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Gas clathrate hydrates or gas hydrates are made of H-bonded water molecules forming cages, within which gaseous (guest) molecules are encapsulated. The formed clathrate structures, which may be metastable, depend on the nature and on the partitioning of the guest molecules in the water cage. This work focuses on the structural and vibrational properties of nitrogen hydrate in its two clathrate forms (namely, SI and SII) in the thermodynamic ranges 50–200 bar and 150–270 K, together with a comprehensive analysis of the transformation from SI to SII of this gas hydrate. The thermal expansion of both structures has been measured at 1 bar, and the melting of the nitrogen hydrate has been measured at ca. 210 K at 1 bar. Moreover, the SI structure is metastable in the studied pressure region: from time-dependent neutron powder diffraction analysis, it is shown that the SI structure transforms over time to the SII structure with a rate of (1.37 ± 0.17) × 105s–1at 100 K and at 1 bar. The transformation is also characterized by an induction time (i.e., the lifetime of the pure SI structure) of 0.49 day. We have also investigated the guest partitioning of the nitrogen hydrate using high-resolution Raman scattering. Vibrational bands of nitrogen molecules encapsulated in large cages are measured at lower wavenumbers than the one associated with encapsulation in small cages (by 1.1 cm–1in SI and 0.8 cm–1in SII). In the case of the thermodynamically stable SII phase, the dependence of the guest partitioning has been characterized as a function of the pressure–temperature conditions. Variation of the relative cage filling is demonstrated. While the small cages remain singly occupied according to previous neutron diffraction analysis, this variation is attributed to large cages of the nitrogen hydrate that easily catch or release nitrogen guest molecules. This study thus provides new opportunities for preparing nitrogen gas hydrates with a “targeted” structure and relative cage filling not only by varying the pressure and temperature but also by playing with the structural metastability.

Surface-enhanced Raman scattering (SERS)-based microfluidic platforms are investigated to optimize the detection of biomolecules using silver nanoparticles. The method is established using pefloxacin (an antibacterial agent) as a probe. We first monitor the continuous SERS signal of a 10–5M pefloxacin solution diffusing continuously into a silver nanoparticle stream across the shared interface separating the two-phase, segmented microfluidic laminar flow system. Diffusion of the pefloxacin adsorbate begins immediately after the two streams merge, generating silver aggregates and producing a huge enhancement of the Raman bands of pefloxacin. We show that the evolution of the SERS signal presents a diffusion-like behavior, whose dynamics can be easily monitored as the signal measured in the flow-wise direction is proportional to the reaction time. Finally, we demonstrate that it is possible to optimize SERS intensity spectra by adding a controlled amounts of chloride ions through a side channel to control silver particles aggregation and further enhance Raman scattering.

Sub-nanolitre droplets engineered in microfluidic devices constitute ideal microreactors to investigate the kinetics of chemical reactions on the millisecond time scale. Up to date, fluorescence detection has been extensively used in chemistry and biology to probe reactants and resultant products within such nanodroplets. However, although fluorescence is a very sensitive technique, it lacks intrinsic specificity as frequently fluorescent labels need to be attached to the species of interest. This weakness can be overcome by using vibrational spectroscopy analysis. As an illustrative example, we use confocal Raman microspectroscopy in order to probe the concentration profiles of two interdiffusing solutes within nanolitre droplets transported through a straight microchannel. We establish the feasibility of the experimental method and discuss various aspects related to the space-time resolution and the quantitativeness of the Raman measurements. Finally, we demonstrate that the droplet internal molecular mixing is strongly affected by the droplet internal flow.

The addition of an inorganic component to polymers leads to improvements in various physical and mechanical properties. Various examples on filled elastomeric networks will show that a mechanical characterization can be nicely combined with a spectroscopic investigation for a better understanding of the properties of the composite materials.

The fabrication of an ordered electrode array based on an etched optical fiber bundle is described. The high density sub‐micrometer electrode array is characterized electrochemically using cyclic voltammetry and geometrically via scanning electron microscopy. The observed steady‐state current indicates that individual diffusion layers do not overlap and that the electrodes are diffusively independent. Spatially resolved chemical information of the etched and insulating paint‐covered surface of the electrode array is obtained from confocal Raman microspectroscopy (CRM) experiments. Finally electroactive spots are probed using CRM through the different Raman spectra of the electroactive species of the redox couple Fe(CN)63−/Fe(CN)64−.

The fabrication of an ordered electrode array based on an etched optical fiber bundle is described. The high density sub-micrometer electrode array is characterized electrochemically using cyclic voltammetry and geometrically via scanning electron microscopy. The observed steady-state current indicates that individual diffusion layers do not overlap and that the electrodes are diffusively independent. Spatially resolved chemical information of the etched and insulating paint-covered surface of the electrode array is obtained from confocal Raman microspectroscopy (CRM) experiments. Finally electroactive spots are probed using CRM through the different Raman spectra of the electroactive species of the redox couple Fe(CN)6³⁻/Fe(CN)6⁴⁻.

Optically isotropic thin films (0.5 μm) of an amorphous side-chain copolymer containing 10% azobenzene moieties and 90% meso-azobenzene groups (K1-10 sample) were irradiated by two interfering orthogonal (±45°) or parallel (p+p) linearly polarized laser beams; permanent holographic diffraction gratings were thus inscribed. From atomic force microscopy (AFM) measurements, relatively weak amplitudes (about 50–60 nm) in the surface relief modulation (SRM) are detected but strong perturbations in the profiles and new substructures are evidenced at half-period positions. Using a confocal microspectrometric technique we have recorded various pre-resonance enhanced polarized Raman spectra from a large grating area and obtained spatially resolved Raman images of the intensity variations. This yields new insight into the photoinduced orientation effects, the angular distributions of the chromophore species, and finally the grating formation mechanisms. Different theoretical equations of the polarized Raman scattering intensities, taking account of the pump polarization directions and the high numerical aperture objective used, are derived. Then, an analysis of the experimental results allows us to extract values of the second 〈P₂〉 and fourth 〈P₄〉 coefficients in the chromophore orientation functions at several positions of the SRM, in particular at the top and bottom regions, and to calculate the corresponding normalized distribution functions via information entropy theory. In both gratings, somewhat broader distributions are found in the bottom regions, regions of greater polymer removal. Thus, mass-transport phenomena have perturbed, to a weak extent in the (±45°) first case and to a larger extent in the (p+p) second case, the primary photoinduced orientations. So, two simultaneous and superimposed mechanisms appear to be responsible for the observed complex SRM in the highly birefringent K1-10 copolymer under study and significant second-order contributions are suggested. The grating surface profiles are thus reproduced by fitting the SRM amplitudes at the fundamental and doubled frequency and the corresponding phase constant parameters: a good agreement between the observed (AFM) and simulated profiles is obtained.

AbstractConfocal Raman Microspectrometry is shown to be a powerful technique to study electrochemical devices under working conditions with a spatial resolution of about l μm3. This is first illustrated on a Li/P(EO)20, LiTFSI/Li symmetrical cell where salt concentration gradients in the polymer electrolyte are measured as a function of current density and time. These data give access to transport properties of the polymer electrolyte, namely transport numbers and diffusion coefficients. A second example is provided by electrostatic supercapacitors using activated carbon fabrics of high specific surface area and proton conducting liquid electrolytes. A mapping of a carbon fiber and of the surrounding electrolyte is recorded for ± IV polarizations. The relative intensity and the frequencies of the D and G Raman lines of carbon are found to be very sensitive to the carbon charge.