Water ingress in Y-type zeolite: anomalous moisture-dependent transport diffusivity.

Nuclear magnetic resonance imaging measurements of liquid water ingress in a large number of nonactivated Y-type (Na) zeolite samples prepared under different conditions are reported on. Using an experimental arrangement that permits the application of Boltzmann's transformation of the 1D (one-dimensional) diffusion equation, the spatiotemporal scaling variables required for a collapse of the measured profiles into universal curves revealed subdiffusive behavior in all cases. It is shown that the one-dimensional fractal time diffusion equation constitutes a powerful tool to analyze the data and provides a connection between the moisture dependence of the effective transport diffusivities and the shapes of the universal curves. Thus, even for anomalous diffusion, the relationship between the universal curves and structural characteristics of the system; such as porosity, tortuosity of the pore space and, in some cases, the interplay between mesopores and nanopores can be addressed.