Comparative study of new shell-type,sub-2 μm fully porous and monolith stationary phases,focusing on mass-transfer resistance

Today sub-2 μm packed columns are very popular to conduct fast chromatographic separations. The mass-transfer resistance depends on the particle size but some practical limits exist not to reach the theoretically expected plate height and mass-transfer resistance. Another approach applies particles with shortened diffusion path to enhance the efficiency of separations. In this study a systematical evaluation of the possibilities of the separations obtained with 5 cm long narrow bore columns packed with new 2.6 μm shell particles (1.9 μm nonporous core surrounded by a 0.35 μm porous shell, Kinetex™, Core-Shell), packed with other shell-type particles (Ascentis Express™, Fused-Core), totally porous sub-2 μm particles and a 5 cm long narrow bore monolith column is presented. The different commercially available columns were compared by using van Deemter, Knox and kinetic plots. Theoretical Poppe plots were constructed for each column to compare their kinetic performance. Data are presented on polar neutral real-life analytes. Comparison of a low molecular weight compounds (MW = 270–430) and a high molecular weight one (MW ∼ 900) was conducted. This study proves that the Kinetex column packed with 2.6 μm shell particles is worthy of rivaling to sub-2 μm columns and other commercially available shell-type packings (Ascentis Express or Halo), both for small and large molecule separation. The Kinetex column offers a very flat C term. Utilizing this feature, high flow rates can be applied to accomplish very fast separations without significant loss in efficiency.     

Synthesis and Characterization of Core‐Shell Selenium/Carbon Colloids and Hollow Carbon Capsules

A novel Se/C nanocomposite with core‐shell structures has been prepared through a facile one‐pot microwave‐induced hydrothermal process. The new material consists of a trigonal‐Se (t‐Se) core and an amorphous‐C (a‐C) shell. The Se/C composite can be converted to hollow carbon capsules by thermal treatment. These products were characterized by transmission electron microscopy (TEM), powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), selected area electron diffraction (SAED), energy‐dispersive X‐ray (EDX) spectroscopy, and X‐ray photoelectron spectroscopy (XPS).     

Preparation of composite polyacrylate latex particles with in situ‐formed methylsilsesquioxane cores

Composite polyacrylate latex particles were prepared through a simple method by dissolving organosilicon monomer methyltrimethoxysilane in a monomer mixture of acrylic monomers methyl methacrylate (MMA), n‐butyl acrylate (n‐BA), and acrylic acid (AA). With the addition of water needed for hydrolysis, methyltrimethoxylsilane hydrolyzed under catalysis by AA and further condensed to form polymeric methylsilsesquioxane (MSQ). The monomer mixture containing in situ‐formed MSQ was then subjected to emulsification and emulsion polymerization. Transmission electron microscopy (TEM) images showed that the obtained latex particles had a core–shell structure. Differences between the X‐ray photoelectron spectroscopy (XPS) results of the contents of silicon atoms on surfaces of films formed at temperatures above and below glass transition temperatures (T_gs) of polyacrylate evidenced that the cores were made up of MSQ and the shells were made up of polyacrylate. The static water contact angle measurements indicated that the incorporation of MSQ can result in composite latex with higher hydrophobicity. Copyright © 2009 John Wiley & Sons, Ltd.     

Density functional study of aurophilic interaction in Cl(AuPH3) and in its dimerization

With the help of quantum mechanical calculations, the geometric structures and electronic structures of the closed‐shell systems Cl(AuPH₃) and [Cl(AuPH₃)]₂ have been determined by DFT and MP2 methods. Experimental structure parameters of the title compounds were reproduced at Xα level. The Mulliken population and HOMO–LUMO gaps were examined. The intermolecular aurophilic interactions in [Cl(AuPH₃)]₂ were analyzed and decomposed. A positive BE value (no bonding) was calculated. When 2PC was added, each pair Au… Au interaction energy was about 83 kJ/mol. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

A finite volume cell‐centered Lagrangian hydrodynamics approach for solids in general unstructured grids

A finite volume cell‐centered Lagrangian hydrodynamics approach, formulated in Cartesian frame, is presented for solving elasto‐plastic response of solids in general unstructured grids. Because solid materials can sustain significant shear deformation, evolution equations for stress and strain fields are solved in addition to mass, momentum, and energy conservation laws. The total stress is split into deviatoric shear stress and dilatational components. The dilatational response of the material is modeled using the Mie‐Grüneisen equation of state. A predicted trial elastic deviatoric stress state is evolved assuming a pure elastic deformation in accordance with the hypo‐elastic stress‐strain relation. The evolution equations are advanced in time by constructing vertex velocity and corner traction force vectors using multi‐dimensional Riemann solutions erected at mesh vertices. Conservation of momentum and total energy along with the increase in entropy principle are invoked for computing these quantities at the vertices. Final state of deviatoric stress is effected via radial return algorithm based on the J‐2 von Mises yield condition. The scheme presented in this work is second‐order accurate both in space and time. The suitability of the scheme is evinced by solving one‐ and two‐dimensional benchmark problems both in structured grids and in unstructured grids with polygonal cells. Copyright © 2013 John Wiley & Sons, Ltd.