Dynamic Sorption and Interfacial Assembly of Polysaccharide on Hydrophobic <i>vs</i> Hydrophilic Surfaces

The molecular structure and wettability of a surface play a major role in dissolved organic matter (DOM) adsorption–desorption dynamics at water/solid interfaces. We studied the retention of a model DOM (i.e., a polysaccharide) at the water/diamond and water/goethite interfaces. Adsorption–desorption experiments were conducted to probe the interfacial dynamicity of sorbed polysaccharide (PS) and its impact on surface wettability. In situ ATR-FTIR and batch experiments revealed distinct bonding and kinetic behavior that depended on the polarity of the surface: goethite presented a higher adsorption capacity and binding strength but slower adsorption kinetics compared to diamond. Further, 2D correlation IR spectroscopy demonstrated that surface chemistry, surface loading, and time alter the PS’s conformation and self-assembly during adsorption and desorption. On goethite, electrostatic interactions with the surface (e.g., ≡FeOH2+) were followed by the formation of inter- and intramolecular H-bonds between hydrophilic side groups of PS chains, while at greater PS loading, interactions between PS hydrophobic groups became predominant. In contrast, the nonpolar diamond surface (e.g., ≡CH) promoted hydrophobic interactions that governed PS retention initially; subsequently, increased PS loading promoted H-bond formation between its charged hydrophilic groups. Both PS-goethite and PS-diamond organo-mineral associations developed a hydrophobic character (i.e., low wettability) upon PS adsorption. We highlight that biomolecules such as PS, possessing multifunctional side groups, exhibit a self-assembly behavior that becomes less dependent on surface type as surface loading increases. Conversely, surface polarity, including surface functional group and charge, plays a crucial role in determining distinct interfacial mechanisms at the early stage of PS adsorption. As adsorption progresses and surface loading increases, surface-driven effects diminish and the self-assembly of PS becomes predominantly governed by organic–organic interactions stemming from PS's own functionalities. This work helps us understand and predict hydrophobic- and hydrophilic-driven interactions relevant to environmental and engineered systems.