(67f) Surface Reorganization in Amphiphilic Monolayers: Linking Molecular Structure to Wetting Behavior

Amphiphilic monolayers offer a versatile platform for engineering responsive interfaces that dynamically adapt to environmental stimuli, enabling surfaces with intelligent, tunable properties. Compared to more extensively studied systems such as block copolymers, amphiphilic monolayers exhibit faster response times and greater stability under varying solvent conditions. These characteristics make them promising for designing solvent-responsive coatings since surface interactions can be rapidly minimized through the conformational rearrangement of their terminal functional groups upon exposure to varying environmental conditions. In this work, we combined experimental techniques and molecular dynamics (MD) simulations to investigate the interfacial structure and chemical responsiveness of monolayers composed of competing polar and nonpolar terminal groups. These moieties can reorient toward or away from the interface in response to contact with polar or dispersive media to minimize the interfacial free energy. To understand how the polarity mismatch of the terminal group influences this surface rearrangement, we have screened different chemical compositions and evaluated their dynamic surface using a range of probe liquids. Sum frequency generation (SFG) spectroscopy revealed that surface composition changes with the polarity of the contacting phase, indicating reversible rearrangement of chemical functionalities. MD simulations supported these findings, showing that longer alkyl chains can embed towards the film, allowing polar groups to become exposed under polar environments. These results suggest that hydrophobicity does not increase as the length of the nonpolar end group increases; instead, the interfacial organization is dominated by chain mobility. To quantitatively describe this behavior, we developed a surface-free energy calculation model that incorporates the effects of molecular rearrangement on the resulting interfacial energy changes under external stimuli. By linking molecular-level organization to macroscopic wetting behavior, this framework provides a new approach to characterizing and designing adaptative surfaces based on fast-responding amphiphilic monolayers. Overall, the insights gained through this work could offer a guideline for the design of coatings with tailored environmental responsiveness.