Structural characterization of porous solids by simultaneously monitoring the low-temperature phase equilibria and diffusion of intrapore fluids using nuclear magnetic resonance
Nuclear magnetic resonance (NMR) provides a variety of tools for
the structural characterization of porous solids. In this paper, we discuss a
relatively novel approach called NMR cryodiffusometry, which is based on a
simultaneous assessment of both the phase state of intraporous liquids at low
temperatures, using NMR cryoporometry, and their transport properties, using
NMR diffusometry. Choosing two model porous materials with ordered and
disordered pore structures as the host systems, we discuss the methodological
and fundamental aspects of the method. Thus, with the use of an intentionally
micro-structured mesoporous silicon, we demonstrate how its structural features
give rise to specific patterns in the effective molecular diffusivities measured
upon progressive melting of a frozen liquid in the mesopores. We then present
the results of a detailed study of the transport properties of the same liquid during
both melting and freezing processes in Vycor porous glass, a material with a
random pore structure.