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468 results on '"Hellmann, R."'

1. Light-controllable hybrid aligning layer based on LIPSS on sapphire surface and PVCN-F film

Author

Gvozdovskyy, I., Bratova, D., Kazantseva, Z., Malyuta, S., Lytvyn, P., Schwarz, S., and Hellmann, R.

Subjects
Condensed Matter - Soft Condensed Matter
Abstract

The creation of aligning layers for the uniform orientation of liquid crystals is significant for both research and the application of liquid crystals. For all applications, the creation of aligning layers possessing controllable characteristics such as azimuthal and polar anchoring energies, easy-axis of director alignment and pre-tilt angle, in the same way as it is achieved by using photoaligning layers processed by light, is very important. Here, aligning properties of hybrid aligning layers created on the basis of sapphire surfaces additionally coated by photoaligning layer of PVCN-F are studied. These hybrid layers possess the properties of the nano-structured sapphire layer and the photosensitive PVCN-F layer, and complement each other. The irradiation time dependence of the azimuthal anchoring energy of the hybrid layers is studied. By using certain experimental conditions during irradiation of hybrid layers, e.g., polarisation of light and irradiation time, a minimum value of the azimuthal anchoring energy, close to zero, was obtained. Atomic force microscope studies of the irradiated hybrid layers were also carried out. It was found that the behavior of the contact angle of nematic droplets placed on treated sapphire surfaces are in good agreement with properties of hybrid aligning layers and parameters of structuring surface obtained from AFM images., Comment: 31 pages, 16 figures, 2 tables

Published
2023

5. Emergency department architecture (2024)

Author

Oberlin, M., additional, Douay, B., additional, Desclefs, J.-P., additional, Depil-Duval, A., additional, Ganansia, O., additional, Giraud, L., additional, Hellmann, R., additional, Noizet, M., additional, Penverne, Y., additional, Rouff, E., additional, Soulat, L., additional, Vergne, M., additional, Reuter, P.-G., additional, and Douillet, D., additional

Published
2024
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7. Deciphering strontium sulfate precipitation via Ostwald's rule of stages: From prenucleation clusters to solution-mediated phase tranformation.

Author

Lauer, A. R., Hellmann, R., Montes-Hernandez, G., Findling, N., Ling, W. L., Epicier, T., Fernandez-Martinez, A., and Van Driessche, A. E. S.

Subjects
*STRONTIUM, *SULFATES, *NUCLEATION, *SUPERSATURATION, *POTENTIOMETRY
Abstract

Multiple-step nucleation pathways have been observed during mineral formation in both inorganic and biomineral systems. These pathways can involve precursor aqueous species, amorphous intermediates, or metastable phases. Despite the widespread occurrence of these processes, elucidating the precise nucleation steps and the transformation mechanisms between each step remains a challenging task. Using a suite of potentiometric, microscopic, and spectroscopic tools, we studied the nucleation pathway of SrSO4 as a function of the physico-chemical solution parameters. Our observations reveal that below a threshold supersaturation, nucleation is driven by bound species, akin to the prenucleation cluster model, which directly leads to the formation of the stable phase celestine, SrSO4. At higher supersaturations, this situation is altered, with nucleation dominated by the consumption of free ions. Importantly, this change in nucleation mechanism is coupled to the formation of a hemihydrate metastable phase, SrSO4 · 1/2H2O, which eventually transforms into celestine, adhering to Ostwald's rule of stages. This transformation is a solution-mediated process, also occurring in the presence of a fluid film and is controlled by the physico-chemical parameters of the surrounding environment. It proceeds through the dissolution of the metastable phase and the de novo crystallization of the final phase. Overall, our results reveal that ion association taking place during the prenucleation stage dictates whether the nucleation pathway goes through an intermediate phase or not. This also underlines that although Ostwald's rule of stages is a common process, it is not a prerequisite for mineral formation—even in systems where it can occur. [ABSTRACT FROM AUTHOR]

Published
2023
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9. Architecture des structures de médecine d'urgence (2024).

Author

Oberlin, M., Douay, B., Desclefs, J.-P., Depil-Duval, A., Ganansia, O., Giraud, L., Hellmann, R., Noizet, M., Penverne, Y., Rouff, E., Soulat, L., Vergne, M., Reuter, P.-G., and Douillet, D.

Subjects
HOSPITAL building design & construction, HOSPITAL emergency services
Published
2024
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13. Deciphering strontium sulfate precipitation via Ostwald's rule of stages: from prenucleation clusters to solution-mediated phase tranformation

Author

Agence Nationale de la Recherche (France), Lauer, A. R., Hellmann, R., Montes-Hernandez, German, Findling, N., Ling, W. L., Epicier, T., Fernandez-Martinez, A., Van Driessche, Alexander E. S., Agence Nationale de la Recherche (France), Lauer, A. R., Hellmann, R., Montes-Hernandez, German, Findling, N., Ling, W. L., Epicier, T., Fernandez-Martinez, A., and Van Driessche, Alexander E. S.

Abstract

Multiple-step nucleation pathways have been observed during mineral formation in both inorganic and biomineral systems. These pathways can involve precursor aqueous species, amorphous intermediates, or metastable phases. Despite the widespread occurrence of these processes, elucidating the precise nucleation steps and the transformation mechanisms between each step remains a challenging task. Using a suite of potentiometric, microscopic, and spectroscopic tools, we studied the nucleation pathway of SrSO4 as a function of the physico-chemical solution parameters. Our observations reveal that below a threshold supersaturation, nucleation is driven by bound species, akin to the prenucleation cluster model, which directly leads to the formation of the stable phase celestine, SrSO4. At higher supersaturations, this situation is altered, with nucleation dominated by the consumption of free ions. Importantly, this change in nucleation mechanism is coupled to the formation of a hemihydrate metastable phase, SrSO4 · 1/2H2O, which eventually transforms into celestine, adhering to Ostwald's rule of stages. This transformation is a solution-mediated process, also occurring in the presence of a fluid film and is controlled by the physico-chemical parameters of the surrounding environment. It proceeds through the dissolution of the metastable phase and the de novo crystallization of the final phase. Overall, our results reveal that ion association taking place during the prenucleation stage dictates whether the nucleation pathway goes through an intermediate phase or not. This also underlines that although Ostwald's rule of stages is a common process, it is not a prerequisite for mineral formation - even in systems where it can occur.

Published
2023

28. S

Author

McLennan, Scott M., Montgomery, Carla W., Richardson, Jean M., Wagner, C., Hutcheon, Ian E., Ilton, Eugene S., Hinman, Nancy W., Mango, Helen N., Mittlefehldt, David W., Fyfe, William S., Königsberger, Erich, Gamsjäger, Heinz, Campbell, Ian T., Brand, Uwe, Clark, Ian D., Rock, Peter A., Casey, William H., Volkman, John K., Hellmann, R., Simmons, E. Craig, Davidson, Jon, Morrison, Joan O., Richards, Jeremy P., Machel, Hans G., Francis, Robert D., Schoonen, Martin A. A., Hannan, Keith, Jović, Vidojko, Ludwig, Christian, Potts, Philip J., Fairbridge, Rhodes W., Marshall, Clare P., editor, and Fairbridge, Rhodes W., editor

Published
1999
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45. Nucleation pathways of sulfate minerals

Author

Lauer, A., Fernandez-Martinez, A, Hellmann, R., Van Driessche, A, Institut des Sciences de la Terre (ISTerre), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), and Talour, Pascale

Subjects
[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry, [SDU.STU.GC] Sciences of the Universe [physics]/Earth Sciences/Geochemistry
Abstract

International audience; Sulfate minerals are abundant materials both on Earth and Mars [1]. Despite their significant role in both natural and engineered environments, MSO4-H2O systems have received surprisingly little attention in the recent flurry of studies addressing alternative (i.e. non-classical) mechanisms of solution-mediated mineral formation [2]. One exception is CaSO4, where extensive experimental work has revealed a rather complex mineralization process, involving different stages and precursor species [3,4]. Spurred by those findings, we have now extended our research using a broad variety of experimental techniques (e.g. in situ SAXS/WAXS, powder-XRD, (cryo)-TEM, potentiometric titration, induction time measurements, etc.) to other sulfate phases such as celestite (SrSO4) and barite (BaSO4). We found that these sulphate phases also undergo a multi-step formation pathway involving transient precursor species under certain physiochemical solution conditions. In particular, we present the effects of supersaturation, ionic strength, and solution hydrodynamics on the precipitation dynamics and stability/persistence of the different precursor phases. Based on the obtained experimental evidence, we construct a tentative unified model for sulfate crystallization from solution. Finally, the key questions that still need to be resolved before a holistic model of the nucleation pathway of solid phases in the MSO4-H2O system is attained will be highlighted. [1] Alpers et al., (2000) Reviews in Mineralogy and Geochemistry, 40. [2] Van Driessche et al. (2017) New Perspective on Mineral Nucleation and Growth, Springer-verlag. [3]Van Driessche et al (2012) Science, 336, 69-72. [4] Stwaski et al (2016) Nat. Commun. 7, 11177.

Published
2019

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