Equilibrium and nonequilibrium states in microfluidic double emulsions

We describe experimental and theoretical studies dedicated to establishing the physics of formation of double droplets in microfluidic systems. We show that the morphologies (complete engulfing, partial engulfing, and nonengulfing) obtained at late times minimize the interfacial energy of the system. We explain that nonequilibrium morphologies generated in the system can have long lifetimes. Remarkably, the physics of formation of the double droplets with microfluidics allows the synthesis of particles with new morphologies.     

Numerical modeling of a four-wave-mixing-assisted Raman fiber laser

We present a new numerical model of cascaded Raman fiber lasers that takes into account the chromatic dispersion of the fiber and includes the full spectrum of the intracavity field. This model explains and describes remarkably well a new operating regime found experimentally and reveals that chromatic dispersion is truly a new degree of freedom in the design of cascaded Raman lasers.     

Chemically modified semiconductor surfaces: 1,4-phenylenediamine on Si(100)

The formation of inorganic/organic hybrid systems in ultra-high-vacuum (UHV) is studied for the adsorption of 1,4-phenylenediamine (PDA) and aniline on Si(100)(2 × 1) single crystal surfaces. X-ray photoemission spectra (XPS) of PDA and aniline adsorbed on silicon are interpreted in terms of an adsorbate configuration involving two covalent bonds between one amino group per molecule and the dangling bonds of the clean silicon surface. Vibrational high resolution electron energy loss spectroscopy (HREELS) allows us to identify the remaining amino groups in the PDA-adsorbate. Ultraviolet photoemission spectroscopy (UPS) and electron energy loss (EELS) data in the valence band range indicate that the aromatic ring stays intact after the chemisorption of PDA. Changes in work function and energetic shifts of the electronic transitions characterize the charge transfer between adsorbate and substrate. The experimental results are finally discussed in the framework of semi-empirical cluster calculations using MNDO-PM3.     

Cover Picture

The cover picture shows the process of hydrogen and helium insertion/expulsion which has been achieved for the first time with an open fullerene derivative (outlined in the background). The experimental activation barrier for helium decomplexation could be obtained and fully agrees with the calculated value (density functional theory). The barrier for H(2) complexation/decomplexation is interestingly almost double that of helium, as illustrated by the energy diagram shown in the foreground. This difference arises from the larger, elongated surface of H(2) undergoing greater van der Waals interaction at the transition state relative to that of helium, even though both atoms have the same radii. More about this process can be found in the article by Rubin, Houk, Saunders, Cross et al. on p. 1543 ff.     

Guided acoustic wave Brillouin scattering in photonic crystal fibers

We experimentally investigate guided acoustic wave Brillouin scattering in several photonic crystal fibers by use of the so-called fiber loop mirror technique and show a completely different dynamics with respect to standard all-silica fibers. In addition to the suppression of most acoustic phonons, we show that forward Brillouin scattering in photonic crystal fibers is substantially enhanced only for the fundamental acoustic phonon because of efficient transverse acousto-optic field overlap. The results of our numerical simulations reveal that this high-frequency phonon is indeed trapped within the fiber core by the air-hole microstructure, in good agreement with experimental measurements.     

Thermal and light-induced spin-crossover in salts of the heptadentate complex [tris(4-{pyrazol-3-yl}-3-aza-3-butenyl)amine]iron(ii)

The syntheses of [FeL][BF(4)](2).H(2)O, [FeL][ClO(4)](2).H(2)O, [FeL][NO(3)](2).CH(3)NO(2) and [FeL][CF(3)SO(3)](2) (L = tris(4-{pyrazol-3-yl}-3-aza-3-butenyl)amine) are described. The isostructural BF(4)(-) and ClO(4)(-) salts are high-spin between 5-300 K, while the other two compounds are high-spin at room temperature but undergo gradual high-->low spin transitions upon cooling. For [FeL][NO(3)](2) this transition is centred at 139 K and proceeds to near-completeness, while for [FeL][CF(3)SO(3)](2) it is centred at 144 K and only proceeds to 50% conversion. The CF(3)SO(3)(-) salt also undergoes spin-crossover centred at 200 K in (CD(3))(2)CO solution, and exhibits dynamic inversion of its helical ligand conformation. All these compounds except the triflate salt have been crystallographically characterised, and show capped trigonal antiprismatic [6 + 1] coordination geometries. The NO(3)(-) and CF(3)SO(3)(-) salts undergo quantitative conversion to trapped, high-spin excited states upon irradiation with a green laser at 10 K (the LIESST effect; LIESST = Light-Induced Excited Spin State Trapping). The thermal stabilities of their LIESST excited states (T(LIESST) = 80-82 K) resemble those found for iron(ii) complexes of bidentate N-heterocyclic ligands. Hence, the LIESST properties of [FeL](2+) are those of a complex of three rigid bidentate domains linked by a flexible spacer, rather than of a single encapsulating podand.     

Nanostructuration of soft hydrogels: synthesis and characterization of saccharidic methacrylate gels

With the tremendous development of biosensors, there is a strong need in new biocompatible materials avoiding possible denaturing of biological species, which can be easily processed with already existing technologies. The scope of this study was to develop new hydrogels which could be nanostructured by common lithographic methods. Therefore, new methacrylate hydrogels are described, which include functionalized monomers bearing either neutral groups, such as saccharidic moieties, anionic, or cationic groups. The gels have been synthesized by redox or photochemical-initiated radical polymerization. Their porosity has been characterized by thermoporometry, AFM, and electronic microscopy. The kinetics of the photocross-linking has been analyzed by piezorheometry on some of the materials and has been shown to be compatible with technological process time range. Although the obtained hydrogels are soft, their nanostructuration into 500-nm patterns could be performed by nanoimprint photolithography process, and these patterns were observed to be stable for several months.     

A memetic algorithm for the Multi Trip Vehicle Routing Problem

We consider the Multi Trip Vehicle Routing Problem, in which a set of geographically scattered customers have to be served by a fleet of vehicles. Each vehicle can perform several trips during the working day. The objective is to minimize the total travel time while respecting temporal and capacity constraints.