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

Abstract

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 μ m 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.