One- and Two-Dimensional NMR in Studying Wood–Water Interaction at Moisturizing Spruce. Anisotropy of Water Self-Diffusion

• Main Author: Victor V. Rodin
• Format: Article
• Language: English
• Published: MDPI AG 2019-08-01
• Series: Colloids and Interfaces
• Subjects: PFG NMR; moisturizing wood; restricted diffusion; DDCOSY; Inverse Laplace Transform
• Online Access: https://www.mdpi.com/2504-5377/3/3/54

This paper examines how wetting the surface of wood affects characteristics of wood materials. An important question is how moisturizing wood has an effect on diffusion parameters of water, which will change conditions of the technological treatment of material. A fibrous structure of wood can result in different diffusivities of water in the perpendicular direction and along the wood fibers. The work explores how 1- and 2-dimensional NMR with pulsed field gradients (PFG) highlights an anisotropic diffusion of water when moisturizing spruce wood. The methods applied: <i>T</i>₂-relaxation (CPMG) measurements with the application of inverse Laplace transform (ILT), cross-relaxation experiments (Goldman&#8722;Shen pulse sequence), 1D PFG NMR on oriented wood pieces or applying gradients in various orientation, and 2D diffusion-diffusion correlation spectroscopy (DDCOSY) with two pairs of colinear gradient pulses. The results showed anisotropic restricted diffusion correlating the size of tracheid cells. The experimental 2D diffusion-diffusion correlation maps were compared with model calculations based on parameters of 2D experiment on spruce and the theory of 2D DDCOSY with ILT. Moisturizing spruce wood resulted in anisotropic diffusion coefficient which can be monitored in 2D NMR to discover different diffusion coefficients of water along the axis of wood fibers and in orthogonal direction.