Two-phase water model in the cellulose network of paper

Water diffusion in cellulose was studied via two-phase Kärger model and the propagator method. In addition to ruling out anomalous diffusion, the mean squared displacements obtained at different diffusion times from the Kärger model allowed to characterize the system's phases by their average confining sizes, average connectivity and average apparent diffusion coefficients. The two-phase scheme was confirmed by the propagator method, which has given insights into the confining phase-geometry, found consistent with a parallel-plane arrangement. Final results indicate that water in cellulose is confined in two different types of amorphous domains, one placed at fiber surfaces, the other at fiber cores. This picture fully corresponds to the phenomenological categories so far used to identify water in cellulose fibers, namely, free and bound water, or freezing and non-freezing water.