Transport and Reaction Characteristics of Reconstructed Polyolefin Particles

The 3D spatial structure of porous polyethylene particles was reconstructed from their X‐ray micro‐tomography images. Several polyolefin particles with an artificial granular structure were generated. Transport in reconstructed particles was calculated for the case of a monomer diffusing through both the pores and the polymer. The calculated degassing characteristics of reconstructed polyolefin particles can be compared to experiments. Monomer mass transport limitations are important not only in the early stage of particle growth, but also in fully‐developed polyolefin particles. The problems and limitations of the developed method are discussed. The method developed allows prediction of the effect of particle structure on mass transport limitations for real particle structures.

     

Elastic modulus of a polymer nanodroplet: theory and experiment

We redevelop a theoretical model that, in conjunction with atomic force microscopy (AFM), can be used as a noninvasive method for determination of the elastic modulus of a polymer nanodroplet residing on a flat, rigid substrate. The model is a continuum theory that combines surface and elasticity theories for prediction of the droplet's elastic modulus, given experimental measurement of its adsorbed height. Utilization of AFM-measured heights for relevant droplets reported in the literature and from our own experiments illustrated the following: the significance of both surface and elasticity effects in determining a polymer droplet's spreading behavior; the extent of a continuum theory's validity as one approaches the nanoscale; and a droplet size effect on the elastic modulus.     

Investigating magnetostructural correlations in the pseudooctahedral trans-[Ni(II){(OPPh2)(EPPh2)N}2(sol)2] complexes (E = S, Se; sol = DMF, THF) by magnetometry, HFEPR, and ab initio quantum chemistry

In this work, magnetometry and high-frequency and -field electron paramagnetic resonance spectroscopy (HFEPR) have been employed in order to determine the spin Hamiltonian (SH) parameters of the non-Kramers, S = 1, pseudooctahedral trans-[Ni(II){(OPPh(2))(EPPh(2))N}(2)(sol)(2)] (E = S, Se; sol = DMF, THF) complexes. X-ray crystallographic studies on these compounds revealed a highly anisotropic NiO(4)E(2) coordination environment, as well as subtle structural differences, owing to the nature of the Ni(II)-coordinated solvent molecule or ligand E atoms. The effects of these structural characteristics on the magnetic properties of the complexes were investigated. The accurately HFEPR-determined SH zero-field-splitting (zfs) D and E parameters, along with the structural data, provided the basis for a systematic density functional theory (DFT) and multiconfigurational ab initio computational analysis, aimed at further elucidating the electronic structure of the complexes. DFT methods yielded only qualitatively useful data. However, already entry level ab initio methods yielded good results for the investigated magnetic properties, provided that the property calculations are taken beyond a second-order treatment of the spin-orbit coupling (SOC) interaction. This was achieved by quasi-degenerate perturbation theory, in conjunction with state-averaged complete active space self-consistent-field calculations. The accuracy in the calculated D parameters improves upon recovering dynamic correlation with multiconfigurational ab initio methods, such as the second-order N-electron valence perturbation theory NEVPT2, the difference dedicated configuration interaction, and the spectroscopy-oriented configuration interaction. The calculations showed that the magnitude of D (～3-7 cm(-1)) in these complexes is mainly dominated by multiple SOC contributions, the origin of which was analyzed in detail. In addition, the observed largely rhombic regime (E/D = 0.16-0.33) is attributed to the highly distorted metal coordination sphere. Of special importance is the insight by this work on the zfs effects of Se coordination to Ni(II). Overall, a combined experimental and theoretical methodology is provided, as a means to probe the electronic structure of octahedral Ni(II) complexes.     

Brane Cosmology From Heterotic String Theory

We consider brane cosmologies within the context of five-dimensional effective actions with higher curvature corrections. The actions are compatible with bulk string amplitude calculations from heterotic string theory. We find wrapped solutions that satisfy the field equations in an approximate but acceptable manner given their complexity, where the internal, four-dimensional, scale factor is naturally inflating, having an exponential De-Sitter form. The temporal dependence of the metric components is nontrivial so that this metric cannot be factored as in a conformally flat case. The effective Planck mass is finite and the brane solutions can localize four-dimensional gravity while the four-dimensional gravitational constant varies with time. The Hubble constant can be freely specified through the initial value of the scalar field, to conform with recent data.     

Ultrasound assisted catalytic wet peroxide oxidation of phenol: kinetics and intraparticle diffusion effects

The combination of ultrasound irradiation and catalytic wet peroxide oxidation was used as a means to degrade phenol. Direct and indirect irradiation were employed, while experiments in the absence of ultrasound were used as reference. A mixed (Al-Fe) pillared clay named FAZA, was used as a catalyst in the form of powder, extrudates and crushed extrudates. Ultrasound was found to clearly enhance the extrudates performance, increasing the conversion at 4h by more than 6 times under direct and almost 11 times under indirect irradiation. This observation is attributed to the reduction of diffusion resistance within the catalyst pores. The overall sonication-catalytic wet peroxide oxidation process appears very promising for environmental purposes.     

Numerical experiments on the efficiency of local grid refinement based on truncation error estimates

Local grid refinement aims to optimise the relationship between accuracy of the results and number of grid nodes. In the context of the finite volume method no single local refinement criterion has been globally established as optimum for the selection of the control volumes to subdivide, since it is not easy to associate the discretisation error with an easily computable quantity in each control volume. Often the grid refinement criterion is based on an estimate of the truncation error in each control volume, because the truncation error is a natural measure of the discrepancy between the algebraic finite-volume equations and the original differential equations. However, it is not a straightforward task to associate the truncation error with the optimum grid density because of the complexity of the relationship between truncation and discretisation errors. In the present work several criteria based on a truncation error estimate are tested and compared on a regularised lid-driven cavity case at various Reynolds numbers. It is shown that criteria where the truncation error is weighted by the volume of the grid cells perform better than using just the truncation error as the criterion. Also it is observed that the efficiency of local refinement increases with the Reynolds number. The truncation error is estimated by restricting the solution to a coarser grid and applying the coarse grid discrete operator. The complication that high truncation error develops at grid level interfaces is also investigated and several treatments are tested.     

Hydrodynamic properties of A8B8 type miktoarm (Vergina) stars

The dilute solution properties of three (PS)₈(PI)₈ miktoarm (Vergina) stars were investigated by viscometry and dynamic light scattering in toluene and tetrahydrofuran (THF) (common good solvents), cyclohexane at 34.5°C (theta solvent for PS and good for PI) and dioxane at 34°C (theta solvent for PI and good for PS). Experimental intrinsic viscosity [η] and hydrodynamic radii, R_h, values in all solvents were larger for the miktoarm stars in comparison to the calculated ones using a simple model which describes the size of the copolymers as a weighted average of the sizes of the homopolymer stars with the same total molecular weight and number of arms as the copolymer. This expansion is discussed on the basis of the increased number of heterocontacts, the topological constrains imposed by the common junction point in this highly branched miktoarm architecture and the asymmetry in molecular weights of the different kinds of arms. The conformation adopted in dilute solutions can explain, to some extent, the morphological results obtained on the same materials. The ratios of viscometric to hydrodynamic radii are consistent with previous investigations on linear and star polymers and in accord with the hard sphere model. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1329–1335, 1999     

Dielectric studies of polymer-water interactions and water organization in PEO/water systems

We report the results of detailed investigations of polymer-water interactions and of the organization of water in the poly(ethylene oxide) (PEO)/water system by dielectric techniques. They include thermally stimulated depolarization currents (TSDC) techniques in the temperature range of 77-300 K and broadband dielectric relaxation spectroscopy (DRS) techniques of frequencies, 5 Hz-10 GHz, and temperatures, 173-300 K. The water content h was varied between 0 and 1.21 (grams of water per gram of dry PEO). The secondary γ mechanism of PEO and the reorientation of absorbed water molecules were extensively studied. The γ mechanism was found to be plasticized up to water contents of about 0.20. The reorientation of water molecules was studied in three different experiments and frequency/temperature regions. The results suggest strong interactions in the PEO/water system and indicate the presence of a separate water phase at high water contents. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1545–1560, 1997     

ChemInform Abstract: Bonding Elucidation of the Three Common Acids H2SO4, HNO3, and HClO4.

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