Analysis of the Thermal Stability of Very Thin Surface Layers of Corrosion Inhibitors by Time-of-Flight Secondary Ion Mass Spectrometry

The powerful nature of the secondary ion mass spectrometry (SIMS) technique was explored in order to analyse very thin surface layers that were self-assembled on steel material from acidic solution. These surface layers are adsorbed corrosion inhibitors. The SIMS technique proved useful to characterise the molecular structure and homogeneity of thin surface layers in the nanometre range of specific analytes on the metallic substrate. Using SIMS, the thermal stability of these layers was further investigated and the desorption energy at a certain temperature was determined, where special attention was devoted to the method’s static limit. In order to compare, and for certain cases emphasise, the benefits gained by using SIMS in such surface analysis compared with the X-ray photoelectron spectroscopy (XPS) method, the same samples were also analysed by means of the latter. XPS is usually considered to be the most powerful analytical tool in surface analysis studies, but, as shown herein, it has certain limitations compared to SIMS. Finally, the surface topography was investigated by employing atomic force microscopy (AFM) in order to carry out a comprehensive surface analysis.

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On the semiclassical analysis of the ground state energy of the Dirichlet Pauli operator III: magnetic fields that change sign

We consider the semiclassical Dirichlet Pauli operator in bounded connected domains in the plane. Rather optimal results have been obtained in previous papers by Ekholm–Kova?ík–Portmann and Helffer–Sundqvist for the asymptotics of the ground state energy in the semiclassical limit when the magnetic field has constant sign. In this paper, we focus on the case when the magnetic field changes sign. We show, in particular, that the ground state energy of this Pauli operator will be exponentially small as the semiclassical parameter tends to zero and give lower bounds and upper bounds for this decay rate. Concrete examples of magnetic fields changing sign on the unit disk are discussed. Various natural conjectures are disproved, and this leaves the research of an optimal result in the general case still open.

     

Molecular Mobility in Amorphous Polylactic Acid Studied Using <Superscript>1</Superscript>H–<Superscript>13</Superscript>C Cross Polarization NMR

The ¹H–¹³C cross polarization nuclear magnetic resonance technique was used for the study of molecular mobility in amorphous polylactic acid. The cross polarization buildup curves for methine and methyl functional groups measured at magic angle spinning rates of 4 and 10 kHz, under Hartmann–Hahn conditions determined from corresponding Hartmann–Hahn matching profiles, confirmed the presence of ¹H–¹³C spin pairs isolated from lattice since transient oscillations were observed in the initial stages of buildup curves. The values of dipolar coupling constants derived from Fourier transforms of cross polarization buildup curves indicate the presence of rigid methine groups and two kinds of methyl functional groups which differ in mobility. This could be due to the presence of amorphous phase with chain aggregations and phase with less spatial restrictions in this material. Fitting of theoretical expressions to experimental data provided additional information on the cross polarization process in this material.     

High basicity of tris-(tetramethylguanidinyl)-phosphine imide in the gas phase and acetonitrile—a DFT study

It is shown by reliable density functional theory (DFT) calculations that compounds 4 and 6 are very powerful neutral organic superbases as evidenced by the calculated proton affinities in the gas phase 305.4 kcal mol⁻¹ (44.8) and 287.8 kcal mol⁻¹ (37.8), respectively, and the corresponding calculated pK_a values in acetonitrile given within parentheses.     

Laser induced mixing in multilayered Ti/Ta thin film structures

The possibility of interlayer mixing in a Ti/Ta multilayer system, induced by laser irradiation, was the main purpose of these experiments. Ti/Ta multilayer system, consisting of ten alternating Ti and Ta thin films and covered by slightly thicker Ti layer, was deposited on Si (100) wafers to a total thickness of 205 nm. Laser irradiation was performed in air by picoseconds Nd:YAG laser pulses in defocused regime with fluences of 0.057 and 0.11 J cm^?2. Laser beam was scanned over the 5?×?5 mm surface area with different steps along y-axes. Structural and compositional characterisation was done by auger electron spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy. Laser processing at lower fluence caused only oxidation of the top Ti layer, despite of the number of applied laser pulses. Interlayer mixing was not observed. Application of laser pulses at fluence of 0.11 J cm^?2 caused partial and/or complete ablation of deposited layers. In partially ablated regions considerable mixing between Ti and Ta films was registered.     

Electronic structures of methylated azaferrocenes and their borane adducts: photoelectron spectroscopy and electronic structure calculations

The preparation and crystal structure of a new 2,5-dimethylazaferrocene (DMAF) adduct of borane (DMAF-BH(3)) are reported. The electronic structures of 1,2,3,4,5-pentamethylazaferrocene (PMAF), its borane adduct 1,2,3,4,5-pentamethylazaferrocene-BH(3) (PMAF-BH(3)) and of DMAF-BH(3) have been studied by HeI-HeII UV photoelectron spectroscopy (UPS) and high-level DFT methods. UPS data reveal the influence of borane and methyl substitution on the electronic structures of azaferrocenes, which have been rationalized by inductive and hyperconjugative effects. UPS data also allow for the estimation of azaferrocene lone-pair stabilization upon coordination to borane, and suggest that pyridine is a slightly stronger sigma donor toward BH(3) than either azaferrocene studied. UV-Vis spectroscopic data for the radical cation of PMAF were also obtained and compared with the UPS data.     

Antimicrobial cotton fibres prepared by in situ synthesis of AgCl into a silica matrix

Functional antimicrobial cotton fibres were prepared in a novel two-step procedure utilising the pad-dry-cure method to apply an inorganic–organic hybrid sol–gel precursor (reactive binder, RB) followed by the in situ synthesis of AgCl particles on the RB-treated fibres. The morphology and surface composition of the modified cotton fibres were investigated by scanning electron microscopy imaging and X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy spectral analyses. The bulk concentration of Ag on the cotton fibres was determined by inductively coupled plasma mass spectroscopy, and the antimicrobial activity against the bacteria Escherichia coli and Staphylococcus aureus was estimated according to the ISO 20645:2004 (E) and AATCC 100-1999 methods. The results showed that this application process yields the following important benefits: (1) the presence of the RB silica matrix increased the fibres’ capacity for adsorbing AgCl particles compared with the same fibres without RB; (2) the in situ synthesis enabled a simple and environmentally friendly preparation of AgCl particles from AgNO₃ and their embedment into the fibres; (3) the AgCl particles were bound to the RB silica matrix by physical forces, which allowed for their controlled release from the fibres; (4) the capacity of the RB-modified cotton samples to hold embedded AgCl particles was sufficient to provide a 100 % bacterial reduction even after 10 repeated washing cycles; and (5) the chemical modification of the cotton fibres did not significantly change their whiteness, wettability or softness.     

Heat kernels of two-dimensional magnetic Schr?dinger and Pauli operators

We study the heat semigroups generated by two-dimensional magnetic Schr?dinger and Pauli operators with compactly supported magnetic field. We show that the large time behaviour of the associated heat kernels is determined by the total flux of the magnetic fields.     

Volatile organic compounds from Centaurium erythraea Rafn (Croatia) and the antimicrobial potential of its essential oil

GC and MS were used for the analysis of Croatian Centaurium erythraea Rafn essential oil (obtained by hydrodistillation) and headspace (applying headspace solid-phase microextraction). The headspace contained numerous monoterpene hydrocarbons (the major ones were terpinene-4-ol, methone, p-cymene, γ-terpinene and limonene). Oxygenated monoterpenes were present in the headspace and oil, while 1,8-cineole, bornyl acetate and verbenone were present only in the headspace. High headspace percentages of toluene and naphthalene were found, followed by hemimellitene. Lot of similarities were observed with Serbian C. erythraea oil [neophytadiene (1.4%), thymol (2.6%), carvacrol (6.1%) and hexadecanoic acid (5.7%)], but different features were also noted such as the presence of menthol, menthone and phytone. The oil fractionation enabled identification of other minor compounds not found in total oil such as norisoprenoides, alk-1-enes or chromolaenin. The essential oil showed antimicrobial potential on Escherichia coli, Salmonella enteritidis, Staphylococcus aureus and Bacillus cereus. On the other hand, no antibacterial activity of the oil was observed on Pseudomonas fluorescens and Lysteria monocytogenes.