Sequential Functional-Group Adsorption in Polymer Chain Assembly at Solid/Liquid Interfaces
Polymer adsorption at solid/liquid interfaces plays a crucial role in many applications, yet the molecular pathway of adsorption remains difficult to resolve experimentally. Here, we investigated the adsorption of poly(methyl methacrylate) (PMMA) and polystyrene (PS) from solution onto silica using in situ, real-time sum frequency generation vibrational spectroscopy. PMMA adsorption proceeds through multiple steps accompanied by changes in molecular orientation. Ester side chains first adsorb onto silica via hydrogen-bonding interactions with silanol groups and adopt a preferred interfacial orientation. This is followed by adsorption and reorientation of chain-end methyl groups and backbone methylene groups, revealing a sequential, functional-group-specific adsorption pathway. In contrast, PS, which lacks hydrogen-bonding interactions with silica, exhibits markedly slower adsorption under otherwise comparable conditions. These results demonstrate that interfacial hydrogen-bonding determines both adsorption kinetics and the molecular structure of the adsorbed layer. This study provides a functional-group-resolved view of polymer adsorption from solution and offers molecular-level insight into the design of polymer interfaces.