Mini-Tensile Experiments of Clock-Rolled Zirconium Plate

We present our efforts to measure the tensile strength of clock-rolled pure zirconium in the through-thickness (TT) direction of the plate. Although the plate is too thin to produce standard ASTM tensile samples in the TT orientation, such measurements are relevant to benchmarking our constitutive models of hardening and texture evolution. We have designed a fixture and sample to perform tensile tests on our 9 mm thick plate. The sample is a double-ligament mini-tensile sample: 8 × 8 × 1 mm overall; each ligament has a gage section of 1 × 1 × 3 mm. In contrast, our standard “macro” tensile sample is a flat dogbone with a gage section of 3 × 1.5 × 25 mm. We validate our design by comparing the results of mechanical tests performed on samples of both geometries. Although the hardening response is nearly identical, the flow stress of the miniature samples is offset by +25 MPa at the onset of plastic yield. We present our efforts to resolve the origin of this offset.     

The dynamo library for molecular simulations using hybrid quantum mechanical and molecular mechanical potentials

The Dynamo module library has been developed for the simulation of molecular systems using hybrid quantum mechanical (QM) and molecular mechanical (MM) potentials. Dynamo is not a program package but is a library of Fortran 90 modules that can be employed by those interested in writing their own programs for performing molecular simulations. The library supports a range of different types of molecular calculation including geometry optimizations, reaction‐path determinations and molecular dynamics and Monte Carlo simulations. This article outlines the general structure and capabilities of the library and describes in detail Dynamo's semiempirical QM/MM hybrid potential. Results are presented to indicate three particular aspects of this implementation—the handling of long‐range nonbonding interactions, the nature of the boundary between the quantum mechanical and molecular mechanical atoms and how to perform path‐integral hybrid‐potential molecular dynamics simulations. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1088–1100, 2000     

Connecting ruthenium substituted Keggin-type tungstophosphates by oxotungstic bridges: Evidence for the steric effect of {RuL3}2+ (L3 = η6-arene, (DMSO)3) fragments

The intrinsic reactivity of the organoruthenium-grafted tungstophosphates [α-PW₁₁O₃₉{Ru(η⁶-arene)(H₂O)}]^5? and [α-PW₁₁O₃₉{Ru(DMSO)₃(H₂O)}]^5? has been studied as a prerequisite for later catalytic studies. Upon reflux in aqueous solution, they partially transform into [{PW₁₁O₃₉Ru(η⁶-arene)}₂{WO₂}]^8? (when arene = benzene, toluene…) and [α-PW₁₁O₃₉{Ru(DMSO)}]^5?, respectively. In the former case, the conversion is markedly increased by deliberate addition of tungstate: through a solution NMR study, we show that [{PW₁₁O₃₉Ru(η⁶-p-cymene)}₂{WO₂}]^8? is quantitatively obtained by refluxing a 2:1:2 mixture of [α-PW₁₁O₃₉]^7?, [Ru(η⁶-p-cymene)Cl₂]₂ and [WO₄]^2? at pH 3. In contrast, a different type of complex, [{PW₁₁O₃₉Ru(DMSO)₃}₂{(WO₂(H₂O))₂O}]^8?, is formed by reaction of [α-PW₁₁O₃₉{Ru(DMSO)₃(H₂O)}]^5? with tungstate; it has been characterized by single crystal X-ray diffraction analysis of an acidic potassium salt, and by ¹⁸³W solution NMR. The more sterically demanding {Ru(DMSO)₃}²⁺ fragment probably does not allow the formation of [{PW₁₁O₃₉Ru(DMSO)₃}₂{WO₂}]^8?, while connection of {PW₁₁O₃₉Ru(DMSO)₃}^5? subunits is possible through the larger {(WO₂(H₂O))₂O}²⁺ bridge.     

Tailor–made Covalent Organic‐Inorganic Polyoxometalate Hybrids: Versatile Platforms for the Elaboration of Functional Molecular Architectures

Post‐functionalization of organically modified polyoxometalates (POMs) is a powerful synthetic tool to devise functional building blocks for the rational elaboration of POM‐based molecular materials. In this personal account we focus on iodoaryl‐terminated POM platforms, describe reliable routes to the synthesis of covalent organic‐inorganic POM‐based hybrids and their integration into advanced molecular architectures or multi‐scale assemblies as well as their immobilization onto surfaces. Valorisation of the remarkable redox properties of POMs in the fields of artificial synthesis and molecular electronic is especially considered.     

Role of the electrostatic interactions on the basic or acidic hydrolysis kinetics of poly-( , -lactide) monolayers

The hydrolysis kinetics of insoluble poly-( , -lactide) monolayers spread on basic or acidic aqueous subphase were followed by measuring simultaneously the decrease in the surface area at constant surface pressure and the evolution of the surface potential. An approach to analyse the role of the electrostatic interactions during the hydrolysis at alkaline pH, interpreting the surface potential data was developed. The theoretical predictions based on the idea of a random fragmentation of polymer molecules leading to the interfacial accumulation of charged insoluble products and solubilisation of small fragments describes well the experimental results. The reversibility of the hydrolysis/esterification reaction at acidic pH is taken into account.     

Enzymatic hydrolysis by cutinase of PEG-co PLA copolymers spread monolayers

The mechanism of the hydrolysis by cutinase and the progressive fragmentation of lactic chains in diblock copolymers of PLA with various sizes attached to PEG were studied in a 2D monolayers model system. The hydrolysis kinetics was followed by measuring simultaneously the decrease of the surface area and evolution of the surface potential with time at barostatic conditions. The decrease of the surface area is due to the solubilization of the copolymers as well as of their hydrolytic products: detached PEG blocks and small soluble PLA fragments. The evolution of the surface potential detects the transient interfacial accumulation of charged insoluble PLA fragments. A kinetic model describing the enzymatic hydrolysis was developed and the values for the global hydrolytic kinetic constant were obtained without any fitting parameter. It was found that the global kinetic constant no practically depend on the length of the lactic and the presence of polyethylene–glycol chains.     

Structure,free energy of adhesion and disjoining pressure in a solid-nematic thermotrope system

Summary Monolayers of hexadecyltrimethylammonium bromide produce homeotropic or planar alignments of liquid crystals p-n-methoxybenzilidene aniline and pmethoxyphenylazo-p-butylbenzene.The effect of the temperature on the free energy of adhesion and on the wetting hysteresis shows that for the planar structure at the solid-liquid interface a thick liquid film is formed on the solid; the existence of this thick liquid film is attributed to the elastic energy imposed on a liquid crystal by different anchorages at the solid-liquid and liquid-vapor interfaces.

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Zusammenfassung Monomolekulare Schichten von Hexadecyltrimethylammoniumbromid erzeugen homeotrope oder planare Anordnung von Flüssigkristallen wie p-nMethoxybenzilidin-anilin und p-Methoxyphenylazo-p-butylbenzol.

     

Reorganization of lipid nanocapsules at air-water interface 3. Action of hydrolytic enzymes HLL and pancreatic PLA2

The action of the hydrolytic enzymes humicola lanuginosa lipase (HLL) and pancreatic phospholipase A2 (PLA2) on monolayers formed from lipid nanocapsules (LNC) and model monolayers containing their components, Labrafac, Solutol and Lipoid, is studied by simultaneous measuring the changes in the film area and the surface potential in the "zero order" trough at constant surface pressure (pi). The kinetic models describing the hydrolysis by HLL of the Labrafac, Solutol and their mixtures have been proposed. By using the developed theoretical approach together with the experimental results the surface concentrations of the substrates, hydrolysis products and values of the global kinetic constants were obtained. The comparison between the global kinetic constants in the case of HLL hydrolysis of pure Labrafac, Solutol monolayers and those of the model mixed Labrafac/Solutol monolayers, shows that the rates of hydrolysis are of the same order of magnitude, i.e. an additively of the HLL enzyme action is observed. The composition of the mixed Labrafac/Solutol monolayer, formed after the interfacial LNC destabilization, was estimated.