Evidence of bayerite clusters within the AAO amorphous bulk alumina. Consequence for AAO SANS matching properties.
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1074-I13-02
Evidence of bayerite clusters within the AAO amorphous bulk alumina. Consequence for AAO SANS matching properties. Karine Lagrené, and Jean-Marc Zanotti CEA-CNRS, Laboratoire Léon Brillouin (CEA-CNRS), CEA Saclay, Gif-Sur-Yvette, 91191, France, Metropolitan ABSTRACT Small Angle Neutron Scattering (SANS) and neutron diffraction are used to probe the structure of Anodized Aluminium Oxide (AAO) in an extended Q range, from 7.10-3 to 16 Å-1. In the small angle region [7. 10-3 Å-1 - 7. 10-2 Å-1], impregnation of a D2O/H2O mixture within the AAO porous structure, leads to a dramatic decrease of the coherent SANS signal by two orders of magnitude, but perfect matching of the membrane cannot be reached. We explain such an imperfect matching by the presence of 1 nm in size Bayerite domains within the bulk of the amorphous Al2O3 matrix, as detected by Neutron diffraction in the [0.3 Å-1 - 4 Å-1] Q range. Traces of sulfur, probably incorporated during the anodic synthesis process in a H2SO4 solution, are also detected by Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM-EDX). We estimate the AAO neutron scattering length to be 4.22 1010 cm-2. This value is an important input, when taking advantage of neutron contrast matching to probe the large scale filling homogeneity (adsorption of a liquid or deposition of a solid) within the porous structure of AAO membranes. INTRODUCTION Pure size effects, the so-called quantum-mechanical confinement effect, can be taken advantage of in electronics where size drives the energy of delocalized electrons. But usually, beside the pure size effect, stand prevailing interactions induced by the presence of an interface between the confined material and the confining matrix. These indirect interfacial effects induced by confinement are of particular interest in the field of electrochemical storage and ion transport at play in batteries [1]. Controlled porous glass (CPG), Vycor [2], MCM41 are notorious example of materials used for the confinement or organic materials or liquids. They share the property that beyond few tens of nanometers their structure is isotropic so that powder average has to be considered, i.e. no specific orientation remains at the macroscopic level. At the opposite, Anodic Aluminium Oxide (AAO) membranes are highly ordered porous systems made of oriented nano-scale parallel cylindrical channels (see figure 1a). It is a remarkable property of this material that the same strong anisotropy shown by AAO in the nanometre range extends up to the hundred of micrometers scale. AAO are therefore a remarkable model system for the study of transport properties in highly anisotropic confining environment. In such a framework, the homogeneity of adsorption of a liquid or a solid, within the porous structure of the confining host material is a key but challenging issue. We show here that Small Angle Neutron Scattering can be a very valuable tool to solve the problem if the length scale at stake is in the nanometer range. We also show a limit of the meth
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