Small Strain Mechanical Properties of Latex-Based Nanocomposite Films

A waterborne latex-based technique, in which functionalized laponite is attached to PS and acrylic latex particles, is used to prepare films containing up to 50 wt% laponite. At high laponite contents this leads to a cellular arrangement of the laponite-rich layers, concentrated at the latex particle interfaces. MDSC shows that a significant proportion of the organic matrix does not contribute to the glass transition. However, this “rigid” matrix fraction arises from intercalation of the laponite stacks, and cannot account for the large increases in global stiffness in the rubbery state (T > T_g) on laponite addition. The mechanical response for T > T_g is therefore discussed in terms of a four-phase structure, in which the intercalated laponite stacks embedded in a matrix with a relatively high rubbery modulus form a cellular structure, which is in turn embedded in a matrix whose modulus is closer to that of the bulk polymer. The importance of the cellular arrangement is underlined by the much lower rubbery modulus observed by DMA in specimens produced by deforming the original films in plane strain compression to produce oriented textures with relatively little connectivity between the laponite-rich layers.     

Solving a class of low rank d.c. programs via a branch and bound approach: A computational experience

Various classes of d.c. programs have been studied in the recent literature due to their importance in applicative problems. In this paper we consider a branch and bound approach for solving a class of d.c. problems. Both stack policies and partitioning rules are analyzed, pointing out their performance effectiveness by means of the results of a computational experience.     

2-Imidazolines. V. The formation of hydroxy derivatives in the synthesis of 4,5-diamino-2-imidazolines from 1,2-diimmonium salts and amidines

During the preparation of 1-aryl- and 1-acyl-4,5-dipiperidino-4,5-dihydroimidazoles (1) from diimmonium salts (3), derivatives in which one of the piperidino groups was substituted by an hydroxy group were often isolated. The structure and the genesis of these compounds are discussed.     

Decarbonylation of complex iridium carbonyls in solution: A problem in chemical dynamics

The kinetics of decarbonylation of [Ir(CO)(dp)₂]Cl and [IrCl(CO)₂(Ph₃P)₂] has been studied in different solvents, at temperatures between ?25° and +70°C, by means of reactors of defined fluid dynamics which allow a separation to be made between “physical” and “chemical” rate constants. Chemical rate constants have been found to depend markedly on the diffusion coefficients of carbon monoxide in the various solvents. The process of decarbonylation has been described, for both reactions, by the sequence: structural isomerization, characterized by a very low preexponential factor, decomposition of the less stable isomer against the solvent's barrier, and diffusion of carbon monoxide to the gas–liquid interface. The kinetic problems involved in the determination of rate constants and their implications have been emphasized.     

Bile enterogastric reflux sensor using plastic optical fibers

A portable optical-fiber sensor for ambulatory assessment of the enterogastric reflux, based on the optical properties of the bile, was developed. It makes use of two light-emitting diodes and of an appropriate electronic circuit that processes the signals and provides the readout on a display. A suitable probe for in vivo measurements was designed. Plastic fiber bundles are used in order to obtain probe flexibility and low price. In vivo measurements performed on different patients show the superiority of this technique over existing methods.     

Bounding the number of connected components of a real algebraic set

For every polynomial mapf=(f ₁,…,f _k): ℝ ⁿ →ℝ ^k , we consider the number of connected components of its zero set,B(Z _f) and two natural “measures of the complexity off,” that is the triple(n, k, d), d being equal to max(degree off _i), and thek-tuple (Δ₁,...,Δ₄), Δ _k being the Newton polyhedron off _i respectively. Our aim is to boundB(Z _f) by recursive functions of these measures of complexity. In particular, with respect to (n, k, d) we shall improve the well-known Milnor-Thom’s bound μ _d (n)=d(2d−1) ⁿ⁻¹. Considered as a polynomial ind, μ _d (n) has leading coefficient equal to 2 ⁿ⁻¹. We obtain a bound depending onn, d, andk such that ifn is sufficiently larger thank, then it improves μ _d (n) for everyd. In particular, it is asymptotically equal to 1/2(k+1)n ^k−1 dⁿ, ifk is fixed andn tends to infinity. The two bounds are obtained by a similar technique involving a slight modification of Milnor-Thom's argument, Smith's theory, and information about the sum of Betti numbers of complex complete intersections.     

v-Triazolines—IV: NMR configuration assignment of 5-dialkylamino-v-triazolines

A series of 1-aryl-5-amino-4,5-dihydro-v-triazoles bearing at least one hydrogen atom at the C-4 position has been prepared. The NMR features of the above compounds have been studied with the purpose of differentiating the triazolines with a trans configuration from those with a cis configuration. It has been shown that the hydrogen atom at C-4 lying on the same side of the amine group at C-5 always resonates at lower field than the hydrogen atom on the opposite side. This rule can be applied for identifying the configuration of the 5-amino-v-triazolines.     

Monitoring of the principal carbonyl compounds involved in malolactic fermentation of wine by solid-phase microextraction and positive ion chemical ionization GC/MS analysis

A new method has been developed to determine acetaldehyde, 2,3-butanedione (diacetyl) and 3-hydroxy-2-butanone (acetoin) in wine by solid-phase microextraction (SPME) and positive ion chemical ionization GC/MS analysis of O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PFBOA) derivatives. For SPME, a 65-microm PEG/DVB fibre was used; chemical ionization was performed with methane as reagent gas. The best analysis-time/sensitivity compromise was to perform the PFBOA reaction at 50 degrees C for 20 min, followed by 5-min SPME at the same temperature. Quantitative analysis was performed in SCAN mode using o-chlorobenzaldehyde as internal standard (IS), on the signal of the [M + H](+) ion at m/z 240 for acetaldehyde, 266 for acetoin (corresponding to the [M + H - 18](+) ion), 282 for diacetyl (protonated mono-derivatized compound), and 336 for IS. The accuracy and repeatability of the method were suitable for the study aims, and linearity was good in the range of concentration studied, with correlation coefficients of calibration curves 0.997, 0.998 and 0.988 for acetaldehyde, diacetyl and acetoin respectively. Due to the higher polarity of acetoin with respect to other two compounds, lower sensitivity in the detection of this compound was observed. By following the variation of the three carbonyl compounds, malolactic fermentations (MLF) were monitored in Merlot wines and this was carried out in the laboratory by two different bacteria strains.     

Thin film deposition from hexamethyldisiloxane fed glow discharges

Hexamethildisiloxane-oxygen fed radiofrequency discharges have been studied under high power density and 0.05÷0.1 torr pressure, i.e., experimental conditions of high monomer fragmentation. Actinometric Optical Emission Spectroscopy of plasma phase, X-Ray Photoelectron Spectroscopy and Infrared Spectroscopy analyses of the deposited films allowed to set the basis of the first “semi-quantitative” mechanism of deposition of siloxane films which can reasonably account for both deposition rates and film compositions. A by-product of the research is the use of CH-to-Ar emission ratio as a probe of carbon content in the film, an important practical parameter for process control.