Photo‐Rheometry/NIR Spectrometry: An in situ Technique for Monitoring Conversion and Viscoelastic Properties during Photopolymerization

Summary: A suitable rheometer for simultaneous dynamic mechanical analysis (DMA) and NIR (Near Infra‐Red) in situ analysis during UV curing was developed. The conversion and viscoelastic properties of a dimethacrylate/styrene‐based system were investigated. The results were plotted against both irradiation time and total average conversion. For the same conversion, a lower intensity delays the reaction but does not affect the viscoelastic properties.

A device for simultaneous photo‐rheology and NIR spectroscopy experiments.     

Neutron brillouin scattering and liquid metal-molten salt mixtures

Summary The dispersion of collective density fluctuations (extended sound modes) has been measured in mixtures of liquid alkali metals and the corresponding molten alkali-halide salts. Mixtures with salt concentrations from 10 to 40% were investigated for momentum transfersQ between 4 and 14 nm⁻¹. ForQ-values larger than 11 nm⁻¹ the collective modes could even in the most favourable case no longer be separated from the quasi-elastic peak, the width of which increases roughly ∼Q ² in this region of momentum transfers. At a concentration of 10% RbCl in Rb we find a dispersion which would correspond to expanded liquid Rb at the temperature of the mixture (∼1000 K), demonstrating the dominant metallic character of the mixture (screening by nearly free electrons) at this salt concentration. At higher concentrations of salt, where influences from different partial dynamic structure factors interplay, the dispersions deviate from this simple structured dispersion curve, most likely due to the influence of an early onset of some ionic type of screening in the liquid. The proofs of this paper have been supervised by the Scientific Committee.     

Characterization of the hydrolysis and polymerization processes of methacryloxypropyltrimethoxysilane

The sol-gel synthesis of hybrid methacrylate-silica materials using methacryloxypropyltrimethoxysilane (MPS) as precursor, has been analyzed using ¹H and ²⁹Si liquid NMR as well as ²⁹Si and ¹³C MAS-NMR. Under the present experimental conditions (H₂O/MPS=3; pH=2), hydrolysis of methoxy groups is fast. However, 5% of unreacted alkoxy groups are still present in the sol after 14 days aging. Condensation reactions lead mainly to cyclic or short linear species. The number of cross-linking points never exceeds 20% of the Si units, which seems to prevent the formation of a gel. Polymerization of methacrylate groups occur easily under short times of U.V. irradiation. A quantitative analysis shows about 20% of residual unreacted groups in the polymerized materials. Addition of free methylmethacrylate in the hydrolyzed sols helps in getting a fully polymerized organic network.     

H-bond dynamics in well-characterized supercooled and glassy aqueous solutions

On the basis of a structural characterization of different thermodynamic states, we investigate the vibrational density of state for a saturated aqueous solution LiCl·RH₂O (R=6 and 4). Intermolecular motions of water deduced from inelastic neutron scattering are discussed. Bending, stretching and vibrational modes exhibit different behaviour in glassy, supercooled and liquid states. Stretching motion appears to be quite sensitive to the glass transition.     

A top surface liquid layer during membrane formation using vapor-induced phase separation (VIPS)—Evidence and mechanism of formation

The formation of a surface liquid layer on the top of membrane forming systems made of poly(ether-imide) (PEI) and N-methylpyrrolidone (NMP) was clearly demonstrated during water vapor-induced phase separation (VIPS) through several in situ investigation methods including optical microscopy and dynamic water contact angle measurements for a qualitative approach, and Raman confocal and FTIR microscopy for a quantitative one. A mechanism involving the shrinkage from the polymer-rich phase consecutively to the surface phase separation is proposed to account for the significantly high concentration of PEI in the surface liquid layer. The emergence of a surface liquid layer during the phase separation process is discussed in terms of implications on morphology of membrane fabricated using VIPS and how it contrasts with liquid-induced phase separation.     

Comparative chemometric analyses of geographic origins and compositions of lavandin var. Grosso essential oils by mid infrared spectroscopy and gas chromatography

Lavandin, a sterile hybrid of Lavandula angustifolia P. Mill. × Lavandula latifolia (L.f.) Medikus (Lamiaceae) is a plant widely cultivated for essential oil production in the South of France. Chemometric treatment by mid-infrared (MID-IR) spectroscopy data was assessed for the differentiation of Grosso Lavandin Essential Oils of Controlled Area (GLEOCA) and results were compared to those obtained by gas chromatography for MID-IR short time technique validation. The quantification of the main 13 hydrocarbons and oxygenated compounds generally controlled by industrial perfumers in GLEOCA samples (n = 83) of three geographic origins: “Simiane”, “Puimoisson” (with two producers) and “Richerenches” and their classification were successfully obtained by partial least square discriminant analysis (PLS-DA) by comparison with gas chromatography. The best prediction results were obtained using first derivate spectral data in the 1800-700 cm⁻¹ range. The spectroscopic interpretation of regression vectors showed that each geographic origin was correlated to components of GLEOCA. Chemometric MID-IR spectra treatments allowed us to obtain similar results than those obtained by time consuming analytical techniques such as GC and therefore constitute a robust and help fast method for authentication of GLEOCA and should be extended to other essential oils for authentication of geographic origin.     

Theory for shock dynamics in particle-laden thin films

We present a theory to explain the emergence of a particle-rich ridge observed experimentally in a thin film particle-laden flow on an incline. We derive a lubrication theory for this system which is qualitatively compared to preliminary experimental data. The ridge formation arises from the creation of two shocks due to the differential transport rates of fluid and particles. This parallels recent findings of double shocks in thermal-gravity-driven flow [A. L. Bertozzi, Phys. Rev. Lett. 81, 5169 (1998); J. Sur, Phys. Rev. Lett. 90, 126105 (2003); A. Munch, Phys. Rev. Lett. 91, 016105 (2003)]. However, here the emergence of the shocks arises from a new mechanism involving the settling rates of the species.     

Small-angle X-ray diffraction study of the thermotropic and lyotropic phases of five alkyl cyclic and acyclic disaccharides: Influence of the linkage between the hydrophilic and hydrophobic moieties

We present a comparative study of the thermotropic and lyotropic phases of 5 surfactants with an aliphatic chain of 12 carbon atoms and a cyclic or acyclic sugar head with different linkages between the two moieties. These linkages can concern different chemical groups or different orientations between the head and the chain. The compounds included the α- and β-N dodecyl-D-maltosides, N-dodecylamino-1-deoxylactitol, N-dodecyl lactobionamide and N-acetyl N-dodecyl lactosylamine. The influence of the polar head (with closed- and opened-type sugars) and the linkage with the hydrocarbon chain on the phases obtained by the heating of the anhydrous compounds and after addition of water was studied by X-ray diffraction and optical microscopy. In the anhydrous state, the surfactants were either crystalline or amorphous. On heating, they went through a liquid crystal smectic phase which, in some cases, was preceded by solid-to-solid transitions. On addition of water, the sequence of phases from the micellar phase to the lamellar phase was accounted for in terms of the geometric model of Sadoc and Charvolin. However, with certain surfactants this sequence was not complete, and the domains of existence of phases were altered. Received 31 March 2000     

Farbenreaktionen von Chloroform, Bromoform und Jodoform

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