Molecular orbital calculations on the ethylene episulfide molecule and its isomers

Systematic non-empirical and semi-empirical molecular orbital studies have been performed on the sulfur atom + ethylene system and its reaction products thiirane and vinylmercaptan. The results are in general agreement with earlier qualitative and semiquantitative rationalizations of the reaction but also bring to light a number of novel features.     

Does the thermal motion of macromolecules really influence the fluorine-atomic concentration of plasma-fluorinated polyolefin surfaces?

The relative fluorine-atomic concentrations and the abundance of CF_x functionalities from CF₄- and C₆F₆-RF-plasma treated polypropylene (PP) film surfaces were evaluated. Survey and high resolution (HR) ESCA data indicate that intense surface fluorination can be carried out, from both fluorine precursors, under relatively low power and treatment time conditions. However, it was found that the stability (under open laboratory conditions and under various solvent and temperature environments) of plasma implanted fluorine based groups significantly depend on the nature of plasma gases involved. Simulation of plasma induced molecular fragmentation, at different electron energy MS conditions, indicates the presence of a much higher fluorine atom concentration from a CF₄-plasma in comparison to a C₆F₆-plasma. It is suggested that fluorine atom mediated fragmentation of macromolecular backbones is probably responsible for the erosion of plasma fluorinated surfaces, rather than thermal motion induced burying processes.     

Stability of silicon and titanium carbide suspensions in electrolyte, poly(ethylene oxide), and PEO-surfactant solutions

It has been shown that the coagulation values of counterions for SiC and TiC suspensions with particle radius from 0.5 to 5 microm obey a z(2.5-3.5) law and there is an insufficient change in the critical concentration of 1-1 electrolytes (CCE) when the surface potential of particles increases more than two times. Also, the CCE values hardly depend on the position of counterions in the lyotropic sequence. This is explained by aggregation of SiC and TiC particles at a secondary minimum, which is proved by calculations of the potential curves of interparticle interactions using the DLVO theory. The adsorption of poly(ethylene oxide) on the surfaces studied does not cause--in contradiction to dispersions with smaller particles--an unlimited growth in the stability of suspensions. This is due to the aggregation of large particles with adsorbed PEO, as in polymer-free dispersions, under barrierless conditions in which the coordinates of the secondary minimum are determined by superposition of molecular attractive forces and steric repulsive forces of adsorbed polymeric chains, without a contribution from the electric repulsion term. PEO-anionic surfactant complexes possess higher stabilizing capacity compared to the individual components of the mixture. Our results show that the adsorbed polymer layers may hinder the aggregation both in the primary and in the secondary minimum for not very large particles only, the critical size of which depends on the dispersed phase nature and the molecular mass of the polymer.     

Surface modification of polypropylene under argon and oxygen-RF-plasma conditions

Polypropylene fabrics samples were surface functionalized under Ar and O₂ RF plasma conditions. Survey and high resolution photoelectron spectroscopy and attenuated total reflectance FTIR comparative evaluation of virgin and plasma treated substrat surfaces, and their pentafluorophenyl hydrazine-derivatized correspondents, indicate that both Ar and O₂-discharge treated PP surfaces undergo intense oxidation. C=O, O−C=O, and C−O linkages were identified on both inert and reactive gas plasma exposed surfaces. It was found that the relative surface atomic concentrations and the relative ratios of newly created functionalities are controlled by the external plasma parameters (RF power and treatment time). The oxidation of Ar-plasma treated surfaces has been related toex situ post plasma mechanisms. Dynamic contact angle measurements from unmodified and plasma exposed substrates demonstrated the presence of increased surface polarity, and its dependence on plasma parameters. AFM evaluations of plasma treated samples indicate the presence of rough surface morphologies. Paper based on the results presented during the workshop of the Engineering Research Center for Plasma-Aided Manufacturing held in Madison, Wisconsin, in Spring 1996.     

On the models for deuterium long-range isotope effects in13C NMR spectroscopy

The long-range deuterium isotope effects on¹³C nuclear shielding are physically not yet completely understood. Two existing models for explaining these effects, vibrational and substituent, are compared here. The vibrational model is based on the Born-Oppenheimer approximation, but it can explain only one-bond deuterium effects. To the contrary, the substituent model may explain many long-range isotope effects, but it is controversial due to the assumption of some distinct electronic properties of isotopes. We explain how long-range deuterium isotope effects may be rationalized by the subtle electronic changes induced by isotope substitution, which does not violate the Born-Oppenheimer approximation.     

Influence of oxidative injury and monitoring of blood plasma by DSC on patients with psoriasis

Oxidative stress induced by oxygen free radicals (OFRs) is a casual factor in psoriasis. Our aim was to detect the oxidative stress parameters and blood plasma changes with differential scanning calorimetry (DSC) in psoriatic patients. The study included untreated (n = 39) and treated (retinoids, methotrexate, biologic response modifiers; n = 33) white adult patients from both sex. To monitor oxidative stress concentration of malondialdehyde (MDA), reduced glutathione and sulfhydryl groups, production of OFRs, and activity of myeloperoxidase (MPO), superoxide dismutase, and catalase were measured. Denaturation of plasma components was detected in SETARAM Micro DSC-II calorimeter. Total production of OFRs and MPO activity, and the concentration of MDA were significantly increased both in untreated patients with moderate and severe symptoms and in all drug-treated groups compared with controls (p < 0.001). All of the scavengers and antioxidants were significantly decreased in untreated patients and better preserved after retinoid and biological therapy. DSC scans of blood plasma showed melting temperature a characteristic parameter to follow the severity of disease. The calorimetric enthalpy is exhibiting a moderate decrease with the progression of the inflammation. These findings suggest that an imbalance exists between pro-oxidants and antioxidants in untreated severe psoriatic patients. All drug therapy reduced the changes, mainly the biologic response modifiers. Similarly, DSC showed differences between untreated and conventional systemic drug treatment.     

A study of the nonlinear refractive index in amorphous Ge–As–S layers and nanocomposites with gold nanoparticles

Nonlinear refractive indices of simple and composite chalcogenide glasses with gold nanoparticles are measured by the Z-scan method using a femtosecond Ti:sapphire laser with a central wavelength of 800 nm and a pulse duration of 40 fs. It is shown that introduction of nanoparticles into thin layers of amorphous GeS₂, As₃₀Ge₂₀S₅₀, and As₃Ge₃₅S₆₂ leads to a decrease in the total nonlinear refractive index due to additional absorption of femtosecond laser radiation without efficient excitation of localized plasmons outside the resonance region. For example, the nonlinear refractive index decreases with addition of gold nanoparticles from 16.1 × 10^–12 to 13.0 × 10^–12 cm²/W for GeS₂, from 3.9 × 10^–12 to 3.2 × 10^–12 cm²/W for As₃₀Ge₂₀S₅₀, and from 5.8 × 10^–12 to 4.7 × 10^–12 cm²/W for As₃Ge₃₅S₆₂.     

Plasma-enhanced synthesis of thin fluoropolymer layers with low Raman and fluorescence backgrounds

Radio-frequency (RF) plasma enhanced chemical vapor deposition (PECVD) provides a promising way to deposit extremely hydrophobic, highly adherent nanometer- to micrometer-thick films with thermal stability, a low coefficient of friction, a low dielectric constant, and a low value of surface energy. We describe the synthesis of these fluorinated thin films using hexafluoropropene as starting material and discuss their properties. These coatings, applied to stainless steel, provide ideal substrates for Raman spectroscopy, when extremely low backgrounds are required. Raman spectroscopy measurements of a low-concentration protein film are used to demonstrate sensitivity and level of detectability.     

A system model for the utilization of mineral resources

A multiobjective dynamic optimization model is described for the optimal utilization of mineral resources. The special forms of the objective functions, state-transition relations, and additional constraints satisfy the conditions for using a special dynamic multiobjective programming method. A case study is also outlined.