Flow-Driven Interfacial Adsorption of Pullulan under Nanoconfinement: Unraveling the Synergistic Regulation by Chain Length and Pore Size

Abstract

Nanoconfined interfacial adsorption of neutral polysaccharides governs membrane fouling, selectivity, and biomolecular transport, yet the synergistic effects of chain length and pore size on this flow-driven process remain incompletely elucidated. Herein, we systematically investigate the adsorption of narrowly distributed pullulan standards in highly uniform anodic aluminum oxide (AAO) nanochannels with varying pore diameters. We uncover that a biphasic adsorption profile is consistently observed across the investigated pore-size and molecular-weight ranges and reveal that chain length dictates adlayer structure and ex situ surface wettability: short chains form thin, dense adlayers and yield less hydrophilic membrane surfaces, whereas long chains form thicker, looser adlayers and retain comparatively greater surface hydrophilicity. More importantly, a robust scaling relationship between the adsorbed layer thickness (H) and molecular weight (Mp), H ∼ Mp0.61 is established within the investigated experimental range. Notably, preadsorbed pullulan layers convert the irreversible lysozyme adsorption on pristine AAO surfaces to nearly fully reversible adsorption. This antifouling effect is attributed to the viscoelastic, dynamic nature of the polysaccharide adlayer. These findings provide molecular-level principles for tuning polysaccharide−surface interactions in confined environments, enabling rational design of intelligent separation membranes, antifouling coatings, and biointerfacial materials.