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Marc-Olivier Coppens

Publications and source records attributed to Marc-Olivier Coppens.

4 recordsLinked to original sources
PubMed2005

Influence of the Al source and synthesis of ordered Al-SBA-15 hexagonal particles with nanostairs and terraces.

We investigated the effect of various aluminum sources on the morphology and microstructure of nanoporous Al-SBA-15. With aluminum tri-sec-butoxide (Al-TSB), very large, ordered hexagonal rods of Al-SBA-15 covered by nanostairs and terraces were synthesized. Such a morphology was not obtained with an inorganic Al source (sodium aluminate) or with organic sources seemingly similar to Al-TSB, such as aluminum tri-tert-butoxide, aluminum tri-n-butoxide, or aluminum isopropoxide. The results obtained from X-ray diffraction, scanning electron microscopy/transmission electron microscopy, N(2) adsorption/desorption, and high-performance (129)Xe NMR suggest that preparing an organic Al-Si precursor by premixing liquid organic Al and Si sources (Al-TSB and tetraethyl orthosilicate) is crucial in obtaining highly ordered mesoporous Al-SBA-15 materials with a well-defined morphology.

Journal Article↗
PubMed2004

Heterogeneity explains features of "anomalous" thermodynamics and statistics.

Phenomena characterized by power-law probability distributions abound in nature and the applied sciences. We show that many of these power laws are well described by the Student, or t, distribution, and we discuss the origin of this universality based on three examples (Brownian motion, Knudsen diffusion in rough pores, and bubbly multiphase flow). These case studies are representative for a large class of systems with heterogeneous features, examples of which can be found from Earth sciences to astrophysics, and even in the social sciences. We show that common forms of polydispersity, such as polydispersity arising naturally as a result of aggregation-fragmentation phenomena, typically lie at the basis of the observed scaling. We conclude that complicated arguments based on long-range correlations or nonergodicity are often incorrect or misleading in explaining many naturally observed power laws and, in particular, those described by the Student distribution.

Journal Article↗