fracture of amorphous materials and polycrystalline solids. In order to apply MCZM to model amorphous materials, the Cauchy–Born rule is linked with the Parrinello–Rahman MD method to associate atom configurations with material deformation by using molecular statics (MS). We found the algorithm allows us to simulate ductile fracture of amorphous materials successfully. In addition, the methodology is applied to model the amorphous grain boundaries of polycrystalline solids, and we show that it can capture ductile fracture of polycrystalline metals.

Intermolecular interactions of the CX3OCHO dimers, and complexes CX3OCHO–n(H2O), CX3OCHO–n(HO2)(X = H,F; n = 1,2)

The intermolecular interaction energies of the CX3OCHO dimers, CX3OCHO–n(H2O), and CX3OCHO–n(HO2) (X = H,F; n = 1,2) complexes are studied by using molecular orbital calculations at the (U)MP2/aug(df,pd)-6-311G**//(U)B3LYP/6-311G** level. We first confirmed the reliability of this level of calculation by utilizing examples of two complexes, CH3OCHO–HO2 (syn) and CF3OCHO–HO2 (syn). The calculated intermolecular interaction energies for the formate dimers (−3.75 to −5.19 kcal mol−1) and CX3OCHO–H2O (−2.39 to −4.90 kcal mol−1) are relatively small. On the other hand, the CX3OCHO–HO2 complexes have larger interaction energies (−4.78 to −9.69 kcal mol−1). The complexes, CX3OCHO–2(H2O) and CX3OCHO–2(HO2), have the largest intermolecular interaction energies (−12.42 to −13.89 kcal mol−1 and −14.47 to −18.39 kcal mol−1, respectively). Except for the formate dimer of syn–syn type, the interaction energies for the complexes with CF3OCHO are always smaller than the corresponding complexes with CH3OCHO. Finally, we estimated the concentrations of the complexes in the low and high water concentration conditions. In conclusion, it has been observed that the complexes studied in this work are not likely to form in the atmosphere.