Nanometric confinement: Toward new physical properties and technological developments

In numerous real life situations, molecular systems are not found in bulk but instead trapped in limited volumes of nanometric size: this is nanometric confinement. The complex interplay of the confinement topology, dimensionality (3D to 1D) and surface/volume ratio significantly affects the physical properties of the confined material. After decades of intense fundamental research, we are now entering a time when the unusual properties of fluids under confinement may be tuned to target specific technological objectives. In this paper, we highlight few situations, all related to the fields of energy production or storage, where diverse neutron scattering techniques (imaging, small angle scattering, diffraction, inelastic and quasi-elastic scattering) may help to bridge basic science and applied research.     

Threshold-photoelectron spectroscopic study of methyl-substituted hydrazine compounds

The valence shell electronic structures of methylhydrazine (CH(3)NHNH(2)), 1,1-dimethylhydrazine ((CH(3))(2)NNH(2)) and tetramethylhydrazine ((CH(3))(4)N(2)) have been studied by recording threshold and conventional (kinetic energy resolved) photoelectron spectra. Ab initio calculations have been performed on ammonia and the three methyl substituted hydrazines, with the structures being optimized at the B3-LYP/6-31+G(d) level of theory. The ionization energies of the valence molecular orbitals were calculated using the Green's function method, allowing the photoelectron bands to be assigned to specific molecular orbitals. The ground-state adiabatic and vertical ionization energies, as determined from the threshold photoelectron spectra, were IE(a) = 8.02 +/- 0.16 eV and IE(v) = 9.36 +/- 0.02 eV for methylhydrazine, IE(a) = 7.78 +/- 0.16 eV and IE(v) = 8.86 +/- 0.01 eV for 1,1-dimethylhydrazine and IE(a) = 7.26 +/- 0.16 eV and IE(v) = 8.38 +/- 0.01 eV for tetramethylhydrazine. Due to the large geometry change that occurs upon ionization, these IE(a) values are all higher than the true thresholds. New features have been observed in the inner valence region and these have been compared with similar structure in the spectrum of hydrazine. The effect of resonant autoionization on the threshold photoelectron yield is discussed. New heats of formation (Delta(f)H) are proposed for the three hydrazines on the basis of G3 calculations: 107, 94, and 95 kJ/mol for methylhydrazine, 1,1-dimethyhydrazine and tetramethylhydrazine, respectively. The previously reported Delta(f)H for tetramethylhydrazine is shown to be erroneous.     

A photoelectron and TPEPICO investigation of the acetone radical cation

The valence shell photoelectron spectrum, threshold photoelectron spectrum, and threshold photoelectron photoion coincidence (TPEPICO) mass spectra of acetone have been measured using synchrotron radiation. New vibrational progressions have been observed and assigned in the X 2B2 state photoelectron bands of acetone-h6 and acetone-d6, and the influence of resonant autoionization on the threshold electron yield has been investigated. The dissociation thresholds for fragment ions up to 31 eV have been measured and compared to previous values. In addition, kinetic modeling of the threshold region for CH3* and CH4 loss leads to new values of 78 +/- 2 kJ mol(-1) and 75 +/- 2 kJ mol(-1), respectively, for the 0 K activation energies for these two processes. The result for the methyl loss channel is in reasonable agreement with, but slightly lower than, that of 83 +/- 1 kJ mol(-1) derived in a recent TPEPICO study by Fogleman et al. The modeling accounts for both low-energy dissociation channels at two different ion residence times in the mass spectrometer. Moreover, the effects of the ro-vibrational population distribution, the electron transmission efficiency, and the monochromator band-pass are included. The present activation energies yield a Delta(f)H298 for CH3CO+ of 655 +/- 3 kJ mol(-1), which is 4 kJ mol(-1) lower than that reported by Fogleman et al. The present Delta(f)H298 for CH3CO+ can be combined with the Delta(f)H298 for CH2CO (-47.5 +/- 1.6 kJ mol(-1)) and H+ (1530 kJ mol(-1)) to yield a 298 K proton affinity for ketene of 828 +/- 4 kJ mol(-1), in good agreement with the value (825 kJ mol(-1)) calculated at the G2 level of theory. The measured activation energy for CH4 loss leads to a Delta(f)H298 (CH2CO+*) of 873 +/- 3 kJ mol(-1).     

Bounds on the extensional strains in elastic homogeneous crystals under simple tension

Within the context of the linearized theory of elasticity, weconsider homogeneous crystals, which have orthorhombic, tetragonal,hexagonal symmetry or cubic symmetry (‘RTHC’ crystals).When such a crystal is subjected to a simple tension (or compression)of amount T in the direction n, there will be three, generallydifferent, extensional strains along the three mutually perpendiculardirections corresponding to the principal axes of strain. Thepurpose of this paper is to present a simple procedure to placebounds, upper and lower, on the possible extensional strainsin the crystal, both in the case when n is fixed in directionand in the case when n is arbitrary. The procedure allows usto determine whether the bounds are attained or not.     

Application of new methodologies based on design of experiments, independent component analysis and design space for robust optimization in liquid chromatography

HPLC separations of an unknown sample mixture and a pharmaceutical formulation have been optimized using a recently developed chemometric methodology proposed by W. Dewé et al. in 2004 and improved by P. Lebrun et al. in 2008. This methodology is based on experimental designs which are used to model retention times of compounds of interest. Then, the prediction accuracy and the optimal separation robustness, including the uncertainty study, were evaluated. Finally, the design space (ICH Q8(R1) guideline) was computed as the probability for a criterion to lie in a selected range of acceptance. Furthermore, the chromatograms were automatically read. Peak detection and peak matching were carried out with a previously developed methodology using independent component analysis published by B. Debrus et al. in 2009. The present successful applications strengthen the high potential of these methodologies for the automated development of chromatographic methods.     

Photocontrolled Synthesis of n-Type Conjugated Polymers

Current approaches to synthesize π-conjugated polymers (CPs) are dominated by thermally driven, transition-metal-mediated reactions. Herein we show that electron-deficient Grignard monomers readily polymerize under visible-light irradiation at room temperature in the absence of a catalyst. The product distribution can be tuned by the wavelength of irradiation based on the absorption of the polymer. Conversion studies are consistent with an uncontrolled chain-growth process; correspondingly, chain extension produces all-conjugated n-type block copolymers. Preliminary results demonstrate that the polymerization can be expanded to donor–acceptor alternating copolymers. We anticipate that this method can serve as a platform to access new architectures of n-type CPs without the need for transition-metal catalysis.     

Coupled diffusion and phase transition: Phase fields,constraints, and the Cahn–Hilliard equation

We develop a constrained theory for constituent migration in bodies with microstructure described by a scalar phase field. The distinguishing features of the theory stem from a systematic treatment and characterization of the reactions needed to maintain the internal constraint given by the coincidence of the mass fraction and the phase field. We also develop boundary conditions for situations in which the interface between the body and its environment is structureless and cannot support constituent transport. In addition to yielding a new derivation of the Cahn–Hilliard equation, the theory affords an interpretation of that equation as a limiting variant of an Allen–Cahn type diffusion system arising from the unconstrained theory obtained by considering the mass fraction and the phase field as independent quantities. We corroborate that interpretation with three-dimensional numerical simulations of a recently proposed benchmark problem.

     

Constituent gluon interpretation of glueballs and gluelumps

Arguments are given that support the interpretation of the lattice QCD glueball and gluelump spectra in terms of bound states of massless constituent gluons with helicity 1. In this scheme, we show that the mass hierarchy of the currently known gluelumps and glueballs is mainly due to the number of constituent gluons and can be understood within a simple flux tube model. It is also argued that the lattice QCD 0^+- glueball should be seen as a four-gluon bound state. We finally predict the mass of the 0^- state, not yet computed in lattice QCD.     

Une théorie de l'effet Faraday dans un diélectrique viscoélastique isotrope polarisable et magnétisable

Résumé Dans ce travail, on étudie l'effetFaraday dans le cadre de la mécanique des milieux continus. On se base sur les équations deMaxwell, ainsi que sur les bilans de quantité de mouvement et d'énergie interne pour un continu polarisable et magnétisable sous la forme obtenue parG. Mayne etPh. Boulanger (4). A ces équations on adjoint des équations constitutives où l'on introduit, en plus des variables qui caractérisent un diélectrique élastique, les dérivées par rapport aux temps de la déformation, de la polarisation et de la magnétisation. Grâce à une linéarisation des équations autour d'un état d'équilibre, on étudie la propagation des ondes planes électromagnétiques et mécaniques dans la direction d'un champ magnétique constant. Cette étude met en évidence l'effetFaraday ainsi qu'un effet analogue pour les ondes mécaniques transversales.

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Summary In this work, theFaraday effect is investigated within the frame of continuum mechanics. We use hereMaxwell equations, and the momentum balance and internal energy balance equations in the form obtained byG. Mayne andPh. Boulanger (4). To these equations are added constitutive equations which contain the time derivatives of the deformation, the polarization and the magnetization, in addition to the variables which caracterize the elastic dielectric. By linearizing the equations about an equilibrium state, we study the propagation of electromagnetic and mechanical plane waves in the direction of a constant magnetic field. By this means, we are able to derive theFaraday effect and an analogous one for transverse mechanical waves.

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Zusammenfassung Die Arbeit befaßt sich mit der Erforschung desFaraday-Effekts im Rahmen der Kontinuumsmechanik. Als Basis dienen hier dieMaxwellschen Gleichungen sowie die Impulsbilanz und Energiebilanz in einem polarisierbaren und magnetisierbaren Kontinuum in der vonG. Mayne undPh. Boulanger festgelegten Form (4). Benützt werden ferner Materialgleichungen, in denen die Zeitableitungen der Deformation, Polarisation und Magnetisierung, sowie die Veränderlichen, die ein elastisches Dielektrikum bestimmen, eingeführt werden. Dank einer linearen Anordnung der Gleichungen um einen Gleichgewichtszustand wird die Ausbreitung elektromagnetischer und mechanischer ebener Wellen, in der Richtung eines magnetischen Feldes, erforscht. Auf diese Weise ist es möglich, denFaraday-Effekt zu überprüfen sowie einen analogen Effekt in mechanischen Transversalwellen.