Analyzing Moisture Self-Diffusion coefficient and Pore Characteristics in Mongolian Scots Pine Using Single- sided NMR

In this study, Single-sided NMR was used to detect the changes of axial and radial chord water self-diffusion coefficient with diffusion time of Pinus sylvestris var.mongolica. The result shows that, The self-diffusion coefficient ranked as axial > radial > tangential. Axial self-diffusion coefficient exhibited free diffusion, averaging 2.0×10⁻⁹ m²/s, while radial and tangential directions showed confined diffusion, decreasing with time. Based on the restricted diffusion theory, the results are as follows, Radial and tangential tracheid surface-to-volume ratios (S/V) were approximately 203,000 ± 10,600/m and 265,000 ± 25,000/m, pit sizes of 6.4 ± 0.33 µm and 6.2 ± 0.49 µm with, tortuosity values τ _R  = 3.96 ± 0.02 and τ _T  = 6.59 ± 0.45. Combining S/V with the form factor (Fs) and the T ₂ relaxation mechanism yields the following results, Average pore sizes for radial and tangential tracheids were 19.7 ± 1.44 µm and 15.09 ± 1.3 µm, Cell water transverse surface relaxation rates were ρ _2R  = 0.103 ± 0.005 µm/ms and ρ _2T  = 0.082 ± 0.007 µm/ms. This study provides a systematic method for wood moisture self-diffusion analysis.