[Self-diffusion of water into silk fibers from magnetic field pulse gradient data]

Self-diffusion of water was studied in fibers of natural silk (Bombyx mori) with a water content of 0.18 g H2O/g dried material. Self-diffusion measurements were conducted by pulsed gradient of magnetic field (stimulated echo) at diffusion times from 10 to 200 mc. The dependence of experimental diffusion coefficients Dexp = f(delta) (observed decrease when delta increased) was determined to be responsible for the restricted diffusion. A model of planar and regularly spaced permeable barriers to diffusion of water molecules was applied to estimate the barrier spacing a and the permeability constant p. The maximal value of Dexp (at short diffusion time) in B. mori silk fibres was about 0.06 of the value of Dexp in bulk free water. The results obtained are compared to literature data on self-diffusion of water in hydrated biopolymer fibers and are discussed in connection with molecular mobility in natural macromolecular systems with low water content.