Neutron Diffraction Cryoporometry-A measurement technique for studying mesoporous materials and the phases of contained liquids and their crystalline forms

摘要

Neutron diffraction is a standard method for determining the structure of matter on an atomic scale; NMR cryoporometry is a recent widely applicable technique for characterising structure on a 2 nm to 2 μm scale. An extension of these techniques is described, Neutron Diffraction Cryoporometry (NDC). The information from a set of neutron diffraction measurements of liquids and their crystalline forms in meso-pores, as a function of temperature, is displayed as a cryoporometry graph. The data may then be conveniently interpreted using the Gibbs-Thomson relationship by analogy with the existing technique, NMR cryoporometry. Clear information is thus obtained on the relationship between phase and nano-structure, in a form well suited to further analysis. This method is applied to an equilibrium study of water/ice in SBA-15 templated silicas, as model nano- to meso-structured systems. The method described here uses global pattern matching (a one-dimensional morphing algorithm inside a linear least-squares fitting algorithm) applied to the full range of the diffraction data. This is a rapid method by comparison with the conventional method of fitting individual (overlapping) peaks, and has already led to NMR observations indicating plastic (rotator phase) ice in the same system.