Molecular dynamics of a short range ordered smectic phase nanoconfined into porous silicon

4-n-octyl-4-cyanobiphenyl (8CB) has been recently shown to display an unusual sequence of phases when confined into porous silicon (PSi). The gradual increase of oriented short-range smectic (SRS) correlations in place of a phase transition has been interpreted as a consequence of the anisotropic quenched disorder induced by confinement in PSi. Combining two quasielastic neutron scattering experiments with complementary energy resolutions, we present the first investigation of the individual molecular dynamics of this system. A large reduction of the molecular dynamics is observed in the confined liquid phase, as a direct consequence of the dynamical boundary conditions imposed by the confinement. Temperature fixed window scans (FWS) reveal a continuous 'glass-like' reduction of the molecular dynamics of the confined liquid and SRS phases on cooling down to 250 K, where a solid-like behavior is finally reached by a two steps crystallization process

Vibration spectra of triiodomesitylene: a combination of DFT calculations and experimental studies. Effects of the Environment

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Structural Organization of π Conjugated Highly Luminescent Molecular Material

International audienceWe report on striking evidence for a room temperature structural phase instability in p-hexaphenyl, inducing a nonplanar conformation of the molecules. Solid state proton NMR and single crystal x-ray diffraction allow the analysis of the organization, the individual dynamics and the involved symmetry breaking. The analysis of Raman spectra above and below room temperature reveals a singular behavior suggesting a modification of the overlap between the electronic wave function induced by the non-planarity. These results provide a new basis to answer fundamental issues related to molecular and electronic materials and, in particular, luminescent organic devices

Bundles of Carbon Nanotubes : a combined spectroscopic and theoretical study-influence of the weak mutual interactions on the optical properties

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Thermal oxidation of oxynitride films as a strategy to achieve (Sr₂Ta₂O₇)_100-x(La₂Ti₂O₇)_x based oxide perovskite films with x = 1.65

International audienceThis study concerns STLTO compounds of the ferroelectric (Sr 2 Ta 2 O 7) 100-x (La 2 Ti 2 O 7) x solid solution. The purpose is to produce the STLTO composition x = 1.65 as thin films by thermal oxidation of the corresponding oxynitride composition. Indeed, the combination of an STLTO oxide target with a dioxygen-rich reactive atmosphere during the sputtering deposition leads to Sr-deficient oxide thin films, shifting composition and structure from the perovskite to the tetragonal tungsten bronze type. An alternative synthesis pathway is to first deposit, under nitrogen-rich atmosphere, stoichiometric oxynitride films and produce, by thermal annealing under air, the stoichiometric oxide. For low oxidation temperatures ([550-600°C]), samples remain intact and display an oxide character but still contain a significant amount of nitrogen; they could be described as intermediate phases containing nitrogen-nitrogen pairs as demonstrated by Raman. Dielectric characteristics of these original film materials are of interest with a tunability value of 26 % at 30 kV/cm (10 kHz)

Raman Spectroscopy: Applications for Clinical Diagnosis of Bacterial Infections and Detection of Antibacterial Resistance

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Consequences of membrane aging on real or misleading evaluation of membrane cleaning by flux measurements

International audienceSkim milk ultrafiltration is worldwide used in dairy. Its management at industrial scale is based on the permeate flux mastering, the first bottleneck, and consequently on the nature of the overall fouling which is not yet fully understood with respect to the membrane lifespan. The second bottleneck is the mastering and control of the cleaning efficiency aiming at the full removal of the initial irreversible fouling mainly made of proteins. In this study, we have deliberately chemically aged several spiral wound membrane elements by filtering NaOCl solution (400 ppm in total free chlorine at pH 8.0 and 50 °C) up to a cumulative chlorine dose of 2,800 ppm.d. The critical/threshold and limiting fluxes have been proven to increase with the membrane ageing together with a decrease in their related transmembrane pressure. This suggest that, at industrial scale, UF might be managed with respect to the chlorine dose received by the membrane during its service life. SEM and Raman spectroscopy have been used to localise the initial irreversible fouling whereas ATR-FTIR was the tool to quantify proteins on membrane. Membrane cleaning was achieved by a non-oxidative alkaline detergent removing the hereafter called “removable fouling” whereas a “residual fouling” remained on/in the membrane. However, the following NaOCl treatment (achieved for disinfection purpose at industrial scale) also acts both as cleaner (polishing the alkaline step by removing part of the residual fouling) and as degradation agent toward the membrane. Unambiguously NaOCl induced a significant decrease in the membrane intrinsic hydraulic resistance associated with an increase of the irreversible fouling, either initial or residual, build during the following skim milk UF. This paper shows how degradation and fouling can transiently compensate each other and lead to the impression of an initial water flux recovery. This phenomenon can lead to misinterpretation of the membrane cleanliness in the specific case of aged membranes. Indeed, for a received chlorine dose close to 400 ppm.d at pH = 8.0, an irreversible residual fouling can remain, strongly anchored in/on the membrane with a water flux recovery after cleaning only 15% less than that of the pristine membrane. This residual fouling favours the rapid build-up of more and more irreversible fouling during the next skim milk filtration steps. However, with respect to the accuracy on flux measurement, the amplitude of the problem will be underestimated, preventing from getting rid of the first and crucial accumulated layers and consequently leading to an irreversible accelerated degrading process. Relationships have been found between the received chlorine dose and the aged membrane resistance and the residual irreversible fouling that could be used for management at industrial scale

Investigating the Detection of Lipids gel/fluid Phase Transition by Change of Scattering Light and Coupling Factor into Optical Microresonators

International audienceThe present paper describes biophotonic sensors realized by way of inexpensive processes. As hybrid silica/polymer resonators, they are suited to detect biological molecules in gel/fluid phase transition at infinitesimal concentrations (sphingomyelin lipids). The photonic structure is made of specific amplified deep UV210 photoresist-polymer waveguides coupled by a sub-wavelength gap with racetrack microresonators allowing a minimal dependence in temperature. Then, temperature dependent wavelength shifts characterizing the optical resonances of the device have been evaluated, highlighting a quite low thermal feature of the sensor advantageous for relevant applications. With an appropriate vesicle lipid deposition process, specific in biology, together with an apt experimental bio-thermo-photonic protocol, the dynamic evolution of the sphingomyelin lipid phase transition has been assessed. The ability to detect their gel/fluid transition phase and melting temperature has been demonstrated with a mass product factor value 1.4×10 7 lower than that of classical methods. The equilibrium regimes of the resonators and the scattered part of the light are clearly highlighted as markedly modified by the dynamic of the sphingomyelin during its own phase transition