Electrochemistry at capped platinum nanoparticle Langmuir Blodgett films: A study of the influence of platinum amount and of number of LB layers

Platinum nanoparticles (n-Pt), over-grafted with 2-thiophenecarbonyl chloride are assembled on gold electrodes, by the Langmuir Blodgett (LB) technique using behenic acid (BHA) as promoting agent. These layers are electrochemically active without any preliminary activation. The [Fe(CN)₆]^3−/4− redox couple was used as electrochemical probe. This paper reports on the influence of the number of deposited LB layers, and the n-Pt density on the electrochemical response. n-Pt density was modified by the change of the “BHA/n-Pt” ratio. Cyclic voltammograms of “[Fe(CN)₆]^3−/4−” were observed whatever the coating conditions. As soon as the first layer was deposited the electrochemical response was associated to the n-Pt coverage, its response slightly increased up to a steady state for five or seven layers. As expected, the increase of the Pt density favored the increase of the current density. XPS analysis performed before and after electrochemical cycling showed that 4-mercaptoaniline capped platinum nanoparticles, and their over grafting were chemically and electrochemically stable. Analysis of influence of the number or the n-Pt density of the layers showed that the electrochemically active part of LB electrodes was provided by the last layer plus a part of the underlying one.     

Electronic transfer through Langmuir-Blodgett layers of capped platinum nanoparticles: An electrochemical approach

Amine functionalized platinum nanoparticles have been modified by over-grafting two different molecules, 2-thiophenecarbonyl chloride (Pt-1) and 1-hexyl-4-(4-isothiocyanatophenyl)-bicyclo (2, 2, 2) octane (Pt-2). Cyclic voltammetry was performed at gold electrodes coated with Langmuir-Blodgett (LB) mixed films of Pt-1 and Pt-2 nanoparticles, and behenic acid. From five layers the electrochemical response was essentially provided by the last LB component. The electrochemical responses towards the [Fe(CN)₆]^3−/4− couple were strongly influenced by the nature of the over-grafted molecules: films of Pt-2 presented an almost complete blocking effect, while films of Pt-1 allowed the redox reaction to occur on Pt nanoparticles. In order to understand the reasons for such different behaviors we built up hetero-nanostructures by superposing Pt-1 and Pt-2 LB layers in different ways, yielding different kinds of “sandwich” structures. The electrochemical response depended on the electrode ending. When Pt-1 nanoparticles were in the outer layer, in contact with the electrolyte solution, the electrode was electroactive toward the redox probe, while when Pt-2 layers were in the outer layer no electroactivity was detected. For sandwiches made of Pt-1, with a variable thickness of an intercalated film of Pt-2, the electrode response to [Fe(CN)₆]^3−/4− was modulated by the thickness of the inter-layer: the thicker the layer, the lower the response.     

Modeling of steel and concrete strains between primary cracks for the prediction of cover-controlled cracking in RC-beams

After cracking, the intact concrete between two consecutive primary cracks remains elastic and the maximum concrete stress is less than the tensile strength of concrete. However, under increasing loading, cover-controlled cracks occur at the steel-concrete interface causing a loss of bond and hence a loss of tension stiffness. The cover-controlled cracks are internal concrete cracks that initiate at steel rib location and are contained within the concrete cover. In this paper, steel and concrete strain distribution between two consecutive primary cracks are modeled based on a linear assumed distribution of the bond stress at the steel-concrete interface. The accurate calculation of the tensile concrete strain allows introducing new criteria for cover-control cracking initiation based on a peak value of steel stress calculated at crack location.     

Failure and scaling properties of a softening interface connected to an elastic block

The damage growth in a softening interface connected to an elastic block is analysed. The elastic block, assumed to be infinite, is modelled as a two-dimensional continuum and the interface is one-dimensional with a constitutive response which follows a scalar damage model. The solution technique is based on the equilibrium of the interfacial forces resulting from the deformation of the elastic block and from the interface constitutive response. The interface failure process is compared to that of a hierarchical model which was obtained analytically (Delaplace et al., 1998). The two are found to be similar, without an internal length scaling the distribution of damage at the inception of macro-cracking. Finally, scale effects on the occurrence of bifurcation and instability are considered. It is shown that bifurcation may occur prior to or after the limit point under displacement control, depending on the elastic block height or stiffness. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chicken fat dry fractionation: Effects of temperature and time on crystallization,filtration and fraction properties

A surface response experimental design was used to quantify the effects of the final cooling temperature and the residence time at this temperature on the filtration characteristics of the crystal suspension and the quality of the fractions during chicken fat dry fractionation. The crystal morphology was monitored to gain insight into the observed effects. Temperature affected crystallization and the characteristics of the olein and stearin fractions. The crystals became fragmented as the residence time increased, thus leading to a decrease in the filterability of the crystal suspension and an increase in the proportion of the entrained liquid phase. The residence time only affected the quality of the stearin fraction. This time effect was noted at high cooling temperatures in the investigated experimental domain. At low temperatures, increasing the residence time enhanced crystal growth and increased the extent of unsaturation of both fractions without modifying the filtration features.     

Development of Chiral Phosphoric Acids based on Ferrocene‐Bridged Paracyclophane Frameworks

This work deals with the development of a new family of planar chiral phosphoric acids based on a ferrocenophane/paracyclophane scaffold. The synthetic approach has been improved by taking advantage of a chiral phosphorylating agent to access enantiomerically enriched acids via diastereomers separation. These phosphoric acids have been used as catalysts for the enantioselective H‐transfer reduction of α‐substituted quinolines with Hantzsch esters. Optimization of both the catalyst and the Hantzsch reductant allowed ee values in the range 82–92% to be attained starting from α‐arylquinolines.

     

An experimental study of a confined and submerged impinging jet heat transfer using Al2O3-water nanofluid

An experimental investigation was performed to study the heat transfer performance of a 36 nm-Al₂O₃-particle–water nanofluid in a confined and submerged impinging jet on a flat, horizontal and circular heated surface. The tests were realized for the following ranges of the governing parameters: the nozzle diameter is 3 mm and the distance nozzle-to-heated-surface was set to 2, 5 and 10 mm; the flow Reynolds number varies from 3800 to 88 000, the Prandtl number from 5 to 10, and the particle volume fraction is ranging from 0 to 6%. Experimental data, obtained for both laminar and turbulent flow regimes, have clearly shown that, depending upon the combination of nozzle-to-heated surface distance and particle volume fraction, the use of a nanofluid can provide a heat transfer enhancement in some cases; conversely, for other combinations, an adverse effect on the convective heat transfer coefficient may occur. Within the experimental parameters used, it has been observed that highest surface heat transfer coefficients can be achieved using an intermediate nozzle-to-surface distance of 5 mm and a 2.8% particle volume fraction nanofluid. Nanofluids with high particle volume fractions, say 6% or higher, have been found not appropriate for the heat transfer enhancement purpose under the confined impinging jet configuration. On the other hand, for a very small and a large distance of nozzle-to-heated-surface, it has been observed that the nanofluid use does not provide a perceptible heat transfer enhancement and has, for some particular cases, produced a clear decrease of the convective heat transfer coefficient while compared to that obtained using distilled water.     

Synthesis and characterization of new cationic surfactants derived from lactic acid

A series of new cationic surfactants was prepared by condensation of lactic acid with N,N-dimethyl propylamine, followed successively by acetylation with acid chloride or ester and by quaternization with dimethylsulfate. Each surfactant and its precursors' structural assignments were based on infrared spectra and ¹H and ¹³C nuclear magnetic resonance spectra. Critical micelle concentrations, contact angles, kinetics of drop spreading, and foam capacities were determined.     

An experimental investigation on oil mist characterization used in MQL milling process

In this study, a method is developed to determine the oil mist characteristics for the minimal quantity lubricant process. The oil mist is characterized by the size, velocity, and volume flow rate of its particles. In each case, a specific measurement process is used: the laser diffraction granulometry method, the particle image velocimetry, and the gravimetric method. These methods are used in the case of static and simple models with different inner channels. Experimental tests have been done with the same inner channel as the existing spindle inner channel. Different output models with different inner canalizations have been tested, using these experimental processes. The main goal is to control the characteristics of output oil mist as a function of the input oil mist device parameters.