Adhesive elastic contact between a symmetric indenter and an elastic film

This paper examines the frictionless adhesive elastic contact problem of a rigid sphere indenting a thin film deposited on a substrate. The result is then used to model the elastic phase of micro-nanoscale indentation tests performed to determine the mechanical properties of coatings and films. We investigate the elastic response including the effects of adhesion, which, as the scale decreases to the nano level, become an important issue. In this paper, we extend the Johnson–Kendall–Roberts, Derjaguin–Muller–Toporov, and Maugis–Dugdale half-space adhesion models to the case of a finite thickness elastic film coated on an elastic substrate. We propose a simplified model based on the assumption that the pressure distribution is that of the corresponding half-space models; in doing so, we investigate the contact radius/film thickness ratio in a range where it is usually assumed the half-space model. We obtain an analytical solution for the elastic response that is useful for evaluating the effects of the film-thickness, the interface film–substrate conditions, and the adhesion forces. This study provides a guideline for selecting the appropriate film thickness and substrate to determine the elastic constants of film in the indentation tests.     

Supramolecular Catalysis of Ester and Amide Cleavage by a Dinuclear Barium(II) Complex

Five components spontaneously self‐assemble to yield the productive complex 1 , where one barium ion delivers an ethoxide to the carbonyl group of an amide substrate anchored by means of a distal carboxylate moiety to the other barium ion. High substrate specificity, fairly high reaction rates with catalytic turnover, and competitive inhibition by inert substrates are observed.     

Influence of the Use of an Ionic Liquid as Pre-Hydrodistillation Maceration Medium on the Composition and Yield of Cannabis sativa L. Essential Oil

Cannabis sativa L. is a multi-purpose crop, whose resilience, adaptability and soil-enriching properties make it a low-impact production. In the last years, the cultivation of the “industrial” hemp varieties (THC < 0.2%) has been promoted by many Countries, opening a whole new market of hemp-derived products, such as its essential oil (EO). Its distillation might represent an effective method to exploit a residue of the hemp fiber production (flowers), complying with the guidelines of the circular economy. In the present work, different concentrations of an ionic liquid (IL; 1,3-dimethyl-1H-imidazol-3-ium dimethylphosphate) have been studied as a pre-hydrodistillation maceration medium. The EO yields have been evaluated, and their compositions have been analyzed by GC-EIMS. The use of 100% and 90% IL concentrations gave a hydrodistillation yield increment of 250% and 200%, respectively. The 200% yield increase was maintained when the 100% IL was recycled after the hydrodistillation. The lower IL concentrations incremented the cannabinoid and oxygenated sesquiterpene contents, while the opposite was true for sesquiterpene hydrocarbons. The proposed IL-enhanced hydrodistillation medium applied to hemp, studied for the first time in the present work, might be used to both (i) noteworthy increment the hydrodistillation yield and (ii) modulate the obtained EO composition based on the desired final product.     

Isomeric composition of the ester fraction from epicuticular waxes of Festuca arundinacea Schreb

The ester portion of epicuticular waxes of tall fescue (Festuca arundinacea Schreb.) is composed of mixtures of homologous series of fatty acids esterfied with fatty alcohols. GC analyses of natural esters gave rise to the separation of several compounds of different chain length. To identify and quantify individual components in the mixture, GC/MS analyses were carried out, and the mass spectra of each peak were recorded and analyzed for characteristic ions. This approach permitted a comparison with data obtained from classical methods using GC analysis of acid and alcohol moieties obtained by hydrolysis.     

New chemical hydrogels based on poly(vinyl alcohol)

The syntheses of two new types of chemical hydrogels based on poly(vinyl alcohol), PVA, are reported. Common to both synthetic routes is the preparation of a telechelic PVA (tel-PVA) obtained by periodate splitting of the vicinal diol units present in few percent along the chain. tel-PVA was then used as crosslinking agent with chitosan and PVA in two simple reactions in aqueous phase such as reductive alkylation of chitosan and acetalyzation of PVA. Both reactions yielded firm wall-to-wall networks showing marked differences in their swelling capability. © 1996 John Wiley & Sons, Inc.     

Polymerization of 3-methyl-1-butene promoted by metallocene catalysts

3-Methyl-1-butene was polymerized in the presence of a number of homogeneous metallocene catalysts (co-catalyst methylalumoxane). Contrary to literature reports, it was found that even the simplest C₂-symmetric metallocenes promote the isotactic polymerization of this monomer with reasonable productivities. Quite surprisingly, a prevailingly isotactic polymer was also obtained in the presence of C_s-symmetric metallocenes, which are instead syndiotactic-specific in propene polymerization.     

New results in the isotactic polymerization of propene promoted by homogeneous metallocene catalysts

In this presentation, some mechanistic aspects of isotactic propene polymerization in the presence of homogeneous Group IV metallocene catalysts are analyzed in the light of new (and still largely unpublished) experimental results. In particular, the regiospecificity of catalyst systems based on two typical C₂-symmetric ansazirconocenes (i.e. rac-ethylenebis(1-indenyl) ZrCl₂ and rac-dimethylsilylbis(1-indenyl) ZrCl₂; co-catalyst, methylalumoxane) is discussed comparatively. An influence of propene concentration on the ratio between 2,1 and 1,3 monomer enchainments and surprisingly - on the stereoregularity of the produced polymers is pointed out. Tentative kinetic explanations of the observed polymerization behaviours are also proposed.     

Development and Characterization of Curcumin-Silver Nanoparticles as a Promising Formulation to Test on Human Pterygium-Derived Keratinocytes

Pterygium is a progressive disease of the human eye arising from sub-conjunctival tissue and extending onto the cornea. Due to its invasive growth, pterygium can reach the pupil compromising visual function. Currently available medical treatments have limited success in suppressing efficiently the disease. Previous studies have demonstrated that curcumin, polyphenol isolated from the rhizome of Curcuma longa, induces apoptosis of human pterygium fibroblasts in a dose- and time-dependent manner showing promising activity in the treatment of this ophthalmic disease. However, this molecule is not very soluble in water in either neutral or acidic pH and is only slightly more soluble in alkaline conditions, while its dissolving in organic solvents drastically reduces its potential use for biomedical applications. A nanoformulation of curcumin stabilized silver nanoparticles (Cur-AgNPs) seems an effective strategy to increase the bioavailability of curcumin without inducing toxic effects. In fact, silver nitrates have been used safely for the treatment of many ophthalmic conditions and diseases for a long time and the concentration of AgNPs in this formulation is quite low. The synthesis of this new compound was achieved through a modified Bettini’s method adapted to improve the quality of the product intended for human use. Indeed, the pH of the reaction was changed to 9, the temperature of the reaction was increased from 90 °C to 100 °C and after the synthesis the Cur-AgNPs were dispersed in Borax buffer using a dialysis step to improve the biocompatibility of the formulation. This new compound will be able to deliver both components (curcumin and silver) at the same time to the affected tissue, representing an alternative and a more sophisticated strategy for the treatment of human pterygium. Further in vitro and in vivo assays will be required to validate this formulation.