Correlation Times of Motion of Deuterium Oxide in Polyamide 6 Rods

This is the authors' abstract. We don't add key points for this paper.

Deuterium nuclear magnetic resonance (NMR) studies of varying amounts of D 2 O absorbed in undrawn commercial polyamide 6 (PA6) rods at room temperature suggest the presence of only one type of water closely associated with amide sites via hydrogen bonding and that its motion can be modeled as both isotropic rotational and translational diffusion. Time constants for spin−lattice relaxation ( T 1 ) and spin−spin relaxation ( T 2 ) are used to obtain correlation times for the motions. The dependence of T 1 on D 2 O content shows a minimum, indicating that the correlation time is on the order of ω 0 τ c ∼ 1. Translational diffusion occurs on the time scale of less than 1 ms and describes the motion of D 2 O hopping between different solvated sites. The corresponding range of diffusivity of D 2 O in PA6, ∼10 -10 cm 2 /s, agrees with values reported for macroscopic diffusion measurements. Within each solvated site the solvent molecules undergo isotropic reorientation diffusion on the order of nanoseconds. The correlation times of both motions increase with decreasing D 2 O content, a trend consistent with plasticization of the polyamide matrix. No evidence is found for “free” water. Solid echo experiments also show that there is slow exchange (∼10 -5 s) between deuterium oxide and the ND bonds of PA6.