Hierarchical pore structure evolution of cellulose fibers and its impact on molecular diffusion behavior

The hierarchical pore architecture of cellulose plays a critical role in regulating molecular accessibility and transport under wet conditions. However, the coupled effects of pore structure and interfacial interactions on diffusion behavior remain unclear. In this study, time-domain nuclear magnetic resonance (TD-NMR) was employed to quantitatively characterize wet-state pore structures of cotton fibers subjected to different chemical treatments, complemented by SEM, XRD, and FTIR analyses. The results reveal distinct structural evolution pathways: mercerization enlarges pore size and enhances accessibility, whereas liquid ammonia treatment refines the pore network by increasing smaller pores and reducing larger channels. Diffusion experiments using probe molecules of different sizes demonstrate that transport behavior is determined by a coupled mechanism involving pore size distribution, connectivity, and interfacial interactions. Enlarged pore-size distributions facilitate molecular transport, while refined pore networks impose size-selective diffusion limitations, particularly for larger molecules. Following TEMPO-mediated oxidation and polyethyleneimine (PEI) modification, a trade-off between enhanced molecular affinity and increased diffusion resistance is observed. These findings establish a structure-transport relationship in cellulose fibers and provide insight into diffusion behavior in cellulose-based fibrous materials.