Lattice response of quantum solids to an impulsive local perturbation

The lattice response of solid para-H2 to an impulsive electronic excitation was studied using femtosecond pump-probe spectroscopy. The evolution of an electronic bubble in the crystal, created upon excitation of the A(3ssigma) Rydberg state of an NO impurity, was followed in real time, with a resolution of 100 fs. The experimental results, interpreted in connection with molecular dynamics simulations with quantum corrections, indicate the presence of three stages in the dynamics: a sub-100 fs "adiabatic" phase, a 0.5-1 ps phase, corresponding to the interaction of the first with the next shells driven by the bubble expansion, and a 5 ps phase, corresponding to a slow rearrangement of the environment surrounding the impurity. These findings indicate that the lattice response in solid para-H2 resembles that of a liquid.     

Modelling of aqueous solvation of eosin Y at the rutile TiO2(1 1 0)/water interface

Molecular dynamics simulations at 298 K are used to study an aqueous dissolved dye (eosin Y) adsorbed at the TiO₂(1 1 0) surface to extract static and dynamic information of solvation. Differences in the physical behaviour of the dye at the surface and in bulk water are compared with recent transient absorption and photon echo experiments within the limits of linear response. The calculated solvent dynamics features fast contributions, which change very little at the surface as well as a slow component, which slows down by a factor of two at the interface, in good agreement with experimental data.     

Biphasic reaction systems for lignocellulosic biomass revalorisation

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Synthesis of high quality zinc blende CdSe nanocrystals

Highly homogeneous and luminescent CdSe colloidal nanocrystals in the less common zinc blende crystal structure have been obtained at high temperature in a noncoordinating organic solvent. The key parameter appears to be the addition of a phosphonic acid to the trioctylphosphine-selenium complex before its injection into the hot cadmium mixture, while the role of temperature is less relevant. Compared to standard (wurtzite) colloidal CdSe preparations, we find that the growth rate is considerably reduced, and the energy gap between the first two absorption bands becomes larger.     

Direct observation of microscopic solvation at the surface of clusters by ultrafast photoelectron imaging

We report on microscopic observation of solvation by argon atoms of excited states of an ethylenic-like molecule, TDMAE (tetrakis dimethylaminoethylene). Two experimental methods were used: gas phase dynamics for the observation of the evolution through excited states, matrix isolation spectroscopy for characterization of the initial states. Excited state dynamics was recorded after the molecule had been deposited on the surface of a large argon cluster (n approximately 100) by pick-up. The deposited cluster was characterized by mass spectrometry and by its shifted photoelectron spectrum. The time evolution of the system was visualized by femtosecond pump/probe velocity map imaging of photoelectrons. The time evolution of deposited TDMAE excited at 266 nm can be modeled via a modified three state model, as in the free molecule. The initially excited state is of valence character, and a Rydberg state mediates the passage to a zwitterionic configuration. The specific solvation of Rydberg states by the surface of the cluster was directly observed and is discussed. It represents the striking outcome of the present work. It is inferred that differently from the gas phase, solvated Rydberg states resulting from state mixing within a R(n/lambda) complex in the presence of the argon surface are reached. Solvation of these Rydberg states should be effective through interaction of the ion core of the excited molecules with the cluster.     

Direct simulation of multiphase flows with modeling of dynamic interface contact angle

We describe a modeling technique for dynamic contact angle between a phase interface and a solid wall using a generalized Navier boundary condition in the context of a front-tracking-based multiphase method. The contact line motion is determined by the generalized Navier slip boundary condition in order to eliminate the infinite shear stress at the contact line. Applying this slip boundary condition only to the interface movement with various slip ratios shows good agreement with experimental results compared to allowing full fluid slip along the solid surface. The interface slip model performs well on grid convergence tests using both the slip ratio and slip length models. A detailed energy analysis was performed to identify changes in kinetic, surface, and potential energies as well as viscous and contact line dissipation with time. A friction coefficient for contact line dissipation was obtained based on the other computed energy terms. Each energy term and the friction coefficient were compared for different grid resolutions. The effect of varying the slip ratio as well as the contact angle distribution versus contact line speed was analyzed. The behavior of drop impact on a solid wall with different advancing and receding angles was investigated. Finally, the proposed dynamic contact model was extended to three dimensions for large-scale parallel calculations. The impact of a droplet on a solid cylinder was simulated to demonstrate the capabilities of the proposing formulation on general solid structures. Widely different contact angles were tested and showed distinctive characteristic behavior clearly.     

Towards the fluorescence resonance energy transfer (FRET) scanning near-field optical microscopy: Investigation of nanolocal FRET processes and FRET probe microscope

The fluorescence resonance energy-transfer (FRET) process is investigated between donor dye molecules deposited on the sample surface and acceptor dye molecules deposited on the tips of scanning near-field and atomic force microscopes. The FRET process was observed only when the tip acquired contact with the sample and took place in regions of sizes of only a few tens of nanometers with only a few thousands (or even hundreds) of molecules involved. The dependence of the FRET intensity on the tip-sample acting force is recorded and interpreted. In relation to the obtained results, the construction of a previously proposed one-atom FRET SNOM is described.     

In situ synthesis of silver nanoparticles on densely amine‐functionalized polystyrene: Highly active nanocomposite catalyst for the reduction of methylene blue

In this contribution, polystyrene (PS) bearing nitrogen‐rich ligands as chelation moieties for both Ag⁺ ions and Ag⁽⁰⁾ nanoparticles was prepared through successive chemical modifications of native PS including nitration (treatment with HNO₃/H₂SO₄), reductive amination (treatment with SnCl₂/HCl), Michael addition of methyl acrylate, and grafting of ethyelenediamine. The as‐synthesized PS derivative was further used to support silver nanoparticles through initial chelation of the silver nanoparticle ions precursor and subsequent chemical in situ reduction with sodium borohydride. Chemical structure of the PS derivatives was confirmed after each synthesis step by using complementary characterization methods including infrared and energy‐dispersive X‐ray spectroscopies, elemental analysis, X‐ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The catalytic activity of the PS‐EAD/AgNP nanocomposite was demonstrated using the reduction of methylene blue to leucomethylene blue, as a model reaction. The reaction was monitored by UV‐vis spectrophotometry and achieved with an excess of sodium borohydride allowing for a pseudo‐first‐order analysis of the kinetic reaction parameters. Quantitative reduction of the methylene blue was obtained upon successive catalytic cycles with a rate constant value of 0.4016 minute^?1.     

Assessment of Bleached and Unbleached Nanofibers from Pistachio Shells for Nanopaper Making

Cellulose and lignocellulose nanofibrils were extracted from pistachio shells utilizing environmentally friendly pulping and totally chlorine-free bleaching. The extracted nanofibers were used to elaborate nanopaper, a continuous film made by gravimetric entanglement of the nanofibers and hot-pressed to enhance intramolecular bonding. The elaborated nanopapers were analyzed through their mechanical, optical, and surface properties to evaluate the influence of non-cellulosic macromolecules on the final properties of the nanopaper. Results have shown that the presence of lignin augmented the viscoelastic properties of the nanopapers by ≈25% compared with fully bleached nanopaper; moreover, the hydrophobicity of the lignocellulose nanopaper was achieved, as the surface free energy was diminished from 62.65 to 32.45 mNm⁻¹ with an almost non-polar component and a water contact angle of 93.52°. On the other hand, the presence of lignin had an apparent visual effect on the color of the nanopapers, with a ΔE of 51.33 and a ΔL of −44.91, meaning a substantial darkening of the film. However, in terms of ultraviolet transmittance, the presence of lignin resulted in a practically nonexistent transmission in the UV spectra, with low transmittance in the visible wavelengths. In general, the presence of lignin resulted in the enhancement of selected properties which are desirable for packaging materials, which makes pistachio shell nano-lignocellulose an attractive option for this field.